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Author's personal copy

Applicability and accuracy of an intraoral

scanner for scanning multiple implants in

edentulous mandibles: A pilot study

Frank S. Andriessen, DDS, MSc,a David R. Rijkens, DDS, MSc,b

Wicher J. van der Meer, DDS, MSc,c andDaniel W. Wismeijer, DDS, PhDd

Academic Centre for Dentistry Amsterdam, Amsterdam,The Netherlands; University Medical Centre Groningen,University of Groningen, Groningen, The Netherlands

Statement of problem. In the past 5 years, the use of intraoral digitizers has increased. However, data are lacking on theaccuracy of scanning implant restorative platforms for prosthodontics with intraoral digitizers.

Purpose. The purpose of this clinical pilot study was to assess the applicability and accuracy of intraoral scans by usingabutments designed for scanning (scan abutments) in edentulous mandibles.

Material and methods. Twenty-five participants with complete mandibular overdentures retained by 2 implants and frameworkswere included in this study. Scan abutments were placed on the implants intraorally and scanned with the iTero intraoral scanner.Also, scan abutments were placed on the implant analogs of the definitive casts and scanned with an extraoral laboratory scanner(Lava Scan ST scanner). Two 3-dimensional computer-aided designmodels of the scan abutments with predetermined center lineswere subsequently imported and registered, together with each of the scanned equivalents. The distance between the centers of thetop of the scan abutments and the angulations between the scan abutments was assessed. These values were compared with themeasurementsmadeon the3-dimensional scansof thedefinitive casts,whichwere theparticipants’original definitive casts used forfabrication of soldered bars. The threshold for distance error was established to be 100 mm.

Results. Four of the 25 intraoral scans were not suitable for research because the intraoral scanner was not able to stitch theseparate scans together. Five of the 21 suitable scans demonstrated an interimplant distance error >100 mm. Three of the 25intraoral scans showed interimplant angulation errors >0.4 degrees. Only 1 scan showed both an acceptable interimplantdistance (<100 mm) and an acceptable angulation error (<0.4 degrees).

Conclusions. Based on the intraoral scans obtained in this study, distance and angulation errors were too large to fabricatewell-fitting frameworks on implants in edentulous mandibles. The main reason for the unreliable scans seemed to be the lackof anatomic landmarks for scanning. (J Prosthet Dent 2014;111:186-194)

Clinical Implications

The scans of 2 implants in edentulous mandibles made with scanabutments by using the iTero IOS system lacked sufficient overlappingand stable reference points to make them usable for implantframeworks.

With the development of intraoralscanning, a shift has occurred inimpression making. Although the firstintraoral digitizers were commercially

available 2 decades ago, it is onlyrecently that the popularity of thesesystems has grown.1-5 In the past5 years, 5 new intraoral digitizers

have been developed and successfullyintroduced.1 Increased accuracy andefficiency seems to be one explanationfor the growing success. Recently

aPostgraduate student, Section of Oral Implantology, Academic Centre for Dentistry Amsterdam.bPostgraduate student, Section of Oral Implantology, Academic Centre for Dentistry Amsterdam.cAssistant Professor, Department of Orthodontics, University Medical Centre Groningen, University of Groningen.dProfessor and Chair, Department of Oral Function and Restorative Dentistry; and Head, Section of Oral Implantology andProsthodontics, Academic Centre for Dentistry Amsterdam.

The Journal of Prosthetic Dentistry Andriessen et al


published studies that have founda comparable or better general ac-curacy of digital scans compared withconventional impression methods con-firm these observations.6,7

Van der Meer et al6 analyzed theaccuracy of the Lava COS (LavaChairside Oral Scanner; 3M ESPE),Cerec AC (Sirona Dental Systems), andiTero (Cadent Inc; later acquired byAlign Technology Inc) by determiningthe distance and angulation errorsin vitro. The absolute distance errorsranged from 2.2 to 287.5 mm. Distanceerrors of the Cerec AC scanners werelargest, at 79.6 mm (95% confidenceinterval, 31.8-127.4 mm) for distancesand 81.6 mm (95% confidence interval,49.1-114.2 mm) for 1 to 3 distances.

Another recent in vitro studyconcluded that the accuracy of digitalimpressions with the Cerec AC and theLava COS scanners was similar to theaccuracy of conventional impressions.7

In that study, accuracy was defined bythe terms ‘trueness’ and ‘precision’.Trueness was defined by the mean de-viation of the model with respect to thetrue size of the object and precision bythe mean deviation of the model withrespect to the true size of the object. Amean trueness of 49 �14.2 mm wasfound for Cerec AC scanners, 40.3�14.1 mm for the Lava COS, and 55mm for traditional polyether impres-sions (Impregum; 3M ESPE). A meanprecision of 30.9 �7.1 mm was foundfor Cerec AC scanners, 60.1 �31.3 mmfor the Lava COS, and 61.3 �17.9 mmfor traditional polyether impressions.

Scan abutments have been devel-oped to make it possible to scan dentalimplants intraorally. As of this writing,the gold standard for impressionsof dental implants is a conventionalimpression with open- or closed-traytechniques.8-11 In spite of the defor-mation of impression materials andexpansion of dental casts, conventionalimpressions of implants have provedsuccessful in clinical practice.12-16

An inaccurate impression may resultin the misfit of the prosthesis, which maylead tomechanical complications suchasscrew loosening and fracture of the

prosthesis or implant components.17-21

Even so, obtaining absolute passive fit ispractically impossible.21-23 Minimizingthe misfit to prevent complications is agenerally accepted goal of prosthodonticimplant procedures.21 Consensus on anacceptable threshold of misfit, however,has yet to be reached.21,24,25

Carr et al26 studied the boneresponse in baboons when comparing a38-mm misfit and a 345-mm misfitwithout functional loads. No significantdifferences in bone response werefound. Jemt et al27studied the correla-tion between marginal bone loss andframework misfit, with an average gapof 111 mm and a maximum gap of 275mm, with functional prostheses in vivo.After 5 years, no statistical correlationshad been found. These studies suggestthat some form of biologic tolerancemay exist between the implant and itssurrounding bone when there is acertain degree of misfit.

The biologic tolerance of bone sur-rounding teeth is different from that ofbone surrounding dental implants.Owing to the elastic nature of peri-odontal ligaments, teeth may move 25to 100 mm in axial directions and 56to 108 mm in lateral directions.28

Osseointegrated dental implants are indirect contact with the surroundingbone, and therefore movement dependson the compression of the surroundingbone. This movement has been re-ported to be approximately 3 to 5 mmaxially and 10 to 50 mm laterally.28

To scan dental implants with thecommercially available intraoral scan-ner, the use of a scan abutment is stillnecessary. Two studies have found ageneral accuracy of intraoral scannersof <100 mm.6,7 These studies were bothin vitro studies and did not usecommercially available scan abutments.Errors could be caused by the use ofscan abutments, which influences theaccuracy of the scan. Therefore, the aimof this in vivo pilot study was to evaluatethe accuracy of the position of 2 im-plants in digital casts obtained fromintraoral scans by using scan abutments.The intraoral scans of 25 participantswere compared with the digitized analog

casts. The null hypothesis was that nosignificant difference would be foundbetween the position of the implants indigital casts obtained from intraoralscans and their position in digital castsobtained from scanned analog casts.

MATERIAL AND METHODS

Participants

Participants (n¼25) with completemandibular overdentures supported by 2implants (Straumann Standard SLA-active, Regular Neck 4.1/12 mm; Strau-mann AG) and splinted with frameworkswere selected from an existing patientgroup at the Academic Centre of DentistryAmsterdam and were asked to participatein this study. All of the participants agreedto participate, and their original definitivecasts, which had been used for fabricationof soldered bars, were used as referencecasts. The soldered bars, made by 1experienced dental laboratory technician,were fabricated on these casts and wereplaced and loaded within 24 hours afterplacement of the implants. After 3 years,all of the participants were reevaluatedclinically; the scan abutments were scan-ned intraorally by means of the iTerointraoral scanner. The studywas approvedby the Medical Ethical Committee of theVU University Medical Center, Amster-dam, the Netherlands.

Intraoral scanner

The intraoral scanner used in this studywas the iTero (Cadent Inc) with softwareversion 3.5.0. The iTero scanner uses aparallel confocal imaging technique tocapture digital images and combine themto construct 3-dimensional (3D) im-ages.29 For implants, 5 scans of the scanabutments were needed (occlusal, 45 de-grees buccal, 45 degrees lingual, mesio-proximal, and distoproximal). Additionalscans were required to capture the rest ofthe jaw. The 3D images were stitchedtogether to compose the complete 3Dmodel. The camera covereda14� 18mmarea at a scan depth of 13.5 mm.30 Forthis system, scanning powder was notrequired on the teeth or scan abutments.

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Scanning the reference casts in thelaboratory

The participants’ original definitivecasts, which had been used for fabri-cation of soldered bars, were used inthis study as reference casts. New scanabutments were placed onto theimplant analogs in the reference casts.Scan powder (Occluspray; SelexionsBV) was needed to scan the casts withan extraoral scanner (Lava Scan STscanner; 3M ESPE).

Scanning the scan abutmentsintraorally

All of the participants were seen forclinical examinations and for scanningthe scan abutments intraorally with theiTero intraoral scanner. The bars wereremoved, and scan abutments (Strau-mann Regular Neck scan abutment)were placed in the correct positionson both implants. The scan abutmentswere hand-tightened with screws(Fig. 1). The manufacturer’s instruct-ions were followed. After correct abut-ment positioning had been checkedclinically, intraoral scans were madewith the intraoral scanner. For salivacontrol and mouth opening, a lip andcheek retractor (OptraGate; IvoclarVivadent AG) was used (Fig. 2). Afterthe intraoral scans were completed, thescan abutments were removed and thebars were replaced. The scan file wassaved, and, following the manufac-turer’s instructions, it was sent to theiTero facility in Israel for subsequentprocessing.

3D measurements

The distance and the angle betweenthe centers of the scan abutmentswere used to assess the accuracy ofthe different scanners. Each of thescans, as well as the 25 intraoral scansand the 25 extraoral scans of thereference casts, was imported into in-dustrial reverse engineering software(Geomagic Qualify, version 12; Geo-magic America), where the scan abut-ments were isolated as separate

objects. Two 3-dimensional computer-aided design (3D CAD) models of thescan abutments with predeterminedcenterlines were subsequently importedand registered, together with each ofthe scanned equivalents (Fig. 3). Thiswas done to secure the proper con-struction of the centerline of each scanabutment.

The distance between the centerlinesof the occlusal surfaces of the scanabutments wasmeasured in the software

with a linear measurement tool. Theangular deflections of the centerlines ofthe scan abutments were measured withan angular measurement tool. Themeasurements were not separated intox-, y-, and z-components, because theobjects’ coordinate system could not beproperly matched with a world coordi-nate system. As no true common coor-dinate system exists, the different castscould only be registered in a virtualcommon coordinate system. Because

1 RN Straumann Scanbody. To scan dental implants withintraoral digitizers, use of some type of scan abutment is stillnecessary. Scan abutment represents position of respectivedental implant in intraoral computer-aided design andcomputer-aided manufacturing scanning procedures. Scanbody consists of 3 parts: scan cap, fixation screw, and scanpost. Scan post has to be placed in dental implant withfixation screw hand-tightened (maximum, 15 Ncm). Afterfixation of scan post, scan cap has to be placed correctly,avoiding any gap between cap and post. For accurate scanresult, it is essential that Scanbody is clean and that it is notdamaged or deformed.

2 Scan abutments.

188 Volume 111 Issue 3



the registrations were based on the sur-faces of the casts, the positions of thecasts differed slightly. This introducederrors into their relative positions andmade it unreliable to compare mea-surements in x-, y-, and z-components.Such an approach was used in anotherstudy.6 In the present study, the mea-surements were noted in a table andcompared with the same measurementsmade with the reference analog casts.

3D comparisons

Each of the scans was imported intoindustrial reverse engineering software(VisCAM, version 5.1; Marcam Engi-neering GmbH) and evaluated forpossible irregularities such as de-formations and wrong stitching sutures.The observations were noted in a table.

Determined threshold for distanceand angulation error

As far as the authors can determine,no evidence-based reports have beenpublished on the maximum amount ofmisfit that can be tolerated in animplant-supported superstructure. Basedon clinical guidelines with a biome-chanical rationale,28 in which the au-thors stated that the maximum lateralmovement of an implant in bone is 50mm, the following was postulated: Themaximum biologic tolerance of bonecaused by misfit of framework may beequal to themaximum lateral movement

of 1 implant in bone, which is 50 mm. Aframework attached to 2 dental im-plants exceeds the biologic tolerance of2 implants when the horizontal misfit islarger than 100 mm. Therefore, for dentalimplants, the inaccuracy of fit for a 2-implant bar attachment must not exceed2 � 50 mm, giving a premise of 100 mm.

The maximum acceptable interim-plant angulation error was calculated byusing trigonometry. The fixation point ofthe framework on an implant was at thetop of the implant. A misfit between theframework and the implant would lead

to a maximum lateral movement at theimplant apex of 50 mm, which is themaximum lateral movement of animplant in bone.28 The implant had atotal length of 14.8 mm (12 mm roughsurface þ 2.8 mm smooth supracrestalsurface; in this instance, the neck of theimplant was supracrestal). Based ontrigonometry, a maximal lateral apexmovement of 50 mm would result in an-gulations of 0.194 degrees. (a ¼ tan�1

(0.05/14.8) ¼ 0.194 degrees; Fig. 4).Between 2 implants, as used in

this study, the maximum acceptable

3 Isolated scan abutment (blue) and 3D CAD model of scan abutment with centerline (red).3D CAD models were imported and registered, together with scanned equivalents (right). 3D,3-dimensional; CAD, computer-aided design.

Bone

14.8 mm14.8 mm

50 µm

0.194

4 Trigonometric calculation of maximum acceptable inter-implant angulation error based on maximum lateral move-ment at implant apex of 50 mm. Fixation point between barand implant will be at top of implant. Misfit between barand implant will lead to lateral movement at implant apex.Implant has total length of 14.8 mm (12 mm roughsurface þ 2.8 mm smooth supracrestal surface), resulting inangulations of 0.194 degrees in case of maximal lateral apexmovement of 50 mm (a ¼ tan�1 (0.05/14.8) ¼ 0.194degrees).

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interimplant angulation error would beapproximately 2� 0.194 degrees¼ 0.39degrees. For this study, a maximum of0.4 degrees was used as the threshold fora clinically acceptable angulation error.

Examiners

One dentist (JP), trained in intraoralscanning, removed the frameworks fromthe implants and did the intraoralscanning of the participants. Scanning

the analog casts was done by the re-searchers (FA, DR) with the help of anexperienced dental technician. The digi-tal files were checked for irregularities bythe researchers (FA, DR). The measure-ments were done by a dentist (JM)experienced in digital imaging.

RESULTS

In total, 4 of the 25 intraoral scanswere not suitable for research because

of a large distance between the 2 im-plants (the computer was not able tostitch the separate scans together) orbecause of a lack of stable referencepoints on the oral mucosa. This led tofinal scans with only 1 or even 3 scanabutments in the image instead of 2scan abutments. The 21 remainingintraoral scans were digitally comparedwith their reference scan, the analogcast. The results have been summarizedin Table I.

Table I. Interimplant distance, interimplant angulations, and optical irregularities in scans

Participant

Distance,Reference

Cast(mm)

Distance,IntraoralScanner(mm)

DistanceError(mm)

Angle,Reference

Cast(Degrees)

Angle,IntraoralScanner(Degrees)

AngulationError

(Degrees) Optical Irregularity

1 16.339 15.813 0.526 6.862 2.740 4.122 Wrong stitching

2 22.471 22.256 0.215 6.979 9.139 �2.160 No optical irregularities

3 22.059 21.848 0.211 4.727 5.971 �1.244 Deformation

4 23.460 23.673 �0.213 12.747 9.466 3.281 No optical irregularities

5 18.024 18.003 0.021 11.336 11.837 �0.501 Wrong stitching

6 18.435 18.690 �0.255 5.323 5.446 �0.123 No optical irregularities

7 24.869 25.038 �0.169 16.074 17.702 �1.628 No optical irregularities

8 30.578 30.478 0.100 13.951 14.751 �0.800 Wrong stitching

9 22.802 22.764 0.038 6.533 12.299 �5.766 Wrong stitching

10 18.212 18.113 0.099 9.596 8.599 0.997 Wrong stitching

11 16.935 16.936 �0.001 4.413 11.264 �6.851 Wrong stitching

12 22.635 22.259 0.376 13.575 12.389 1.186 Wrong stitching þdeformation

13 21.217 21.456 �0.239 7.560 11.042 �3.482 Wrong stitching

14 18.069 18.196 �0.127 10.719 1.157 9.563 Wrong placement ofscan abutment

15 17.475 16.825 0.650 2.226 4.164 �1.938 Deformation

16 17.299 17.192 0.107 5.599 5.936 �0.337 Wrong stitching

17 13.758 13.698 0.060 3.587 3.911 �0.324 No optical irregularities

18 26.148 26.786 �0.638 10.091 3.393 6.698 Deformation

19 17.765 18.091 �0.326 13.832 10.642 3.190 Wrong stitching

20 20.348 20.622 �0.274 7.513 11.508 �3.995 Wrong stitching

21 15.699 15.842 �0.143 4.957 3.156 1.801 Deformation

22 ND ND ND ND ND ND Not possible to performintraoral scan

23 ND ND ND ND ND ND Not able to makecomplete scan



ND, no data (not possible to make a complete scan).




Distance

The interimplant distance, assessed bya digital measurement of the mid-centerline of the 2 scan abutments, showed adistance error ranging from 21 to 638 mmcompared with the reference scan (seeTable I; Fig. 5). The mean of these dis-tance errors was 226.0 mm. The distanceerrors occurred in both the negative andpositive ranges.Adifference error of<100mm was found in 5 of the 21 scans.

Angulations

The angulation error, assessedby a comparison of the differencein implant angulations of the in vivo scanand the reference scan, ranged from0.123 degrees to 9.563 degrees (seeTable I; Fig. 6). The mean absoluteangulation error for the scan abutmentswas 2.582 degrees. An angulationerror <0.4 degrees was recorded in 3 ofthe 21 scans.

Scan irregularities

The scans were optically analyzed bythe researchers to find explanations forthe digitally assessed discrepancy. Nooptical irregularities were found on thereference scans. Figure 7 shows irregu-larities for each scan with the intraoralscanner.

Creating a final digital scan of thescan abutments was not possible in 4of the 25 participants: in the final scan1 or 3 scan abutments appeared in theimage. Stitching errors, where the digi-tal stitching of the photos was mis-aligned, were found in 10 of the 21scans (Fig. 8). In 4 of the 21 scans, adeformation of the scan abutments wasobserved (Fig. 9). For 1 participant, astitching error occurred as well as adeformation error. Five scans seemed tobe optically good scans, although 1 ofthese scans had minor errors comparedwith the gold standard (distance errorof 60 mm and angle error of 0.342 de-grees) (see Table I; see Fig. 7).

DISCUSSION

The wide range of angulation errorsand distance errors and the fact thatthese negated the null hypothesisof <100 mm and <0.4 degrees, withhigher values for most participants,made statistical analysis irrelevant. Thisis the first clinical study comparingintraorally scanned scan abutments onimplants with extraoral scanned analogcasts. The results of this study foundthat a large discrepancy exists betweenthe intraoral scans and the referencescans in situations in which 2 implantswere used in the edentulous mandible.The data indicate that the null hy-pothesis should be rejected. In thisdiscussion are listed the complicationsthat arose after the scanning of 2 scanabutments by means of an intraoralscanner in an edentulous jaw.

The use of analog casts as referencecasts can be debated because of thepossible transformation of the impres-sion material and the possible expan-sion of the cast.15 The fact that thesoldered bars fabricated on these casts

Thre

shol

d

0-100

100-200

200-300

300-400

400-500

500-600

600-700

8

6

4

2

0

5 Bars showing interimplant distance difference. On x-axisis difference between distance of implants scanned withintraoral scanner and reference cast. On y-axis is number ofparticipants for each distance difference group. Thresholdis set at 100 mm.

5

4

3

2

1

00-0.4 0.4-1 1-2 2-3 3-4 4-5 >5

Thre

shol

d

6 Bars showing interimplant angle difference. On x-axisis difference between angle of implants scanned withintraoral scanner and reference cast. On y-axis is numberof participants for each angle difference group. Thresholdis set at 0.4 degrees.

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Andriessen et al


were placed within 24 hours afterimplant placement accounts for thesepossible small differences between thecasts and the in vivo situation; the im-plants have the ability to migrate to thebest-fit position on the bar.25,31,32

Thus, the implants will osseointegrateinto the same position as the analogimplants in the cast on which the barwas fabricated. This makes the cast areliable reference, on the condition thatthe bars fit their casts precisely.

Another point of debate is thechoice of threshold. At this moment,no clear guidelines are available onthe acceptable thresholds for misfitbetween superstructures and im-plants.21,24,25 However, a passive fit ofthe superstructure should be the maingoal to avoid mechanical and biologiccomplications.17-21 A previous studyassessed a maximum lateral implant

movement of 50 mm. This could indi-cate that every lateral implant move-ment due to a misfit that exceeds 50mm will lead to a certain tension be-tween the implant and the superstruc-ture. The thresholds chosen in thisstudy are based on this 50 mmmaximum movement of implants.

In 4 of the 25 intraoral scans,making a complete scan that wouldcontain the 2 scan abutments in thesame capture was impossible. Thecamera of the intraoral scanner covers amaximum area of 14 � 18 mm for eachseparate photo.30 For these partici-pants, a large interimplant distance incombination with a lack of mucosallandmarks to serve as reference pointsmade it impossible to stitch the pho-tographs in the right position relative toone another. When the scan abutmentswere scanned for these participants, the

intraoral scanner combined the photo-graphs of both scan abutments andcreated a scan file with just 1 scanabutment instead of 2 separate scanabutments. These incorrect scans werenot included in this study. Some par-ticipants with a large interimplant dis-tance (30 mm) were scannedsuccessfully because of a stable mucosawith sufficiently variable height to pro-vide sufficient reference for the intraoralscanner.

Only one other study has deter-mined the accuracy of the iTerointraoral scanner. Van der Meer et al6

compared the iTero with an industrialscanner to determine its general accu-racy. The distance errors of the iTerooccurred in the range of 7.2 to 126.8mm. The mean absolute angulation er-rors were in the range of 0.0069 to0.6833 degrees. In that study, the dis-tance errors and angulation errors weremuch smaller than in this study. How-ever, that study was an in vitro study inwhich casts with fixed cylinders werescanned. The surface of these casts hada large number of stable referencepoints, enabling the scans to bestitched in the right position. In thecurrent study, the major issue was tofind reference points, because the mu-cosa did not vary much in height, whichresulted in poor and unreliable scans.

Out of 25 scans, 4 were notincluded in the study. From 21 suitablescans, only 1 scan showed both anacceptable distance error (<100 mm)and an acceptable angulation error(<0.4 degrees). Based on these data,

12

10

8

6

4

2

0

No irreg

ulariti

es

Deform

ation

Wro

ng stit

ching

BothOth

er

7 Bars showing irregularities for each scan with intraoralscanner. On x-axis are irregularities. On y-axis is number ofparticipants for each group.

8 A and B, Clear suture has been identified (red arrow) where photos were stitched.




the iTero intraoral scanner is not atpresent an adequate tool for scanning 2implants in the edentulous mandible.This intraoral scanner was not designedto make a digital scan that can be usedto fabricate a bar on 2 implants.

With a point-and-click system, the3D surfaces should be scanned with atleast one-third overlap of the adjoiningsurface. The registration of the neigh-boring surfaces will be made on thebasis of this overlap. If the adjacentsurfaces are unstable or show little tono variation in height, it will be difficultto find the one-third overlap of theadjoining surface. This will lead to anunreliable registration. Conversely, indentate situations, the neighboringsurfaces are stable and vary in shapeand height. Therefore the results ofthis study cannot be extrapolated todentate participants.

In future studies, other scannersshould be used, because this studyfocused only on 1 point-and-click sys-tem. Other technologies may producedifferent outcomes when edentulousparticipants are scanned. The numberof implants can be increased, and acomparison with a traditional impres-sion material should be added. Also,the use of 2 or more implants in den-tate situations instead of in edentulousparticipants should be considered todetermine accuracy. A new software

version for the iTero has recently beenreleased. In this software (version 3.9),it is possible to make more photo-graphs to create the scan, which mayproduce different results.

CONCLUSIONS

Within the limitations of this study,the following conclusions were drawn:

1. Based on the intraoral scan, thedistance errors were too large to pro-duce a well-fitting superstructure on 2implants in an edentulous mandible.

2. The mean angular errors weretoo large to produce superstructureswith a passive fit on 2 implants in anedentulous mandible.

3. The unreliable scans in this studywere the result of poor reference pointscaused by mucosa with little variationin texture and height.

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9 Deformation of scan abutment. Top of scan abutmenthas square configuration. Wrong stitching of multiple cap-tures will lead to lozenge-shaped top of scan abutment (redarrow) in some situations, which does not match real squareconfiguration.

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Corresponding author:Dr F.S. AndriessenWilhelminakade 363072 AR RotterdamTHE NETHERLANDSE-mail: [email protected]

Copyright ª 2014 by the Editorial Council forThe Journal of Prosthetic Dentistry.

Noteworthy Abstracts of the Current Literature

In vitro precision of fit of computer-aided design and computer-aided manufacturing titanium andzirconium dioxide bars

Katsoulis J, Mericske-Stern R, Yates DM, Izutani N, Enkling N, Blatz MBDent Mater 2013;29:945-53

Objectives: Optical scanners combined with computer-aided design and computer-aided manufacturing (CAD/CAM)technology provide high accuracy in the fabrication of titanium (TIT) and zirconium dioxide (ZrO) bars. The aim of this studywas to compare the precision of fit of CAD/CAM TIT bars produced with a photogrammetric and a laser scanner.

Methods: Twenty rigid CAD/CAM bars were fabricated on one single edentulous master cast with 6 implants in the positionsof the second premolars, canines and central incisors. A photogrammetric scanner (P) provided digitized data for TIT-P(n¼5) while a laser scanner (L) was used for TIT-L (n¼5). The control groups consisted of soldered gold bars (gold, n¼5) andZrO-P with similar bar design. Median vertical distance between implant and bar platforms from non-tightened implants(one-screw test) was calculated from mesial, buccal and distal scanning electron microscope measurements.

Results: Vertical microgaps were not significantly different between TIT-P (median 16mm; 95% CI 10-27mm) and TIT-L(25mm; 13-32mm). Gold (49mm; 12-69mm) had higher values than TIT-P (p¼0.001) and TIT-L (p¼0.008), while ZrO-P(35mm; 17-55mm) exhibited higher values than TIT-P (p¼0.023). Misfit values increased in all groups from implant position23 (3 units) to 15 (10 units), while in gold and TIT-P values decreased from implant 11 toward the most distal implant 15.

Significance: CAD/CAM titanium bars showed high precision of fit using photogrammetric and laser scanners. In compar-ison, the misfit of ZrObars (CAM/CAM, photogrammetric scanner) and soldered gold bars was statistically higher but valueswere clinically acceptable.

Copyright ª 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.



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