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Implant-supported removable partial denturesin the mandible

Charlotte Louwerse

Rijksuniversiteit Groningen

ISBN: 978-94- 623-3581- 3ISBN e-book: 978-94- 623-3582- 0Bookdesign: Linde ExPrinted by: GildeprintCopyright: C. Louwerse, 2017All rights reserved. No part of this publication may be reported or transmitted, in any form or by any means, without permission of the author.

Implant-supported removable partial dentures in the mandible

Proefschrift

ter verkrijging van de graad van doctor aan deRijksuniversiteit Groningen

op gezag van derector magnificus prof. dr. E. Sterken

en volgens besluit van het College voor Promoties.

De openbare verdediging zal plaatsvinden op

woensdag 19 april 2017 om 16.15 uur

door

Charlotte Louwerse

geboren op 6 oktober 1975te Rheden

PromotoresProf. dr. M.S. Cune Prof. dr. H.J.A. Meijer Prof. dr. G.M. Raghoebar

BeoordelingscommissieProf. dr. E.B. Wolvius Prof. dr. D. Wismeijer Prof. dr. F. Abbas

ParanimfenDr. M.R. LuingeDr. J.W.A. Slot

CONTENTS

Chapter 1General introduction and outline of this thesis

Chapter 2Implant-supported removable partial dentures in the mandible: a 3-16 year retrospective study

Chapter 3Implant-supported removable partial dentures in the mandible: patient-based outcome measures in relation to implant position

Chapter 4Implant-supported removable partial dentures in the mandible: functional, clinical and radiographical parameters in relation to implant position

Chapter 5Cost-effectiveness of implant-supported mandibular removable partial dentures

Chapter 6Comparing two diagnostic procedures in planning dental implants to support a removable partial denture in the mandible

Chapter 7General discussion, conclusions and future perspectives

Chapter 8 Summary

Chapter 9Nederlandse samenvatting

Chapter 10Dankwoord en curriculum vitae

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CHAPTER 1

GENERAL INTRODUCTION

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Introduction

Partial edentulism is seen more frequently with increasing age. It is more prevalent in the mandible compared to the maxilla.1 For inter-professional communication many classifications to describe different partial edentate situations have been proposed. The most widely used is the one originally proposed by Edward Kennedy in 1928: the Ken-nedy classification.2 It was modified by Applegate some decades later.3 This classifica-tion basically divides partial edentulism into four classes, depending on the position and the extent of the edentulous breaches. It allows quick visualization of the dental situation (Figure 1):

Kennedy class I: bilateral edentulous areas at the end of the dental arch: bilateral free-end saddle;

Kennedy class II: a unilateral edentulous area at the end of the dental arch: unilateral free-end saddle;

Kennedy class III: a single, unilateral interrupted posterior dental arch. The edentu-lous gap is bounded by natural teeth: unilateral bounded posterior saddle;

Kennedy class IV: a single, bilateral interrupted dental arch crossing the midline in the anterior: single anterior bounded saddle.

A combination of classes is possible for which the Applegate rules apply.

Figure 1. Kennedy classification

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Free-ending situations with missing molars and/or premolars as classified in a Kennedy class I or II are seen more often in elderly patients.1 This thesis focusses on some aspects of the Kennedy class I situation, in particular on the merits of implant-support to a re-movable partial denture in a bilaterally free-ending situation in the mandible. However, there are other restorative approaches to handle this predicament as well. These are described and discussed in general terms underneath as well in light of the knowledge available at the initiation stages of this PhD project.

Dealing with the Kennedy class I situation

Generally speaking there are two treatment philosophies to deal with the Kennedy class I situation. One could choose to maintain the partially edentulous state. This is also described as the ‘shortened dental arch’ concept (Figure 2). On the other hand functional, occluding units can be added, either by fixed or by removable restorative means. Options that can be distinguished are a cantilever bridge, an implant-supported crown or bridge or a tooth-implant-supported bridge, a removable partial denture or an implant-supported removable partial denture.

1. The shortened dental arch concept The shortened dental arch (SDA) treatment philosophy builds on the idea that to main-tain adequate objective and subjective oral function, not all missing (pre-) molar teeth need to be replaced.4 This idea has been substantiated by a large number of studies, initially with short term results, but later also documenting consequences in the longer run 5-10 as well as by several systematic reviews.11,12 From an extensive review of the literature focusing on subsets of oral function like mas-ticatory efficiency and ability, appearance, psychological ability and comfort, social abili-ty and comfort, occlusal support and dental arch stability, as well as other functions like tactile perception, phonetics and taste it is concluded that a minimum of 20 teeth with 9-10 pairs of contacting units (including anterior teeth) is associated with adequate oral function.13 Restorative and non-restorative approaches do not differ in effectiveness, although a fixed substitution of teeth is considered better than a removable one.14 In a more recent systematic review comparing prosthodontically- treated and untreated shortened dental arches and including only papers of high methodological quality, the merits of the SDA concept are underscored again.15 All former findings rationalise the highly ambitious goal that was set by the World Health Organisation in 1992 to be achieved for the year 2000: individuals worldwide should maintain a dentition of at least 20 teeth throughout life, which they presumed would be associated with adequa-te oral function.16 An example of a mandibular shortened dental arch is given in figure 2

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2. Fixed Partial Denture (FPD): the cantilever bridge With a distally cantilevered FPD a single premolar can be added to the mutilated den-tition. A cantilever bridge, whether conventional or adhesive, has a good prognosis if properly executed.17 When this option is considered, careful treatment planning is particularly important. The abutment teeth need to be strong and in a healthy, stable biomechanical, endodontic and periodontal state. Functional forces should be control-led and the connector should be strong and rigid.18,19 If these prerequisites are met it can result in a stable occlusal stop for the mandible (Figure 3).In general, survival rates of cantilever FPD’s (82 % after 10 years) are lower and compli-cation rates are higher than those of end-butted FPD’s.20,21 On the other hand, compa-rable survival rates to FPD’s with two end abutments are also reported.22 Randomized clinical trials comparing the two are quite rare. In one well designed split mouth study, replacing second premolars by means of a cantilever FPD, did not lead to a compromi-sed survival of the abutment teeth compared to the non-restored contra-lateral teeth after 5 years (94 % versus 92 %).23

Figure 2. Shortened dental arch in the man-

dible

Figure 3. Fixed Partial Denture (FDP) with two

abutment teeth and a cantilevered pontic.

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3. Fixed Partial Denture (FPD): implant-supported crown or bridge Fixed implant-supported and tooth-implant-supported restorations can in theory re-place each and every missing posterior tooth (Figure 4). They have a good prognosis with reported 10-year survival rates in the order of 93 %.24,25 Unfortunately, such tre-atment is expensive and local anatomical conditions sometimes render treatment com-prising of multiple implant crowns or a FPD not feasible. Limited vertical bone height would jeopardize the mandibular alveolar nerve when implant surgery is contemplated. With implants becoming increasingly shorter, the former can be overcome. However, their clinical performance has not been properly documented to date. Clinical trials are running.

4. Removable Partial DentureConventional distal extension base removable partial dentures (RPD’s) are a restorative option replacing all missing teeth but they generally yield poor patients’ acceptance. Adding occlusal units has aesthetic and functional benefits.26 However, the effect on patients’ health related quality of life and oral comfort seems unwarranted, at least not to a level that outweighs that of not replacing missing molars. This was demonstrated in a rare randomized clinical trial comparing RPD’s with the shortened dental arch treat-ment concept.27 Approximately 10, 25 and 50 % of distal extension base RPD’s are no longer in service after respectively 1, 5 and 10 years.28

Not surprisingly, ‘pain when wearing a removable partial denture’ is significantly rela-ted to patients’ appreciation of treatment.29 Because of the discrepancy between the compressibility of the alveolar mucosa on the one hand and the limited freedom of mo-vement of a natural tooth in its alveolus on the other hand, discomfort in free-ending RPD’s can be expected. Under such conditions occlusal forces are also detrimental for

Figure 4. 3-unit implant-supported Fixed Par-

tial Denture (FDP)

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the abutment teeth. To reduce or more evenly distribute the load on abutment teeth and on the residual alveolar ridge several solutions have been proposed, among which are reduction in the number of artificial teeth and in their occlusal surface, lengthening of the saddle, meticulous attention to occlusion and articulation and several variations in retainer design.30 An example of a distal extention base Removable Partial Denture (RDP) in the mandible is given in figure 5.

5. Implant-Supported Removable Partial Denture (ISRPD)By placing posterior implants, a Kennedy class I situation is basically transformed into a more favourable situation with transfer of forces from the mucosa toward the im-plant(s) and the abutment teeth (Figure 6). The first report suggesting the potential merits of implants to support an RPD dates from 1991.31 Since then several studies have pointed out that providing implant-support to an RPD is of benefit to the patient.32-36 The use of unaesthetic clasps can often be avoided with implant support.37

Figure 6. Implant-supported Removable Pati-

al Denture (ISRPD)

Figure 5. Distal extention base Removable Partial Denture (RDP) in the mandible

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Outline of this thesis

Taking into account all advantages and disadvantages of alternative treatment options it seems that an ISRPD is a viable treatment option for patients with a Kennedy class I situation. However, the provided evidence for ISRPD’s is obtained from a rather hetero-geneous collection of studies. Populations often include a variety of intraoral conditions and retention concepts. Furthermore, evidence is often based on case reports or studies of a retrospective nature with few subjects or finite element methods. Consequently, better controlled and randomized clinical trials to validate the outcomes of ISRPD’s are needed.38,39 Besides the function of the implants, outcome parameters should entail functional and patient-based outcome measures.When competing treatment options are available, their documented or presumed effec-tiveness and their (additional) costs should be considered and critically assessed when favouring one treatment over the other. A cost-effectiveness analysis can provide in-sight into whether the more costly treatment option offers sufficient added value to the patient to justify its application and it can aid dentists and patients to make treatment decisions in the most cost-effective way.40,41 No information comparing the anticipated benefits of RPD’s and ISRPD’s and relating these to the expected extra costs is available.

The position for the implant that offers the optimal support is also not elucidated in the literature. With the cuspid or the first bicuspid as most distal tooth, the position of the implant in the edentulous zone is more or less optional and at the discretion of the prosthodontist or surgeon. Little evidence is available with respect to functional and cli-nical outcomes on which to base the decision. Theoretical models indicate that a more posterior position, i.e. at the position of the first or second molar, reduces the pressure to soft tissues and alveolar bone the most, whereas an implant positioned directly distal to the remaining dentition reduces the stress on the abutment teeth.42 When planning implants for the lateral parts of the mandible, clinical inspection and a panoramic radiograph suffice in cases with ample bone volume. A cone beam compu-ted tomography (CBCT) may provide additional value in challenging cases because it provides data to produce slices in three dimensions of the anticipated implant location, enhancing the decision whether or not implant placement is possible and safe, i.e. re-ducing the risk of jeopardizing the alveolar nerve during implant surgery.43,44 The ALARA principle raises the question under which conditions the additional information gained from CBCT outweighs the extra biological and financial risks and costs when evaluating implant sites pre-operatively.

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The general aim of the research described in this thesis was to assess the treatment outcome of implant-supported removable partial dentures in the mandible. More spe-cifically:- to assess, in a retrospective study, the performance, biological and technical compli-cations, of ISRPD’s in mandibular Kennedy class I situations with implants placed in the anterior or posterior position (chapter 2);

- to assess patients’ appreciation of implant support to removable partial dentures in patients with a bilateral free-ending situation in the mandible and to determine the most favourable implant position: premolar or molar region (chapter 3);

- to assess the functional benefits of implant support to removable partial dentures in patients with a bilateral free-ending situation in the mandible, to assess clinical and radiographical performance of the implants and to determine the most favourable im-plant position with respect to these aspects: premolar or molar region (chapter 4);

- to conduct a cost-effectiveness analysis comparing conventional removable partial denture and implant-supported removable partial denture treatment in the mandible (chapter 5);

- to compare two imaging modalities (panoramic radiograph and cone-beam computed tomography) in pre-operative implant planning in the severely resorbed mandible and the influence on the observers assessments (chapter 6).

The findings are discussed in light of the current literature in chapter 7, leading to re-commendations for clinical practice and future research.

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CHAPTER 2

IMPLANT-SUPPORTED REMOVABLE PARTIAL DENTURES IN THE MANDIBLE:

A 3-16 YEAR RETROSPECTIVE STUDY

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This chapter is an edited version of the manuscript.Jensen C, Meijer HJ, Raghoebar GM, Kerdijk W, Cune MS. Implant-supported removable partial dentures in the mandible: A 3-16 year retrospective study. J Prosthodont Res. 2016. Epub ahead of print.

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Abstract

Purpose. The purpose of this retrospective study was to assess performance, together with biological and technical complications, of implant-supported removable partial dentures (ISRPD) in mandibular Kennedy class I situations with implants placed in the premolar (PM) or molar (M) region.

Methods. 23 subjects with two endosseous implants to support a bilateral-free-ending mandibular removable denture were examined. Eight subjects had implants in the PM region (PM group) and 15 subjects implants in the M region (M group). Biological and technical complications were recorded from the patients’ medical record. Patients filled out a validated questionnaire regarding their appreciation of oral health related quality of life (OHIP-NL49) and a VAS score on overall satisfaction.

Results. Over a mean follow-up period of 8 years (median 8 years, range 3-16 years) the cumulative implant survival rate was 91.7% (SE 0.05). Mean peri-implant bone loss was 0.9mm (SD 1.0mm). Scores for bleeding on probing, plaque and mucosal health were generally low, but significantly worse for implants placed in the M region. Significantly more biological complications occurred in the M group (X2(1)=3.9; p=0.048). In 65% of the cases no technical complications were registered. Mean overall OHIP score was 16.1 (SD 18.4) and patients were highly satisfied (VAS: 8.4; SD 2.1).

Conclusions. Within the limitations of this retrospective study, in case of a Kennedy class I situation in the mandible, an ISRPD is a viable treatment option with a high implant survival rate and satisfied patients after a maximum of 16 years. Technical and biolog-ical complications should be anticipated. Implants placed in the PM region performed slightly better.

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Introduction

Fixed implant-borne restorations have a good prognosis and seem the ideal solution in case of extended posterior uni- or bilateral partial edentulism in the mandible.1 Un-fortunately, such treatment is expensive and local anatomical conditions often render treatment comprising of multiple implant crowns infeasible. Removable dentures are the economic alternative in case of partial edentulism 2 that may improve quality of life 3, although conventional distal extension partial dentures generally yield poor patients’ acceptance. Adding occlusal units has aesthetic and functional benefits 4 but the effect on patients’ oral health-related quality of life (OHRQoL) and oral comfort seems unwar-ranted.5 Approximately 10, 25 and 50% of such removable partial dentures (RPD) are no longer in service after respectively 1, 5 and 10 years.6

Not surprisingly, ‘pain when wearing a removable partial denture’ is significantly related to patients’ appreciation of treatment7. Because of the discrepancy between the compressibility of the alveolar mucosa on the one hand and the limited freedom of movement of a natural tooth in its alveolus on the other hand, discomfort in free-end-ing RPD’s can be expected. Under such conditions occlusal forces are also detrimental for the abutment teeth. To reduce or more evenly distribute the load on abutment teeth and on the residual alveolar ridge several ‘solutions’ have been proposed, among which are a reduction in the number of artificial teeth and their occlusal surface, lengthening of the saddle, meticulous attention to occlusion and articulation and several variations in retainer design.8 In selected patients with free-ending RPD’s extra retention and re-lieve of the mucosal tissues can also be created by placing implants distally from the most posterior natural teeth. It reduces tissue-ward rotation around the fulcrum line through the most distally positioned natural abutment teeth.9-14

The first report suggesting the potential benefits of implants to support an RPD dates from 1991.15 Since then several retrospective studies and case-studies have point-ed out the benefits, but also addressed some pitfalls: mainly frequent need for repairs of the implant-supported removable partial denture (ISRPD).14,16 In a recent systematic review on removable implant-tooth supported mandibular partial dentures, 9 studies have been included. It is tentatively concluded that an improvement in function, aes-thetics and denture stability has been demonstrated, whereas prosthetic maintenance and implant complications are minor. The authors of this systematic review stress the need for prospective studies to demonstrate the efficacy of this treatment module.17 In another recent systematic review the same conclusions have been drawn.18

The patient-reported benefits of implant support in removable partial denture treatment have been established in a recent prospective clinical trial.19 Although the follow-up period after supporting the RPD by implants is only two months, the reported improvement of patient satisfaction and mastication is reported promising.

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From a clinical perspective the choice for the position of the implant bears relevance. The influence of implant position on peri-implant tissue health, implant survival, pros-thetic maintenance and patient satisfaction has never been subject of investigation in clinical practice although finite element analyses report a better stress-distribution and increasing displacement of an ISRPD with an implant placed in the premolar region in combination with a distal plate.20

The purpose of this retrospective study was to assess performance, together with biological and technical complications, of implant-supported removable partial dentures (ISRPD) in mandibular Kennedy class I situations with implants placed in the premolar (PM) or molar (M) region.

Materials and Methods

Study designA retrospective analyses was performed of all patients treated between 1-1-1999 and 1-1-2014 with a Kennedy class I situation with two implants (either tissue level (TL) im-plants or bone level (BL) implants) bilateral in the mandible supporting a removable par-tial denture in a private referral practice (De Mondhoek, Apeldoorn, the Netherlands) and a general hospital (Nij Smellinghe Hospital, department of Oral and Maxillofacial Surgery, Drachten, the Netherlands). Inclusion criteria for treatment were:- a shortened dental arch in the mandible (premolar or cuspid as most posterior abut-ment tooth) and the need for improvement of oral function;- sufficient bone volume to place two implants in PM or M region of the mandible on the left and right side.- adequate oral hygiene.

Patients with medical and general contraindications for the surgical procedures, were excluded from treatment as well as patients with active periodontal disease. Twenty-six patients were eligible and invited to participate. After consulting the Medi-cal Ethical Committee of the University Medical Center Groningen, it appeared that this retrospective study was not subject to the Medical Research Involving Human Subjects Act (Number M15.180693).

Patients were categorized in two subgroups depending on the position of the implants: patients with implants in the premolar region (the PM group) and patients who had im-plants placed in the molar region (the M group). Because of the retrospective character of this study it was not always clear on what criteria the implant position was deter-mined. An example of a typical case for the PM group is shown in Figure 1.

Two moments of observation were used to obtain the data. A panoramic radio

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Figure 1a. A typical case of a Kennedy class I Implant-supported Remova-

ble Partial Denture in the mandible. Ball attachment in situ

Figure 1b. Bottom side of an Implant Supported Removable Partial Den-

ture showing the retentive matrix.

Figure 1c. Panoramic radiograph showing two implants with ball attach-

ment in the premolar region (group anterior) after 8 years of function.

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graph, taken two weeks after implant placement, was collected from the medial file (Tbaseline). Data were obtained during a regular control visit (Tfollow-up).

Clinical assessmentsClinical assesments were calibrated with investigators from previous studies using the same criteria. Thereafter clinical data were collected by one observer (CJ). The following clinical variables were assessed at Tfollow-up.- Plaque: assessed per implant using the index according to Mombelli et al. 21 (score range 0-3). - Bleeding on probing: assessed per implant using the bleeding index according to Mombelli et al. 21 (score range 0-3).- Soft tissue health: assessed per implant using the gingiva index according to Loë & Silness 22 (score range 0-3).- Probing pocket depth: assessed at three sites per implant using a manual standardized pressure periodontal probe (Click-Probe®, Kerr, Bioggio, Switzerland) measuring to the nearest 1 mm. The highest value per implant was recorded.

The prevalence of peri-implant mucositis and peri-implantitis was calculated. The translation from bleeding index into Bleeding on Probing (BoP) was score 0 = BoP - and score 1,2 and 3 = BoP + 23. As definition for peri-implant mucositis and peri-implantitis, the consensus reached at the Seventh European Workshop on Periodontology has been used 24, being: peri-implant mucositis (radiographic bone loss <2 mm): BoP+ and/or suppuration and peri-implantitis: BoP+ and/or suppuration in combination with radio-graphic bone loss ≥2 mm.

Radiographic assessmentsTwo weeks after implant (Tbaseline) placement panoramic radiographs were taken of all patients and at Tfollow-up a new panoramic radiograph was ordered if no recent ra-diograph was available. The marginal bone levels (MBL) were analysed using the known implant length as a reference. The interface of the implant and the abutment was used as a reference line, from which all distances were measured using designated software (DicomWorks, Biomedical Engineering, University Medical Center Groningen, the Netherlands).25 The error of the method used was reported 0.13 ± 0.01 mm for the assessment of the radiographic marginal bone height.26 All radiographic assessments were performed by a single observer (CJ). Marginal bone loss was calculated both me-sially and distally per implant. The highest scores per implant were used to calculate the overall mean marginal bone loss.

Implant survival rateImplant survival was defined as the presence of an immobile implant at Tfollow-up.

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Implant mobility was tested by tapping on the implant and testing mobility between 2 back ends of a dental hand instrument.

Clinical record assessmentsThe following issues were scored from medical record and Tfollow-up to calculate bio-logical and technical complications:- Post-operative complications: sensibility disturbances, excessive pain;- Implant complications: early- and late failure, peri-implant mucositis and peri-implan-titis;- Maintenance of the ISRPD: repair or replacement.

Patient-based assessmentsPatients filled out a validated questionnaire regarding their appreciation of oral health related quality of life (OHIP-NL49)27,28 and a Visual Analogue Scale (VAS) on overall sat-isfaction. OHIP-NL49 relates to a questionnaire on which the subjects answers 49 items on a 0-4 scale,that are subsequently arranged into 7 domains. The sum-score ranges from 0-196 points. The lower the score, the higher the oral health related quality of life of the patient. All data were retrieved by one examiner (CJ), who was not involved with the original treatment.

Statistical analysesDemographic characteristics were summarized for included patients. Differences in clin-ical and radiographical measurements and patients’ OHIP-NL49 and VAS scores be-tween the PM and M group were analyzed using Mann-Whitney U tests. As a measure of effect size of the Mann-whitney U tests r was calculated and reported. An r of 0.1, 0.3 and 0.5 correspond with a small, medium and large effect size, respectively. The in-cidence of biological and technical complications was compared across conditions with chi-squared tests. Implant survival rate was established by means of the Kaplan-Meier estimate.29 P-values <0.05 were considered statistically significant. All computations were performed using a standard statistical program (SPSS, version 23.0 for Windows, SPSS inc., Chicago, USA).

Results

From the 26 included patients, three patients were unable to attend because of travel distance or health problems. Their data were not obtained. Two patients did fulfill the inclusion criteria upon Tbaseline, but lost their remaining mandibular dentition after re-spectively 4.5 and 14.4 years of functioning with the ISRPD. A mandibular overdenture

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was provided, for which additional implants were placed in the interforaminal region. Therefore, their data were only used for clinical outcomes and not for patient-based assessments. Consequently data from 23 and 21 patients was obtained for clinical out-comes and patient-based assessments respectively.

Patient- and treatment characteristics of the study group are depicted in Table 1. Attachment types were ball attachments, Locator attachments or healing abutments. The healing abutments were not used as retentive attachments but were used as studs. Usually three teeth were replaced at both sides. Eight patients had PM implants, while fifteen patients had M implants. Participants had an average follow up period of 8.1 years (SD 3.7) with a minimum of 3 and a maximum of 16 years. For the PM and M group the average follow-up period was 7.4 years (SD 4.1) and 8.5 years (SD 3.6) re-spectively.

Clinical outcomesClinical outcome measures are presented in Table 2. Overall plaque-, bleeding- and soft tissue health scores were low. However, M implants scored significantly higher on the plaque (U= 138.0; p=0.035; r=0.32) and gingiva index (U=91.5; p<0.001; r=0.54). The overall mean probing depth was 3.3 mm (SD 1.4mm) and did not differ significantly between groups.

Change in marginal bone levelMean change in MBL is presented in Table 2. A mean change in MBL of -0.9 mm (SD 1.0mm) was observed between Tbaseline and Tfollow-up after a mean period of 8 years (range 3-16 years). There was no significant difference between the PM and M group.

Implant survival rateNo implants were lost in the PM group. In total, three implants were lost in the M group. One implant failed to osseointegrate and was lost within six months following implant placement. Another two implants in two patients were lost due to peri-implan-titis after 3 and 6 years of function, respectively. The lost implants were not replaced in these two patients. The ISRPD was supported by the one remaining implant on the contralateral side. This resulted in an overall cumulative implant survival rate of 91.7% (SE 0.05%) after 16 years (Figure 2).

Biological complicationsBiological complications occurred in 29 out of 46 implants (63%; Table 3). Implants in the M region demonstrated significantly more complications than in the PM region (X2(1)=3.9; p=0.048). These complications mainly concerned peri-implant mucositis. The 3 out of 46 implants that were lost, were also all in the M group.

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Technical complicationsOverall, in 65% (n=15) of 23 cases no complications occurred during the mean obser-vation period of 8 years. Two prostheses required minor repairs whilst three had been replaced (n=3) after 5.5, 5.5 and 7 years of function. In three patients the implant borne removable partial denture was not in function anymore. Two cases were reverted to a full overdenture. One patients’ appreciation of oral function was disappointing and the patient decided to function without ISRPD. There were no significant differences between the RPD’s on M and PM implants. (X 2(1)=1.25; p=0.26, Table 3).

Patient-based assessments Table 4 gives an overview of the patients’ oral health related quality of life and the pa-tients’ satisfaction at Tfollow-up. The overall sum score of the OHIP-NL 49 questionnaire was 16.1 points (SD 18.4) on a 0-196 scale, which corresponds to favourable perceived oral health related quality of life. The patients scored 8.4 (SD 2.1) on general satisfac-tion on a 0-10 numeric scale. There were no significant differences between the PM and M group.

Figure 2. Cumulative survival of implants supporting mandibular

removable partial dentures according to Kaplan-Meier.

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Tab

le 1

. Pat

ien

t ch

arac

teri

stic

s

All

pat

ien

tsPa

tien

ts a

t fo

llow

up

Nu

mb

er o

f p

arti

cip

ants

2623

Cen

ter

(Ap

eld

oo

rn/D

rach

ten

)14

/12

12/1

1

Ag

e (m

ean

/ran

ge)

59/5

1-75

59/5

1-75

Gen

der

(m

ale/

fem

ale)

7/19

6/17

Rem

ain

ing

den

titi

on

(P1

-P1/

C-C

) *

8/18

8/15

Imp

lan

t ty

pe

(Tis

sue

Leve

l /B

on

e Le

vel)

11/1

510

/13

Imp

lan

t lo

cati

on

(p

rem

ola

r/m

ola

r)9/

178/

15

Att

ach

men

t ty

pe

(bal

l/Lo

cato

r/h

ealin

g a

bu

tmen

t)21

/3/2

18/3

/2

* fir

st-p

rem

olar

to

first

pre

mol

ar a

nd c

uspi

d to

cus

pid

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tive

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Tab

le 2

. Clin

ical

ass

essm

ents

at

follo

w u

p

(n=

23 p

atie

nts

an

d 4

3 im

pla

nts

, 3 im

pla

nts

wer

e lo

st, m

ean

an

d s

tan

dar

d d

evia

tio

n (

SD)

Tota

l A

nte

rio

rPo

ster

ior

p-v

alu

eEf

fect

siz

e (r

)

(n=

43)

(n=

16)

(n=

24)

Plaq

ue

Ind

ex0.

9 (0

.7)

0.6

(0.7

)1.

1 (0

.7)

0.03

5 0.

32

Ble

edin

g In

dex

0.7

(0.6

)0.

5 (0

.6)

0.8

(0.6

)0.

074

0.27

Gin

giv

a In

dex

0.5

(0.7

)0.

1 (0

.3)

0.8

(0.8

)<

0.00

10.

54

Pro

bin

g D

epth

(m

m)

3.3

(1.4

)3.

3 (1

.2)

3.3

(1.5

) 0

.634

0.07

Ch

ang

e in

mar

gin

al b

on

e b

evel

(m

m)*

-0.9

(1.0

)-1

.0 (1

.1)

-0.8

(1.0

)0.

821

0.03

* fir

st-p

rem

olar

to

first

pre

mol

ar a

nd c

uspi

d to

cus

pid

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tive

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Table 3. Number of biological and technical complications related to implants and removable partial dentures (RPD) respectively.

Total Anterior Posterior

Biological complications implants* (n=46) (n=16) (n=30)

No complications 17 9 8

Complications 29 7 22

Peri-implant mucositis 24 6 18

Peri-implantitis 2 1 1

Implant loss 3 0 3

* Statistically significant more complications associated with posterior implants (p=0.048).

Total Anterior Posterior

Technical complications RPD’s (n=23) (n=8) (n=15)

No complications 15 4 11

Complications 8 4 4

Minor repair 2 1 1

Replaced 3 2 1

Not in function 1 1 0

Reverted into a full arch denture 2 0 2

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Tab

le 4

. Mea

n s

um

sco

res

of

OH

IP-N

L49

(SD

bet

wee

n b

rack

ets)

an

d m

ean

VA

S sc

ore

(ra

ng

e 0-

10).

Tota

l A

nte

rio

rPo

ster

ior

(n=

21)

(n=

8)

(n=

13)

p-va

lue

effe

ct s

ize

(r)

Fun

ctio

nal

lim

itat

ion

(m

ax. s

core

36)

5.1

(3.1

)5.

9 (4

.7)

4.6

(1.6

)0.

941

0.02

Phys

ical

pai

n (

max

. sco

re 3

6)4.

6 (4

.6)

5.5

(6.1

)4.

0 (3

.4)

0.74

20.

07

Psyc

ho

log

ical

dis

com

fort

(m

ax. s

core

20)

2.0

(3.8

)2.

9 (5

.6)

1.4

(2.3

)0.

863

0.04

Phys

ical

dis

abili

ty (

max

. sco

re 3

6))

2.0

(3.1

)2.

9 (4

.2)

1.5

(2.0

)0.

513

0.14

Psyc

ho

log

ical

dis

abili

ty (

max

. sco

re 2

4)1.

3 (2

.8)

1.6

(3.9

)1.

1 (2

.0)

0.69

6 0.

09

Soci

al d

isab

ility

(m

ax. s

core

20)

0.4

(1.7

)1.

0 (2

.8)

0.1

(0.3

)0.

670

0.09

Han

dic

ap (

max

. sco

re 2

4)0.

8 (2

.0)

1.1

(3.2

)0.

5 (1

.0)

0.46

7 0.

16

OH

IP-N

L49

(to

tal)

(m

ax. s

core

196

)16

.1 (1

8.4)

20.9

(27.

8)13

.2 (9

.4)

0.97

10.

01

Ove

rall

sati

sfac

tio

n s

core

(m

ax. s

core

10)

8.4

(2.1

)7.

6 (3

.2)

8.9

(1.0

)0.

423

0.18

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Discussion

The results from the present study, with a mean observation period of over 8 years (range 3-16 years) suggests a good prognosis with respect to implant survival (91.7%). Results in other studies are even better with survival rates varying from 93.8 to 100% after follow-up periods of up to 15 years.16,18,30,31 In the present study, the three patients who experienced implant loss still could function successfully with the one remaining implant. The lower cumulative survival rate compared to other studies might be due to the group of patients that was examined, with all Kennedy class I situations in the mandible. In a recent study the authors conclude that implants placed in the mandible are at higher risk of complications compared to the maxilla.32

The complication rate of the ISRPD’s is considered relatively low as well, as can be concluded both from the data in the present study as from the observations of oth-ers. Kaufmann et al. concluded that 30% of the ISRPD’s needed maintenance within 3 years, but this consisted mainly of minor repairs like tightening, loosening or replacing the matrices. Another study shows hardly any prosthetic complications in a group of 20 patients with mandibular and maxillary ISRPD’s during 15 years of follow up.31

Most studies report stable implant conditions over time 31,33, nevertheless Bortolini et al. reported that almost every patient with an ISRPD exhibited a slightly inflamed peri-im-plant mucosa.30 It is striking that in our study, the implants placed in the PM zone per-form significantly better regarding plaque and (absence of) signs of inflammation. The reason might be a compromised cleaning possibility for distally placed implants: This emphasizes the importance of permanently monitoring and adjusting oral hygiene and this is confirmed by others.16

Two patients had lost their remaining natural dentition after respectively five and fourteen years of functioning with an ISRPD. They both received extra implants in the interforaminal region to support a full arch implant-retained overdenture. Strategic implant positioning implies that the implants can support both the present ISPRD and future prosthetic provisions. From a biomechanical perspective implants placed more to the posterior enhance a more favourable loading situation by moving the fulcrum-axis distally and reducing the load to the soft tissues and underlying bone. However, given the fact that healthier peri-implant conditions were generally observed around implants placed in the PM region compared to implants placed in the M region and the fact that, in case of further tooth loss, an implant-retained denture is better served with implants in the position of the premolars, the PM position may be preferred from a clinical per-spective.

Maintenance protocols differed between centers and for individuals, and the disadvantages of a retrospective study should be emphasised as well. A limitation is the multi-centre design with different clinicians and the lack of a uniform treatment proto-

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col. Also, there is a rather long inclusion period with a relatively low number of patients; this means that the treatment is not carried out on a regular basis, which hampers stan-dardization and familiarization with the method. In addition, different implant systems with different attachment systems have been used throughout the treatment period; this means that possible complications and also patient satisfaction could be influenced by the system, hindering a clear causality with the treatment method as such and with the position of the implants. No corrections were made for multiple observations within the same patient the impact of this dependency in the data is uncertain. However, giv-en the clinical difference that were found have medium to large effect sizes, they are likely to hold if dependency was not present. In general, peri-implant probing depths of implants placed in sites outside the aesthetic zone range between 2-4 mm under healthy conditions, depending on the implant type.24,34 Although change in probing depth over time can give an indication on the health of peri-impant tissue 35, it is im-portant to realize that these measurements are more sensitive to force variation than periodontal pocket probing.36 Therefore we used the criteria for peri-implant mucositis and peri-implantitis described in an earlier study by Lang et al. to determine whether peri-implant tissues were healthy or not.24 Although the overall plaque-, bleeding- and gingiva indexes are rather low in our study, the overall mean probing depth is within the above mentioned healthy range and the overall MBL change is acceptable, peri-implant mucositis was seen in 57% of the implants (n=24). This finding was confirmed by Derks et al.32 This too urges the need for a strict oral health regime consisting in regular visits and a constant monitoring of self-care, although the impact on marginal bone levels within the studied time frame seems limited.

Patients filled out questionnaires after having functioned with the ISRPD’s for dif-ferent periods of time, the effect of which was not studied in further detail. In addition, the position of the implant was determined by the subjective perception of the treat-ing surgeon/prosthodontist that an individual patient may benefit most from PM or M support. Hence, for instance, patients are included that have a cuspid as most posterior tooth, yet an implant positioned at the M position. To the knowledge of the authors, this choice cannot (yet) be substantiated by results from the literature. Patient outcome should be interpreted bearing this in mind.

Overall patient satisfaction seems to be very good with an overall score of 8.4 (SD 2.1) on a scale from 0 to 10. The standard deviation is somewhat high and is ex-plained by the one outlier in our study group who scored very low compared to the other patients. Analysing the data without this outlier results in an even higher overall patient satisfaction of 8.8 (SD 1.0). Several other studies report a high overall patient satisfaction as well.31,33,37

The OHIP-49 questionnaire is a commonly used tool to measure the oral health related quality of life. Despite the fact that questions are standardized, the differences

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in reporting the outcome of this questionnaire makes comparisons difficult.5,37 In a prospective study, Gates et al. observed a reduction of more than 41 units on the OHIP questionnaire when turning an RPD into an ISRPD, resulting in a mean overall score of approximately 20.38 The findings of Fueki et al. are comparable with a mean score of 23.8 (range 15.1-32.6) for patients with an ISRPD, in a prospective study with a fol-low-up of at least 1 year.39

The outcome can be considered indicative for the long-term prognosis of an ISRPD. Even though there was no randomization, the group under study is very homog-enous with all Kennedy class I situations in the mandible. Nevertheless, the disadvantag-es of this retrospective study should be emphasised, like the multi-centre design with a different clinicians and the lack of a uniform treatment protocol. Therefore a prospec-tive randomized clinical trial is mandatory to be able to make strong and universal rec-ommendations for the ISRPD in a Kennedy class I in the mandible with a randomization on the implant position.

Conclusions

Within the limitations of this retrospective study, in case of a Kennedy class I situation in the mandible, an implant-supported removable partial denture is a viable treatment option with a high implant survival rate after a maximum of 16 years. Technical and bi-ological complications should be anticipated. Implants placed in the PM region showed slightly better clinical results. Overall patient satisfaction is high.

Acknowledgement

The authors thank Dr. Felix Guljé (De Mondhoek, Apeldoorn, the Netherlands) and Dr. Jan-Peter Wymenga (Nij Smellinghe Hospital, department of Oral and Maxillofacial Sur-gery, Drachten, the Netherlands) for their time, support and hospitality to investigate patients at their clinics.

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on the quality of life. Ned Tijdschr Tandheelkd.

2011;118(3):134-139.

29. Kaplan E. L., Meier P. Nonparametric esti-

mation from incomplete observations. J. Am.

Stat. Assoc. 1958;53(282):457-481.

30. Bortolini S, Natali A, Franchi M, Coggio-

la A, Consolo U. Implant-retained removable


J Prosthodont. 2011;20(3):168-172.

31. Mijiritsky E, Lorean A, Mazor Z, Levin L.

Implant tooth-supported removable partial

denture with at least 15-year long-term fol-

low-up. Clin Implant Dent Relat Res. 2013.

32. Derks J, Schaller D, Hakansson J, Wenn-

strom JL, Tomasi C, Berglundh T. Effectiveness

of implant therapy analyzed in a swedish pop-

ulation: Prevalence of peri-implantitis. J Dent

Res. 2016;95(1):43-49.

33. Mitrani R, Brudvik JS, Phillips KM. Posterior

implants for distal extension removable pros-

theses: A retrospective study. Int J Periodontics

Restorative Dent. 2003;23(4):353-359.

34. Lang NP, Berglundh T, Heitz-Mayfield LJ,

Pjetursson BE, Salvi GE, Sanz M. Consensus

statements and recommended clinical proce-

dures regarding implant survival and complica-

tions. Int J Oral Maxillofac Implants. 2004;19

Suppl:150-154.

35. Heitz-Mayfield LJ. Peri-implant diseases:

Diagnosis and risk indicators. J Clin Periodon-

tol. 2008;35(8 Suppl):292-304.

36. Mombelli A, Muhle T, Bragger U, Lang

NP, Burgin WB. Comparison of periodon-

tal and peri-implant probing by depth-force

pattern analysis. Clin Oral Implants Res.

1997;8(6):448-454.

37. Wismeijer D, Tawse-Smith A, Payne AG.

Multicentre prospective evaluation of im-

plant-assisted mandibular bilateral distal

extension removable partial dentures: Pa-

tient satisfaction. Clin Oral Implants Res.

2013;24(1):20-27.

38. Gates WD,3rd, Cooper LF, Sanders AE, Re-

side GJ, De Kok IJ. The effect of implant-sup-

ported removable partial dentures on oral


2014;25(2):207-213.

39. Fueki K, Igarashi Y, Maeda Y, et al. Effect

of prosthetic restoration on oral health-related

quality of life in patients with shortened den-

tal arches: A multicentre study. J Oral Rehabil.

2015;42(9):701-708.

43

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CHAPTER 3

IMPLANT-SUPPORTED REMOVABLE PARTIAL DENTURES IN THE MANDIBLE;

PATIENT-BASED OUTCOME MEASURES IN RELATION TO IMPLANT POSITION

46

This chapter is an edited version of the manuscript:Jensen C, Raghoebar GM, Kerdijk W, Meijer HJA, Cune MS, Implant-supported mandibular removable partial dentures; patient-based outcome measures in relation to implant position. J Dent. 2016;55:92-98.

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Abstract

Objectives. To assess the benefits of implant support to Removable Partial Dentures (RPD) in patients with a bilateral free-ending situation in the mandible and to determine the most favourable implant position: the premolar (PM) or the molar (M) region.

Methods. Thirty subjects with a bilateral unbounded posterior saddle received 2 PM and 2 M Implants. A new RPD was placed. Implant support was provided 3 months later. Two PM implants supported the RPD. After 3 months the 2 M implants were used or vice versa. Outcome measures included oral health related quality of life (OHIP-NL49), general health status (SF-36), contentment assessed on a Visual Analogue Scale (VAS) and the number of hours that the RPD was worn. Data were collected prior to treatment, 3 months after having functioned with a new RPD and after 3 months with implant support. Finally, patients expressed their preferred implant position.

Results. The general health status (SF-36) was not influenced. OHIP-NL49 values and mean wearing-time were statistical significantly more favourable for ISRPD’s, regardless of the implant position. Per day, the ISRPD’s were worn 2-3 hours more than the unsupported new RPD. Patients’ expectations were met as the VAS-scores of anticipated and realized contentment did not reach a statistical significant level (p > 0.05). VAS scores for ISRPD’s with M implant support were higher than for PM implant support. Finally, 56.7% of subjects preferred the M implant support, 13.3% expressed no preference and 30% opted for PM implant support.

Conclusions. Mandibular implant support favorably influences oral health related patient-based outcome measures in patients with a bilateral free-ending situation. The majority of patients prefer the implant support to be in the molar region.

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Introduction

According to the concept of the shortened dental arch, patients with reduced numbers of posterior teeth generally have ample adaptive capacity to function adequately as long as 3-5 occlusal units remain, even though their masticatory performance is impaired.1,2 Nevertheless, recent prospective studies suggest an improvement in patients’ Oral Health Related Quality of Life (OHRQoL) after replacing posterior teeth with a fixed implant-supported restoration3,4 or with a Removable Partial Denture (RPD). RPD problems are frequently recurrent and the positive effect on OHRQoL is more pronounced in case of an arch that is interrupted in the anterior.5-8 The former findings are particularly interesting, since they relate to a common condition in clinical practice: the mandibular Kennedy class I or II situation opposed by a full maxillary denture. Under these conditions, conventional RPD’s may be troublesome and unpredictable as patients frequently complain from a lack of stability and retention, discontinue wearing them or insist on replacement by a new one 9-11, particularly so in cases with unbounded posterior saddles.12,13 Occlusal forces move the saddles into a tissue-ward direction because distal support is lacking, compromising the anterior abutment teeth as well through potentially destructive rotational forces. Long term use of an RPD is associated with poor adaptation of retainers, occlusal disharmony, pain, periodontal problems and ongoing resorption.14-16

Several studies in a systematic review showed that providing a removable partial denture with implant support improves patient satisfaction in case of bilateral distal-extension partial edentulism, although they stress the need for long-term randomized controlled trials.17 Providing implant support may help improve stability, retention and chewing ability, patient comfort in general, and even nutrient intake.15,16,18-22 A Kennedy class I or II situation is basically transformed into a class III situation, with a more favourable transmission of forces from the mucosa toward the implant(s) and tooth abutment(s). The use of unaesthetic clasps can often be avoided with implant support.17 However, the evidence for implant-supported RPD’s (ISRPD’s) is obtained from a rather heterogeneous group of studies. Populations studied often include patients with a variety of intraoral conditions and prostheses with different retention concepts. Furthermore, evidence is often based on case reports or studies of a retrospective nature with few subjects or finite element methods. Consequently, better controlled and randomized clinical trials to validate the outcomes of ISRPD’s are needed.17,23 The position for the implant that offers the optimal support is also not elucidated in the literature.

The aim of this study was to assess the perceived benefits of implant-supported Removable Partial Dentures (ISRPD) in patients with a bilateral free-ending situation in the mandible who perceive functional problems with their RPD, yet would like to continue wearing one and to determine the most favourable implant position: the

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premolar (PM) region or molar (M) region.

Materials and methods

Study set-up and patient populationThe study was set up as a within-subject comparison randomized clinical trial for which permission from the medical ethical committee of the University Medical Center of Groningen was granted (METc 2011.194). Thirty subjects with a full upper denture and complaints regarding their bilateral free-ending mandibular RPD were included. They all had conventional RPD’s made in the past and either still wore them or had discontinued wearing them. The following inclusion criteria applied:- ≥ 18 years of age;- the saddle area reaches until the first mandibular premolar or cuspid, both left and right;- the bone volume distal from the most posterior abutment teeth is sufficient to place the implants. In the premolar region, implants with a length of 8 mm and a diameter of 3.3 mm and in the molar region with a length of 6 mm and diameter of 4.1 mm were used. A cone beam CT (CBCT) was used to measure the bone volume 24 ;- the patient is capable of understanding and giving informed consent.

Potential subjects with medical and general contraindications for the surgical procedures, with a history of local radiotherapy to the head and neck region, who experienced implant loss in the past, who are incapable of performing basal oral hygiene measures, with decreased masticatory function due to physical disability or with active, uncontrolled periodontal pathology of the remaining dentition were excluded from participation.

Surgical and prosthetic proceduresAll subjects gave informed consent and received 2 implants on either side of the mandible (Straumann RN, Straumann, Switzerland) that were provided with cover screws and submerged. Two implants were placed in the premolar region (PM implant support) and two were placed in the molar region (M implant support). A surgical guide was used to achieve the right position and inclination. After 3 months, all implants were exposed in a second-stage surgery and low healing abutments were inserted. A new RPD was made according to standard prosthetic procedures. The design involved a lingual plate and a clasp on either side. The housing of the Locator® abutment (Zest Anchors, Inc., Escondido, California, USA) was already incorporated in the RPD, but not the Teflon matrix so it provided neither retention nor support to the RPD. Three months later and following a randomization scheme, either the PM or M implants were

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provided with a Locator® abutment. The remaining implants were left unloaded for future investigation. After 3 months, the other pair of implants was loaded. Figure 1 shows an example of a typical clinical case. A clear timeline is displayed in Figure 2.

Patient-based outcome measuresFive patient-based outcome measures were assessed: oral health related quality of life, patient reported general health status, general contentment, daily wearing-time of the RPD and patients’ preference for the PM or M implant position. The clinician who collected the data (CJ) was involved during the inclusion of the subjects and the organisation of the trial, but provided neither surgical, nor prosthodontic care.

Oral Health Related Quality of Life (OHRQoL) was considered the primary outcome measure and assessed using the Dutch translated and validated version of the Oral Health Impact Profile questionnaire (OHIP-NL49).25-27 It consists of 49 questions arranged in seven conceptually formulated domains: functional limitation, physical pain, psychological discomfort, physical disability, psychological disability, social disability and handicap. For each item, subjects were asked how frequently they had experienced the impact of that item in the last month. Responses are given on a Likert-scale (0-never, 1-hardly ever, 2-occasionally, 3-fairly often, 4-very often). OHIP-NL49 sum scores per domain and an overall score characterize the OHRQoL impairment in which higher scores indicate greater OHRQoL impairment.

Patient-reported perceived general health status was determined using the Dutch translated and validated version of the Short Form Health Survey (SF-36). It measures to what degree patients feel disabled during their daily activities.28 It is comprised of 36 questions divided into 8 scaled scores which are transformed into a range from 0-100: vitality, physical functioning, bodily pain, general health perceptions, physical role functioning, emotional role functioning, social role functioning and mental health. One additional question addresses changes in health condition. The lower the score, the more disability.

In addition, patients were asked to express their general contentment with their oral function during the different stages of treatment on a Visual Analogue Scale (VAS) ranging from 0 (very discontent, major concerns) to 100 (very content, no concerns at all). At the start of treatment they were also asked to express their expectation with respect to the anticipated ISRPD as a means to evaluate whether or not patients’ expectations were met at the end of the study.

Data on OHIP-NL49, SF-36 and general contentment were collected prior to treatment (with the old RPD), after 3 months of function with the new RPD without implant support, after 3 months of function with PM implant support and finally after 3 months with M implant support (vice versa, Figure 2).

The mean wearing-time per day reflects the patients’ wearing habits. Alterations

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Figure 1a. Occlusal view. Locator abutments in the premolar region provide support and

retention to the Removable Partial Denture. The 2 molar implants are not in function.

Figure 1b. Frontal view. Removable Partial Denture in situ. Blue shimmering lateral in the

denture is caused by the electronic chip to measure wearing-time.

Figure 1c. Occlusal view. Removable Partial Denture in situ.

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ure

2.

Tim

elin

e o

f th

e ra

nd

om

ized

clin

ical

cro

ss-o

ver

tria

l in

clu

din

g m

om

ents

of

dat

a

colle

ctio

n.

53

assume a shift in patient satisfaction and/or comfort. A commercially available microelectronic sensor (TheraMon®, Handelsagentur Gschladt, Hargelsberg, Austria) was embedded in the lingual or buccal flange of the new removable partial denture at the position of the first premolar by means of methylmetacrylate, as described by the manufacturer. It runs over a period of at least 18 months, measuring the intraoral temperature in regular intervals and storing it into the integrated memory microchip. Stored data were transferred to a desktop computer by a reading station and analysed using dedicated software (TheraMon® software, version 2.1.0.13; Handelsagentur Gschladt). Wearing-time was established for the period with the new RPD and with the ISRPD during PM as well as M implant support. Patients were presumed to have worn the denture when the recorded temperature ranged between 31°C to 39°C. Under normal conditions, this is the range that covers the vast majority of intraoral temperature values.29,30

At the end of the experiment patients were asked to express their preferred implant position: PM or M after being counselled about the consequences with respect to the design of their denture. When favouring the M position, the anterior clasps would have to remain. Eventually, the dentures were modified according to their wishes.

Sample size calculation and statistical analysisSample size estimation was based on the primary outcome measure (OHIP-NL49) given X = 0.05, power = 0.80 and on the basis of the expected effect size for 2 dependent means (matched pairs).31 The prospected outcome was obtained from a study on oral health related quality of life as measured by the Oral Health Impact Factor (OHIP-49) comparing patients treated with implant-supported fixed dentures (implant bridges) and removable partial dentures without implant support. Mean scores were respectively 22.0 (SD 18.8) and 38.0 (SD 22.2).32 Since we included patients with free-ending bilateral situations only, we presumed the OHIP value for this particular situation to be higher (i.e. 40) and the effect of implant support to be less (i.e. 24). Sample size calculation revealed that 23 subjects were needed to detect this increase in the primary outcome measure from 40 in the control group (RPD) to 24 in the experimental group (ISRPD, regardless of implant position). Given the fact that the expected effect in patients with some remaining natural teeth is presumably smaller than that in edentulous subjects and compensating for potential dropouts, the intended number of subjects to be included in the study was set at 30 patients.

The outcomes of the old, the unsupported new, the PM implant-supported and the M implant-supported RPD’s were compared by 1-way analysis of variance and multiple comparison tests after verification of normal distribution. When the data were not normally distributed a non-parametric test for related samples (Friedman’s test) was used. In case of statistical significance (X = 0.05), post-hoc Wilcoxon signed rank tests were performed with Bonferroni adjustment for multiple testing. Mann-Whitney U

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tests were performed to detect any effects from treatment sequence (first M, then PM implant support versus first PM, then M implant support).

Results

Patient and treatment characteristics are presented in Table 1. The sum scores for OHIP-NL49, SF-36, VAS and the mean wearing-time were not normally distributed (Kolmogorow-Smirnow test’s, p<0.05). No differences were found between the treatment sequences, indicating that which position for implant position was first administered did not influence patients’ perceptions (Mann-Whitney U tests, p > 0.05). Hence a possible sequence effect was not considered in further analyses.

OHIP-NL49The mean values for the OHIP-NL49 domains and the OHIP-NL49 sum score are presented in Table 2. Comparison for the OHIP-NL49 sum score showed a statistically significant difference between the 4 groups (X2(3) = 39.600, p < 0.001). Post-hoc analysis revealed that overall OHIP-NL49 scores for both implant-supported partial denture groups (PM or M) were significantly lower, than for the old partial denture and for the new partial denture without implant support. Providing a new RPD without support did not lead to a statistical significant improvement of the OHIP-NL49 sum-score as compared to the old RPD. Analysing the different domains in detail, a similar trend was seen for domain entailing ‘Physical disability’. For the domains ‘Functional Limitation’, ‘Physical Pain’ and ‘Psychological Discomfort’ the new RPD without support already gave some improvement, which was further enhanced once the implants were used, be it with M or PM implant support (Table 2). Psychological disability was improved by M implant support and not so much when the PM implants were loaded. For the domains ‘Social

Table 1. Patient characteristics

Gender (male/female) 15/15

Mean Age (SD/range) 60.9 (1.2/43.8-71.0)

Group (PM*/M**) 15/15

Number of remaining natural teeth (5-6/7-8) 16/14

*PM = implants in premolar region first loaded*M= implants in molar region first loaded

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Disability’ and ‘Handicap’ no statistically significant differences between the M or PM implant support were observed.

SF-36The mean values for the SF-36 domains are presented in Table 3. No statistically significant difference could be demonstrated between conditions for any domains nor for the overall score of the SF-36.

Visual Analogue Scale on contentmentBefore the trial started, the subjects expressed their expectation of contentment with their RPD after treatment with implant support. Furthermore, they expressed their contentment with the old RPD, with the new RPD and with the ISRPD’s.

Comparison for contentment with the different RPD’s, old, new and with implant support were significantly different (X2(3) = 62.56, p < 0.001). Post hoc analysis revealed that contentment with new unsupported RPD’s was significantly higher than contentment with the old RPD’s (p = 0.008). Contentment with ISRPD’s was higher than contentment with either old or new unsupported RPD’s (p<0.005). Contentment with the ISRPD’s with M implant support was similar to contentment with PM implant support (p = 0.18). Prior to treatment, patients were asked to express their functional expectations with the final result once their new RPD was provided with implant support, regardless of the implant position. Hence the VAS scores for ISRPD’s (M and PM) were averaged and graphically displayed with patients’ expectations, and perceived contentment with the old and new, unsupported RPD in Figure 3. Patient expectations were met, as indicated by the fact that the scores for expected and realized contentment with an ISRPD were not statistically significant different (T=11, p = 0.78).

Mean Wearing-timeThe mean wearing-time per day with the new RPD and with the ISRPD’s with M and PM implant support were 12.4 hours (SD 7.3 hours), 15.2 hours (SD 6.6 hours) and 14.1 hours (SD 7.4 hours) respectively. Wearing-time for all conditions ranges from 0.3-23.8 hours per day. One patient poorly adapted to the unsupported RPD and his ISRPD as well because of severe general health problems that occurred during the course of the study. Comparison for mean wearing-time was significantly different between these 3 groups (X2(2) = 25.655, p < 0.001). Post-hoc Wilcoxon signed-rank tests, revealed that patients wore their dentures longer on average per day, once they were supported by implants. The position of the implants, either PM or M did not significantly influence wearing-time.

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Patient preferenceWhen asked what location they preferred, 13.3% of patients expressed no preference, 30% preferred the PM implant support whereas 56.7% preferred the M implant support.

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Figure 3. Mean visual analogue scale (VAS) scores and standard deviations of patients’

expected contentment with an Implant Supported Removable Partial Denture (ISRPD)

assessed prior to treatment, present contentment with their old denture (Old RPD)

and the actually achieved level of contentment after having functioned with a newly

made Removable Partial Denture without implant support for 3 months (new RPD) or

with implant support (ISRPD). Scores for PM and M implant support were averaged.

Range 0 (very discontent, major concerns) to 100 (fully content, no concerns at all).

Statistical analysis: Expectation = ISRPPD > New RPD > Old RPD.

57

Tab

le 2

. M

ean

su

m s

core

s o

f O

ral

Hea

lth

Im

pac

t Pr

ofi

le q

ues

tio

nn

aire

(O

HIP

-NL4

9) (

ran

ge

0-19

6, S

D b

etw

een

bra

cket

s) a

t d

iffe

ren

t st

ages

of

trea

tmen

t: o

ld r

emo

vab

le p

arti

al d

entu

re (T

bas

elin

e), n

ew r

emo

vab

le p

arti

al d

entu

re

(Tn

ew R

PD),

im

pla

nt-

sup

po

rted

rem

ova

ble

par

tial

den

ture

wit

h s

up

po

rt a

t th

e m

ola

r p

osi

tio

n (

T ISR

PD-M

), i

mp

lan

t-

sup

po

rted

par

tial

den

ture

wit

h s

up

po

rt a

t th

e p

rem

ola

r p

osi

tio

n (

T ISR

PD-P

M).

T bas

elin

eT n

ew R

PDT IS

RPD

-MT IS

RPD

-PM

Fun

ctio

nal

lim

itat

ion

(m

ax. 3

6)

14.9

(6.9

)11

.3 (6

.1)*

6.5

(3.8

) $6.

9 (4

.5) $

Phys

ical

pai

n (

max

. 36)

10

.7 (6

.6)

11.4

(7.3

)4.

2 (4

.1) $

4.5

(5.3

) $

Psyc

ho

log

ical

dis

com

fort

(m

ax.

20)

6.9

(5.8

)4.

6 (5

.2)*

1.8

(2.8

) $2.

3 (4

.4) $

Phys

ical

dis

abili

ty (

max

. 36)

9.

2 (7

.6)

8.2

(7.4

)2.

6 (3

.0) $

3.1

(4.0

) $

Psyc

ho

log

ical

dis

abili

ty (

max

. 24)

3.

6 (5

.5)

3.0

(4.4

)1.

0 (2

.3) $

2.0

(4.1

)

Soci

al d

isab

ility

(m

ax. 2

0)1.

9 (3

.3)

1.5

(2.2

)0.

7 (1

.5)

1.1

(2.2

)

Han

dic

ap (

max

. 24)

2.

5 (5

.0)

1.4

(2.4

)0.

8 (1

.9)

1.3

(3.4

)

OH

IP (

tota

l) (

max

. 196

) 49

.6 (3

5.2)

40.3

(31.

2)17

.6 (1

6.6)

$21

.2 (2

6.0)

$

*

< T

base

line (

p <

0.0

08)

$

< T

base

line a

nd <

Tne

w R

PD (p

< 0

.008

)

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Tab

le 3

. M

ean

sco

res

for

SF-3

6 (s

tan

dar

d d

evia

tio

n b

etw

een

bra

cket

s) a

t d

iffe

ren

t st

ages

of

trea

tmen

t: o

ld

rem

ova

ble

par

tial

den

ture

(T b

asel

ine)

, n

ew r

emo

vab

le p

arti

al d

entu

re (

T new

RPD

), i

mp

lan

t-su

pp

ort

ed r

emo

vab

le

par

tial

den

ture

wit

h s

up

po

rt a

t th

e m

ola

r p

osi

tio

n (

T ISR

PD-M

), im

pla

nt-

sup

po

rted

par

tial

den

ture

wit

h s

up

po

rt a

t

the

pre

mo

lar

po

siti

on

(T IS

RPD

-PM).

T bas

elin

eT n

ew R

PDT IS

RPD

-MT IS

RPD

-PM

Phys

ical

fu

nct

ion

ing

83.8

(21.

0)79

.7 (2

4.9)

80.5

(22.

8)82

.5 (2

3.3)

Soci

al r

ole

fu

nct

ion

ing

93

.5 (1

3.7)

91.1

(13.

3)89

.3 (1

9.0)

89.3

(15.

3)

Phys

ical

ro

le f

un

ctio

nin

g85

.8 (3

1.3)

80.8

(34.

5)79

.2 (3

6.0)

82.5

(36.

0)

Emo

tio

nal

ro

le f

un

ctio

nin

g94

.5 (1

9.7)

94.4

(21.

6)90

.0 (2

3.4)

92.2

(24.

3)

Men

tal h

ealt

h81

.2 (1

6.8)

83.6

(10.

5)83

.0 (1

3.2)

82.8

(15.

9)

Vit

alit

y 74

.3 (1

6.1)

72.0

(18.

1)70

.0 (1

7.3)

72.8

(19.

5)

Bo

dily

pai

n79

.4 (2

4.5)

74.0

(26.

9)74

.1 (2

7.6)

78.2

(26.

7)

Gen

eral

Hea

lth

Per

cep

tio

ns

75.5

(13.

9)73

.7 (1

8.8)

73.2

(16.

1)71

.5 (1

8.5)

Tota

l SF3

6-sc

ore

719.

7 (1

17.1

)70

1.7

(123

.2)

692.

6 (1

32.0

)70

2.6

(142

.9)

No

sign

ifica

nt d

iffer

ence

s am

ong

the

grou

ps f

or a

ny o

f th

e va

riabl

es.

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Discussion

To investigate whether implant support to an RPD in patients with a mandibular bilateral free-ending situation has a favourable influence on patient satisfaction, five patient-based outcome measures were explored, covering the impact of treatment on Oral Health Related Quality of Life (OHRQoL), patient reported general health status, general contentment, daily wearing-time of the RPD and patients’ preference for the PM or M implant position, thus covering a wide range of aspects that are assumed to reflect the patients’ perception of the effect of the treatment. The design of this study was a cross-over randomized clinical trial. Patients were offered a new unsupported RPD and after three months both an ISRPD supported in the molar and premolar region for three months in a random order. In between, we feel that a wash-out period was not necessary, since it is not likely that the outcome parameters studied during one intervention would have been of influence on the following interventions, which were recorded 3 months later. This is confirmed by the fact that no statistically significant sequence effect was found.

OHRQoL as measured by OHIP-49 improved significantly when implant support was provided to a newly made RPD (ISRPD), which is in agreement with the findings of others.7,21,33 A minimal important difference (MID) of 6 points (95% CL, 2-9) has been suggested for OHIP use in dentistry.34 The MID was defined as ‘the smallest difference in score in the domain of interest which patients perceive as beneficial and which would mandate, in the absence of troublesome side effects and excessive cost, a change in the patient management. John et al (2009) suggested in the same study that this MID can be used to approach clinical relevance of changes in perceived oral health. The observed reduction in OHIP sum-score and values in the present study amply exceed this threshold. That being the case, for a patient a cost-effectiveness consideration needs to be made.35

The OHRQoL is reported to be highly correlated with the quality of the prosthesis36, suggesting that a denture of poor quality which is replaced by a technically optimized one, acceptance and satisfaction will improve. In the present study of patients with a poorly functioning bilateral free-ending mandibular RPD, solely providing a new RPD proved also being effective. It may mean that the new RPD provided without support did suffice in increasing the quality. Patients were even more satisfied when implant support was provided, meaning that the addition of implant support did significantly improve overall quality of the construction.Furthermore, the data suggest that patients’ expectations of contentment with an ISRPD were met since no significant difference was seen between expected and actually achieved contentment. This is seen as an important indicator of the quality of treatment. It enhances the reputation of the health care provider and implant dentistry

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in general. It transforms new patients into loyal customers and brings new referrals by ‘word of mouth’. Food getting underneath was and remains a recurrent complaint despite implant support, as also was observed by others.37

Whether or not patients wear their (IS)RPD is related to their contentment with the aesthetics and the absence of pain.11 An association between the actual wearing of an RPD and satisfaction was described before.38 Objectively documenting the wearing-time of the (IS)RPD was performed by means of a thermosensitive device (TheraMon), that is promoted for use in orthodontics to stimulate (but also check) young patients’ compliance with treatment.39 To the knowledge of the authors it has not been operationalized as an outcome variable for patient satisfaction in prosthodontics yet. However using a thermosensitive device may be a useful tool. Electronic wearing-time tracking provides an accurate estimate. Because of the small size of the chip it is not uncomfortable to the patient and does not impair function. The subjects were aware that the blue chip was incorporated in their (IS)RPD and to what purpose, which may have stimulated them to wearing the (IS)RPD. Consequently, an overestimation of wearing time may be present in the data. However, patients’ were aware of the chip in all conditions so in each condition a similar effect of the chip may be expected. As a corollary, results in the different phases of the trial are best judged relative to each other. The improvement in wearing-time that is seen once implant support is provided, objectively underscores the observed improved OHIP- and VAS scores.

In contrast to specific oral health related domains, general health as measured by SF-36 was not significantly influenced by the different treatments. Apparently, in the included, reasonably healthy subjects, the impact of maxillary edentulism in combination with a bilateral mandibular free-ending situations has little impact on their general health concerns, nor do the different operationalized prosthetic solutions that were offered for this predicament. This may not be surprising. For edentulous subjects a disease specific outcome measure like OHIP had better construct validity properties than a generic one, like SF-36.40

Although not evident from the questionnaires or the wearing-time outcome parameter, over half of the patients express a clear preference for M implant support. Perhaps the other patient-based measures are not sensitive or specific enough to record this. The preference for M implant support may stem from minor differences in stress or discomfort between the two implant positions. In mathematical model studies and in a study with a pressure-sensitive foil it was shown that more distal positions (in the region of the first or second mandibular molar) induce lower amounts of stress on the implants and on the residual alveolar ridge, compared to situations where implants were situated more anteriorly (the second bicuspid position).41-43 From various tested positions, M support is associated with the least amount of displacement of the tissues under load.14,44-46 A more distal position is also favoured by Grossman et al who recommended

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the second molar position.15 Hence, the less rotation and the more relieve from mucosal pressure, the better an RPD is tolerated.

With respect to the biomechanics and design of the denture, when the support is brought further to the distal, an anterior clasp or support can usually not be avoided, with aesthetic consequences. During the course of the present study, a labial retainer to an anterior natural abutment tooth was always present, both when the M and when the PM implant support was operationalized. Patients were informed that that would be an inherent consequence when they would finally choose for M implant support and that they could probably do without this anterior clasp in case they would opt for PM implant support. Evidently the patients’ comfort with M implant support outweighed their dislike of a potentially aesthetically disturbing anterior retainer since the vast majority favoured M implant support.

To date there is no information available regarding a difference in clinical performance between PM or M positioned implants when used as support for an RPD. The implant placement itself in the posterior can usually be planned safely on a panoramic radiograph.24 With (ultra) short implants becoming available, the possibilities to provide implant support to a removable partial denture or provide fixed partial dentures in the resorbed posterior regions is increasing. It is well advised to plan the position of the implants in such a way that a fixed partial denture, be it a single or multiple unit restoration, would still be possible if the patient desires to convert from a removable to a fixed restorative solution.

In conclusion, in patients with a bilateral free-ending situation in the mandible who perceive functional problems with their RPD yet would like to continue wearing one, mandibular implant support favorably influences oral health related patient-based outcome measures. The majority of patients prefer the implant support to be in the molar region.

Acknowledgments

This project was supported by a grant from the ITI Foundation, Switzerland, and by the authors’ institutions. The microelectronic chips (TheraMon) were offered by Orthosmart, Heerhugowaard, the Netherlands at a reduced cost. Martijn Brenkman of the Department of Fixed and Removable Prosthodontics and Biomaterials of the Center for Dentistry and Oral Hygiene, University Medical Center Groningen is recognized for providing and modifying all partial dentures during the different stages of treatment. All removable partial dentures were made at the maxillofacial dental laboratory Gerrit van Dijk, Groningen the Netherlands. The authors state that they have no conflicts of interest.

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CHAPTER 4

REMOVABLE PARTIAL DENTURES IN THE MANDIBLE;

FUNCTIONAL, CLINICAL AND RADIOGRAPHICAL

PARAMETERS IN RELATION TO IMPLANT POSITION

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This chapter is an edited version of the manuscript:Jensen C, Speksnijder CM, Raghoebar GM, Kerdijk W, Meijer HJA, Cune MS. Implant-supported mandibular removable partial dentures; functional, clinical and radiographical parameters in relation to implant position. (Accepted for publication)

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Abstract

Background. Patients with a Kennedy class I situation often encounter problems with their Removable Partial Denture (RPD).

Objectives. To assess the functional benefits of implant support to Removable Partial Dentures (RPD) in patients with a bilateral free-ending situation in the mandible, to assess clinical and radiographical performance of the implants and to determine the most favourable implant position with respect to these aspects: premolar (PM) or molar (M) region.

Materials and methods. Thirty subjects received 2 PM and 2 M Implants. A new RPD was made. Implant support was provided 3 months later. Two PM implants supported the RPD. After 3 months the 2 M implants were used or vice versa. Masticatory performance was determined by assessing the Mixing Ability Index (MAI) at the end of each stage of treatment. Clinical and radiographic parameters regarding implants and abutment teeth were assessed. Non-parametric statistical analysis for related samples and post-hoc comparisons were performed.

Results. Masticatory performance differed significantly between the stages of treatment (p<0.001). MAI-scores did not change significantly after a new RPD was provided, but improved with implant support. The implant position had no significant effect on MAI when functioning with an ISRPD.

No implants were lost, mechanical complications to the implants or RPD were not observed and clinical and radiographical parameters for both implants and teeth during the relatively short observation period were favourable. Higher scores for bleeding on probing were seen for molar implants.

Conclusions. In patients with a bilateral free-ending situation in the mandible who perceive functional problems with their conventional RPD yet would like to continue wearing one, implant support significantly improves masticatory function. No marked difference was seen between molar and premolar implant support. No major problems in relation to the clinical function of the implants, the abutment teeth and the RPD itself were observed.

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Introduction

Loss of posterior teeth reduces masticatory performance1-4, the degree of which relates to the number of remaining occlusal units.5 They compensate their masticatory impairment by increasing the number of chewing cycles before swallowing, so chewing their food takes them longer than others with a full dentition.6

In patients with bilateral mandibular posteriorly unbounded saddles, providing a Removable Partial Denture (RPD) is one of the means available to restore function and aesthetics. However, data regarding the effect on masticatory performance are contradictory. Some report improved masticatory performance, particularly in patients with more serious functional problems.7-10 Others don’t see improvement when providing an RPD or differences between subjects with or without an RPD in shortened dental arches.11 In clinical practice mandibular distal extension RPD’s enjoy a poor reputation among both dentists and patients. Patients’ appreciation is unpredictable and complaints include food retention underneath the saddle and pain, resulting from a lack of stability and retention of the RPD. Patients discontinue wearing them or insist on replacement by a new one at a high rate.12-17

The main problem with bilateral mandibular distal extension RPD’s is of biomechanical origin. Occlusal forces move the saddles into a tissue-ward direction because distal support is lacking, compromising the anterior abutment teeth as well through potentially destructive rotational forces. As a corollary, long term use of an RPD is associated with poor adaptation of retainers, occlusal disharmony, pain, periodontal problems and ongoing resorption.18-20

In fully edentulous subjects there is overwhelming evidence that implant support to mandibular dentures effectively improves various oral functions, among which is masticatory performance.21-23 Since denture complaints from partly edentulous patients resemble those of fully edentulous patients, providing implant support to RPD’s may be to the functional and psychological benefit of partly edentulous patients too. It presumably improves stability, retention and chewing ability, patient comfort in general, and even nutrient intake.19,20,24-30 The use of unaesthetic clasps can often be avoided with implant support.31

Implant-supported RPD (ISRPD) treatment is relatively cheap and easy to perform. A Kennedy class I or II situation is basically transformed into a class III situation, with a more favourable transfer of forces from the mucosa toward the implant(s) and abutment teeth. With the cuspid or first bicuspid as most distal tooth, the position of the implant in the edentulous zone is more or less optional and at the discretion of the prosthodontist or surgeon. Little evidence is available with respect to functional and clinical outcomes on which to base the decision. Theoretical models indicate that a more posterior position, i.e. at the position of the first or second molar, reduces the

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pressure to soft tissues and alveolar bone the most, whereas an implant positioned directly distal to the remaining dentition reduces the stress on the abutment teeth.32

The aim of this study was to assess the functional benefits of implant support to removable partial dentures in patients with a full upper denture and a bilateral free-ending situation in the mandible, to assess the clinical and radiographical performance of the implants and abutment teeth, and to determine the most favourable implant position with respect to these aspects: premolar (PM) or molar (M) region.


Study setup and patient populationThe study was set up as a within-subject comparison randomized clinical trial for which permission from the medical ethical committee of the University Medical Center of Groningen was granted (METc 2011.194). Thirty subjects with a full upper denture and complaints regarding their bilateral free-ending mandibular RPD were included fulfilling the following criteria:- ≥ 18 years of age;- the saddle area reaches until the first mandibular premolar or cuspid, both left and right;- the bone volume distal from the most posterior abutment teeth allows the placement of implants with a minimum length of 8 mm and minimum diameter of 3.3 mm;- the patient is capable of understanding and giving informed consent.

Potential subjects with medical and general contraindications for the surgical procedures, those with a history of local radiotherapy to the head and neck region, those who experienced implant loss in the past, subjects who are incapable of performing basal oral hygiene measures and those with decreased masticatory function due to physical disability or with active, uncontrolled periodontal pathology of the remaining dentition were excluded from participation.

One of the authors (CJ) was involved during the inclusion of the subjects, coordination of the trial and performed all measurements but did not provide surgical or prosthodontic care.

Surgical and prosthetic proceduresAll subjects gave informed consent and received 2 implants on either side of the mandible (Straumann RN, Straumann, Switzerland) that were provided with cover screws and submerged. Two implants were placed in the premolar region (PM implant support) and two were placed in the molar region (M implant support). A surgical guide was used to achieve the right position and inclination. After 3 months, all implants were

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exposed in a second-stage surgery and low healing abutments were inserted. A new RPD was made according to standard prosthetic procedures. The design

involved a lingual plate and a clasp on either side. The housing of the Locator® abutment (Zest Anchors, Inc., Escondido, California, USA) was already incorporated in the RPD, but not the Teflon matrix so it provided neither retention nor support to the RPD. Three months later and following a randomization scheme, either the PM or M implants were provided with a Locator® abutment. The remaining implants were left unloaded for future investigation. After 3 months, the other pair of implants was loaded. Consequently, 2 groups can be distinguished (PM -> M support and M -> PM support). Figure 1a-d represent a typical clinical case. A clear timeline of the trial and moments of data collection is depicted in Figure 2.

Figure 1a. Implant-supported bilaterally free-ending mandibular partial denture with red nylon

matrices incorporated to engage with 2 locator abutments at the position of a premolar (premolar-

implant support). Molar implant not active, housing without a matrix.

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Figure 1b Occlusal view of cast model. Locator abutments at the premolar implants, low healing

abutments in the molar implants (premolar support).

Figure 1c. Vice versa. Molar implants active after placement of locator abutments, premolar implants

with low healing abutments (molar support).

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Masticatory performanceMasticatory performance was studied by means of a mixing ability test and constituted the primary outcome measure of the study.33-35 The test and method of analysis are described in detail by others and is described here in brief. The test measures how well a subject is able to mix a wax tablet by chewing on it for a total number of fifteen chewing strokes. The tablet (Figure 3a,b) consists of two, 3-mm layers of red and blue wax and has a diameter of 20 mm. The wax is a soft material that forms a compact bolus during chewing.

After being chewed, the wax is flattened between foil to a thickness of 2.0 mm to avoid shadows in the image by the oblique illumination of the scanner’s lamp. The flattened wax is then photographed using a high-quality scanner (Epson® V750, Long Beach, CA, USA). The images of the wax are analysed and processed using a commercially available program for image analysis (Adobe Photoshop CS3, San Jose,

Figure 1d. The housings are laser welded to the metal base of

the removable partial denture. Matrix in situ at the position of

the premolar implant.

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CA, USA). Intermediate colour intensities appear and the spreads of the intensities for red and blue decrease. A lower MAI score implies a better mixed tablet, hence better masticatory performance.

Figure 3b. Mixed tablet and flattened after 15 chewing strokes.

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Figure 3a. Pristine wax tablet for the mixing ability test.

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Clinical and radiographical parameters of the implantsClinical and radiographical parameters included probing pocket depth (PPD), recession (REC) and bleeding on probing (BOP) and were assessed at 3 sites per implant (mesial, distal, buccal). A plastic periodontal probe with 0.25 N of calibrated probing force was used (Click-probe®, KerrHawe, Bioggio, Switzerland). PPD was measured in millimetres from the mucosal margin to the clinical pocket. REC was measured from the edge of the locator abutment to the mucosal margin in case of the implants. BOP was noted as no bleeding (score=0), small punctuated bleeding (score=1) or severe bleeding (score=2).

Marginal bone levels (MBL) were analysed on a digital panoramic radiograph (Oldelft, Orthoceph, OC100D, 85 KV) using the known implant length as a reference. The interface of the implant and the abutment was used as a reference line, from which all distances were measured using designated software (DicomWorks, Biomedical Engineering, University Medical Center Groningen, the Netherlands.36 The error of the method used was reported 0.13 ± 0.01 mm for the assessment of the radiographic marginal bone height.37,38 All radiographic assessments were performed by a single observer (CJ). Mean values per M or PM implant pair (left/right) were calculated for all variables. Depending on the group (PM -> M support or M -> PM support) the implant belonged to, data were obtained after 6 or 9 months following placement of the new RPD, hence 7.5 months on average.

Clinical and radiographical parameters abutment teethClinical parameters were assessed at 6 sites for the most distal abutment teeth, both left and right and included PPD, BOP and REC. REC was measured in millimetres from the cemento-enamel junction to the marginal gingiva for the abutment teeth. PPD and BOP of teeth were assessed the same as those of the implants.

MaintenanceMechanical complications regarding the (IS)RPD and locator abutments were noted during the course of the trial.

Sample size calculation and statistical analysisThe required sample size was calculated given X=0.05, power=0.80 and on the basis of the expected effect size for 2 dependent means (matched pairs).39 The prospected outcome was based on a study on masticatory ability as reflected by the mixing index in edentulous subjects with and without implant support in the mandible after 15 chewing cycles (20.4 SD 2.3 versus 22.2 SD 3.4).33 Twenty-two subjects would be required to have a 80 % chance of detecting, as significant at the 5 % level, an increase in the primary outcome measure from 20.4 in the control group to 22.2 in the experimental group, be it with the implants positioned anteriorly or posteriorly. Given the fact that

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the expected effect in patients with some remaining natural teeth is presumably smaller than that in edentulous subjects and compensating for potential dropouts, the intended number of subjects to include in the study was determined at 30 patients.

Masticatory performance as expressed by the MAI with the old, the unsupported, the M implant-supported and the PM implant-supported RPD’s will be compared with a Friedman test. In case of statistical significance (X < 0.05), post-hoc Wilcoxon signed rank tests will be performed with Bonferroni adjustment for multiple testing. Mann-Whitney U tests will be performed to detect any effects from treatment sequence (PM -> M support or PM -> M support).

Clinical parameters were compared during the stage with PM and M implant support only. Here, the effect of treatment sequence as well as left-right differences were examined first. Statistical analyses were performed using standard statistical software (SPSS, version 23). The statistician (WK) was blinded with respect to the groups that were being evaluated.

Results

Patient and treatment characteristics are presented in table 1. No implants were lost, nor were mechanical complications related to the implants, locator abutments or RPD’s noted during any of the stages of treatment. All patients have worn there RPD’s during the whole course of the study.

Kolmogorov-Smirnov tests revealed that variables were indeed not normally distributed and therefore the anticipated non-parametric tests were used. No statistical significant effect of the sequence in which the implants were loaded was observed for any of the variables and for further analysis all data were grouped into either PM- or M-implant support.

Table 1. Patient characteristics

Gender (male/female) 15/15

Mean Age (SD/range) 60.9 (1.2/43.8-71.0)

Group (PM*/M**) 15/15

Number of remaining natural teeth (5-6/7-8) 16/14

*PM = implants in premolar region first loaded*M= implants in molar region first loaded

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Table 2. Masticatory performance (Mixing Ability Index) at different stages of

treatment: old removable partial denture (Tbaseline), new removable partial denture

(Tnew RPD), implant-supported removable partial denture with support at the molar

position (TISRPD-M), implant-supported partial denture with support at the premolar

position (TISRPD-PM). Mean values, standard deviations and range between brackets.

Lower numbers indicate a better mixed tablet.

Tbaseline Tnew RPD TISRPD-M TISRPD-PM p-value

19.2 (2.2; 15.0 – 22.9)

20.2 (2.1; 16.5 – 25-1)

18.0 (1.4; 14.3 – 20.4)

17.9 (1.5; 15.7 – 21.3)

p < 0.001*

* Post-hoc tests: Tbaseline = Tnew RPD > TISRPD-M = TISRPD-PM

Table 3. Clinical and radiographical data regarding the M- and PM implants after 1

year of function. Data for the left and right implants were averaged. Mean values,

standard deviation between brackets. Positive values denote an increase.

M-Implant PM-Implant p-value

Probing pocket depth (mm) 1.69 (0.43) 1.76 (0.45) ns

Recession (mm) 0 0 ns

Bleeding on probing 0.26 (0.29) 0.11 (0.11) p=0.006

Marginal bone level (mm) -1.10 (0.53) -1.06 (0.59) ns

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Masticatory performanceMasticatory performance as expressed by the MAI differed significantly between the stages of treatment (X2(3) = 31.68, p<0.001). MAI-scores did not change significantly after a new RPD was provided, but improved with implant support, to a level that was statistical significantly higher than prior to treatment and after provision of a new, unsupported RPD. The implant position, M or PM, had no significant effect on masticatory performance (table 2).

Clinical and radiographical parameters implantsThe implants functioned well as reflected by the parameters measured, with low probing depths and bleeding scores. A statistical significantly higher score for BOP was seen around the molar implants (Wilcoxon signed-ranks test, Z=47.5, p=0.006). No recession was seen during the observation period around any of the implants. Approximately 1 mm of marginal alveolar bone was lost on average 12 months after implant placement both around the M- and the PM-implants (table 3).

Clinical parameters abutment teethDuring the 3 month periods with M- and PM-support the periodontal health of the abutment teeth was stable. Values at the start and the end of an interval did not differ to a significant level (table 4).

Table 4. Clinical data regarding abutment teeth. Differences occurring during the

period with molar (TISRPD-M) or premolar implant-support (TISRPD-PM). Data for the

left and right teeth were averaged. Mean values, standard deviation between

brackets. Positive values denote an increase during the interval.

TISRPD-M TISRPD-PM p-value

Probing pocket depth (mm) 0.01 (0.35) 0.04 (0.32) ns

Recession (mm) 0.01 (0.62) 0.37 (0.73) ns

Bleeding on probing 0.10 (0.40) 0.00 (0.42) ns

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Discussion

To investigate whether implant support to a Removable Partial Denture in patients with a mandibular bilateral free-ending situation improves masticatory function, a within subject comparison clinical trial was set up in which several clinical and radiographical outcome measures regarding implants and teeth were assessed as well. These variables were related to 2 different implant positions: the molar (M) or the premolar (PM) position. The studied population is rather homogenous. The cross-over study design employed has several advantages among which are the unchanged occlusion and vertical dimension and length of the borders of the RPD. Consequently, several sources of bias were avoided.

In this study masticatory performance was expressed as the Mixing Ability Index (MAI) which evaluates the ability to mix and knead a food bolus by mixing a paraffin wax tablet with a blue and red layer (see also the method section).33 It has been shown that chewing on two-coloured paraffin wax is a reliable alternative for the often used comminution tests.33,35,40 Comminution tests measure the degree of breakdown of a natural or artificial food by sieving the comminuted food.1,21,41-46 However, subjects with a compromised oral function e.g. by wearing dentures are not always capable to fragment the test food, because their maximum bite force appeared to be lower than the force needed to break the test food particles.21,45,47 For patients with compromised oral conditions, the MAI is a good alternative for food comminution tests: the test food is soft enough and forms a bolus that can be easily chewed on.47 In previous studies the parameter ‘masticatory performance’ was operationalized in various ways with contradictory findings.7-11 This makes the interpretation of those findings and comparison with the present one troublesome.

In in vitro studies dealing with Kennedy class I or II situations, it has been demonstrated that positions more to the posterior reduce the pressure on the alveolar ridge and hence the periosteum more favorably in comparison to situations where implants are positioned more to the anterior.48-50 In situations with molar support the least amount of displacement of the mucosal tissues under load is seen.18,32,51,52 The present data clearly demonstrate an improvement in masticatory performance when implant support was provided 3 months earlier. Three months functioning with a new denture is tentatively considered long enough for a patient to adapt. No noticeable differences with respect to the 2 implant positions tested was seen. Although not statistical significantly different, masticatory performance worsened after provision of a new, optimally made RPD without implant support. A similar trend was seen when a new denture was made for patients with lower denture complaints, despite the fact that they considered their new denture superior to their old one.21,22 The results underscore the findings by others who reported an increase in bite force and mastication after

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implant support to an RPD was provided, be it not to the level of that of a fixed implant-borne restoration.26,28,53,54

After fifteen chewing strokes the implant-supported RPD on the molar position and premolar position showed MAI colour spreads of the intensities for red and blue of 18.0 ± 1.4 and 17.9 ± 1.5 respectively. These results are comparable to outcomes of healthy persons of the same age with natural dentition (18.3 ± 2.0) and are much better than healthy persons of the same age with full dentures (22.2 ± 3.4) or full dentures with mandibular implant retention (20.4 ± 2.3).33

The observation period in the present study is relatively short to evaluate clinical performance. No implant loss was observed and clinical and radiographical data are representative for healthy and stable implant conditions, in line with the studies that follow a group of patients over a longer period of time.55-57 No mechanical complications were observed, nor was maintenance required during the course of present study. Conventional mandibular free-ending RPD’s are often not worn by patients. The ISRPD’s in the present study were worn throughout the study.

Most clinical parameters (both concerning the implants and the teeth) revealed no difference when the implants at the molar or the premolar sites were loaded. Bleeding on probing around the implants was an exception, with a less favourable score being noted around molar (M) implants. During the observation period this has not lead to deeper probing depths or more marginal bone loss, but it remains to be seen what the long term effect may be.

No strong preference for implant position can be identified on the basis of the current data. A choice would have to be made on other grounds. This could be bone volume or risk to the alveolar nerve, ease of cleaning, or the choice for a strategic position for the future if a fixed restoration is desired. On the other hand, in a similar population as the one in the present study, others started seeing late implant failures (> 3 years) predominantly in short, implants at the second molar position.57 They also observed a fairly large number of puncture fractures in the acrylic at the area of the matrix at posterior positions, which is not very likely to occur in the present population because of the metal framework used. The matrices were fused to the framework by laser welding. Studies comparing patients’ preference regarding implant position have not been published to date.

In conclusion, in patients with a bilateral free-ending situation in the mandible who perceive functional problems with their conventional RPD yet would like to continue wearing one, implant support significantly improves masticatory function. No marked difference was seen between molar and premolar implant support. No major problems in relation to the clinical function of the implants, the abutment teeth and the RPD itself were observed.

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Acknowledgments

This project was supported by a grant from the ITI Foundation, Switzerland, and by the authors’ institutions. Martijn Brenkman DDS, Department of Fixed and Removable Prosthodontics and Biomaterials of the Center for Dentistry and Oral Hygiene, University Medical Center Groningen is recognized for providing and modifying all partial dentures during the different stages of treatment. All removable partial dentures were made at the maxillofacial dental laboratory Gerrit van Dijk, Groningen the Netherlands. The authors state that they have no conflicts of interest.

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CHAPTER 5

COST-EFFECTIVENESS OF IMPLANT-SUPPORTED MANDIBULAR REMOVABLE

PARTIAL DENTURES

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This chapter is an edited version of the manuscript:Jensen C, Ross J, Feenstra TL, Raghoebar GM, Speksnijder CM, Meijer HJA, Cune MS. Cost-effectiveness of implant-supported mandibular removable partial dentures. Clin Oral Implants Res. 2016. Epub ahead of print.

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Abstract

Objectives. Aim of this study was to conduct a cost-effectiveness analysis comparing conventional Removable Partial Denture (RPD) and Implant-supported RPD (ISRPD) treatment in patients with an edentulous maxilla and a bilateral free-ending situation in the mandible.

Materials and methods. Thirty subjects were included. A new RPD was made and implant support was provided 3 months later. Treatment costs (opportunity costs and based on tariffs) were calculated. Treatment effect was expressed by means of the Dutch Oral Health Impact Profile questionnaire (OHIP-NL49), a chewing ability test (Mixing Ability Index, MAI) and a short-form health survey measuring perceived general health (SF-36), which was subsequently converted into Quality-adjusted-life-years (QALYs). The incremental cost-effectiveness ratio (ICER) was the primary outcome measure of cost-effectiveness, comparing both treatment strategies.

Results. The mean total opportunity costs were €981 (95 % CI €971 to €991) for the RPD treatment and €2.480 (95 % CI €2.461 to €2.500) for the ISRPD treatment. The total costs derived from the national tariff structure were €850 for the RPD treatment and €2.610 for the ISRPD treatment. The ICER for OHIP-NL49 and MAI using the opportunity costs was €80 and €786 respectively. When using the tariff structure, corresponding ICERs were €94 and €921. The effect of supporting an RPD with implants when expressed in QALYs was negligible, hence an ICER was not determined. Conclusions. It is concluded that depending on the choice of outcome measure and monetary threshold, supporting an RPD with implants is cost-effective when payers are willing to pay more than €80 per OHIP point gained. Per MAI point gained an additional €786 has to be invested.

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Introduction

Removable partial dentures (RPD’s) have a poor reputation as patients frequently complain from a lack of stability and retention, discontinue wearing them or insist on replacement by a new RPD in 25-50 % of cases between 5 and 10 years.1-3 Supporting an RPD with implants can be beneficial by increasing stability, retention and chewing ability as well as improving patient comfort in general.4-7 The use of unaesthetic clasps can often be avoided.8 However, providing implant support to an RPD is likely to increase treatment costs.

In recent years the rise in health care costs has been a controversial topic in the public debate. In the Netherlands for instance, whilst the share of health care costs in the gross domestic product (GDP) in the year 2000 was only 10.4 %, in 2014 it rose to 14.3 %.9,10 It is uncertain whether health care costs continue to grow at this rate, but it is predicted that the share of health care costs in the GDP will be 22 % in 2040. According to the Dutch Bureau for Economic Policy Analysis (Centraal Plan Bureau, CPB), health care costs rise faster than the country’s economic growth.11 This cannot merely be explained by the fact that the population is aging. Technological advances and increased treatment possibilities are thought to play an important role in the increasing demand for care as well.12 This increasing demand for care, the associated escalated costs, the limited funds available, and the intent to maintain affordable health care for everyone over the years to come requires an efficient use of available resources.13

When competing treatment options are available, their documented or presumed effectiveness and their (additional) costs should be considered and critically assessed when favoring one treatment over the other. A cost-effectiveness analysis can provide insight into whether the more costly treatment option offers sufficient added value to the patient to justify its application. In addition, given similar effectiveness, it could help Health Care Insurance Companies in deciding which therapies to reimburse and which not in order to control expenditures. Currently, in the Dutch setting, economic evaluation is mainly important for new pharmaceuticals, and still has a limited weight in reimbursement decisions. In dentistry in general economic appraisal is not yet widely used either. This can be explained in part by the fact that dental care is usually not paid for by the national health insurance scheme, but mainly through private insurance or out of pocket (for the Dutch situation: circa 73 % in 2011).

Nevertheless, the use of economic evaluation in oral health care is slowly increasing.14,15 There is a tendency toward a more value-based oral health care system with more emphasis on proven cost-effectiveness and utility of therapies that are provided. In the field of restorative and prosthetic dentistry for example Zitzmann et al. examined the cost-effectiveness of implant-supported overdentures and they found that over an assumed time horizon of 10 years, implant treatment becomes cost-effective

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with implant-supported overdentures being the treatment of choice if the patient is willing to pay at least CHF 3800 for a Quality-adjusted Prosthesis Year gained.16 Single tooth replacement by means of an implant-supported restoration was calculated to be more cost-effective than a 3-unit fixed partial denture.17-19 In a recent study it was shown that treatment according to the shortened dental arch concept was more cost-effective in improving Oral Health Related Quality of Life (OHRQoL) than replacing missing teeth by means of a removable partial denture.20 The cost-effectiveness of mandibular overdentures on 2 anterior implants with conventional dentures was compared using the 20-item Oral Health Impact Profile (OHIP-20) instrument as outcome measure. It was concluded that for improvement by one OHIP-20 point CAN$ 14 per year has to be invested (Heydecke et al, 2005). Studies like these can aid dentists and patients to make treatment decisions in the most cost-effective way.21,22 However, the used outcome measures vary and no study as of yet has operationalized QALY’s as an outcome, which is a general measure of health benefits, allowing comparison across different disease areas. No information comparing the anticipated benefits of RPD’s and ISRPD’s and relating these to the expected extra costs is available.

The aim of the present study is to conduct a cost-effectiveness analysis comparing treatment with RPD and implant-supported removable partial dentures in patients with a bilateral free-ending situation (Kennedy class I) in the mandible and functional complaints.


Patient populationAll data was retrieved from a comprehensive clinical trial on implant-supported removable partial dentures, approved by the Medical Ethical Committee of the University Medical Center Groningen (METc 2011.194) and written informed-consent was obtained from all subjects prior to inclusion. Thirty subjects with a full upper denture and complaints regarding their bilateral free-ending mandibular RPD were included according to the following inclusion criteria:- minimum age of 18 years;- bone volume distal from the most posterior abutment teeth allows the placement of implants with a minimum length of 8 mm and minimum diameter of 3.3 mm;- the patient is capable of understanding and giving informed consent.

Potential subjects with medical and general contraindications for the surgical procedures, those with a history of local radiotherapy to the head and neck region, those who experienced implant loss in the past, subjects who were incapable of performing basal oral hygiene measures and those with decreased masticatory function due to

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physical disability or with active, uncontrolled periodontal pathology of the remaining dentition were excluded from participation.

All subject received 4 bilateral implants (Straumann RN, Straumann, Switzerland) provided with cover screws; two implants in the premolar region and two implants in the molar region. After a healing period of 3 months, a new RPD was made. The housing of the Locator® abutment (Zest Anchors, Inc., Escondido, California, USA) was already incorporated in the RPD, but not the Teflon matrix so it neither provided retention nor support to the RPD. Three months later, one single implant on either side (in the premolar (PM) or molar (M) region) was provided with a Locator® abutment. The other implant on either side, was left unloaded for future investigation. Figure 1 shows an example of a typical clinical case.

Patient-based and functional outcome measures were among the parameters of evaluation collected at 3 months of function with an RPD (T1) and at 3 months of function with implant support (T2).

Figure 1a. Intra oral situation with 2 implants provided with Locator® abutments in premolar

(PM) region. The 2 ‘sleeping’ implants in the molar (M) region are placed for future research.

Figure 1. Example of a typical clinical case.

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Figure 1b. Inside of the Implant-supported Removable Partial Denture (showing the matrix

which provides support and retention to the ISRPD).

Figure 1c. Kennedy class I ISRPD.

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Treatment costsA cost-effectiveness analysis from a societal perspective was performed to be able to compare treatments that are reimbursed by public insurance. This analysis estimated costs by calculating the opportunity costs of the different procedures. The term opportunity costs refers to the estimation of costs based on the notion that instead of performing the costed activity the relevant professionals could spend their time on another activity (opportunity). Hence the value of these alternative activities represents the opportunity cost of a certain treatment. 23 In practice, this implied assessing the time costs of professionals involved and using the Dutch costing manual and the standard salary scales of the Collective Labor Agreement (CAO) to value this.24 Because all resource use occurred at the same point in time (2013) discounting was not applicable.

In addition, this cost-effectiveness study was also performed from a payer perspective. This would usually be a private person but could also be a health care insurer. Hence, health care costs were included and valued at their market prices using tariffs for the Dutch situation.

Outcome measuresThree outcome measures were used as effect parameters. The OHIP-NL49 is a validated questionnaire measuring various domains of OHRQoL.25,26 A chewing ability test (Mixing Ability Index, MAI) was carried out as an objective measure of oral function. Two-colour wax tablets were used to evaluate the ability to mix and kneed a food bolus. After fifteen chewing strokes the mixing of the chewed wax was determined by means of computer analyses of images.27-29 The MAI has no unit of effect and ranges from 5-30 (respectively fully mixed tablet and pristine tablet). A short-form health survey measured perceived general health (SF-36).30 The SF-36 dataset was subsequently converted into Quality-Adjusted-Life-Years (QALYs) using the SF-6D excel scoring program provided by the University of Sheffield.31

Patients were asked to complete both questionnaires and performed the chewing ability test at 2 moments in time: after having worn a newly made RPD for 3 months (T1) and 3 months after implant support was provided to the RPD (T2) (Figure 2).

Figure 2. Timeline. Effect parameters are measured at T1 and T2. RPD: Removable Partial

Denture, ISRPD: Implant-supported Removable Partial Denture.

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Cost-effectivenessThe incremental cost-effectiveness ratio (ICER) represents the difference in costs divided by the difference in effects between the 2 treatment strategies and is expressed by the following formula:

Here, costs A are the average costs per patient for ISRPD treatment and costs B are the average costs per patient for RPD treatment. Effects A and B are the average effects per patient for ISRPD and RPD treatment respectively. The ICER was calculated for the 2 treatment strategies, both from a payer perspective and from a societal perspective and was determined for the 3 outcome measures mentioned before. It describes the costs per additional unit of effect for the ISRPD treatment compared to an RPD treatment and as such is a measure of efficiency.23

Statistical analysisTo analyze the data Microsoft Office Excel (2011) was used. Uncertainty around the outcome measures was estimated using bootstrapping, generating 5000 replications of the original data set and creating a 95 % confidence interval (CI). Bootstrapping is a simulation based way to estimate the uncertainty around a certain statistic which was based on a random sample. It is performed by generating a large number of new simulated samples by sampling with replacement from the original random sample.32 To reflect uncertainty around the opportunity costs, a 10 % margin was assumed around the established total time requirements of the professionals. A uniform distribution of actual time was then assumed within this range and used to estimate the variation in costs over individual patients. No uncertainty range was set around the costs based on the tariff structure, because these are fixed values. To visualize the uncertainty in costs and effects a scatter plot of these simulated incremental costs and effects is displayed in the cost-effectiveness plane.

Results

Clinical outcomesFifteen men and fifteen women were included with a mean age of 61.0 ± 6.6 years. The mean gain in OHRQoL (OHIP-NL49), after bootstrapping and correcting by multiplying with -1 so that a lower score constitutes a better result, was 18.8. The mean improvement in chewing ability as expressed by the MAI, after bootstrapping and correcting by multiplying with -1 so that a lower score constitutes a better result, was

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1.9. A small mean decrease in QALYs was found, i.e. -0.01 (Table 1).

Treatment costsThe mean total opportunity costs were €981 (95 % CI €971 to €991, median €981, range €946-€1028) for the RPD treatment and €2.480 (95 % CI €2.461 to €2.500, median €2.480, range €2.386-€2.559) for the ISRPD treatment. The total costs derived from the national tariff structure were €850 for the RPD treatment and €2.610 for the ISRPD treatment. The breakdown of the costs is presented in table 2.

Cost-effectivenessThe incremental cost ratios for the 2 treatment options and corresponding outcome measures (OHIP-NL49, MAI, QALYs) are presented in Figure 3 and table 3. The ICER for the outcome measure OHIP-NL49 using the opportunity costs was €80. This means that per OHIP point gained an additional €80 has to be invested. The ICER for the outcome measure OHIP-NL49 using the tariff structure based costs was €94, implying that that per OHIP point gained an additional €94 has to be invested. The ICER for the outcome measure MAI using the opportunity costs was €786. Hence, per MAI point gained an additional €786 has to be invested. The ICER for the outcome measure MAI using the tariff structure based costs was €921, implying that per MAI point gained an additional €921 has to be invested. The ISRPD had hardly any effect when expressed in QALYs, which would lead to very high ICER in terms of costs per QALY.

Table 1. Mean effects after bootstrapping for the Oral Health Impact Profile (OHIP-

NL49), for the Mixing Ability Index (MAI) and for the Quality Adjusted Life Years

(QALY). 95% confidence interval (C I) between brackets. RPD: Removable Partial

Denture, ISRPD: Implant-supported Removable Partial Denture, CI: confidence

interval.

OHIP-NL49

95% C I

MAI

95% C I

QALY

95% C I

T1: RPD41.1

(31.2-52.5)

20.2

(19.4-20.9)

0.8

(0.8-0.8)

T2: ISRPD22.4

(15.6-30.3)

18.3

(17.8-18.7)

0.8

(0.7-0.8)

Δ T2-T118.8*

(11.3-28.0)*

1.9*

(1.2-2.7)*

-0.0

(-0.0-0.0)

* Corrected by multiplying with -1 so that a lower score constitutes a better result.

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Table 2. Mean opportunity costs and costs based on tariff structure for Removable Partial Dentures (RPD) and Implant-supported Removable Partial Dentures (ISRPD). Range because of uncertainty labor costs ± 10 % between brackets.

RPD ISRPD

Opportunity costs

Labor costs dentist* €455 €663

Labor costs Oral and Maxillofacial Surgeon and assistant (incl. 42 % overhead)*

€242

Invoice laboratory work (excl. VAT) €530 €1037

Purchase price implants and abutments (excl. VAT) €530

Total opportunity costs €985 €2472

(range labor costs ± 10 %) (€939-€1031) (€2381-€2562)

Costs (tariff)**

Labor costs dentist €320 €320

Labor costs Oral and Maxillofacial Surgeon

€720

Invoice laboratory work (excl. VAT) €530 €1040

Purchase price implants and abutments (excl. VAT) €530

Total costs (tariff) €850 €2610

* Cost manual Hakkaart-van Roijen standard salary scales of Collective Labor Agreement 2013-2015 (CAO UMCs), including Labor costs Oral and Maxillofacial Surgeon and assistant.** www.nza.nl

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Table 3. Incremental costs ratios (ICER) for Removable Partial Dentures (RPD) and Implant-supported Removable Partial Dentures (ISRPD) using the Dutch Oral Health Impact Profile questionnaire (OHIP-NL49), the Mixing Ability Index (MAI) and the Quality Adjusted Life Years (QALY) as outcome measures.

Type of costs EffectIncremental costs (€)**

Incremental effects*

ICER**

Opportunity costs OHIP €1500 18.8 80

MAI €1500 1.9 786

QALY €1500 -0.0 N/A

Costs (tariff) OHIP €1760 18.8 94

MAI €1760 1.9 921

QALY €1760 -0.0 N/A

* Displayed numbers are rounded to one decimals, full numbers were used for analysis.** Displayed numbers are rounded to tens.

Figure 3a. Analysis based on opportunity costs and OHIP-NL49.

Figure 3. Incremental cost-effectiveness analysis based on opportunity costs or health

care costs using Dutch tariffs for 3 different outcome measures: Dutch Oral Health Impact

Profile questionnaire (OHIP-NL49), Mixing Ability Index (MAI) and (Quality Adjusted Life

Years) QALY.

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Figure 3b. Analysis based on opportunity costs and MAI.

Figure 3c. Analysis based on the opportunity costs and QALY.

Figure 3d. Analysis based on health care costs using Dutch tariffs and

OHIP-NL49.

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Figure 3e. Analysis based on health care costs using Dutch tariffs and

MAI.

Figure 3f. Analysis based on health care costs using Dutch tariffs and

QALY.

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Discussion

A cost-effectiveness analysis comparing treatment with a removable partial denture (RPD) and an implant-supported removable partial denture (ISRPD) in patients with a bilateral free-ending situation (Kennedy class I) in the mandible and functional complaints was conducted. The relevance of efforts like the present study are underlined by the conclusions that were drawn in a recent consensus conference on economic evaluation of implant-supported prostheses. They showed that the incremental benefits of implant-supported prostheses came at substantial additional costs. For implant-supported removable partial dentures (ISRPD) a similar result may be expected. It was also stipulated that more economic evaluations are needed that follow well-established methodologies obtained from health economics to better assess the efficiency of implant-supported prostheses.33 The efforts made in the present paper are in line with this recommendation.

When applying economic evaluation in dentistry, specifically in prosthodontics, several difficulties remain. Attempts at determining the costs of treatment vary widely.15 The same can be said for outcome measures. A lack of a common outcome measure makes comparison of different treatments complicated.34 In addition, assessing the value that a patient derives from his dental treatment is difficult and the dental profession has not yet reached consensus on how to measure this added value.14 Biological, clinical and functional outcome measures are necessary, but equally important are patients’ improvements in oral health status, satisfaction, oral and psychological function, self-esteem and quality of life considerations.34 For economic evaluation in general, an often used outcome is the QALY. This measure can be used over all areas of disease and combines length of life with quality of life. Quality of life is for instance assessed by several validated instruments like the Health Utilities Index 2 and 3 (HUI2, HUI3) and the EuroQol 5D (EQ-5D).35,36 However, these general instruments are often insensitive to health benefits in dentistry, as we also see in our current study, with negligible changes in SF36 or QALYs based on the SF6 instrument. Attempts have been made to introduce a universal outcome measure similar to the QALY, but specifically for use in dentistry. For example, Zitzmann et al. used Quality-adjusted Prosthesis Years, which is defined as the number of years of service of a prosthesis adjusted by quality, as introduced in the 1990’s.16,37 Unfortunately these attempts are not yet broadly used in literature or validated. In order to overcome this problem, in the present study different outcome measures were used. By using the OHIP-NL49 as a subjective measure for patient perceived oral health quality, the MAI as an objective measure of chewing ability and the QALY as a measure for general health, a wide range of outcomes is covered.

This study shows that when assessing the health benefits using the OHIP-NL49 or MAI, the ISRPD treatment does result in an additional effect, and results ICER’s Figure

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in the northeast quadrant of the cost-effectiveness plane. In contrast, assessing the cost-effectiveness using QALYs as the outcome measure moves the ICER towards the northwest quadrant of the cost-effectiveness plane, indicating additional cost but no incremental effect. These varying results emphasize the leverage of outcome measure choice when conducting a cost-effectiveness analysis.

Although the number of patients included in this study is relatively small, the minuscule difference in QALY score between the 2 treatment options is noteworthy.36 SF-36 as an effect measure in prosthodontic treatment is questionable since it has not always proved to be able to discriminate between clinically distinct groups and thus may not be sensitive enough for this purpose.38 However the SF-36 is a well validated questionnaire and can therefore be assumed to measure what it claims to measure.30,39 This indicates that no changes to perceived general health can be attributed to supporting an RPD with implants. This underlines the aforementioned importance of outcome measure choice when economic evaluation is used in dentistry. Using more specific measures will help to choose wisely between the various dental procedures.

The finding that 2 procedures made no difference in general health outcomes also raises doubt regarding the manner in which continuous effort is invested in associating dental issues in all fields of study to overall general health matters. A clear improvement in quality of life can be seen after prosthodontic rehabilitation in patients surgically treated for malignancies in the oral cavity resulting in severe comprised oral function and/or esthetics.40 However, an overestimation of the desired results might occur when less intrusive dental health issues are sought to influence perceived general health and overall quality of life. In addition, the chosen experimental study setup, where patients knew beforehand that after 3 months the already inserted implants were to be used, may have influenced their ratings on the subjective outcome measures to an uncertain degree as a result of cognitive dissonance. Cognitive dissonance can be defined as the discomfort that is experienced by a person who holds contradictory beliefs, in this case that a conventional RPD will not work sufficiently and that implant support will provide the desired additional comfort as projected by the treating physician.41

The mean reduction of 18.8 point in OHIP-NL49 is consistent with results found by Gates et al. who reported an OHIP-49 reduction of 11.8 points and several other retrospective studies and case reports using other patient-based measures.4-7 However, Campos et al (2015) reported median OHIP-49 (Brazilian translation) values of 75 and 10 for RPD’s and ISRPD’s respectively, hence a far larger improvement for which no explanation can be offered.42

A minimal importance difference (MID) of 6 points (95 % CL, 2 to 9) has been suggested for OHIP use in dentistry.43 The MID was defined as “the smallest difference in score in the domain of interest which patients perceive as beneficial and which would mandate, in the absence of troublesome side effects and excessive cost, a change in

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the patients’ management. As suggested in the same study this MID can be used to approach clinical relevance of changes in perceived oral health. This indicates that the observed reduction of 18.8 OHIP points, leads to a clinically relevant change in oral health related quality of life. When assessing the clinical relevance of the incremental effects of the MAI there is no such thing as a MID or another threshold available. This makes interpretation of the observed reduction in MAI points difficult. Some insight could be derived from a study on loss of chewing ability after surgery in patients with squamous cell carcinoma of the tongue and/or floor of mouth an average reduction of the MAI score by 2 points was statistically significant (p=0.045).44 Although this gives a slightly better understanding of the outcome measure it does not provide a threshold to determine whether the results of the current study, with an average increase of 1.9 points, are clinically relevant.

Resource use was determined by interviewing the professionals involved. Timing each individual procedure would have been an even more accurate approach to resource use.

To decide if an intervention is cost-effective and thus offers “good” value for money, the ICER should be compared to a specified monetary threshold as done by Zitzmann et al. 16. This threshold represents the maximum amount of money that a decision-maker is willing to pay for an additional effect.45 In the present study the height of the threshold for MAI or OHIP scores was not examined and standardized values are not available, so this could not be determined. An effort to set such a threshold (range) would complement a future study.

Finally, another important factor in assessing cost-effectiveness is the time horizon that is adopted. The current study used a short time horizon, only examining the treatment costs and effects during the timeline of the underlying experimental study. Hence, it only took initial costs and effects of treatment into account. Aftercare costs, other future expenses and the sustainability of the prosthetic solution were not taken into consideration and this would make a valuable addition for further studies. Large, long term benefits of ISRPD that might be expected when supporting an RPD with implants may positively influence its duration and/ or lifetime. This would require sufficient existing evidence concerning long-term outcomes of (IS)RPD’s to warrant a modelling approach or a new study to gather such evidence with adequate follow-up time. As in medicine, these longitudinal analyses are complex and difficult to implement.34 These issues combined with the difficulties referred to above is why further collaboration with health economists to guide future research is advised.15 An increased proficiency in health care economics amongst dental researchers could favor this collaboration. The data presented in this study could aid patients, health care providers and insurers in decision making from their different perspectives regarding the cost-benefit aspects

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of implant retained RPD’s. The approach used can serve as an example for addressing other restorative and prosthodontic cost-effectiveness dilemmas.

When SF-36 was used as an outcome measure to determine the impact on general health no incremental effect and thus no added value was found. When outcomes measures were chosen that are dentistry specific, such as MAI or OHIP-NL49, the additional costs of ISRPD’s resulted in better outcomes. For the OHIP, the improvement was larger than the MID. For the MAI, although improvement of chewing ability was seen, no MID was available. Consequently, it was not possible to determine whether the observed gain in chewing ability was clinically relevant. Considering the clinical relevance of the gain in OHRQoL, an implant-supported removable partial denture (ISRPD) is cost-effective when payers are willing to pay more than €80 per OHIP point gained. Per MAI point gained an additional €786 would have to be invested.

Acknowledgments

This study was partially funded by a grant from ITI Foundation (Switzerland) and by the authors’ institutions. The authors state that they have no conflicts of interest.

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CHAPTER 6

COMPARING TWO DIAGNOSTIC PROCEDURES IN PLANNING DENTAL

IMPLANTS TO SUPPORT A REMOVABLE PARTIAL DENTURE IN THE MANDIBLE

116

This chapter is an edited version of the manuscript:Jensen C, Raghoebar GM, Meijer HJA, Schepers R, Cune MS. Comparing two diagnostic procedures in planning dental implants to support a mandibular free-ending removable partial denture. Clin Implant Dent Relat Res. 2016;18(4):678-685.

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Abstract

Objectives. The use of a cone beam computed tomography (CBCT) for the pre-operative implant planning is increasing. A clear guideline is needed in which cases a CBCT is essential. In this study two imaging modalities (panoramic radiograph and CBCT) are compared in pre-operative implant planning in the severely resorbed mandible and the influence on the observers assessments.

Methods. Thirty-four consecutive patients with bilateral edentulous regions in the mandible were included. The feasibility of implant placement in the premolar and molar region was judged by 3 observers on basis of casts either with a panoramic radiograph or a CBCT.

Cohen’s kappa, sensitivity and specificity rates, odds of agreement and disagreement as well as the Odds Ratio’s (OR, ratio between odds of agreement and disagreement) were calculated per observer and overall for all observers assuming the majorities agreement as the prevailing opinion.

Results. Overall outcome for premolar region revealed true-positive and true-negative rates of 90 % and 0 % respectively, with Cohen’s kappa (X) = -0.04. The OR’s for the three observers varied between 2.6 and 158.8, with an overall OR = 76.

For the molar region overall true-positive and true-negative rates were 65 % and 22 % respectively, with Cohen’s (X) = 0.68, representing a reasonable amount of agreement. Sensitivity and specificity as well as the OR’s for individual observers were fairly consistent with an overall OR = 43.

Conclusions. Implant placement in the resorbed posterior mandible can be well assessed with a cast in combination with a panoramic radiograph in the vast majority of the cases. Misclassification amounts to approximately 10-13 %. In all cases of misclassification a critical bone height, or an unclear course of the mandibular nerve or a knife edge ridge was present. In these cases the use of a CBCT is justified.

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Introduction

Pre-surgical evaluation of dental implant sites is based on clinical inspection and radiographic imaging. With respect to the former, intraoral and panoramic radiographs are generally used, but cone beam computed tomography (CBCT) has made its mark since the late 1990’s as a tool for 3D imaging, replacing the conventional CT scanner which requires a higher radiation dose in most of the cases.1 The CBCT equipment has been improved ever since with respect to (reduction of) the radiation dose and the quality of the images and there has been growing acceptance of CBCT as an imaging modality in dentistry.2-4

When planning implants for the lateral parts of the mandible, clinical inspection and a panoramic radiograph suffice in cases with ample bone volume. A CBCT may provide additional value in challenging cases because it provides 3D images of the anticipated implant location, enhancing the decision whether or not implant placement is possible and safe, i.e. reducing the risk of jeopardizing vital anatomical structures during implant surgery.5,6

The European Commission Council Directive on health protection of individuals against the danger of ionizing radiation in relation to medical exposure7 makes comprehensive recommendations about the use of a CBCT scanner as well as the final guidelines of the SEDENTEXCT project (2008-2011).8 At present, the effective radiation dose range of CBCT is considerably higher than that of panoramic radiography (0.019-0.674 mSv versus 0.003-0.024 mSv).9,10 As always and according to the ALARA principle its use should be restricted to those indications in which the benefits to the patient outweigh the potential risks of the patients’ exposure to ionizing radiation, thus reducing the radiation dose as much as possible.11

The ALARA principle raises the question under which conditions the additional information gained from CBCT outweighs the extra biological and financial risks and costs when evaluating implant sites pre-operatively. Four scenarios can be distinguished, when the information obtained from the CBCT is considered to represent the actual anatomical conditions in the mandible:

1. It is decided on the basis of a panoramic radiograph that implant placement is not feasible and this is confirmed by the observations on a CBCT (true-negative). An unnecessary additional dose of radiation was administered to the patient, which violates the ALARA principle;

2. It is decided on the basis of a panoramic radiograph that implant placement is not feasible, but based on the observations on a CBCT, implant placement is possible (false-negative). The patient can be offered treatment to his benefit and the administration of the extra dose of radiation can be readily justified, be it in hindsight;

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3. It is decided on the basis of a panoramic radiograph that implant placement is feasible, but based on the observations on a CBCT implant placement would confront the surgeon with insufficient bone volume or implant insertion would damage vital anatomical structures (false-positive). The patient would suffer inadequate treatment and is protected from serious surgical complications with possible lasting consequences. The extra radiation dose can be easily justified;

4. It is decided on the basis of a panoramic radiograph that implant placement is feasible which is confirmed by the observations on a CBCT (true-positive). This will frequently be the case in situations when a panoramic radiograph reveals a significant amount of bone height and palpation of the alveolar ridge indicates adequate bone width. The ALARA principle is again violated.

In this study two imaging modalities (panoramic radiograph and CBCT) are compared in pre-operative implant planning in the severely resorbed mandible and the influence on the observers assessments.

Material and methods

Study set-up and patient populationIn the context of an ongoing randomized clinical trial on implant-supported free-ending removable partial dentures in the mandible (approved by the Medical Ethical Committee of the University Medical Centre Groningen (METc 2011-194), 69 patients were referred to our clinic between January 2010 - December 2013. Patients were selected using the following inclusion criteria: Patient should- be at least 18 years of age;- have persistent complaints regarding their mandibular bilateral free-ending

removable partial denture (FRPD)- Their remaining mandibular natural dentition consisted of 6-8 anterior teeth,

stretching to either the cuspid or first premolar(s). - be capable of giving Informed Consent

Exclusion criteria used for the clinical trial were:- medical and general contraindications for the surgical procedures;- a history of local radiotherapy to the head and neck region;- previous implant loss- incapability of performing basal oral hygiene measures as a result of physical or

mental disorders; - active, uncontrolled periodontal pathology of the remaining dentition;

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- ample too little bone height in the lateral parts of the mandible to place implants

Study proceduresConsecutive patients underwent a comprehensive clinical investigation and evaluation of the present denture by an experienced prosthodontist and if indicated a radiographic investigation by means of panoramic radiography was performed to evaluate if they could possibly benefit from an implant-supported removable partial. (Oldelft Benelux, Veenendaal, The Netherlands, OC100D, 85 kV, magnification factor 15-30 %). Thirty-five out of 69 patients did not fulfil the inclusion criteria or were excluded because of the above mentioned exclusion criteria. For the remaining 34 patients with severe posterior mandibular atrophy a CBCT was ordered (i-CAT, Imaging Sciences International, USA with a 0.3 mm voxel size and a diameter of 16 cm. The height was individually adjusted to each patient with a maximum of 13 cm). Casts were made to be able to judge the intra-oral situation without the patient being present at a later stage. Illustrative pictures and radiographic images of a representative case are presented in Figure 1-5.

Figure 1. Representative case. Cast of mandible.

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Figure 2. Representative case. Panoramic radiograph.

Figure 3. Representative case. CBCT, 3D reconstruction.

Figure 4. Representative case. CBCT, axial slice of mandible

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Implant planningWe considered at least 2 bilateral implants to be desirable to support the removable partial denture, positioned either in the premolar region (PM), at a planned position 3-4 mm from the centre of the implant to the distal aspect of the natural teeth or in the molar region (M), at the position of the former first mandibular molar. This is at 19-21 mm from the centre of the implant to the distal aspect of the cuspid or 12-14 mm from the centre of the implant to the distal aspect of the premolar (molar region, Figure 6).

Implants to be used in the randomized clinical trial were 3.3 and 4.1 mm wide and 8 and 6 mm long for PM and M position, respectively (Straumann tissue level implants, Straumann, Basel, Switzerland). Eventually, the implants are to be provided with Locator abutments (Zest Anchors, Inc., Escondido, CA). To obtain successful osseointegration, to avoid damage to vital anatomical structures and to end up with the proper implant angulation, the following criteria were considered12,13,14,15,16:

1. at least 2 mm distance between the implants at their designated positions and the alveolar nerve and the neighbouring teeth can be maintained after placement of the implant;

2. at least 5 mm distance remains between the implants at their designated positions and the mental foramen to avoid contact with the anterior loop of the mental nerve;

3. at least 1 mm of alveolar bone around the implants at their designated position remains, either with or without vertical reduction of the alveolar ridge prior to implant placement. Consequently, bone width should be at least 5.3 and 6.1 mm for implants with a diameter of 3.3 and 4.1 mm respectively;

Figure 5. Representative case. CBCT, cross section of planned implant region 37.

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4. implant angulation of the two proposed implants will not exceed 40°, relative to the contralateral implant, or 20° to the occlusal plane. Removable partial dentures with Locator® abutments are foreseen, which has ramifications for the maximum deviation of implants relative to each other.

5. at least the surface treated part of the implant is to be surrounded by bone. In all cases there is ample intermaxillary space.

On the basis of these terms, treatment was judged as surgically and prosthetically ‘feasible’ or ‘not feasible’ by 3 observers, all recognized, nationally registered oral implant surgeons, on the basis of both diagnostic procedures. The observers were calibrated during a joined session. Cases were anonymized and presented to the observers in random order, with a washout period of 3 months.

Assessment on basis of a panoramic radiographAll panoramic radiographs were extracted from the originating software as uncompressed images (TIFF files) and presented to each observer in separate sessions under standardized conditions (dimmed light, image size and projector: Panasonic DLP Projector PTD7700E, Panasonic Corporation, Osaka, Japan). For each intended implant location the observers scored ‘yes’ or ‘no’ depending on their assessment whether implant placement would be feasible or not.

Figure 6. Example of the clinical situation and the desired implant positions (either

the premolar region (PM) or the molar region (M)) to support a free-ending RPD.

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Assessment on basis of a CBCTAll sets of data were imported into SimPlant® software (Materialise Dental Inc., USA). Four implants were planned at the intended location. The sessions took place under standardized conditions (dimmed light, monitor: NEC MultiSync EX231W, NEC Display Solutions of America, USA). Observers were allowed to displace the implants within the limits of the criteria mentioned above, using all tools provided by the software. For each intended implant location the observers scored ‘yes’ or ‘no’ depending on their assessment whether implant placement would be feasible or not.

Statistical analysisIntraobserver variability for categorical data is generally expressed as Cohen’s kappa when two diagnostic procedures are compared.17 Values exceeding 0.60 indicate substantial to perfect agreement.18

2 x 2 contingency tables are created for each observer comparing the presumed feasibility of treatment on the basis of both diagnostic procedures at the PM and M position. In addition, an overall table is produced. Here, treatment is tentatively considered ‘feasible’ if the majority of observers (two or more) are of that opinion.

Outcome is the encountered level of agreement between the 2 diagnostic procedures, which is further expressed in terms of sensitivity (true-positive rate) and specificity (true-false rate) (SPSS, version 22.0 for Windows, SPSS inc., Chicago, USA). In addition, the odds of agreement and disagreement and the odds ratios are calculated to illustrate the encountered paradox of Cohen’s kappa.

Results

For the PM position poor intraobserver agreement was observed for the two diagnostic procedures, with non-significant Cohen’s kappa values ranging from -0.02 to 0.09 among observers and an overall value of X = -0.04 (Table 1). The Odds Ratio’s (OR) for the three observers varied between 2.6 and 158.8, with an overall OR of approximately 76. Hence, the overall chance of agreement is approximately 76 times higher than the chance of disagreement. Overall true-positive and true-false rates were 90 % and 0 %, respectively. In 3 % of the cases the implant treatment was judged feasible based on the panoramic radiograph whereas the CBCT revealed that there would have been a great risk of damaging vital tissues when placement would actually have been attempted (false-positive rate). On the other hand, in 7 % of the cases the combined judgement of the three observers was ‘not feasible’ based on the panoramic radiograph, yet based on the observations on the CBCT implant placement would be possible and safe (false-negative rate). These patients would have been denied a potentially valuable treatment

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option. There were considerable differences in sensitivity and specificity rates among observers.

For the M position results are shown in Table 2. Moderate to substantial intraobserver agreement was observed for the two diagnostic procedures, with Cohen’s kappa’s exceeding 0.60 and with a statistically significant overall value of X = 0.69 (p<0.001). The OR’s and sensitivity and specificity rates were fairly consistent for the three observers with an overall OR of approximately 43. Overall true-positive and true-negative values were 65 % and 22 %, respectively. Attempting implant placement solely on the basis of a panoramic radiograph could have resulted in damage to vital tissues in 4 % of cases (false-positive rate). In 9 % of cases a too conservative approach would have been adopted if judgement was based on clinical examination and the panoramic radiograph (false-negative rate).

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Tab

le 1

. O

utc

om

e fo

r th

e p

rem

ola

r (P

M)

reg

ion

, p

er o

bse

rver

an

d o

vera

ll in

% o

f to

tal

(yes

= j

ud

ged

as

‘fea

sib

le’,

no

=

jud

ged

as

‘no

t fe

asib

le’)

. N=

68 o

bse

rvat

ion

s

Ob

serv

er 1

Ob

serv

er 2

Ob

serv

er 3

Ove

rall

CBC

TC

BCT

CBC

TC

BCT

yes

noye

sno

yes

noye

sno

OPT

yes

92.6

%5.

9 %

57.4

%1.

5 %

88.2

%5.

9 %

89.7

%2.

9 %

no1.

5 %

0.0

%36

.8 %

4.4

%5.

9 %

0.0

%7.

4 %

0 %

Kap

pa =

-0.

02

Kap

pa =

0.0

9K

appa

= -

0.06

Kap

pa =

-0.

04

p =

0.8

0p

= 0

.16

p =

0.6

1p

= 0

.69

OR

= 1

58.7

6O

R =

2.6

1O

R =

56.

25O

R =

75.

94

Odd

s of

agr

eem

ent

= 1

2.60

Odd

s of

agr

eem

ent

= 1

.62

Odd

s of

agr

eem

ent

= 7

.50

Odd

s of

agr

eem

ent

= 8

.71

Odd

s of

dis

agre

emen

t =

0.

08O

dds

of d

isag

reem

ent

=

0.61

Odd

s of

dis

agre

emen

t =

0.

13O

dds

of d

isag

reem

ent

=

0.11

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Tab

le 2

. Ou

tco

me

for

the

mo

lar

(M)

reg

ion

, per

ob

serv

er a

nd

ove

rall

as a

per

cen

tag

e o

f to

tal (

yes

= ju

dg

ed a

s ‘f

easi

ble

’,

no

= ju

dg

ed a

s ‘n

ot

feas

ible

’). N

=68

ob

serv

atio

ns.

Ob

serv

er 1

Ob

serv

er 2

Ob

serv

er 3

Ove

rall

CBC

TC

BCT

CBC

TC

BCT

yes

noye

sno

yes

noye

sno

OPT

yes

60.3

%4.

4 %

55.9

%8.

8 %

64.7

%14

.7 %

64.7

%4.

4 %

no11

.8 %

23.5

%8.

8 %

26.5

%1.

5 %

19.1

%8.

8 %

22.1

%

Kap

pa =

0.6

3 K

appa

= 0

.61

Kap

pa =

0.6

0K

appa

= 0

.68

p< 0

.001

p< 0

.001

p< 0

.001

p< 0

.001

OR

= 2

6.85

OR

= 2

1.78

OR

= 3

1.77

OR

= 4

2.98

Odd

s of

agr

eem

ent

= 5

.18

Odd

s of

agr

eem

ent

= 4

.67

Odd

s of

agr

eem

ent

= 5

.64

Odd

s of

agr

eem

ent

= 6

.56

Odd

s of

dis

agre

emen

t =

0.

19O

dds

of d

isag

reem

ent

=

0.21

Odd

s of

dis

agre

emen

t =

0.

18O

dds

of d

isag

reem

ent

=

0.15

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Discussion

CBCT is readily available in many clinics but its use should be restricted to cases in which it is of added value to conventional techniques that are less biologically and financially costly.19 It may become clear that in cases of ample sufficient bone width on basis of the clinical investigation and ample enough bone height on basis of a panoramic radiograph the ordering of a CBCT would be unnecessary and thus violating the ALARA principle. From a retrospective study on the efficacy of panoramic radiographs regarding the incidence of sensory disturbances it was concluded that a panoramic radiograph is generally an adequate diagnostic tool when a 2 mm safety margin is respected.20 Limited available bone height and/or width has been putted forward as an indication in which a 3D radiograph is justified.9 In the present study, cases with severe posterior mandibular atrophy in which implant placement is contemplated, are evaluated based on casts with a panoramic radiograph as well as a CBCT. The obtained sensitivity and specificity values can be indicative for the benefits and risks when a CBCT is ordered or renounced in selected cases with clinically evident mandibular posterior atrophy.

In this study terms like ‘true’ and ‘false’ positive and negative findings were used for readability, but one has to be aware that, even though a CBCT is rather an accurate imaging modality, there may well be a discrepancy between the images and the actual clinical condition. For instance, mean discrepancies from linear measurements of -0.17 ± 0.53 mm were observed for the mandible 21 or less than 0.5 mm.22 Safety margins were taken into account when assessing the bone volume on the CBCT images as described earlier.

So, although CBCT measurements are a good indication for the actual anatomical condition, some margin for error remains. The reader has to bear in mind that in the present study findings from both imaging techniques are actually compared relative to each other and some discrepancy between the observation on the CBCT and clinical anatomy will exist.

Based on the presented Cohen’s kappa values, it seems that there is almost no coherence between the two diagnostic procedures for the planning of implants in the premolar (PM) region of the mandible. However, this should be interpreted with care. The cross tabulations show that in 90 % of the cases the panoramic radiograph was sufficient to determine the adequacy or lack of bone volume. This phenomenon has been referred to as ‘the paradox of Kappa’ by Feinstein and Chicchetti.23,24 Kappa values can be distorted by an uneven distribution of numbers in a 2 x 2 cross table, as is the case in the present dataset. The overall Odds Ratio (OR) for the anticipated PM implant position is approximately 76, which indicates a much higher chance for agreement than for disagreement between the two diagnostic procedures.

The overall value of kappa for the molar (M) region shows a rather high sensitivity

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and specificity, implying that the bone volume in that region can be estimated rather accurately on a 2D image. This is confirmed by the overall OR for the M position (≈ 43).

Despite substantial agreement between the two diagnostic procedures as expressed by the high percentages of true-positive and true-negative values, numerous cases remain in which patients run a substantial risk on complications or are deprived of a chance to be treated with implants when only a panoramic radiograph was to be used. The ALARA principle forces clinicians to justify the use of additional 3D radiography on a patient-to-patient basis. After having informed the patient, justification will depend on the willingness of both patient and clinician to accept the false-positive or false-negative classifications in the order of magnitude as presented here, 10-13 % dependent on the region.

When analyzing the cases in which the observers overall displayed false-positive and false negative outcomes, it is striking that there are three clear findings: all these cases show a critical bone height on the panoramic radiograph, or the course of the mandibular canal is unclear on the panoramic radiograph, or the lateral parts of the mandible display a knife edge ridge. These three diagnostic findings contribute to the justification of ordering a CBCT. In an earlier study is was stated that, compared to a panoramic radiograph, the depiction of the mandibular canal is better on a CBCT image when using a reformatted slice of the mandible.25 These slices are free of magnification, superimposition or other problems encountered in the panoramic radiology.

Observers are all oral and maxillofacial surgeons with extensive expertise on implant planning and placement, but they undoubtedly differ regarding their surgical experience and their personal willingness to accept (such) misclassifications in clinical practice. The considerable variation in their willingness to undertake implant surgery in the premolar area is probably a reflection of this. For the molar region this is the case to a lesser degree, probably because the bone volume can be assessed with more certainty in this region and is therefore less dependent on the surgeon’s experience and assumptions. Hence, the information obtained from a CBCT will not actually change the treatment plan in this area very often and to do without it could be justified. Frei et al. reported on the minor impact of conventional spiral tomography on treatment plans when compared to plans based on a panoramic radiograph.26 They included only standard implant cases with uncompromised bone volumes, which make the outcome not comparable to the present study in which patients presented severely resorbed posterior mandibles. In a more recent study the preoperative planning of implants based on a panoramic radiograph was compared to that after CBCT planning in all areas of the maxilla and the mandible.27 They concluded that both diagnostic procedures sufficed, but that care should be taken when planning implants in the M region based solely on panoramic radiograph: there was a clear predisposition to choose longer implants which can be hazardous in terms of jeopardizing the inferior alveolar nerve. In contrast, in our

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study the observers were asked to plan implants with a certain length and besides, the fact that ‘standard cases’ were described challenges the external validity with respect to the population described in the present study.

Within the limitations of the present study, it is concluded that implant placement in the resorbed posterior mandible can be well assessed on a panoramic radiograph in the vast majority of cases. The degree of consistency between the two diagnostic procedures, panoramic radiograph and CBCT is observer dependent. Justification for ordering a CBCT will depend on the willingness of both patient and clinician to accept the number of misclassifications, which amount to approximately 10-13 % of the observations, dependent on the area. Special care should be taken if a knife edge ridge is present in the lateral parts of the mandible, if the bone height is critical or if the course of the mandibular canal is unclear on the panoramic radiograph. In these cases the ordering of a CBCT will be of benefit to the patient and can be justified.

Acknowledgements

The authors are grateful to dr. Wouter Kerdijk, PhD from the Center for Dentistry and Oral Hygiene for offering statistical advice. Dr. Wim Slot, PhD from the Center for Dentistry and Oral Hygiene (department of Fixed and Removable Prosthodontics and Biomaterials) of the University Medical Centre Groningen and dr. Laurens den Hartog, PhD from the department of Oral and Maxillofacial Surgery of the University Medical Centre Groningen judged the radiographic images.

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CHAPTER 7

GENERAL DISCUSSION,CONCLUSIONS

AND FUTURE PERSPECTIVES

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Introduction

The PhD research described in this thesis was performed to provide evidence for the use of dental implants to support a removable partial denture (RPD) in the mandible in case of a Kennedy class I situation. Based on the studies performed in this PhD study, it can be concluded that providing implants to enhance retention, support and stability of an RPD is a favourable treatment option, considering all parameters that were investigated.

The results from the retrospective study, with a mean observation period of more than 8 years (range 3-16 years) suggest a successful treatment option. Implant survival is 91.7%. Even after a long period of time, patients are very satisfied although some minor technical and biological complications should be taken into account. The outcome can be considered indicative for the long-term prognosis of an implant-supported RPD (ISRPD). Nevertheless, the drawbacks of this and any retrospective study should be emphasised, like the multi-centre design with different clinicians, the lack of a uniform treatment protocol and lack of randomisation, to name but a few. Therefore a prospective randomized clinical trial had to be performed to get insight in different aspects of an ISRPD and to be able to make more valid and sound recommendations for ISRPD treatment in a mandibular Kennedy class I situation. The dilemma of where to ideally position the implants is these cases, the premolar (PM) or the molar (M) region, for which theoretical models and lines of reasoning that lacked clinical verification are available, were another reason to perform the work.

Patient satisfaction

Oral Health Related Quality of Life (OHRQoL) as measured with the dutch of the Oral Health Impact Profile (OHIP-NL49) questionnaire improved significantly when implant-support was provided to a newly made RPD. This is in agreement with the findings of others.1-4 A minimal important difference (MID) of 6 points (95% CL, 2-9) has been suggested for OHIP use in dentistry.5 The MID was defined as ‘the smallest difference in score in the domain of interest which patients perceive as beneficial and would mandate, in the absence of troublesome side effects and excessive cost, a change in patient management. John et al (2009) suggested in the same study that this MID can be used to approach clinical relevance of changes in perceived oral health.5 The observed reduction in OHIP sum-scores and values in the present study amply exceed this threshold: The mean sum scores were reduced with 12.7 and 19.1 points respectively when the RPD was supported by implants in either the molar (M) or the premolar (PM) region.

The OHRQoL is reported to be highly correlated with the technical quality of the

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prosthesis6, suggesting that when a denture of poor quality is replaced by a technically optimized one, acceptance and satisfaction will improve. In the present study of patients with a poorly functioning bilateral free-ending mandibular RPD, solely providing a new RPD also proved effective when considering certain domains of the questionnaire, like functional limitation and psychological discomfort. It may implicate that the new RPD provided without support actually sufficed in increasing the quality of life, but social desirability bias may have played a role as well. Although the researcher performing the investigation was not involved with the surgical or restorative treatment, it is well known that patients tend to over-report good and under-report undesirable outcomes, especially when questionnaires are used. They tend to please their physician or the researcher or seek confirmation for their own decision to undergo the treatment in the first place. This should be considered when interpretating the data.

Adding implant-support significantly improved the overall OHRQoL. In addition, at the start of treatment patients were asked to express their expectations with respect to the anticipated ISRPD on a Visual Analogue Scale (VAS) ranging from 0 (very discontent, major concerns) to 100 (very content, no concerns at all) as a means to evaluate whether or not patients’ expectations were met at the end of the study. This is a rather unconventional approach to investigate patient satisfaction and is hardly ever used in the literature, yet seems rational. The data suggests that patients’ expectations of contentment with an ISRPD were met since no significant difference was seen between expected and actually achieved contentment levels. This is seen as an important indicator of the quality of treatment. It enhances the reputation of the health care provider and implant dentistry in general. It transforms new patients into loyal customers and brings new referrals by ‘word of mouth’. Although patients were very satisfied, food getting underneath the denture was and remains a recurrent complaint despite implant-support, as also was observed by others.2

It is interesting to consider whether or not public awareness of a treatment option being very successful raises expectations, which as a result will be more and more difficult to meet. Put differently: when a treatment option is seen as a last resort that, despite the physicians’ tendency to downplay expectations proves successful without many drawbacks, future patients will be biased towards higher, or even unrealistic expectations.

When a patients’ prosthesis is more comfortable and functional, one would expect that he is less prone to remove it during the day and/or night. In other words, one would expect that the mean wearing time will increase with ameliorated quality of the prosthesis. This is indeed confirmed by the data as measured by temperature sensitive chips. This feature proved a valuable, objective outcome that is presumed to relate strongly to satisfaction. Thermosensitive chips are originally used to improve compliance in young patients wearing removable orthodontic appliances, but can also

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be used successfully in prosthodontic research.The favourable satisfaction rate was also reflected in a high rate of prostheses

still being in functional use after one year. Conventional mandibular free-ending RPD’s are often not worn by patients. In this PhD study only one patient, who encountered severe health problems during the course of the study, could not really get used to his new (IS)RPD and only wore it occasionally.

Clinical performance of implants and Implant-Supported Removable Partial Dentures

No implant loss was observed and clinical data are representative for healthy and stable implant conditions, after one year of observation. The mean probing pocket depth after 1 year of function was 1.69 mm (SD 0.43 mm) for the M implant and 1.76 mm (SD 0.45 mm) for the PM implant which is within the range of the physiological limit of 3 mm7 and matching with the design of the used tissue-level implant. Patients exhibited a mean marginal bone loss of 1.10 mm (SD 0.53 mm) for the M implant and 1.06 mm (SD 0.59 mm) for the PM implant, which is also in line with the studies that followed a group of patients over a longer period of time.8-10

Functional performance

In this study masticatory performance was expressed as the Mixing Ability Index (MAI) which evaluates the ability to mix and knead a food bolus by mixing a paraffin wax tablet with a blue and red layer (see also the method section).11 It has been shown that chewing on two-coloured paraffin wax is a reliable alternative for the often used comminution tests.11-13 In previous studies the parameter ‘masticatory performance’ was operationalized in various other ways with contradictory findings.14-18 This makes the interpretation of those findings and comparison with the present ones troublesome. Nevertheless, the data clearly demonstrate an improvement in masticatory performance when implant-support was provided. The results underscore the findings by others who reported an increase in bite force and mastication after implant-support to an RPD was provided, be it not to the level of that of a fixed implant-borne restoration.4,19-21

Three months functioning with a new denture is tentatively considered long enough for a patient to adapt and this period of evaluation is also used by others.22,23 Nevertheless, it would be interesting to evaluate the masticatory performance over a longer period of time.

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Implant position: molar or premolar support

Although not evident from the OHIP-NL 49 questionnaires or the wearing-time outcome parameter, the outcome of VAS scores on general satisfaction pointed towards a patient preference for support in the molar region. Over half of the patients expressed a strong preference for M implant-support, approximately one third of the patients preferred PM support and the others gave no preference. In light of value-based health care this is considered a meaningful result. Perhaps the other patient-based measures are not sensitive or specific enough to pick this up or differentiate.

The preference for M implant-support may stem from minor differences in stress or discomfort between the two implant positions. In mathematical model studies and in a study with a pressure-sensitive foil it was shown that more distal positions (the first or second mandibular molar) induce lower amounts of stress on the implants themselves and on the residual alveolar ridge, compared to situations where implants were modeled more anteriorly (the second bicuspid position).24-26 From various tested positions, M support is associated with the least amount of displacement of the tissues under load.27-

30 A more distal position is also favoured by Grossman et al. (2009), who recommended the second molar position.31 Hence, the less rotation and the more relieve of mucosal pressure, the better an RPD is tolerated, and our patients seem to agree with this.

With respect to the biomechanics and design of the denture, when the support is brought further to the distal, an anterior clasp or support can usually not be avoided, with aesthetic repercussions. During the course of the present study, a labial retainer to an anterior natural abutment tooth was always present, both when the M and when the PM implant-support was operationalized. Patients were informed that that would be an inherent consequence when they would finally choose for M implant-support and that they could probably do without this anterior clasp in case they would opt for PM implant-support. Evidently patients’ comfort with M implant-support outweighed their dislike of a potentially aesthetically disturbing anterior retainer since the vast majority favoured M implant-support.

Most clinical parameters (both concerning the implants and the teeth) revealed no difference when the implants at the molar or the premolar sites were loaded but one has to bear in mind that the observation period in the present study is relatively short to evaluate clinical performance. Bleeding on probing around the implants was an exception, with a less favourable score being noted around M implants. During the observation period, this has not led to deeper probing depths or increased marginal bone loss, but it is uncertain what the long-term effect may be. From the retrospective study it tentatively concluded that implants in the PM region clinically perform better than implants in the M region when supporting an RPD. One of the reasons might be a compromised cleaning possibility for more distally placed implants.

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As mentioned the present data clearly demonstrate an improvement in masticatory performance when implant-support was provided, but no noticeable differences with respect to the 2 implant positions tested were seen.

Combining all these observations and all in all, it can be concluded from the patient’s point of view that the ISRPD, in a Kennedy class I situation in the mandible, is best supported by implants placed in the molar region in case of the situation of sufficient bone volume. However, healthier peri-implant conditions can be expected around implants placed in the PM region compared to implants placed in the M region. This, together with the fact that, in case of further tooth loss, an implant-retained denture is better served with implants in the position of the premolars, the PM position may be preferred from a clinical perspective. In addition, it is well advised to plan the position of the implants in such a way that a fixed partial denture, be it a single or multiple unit restoration, would still be possible if the patient desires to convert from a removable to a fixed implant-borne restorative solution or an implant-supported full arch denture.

Cost-effectiveness

Achieving high value for our patients is a major goal of health care delivery in general and subsequently also for dental care. Here ‘value’ is defined as the health outcomes achieved per monetary unit spent.32 Porter postulates this goal as a ‘priority achievement for patients’. It unites the interests of all parties involved: patients, health care providers, suppliers and health care insurance companies. They will all benefit, while the economic sustainability of the health care system increases.

When health care is drifting from volume to value, it is important for health care organizations to measure and analyse costs.33 Therefore, an accurate cost accounting system is necessary. Since a uniform strategy is lacking in dentistry we chose to use the opportunity cost, although it is difficult to be encompassing and in measuring all the expenditures necessary for personnel, supplies, treatment room and other costs. For this study the patients’ contexts were not taken into account although it could play an important role in cost-effectivity. The other different approach for cost accounting we used was the Dutch tariff structure. The advantage of this strategy is the possibility to compare two treatment modalities for all parties. The disadvantage however is that is leaves out a lot of aspects of costs like chair time and the number of visits and besides it is impossible to extrapolate the conclusions to other countries.

Besides analysing the cost, quality assessment is the other prerequisite to determine the value of a treatment. In our study we chose several outcome parameters. The Incremental Cost-effectiveness Ratio (ICER) for OHIP-NL49 and MAI using the

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opportunity costs was €80 and €786 respectively. This means that depending on the choice of outcome measure and monetary threshold, supporting an RPD with implants is cost-effective when payers are willing to pay more than €80 per OHIP point gained. Per MAI point gained an additional €786 has to be invested. When using the tariff structure, corresponding ICERs were €94 and €921. These data cannot yet be compared to other studies and therefore are hard to value. It would be recommendable to use these quality parameters for other treatment options as well to be able to compare data and to make a substantiated choice between alternative treatment modalities. The effect of supporting an RPD with implants when expressed in QALYs was negligible, hence an ICER was not determined. In patients with a Kennedy class I in the mandible and a full arch denture in the maxilla, the general health perception was not influenced by any of the treatment phases of this study. Probably this outcome measure is not sensitive enough and it raises doubt regarding the manner in which continuously effort is invested in associating dental issues in all fields of study to overall general health matters. QALYs seem not to be an accurate parameter in dentistry with relatively healthy patients.

The data presented in this PhD study could aid in analyzing costs and standardizing quality assessment, leading to value-based dental care. This will allow patients, health care providers and insurers in decision making from their different perspectives regarding the cost-benefit aspects of implant-supported RPD’s.

Radiographical treatment planning

The implant placement itself in the posterior manable can usually be planned safely on a panoramic radiograph.34 With (ultra) short implants becoming available, the possibilities to provide implant-support to a removable partial denture or provide fixed partial dentures in the resorbed posterior regions are increasing as well. Based on the presented Cohen’s kappa values, it seems that there is almost no coherence between the two diagnostic procedures for the planning of implants in the premolar (PM) region of the mandible. However, this should be interpreted with care. The cross tabulations show that in 90 % of the cases the panoramic radiograph was sufficient to determine the adequacy or lack of bone volume. This phenomenon has been referred to as ‘the paradox of Kappa’ by Feinstein and Chicchetti.35,36 Kappa values can be distorted by an uneven distribution of numbers in a 2 x 2 cross table, as is the case in the present dataset. The overall Odds Ratio (OR) for the anticipated premolar implant position is approximately 76, which indicates a much higher chance for agreement than for disagreement between the two diagnostic procedures.

The overall value of kappa for the molar (M) region shows a rather high sensitivity

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and specificity, implying that the bone volume in that region can be estimated rather accurately on a 2D image. This is confirmed by the overall OR for the posterior position (≈ 43).

Despite substantial agreement between the two diagnostic procedures as expressed by the high percentages of true-positive and true-negative values, numerous cases remain in which patients run a substantial risk of complications or are deprived of a chance to be treated with implants when only a panoramic radiograph had been used for diagnostic aid. The ALARA principle forces clinicians to justify the use of additional 3D radiography on a patient-to-patient basis. After having informed the patient, justification will depend on the willingness of both patient and clinician to accept the false-positive or false-negative classifications in the order of magnitude as presented here, 10-13 % dependent on the region of interest.

Within the limitations of the present study, it is concluded that implant placement in the resorbed posterior mandible can be well assessed on a panoramic radiograph in the vast majority of the cases. The degree of consistency between the two diagnostic procedures, panoramic radiograph and CBCT is observer dependent. Special care should be taken if a knife edge ridge is present in the lateral parts of the mandible, if the bone height is critical or if the course of the mandibular canal is unclear on the panoramic radiograph. In these cases the ordering of a CBCT will be of benefit to the patient and can be justified.

Conclusions

The cumulated findings of the studies presented in this PhD study lead to the following general conclusion. Placing implants, either in the premolar or molar region of the mandible, to support a bilaterally free-ending removable partial denture in patients who expressed complaints regarding their conventional RPD yet would like to continue wearing one, yields favourable results.

The specific conclusions are:- from a 3-16 year retrospective study it appeared that treatment with an implant-supported removable partial denture is a viable option with a high implant survival rate and resulting in satisfied patients, although technical and biological complications should be anticipated;- mandibular implant-support favourably influences oral health related patient-based outcome measures. Although it was not significantly shown for all operationalized patient based outcome assessments, the majority of patients expressed their preference for implant-support in the molar region;

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- implant-supported removable partial dentures and their supporting implants and abutment teeth function without clinically relevant complications after 1 year and significantly improve masticatory function. No marked difference was seen between molar and premolar implant-support.- depending on the choice of outcome measure and monetary threshold, supporting a removable partial denture with implants is cost-effective when payers are willing to pay more than €80 per Oral Health Impact Profile (OHIP) point gained. Per Mixing Ability Index (MAI) point gained an additional €786 has to be invested;- the possibility of implant placement in the resorbed posterior mandible can be well assessed on a panoramic radiograph in the vast majority of the cases compared to assessment on a cone beam computed tomography scan.

Future perspectives

In this PhD-study different aspects of the ISRPD were evaluated during 1 year. The treatment has been found successful, with minimal complications and a high patient satisfaction rate. One year is a relatively short period of time and therefore it is important to follow the patients in this study group during the next years, leading to 5- and 10- year results.

The study group is very homogeneous, which makes the evidence relatively strong compared to heterogeneous groups as found in the literature. On the other hand, it makes extrapolating the results difficult for situations that are not similar. For example, the results reported only apply to the bilaterally partially edentulous mandible. It would be interesting to investigate whether this treatment modality is as suitable for the maxilla in case of a shortened dental arch as well. Another question can be whether the same conclusions can be drawn in case of an opposing natural dentition instead of a complete removable denture.

The investigated group consisted of patients with complaints regarding their RPD. They did not want their remaining natural dentition to be removed, but perceived that they could not function with their conventional RPD either. Another treatment option for this group of patients is a fixed implant-supported partial denture on both sides of the mandible. It would be interesting to conduct a randomized clinical trial in order to compare the implant-supported fixed denture with an ISRPD on aspects like OHRQoL, functioning, technical and biological complications and cost-effectiveness.

From finite element analyses (FEA) it is known that different retention systems result in a different stress distribution on the abutment teeth, implants and the surrounding bone.37,38 This phenomenon should be investigated in vivo as well. In addition, from another FEA it is concluded that it is a good choice to use an implant

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size with maximum bone-to-implant contact.39 This has never been investigated in vivo and in light of the present prospective study with relatively short implants (6-8 mm in length) with good results it is interesting to set up a research in which longer implants are compared with (ultra) short implants. The same can be done with small-diameter implants.

Finally, it would help to know that, whether or not the inserted implants would indeed be suitable support to a complete denture if these patients with a Kennedy class I situation lose their remaining teeth in the future. Therefore it is important to study the long-term prognosis of the implants as well as the abutment teeth, together with treatment options if complications occur.

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CHAPTER 8

SUMMARY

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Introduction

For the mandibular shortened dental arch several treatment options are available as described in Chapter 1. When there is a need for improving oral function, it is assumed that one of the options is an Implant-supported Removable Partial Denture (ISRPD). There is only scarce evidence in the literature for this treatment to be successful and a uniform treatment concept is lacking. There is no consensus on where to place the implants in case of a Kennedy class I situation. The general aim of this study was to assess the treatment outcome of ISRPD’s in the mandible with regard to patient based outcome assessment, chewing ability and clinical and radiographical performance in relation to implant position: the premolar (PM) or molar (M) region.

When competing treatment options are available, their documented or presumed effectiveness and their (additional) costs should be considered and critically assessed in order to make a valuable decision possible for patients, clinicians and insurance companies. Therefore we aimed to conduct a cost-effectiveness analysis comparing conventional removable partial denture and implant-supported removable partial denture treatment in the mandible.

The diagnostic procedure before placing dental implants contains a radiographic investigation among other things. For this purpose the most commonly used methods are the use of a panoramic radiograph and the cone beam computed tomography (CBCT). The latter implicates a higher dose of radiation to the patient. The ALARA principle raises the question under which conditions the additional information gained from CBCT outweighs the extra biological risks and costs when evaluating implant sites pre-operatively. A clear guideline is lacking. In this thesis two imaging modalities (panoramic radiograph and CBCT) are compared in pre-operative implant planning in the severely resorbed mandible and the influence on the observers assessments to make valuable recommendations for the use of a CBCT in these specific cases.

Studies in this thesisIn the first part of this thesis, a retrospective study is described in which we assessed performance, together with biological and technical complications, of implant-supported removable partial dentures (ISRPD) in mandibular Kennedy class I situations (Chapter 2).We were able to include 23 subjects who were treated with two endosseous implants to support a bilateral-free-ending mandibular removable denture in the past. Eight subjects had implants placed in the premolar region and 15 subjects in the molar region. Biological and technical complications were recorded from the patients’ medical record. Patients filled out a validated questionnaire regarding their appreciation of oral health related quality of life (OHIP-NL49) and a VAS score on overall satisfaction.

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Over a mean follow-up period of 8 years (median 8 years, range 3-16 years) the cumulative implant survival rate was 91.7 % (SE 0.05). Mean peri-implant bone loss was 0.9 mm (SD 1.0 mm). Scores for bleeding on probing, plaque and mucosal health were generally low, but significantly worse for posteriorly placed implants. Significantly more biological complications occurred in the posterior group (X2(1)=3.9; p=0.048). In 65 % of the cases no technical complications were registered. Mean overall OHIP score was 16.1 (SD 18.4) and patients were highly satisfied (VAS: 8.4; SD 2.1). We concluded that, within the limitations of this retrospective study, in case of a Kennedy class I situation in the mandible, an ISRPD is a viable treatment option with a high implant survival rate and satisfied patients after a maximum of 16 years, although technical and biological complications should be anticipated. More anteriorly placed implants performed slightly better.

In the second part of this thesis the outcomes of a within subject randomized clinical trial are described. These data form the backbone of this PhD study. Firstly, the patient based outcome of implant support to Removable Partial Dentures (RPD) in case of a bilateral free-ending situation in the mandible was assessed. The most favourable implant position was assessed: the premolar (PM) or molar (M) region (Chapter 3). Secondly, the focus shifted to the masticatory benefits of an ISRPD, as well as the clinical and radiographical performance of the supporting implants. Again, the most favourable implant position with respect to these aspects was determined: the PM or M region (Chapter 4).

Thirty subjects received 2 PM and 2 M Implants. A new RPD was made and patients wore these conventional (unsupported) RPD for three months. By then, implant support was provided: 2 PM or 2 M implants supported the RPD. After 3 months the 2 other implants were used (respectively the M or PM implants). Outcome measures included oral health related quality of life (OHIP-NL49), general health status (SF-36), the number of hours that the RPD was worn, contentment assessed on a Visual Analogue Scale (VAS), Mixing Ability Index (MAI) and clinical and radiographic parameters regarding implants and abutment teeth. All data were collected prior to treatment, 3 months after functioning with a new RPD and after 3 and 6 months with implant support, be it in the PM or M region. At the end, patients expressed their preferred implant position.

OHIP-NL49 values and mean wearing-time were statistical significantly more favourable for ISRPD’s regardless of the implant position. The general health status (SF-36) was not influenced. The ISRPD’s were worn 2-3 hours more per day than the unsupported new RPD. Patients’ expectations were met as the VAS-scores of anticipated and realized contentment did not differ (p > 0.05). VAS scores for ISRPD’s with M implant support were higher than for PM implant support (Chapter 3).

Masticatory performance differed significantly between the stages of treatment

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(p<0.001). MAI-scores did not change significantly after a new RPD was provided, but improved with implant support (p<0.05). The implant position had no significant effect on MAI when functioning with an ISRPD (Chapter 4).

No implants were lost, mechanical complications to the implants or RPD were not observed during the 1-year observation period and clinical and radiographical parameters for both implants and teeth during this relatively short observation period were favourable. Higher scores for bleeding on probing were seen for molar implants. Finally, 56.7 % preferred the M implant support (13.3 % no preference, 30 % PM implant support), probably due to minor reduction in stress or discomfort compared to the PM implant position (Chapter 3 and Chapter 4).

All subjects involved in the clinical trial had a Kennedy class I situation in the mandible and a complete maxillary denture. They were dissatisfied with their conventional RPD, yet did not want to go without one and function with a shortened dental arch. All in all, the data support the conclusion that for patients with such a profile, implant support to an RPD has a favourable outcome on various aspects. It positively influences oral health related patient-based outcome measures and significantly improves masticatory function, with rare short-term biological or technical complication. Patients’ expectations are met, which results in satisfied patients.

No marked difference is seen between molar and premolar implant support except for the VAS scores on general satisfaction: the scores were significantly higher when the ISRPD was supported by implants in de molar region. No major problems in relation to the clinical function of the implants, the abutment teeth and the RPD itself were observed. The majority of patients prefer the implant support to be in the molar region.

In Chapter 5 a cost-effectiveness analysis is reported comparing a conventional Removable Partial Denture (RPD) and Implant-supported RPD (ISRPD) treatment in the same group of patients described above. For all patients, treatment costs (opportunity costs and costs based on tariffs) were calculated for a new RPD and an ISRPD. Treatment effect was expressed by means of the Dutch Oral Health Impact Profile questionnaire (OHIP-NL49), a chewing ability test (Mixing Ability Index, MAI) and Quality-Adjusted-Life-Years (QALYs).

The mean total opportunity costs were €980 (95 % CI 969 to 1000) for the RPD treatment and €2.470 (95 % CI 2.439 to 2.501) for the ISRPD treatment. The total costs derived from the national tariff structure were €850 for the RPD treatment and €2.610 for the ISRPD treatment. The ICER for OHIP-NL49 and MAI using the opportunity costs was €79 and €779 respectively. When using the tariff structure, corresponding ICERs were €94 and €921. The effect of supporting an RPD with implants when expressed in QALYs was negligible, hence an ICER was not determined.

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It is concluded that, depending on the choice of outcome measure and monetary threshold, supporting an RPD with implants is cost-effective when payers are willing to pay more than €79 per OHIP point gained. Per MAI point gained an additional €779 has to be invested.

Finally a study is presented in which two diagnostic regimes were compared for pre-operative implant planning in cases with severe posterior mandibular atrophy: a (2D) panoramic radiograph or a (3D) CBCT and implant planning software (Chapter 6). Thirty-four patients with bilateral edentulous regions were included. The feasibility of implant placement in both the PM and the M region at both sides was judged by 3 observers on the basis of the clinical situation with a panoramic radiograph or with a CBCT. The observation on the CBCT was accepted as the true representation of bone volume. Cohen’s kappa, sensitivity and specificity rates, odds of agreement and disagreement as well as the Odds Ratio’s (OR) were calculated.

Overall outcome for the PM position revealed true-positive and true-false rates of 90 % and 0 % respectively, hence 10 % of cases were misclassified. There were considerable interobserver differences concerning sensitivity and specificity and Cohens’ X values were low. The Odds Ratio’s (OR) for the three observers varied between 2.6 and 158.8, with an overall OR = 76.

For the M position overall true-positive and true-negative values were 65 % and 22 % respectively, with Cohens’ X = 0.69. Thirteen percent of cases were misclassified. Sensitivity and specificity as well as the OR’s for individual observers were fairly consistent, with an overall OR = 43.

It is concluded that implant placement in the resorbed posterior mandible can be well assessed on a panoramic radiograph in the vast majority of cases. The amount of consistency between the two diagnostic regimes, panoramic radiograph and CBCT is observer dependent and better for the posterior than for the anterior region. Justification of ordering a CBCT for implant planning for the support of mandibular free-ending removable partial dentures will depend on the willingness of both patient and clinician to accept the misclassifications, which amount to approximately 10-13 % of the observations, dependent on the area.

Clinical considerations

Combining all observations, the following considerations should play a role in the decision making for an implant-supported removable partial denture in a Kennedy class I situation in the mandible and based on the situation of sufficient bone: from the patient’s point of view, the ISRPD is best supported by implants placed in the molar

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region. However, healthier peri-implant conditions can be expected around implants placed in the PM region compared to implants placed in the M region. This, together with the fact that, in case of further tooth loss, an implant-supported denture is better served with implants in the position of the premolars, the PM position may be preferred from a clinical perspective. In addition, it is well advised to plan the position of the implants in such a way that a fixed partial denture, be it a single or multiple unit restoration, would still be possible if the patient desires to convert from a removable to a fixed restorative solution or a full arch denture.

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CHAPTER 9

NEDERLANDSE SAMENVATTING

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IntroductieVoor de (extreem) verkorte tandboog in de onderkaak zijn verschillende behandelopties beschikbaar waaronder een implantaat-gesteunde frameprothese. Er is maar weinig bewijs in de literatuur voor de doelmatigheid van deze behandeling en een uniform behandelconcept ontbreekt. Er is geen consensus over de locatie waar de implantaten het beste kunnen worden geplaatst in het geval van zo’n Kennedy klasse I situatie. Het algemene doel van de (deel)studies die tot dit proefschrift hebben geleid was om de resultaten van de behandeling met een implantaat-gesteund frame in de onderkaak te evalueren op basis van de beleving van de patiënt, het kauwvermogen en klinische en röntgenologische parameters in relatie tot de verschillende posities van het implantaat: het frame werd afgesteund door implantaten in de premolaar (PM) regio dan wel door implantaten in de molaar (M) regio.

Wanneer concurrerende behandelopties beschikbaar zijn, moeten hun gedocumenteerde of vermoedelijke effectiviteit en de (extra) kosten kritisch worden beschouwd en geëvalueerd om een afgewogen beslissing mogelijk te maken voor de patiënt, voor clinici en voor de zorgverzekeraar. Daarom voerden we een vergelijkende kosten-batenanalyse uit tussen een conventionele frameprothese en een implantaat-gesteunde frameprothese in het geval van een Kennedy klasse I situatie in de onderkaak.

Gedurende het vooronderzoek, voorafgaand aan de behandeling, wordt onder andere röntgendiagnostiek toegepast. De meest gangbare methoden daartoe zijn het gebruik van een panoramische röntgenopname (orthopantomogram, OPT) en een cone beam computed tomography (CBCT). De laatste methode impliceert een hogere stralingsdosis voor de patiënt. Het ALARA-principe roept de vraag op onder welke omstandigheden de aanvullende informatie die verkregen is van een CBCT, opweegt tegen de extra biologische schade en daarmee dus gerechtvaardigd is in het diagnostische proces. Een duidelijke richtlijn voor deze situatie ontbreekt. In dit proefschrift werden de twee vormen van beeldvorming (OPT en CBCT) vergeleken bij de implantaatplanning in de zijdelingse delen van sterk geresorbeerde onderkaken, om zo te komen tot aanbevelingen voor de beroepsgroep.

Studies in dit proefschriftIn Hoofdstuk 2 wordt een retrospectieve studie beschreven waarin het functioneren van implantaat-gesteunde frameprothesen in de Kennedy klasse I situaties in de onderkaak werd onderzocht, evenals de biologische en technische complicaties. Dit alles in relatie tot de implantaatpositie. Er konden 23 proefpersonen worden geïncludeerd die in het verleden waren behandeld met twee implantaten in de zijdelingse delen van de onderkaak en een bilateraal vrij-eindigende frameprothese. Acht proefpersonen hadden implantaten in de premolaar regio en 15 proefpersonen in de molaarstreek. Biologische en technische complicaties werden uit het medisch dossier van de patiënt

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opgetekend. Patiënten vulden een gevalideerde vragenlijst in omtrent hun waardering voor de aan de mondgezondheid gerelateerde kwaliteit van leven (OHIP-NL49) en een score op een Visuele Analoge Schaal (VAS, 0-10) voor hun algemene tevredenheid.

Over een gemiddelde follow-up periode van 8 jaar (mediaan 8 jaar, range 3-16 jaar) was de cumulatieve kans op implantaatoverleving 91,7% (SE 0,05%). Het gemiddelde peri-implantaire botverlies was 0,9 mm (SD 1,0 mm). Scores voor bloeding na sonderen, plaque en aanwezigheid van tekenen van ontsteking van de peri-implantaire mucosa waren over het algemeen laag, maar aanzienlijk slechter voor de verder naar dorsaal geplaatste implantaten. Significant meer biologische complicaties waren opgetreden bij implantaten in de molaarstreek (p = 0,048). In 65% van de gevallen werden geen technische complicaties geregistreerd. De gemiddelde totale OHIP-score was 16,1 (SD 18,4) en patiënten waren in de regel zeer tevreden (VAS: 8,4; SD 2.1). Wij concludeerden dat bij een Kennedy klasse I situatie in de onderkaak, een implantaat-gesteunde frameprothese een potentiële behandeloptie is met een hoge implantaatoverleving en tevreden patiënten na maximaal 16 jaar. Wel moet geanticipeerd worden op technische en biologische complicaties. Meer naar voren geplaatste implantaten functioneerden iets beter. In het tweede deel van dit proefschrift worden de resultaten van een cross-over gerandomiseerde klinische studie beschreven. Deze gegevens vormen de ruggengraat van het proefschrift. Ten eerste werden de subjectieve patiënt-gerelateerde uitkomsten geëvalueerd van een implantaat-gesteund frame in een Kennedy klasse I situatie in de onderkaak. De meest gunstige positie van het implantaat werd bepaald: de premolaar (PM) of molaar (M) regio (Hoofdstuk 3). Daarna lag de focus op verbetering van de kauwfunctie, evenals op de klinische en röntgenologisch aspecten van de ondersteunende implantaten. Wederom werd de meest gunstige positie van het implantaat bepaald: de PM of M-regio (Hoofdstuk 4).

Dertig proefpersonen kregen 2 PM en 2 M implantaten, die werden voorzien van cover screws. Een nieuwe frameprothese werd gemaakt en patiënten droegen dit conventionele (niet ondersteunde) frame gedurende drie maanden. Daarna werden 2 implantaten voorzien van een locator® abutment: 2 PM óf 2 M implantaten ondersteunden de frameprothese. Na 3 maanden werden de 2 andere implantaten gebruikt (respectievelijk de M of PM implantaten). Uitkomstmaten waren aan de mondgezondheid gerelateerde kwaliteit van leven (middels OHIP-NL49 vragenlijst), de algehele gezondheidsbeleving (middels de SF-36 vragenlijst), het aantal uren dat de frameprothese gedragen werd, patiënttevredenheid beoordeeld op een visuele analoge schaal (VAS), kauwvermogen op basis van de Mixing Ability Index (MAI) en klinische en röntgenologische parameters voor de implantaten en natuurlijke pijlerelementen. Alle gegevens werden verzameld voorafgaand aan de behandeling, 3 maanden

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na functioneren met een nieuw conventioneel frame en na 3 en 6 maanden met ondersteuning van 2 implantaten, hetzij in de PM of M regio. Aan het einde van het onderzoek gaven de patiënten desgevraagd hun voorkeursposities voor de implantaten aan.

De scores op de OHIP-NL49 vragenlijst en de gemiddelde draagduur waren statistisch significant gunstiger voor de implantaat-gesteunde frameprothesen, ongeacht de positie van het implantaat. De algemene gezondheidsbeleving (SF-36) werd gedurende het hele onderzoek niet wezenlijk beïnvloed. Het implantaat-gesteunde frame werd gemiddeld 2-3 uur per dag meer gedragen dan het nieuwe conventionele frame. Aan de verwachtingen van de patiënten werd voldaan aangezien de VAS-scores van de verwachte en gerealiseerde tevredenheid niet verschilden (p > 0,05). De VAS-scores voor het implantaat-gesteunde frame met implantaten in de M regio waren hoger dan voor frames met steun van implantaten in de PM regio (Hoofdstuk 3).

De kauwfunctie verschilde significant tussen de verschillende stadia van de behandeling (p < 0,001). De MAI-scores veranderden niet significant nadat een nieuwe frameprothese was aangeboden, maar verbeterden met implantaat ondersteuning (p < 0,05). De positie van de implantaten had geen significant effect op de MAI (Hoofdstuk 4). Er gingen geen implantaten verloren. Ook werden er geen mechanische complicaties aan de implantaten of aan de frameprothese waargenomen tijdens de relatief korte 1-jaar observatieperiode. De klinische en röntgenologische parameters voor zowel de implantaten als de natuurlijke pijlerelementen waren gunstig. Hogere scores voor bloeding na sonderen werden gezien voor implantaten in de molaarregio. Tenslotte had 56,7% van de proefpersonen voorkeur voor ondersteuning van het frame door implantaten in de M regio (13,3% had geen voorkeur, 30% had voorkeur voor implantaten in de PM regio), mogelijk als gevolg van geringe drukvermindering of reductie van ongemak vergeleken met ondersteuning in de PM regio (Hoofdstuk 3 en Hoofdstuk 4).

Alle proefpersonen die betrokken waren bij deze klinische studie hadden een Kennedy klasse I situatie in de onderkaak en een volledige gebitsprothese in de bovenkaak. Ze waren ontevreden over hun conventionele frame, maar wilden of konden niet functioneren met een verkorte tandboog. De onderzoeksresultaten ondersteunen de conclusie dat voor patiënten met een dergelijk profiel, implantaten onder een frameprothese een gunstig effect hebben op verschillende aspecten. Het beïnvloedt de uitkomstmaten van de mondgezondheid in positieve zin en het verbetert de kauwfunctie. Daarbij zijn er nauwelijks biologische of technische complicaties op korte termijn. Aan de verwachting van de patiënten wordt voldaan, wat resulteert in tevreden patiënten.

Er is geen duidelijk verschil te zien tussen de ondersteuning door implantaten in de PM of de M regio, met uitzondering van de VAS scores over de algemene

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tevredenheid: de scores waren significant hoger wanneer het frame werd ondersteund door implantaten in de molaarstreek. Verder werden er geen grote problemen waargenomen met betrekking tot het klinische en technische functioneren van de implantaten, de natuurlijke pijlers en de frameprothese zelf. De meeste patiënten gaven de voorkeur aan implantaten in de molaar regio.

In Hoofdstuk 5 wordt gerapporteerd over een kosten-batenanalyse waarbij de behandelingen met een conventionele frameprothese en een implantaat-gesteunde frameprothese met elkaar werden vergeleken. De resultaten zijn afkomstig uit dezelfde groep proefpersonen als hierboven beschreven. Voor alle patiënten werden de behandelkosten (opportuniteitskosten en kosten op basis van behandeltarieven) berekend voor een nieuwe frameprothese en een implantaat-gesteunde frameprothese. Het effect van de behandeling werd gemeten door middel van de scores op de Nederlandse versie van de Oral Health Impact Profile vragenlijst (OHIP-NL49), een kauwtest (Mixing Ability Index, MAI) en Quality-Adjusted-Life-Years (QALY’s). Deze laatst gegevens werden berekend uit de scores van de algemene gezondheidsvragenlijst (SF36).

De gemiddelde totale opportuniteitskosten waren € 980 (95% CI €969-1.000) voor de behandeling met een conventionele frameprothese en € 2.470 (95% CI €2.439-2.501) voor de behandeling met een implantaat-gesteunde frameprothese. De totale kosten ontleend aan de tarieven voor tandartsen en kaakchirurgen waren € 850 voor de behandeling met een conventionele frameprothese en € 2.610 voor de behandeling met een implantaat-gesteunde frameprothese. De kosten-baten ratio’s, of wel Incremental Cost Effectiveness Ratio (ICER) voor OHIP-NL49 en MAI wat betreft de opportuniteitskosten waren respectievelijk € 79 en € 779. Bij de berekeningen aan de hand van tarieven, bedroegen de ICER’s € 94 en € 921. Het effect van de ondersteuning met implantaten uitgedrukt in QALY was verwaarloosbaar, waardoor een ICER niet werd bepaald.

Geconcludeerd werd dat, afhankelijk van de keuze van de uitkomstmaat en het drempelbedrag, het ondersteunen van een frameprothese met implantaten kosteneffectief is als betalers bereid zijn meer dan € 79 per OHIP punt te betalen. Per MAI punt moet € 779 worden geïnvesteerd.

Tot slot wordt een studie gepresenteerd waarin twee diagnostische modaliteiten werden vergeleken in de pre-operatieve implantaat planning in situaties met ernstige kaakresorptie in de zijdelingse delen van de onderkaak: een 2-dimensionale panoramische röntgenopname (OPT) met een 3-dimensionale Cone-Beam CT (CBCT) en bijbehorende implantaat planningssoftware (Hoofdstuk 6).

Vierendertig patiënten met een (extreem) verkorte tandboog werden

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geïncludeerd. Of het veilig zou zijn om implantaten in zowel de PM als de M-regio te plaatsen aan beide zijden van de onderkaak, werd beoordeeld door drie waarnemers op basis van de klinische situatie en een OPT of een CBCT. De meting op basis van de CBCT werd beschouwd als de werkelijke bothoogte. Cohen’s kappa (Cohens’ X), sensitiviteit en specificiteit, de kans op overeenstemming en de kans op geen overeenstemming, evenals de verhouding tussen deze twee (Odds Ratio, OR) werden berekend.

Voor de premolaar regio waren de terecht positieve en de terecht negatieve scores respectievelijk 90% en 0%. Dus in 10% van de gevallen werd er een verkeerde conclusie getrokken. Er waren aanzienlijke verschillen tussen waarnemers inzake sensitiviteit en specificiteit en Cohens’ X-waarden waren laag. De Odds Ratio’s (OR) voor de waarnemers varieerde tussen de 2,6 en 158,8, met een totale OR = 76.

Voor de molaar regio waren de terecht positieve en de terecht negatieve scores respectievelijk 65% en 22%, met een Cohens’ X = 0,69. In dertien procent van de gevallen werd gemisclassificeerd. Sensitiviteit en specificiteit, evenals de OR zijn voor de individuele waarnemers vrij constant is, met een totale OR = 43.

Geconcludeerd werd dat in de meeste gevallen de mogelijkheid tot het plaatsen van een implantaat in de geresorbeerde zijdelingse delen van de onderkaak goed kon worden beoordeeld op een OPT. De mate van overeenstemming tussen de twee diagnostische regimes, een OPT of een CBCT, is waarnemer-afhankelijk en beter voor de molaarregio dan voor de premolaar regio. De rechtvaardiging voor het maken van een CBCT voor de planning van implantaten ten behoeve van de ondersteuning van een vrij-eindigende frameprothese in de onderkaak zal afhangen van de bereidheid van zowel de patiënt als de behandelaar om misclassificaties, die neerkomen op ongeveer 10-13% van de gevallen, te accepteren.

Klinische overwegingen

Wanneer alle bevindingen gecombineerd worden, spelen de volgende overwegingen een rol bij de besluitvorming voor een implantaat-gesteunde frameprothese in een Kennedy klasse I situatie in de onderkaak. Vanuit het oogpunt van de patiënt lijkt zo’n frameprothese het beste ondersteund te worden door implantaten in de molaar regio. Echter kunnen er gezondere peri-implantaire condities verwacht worden rond implantaten geplaatst in de premolaar regio. Dit, samen met het feit dat, in geval van verder verlies van de natuurlijke elementen een implantaat-gesteunde volledige gebitsprothese beter is gediend met implantaten op de positie van de premolaren, heeft de premolaar regio de voorkeur vanuit klinisch perspectief. Ook wordt geadviseerd om bij de positionering van de implantaten rekening te houden met een eventuele toekomstige vaste voorziening op implantaten, bestaande uit één of meerdere

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kroondelen, voor het geval de patiënt wenst over te gaan van een uitneembare naar een vaste voorziening.

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CHAPTER 10

DANKWOORD EN CURRICULUM VITAE

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Bij de totstandkoming van dit proefschrift zijn heel veel mensen betrokken geweest. En wat gaaf dat het nu eindelijk af is! Ik realiseer me dat het een enorme kans is geweest en dat het een samenspel is geweest van vele betrokkenen. Zonder iemand tekort te willen doen, wil ik een aantal mensen in het bijzonder bedanken.

Allereerst wil ik alle deelnemers aan de klinische en retrospectieve studie bedanken. Zonder proefpersonen geen wetenschap dus bedankt voor jullie bijdrage! Ook nu, na afronding van dit proefschrift hoop ik jullie te kunnen blijven volgen en van dienst te blijven als zorgverlener.

Prof. dr. M.S. Cune, hooggeleerde eerste promotor, beste Marco. Dank je voor de kans die je mij gegeven hebt om onderzoek te doen. Samen formuleerden we de hypothesen en bedachten we de opzet. Jouw onuitputtelijke inzet, het plezier dat jij hebt in het doen van onderzoek en het schrijven is onevenaarbaar. Je doet het graag, overal en altijd. Niets dan lof. Het enige nadeel is dat ik skiën heel leuk ben gaan vinden.

Prof. dr. H.J.A. Meijer, hooggeleerde tweede promotor, beste Henny. Het was een eer om met jou onderzoek te doen, een enorme brok aan kennis en ervaring waar ik vaak gebruik van kon maken. Ik heb de gezamenlijke ritten naar Apeldoorn en Drachten gewaardeerd, ook daarin ben je onvoorwaardelijk, evenals de uren samen achter de computer. Hartelijk dank voor alles.

Prof. dr. G.M. Raghoebar, hooggeleerde derde promotor, beste Gerry. Jij maakt de drie-eenheid compleet. Met je uitgebreide onderzoekservaring, ontelbare publicaties en je uitstekende reputatie in je vakgebied was je voor mij een bron van informatie en inspiratie. Ik wil je bedanken voor het op professionele wijze behandelen van alle patiënten uit het klinisch onderzoek en de prettige samenwerking.

Geachte prof. dr. F. Abbas, prof. dr. D. Wismeijer en prof. dr. E.B. Wolvius, leden van de beoordelingscommissie. Bedankt voor de tijd die u heeft genomen heeft om mijn proefschrift zorgvuldig te beoordelen.

Geachte dr. L.W.M. van der Sluis, beste Luc, afdelingshoofd van de opleiding Tandheelkunde van de Rijksuniversiteit Groningen. Bedankt voor het constructief meedenken in de laatste fase van mijn promotie traject om alles in goede banen te leiden.

Geachte prof. dr. F. Abbas, beste Frank, ook in je rol als voormalig afdelingshoofd van de opleiding Tandheelkunde van de Rijksuniversiteit Groningen wil ik je bedanken voor

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het mogelijk maken van de start van mijn onderzoek. Ook ben ik je erkentelijk voor de prettige samenwerking, je deskundigheid en enthousiasme.

Drs. H.J. Lohr, beste Henri, chef de clinique van de opleiding Tandheelkunde van de Rijksuniversiteit Groningen. Bedankt voor je faciliterende houding in de allereerste en allerlaatste fase van mijn promotie traject. Fijn om jou weer aan het roer te hebben van de patiëntenzorg.

Dr. T. L. Feenstra, dr. W. Kerdijk, dr. R.H. Schepers, dr. C.M. Speksnijder, beste Talitha, Wouter, Rutger en Caroline. Bedankt voor de constructieve manier van samenwerken. Het is gebleken dat het bundelen van de krachten leidt tot prachtige resultaten. Dank jullie voor jullie inzet en het delen van jullie kennis.

Drs. R. M. B. Brenkman, beste Martijn, roommie. Jij was bereid om alle patiënten van mijn klinische studie te behandelen. Het was soms moeilijk om jouw passie voor goede zorg te evenaren, mijn patiënten liepen met jou weg. Dank daarvoor en ook voor je luisterend oor, erg waardevol.

Beste Gerrit van Dijk en alle medewerkers van het Tandtechnisch Laboratorium Gerrit van Dijk. Jullie ben ik veel dank verschuldigd voor de perfecte manier waarop jij en jouw medewerkers alle frameprothesen hebben gemaakt. Je bent altijd bereid om mee te denken en een stap extra te zetten. Met weemoed denk ik terug aan onze fijne samenwerking.

Dr. F.L. Guljé en dr. J.P.H. Wymenga, beste Felix en Jan Peter, bedankt voor de gastvrije ontvangst in respectievelijk praktijk “de Mondhoek” te Apeldoorn en op de Afdeling MKA van Ziekenhuis Nij Smellinghe te Drachten en voor de mogelijkheid die jullie me boden om de gegevens van jullie patiënten in kaart te brengen en te analyseren.

Beste Anne Wietsma en Aswin Beekes, bedankt voor jullie vakkundig meedenken en het maken van alle boormallen. Het was fijn om met jullie te mogen samenwerken.

Beste dames van van de röntgenafdeling van de afdeling Mond-, Kaak-, en Aangezichtschirurgie van het UMCG. Ontzettend bedankt voor de bereidwilligheid om tijd en energie te steken in mijn onderzoekspatiënten. Het is altijd fijn om even bij jullie te ‘buurten’.

Beste dames-assistentes van de implantologie van de afdeling Mond-, Kaak-, en Aangezichtschirurgie van het UMCG. Wat zijn en blijven jullie een geweldig geoliede

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machine, bedankt voor jullie inzet, hulp en stroomlijning van mijn patiëntengroep.

Beste Linda, Linda, Chantal en Esther. Ook jullie ben ik dank verschuldigd voor jullie inzet bij planwerk en hand en spandiensten tijdens mijn onderzoek. Jullie zijn topassistentes en ik hoop nog lang met jullie te mogen samenwerken.

Lieve Carline en Marieke. Samen werken aan onze onderzoeken op het UMCG en op Schiermonnikoog (met dank aan Tatjana), hoe leuk is het om samen met jullie onderzoeker te zijn! Dank jullie voor deze topmomenten en ik wens jullie alle succes bij de voortzetting en afronding van jullie promotie trajecten.

Lieve (overige) mede-onderzoekers, Carina, Christiaan, Eric, Elise, Gerdien, Kees, Kirsten, Laurens, Marco, Maurits, Yvonne en Ulf. Dank jullie voor alle gezelligheid tijdens onze gezamenlijke reizen. Bewonderenswaardig om jullie doorzettingsvermogen te zien. Allen veel succes en ik kijk uit naar jullie publicaties en/of promoties.

Beste Alexander, fijn om je kamergenoot te zijn, dank voor de lekkere chocola op momenten dat het echt nodig was.

Beste Jamila, Henk, Reinier, Paulien, Anton, Cathy, Maria, Saskia en Caroliene, student-onderzoekers en -assistenten, bedankt voor jullie hulp en samenwerking. Het heeft tot mooie resultaten mogen leiden. Inmiddels zijn jullie allemaal al afgestudeerd en bezig met een mooie carrière. Caroliene en Jamila, veel succes met de voortzetting van jullie eigen onderzoek.

Beste sectiegenoten Orale Functieleer, (overige) collega’s en assistentes van het Centrum voor Tandheelkunde en Mondzorgkunde van het UMCG. Zonder jullie allemaal bij naam te kunnen noemen, dank voor ieder afzonderlijk steentje dat jullie bijgedragen hebben. Het is een tumultueuze tijd geweest op ons Centrum, maar het persoonlijke plezier was er niet minder om.

Lieve Hubert en Linde, wat fijn dat we jullie troffen in de Marsmanlaan, het voelt alsof we jullie al jaren kennen. Linde ik ben je erg dankbaar dat je het ontwerp en de lay-out van mijn boekje voor je rekening wilde nemen ondanks alle hectiek. Op nog veel relaxte borrels in onze nieuwe huizen!

Lieve wijkkringleden, dank jullie voor jullie interesse en steun die ik voel en ervaar. Fijn dat we zoveel kunnen delen, daar ben ik dankbaar voor.

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Lieve Juul, dank je voor je vriendschap, al vanaf de middelbare school, zo vertrouwd. Allebei een roeier aan de haak geslagen en allebei drie meiden, hoe mooi is dat! Zoveel om te delen, vaak via de telefoon. Na deze promotie moet het traject Groningen-Amersfoort maar weer vaker afgelegd worden… Ik kijk er naar uit!

Lieve daaaaames ’95 van G.S.R. Aegir, Annelies, Susan, Carolien en Joséphine. Wat gaaf om nog steeds zo met elkaar op te mogen trekken. Jullie zijn stuk voor stuk bijzonder, intelligent, sterk en nooit saai. Ik geniet altijd erg van ons samenzijn, dank daarvoor.

Beste meiden van KWGF, beste Mirjam, Sietske, Margreet, Paulien en Esther. Het racefietsen met jullie is een enorme uitlaadklep geweest. Ik ben trots op een ieder van jullie, mooie, stoere mama’s! Ik hoop dat we tot in lengte van jaren samen op de pedalen blijven staan.

Lieve Harm, Marieke, Jan en Maaike. Wat fijn om het leven zo vaak met jullie te mogen vieren. Shoppen, eten, kletsen en opvoeden. Maar ook de serieuze dingen kunnen we delen. Dank voor jullie waardevolle vriendschappen.

Lieve familie en vrienden, kaere familie, heel veel dank voor het geduld, een luisterend oor, een kop koffie, een kaartje. Jullie zijn me veel waard. Tusinde tak, jeg glaeder mig til naeste gang…

Dr. J.W.A. Slot, beste Wim. Jij ging me voor in veel stappen van mijn carrière. Je leerde me implanteren en legde me uit dat promoveren heel relaxed en leuk is. Wat hebben we al veel gaafs gedaan en het is altijd gezellig en ontspannen met jou. Ontzettend bedankt daarvoor en geweldig dat je mijn paranimf bent. Ik kijk uit naar nog veel mooie jaren samen werken.

Lieve Margreet. Samen wandelen, fietsen, spinnen, koffie drinken en werken. Elke week rond het Paterswoldse meer wandelend bespreken we het leven. Onderzoek, gezin, politiek, jeugd en de diepere betekenis van dingen. Je bent een waardevolle vriendin van me geworden. Dank voor je support en kritisch denken en super dat je mijn paranimf wilt zijn.

Lieve farmor, lieve mamsie. Ik ben zo blij en dankbaar dat je dicht bij ons bent komen wonen. Dat dit boekje nu af is, is zeker ook aan jou te danken. Je staat altijd voor ons klaar en je vertroetelt je kleinkinderen, onze meiden: daar geniet ik enorm van. Jij was en bent echt onmisbaar. Love you!

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Lieve papa. Mijn nieuwsgierigheid en analytisch denkvermogen heb ik van jou. Ik zie grote overeenkomsten tussen jou en mij. Dank je voor alles wat je me meegegeven hebt en wat ik kon gebruiken om op dit punt te komen. En dat je altijd voor ons klaar staat. Ik zie daar een trotse papa!

Lieve mama. Van jou heb ik geleerd om vol te houden (eve deurdoe hé) en oh ja, nog zoveel, zoveel meer. Bedankt voor je onvoorwaardelijke steun: oppassen, verhuizen, maar ook mentaal. Als jij je spierballen even laat knappen, nou, berg je dan maar! Fijn om je Smoeltje te zijn.

Lieve Trees, mijn grote zus. Wat ben ik ongelofelijk blij met jou. Je was altijd mijn voorbeeld in onze jonge jaren en nog steeds kan ik veel van je leren. Ik bewonder je om je liefde, geduld en je wilskracht. Wat hebben we samen al veel gelachen, gehuild, gebeden, gemopperd, gezanikt en gek gedaan. Ik koester die momenten. Dank je zus!

Lieve Roos, twinnie. Een beter idee dan samen met jou op de wereld gezet te zijn bestaat niet! Met jou kan ik tranen met tuiten lachen en huilen, alles is goed. Als we samen zijn, maken we de meest bijzondere dingen mee. Deze promotie gooide roet in de verhuisplannen naar het zuiden, maar onze verbondenheid rijkt veel verder dan een paar honderd kilometer. © always! ®

Lieve Sonni, mijn grootste cadeau ooit! Elke dag verwonder ik me erover hoe leuk je wel niet bent. Wat heerlijk om mijn leven met jou te delen. Dank je voor al je steun in woorden, knuffels en actie. Ik weet dat je heel trots op me bent en voor deze ene keer zal ik het aannemen…Maar ik ben ook erg trots op jou. En man, wat kijk ik uit naar nog veel meer van jou!

Lieve Elin, Merit en Stine, samen met papa maken jullie mijn leven zó fijn. Het is bijzonder om jullie groter te zien groeien. Te zien hoe jullie steeds meer jezelf worden. Als ik aan jullie denk komt er vanzelf een gelukkig mama-glimlachje op mijn lippen. Jullie zullen nog niet goed begrijpen waarom mama dit boekje heeft gemaakt en waar het over gaat. Maar wat zullen we een feestje vieren als de promotie achter de rug is. Ik geniet al elke dag van jullie, maar reken maar dat dat er niet minder op zal worden ;-)

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CURRICULUM VITAE

Charlotte Jensen-Louwerse was born in Rheden (October 6th 1975). In 2001 she graduaded with honors from the dental school at the University of Groningen. She worked at the department of Oral and Maxillofacial Surgery of the University Medical Center Groningen were she was trained in dental surgery. Besides she worked as a dentist in a general practice in Grou and at a nursing home ‘Maartenshof’ in Groningen. In 2007 she started at the Center for Dentistry an Oral Health and since then she practices and teaches dentistry and oral implantology. In 2011 she started the PhD project presented in this thesis and in the same year she was registered as an oral implantologist at de Dutch Association for Oral Implantology (NVOI). Charlotte is married to Sonni Jensen and together they have 3 daughters, Elin (2006), Merit (2008) and Stine (2010).

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The research presented in this thesis was performed at the Department of Fixed and Re-movable Prosthodontics, Center for Dentistry and Oral Health, and at the Department of Oral and Maxillofacial Surgery, University Medical Center Groningen, University of Groningen, the Netherlands.

This research was supported byITI Foundation Switzerland

The printing and distribution of this thesis was kindly supported by:

Dentsply Sirona implants BeneluxDentaid BeNeLux B.V. (Perio•Aid, Chloorhexidine) Dent-Med Materials b.v., importeur Geistlich Bio-Oss® en Geistlich Bio-Gide®ExamVision BeneluxKoninklijke Nederlandse Maatschappij tot bevordering der Tandheelkunde (KNMT)Nederlandse Vereniging voor Gnathologie en Prothetische Tandheelkunde (NVGPT)Nederlandse Vereniging voor Mondziekten, Kaak- en Aangezichtschirurgie (NVMKA)Nederlandse Vereniging voor Orale Implantologie (NVOI)Nobel Biocare Nederland B.V.Straumann B.V.Tandtechnisch en Maxillofaciaal Laboratorium Gerrit van Dijk, GroningenTandtechnisch laboratorium Elysee Dental OosterwijkUniversitair Medisch Centrum GroningenRijksuniversiteit Groningen

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