Multiple implants impression accuracy of edentulous jaw: digital and conventional implant

impression comparative study

by

Sahr AlTuwaijri

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF

THE REQUIREMENTS FOR THE DEGREE OF

MASTER OF SCIENCE

in

THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES

(Craniofacial Science)

THE UNIVERSITY OF BRITISH COLUMBIA

(Vancouver)

August 2018

© Sahr AlTuwaijri, 2018

ii

The following individuals certify that they have read, and recommend to the Faculty of Graduate

and Postdoctoral Studies for acceptance, a thesis/dissertation entitled:

Multiple implants impression accuracy of edentulous jaw: digital and conventional implant

impression comparative study

Submitted by Sahr AlTuwaijri in partial fulfillment of the requirements for

the degree of Master of Science in “Craniofacial Science”

Examining Committee:

Dr. Caroline Nguyen

Supervisor

Dr. Chris Wyatt

Supervisory Committee Member

Dr. Dorin Ruse

Supervisory Committee Member

Dr. Huge Kim

Additional Examiner

Additional Supervisory Committee Members:

Dr. Vincent Lee

Supervisory Committee Member

iii

Abstract

Statement of problem: The use of digital impressions for implants are limited to single and short

span bridges due to the few available studies supporting their usage in more complex cases.

Therefore, its essential to evaluate their accuracy in full arch cases to benefit from their great

advantages.

Purpose: Evaluate and compare the accuracy of digital and conventional impressions for multiple

straight and angulated implants of full arch implant supported fixed prosthesis. Also, assess the

effect of implant angulation of 45 and increased length on the accuracy of both methods.

Materials and methods: A stereolithographic (SLA) model of edentulous mandibular cast was

fabricated and used to produce the master stone cast with four Nobel CC RC implants placed at

tooth positions 3.4, 3.2, 4.2 and 4.4. Implants at #32 and 42 were perpendicular to the occlusal

plane and parallel to each other while implants at #34 and 44 were distally angulated with 45.

Three impression methods were made from the master stone cast. Digital impressions were made

with Trios (3Shape, Copenhagen, Denmark) intraoral scanner (IOS) (n=10). Conventional

splinted open-tray implant–level impressions were made with Polyvinyl (PVS) (n=10) and

Polyether (PE) (n=10). All stone casts were digitized using a 3shape D800 lab scanner to obtain

STL (standard tessellation language) files, which then were imported into Rhino5 3D software.

Six linear measurements were obtained for each cast to evaluate their discrepancies from the

master cast. Absolute values of the linear deviation of each line among the three groups were

compared using Kruskal-Wallis test and Dunn's post hoc test.

Results: Significant difference (P< 0.05) were found between Trios and PVS and between PE and

PVS for the distance between Implant #42 and 44. Also, for the distance between implant #32 and

iv

44 between PE and Trios, and between PE and PVS. No significant difference was found for the

other lines.

Conclusion: The PE impression technique was more accurate than the others and all methods were

considered clinically acceptable. The 45 degree of angulation and the increased length had

affected the accuracy of PVS and Trios groups.

v

Lay Summary

People who have lost all their teeth search for solutions other than complete removable dentures.

They are keen on having teeth that are fixed into their mouths. Complete dentures can be fixed to

dental implants surgically placed in bone. The first step in fabricating complete fixed dentures is

making an impression of the implants. Currently, new impression methods (digital scanning) have

become widely available, and are introduced as a comparable alternative to the previous techniques

(conventional Polyether and Polyvinyl impressions). In this study, a comparison was made

between these methods to evaluate how accurate they are and what factors can influence their

accuracy and their eventual usage. All tested methods found to be clinically acceptable, with

polyether impression method being significantly better than the rest. The Trios digital scanning

was affected by the inter-implants increased distance, while the conventional Polyvinyl method

was influenced by the angulated position of the implants.

vi

Preface

The research was designed by myself with the modification and supervision of the supervisor Dr.

Caroline Nguyen and the committee member Dr. Chris Wyatt. The literature review was performed

by myself. The master acrylic cast was fabricated by the lab technician at Paul Ro dental

laboratory. The fabrication of the stone master cast (reference cast), all test groups of the study

including; Group 1 (10 PE implant impression) / Group 2 (10 PVS implant impression) / Group 3

(10 Trios IOS implant impression) were done by myself in addition to the 20 stone casts of group

1 and 2. The conventional implant impressions (group 1 and 2) included the fabrication of the

custom tray and the impression coping splinting. All stone casts; master cast and the 20 test casts

were digitized by the same lab technician. The accuracy measurements with Rhino 3D software

for all the digital casts were analyzed and performed by myself with the supervision of Dr. Alan

Hannam. The statistical analysis was performed by the statistical department at UBC.

vii

Table of Contents

Abstract ......................................................................................................................................... iii

Lay Summary .................................................................................................................................v

Preface ........................................................................................................................................... vi

Table of Contents ........................................................................................................................ vii

List of Tables ..................................................................................................................................x

List of Figures ............................................................................................................................... xi

List of Symbols ........................................................................................................................... xiii

List of Abbreviations ................................................................................................................. xiv

Glossary ........................................................................................................................................xv

Acknowledgements .................................................................................................................... xvi

Dedication .................................................................................................................................. xvii

Chapter 1: Introduction ................................................................................................................1

1.1 Passive fit ............................................................................................................................ 2

1.1.1 Misfit: biological and mechanical complication ..................................................... 3

1.1.2 Load distribution differences between teeth and implants ..................................... 3

1.2 Determining passivity ......................................................................................................... 4

1.3 Conventional implants impression ...................................................................................... 5

1.3.1 Impression materials ............................................................................................... 5

1.3.2 Impression techniques ............................................................................................. 6

1.3.2.1 Open tray vs closed tray impressions.................................................................. 6

1.3.2.2 Splinting vs non-splinting ................................................................................... 6

viii

1.4 Modern fabrication methods in implant dentistry ............................................................... 8

1.5 Digital Intra-Oral Scanning (IOS) ...................................................................................... 8

1.5.1 Scan body ................................................................................................................ 9

1.5.1.1 Scan body accuracy related factors ................................................................... 10

1.5.2 Advantages of IOS ................................................................................................ 10

1.5.3 Challenges with IOS ............................................................................................. 11

1.5.4 Accuracy of IOS in complete implant supported prosthesis ................................. 12

1.5.5 Trios IOS accuracy ............................................................................................... 13

1.6 Patient preference.............................................................................................................. 16

1.7 Accuracy of lab scanner .................................................................................................... 16

1.8 Rhino 5 3D software ......................................................................................................... 16

1.9 Rationale ........................................................................................................................... 17

1.10 Research questions ............................................................................................................ 17

1.11 Null Hypotheses ................................................................................................................ 18

1.12 Specific aims ..................................................................................................................... 18

1.13 Significance....................................................................................................................... 18

Chapter 2: Materials and methods .............................................................................................19

2.1 Master cast fabrication ...................................................................................................... 19

2.2 Custom tray fabrication..................................................................................................... 22

2.3 Implant impression (test groups) (Figure 9) ..................................................................... 23

2.3.1 Group 1: Splinted implant level open-tray polyether impression ......................... 24

2.3.2 Group 2: Splinted implant level open-tray polyvinyl impression ......................... 25

2.3.3 Group 3: Digital Intra-Oral scanning (TRIOS) ..................................................... 27

ix

2.4 Digitizing the master cast.................................................................................................. 28

2.5 Accuracy measurement ..................................................................................................... 28

2.6 Statistical analysis ............................................................................................................. 33

2.6.1 Comparing the accuracy of implants impression between the three test groups. . 33

2.6.2 Comparing the implants position errors between the groups................................ 34

2.6.3 Intraclass Correlation ICC. ................................................................................... 34

Chapter 3: Results........................................................................................................................35

3.1 Effect of implant angulation: ............................................................................................ 35

3.2 Effect of increased distance (cross arch): ......................................................................... 36

3.3 Comparing the implants position errors between the groups: .......................................... 38

3.4 The intraclass correlation test ........................................................................................... 40

Chapter 4: Discussion ..................................................................................................................41

4.1 Limitations of the study .................................................................................................... 44

4.2 Strength of the study ......................................................................................................... 44

Chapter 5: Conclusion .................................................................................................................46

Bibliography .................................................................................................................................47

x

List of Tables

Table 1: Measurements and comparison of line deviation in micrometer for three methods....... 37

Table 2: Measurements and comparison of implants errors in micrometer for the three methods

....................................................................................................................................................... 39

Table 3: The Intraclass Correlation test (ICC) results .................................................................. 40

xi

List of Figures

Figure 1: Scan body ........................................................................................................................ 9

Figure 2: Trios IOS ....................................................................................................................... 15

Figure 3: Digital design of the master cast in Co-diagnostic software ......................................... 19

Figure 4: Master cast digital design in Rhino 5 3D software ....................................................... 20

Figure 5: Master cast in clear acrylic ............................................................................................ 21

Figure 6: Master stone cast (control) ............................................................................................ 21

Figure 7: Impression coping ......................................................................................................... 22

Figure 8: Splinted implant level impression coping ..................................................................... 23

Figure 9: Methodology flow chart ................................................................................................ 23

Figure 10: Intaglio surface of PE Implant level impression ......................................................... 24

Figure 11: Group 1 (PE) stone cast ............................................................................................... 25

Figure 12: Intaglio surface of PVS implant level impression ....................................................... 26

Figure 13: Group 2 (PVS) stone cast ............................................................................................ 26

Figure 14: Trios Digital scan ........................................................................................................ 27

Figure 15: Plane through points .................................................................................................... 30

Figure 16: Plane parallel to CP ..................................................................................................... 30

Figure 17: Surface extension and offset by 2mm ......................................................................... 31

Figure 18: Mesh split by the offset surface ................................................................................... 31

Figure 19: Surface from curve and perpendicular line ................................................................. 32

Figure 20: Line split and formation of the implant surface centroid ............................................ 32

xii

Figure 21: Six linear measurements in Rhino 5 ............................................................................ 33

Figure 22: Implants positions diagram ......................................................................................... 35

Figure 23: Linear deviation among the three groups .................................................................... 38

Figure 24: Comparison of implant errors among the groups ........................................................ 39

xiii

List of Symbols

: indicate the angle degree

m: micrometer

xiv

List of Abbreviations

CAD: “Computer assisted design”

CAM: “Computer assisted manufacturing”

IOS: Intra-Oral scanner

PE: Polyether impression material

PVS: Polyvinyl Siloxane impression material

STL: Standard tessellation language

SLA: Stereolithographic

xv

Glossary

Dental Implant: “a prosthetic device made of alloplastic material(s) implanted into the oral tissues

beneath the mucosal and/or periosteal layer and on or within the bone to provide retention and

support for a fixed or removable dental prosthesis; a substance that is placed into and/or on the jaw

bone to support a fixed or removable dental prosthesis” (GPT9).

Digital scan: “in dentistry, capturing the optical image directly of the patient’s anatomy or

indirectly of a definitive cast of the anatomy” (GPT9).

Edentulous: “without teeth, lacking teeth” (GPT9).

Implant-supported denture: “dental prosthesis, such as fixed complete denture, fixed partial

denture, removable complete overdenture, removable partial overdenture, as well as maxillofacial

prostheses, which can be supported and retained in part or whole by dental implants” (GPT9).

Polyether: “an elastomeric impression material of ethylene oxide and tetra-hydrofluro copolymers

that polymerizes under the influence of an aromatic ester” (GPT9).

Poly (vinyl siloxane): “an addition reaction silicone elastomeric impression material of silicone

polymers having terminal vinyl groups that cross-link with silanes on activation by a platinum or

palladium salt catalyst” (GPT9).

Removable complete denture: “a removable dental prosthesis that replaces the entire dentition and

associated anatomy of the maxillae or mandible; the removable complete denture can be readily

inserted and removed from the mouth by the patient; comp, COMPLETE DENTURE” (GPT9).

xvi

Acknowledgements

I wish to express my great appreciation to my supervisor Dr. Caroline Nguyen and my Committee

members Dr. Chris Wyatt, Dr. Dorin Ruse and Dr. Vincent Lee for their substantial support,

guidance and precious time. Special thanks to Dr. Caroline Nguyen for her generosity and

guidance providing a safe environment throughout the thesis journey. My dear committee

members, this entire experience wouldn’t have been as good as it was without your great ideas and

continuous encouragement. I would like to express my gratitude to Dr. Alan Hannam for his

generous impact in teaching me how to use the Rhino 5 3D software for the accuracy analysis of

the study. I really appreciate the valuable time, your patience and kindness. I would love to thank

Mrs. Erikka Gilmore, the Territory representative of Nobel Biocare Canada, for her amazing

personality, support and kindness as well as the Nobel Biocare company for their generosity in

supporting the study through providing all the implant replicas, scan bodies and impression coping

needed for the study. Finally, special thanks to my colleague Dr. Arwa Gazzaz for being a great

friend who supported me throughout the process, giving me feedback and making this journey

unforgettable.

xvii

Dedication

Every great achievement requires endless personal effort, I would not be able to progress, bear the

burdens required and succeed without the support of my loving family.

I dedicate my humble work to my family, my beloved husband Eng. Emad Al Fouzan. Your

presence, continuous emotional support, endless reassurances and valuable suggestions made this

journey unforgettable. No words will be enough to describe my gratitude.

I would love to dedicate my work to my great and amazing parents, my dad Eng. Homood Al

Tuwaijri and my mom Joharah Al Tuwaijri; my life wouldn’t have been as good without you. You

were the role models that every child wants to have; your endless love, support and

encouragements made me who I am. I really cannot explain my gratitude to you.

I would like to express my special thanks to my parents-in-law Ahmed Al Fouzan and Munerah

Al Essa, your infinite support and prayers were such a motivation for me to keep going.

Finally, my brother and sisters: thank you so much for being in my life. You were always there

whenever I felt weak or lost, thank you for being my source of strength and wisdom.

1

Chapter 1: Introduction

Historically, people who lost their entire teeth will replace them with complete removable denture.

In 1950-1960s Professor Branemark and colleagues developed and introduced the titanium

endosseous dental implant (Albrektsson, Brånemark and Zarb). After that, dental implants were

accepted as a treatment modality and has become widely used in dentistry. Nowadays, with the

dentistry evolution, implant prosthetic rehabilitation is the preferred treatment option for replacing

missing teeth. People are increasingly aware of all the available possible treatments and seek the

best. Several studies have proven the long-term success of implant treatments (Buser et al.).

Restoring function and esthetics are essential components in prosthodontic treatment planning.

There are different types of Implant supported dentures, whether it is removable or fixed and

whether it is complete or partial. For people who are completely edentulous and seek a treatment

that is fixed and feels like natural teeth, the treatment of choice will be the full arch implant

supported fixed prosthesis. Patients that will benefit the most from such a treatment are those who

are young, people who suffer from xerostomia or gag reflex. This treatment modality consists

from either a metal framework with veneered acrylic resin, a zirconia framework with layered

ceramic or a full counter monolithic zirconia framework. To fabricate this prosthesis, several steps

are involved:

1- Prosthetically driven implant planning according to the ideal tooth position in the arch

2- Implants surgical placement in the desired locations using surgical guide

3- Implant impression to fabricate the master cast

2

4- Jaw relation record including; centric relation and vertical dimension of occlusion

5- Teeth try in to assess the esthetic, phonetics and the previous jaw records

6- Framework design and fabrication

7- Framework intra-oral try in

8- Framework/teeth try in,

9- And finally processing and insertion of the implant supported prosthesis.

All these fabrication steps should be done meticulously and precisely to ensure longevity and avoid

any future complications. An accurate fit of the implant supported prosthesis is one of the main

success factors of implant treatments. Prostheses misfits can lead to several mechanical

complications including; screw loosening, prosthesis fracture, or even more advanced

complications like implant fracture or failure (Papaspyridakos, Lal, et al.; Duyck and Naert). Half

of the misfits are caused by the impression procedures, while the other half are due to the prosthesis

casting and fabrication process (Heckmann et al.).

1.1 Passive fit

Branemark determined “passive fit” in 1983, when he suggested that it should not exceed 10 μm

to permit bone remodeling under occlusal forces (Branemark). A few years later in 1985, Klineberg

and Murray recommended that discrepancies higher than 30 μm over more than 10% of the

circumference of the abutment interface were unacceptable (Klineberg and Murray). Jemt has

defined “passive fit” as the fit that will not cause any type of long term clinical complication. It

3

was suggested that an unacceptable level of framework misfit happened when more than half-a-

turn was required to completely tighten the gold screw after its initial seating resistance was faced

(Jemt). To have passive fit, the prosthetic superstructure should have zero strain over the

underlying implant when it is unloaded (Sahin and Cehreli). An implant-supported fixed prosthesis

with discrepancies or misfit up to less than 150 μm is considered clinically acceptable (Jemt; Jemt

and Lie; Jemt and Book) which was considered in the study as the clinically accepted discrepancy.

1.1.1 Misfit: biological and mechanical complication

In a study done by Carr et al., they found that the bone biologic reaction for different misfit

levels, ranging between 38 μm and 345 μm, was similar, with no signs of bone resorption over

the period of the study in unloaded implants (Carr, Gerard and Larsen). Similar findings were

found in the retrospective study done by Kallus and Bessing who stated that 236 patients with

misfitting implant-supported prostheses for a period of five years had no signs of

osseointegration or marginal bone level loss, while misfit of the prosthetic superstructure was the

cause of gold screw loosening (Kallus and Bessing).

1.1.2 Load distribution differences between teeth and implants

Natural teeth demonstrate buccolingual movement ranging between 56 μm and 108 μm and

intrusion of 28 μm under load, that is mainly related to the presence of the periodontal ligament

(Shillingburg, Hobo and Whitsett), while implants are osseointegrated and completely encircled

by bone, so the interface is stiffer and minimum movement is detected, which is attributed to the

bone deformation under load around implants (Sahin and Cehreli).

4

1.2 Determining passivity

The evaluation of the strains on each prosthetic implant component is the only in vivo technique

to assess the actual amount of the prosthesis passivity. Such a process is definitely time consuming

that demand the connection of strain gauges which also requires the use of complex and costly

equipment. Therefore, it is considered unrealistic to use strain gauges as part of a regular clinical

treatment protocol (Sahin and Cehreli).

Kan et al. suggested numerous clinical assessment techniques to evaluate the misfit of the implant

framework:

1- “Alternate finger pressure”, to evaluate the instability of the prosthetic superstructure

and observe the misfit gap for any bubbling around.

2- Direct visualization and tactile sensation by using the explorer tip to confirm the

marginal fit, which is restricted by the explorer tip dimension (a pristine explorer tip is

approximately 60 m).

3- Radiographs, which have the disadvantages of possible overlap or superimposition,

depending on different angulations.

4- “The Sheffield test” (“the one screw test”): tightening one screw at the end of one side

of the framework and then discrepancies are detected at the other end screw.

5- “Screw resistance test”, where one starts with the midline nearest implant; the screws

are then tightened one after the other one until the initial resistance is met at one of the

screws. If the screw needs more than an extra half a turn to reach the optimal screw

seating, the framework is considered mis-fitting.

6- Disclosing media, like “fit checker” (GC), “pressure indicating paste” (mizzy

Keystone) or disclosing wax.

5

7- 3D photogrammetric test has been considered as a quantifying method that can assess

discrepancies to the nearest 10 μm. Other 3D quantifying procedures, such as

“coordinate measuring machine”, can only be utilized extra-orally (Kan et al.).

1.3 Conventional implants impression

Several factors affect the accuracy of the impression and hence the accuracy of the implant cast,

including the type of impression, implant position and angulation, the number of implants, the

impression technique: whether to splint or not, open or close tray impressions and the use of stock

tray or customized impression tray, and finally, the type of prostheses (Lee et al.).

1.3.1 Impression materials

Multiple studies have been conducted to compare the accuracy of different impression materials,

most of them evaluating the differences between polyether and polyvinyl impression materials as

they are the most frequently used implant final impression materials (Lee et al.) . Most of these

studies show no difference between these two materials. Daoudi MF et al. and Chang et al. both

reported no difference between polyether and polyvinyl impression material with regards to their

accuracy for single implant impression (Daoudi, Setchell and Searson; Chang et al.). Similar

results were reported by Lorenzoni M et al. and Gökçen-Rohlig et al. where they found no

significant difference in distortion between polyvinyl and polyether implant impressions

(Lorenzoni et al.; Gokcen-Rohlig et al.). With regards to different implant angulation, S Reddy et

al. found no difference in the accuracy of the two materials when the angle of the implants were 0

°, 10°, and 15° (Reddy et al.). In contrast, Sorrentino et al. found a difference in accuracy,

6

with polyvinyl being more accurate in 5 angled implants and polyether in straight implants

(Sorrentino et al.). Similarly to Sorrentino, Kurtulmus-Yilmaz et al. found a difference with

polyvinyl being more accurate with the angled implants at 10 and 20 (Kurtulmus-Yilmaz et al.).

1.3.2 Impression techniques

Several factors are related to the impression technique, including type of the tray, open vs closed

tray impression and splinting vs non-splinting impression, as detailed below.

1.3.2.1 Open tray vs closed tray impressions

Several studies were done evaluating the difference in accuracy between open tray and close tray

impression techniques. One of these studies is the one conducted by Al Quran FA et al. where they

reported that the direct (open tray) technique showed the lowest mean of distortion (Al Quran et

al.). Similar results were found by Assif D et al. with the open tray technique being more accurate

(Assif et al.). In contrast, Chang WG et al. reported no difference between the two techniques

(Chang et al.). In a recent systematic review in 2014, it was reported that out of 21 studies, 11 of

them preferred the open tray impression technique, 1 study supported the closed tray and the

remaining 10 studies found no difference (Papaspyridakos, Chen, et al.) .

1.3.2.2 Splinting vs non-splinting

Numerous studies have been done to detect the differences between splinting and non-splinting,

and also examine different splinting materials and techniques. Several studies recommended

7

splinting over non-splinting (de Avila et al.; Pujari, Garg and Prithviraj) (Papaspyridakos,

Hirayama, et al.; M. Stimmelmayr et al.). Papaspyridakos P et al. concluded that the splinting

resulted in more accurate casts compared to the non-splinted impressions in the overall 3D

measurements, which coincided with clinical assessment of the prosthesis, where the clinical fit of

the CAD/CAM Zirconia full arch implant supported prostheses were acceptable in 11 casts out of

12 in the splinted group and 6 out 12 in the non-splinted group (Papaspyridakos, Benic, et al.). In

addition, another study was conducted to compare the splinting with acrylic resin and metal drill

bars, and non-splinting impression technique. Four parallel implant analogs were placed

simulating the Branemark protocol. A metal framework was made to fit the master cast, with mean

gap value of 39.64 μm, and used to check the amount of discrepancy between the two techniques.

This study resulted in significant differences, where the splinted technique resulted in lesser gaps

(99.19 μm) compared to the non-splinted technique with a mean gap value of (205.86 μm) (Avila

et al.).

When comparing splinting, with auto-polymerizing acrylic resin/light curing composite resin, and

non-splinting technique, involving air abraded impressions coping with aluminum oxide of 50 μm

under 75 lbs pressure in two different situations, straight and 65°of angulation, no difference was

found with the straight implants, while the angulated implants showed statistically significant

difference, being more accurate in splinted techniques compared to the non-splinted air-abraded

impression post (Assuncao et al.). In addition, three different splinting materials (light

polymerizing resin (Triad gel) and autopolymerizing resin (GC resin and Fixpeed resin)) were

tested to evaluate their 3D accuracy for full arch implant cast verification jig. Triad gel had the

lower 3D deviation compared to other two materials although the results were not statistically

8

significance (Papaspyridakos, Kim, et al.) which can be explained by the 0.20% linear shrinkage

of Triad gel (Harvey and Harvey) and the 0.80% of GC resin (Mojon et al.) .

1.4 Modern fabrication methods in implant dentistry

The CAD/CAM technology provided better fit and improved accuracy when compared to the

conventional casting procedures for implant-supported cobalt-chromium and zirconia fixed

prostheses (de França et al.). Discrepancies of less than 40 μm were obtained using CAD/CAM

for implant-supported short and long FPD prosthesis (Katsoulis et al.).

1.5 Digital Intra-Oral Scanning (IOS)

Digital IOS was introduced in the 1980’s by Professor Mormann and Dr. Brandistini. It is

considered the first step towards a full digital work flow, which is the data acquisition. Cerec 1

(Redcam) was the first 3D intra-oral camera, introduced in 1985 (Mormann, Brandestini and Lutz).

Several available IOS are available on the market, such as Cerec Bluecam, Omnicom (Sirona), I

Tero (Cadent Inc), True definition (3M), Lava COS (3M ESPE), Trios (3Shape), CS 3500

(Carestream) and PlanScan (Planmeca). Each IOS has its own working principle such as, active

triangulation for the CEREC system, CS 3500 and PlanScan while Parallel conofocal technology

for I Tero, Active wavefront sampling for True definition and Lava C.O.S and Confocal laser

technology for Trios. Each one has its advantages, and disadvantages, with different levels of

9

accuracy and specific indications (Zimmermann et al.). Nowadays, IOS are widely available and

are known for having a wide range of accuracy, similar or comparable to conventional impressions

in tooth-borne fixed prostheses (Ender and Mehl; Luthardt, Loos and Quaas; Patzelt et al.).

1.5.1 Scan body

The scan abutments are used to capture the position, trajectory, and rotation of the lab analogs in

the working cast. Using dental scanners, the scan abutments are registered optically and the digital

information is used to produce individual abutments and crown and bridge frameworks using

innovative CAD/CAM technology (Figure 1).

Figure 1: Scan body

10

1.5.1.1 Scan body accuracy related factors

The implant scan body accuracy is affected by several factors including: the design of the scan

body, material, type of scanner and the repositioning.

1- Accuracy of geometric representations of implant scan bodies: algorithm is a sufficient

means to obtain surface data of the scan bodies.

2- Accuracy of scanning implant scan bodies: The accuracy of an extra-oral scanner varied

between the scan design and the distances between the scan bodies.

3- Accuracy of positioning the implant scan body in the implant analogs: The precision of

scanning was not significantly affected by removing and repositioning of the scan body

(Fluegge et al.) .

4- Scanning stone casts has less errors in contrast to polymer casts when using lab scanners

(white- light scanners) for the scanning of scan bodies.

5- The repositioning of the scan body is better on implant analogs compared to original

implants with original implants having less reproducible fit of scan bodies (Michael

Stimmelmayr et al.).

1.5.2 Advantages of IOS

IOS has several advantages over the conventional impression technique that affect the efficiency

and accuracy of the procedure as well as the patient experience.

1. Improved patient acceptance (Joda and Brägger; Schepke et al.).

2. Reduced distortion of conventional impression materials.

3. Potential cost and time effectiveness.

11

4. Elimination of all laboratory procedures.

5. A full digital work flow with the CAD/CAM technology (Christensen) .

6. More efficiency in relation to the total working time.

7. Allows for additional re-scans without repeating the entire procedure.

8. Less difficult to learn by unexperienced participants (Lee and Gallucci) .

1.5.3 Challenges with IOS

The accuracy of IOS in implant dentistry can be affected by multiple factors that require proper

case selection;

• Possible scan bodies fit discrepancies on implants compared to implant analogs (Michael

Stimmelmayr et al.).

• The lack of landmarks or reference points in scanning implants in edentulous jaw (Andriessen

et al.).

• The scanned implants inter-distance length influence on the accuracy of scanner (Gimenez,

Ozcan, et al.; Flugge, Att, et al.)

• The geometrical shape of the scan body can affect the precision of the intra-oral scans (Fluegge

et al.)

12

• The intra-oral conditions such as saliva and limited mouth opening decrease the accuracy of

intra-oral scanning (Flugge, Schlager, et al.).

• The position of the camera when moving from the first quadrant to the second one affect the

distance accuracy (Gimenez, Ozcan, et al.) .

• The operator experience, inexperienced operators showed higher accuracy with less variations

compared to the experienced operators (Gimenez, Ozcan, et al.).

1.5.4 Accuracy of IOS in complete implant supported prosthesis

Several studies have recently conducted evaluations of the accuracy of IOS. Moreno et al and

Gherlone et al. have evaluated the Lava COS (3M ESPE) IOS, which resulted in clinically accurate

implant supported prosthesis (Moreno et al.; E. F. Gherlone et al.), which is in contrast with

Andiersson et al study, where they used I Tero IOS and found it less accurate with a mean of

distance errors of 226 m and stated that it can’t be use to fabricate the prosthesis (Andriessen et

al.).

Gimenez et al tested the accuracy of several IOS (I Tero (Cadent Inc), Lava COS (3M ESPE),

CEREC Blue cam (Sirona), 3D progress and ZFX(MHT)) for 6 implants placed in an edentulous

maxilla and found that different depth of the implants and angulation didn't influence the accuracy

of the scan and only the length of the scanned section had adversely affected the accuracy of

CEREC with a mean distance deviation of -116m and SD of 103m. Also, generated a large

number of errors with 3D progress and ZFX with mean distance deviation of 382.2m and -

13

170.1m.(Gimenez, Ozcan, et al.; Giménez et al.; Gimenez, Pradies, et al.; Gimenez, Ozcan, et

al.).

Another in-vitro study by Mangano et al. in 2016 to evaluate the accuracy of four different IOSs

(Trios, CS3500, ZFX Intascan and Planscan) in both partially and completely edentulous maxillary

arch casts. No difference in accuracy was found between partially and completely edentulous casts

scanning, while the different scanners had significantly different levels of accuracy, with Trios

(71.6m) and CS3500 (63.2m) being the most accurate (Mangano et al.).

In another study comparing the accuracy of single-unit dental implants and complete arch

frameworks on implants in regard to the impression making and framework fabrication. They

compared the digital scanning using I Tero and fabrication (CAD/CAM) of a single unit implant

crown to a conventional impression made of polyvinyl material and conventional cast fabrication

method, as well as for complete arch frameworks. They found that for the complete arch

framework the digital method provided a more accurate implant supported framework prosthesis

with 63.14m, while the conventional method was more accurate for the implant single framework

(Abdel-Azim et al.) .

1.5.5 Trios IOS accuracy

Trios (3Shape; Copenhagen, Denmark) is a IOS that Utilize Confocal microscopy working

principle that recognize variations of focus plane positions. It takes multiple colored images and

doesn’t require surface coating (Figure 2). Also, it’s an open system that allows scans to be

exported as STL files or propriety files (Ting-shu and Jian). The accuracy of four different IOS

14

(Trios, 3M true definition, Omnicam and Lava COS) were compared using a highly accurate

laboratory scanner as a control, when placing 6 relatively parallel implants in an edentulous

mandible. The Trios and 3M true definition scanners showed the best accuracy while the Lava

COS scanner showed the least accurate scanning and found to be not suitable to be used in a

complete edentulous jaw with accuracy of 0.112 mm. (Vandeweghe et al.).

In a clinical comparative study conducted by Gherlone and colleagues, they had 25 patients with

clinical conditions that were recommended for “All-On-Four” prostheses (fixed implant supported

prostheses on four implants) with a total of 30 conditions between mandible and maxilla suitable

for implanted supported prostheses. For the test group, digital IOS with Trios from 3Shape

(confocal microscopy) were used to fabricate 15 implant supported prostheses. For the control

group, 15 conventional impressions (polyether pick-up impressions) were made. 30 CAD/CAM

milled prosthetic frameworks were made and the final prostheses were seated on the implants and

the fit of the prostheses was checked using the Sheffield test. The total time and the number of re-

takes were counted to check the efficacy of both procedures. Intra-oral digital radiographs were

taken immediately after placement and after 3, 6 and 12 months follow ups to evaluate the amount

of bone loss. All the definitive prostheses were clinically accurate. No significant difference was

found between the groups with regards to the amount of bone loss for the straight and tilted

implants. The digital group was significantly more efficient, according to the total time needed,

although the retakes there were more in the digital compared to the conventional impressions (E.

Gherlone et al.) .

15

Different conventional implant impressions (implant level impression splinted/non-splinted and

abutment level impression splinted/ non-splinted) were compared for five implants placed in an

edentulous mandible with digital impression using 3Shape Trios IOS. The study concluded that

there was no significant difference between conventional and digital impressions, with the digital

impression being as accurate as conventional impression even with 15° implant angulation

(Papaspyridakos, Gallucci, et al.).

Figure 2: Trios IOS

16

1.6 Patient preference

Two in-vivo studies were done evaluating patients’ preference and acceptance between digital and

conventional single implant impressions. Both concluded that digital IOS was preferred by the

participants and that it was more time effective (Joda and Brägger; Schepke et al.).

Similar results were found by another study done by Wismeijer et al. evaluating patients’

preference between analog conventional implant impression, using polyether impression material,

and digital implant impressions, using I Tero IOS. They conducted a questionnaire with seven

different questions for both types, including general opinion, preparation needed, time involved,

taste, intra-oral bite registration, size of impression tray and gag reflex. The thirty patients involved

in the study preferred the digital IOS for all the factors except the time duration, which significantly

favored the analog conventional implant impression (Wismeijer et al.)

1.7 Accuracy of lab scanner

3Shape D800 has 2 cameras with 5.0 MP that utilize light technology with red laser with 8 μm

accuracy for implant supported bars and bridges. It takes up to 25 secs to finish a scan.

W Renne and colleagues, concluded that the trueness of the full arch scan of the 3Shape D800 was

the best among all other scanners (Renne et al.). The accuracy of the lab scanner D800 is not

affected by the location or extent of the scan (Su and Sun)

1.8 Rhino 5 3D software

Rhino 5 three-dimensional software can generate, edit, evaluate, document, render, animate, and

translate 3D geometry that define any shape from a simple 2D line. In addition, you can import

17

any design or 3D object scan as STL files and utilize the software features such as analyzing

distances, angles, radiuses and lengths. It has been used in dentistry mostly as a CAD software,

3D designing for Rapid prototype for experimental (Porojan, Topală and Porojan) or educational

goals (Soares et al.)

1.9 Rationale

As the demand for full arch implant supported is increasing, utilizing the most efficient methods

available is highly recommended. IOS with all their advantages can provide both the patient and

the clinician pleasant experiences with short appointments, reduced costs and treatment time. IOS

are well known for their accuracy in implant supported single and short span fixed prostheses.

There are very few studies supporting their use in full arch prostheses where the cross arch

accuracy is important as well as with extremely angulated implants that are commonly used to

avoid bone grafting and reduce the cost of such a treatment by utilizing fewer implants.

1.10 Research questions

In the development of the research project two research questions were formulated. Firstly, we

would like to know if Trios IOS digital impressions of multiple straight implants more accurate

than conventional PVS/PE impressions? Secondly, are Trios IOS digital impressions more

accurate than conventional PVS/PE impressions for angulated implants?

18

1.11 Null Hypotheses

H01: No significant difference in the accuracy of implant impressions between Trios IOS and

conventional PVS and PE impression techniques for multiple implants in edentulous jaw.

H02: No significant difference in the accuracy of implant impression between Trios IOS and

conventional PVS and PE impression techniques for angulated implants in edentulous jaw.

1.12 Specific aims

1- To measure the accuracy of conventional vinyl polysiloxane impressions for multiple (straight

and angulated) implants in an edentulous mandible.

2- To measure the accuracy of conventional polyether impression for multiple (straight and

angulated) implants in an edentulous mandible.

3- To measure the accuracy of intra-oral digital scanning (TRIOS 3SHAPE) for multiple (straight

and angulated) implants in an edentulous mandible.

4- To compare the accuracy of conventional and digital impression method in angulated

implants.

1.13 Significance

Precise and accurate passive fit of implants prostheses depends on accurate implants impressions.

If digital impressions are more accurate than conventional methods, this would provide patients

with a treatment option leading to better long-term success, and efficient treatment. In addition,

digital impressions are very convenient and well-tolerated methods, especially for patients with

gag reflex and for geriatric patients.

19

Chapter 2: Materials and methods

2.1 Master cast fabrication

To stimulate a clinical scenario, a stone cast of a patient’s edentulous mandible was used to

fabricate the master acrylic cast. The cast was scanned with 3Shape D800 lab scanner. Implants

were planned according to the (All-on-Four) design at the locations of teeth number 3.4, 3.2, 4.2,

4.4. Implants at 3.2 and4.2 were placed perpendicular to the horizontal plane. Subsequently,

implants at 3.4 and 4.4 were distally angled by 45 , relative to the 3.2 and 4.2 implants, in Co-

diagnostic software (Figure 3) and then designed on Rhino 5 3D (Figure 4).

Figure 3: Digital design of the master cast in Co-diagnostic software

20

Figure 4: Master cast digital design in Rhino 5 3D software

The cast was then fabricated on a desktop Stereolithography (SLA) 3D printer with clear acrylic

resin using Nobel CC RP implants (Figure 5). Because the acrylic master cast cannot be digitized

as the light will go through the cast surface and cause distortion, a stone cast was fabricated through

conventional splinted open tray polyether impression, the impression was then poured with type

IV die stone (silky rock, Whipmix, Louisville, USA) after connecting the implants analogs to the

impression posts (Figure 6).

21

Figure 5: Master cast in clear acrylic

Figure 6: Master stone cast (control)

22

2.2 Custom tray fabrication

A two-millimeter wax spacer was used on the master stone cast that will allow uniform proper

amount of impression material, and a light cured acrylic resin Triad sheet was used to fabricate the

custom tray 2 mm away from the depth of the sulcus. The custom tray was cured for 2 minutes in

(Enterra VLC curing unit, DENTSPLY). Custom tray has been used with all the conventional

implant impressions. All impression copings (Figure 7) were splinted with light cured acrylic resin

(Triad Gel; Dentsply, York, USA) which is urethane-dimethacrylate resin (UDMA), sectioned and

then re-luted to reduce any polymerization shrinkage that might happened (Figure 8).

Figure 7: Impression coping

23

Figure 8: Splinted implant level impression coping

2.3 Implant impression (test groups) (Figure 9)

Figure 9: Methodology flow chart

Group1 (PE)Digitized to have 10 digital casts

Group2 (PVS)Digitized to have 10 digital casts

linear measurment compared to

control

Master castDigitized to have

control digital castlinear measuremnt

Group3 (Trios)10 digital casts

linear measurment compared to

control

24

2.3.1 Group 1: Splinted implant level open-tray polyether impression

First, the open tray non- engaging impression copings were connected to the implants of the master

stone cast, then they were splinted using light cured acrylic resin (Triad Gel; Dentsply, York, USA)

(Figure 8). Then, PE impression adhesive (3M ESPE; impregum) was applied on the custom tray

intaglio surface. The adhesive was then allowed to dry for 15 minutes. Next, the impression was

taken using polyether impression material (Impregum; 3M ESPE) (Figure 10). PE light body was

applied around the implant impression coping while the heavy body was injected to fill the custom

tray. The impressions were finally poured using type IV die stone (silky rock, Whipmix,

Louisville, USA), after connecting the implants analogs to the impression copings. This entire

procedure was then repeated 10 times, which resulted in 10 stone casts (Figure 11).

Figure 10: Intaglio surface of PE Implant level impression

25

Figure 11: Group 1 (PE) stone cast

2.3.2 Group 2: Splinted implant level open-tray polyvinyl impression

In this group, the open tray non- engaging impression copings were connected to the implants of

the master stone cast, then they were splinted using light cured acrylic resin (Triad Gel; Dentsply,

York, USA) (Figure 8). Then, PVS impression adhesive (Extrude; Kerr, Orang, USA) Afterwards,

the impression was done using polyvinyl impression material (Extrude; Kerr, Orang, USA) (Figure

12). PVS light body was applied around the implant impression coping while the medium body

was injected to fill the custom tray. The impressions were finally poured using type IV die stone

(silky rock, Whipmix, Louisville, USA), after connecting the implants analogs to the impression

copings. This procedure was then repeated 10 times, which resulted in 10 stone casts (Figure 13).

26

Figure 12: Intaglio surface of PVS implant level impression

Figure 13: Group 2 (PVS) stone cast

27

2.3.3 Group 3: Digital Intra-Oral scanning (TRIOS)

ELOS scan bodies (ELOS MedTech) with titanium insert and PEEK material were connected to

the implants of the stone master cast. Then, the cast was scanned with IOS, utilizing confocal

microscopy (TRIOS 3Shape) 10 times without removing the scan bodies, starting with quadrant 3

from occlusal, buccal and then lingual, with one continuous stroke of each surface. Then the virtual

cast scan was checked and any deficiencies were rescanned. Finally, the scanned data were

exported as STL (standard tessellation language) files (Figure 14).

Figure 14: Trios Digital scan

28

2.4 Digitizing the master cast

ELOS scan bodies were screwed in to the implants. The master stone cast was then scanned with

the 3Shape D800 scanner, which worked as the reference (control) scan for the study. All stone

casts fabricated from both conventional techniques, Group 1 and Group 2, were digitized with

3Shape D800 scanner as well using the same ELOS scan bodies.

2.5 Accuracy measurement

3D modeling and designing software (Rhino 5) was used to measure the accuracy of the implants

impressions test groups. As far as this researcher knows, this is the first time that this software had

been used to assess accuracy. Previous studies were mainly assessing the 3D deviation through

superimposition of casts. In our study, each STL file from control cast, PE, PVS and Trios groups

were named, numbered and imported into the software. The control scan was done first. The scan

was displayed using prospective view from the software desktop, and shaded view of the cast, to

make it clearly visible. The scan bodies were identified as A, B, C and D. Scan body A corresponds

to the 3.4 implant, B to the3.2 implant, C to the4.2 implant and D to the 4.4 implant. The analysis

started with scan body A for all the casts, followed by B, C and D following these steps:

1- A constructor plane with X, Y, Z coordinates at the horizontal top of the scan body was created,

so the flat top of the scan body is considered the horizontal plane with X and Y axis’s for this

implant. Vertices were selected from the flat top of the scan body; the target number of vertices

was 10 with a minimum of 5 that were all located away from the borders. Then, the selected

vertices were highlighted to construct a plane through command (plane through points) (Figure

15).

2- The plane was set parallel to the constructor plan (Figure 16).

29

3- The surface to cover the borders of the scan body was enlarged. The centroid of the surface was

determined through the object propriety command and enlarged through scale 3D object up to 2.

4- The surface was offset to a parallel surface below by 2 cm (Figure 17).

5- The mesh was selected and split through the second offset surface (Figure 18). Then, hiding the

upper part of the scan body, a (curve from object) command was selected along with the end curve

of the split mesh. After that, the (construct a surface from curve) command was done. Then,

centroid was identified for the surface and a perpendicular line was constructed (Figure 19).

Finally, this line was split by the top surface to locate the point at the intersection of the line and

the top surface as the point in which the measurement will be started (Figure 20). These steps were

then done for each scan body of each cast. These points were used to obtain 6 measurements for

each cast by constructing a line connecting each point together to create the following lines: AB,

BC, CD, DA, AC and BD (Figure 21). All these measurements were done for every cast scan of

the PE, PVS and IOS group to be compared with the control cast scan measurements for trueness

and, within each group, for precision. The mean deviation of each measurement was obtained for

the comparison between the groups, to evaluate the trueness. The linear deviation was used to

compare the accuracy of three test groups between each other rather than comparing each group

to the controls measurements. This was done by subtracting the control reading from each test

reading for every line in each group.

Test reading of line (AB) – Control reading of line (AB)

After that, all the measurements were converted from millimeter to micrometer.

30

Figure 15: Plane through points

Figure 16: Plane parallel to CP

31

Figure 17: Surface extension and offset by 2mm

Figure 18: Mesh split by the offset surface

32

Figure 19: Surface from curve and perpendicular line

Figure 20: Line split and formation of the implant surface centroid

33

Figure 21: Six linear measurements in Rhino 5

2.6 Statistical analysis

2.6.1 Comparing the accuracy of implants impression between the three test groups.

Absolute values were used as the magnitude of deviation was the interest rather than the direction;

otherwise, positive and negative results would reduce the total value and mislead the results to less

deviation. Because of the small size of the sample, a non-parametric Kruskal-Wallis test was used

on each pair of measurement deviations on same line to test if there was a significant difference

among three methods for each line. If there was a significant difference, then Dunn's post-hoc test

was used to detect which two measurement deviations had a significant difference in median.

34

2.6.2 Comparing the implants position errors between the groups.

Kruskal-Wallis was used to test if there was any significant difference among the three methods

for each implant. If there was a significant difference, then Dunn's post-hoc test was used to detect

which two measurement errors had a significant difference on the median.

2.6.3 Intraclass Correlation ICC.

The (ICC) was done to test the agreement and the reliability of each impression method with value

range between 0-1. The procedure considered more accurate as it gets closer to 1.

35

Chapter 3: Results

The comparison of linear deviation median for all the lines between the three groups are

summarized in (Table 1). To evaluate the effect of implant angulation on the accuracy of the

implant impression, four lines were used to assess any difference; these lines are the ones

connecting implants from Quadrant 3 to Quadrant 4 (AB, CD, BD, AC). The other factor to

evaluate was the cross arch (long span) effect on the accuracy. These lines were connecting one

straight implant to angulated implant in the whole cast (DA, BC, AC, BD) (Figure 22).

3.1 Effect of implant angulation:

1- The median deviation for the PE group in AB line was 37 m, for CD line 52.5 m,

for BD line 21.5 m and for AC line 46 m.

2- The median deviation for the PVS group in AB line was 44 m, for CD line 110. 5m,

for BD line 79 m and for AC line 63 m.

3- The median deviation for the Digital (trios) group in AB line was 41 m, for CD line

50 m, for BD line 68.5 m and for AC line 53.5 m.

A

B C

D

Figure 22: Implants positions diagram

36

3.2 Effect of increased distance (cross arch):

1- The median deviation for the PE group in DA line was 45 m, for BC line 61.5 m,

for AC line 46 m and for BD line 21.5 m.

2- The median deviation for the PVS group in DA line was 86.5 m, for BC line 30.5 m,

for AC line 63 m and for BD line 79 m.

3- The median deviation for the Digital (trios) group in DA line was 132.5 m, for BC

line 24 m, for AC line 53.5 m and for BD line 68.5 m.

Significant differences in the deviations were found for the CD line between Trios and PVS and

Between PE and PVS, with PVS having the highest deviation of 110.5 m. No difference was

found between PE and Trios, with median values of 52.5 m and 50 m, respectively. Similarly,

for the BD line there was significant differences between PE and Trios, and between PE and PVS,

with PE having the least deviations of 21.5 m. There was no difference between PVS and Trios,

with median deviation of 79 m and 68.5 m, respectively.

So, the null hypotheses were rejected because of the significant difference found between Trios

IOS with median of 68.5 m and PE group with median of 21.5 m in the (BD) linear measurement

as its contribute to the null hypotheses.

37

Line PE PVS D P-value Post hoc test

AB, Median

(Range)

37

(0-117)

44

(2-97)

41

(2-102)

0.95 No significant

difference in median

CD, Median

(Range)

52.5

(22175)

110.5

(47-243)

50

(11-76)

0.0013* D vs. PVS &

PE vs. PVS

AC, Median

(Range)

46

(1-163)

63

(7-99)

53.5

(16-120)

0.99 No significant

difference in median

BD, Median

(Range)

21.5

(2-74)

79

(22-173)

68.5

(10-100)

0.0079* PE vs. D &

PE vs. PVS

DA, Median

(Range)

45

(2-133)

86.5

(13-721)

132.5

(25-434)

0.08 No significant

difference in median

BC, Median

(Range)

61.5

(0-135)

30.5

(16-72)

24

(1-90)

0.249 No significant

difference in median

For post hoc comparison, the Kruskal-Wallis test is used with the Dunn’s test.

Statistical significance is at p-value<0.05

Table 1: Measurements and comparison of line deviation in micrometer for three methods

Box plot (Figure 23) was used to visualize the precision of each method. Variability in a data set

is measured by interquartile range (IQR). The IQR is equal to (Q3- Q1). PVS group at DA line

shows the wider variation compared to the other lines in the same group. DA line showed the

higher variation among the lines for both PVS and Trios IOS groups. While AC line was the line

with the wide variation in the PE group.

38

Figure 23: Linear deviation among the three groups

3.3 Comparing the implants position errors between the groups:

The comparison of the implant position errors was carried out through the summation of three

lines' absolute deviations that are related to each implant (Table 2). No significant difference was

found for implant A and B between the three different implant impression groups. Implant C

showed a significant difference between the groups, with the Trios digital group having less

deviation compared to PE and PVS groups, whereas Implant D had a significant difference

between PE and Trios as well between PE and PVS groups, with PE group having the least

deviation (Figure 24).

39

Implant PE PVS D P-value Post hoc test

A, Median

(Range)

156.5

(18-304)

208.5

(54-917)

208.5

(72-656)

0.4973 No significant

difference in median

B, Median

(Range)

138.5 (2-

262)

183.5

(93-232)

117 (64-

263)

0.4229 No significant

difference in median

C, Median

(Range)

205.5

(60-300)

219

(136-354)

116.5

(90-285)

0.0331* D vs. PE &

D vs. PVS

D, Median

(Range)

113

(83-247)

308.5

(129-988)

210.5

(102-580)

0.0045* PE vs. D &

PE vs. PVS

For post hoc comparison, the Kruskal-Wallis test is used with the Dunn’s test.

Statistical significance is at p-value<0.05

Table 2: Measurements and comparison of implants errors in micrometer for the three methods

Figure 24: Comparison of implant errors among the groups

40

3.4 The intraclass correlation test

The average value for all the six-linear measurement of all the sample sizes of each group is

displayed in (Table 3). PVS method has the higher ICC value followed by PE and lastly by Trios

IOS.

ICC Average value

PE 0.74

PVS 0.88

Trios IOS 0.55

Table 3: The Intraclass Correlation test (ICC) results

41

Chapter 4: Discussion

Implant impression accuracy is the first step in providing the patient with the best prosthesis with

long term success through ensuring passive fit of the prosthesis. Digital implant impressions were

introduced to the market as a new technique that can provide accurate impressions of fixed tooth

borne prosthesis and small partial edentulous implant supported prosthesis. To our knowledge, few

studies have assessed the accuracy of IOS for implant impressions of complete edentulous arches.

Only two studies compared the accuracy of digital vs conventional implant impression

(Papaspyridakos, Gallucci, et al.; Amin et al.). Before our study, no studies have been conducted

to compare implant impression accuracy of full edentulous arch with angled implants up to 45.

The (BD) line represents the distance between one straight and one angulated implant, located in

quadrant 1 and quadrant 2, which describes the cross arch accuracy of IOS. Also, significant

difference was found between the Trios IOS and PVS impression for (CD) line, where the Trios

had better accuracy with median of 50 m while the PVS had a median of 110.5 m. This line

represents the effect of the implant angulation of implant D with 45 distally. The comparison

between the test groups and the control cast was conducted through digitizing the stone casts

produced from both conventional techniques and the control cast to be compared with the digital

casts, which is similar to several published papers (Amin et al.; Papaspyridakos, Gallucci, et al.;

Güth et al.; Vecsei et al.). For accuracy measurement, Rhino 5 3D software was used. All STL

files of all the test groups and the control cast were imported into the software. This is a new

method to evaluate accuracy through 6 linear measurements between the four implants, where each

line starts from the central long access of the implant. This technique helped in providing

information regarding the effects of cross arch accuracy and the implant angulation.

42

The results of our study showed similarity in the accuracy of implant impression between digital

and conventional methods, except for the two-linear measurements (BD and CD) mentioned

above. In regard to the effect of implant angulation on the accuracy of the full arch implants

impression, the current study had two distally angulated implants with 45 in the mandibular

edentulous arch. The first angulated implant at #34 (A) related measurement (AB), (AC) and (DA)

had no significant difference between the three groups which coincides with the study findings of

Papaspyridakos et al. where the angulation of 10 and 15 didn’t affect the accuracy of the Trios

3 shape scanner when used for mandibular full arch implants impression (Papaspyridakos,

Gallucci, et al.). Also, Gimenez et al.’s study on maxillary edentulous model with 6 implants and

angulation up to 30 had similar results to our study with no effect of the implant angulation in the

accuracy of implants impression using the LAVA C.O.S IOS (Giménez et al.). In addition, another

study by Gimenez et al. utilizing the same previous study protocol with implant angulation of 30

but with iTero IOS had the same result with no significant difference on the implant impression

accuracy in regard to the angulation (Gimenez, Ozcan, et al.). By assessing the accuracy of parallel

0 implants (B) and (C) and the distance between the implants (BC), no significant difference was

found among the three groups with accurate measurements compared to the control. This finding

is comparable with the Mangano et al. study which examined the accuracy of four IOS for partially

and complete edentulous maxilla with six implants. No information was mentioned regarding the

angulation of the implants which were most likely relatively parallel implants. The authors

concluded in their study that CS3500 and Trios IOS were significantly more accurate than the

other two IOS Zfx intra scan and Planscan which were not recommended to be used in the long

43

span prosthesis or multiple full arch implants (Mangano et al.). Additionally, Vandeweghe et al.

conducted a study where they placed 6 relatively parallel implants in an edentulous mandible, and

concluded that the Trios and 3M true definition IOS showed the best accuracy while LAVA C.O.S

IOS was not recommended for cross arch prosthesis (Vandeweghe et al.).

The other concern with the accuracy of multiple implants impression in edentulous jaw is the cross

arch accuracy or the long span factor especially with the second quadrant accuracy. In our study,

we found a significant difference between the groups for (BD) line which is crossing the midline

with PE group having the least discrepancy compared to PVS and to Trios IOS with no significant

difference between PVS and Trios IOS groups. This could be due to the long distance between the

two implants as well as the position of implant (D) which is distally angulated implant with 45.

Similar results were concluded by Gimenez et al. where they found that CEREC blue cam had

high deviation in the second quadrant compared to the first scanned quadrant in maxillary cast

with six implants placed with angulation ranged from 0 to 30 (Gimenez, Ozcan, et al.). The

boxplot of figure 23 shows the variation of the linear discrepancy for every impression method

that can describe the precision of each method and each line. The highest variation was found for

the (DA) line for the PVS and the Trios IOS groups, although the differences were not statistically

significant. This could be due to the long distance between implant (A) and (D) which caused the

wide rang in the Trios values and that the cross arch factor should be taken into consideration.

While the variability of the PVS group reading could be explained by the material physical

properties which is more resilience compared to the PE rigidity.

44

Table 2 demonstrates the comparison of implants errors between the three methods. The results

are in agreement with the linear discrepancy presented in table 1. Implant (C) and (D) had

significant difference among the three groups with PVS having higher discrepancy in both

implants which can be happened due to the impression removal technique of the conventional

impression method which was started slightly with quadrant 4 followed by quadrant 3. This didn’t

affect the PE due to the stiffer nature of the material. The ICC test was done to test the reliability

of each method, the ICC range from 0-1 with reading closed to 1 considered more reliable and

producible. The reading showing in table 3, demonstrates that PVS impression method has the

highest reliability among the three groups while Trios IOS has the lowest. This means that PVS

will provide a more constant impression, although it showed the highest deviation in (AD) but in

general for all the lines of the whole sample of each group it was more constant.

4.1 Limitations of the study

The project is an in-vitro study which is very different from the oral environment, where patient’s

cooperation is paramount and there are isolation concerns. One IOS system was used, which limits

generalizing the result of IOS accuracy due to the unique data acquisition of each IOS system. The

method of the accuracy evaluation is new, which limits the comparison between the results

obtained with those of other studies. Finally, the relatively small sample size used, even though

similar to that of other studies, limits the generalization of the results.

4.2 Strength of the study

Although this is an in-vitro study, the master cast used was obtained from a patient cast rather than

a standard acrylic block to simulate a real clinical scenario. No markers or reference structures

45

were imbedded in the cast, to be similar to a patient edentulous arch. In addition, all the clinical

steps for implant impression technique of the conventional impressions, as well as the sequence

recommended for the IOS, were followed in the study to simulate a clinical situation as closely as

possible. The study evaluated the accuracy of multiple implants with angulation up to 45 , which

can provide estimation of the accuracy of any clinical case that has non- parallel implants or

implants with different angulation, in addition to a recommendation to which technique can result

in the least deviation. The study was done by one clinician (the MSc student) to ensure that the

level of the experience was the same with both the IOS and the conventional PVS and PE

impression techniques through all the samples. Also, one dental laboratory technician was

responsible for the digitizing process of the control master cast and the two conventional test

groups to eliminate any inter-operator errors. The accuracy analysis through the Rhino 5 3D

software for all the digital casts was obtained by the MSc student for the same reason.

46

Chapter 5: Conclusion

Using Rhino 5 3D software to obtain the linear measurements in order to compare the linear

discrepancies between the three test groups reveals that Polyether implant impression of the

edentulous jaw had the best accuracy compared to the other two groups. The PE group was

significantly better than the PVS group in the CD line and significantly more accurate than the

PVS and Trios digital groups in the BD line. Hence, PE impression is the superior in full

edentulous multiple implants impression with angulated implants that is quite reproducible with

0.74 ICC value. PVS impression technique was affected by the implant angulation and Trios IOS

was influenced by the increased distance between the implants that was shown in the wide

variation of the DA line discrepancy of both groups. Although all the impression techniques

resulted in discrepancies that are clinically accepted and ranged from 21.5-132.5 m, PE

impression was significantly better among the test groups. PVS impression was the most

reproducible method with ICC value of 0.88. In conclusion, all methods are clinically acceptable

to use in multiple implants impression of full arch fixed prosthesis, with PE being recommended

due to the better performance. PVS impression and IOS with Trios are very valid options as

implant final impression of full arch implant supported fixed prosthesis, but the degree of

angulation as well as the inter-implant distance need to be taken into consideration prior to the

selection of these two methods. Finally, these recommendations should be taken with caution as

they are based on in-vitro study that might differ from a real clinical situation. Further clinical

studies comparing the accuracy of conventional and digital methods would be very beneficial and

a natural extension of this project, in addition to testing different IOS systems that are available in

the market.

47

Bibliography

Abdel-Azim, T., et al. "The Influence of Digital Fabrication Options on the Accuracy of Dental

Implant-Based Single Units and Complete-Arch Frameworks." INTERNATIONAL

JOURNAL OF ORAL & MAXILLOFACIAL IMPLANTS 29.6 (2014): 1281-88. Print.

Al Quran, F. A., et al. "Passive Fit and Accuracy of Three Dental Implant Impression

Techniques." Quintessence Int 43.2 (2012): 119-25. Print.

Albrektsson, Tomas, Per-Ingvar Brånemark, and George Albert Zarb. Tissue-Integrated

Prostheses: Osseointegration in Clinical Dentistry. Quintessence, 1985. Print.

Amin, Sarah, et al. "Digital Vs. Conventional Full-Arch Implant Impressions: A Comparative

Study." Clinical Oral Implants Research 28.11 (2016): 1360-67. Print.

Andriessen, Frank S., et al. "Applicability and Accuracy of an Intraoral Scanner for Scanning

Multiple Implants in Edentulous Mandibles: A Pilot Study." The Journal of Prosthetic

Dentistry 111.3 (2014): 186-94. Print.

Assif, D., et al. "Comparative Accuracy of Implant Impression Procedures." Int J Periodontics

Restorative Dent 12.2 (1992): 112-21. Print.

Assuncao, W. G., et al. "Prosthetic Transfer Impression Accuracy Evaluation for Osseointegrated

Implants." Implant Dentistry 17.3: 248-56. Print.

Avila, Erica Dorigatti de, et al. "Effect of Splinting in Accuracy of Two Implant Impression

Techniques." Journal of Oral Implantology 40.6 (2014): 633-39. Print.

Branemark, Per-Ingvar. "Osseointegration and Its Experimental Background." The Journal of

Prosthetic Dentistry 50.3 (1983): 399-410. Print.

Buser, Daniel, et al. "10‐Year Survival and Success Rates of 511 Titanium Implants with a

Sandblasted and Acid‐Etched Surface: A Retrospective Study in 303 Partially

Edentulous Patients." Clinical Implant Dentistry and Related Research 14.6 (2012): 839-

51. Print.

Carr, Alan B., David A. Gerard, and Peter E. Larsen. "The Response of Bone in Primates around

Unloaded Dental Implants Supporting Prostheses with Different Levels of Fit." The

Journal of Prosthetic Dentistry 76.5 (1996): 500-09. Print.

Chang, W. G., et al. "Accuracy of Three Implant Impression Techniques with Different

Impression Materials and Stones." Int J Prosthodont 25.1 (2012): 44-7. Print.

Christensen, Gordon J. "Impressions Are Changing: Deciding on Conventional, Digital or Digital

Plus in-Office Milling." The Journal of the American Dental Association 140.10 (2009):

1301-04. Print.

Daoudi, M. F., D. J. Setchell, and L. J. Searson. "A Laboratory Investigation of the Accuracy of

Two Impression Techniques for Single-Tooth Implants." INTERNATIONAL JOURNAL

OF PROSTHODONTICS 14.2 (2001): 152-58. Print.

de Avila, E. D., et al. "Comparison of the Accuracy for Three Dental Impression Techniques and

Index: An in Vitro Study." Journal of Prosthodontic Research 57.4: 268-74. Print.

de França, Danilo Gonzaga B., et al. "Influence of Cad/Cam on the Fit Accuracy of Implant-

Supported Zirconia and Cobalt-Chromium Fixed Dental Prostheses." The Journal of

Prosthetic Dentistry 113.1 (2015): 22-28. Print.

48

Duyck, J., and I. Naert. "Influence of Prosthesis Fit and the Effect of a Luting System on the

Prosthetic Connection Preload: An in Vitro Study." INTERNATIONAL JOURNAL OF

PROSTHODONTICS 15.4 (2002): 389-96. Print.

Ender, A., and A. Mehl. "Full Arch Scans: Conventional Versus Digital Impressions--an in-Vitro

Study." International journal of computerized dentistry 14.1 (2011): 11. Print.

Fluegge, Tabea, et al. "A Novel Method to Evaluate Precision of Optical Implant Impressions

with Commercial Scan Bodies-an Experimental Approach: Precision of Optical Dental

Implant Impressions." Journal of Prosthodontics (2015): n/a-n/a. Print.

Flugge, T. V., et al. "Precision of Dental Implant Digitization Using Intraoral Scanners." Int J

Prosthodont 29.3 (2016): 277-83. Print.

Flugge, T. V., et al. "Precision of Intraoral Digital Dental Impressions with Itero and Extraoral

Digitization with the Itero and a Model Scanner." AMERICAN JOURNAL OF

ORTHODONTICS AND DENTOFACIAL ORTHOPEDICS 144.3 (2013): 471-78. Print.

Gherlone, E., et al. "Conventional Versus Digital Impressions for "All-on-Four" Restorations."

INTERNATIONAL JOURNAL OF ORAL & MAXILLOFACIAL IMPLANTS 31.2 (2016):

324-30. Print.

Gherlone, E. F., et al. "Digital Impressions for Fabrication of Definitive "All-on-Four"

Restorations." IMPLANT DENTISTRY 24.1 (2015): 125-29. Print.

Gimenez, B., et al. Int J Oral Maxillofac Implants 29.4 (2014): 853-62. Print.

---. IMPLANT DENTISTRY 24.5 (2015): 498-504. Print.

Gimenez, B., et al. "Accuracy of Two Digital Implant Impression Systems Based on Confocal

Microscopy with Variations in Customized Software and Clinical Parameters."

INTERNATIONAL JOURNAL OF ORAL & MAXILLOFACIAL IMPLANTS 30.1 (2015):

56-64. Print.

Giménez, Beatriz, et al. "Accuracy of a Digital Impression System Based on Active Wavefront

Sampling Technology for Implants Considering Operator Experience, Implant

Angulation, and Depth." Clinical Implant Dentistry and Related Research 17 (2015):

e54-e64. Print.

Gokcen-Rohlig, B., et al. "Comparative Evaluation of the Effects of Implant Position, Impression

Material, and Tray Type on Implant Impression Accuracy." Implant Dentistry 23.3: 283-8.

Print.

GPT9. "The Glossary of Prosthodontic Terms: Ninth Edition." J Prosthet Dent 117.5s (2017): e1-

e105. Print.

Güth, Jan-Frederik, et al. "Accuracy of Digital Models Obtained by Direct and Indirect Data

Capturing." Clinical Oral Investigations 17.4 (2013): 1201-08. Print.

Harvey, Wayne L., and Eric V. Harvey. "Dimensional Changes at the Posterior Border of

Baseplates Made from a Visible Light-Activated Composite Resin." The Journal of

Prosthetic Dentistry 62.2 (1989): 184-89. Print.

Heckmann, Siegfried M., et al. "Cement Fixation and Screw Retention: Parameters of Passive

Fit: An in Vitro Study of Three-Unit Implant-Supported Fixed Partial Dentures." Clinical

Oral Implants Research 15.4 (2004): 466-73. Print.

Jemt, T. "Failures and Complications in 391 Consecutively Inserted Fixed Prostheses Supported

by Brånemark Implants in Edentulous Jaws: A Study of Treatment from the Time of

Prosthesis Placement to the First Annual Checkup." The International journal of oral &

maxillofacial implants 6.3 (1991): 270. Print.

49

Jemt, T., and K. Book. "Prosthesis Misfit and Marginal Bone Loss in Edentulous Implant

Patients." The International journal of oral & maxillofacial implants 11.5 (1996): 620.

Print.

Jemt, T., and A. Lie. "Accuracy of Implant-Supported Prostheses in the Edentulous Jaw: Analysis

of Precision of Fit between Cast Gold-Alloy Frameworks and Master Casts by Means of

a Three-Dimensional Photogrammetric Technique." Clinical oral implants research 6.3

(1995): 172-80. Print.

Joda, Tim, and Urs Brägger. "Patient-Centered Outcomes Comparing Digital and Conventional

Implant Impression Procedures: A Randomized Crossover Trial." Clinical Oral Implants

Research (2015): n/a-n/a. Print.

Kallus, T., and C. Bessing. "Loose Gold Screws Frequently Occur in Full-Arch Fixed Prostheses

Supported by Osseointegrated Implants after 5 Years." The International journal of oral

& maxillofacial implants 9.2 (1994): 169. Print.

Kan, Joseph Y. K., et al. "Clinical Methods for Evaluating Implant Framework Fit." The Journal

of Prosthetic Dentistry 81.1 (1999): 7-13. Print.

Katsoulis, Joannis, et al. "Cad/Cam Fabrication Accuracy of Long‐ Vs. Short‐Span Implant‐

Supported Fdps." Clinical Oral Implants Research 26.3 (2015): 245-49. Print.

Klineberg, I. J., and G. M. Murray. "Design of Superstructures for Osseointegrated Fixtures."

Swedish dental journal. Supplement 28 (1985): 63. Print.

Kurtulmus-Yilmaz, Sevcan, et al. "Digital Evaluation of the Accuracy of Impression Techniques

and Materials in Angulated Implants." Journal of Dentistry 42.12 (2014): 1551-59. Print.

Lee, H., et al. "The Accuracy of Implant Impressions: A Systematic Review." J Prosthet Dent

100.4 (2008): 285-91. Print.

Lee, S. J., and G. O. Gallucci. "Digital Vs. Conventional Implant Impressions: Efficiency

Outcomes." Clin Oral Implants Res 24.1 (2013): 111-5. Print.

Lorenzoni, M., et al. "Comparison of the Transfer Precision of Three Different Impression

Materials in Combination with Transfer Caps for the Frialit®-2 System." Journal of Oral

Rehabilitation 27.7 (2000): 629-38. Print.

Luthardt, R. G., R. Loos, and S. Quaas. "Accuracy of Intraoral Data Acquisition in Comparison

to the Conventional Impression." International journal of computerized dentistry 8.4

(2005): 283. Print.

Mangano, Francesco G., et al. "Trueness and Precision of Four Intraoral Scanners in Oral

Implantology: A Comparative <Italic>in Vitro</Italic> Study." PLoS ONE 11.9 (2016):

e0163107. Print.

Mojon, Philippe, et al. "Polymerization Shrinkage of Index and Pattern Acrylic Resins." The

Journal of Prosthetic Dentistry 64.6 (1990): 684-88. Print.

Moreno, A., et al. "A Clinical Protocol for Intraoral Digital Impression of Screw-Retained

Cad/Cam Framework on Multiple Implants Based on Wavefront Sampling Technology."

IMPLANT DENTISTRY 22.4 (2013): 320-25. Print.

Mormann, W. H., M. Brandestini, and F. Lutz. "[the Cerec System: Computer-Assisted

Preparation of Direct Ceramic Inlays in 1 Setting]." Quintessenz 38.3 (1987): 457-70.

Print.

Papaspyridakos, P., et al. "Accuracy of Implant Casts Generated with Splinted and Non-Splinted

Impression Techniques for Edentulous Patients: An Optical Scanning Study." Clinical

Oral Implants Research 23.6: 676-81. Print.

50

Papaspyridakos, P., et al. "Accuracy of Implant Impressions for Partially and Completely

Edentulous Patients: A Systematic Review." Int J Oral Maxillofac Implants 29.4 (2014):

836-45. Print.

Papaspyridakos, P., et al. "Full-Arch Implant Fixed Prostheses: A Comparative Study on the

Effect of Connection Type and Impression Technique on Accuracy of Fit." Clin Oral

Implants Res (2015). Print.

Papaspyridakos, P., et al. "Effect of Splinted and Nonsplinted Impression Techniques on the

Accuracy of Fit of Fixed Implant Prostheses in Edentulous Patients: A Comparative

Study." Int J Oral Maxillofac Implants 26.6 (2011): 1267-72. Print.

Papaspyridakos, Panos, et al. "Digital Versus Conventional Implant Impressions for Edentulous

Patients: Accuracy Outcomes." Clinical Oral Implants Research 27.4 (2016): 465-72.

Print.

Papaspyridakos, Panos, et al. "Digital Evaluation of Three Splinting Materials Used to Fabricate

Verification Jigs for Full-Arch Implant Prostheses: A Comparative Study." Journal of

Esthetic and Restorative Dentistry 29.2 (2016): 102-09. Print.

Patzelt, Sebastian B. M., et al. "Accuracy of Full-Arch Scans Using Intraoral Scanners." Clinical

Oral Investigations 18.6 (2014): 1687-94. Print.

Porojan, LILIANA, FLORIN Topală, and SORIN Porojan. "Biomechanical Impact During

Protrusion Loading on an Incisor Restored with a Ceramic Crown." Print.

Pujari, Malesh, Pooja Garg, and D. R. Prithviraj. "Evaluation of Accuracy of Casts of Multiple

Internal Connection Implant Prosthesis Obtained from Different Impression Materials

and Techniques: An in Vitro Study." Journal of Oral Implantology 40.2 (2014): 137-45.

Print.

Reddy, S., et al. "Accuracy of Impressions with Different Impression Materials in Angulated

Implants." Nigerian Journal of Clinical Practice 16.3: 279-84. Print.

Renne, Walter, et al. "Evaluation of the Accuracy of 7 Digital Scanners: An In vitro Analysis

Based on 3-Dimensional Comparisons." The Journal of Prosthetic Dentistry 118.1

(2017): 36-42. Print.

Sahin, S., and M. C. Cehreli. "The Significance of Passive Framework Fit in Implant

Prosthodontics: Current Status." Implant dentistry 10.2 (2001): 85-92. Print.

Schepke, Ulf, et al. "Digital Versus Analog Complete-Arch Impressions for Single-Unit Premolar

Implant Crowns: Operating Time and Patient Preference." Journal of Prosthetic Dentistry

114.3 (2015): 403-06. Print.

Shillingburg, Herbert T, Sumiya Hobo, and Lowell D Whitsett. "Fundamentals of Fixed

Prosthodontics, Quintessence Pub." Co, 2011. Print.

Soares, Paulo Vinícius, et al. "Rapid Prototyping and 3d-Virtual Models for Operative Dentistry

Education in Brazil." Journal of Dental Education 77.3 (2013): 358. Print.

Sorrentino, R., et al. "Effect of Implant Angulation, Connection Length, and Impression Material

on the Dimensional Accuracy of Implant Impressions: An in Vitro Comparative Study."

Clin Implant Dent Relat Res 12 Suppl 1 (2010): e63-76. Print.

Stimmelmayr, M., et al. "Clinical Study Evaluating the Discrepancy of Two Different Impression

Techniques of Four Implants in an Edentulous Jaw." Clin Oral Investig 17.8 (2013):

1929-35. Print.

Stimmelmayr, Michael, et al. "Digital Evaluation of the Reproducibility of Implant Scanbody

Fit—an in Vitro Study." Clinical Oral Investigations 16.3 (2012): 851-56. Print.

51

Su, Ting-shu, and Jian Sun. "Comparison of Repeatability between Intraoral Digital Scanner and

Extraoral Digital Scanner: An in-Vitro Study." Journal of Prosthodontic Research 59.4

(2015): 236-42. Print.

Ting-shu, Su, and Sun Jian. "Intraoral Digital Impression Technique: A Review: Intraoral Digital

Impression Review." Journal of Prosthodontics 24.4 (2015): 313-21. Print.

Vandeweghe, S., et al. "Accuracy of Digital Impressions of Multiple Dental Implants: An in Vitro

Study." Clin Oral Implants Res (2016). Print.

Vecsei, Bálint, et al. "Comparison of the Accuracy of Direct and Indirect Three-Dimensional

Digitizing Processes for Cad/Cam Systems – an in Vitro Study." Journal of Prosthodontic

Research 61.2 (2017): 177-84. Print.

Wismeijer, D., et al. "Patients' Preferences When Comparing Analogue Implant Impressions

Using a Polyether Impression Material Versus Digital Impressions (Intraoral Scan) of

Dental Implants." Clinical Oral Implants Research 25.10 (2014): 1113-18. Print.

Zimmermann, M., et al. "Intraoral Scanning Systems - a Current Overview." International

journal of computerized dentistry 18.2 (2015): 101. Print.