RESEARCH AND EDUCATION

Supported inWashington,aGraduate stubProfessor, DcResearch AsdAssistant PreProfessor, D

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Assessment of reliability of CAD-CAM tooth-coloredimplant custom abutments

Nuno Marques Guilherme, DMD, MS, MSD,a Kwok-Hung Chung, DDS, MS, PhD,b

Brian D. Flinn, MS, PhD,c Cheng Zheng, PhD,d and Ariel J. Raigrodski, DMD, MSe

ABSTRACTStatement of problem. Information is lacking about the fatigue resistance of computer-aideddesign and computer-aided manufacturing (CAD-CAM) tooth-colored implant custom abutmentmaterials.

Purpose. The purpose of this in vitro study was to investigate the reliability of different types ofCAD-CAM tooth-colored implant custom abutments.

Material and methods. Zirconia (Lava Plus), lithium disilicate (IPS e.max CAD), and resin-basedcomposite (Lava Ultimate) abutments were fabricated using CAD-CAM technology and bondedto machined titanium-6 aluminum-4 vanadium (Ti-6Al-4V) alloy inserts for conical connectionimplants (NobelReplace Conical Connection RP 4.3×10 mm; Nobel Biocare). Three groups (n=19)were assessed: group ZR, CAD-CAM zirconia/Ti-6Al-4V bonded abutments; group RC, CAD-CAMresin-based composite/Ti-6Al-4V bonded abutments; and group LD, CAD-CAM lithium disilicate/Ti-6Al-4V bonded abutments. Fifty-seven implant abutments were secured to implants andembedded in autopolymerizing acrylic resin according to ISO standard 14801. Static failure load(n=5) and fatigue failure load (n=14) were tested. Weibull cumulative damage analysis was usedto calculate step-stress reliability at 150-N and 200-N loads with 2-sided 90% confidence limits.Representative fractured specimens were examined using stereomicroscopy and scanningelectron microscopy to observe fracture patterns.

Results. Weibull plots revealed b values of 2.59 for group ZR, 0.30 for group RC, and 0.58 for groupLD, indicating a wear-out or cumulative fatigue pattern for group ZR and load as the failureaccelerating factor for groups RC and LD. Fractographic observation disclosed that failuresinitiated in the interproximal area where the lingual tensile stresses meet the compressive facialstresses for the early failure specimens. Plastic deformation of titanium inserts with fracture wasobserved for zirconia abutments in fatigue resistance testing.

Conclusions. Significantly higher reliability was found in group ZR, and no significant differences inreliability were determined between groups RC and LD. Differences were found in the failurecharacteristics of group ZR between static and fatigue loading. (J Prosthet Dent 2016;116:206-213)

Titanium-6 aluminum-4 vana-dium (Ti-6Al-4V) alloy designedand machined using computer-aided design and computer-aided manufacturing (CAD-CAM) technology has been acommonly used material forimplant abutments because ofits desirable physical andmechanical properties.1,2 How-ever, the metallic color of Ti-6Al-4V abutments can reflectthrough soft tissue, especiallyin thin and/or translucentphenotypes.3 The developmentof high-strength ceramics, suchas zirconia, has provided anapplicable ceramic alternativefor anterior sextants, withimproved gingival estheticseven with compromised softtissue thickness.4,5 Some im-plant abutments are madeentirely of zirconia, whereasothers are hybrid, made with atitanium insert, either friction fitor bonded to zirconia.6-8 When

part by American Academy of Fixed Prosthodontics Stanley D. Tylman Research Grant Program and Department of Restorative Dentistry, University ofgrant 66-7812. This project was awarded Second Place at the Tylman Research competition in 2015.dent, Department of Restorative Dentistry, School of Dentistry, University of Washington, Seattle, Wash.epartment of Restorative Dentistry, University of Washington School of Dentistry, Seattle, Wash.sociate Professor, Materials Science and Engineering, University of Washington School of Engineering, Seattle, Wash.ofessor, Biostatistics, Joseph J Zilber School of Public Health, University of Wisconsin, Milwaukee, Wis.epartment of Restorative Dentistry, University of Washington School of Dentistry, Seattle, Wash.

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Clinical ImplicationsBased on the results of this in vitro study, CAD-CAMzirconia custom abutments are the least sensitiveto load level and the most reliable tooth-coloredmaterial for abutments with titanium inserts andconical implant connections.

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bonded to the zirconia component, the titanium insertis in contact with the implant platform and abutmentscrew.9-12 Addition of the bonded insert to the tooth-colored material in the abutment design allows fordevelopment of an abutment/implant titanium/titaniuminterface, which has been shown to reduce the risk ofimplant platform damage under function.13-15 The useof heat-pressed lithium disilicate (LD) bonded to atitanium alloy insert as a tooth-colored implant abut-ment system has been reported, and lately, CAD-CAMLD blocks have been developed to optimize laboratoryprocedures.16,17 Studies have investigated the feasibilityof using CAD-CAM resin-based composite (RC) ma-terials for implant abutments because their mechanicaland esthetic behaviors are similar to those of the dentinstructure.18,19 Moreover, a standardized test methodfollowing ISO recommendations for a worst-case sce-nario is essential to provide insight into the perfor-mance of these new abutment materials within themaximal reported incisal forces (90 to 370 N).20-24 Thepurpose of this in vitro study was to evaluate andcompare the reliability of 3 different types of CAD-CAM tooth-colored implant custom abutments formaxillary anterior teeth after cyclic loading and toassess the failure characteristics of the tested abut-ments. The null hypothesis was that no differenceswould be found in the reliability between implantabutments for conical connection fabricated withdifferent CAD-CAM tooth-colored materials.

MATERIAL AND METHODS

Fifty-seven implant abutments for conical connectionimplants (NobelReplace Conical Connection RP 4.3×10mm; Nobel Biocare) were fabricated from 3 differentmaterials (Fig. 1) and divided into 3 groups (n=19). Eachgroup was further divided into specimens for staticcompressive testing (n=5) and specimens for cyclic loadtesting (n=14). The groups of abutments, abutmentcompositions, and manufacturers are shown in Table 1.Treatment protocols for custom-made CAD-CAMTi-6Al-4V alloy insert surfaces, abutment internal sur-faces, and bonding and luting agents used for adhesivecementation procedures are shown in Table 2. Groupzirconia (ZR) consisted of a CAD-CAM customizedzirconia abutment (Lava Plus; 3M ESPE) bonded to a

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Ti-6Al-4V alloy insert and used as a control. Group RCwas a CAD-CAM custom resin-based composite abut-ment (Lava Ultimate; 3M ESPE) bonded to a Ti-6Al-4Valloy insert; and Group LD was a CAD-CAM custom-ized lithium disilicate abutment (IPS e.max CAD, IvoclarVivadent) bonded to a Ti-6Al-4V alloy insert. A singleabutment cement-retained implant-supported restora-tion for a maxillary left central incisor was fabricated witha CAD-CAM system (3Shape Dental System; 3ShapeA/S) from a prototype customized abutment waxing. Thisallowed for standardization and identical abutmentdimensions (0.5-mm-deep chamfer at the finish line,8-mm incisogingival buccal height and lingual axial sur-face) and space for luting agent (150 mm at the axial wallsand 400 mm at the antirotational features). Thicknesses ofthe axial walls of the abutments were 1.0 mm at themid-facial and mid-palatal surfaces and 0.6 mm at themid-mesial and mid-distal surfaces. All CAD-CAMcustomized implant abutments were bonded to Ti-6Al-4V alloy inserts (Fig. 1A), with a bonding surface areaof approximately 33 mm2. Bonding surfaces of the insertswere airborne particle-abraded with 50-mm aluminumoxide (0.4 MPa, 10 mm in distance for 10 seconds).Subsequently, adhesives were applied according tomanufacturers’ instructions for the different groupstested (Table 2).

In total, 57 implant abutments were fabricated andconnected with implants (NobelReplace ConicalConnection RP 4.3×10 mm; Nobel Biocare) embedded inautopolymerizing acrylic resin (Crown & Bridge Resin;Dentsply Intl) according to ISO standard 14801.25 Alltested abutments were then secured to the implants at35-Ncm torque (Fig. 2). Loading caps to simulate crownswere fabricated from monolithic zirconia (Lava Plus; 3MESPE) for all test specimens, using a uniform thickness of1.5 mm. The intaglio surfaces of the zirconia loading capswere airborne particle-abraded with 30-mm silica-coatedaluminum oxide (Rocatec Soft; 3M ESPE), followed byapplication of an adhesive (Scotchbond Universal adhe-sive; 3M ESPE). Cameo bonding surfaces of the testedabutments of all groups received surface treatmentssimilar to those of their intaglio surfaces according to themanufacturers’ instructions (Table 2) and were bonded tothe zirconia loading caps with a dual-polymerizingcomposite resin cement (RelyX Ultimate adhesive resincement; 3M ESPE). Five specimens from each group weretested in a single compressive load to failure to determineinitial load for the cyclic loading test. After 24 hours ofstorage in a 37�C water bath, specimens were mountedwith a special jig9 and subjected to compressive load,using a universal testing machine (Instron model 5500R;Instron Corp) at a crosshead speed of 1 mm/min. A pieceof polytetrafluoroethylene (PTFE) tape (Harvey’s WhitePTFE thread seal tape; William H. Harvey Co) was usedin the loading cell to minimize the friction effect during

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Figure 1. A, CAD-CAM Ti-6Al-4V alloy insert. B, CAD-CAM tooth color implant custom abutments. CAD-CAM, computer-aided design andcomputer-aided manufacture.

Table 1.Materials used

Group Material Abutment Composition Manufacturer

ZR Lava Plus Zirconia 3M ESPE

RC Lava Ultimate Resin-based composite 3M ESPE

LD IPS e.max CAD Lithium disilicate Ivoclar Vivadent

CAD, computer-aided design; LD, lithium disilicate; RC, resin-based composite; ZR, zirconia.

Table 2. Treatment protocol for preparation of CAD-CAM tooth-coloredimplant abutments

Abutment Group ZR Group RC Group LD

Ti-6Al-4Vinsertsurface

50-mm aluminumoxide abrasion+ScotchbondUniversaladhesivefor 20 s

50-mm aluminumoxide abrasion+ScotchbondUniversaladhesivefor 20 s

50-mm aluminumoxide abrasion+Monobond Plusfor 60 s

Tooth-coloredabutmentInnersurface

Rocatec Softat 0.2 MPa+ScotchbondUniversaladhesivefor 20 s

Rocatec Softat 0.2 MPa+ScotchbondUniversaladhesivefor 20 s

IPS Ceramic EtchingGel for 20 s+Monobond Plusfor 60 s

Lutingagent

RelyX Ultimateadhesive resincement

RelyX Ultimateadhesive resincement

Multilink HybridAbutment resincement

CAD-CAM, computer-aided design and computer-aided manufacture; LD, lithium disilicate;RC, resin-based composite; ZR, zirconia.

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testing.9 Maximum loads were recorded and used asfailure loads. For the cyclic loading test (n=14), a step-stress accelerated life testing model was used for thisstudy.26,27 Data were gathered from across light, mod-erate, and aggressive fatigue profiles in a ratio of 4:2:1,respectively (Fig. 3). This ratio has been shown to resultin data that correspond well to the actual service life ofmost materials.26 The minimum number of specimensper group (n=14) was determined by doubling thenumber of specimens per profile.28 Approximately 30%of the static compressive mean load to failure was used asa baseline and an initial load to begin testing.27 Eachimplant abutment was subjected to sinusoidal, cyclicloading at 2 Hz in a 37�C water bath in a coil cyclerelectromechanical fatigue machine (Fatigue Cycler;Proto-Tech) until failure or suspension. Failure wasdefined as the fracture of specimens or an abrupt loaddecrease, in which case the testing apparatus was auto-matically stopped. Representative specimens wereexamined using stereomicroscopy (SZH-10; Olympus)and scanning electron microscopy (SEM) (JEOL JSM-6010PLUS/LA; JEOL Ltd) to determine the pattern offailure.

The reliability of abutment groups was calculatedbased on the step-stress distribution of the failures, with2-use level probability Weibull curves (probability offailure versus cycles). A power law relationship fordamage accumulation of the 2 plots was developedusing stress levels at 150 N and 200 N with 90% 2-sided confidence intervals (Alta Pro 9; Reliasoft).29 The

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probability of an abutment functioning for a givenamount of time without failure was used to determinethe reliability of each abutment group. The slope of theWeibull plot, called the slope shape parameter (b),and the parameter that reflected how sensitive thefailure was to different loads (a1) were used to provideinformation as to the physics of the failure inquestion.29,30

RESULTS

The mean maximum load capacity ±SD of the staticload testing was 318.3 ±28.2 N for group ZR, 149.2±37.2 N for group RC, and 160.1 ±21.6 N for groupLD (Fig. 4). Abutments of group ZR experienced ad-hesive failures, and brittle failures were observed ingroups RC and LD. All specimens in the cyclicloading tests failed. The use level probability plotgenerated with a cumulative damage Weibull modelfor a use stress level of 150 N with 90% confidence

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Figure 2. A, Cross sections of specimens from different groups. A, Zirconia (ZR). B, Resin-based composite (RC). C, lithium disilicate (LD).

500015 00025 00035 00045 00055 00065 00075 00085 00095 000

105 000115 000125 000135 000

Load

(N)

Cycles

400

350

300

Aggressive profileModerate profileLight profile

250

200

150

100

50

0

Figure 3. Step-stress profiles used for fatigue testing. Note that loadsstarted at 100 N end at approximately 340 N. Specimens from eachgroup were distributed across 3 profiles following a 4:2:1 ratio (n=8 inlight profile, n=4 in moderate profile, and n=2 in aggressive profile).

Frac

ture

Loa

d (N

)

400

350

300

250

200

150

100

50

ZR RC

Group

LD0

Figure 4. Box plot of maximum single-load capacity of tested CAD-CAMtooth-color implant custom abutments. CAD-CAM, computer-aideddesign and computer-aided manufacture; LD, lithium disilicate; RC,resin-based composite; ZR, zirconia.

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limits (Fig. 5) showed statistically significant differ-ences among group ZR (P<.10) and the remaininggroups, with group ZR being significantly more reli-able at 10% failure time. Although significant differ-ences were found between the reliability of groups RCand LD for 100 000 cycles at a 150-N stress level(Table 3), the overlap of confidence limits at 10%failure time showed no statistically significant differ-ences (P>.10) for 10% failure time (Fig. 5). The uselevel probability plot for 200 N with 90% confidencelimits (Fig. 6) showed statistically significant differ-ences between group ZR (P<.10) and those of the

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remaining groups at 10% failure time. Mean life-to-failure calculations for the different stress levelsshowed a survival time decrease of 73.8% for groupZR, 98.7% for group RC, and 99.9% for group LD(Table 4) with load increase. Groups RC and LDdemonstrated extensive fragmentation patterns afterthe cyclic loading test, and the fractures for thesegroups occurred within a load range of 130 N to 220 N.

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Unr

elia

bilit

y

Time (t) (Cyc)

99.0

50.0

Use level CB@90% 2-sidedE.max CAD\E.max CADCumulative damageWeibull150F=14 | S=0

10.0

5.0

1.01E+03100101 1E+04 1E+05 1E+06 1E+07 1E+08 1E+09 1E+10

Data pointsTop CB-IBottom CB-I

Lava plus\lava plusCumulative damageWeibull150F=14 | S=0

Data pointsTop CB-IBottom CB-I

Lava ultimate\lava ultimateCumulative damageWeibull150F=14 | S=0

Data pointsTop CB-IBottom CB-I

Figure 5. Probability of failure versus cycles plot (90% 2-sidedconfidence limits) at 150 N use stress for zirconia (ZR) ([green] F=14,S=0), composite-based resin (CR) ([blue] F=14, S=0), and lithium disilicate(LD) ([red] F=14, S=0) groups. ZR group exhibited significantly higherreliability than CR and LD groups. Overlap between CR and LD groupsdemonstrate no statistically significant differences at 10% failure timefor these groups.

Unr

elia

bilit

y

Time (t) (Cyc)

99.0

50.0

10.0

5.0

1.01E–011E–021E–031E–04 1 10 100 1E+041E+03 1E+05 1E+06 1E+07

Use level CB@90% 2-sided

E.max CAD\E.max CADCumulative damageweibull200F=14 | S=0

Data pointsTop CB-IBottom CB-I

Lava plus\lava plusCumulative damageweibull200F=14 | S=0

Data pointsTop CB-IBottom CB-I

Lava ultimate\lava ultimateCumulative damageweibull200F=14 | S=0

Data pointsTop CB-IBottom CB-I

Figure 6. Probability of failure versus cycles plot (90% 2-sidedconfidence limits) at 200 N use stress for zirconium (ZR) ([green] F=14,S=0), composite-based resin (CR) ([blue] F=14, S=0), and lithium disilicate(LD) ([red] F=14, S=0) groups. ZR group exhibited significantly higherreliability than CR and LD groups. Overlap between CR and LD groupsdemonstrates no statistically significant differences at 10% failure timefor these groups.

Table 3. Results of calculated 90% confidence limits for reliability at100 000 cycles for stress level of 150 N for tested groups

Limit Group ZR Group RC Group LD

Upper confidence limit 0.999893 0.795761 0.09834

Reliability 0.998208 0.624695 0.001897

Lower confidence limit 0.970398 0.379481 0

b value 2.59 0.30 0.58

LD, lithium disilicate; RC, resin-based composite; ZR, zirconia.

Table 4. Comparison of results of calculated 90% confidence limits formean life-to-failure (cycle) stress levels for 150-N and 200-N stress levels

Limit

Group ZR Group RC Group LD

150 N 200 N 150 N 200 N 150 N 200 N

Upper confidencelimit

4 044 980 615 795 28 873 676 61 371 14 560 178.4

Mean life to failure 1 013 353 265 474 1 067 974 13 731 6737 6.5

Lower confidencelimit

253 867 114 448 395 020 3072 3117 0.2

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Fractures originated in the interproximal area wherethe lingual tensile stresses meet the compressive facialstresses. This area also corresponded to the area ofthe antirotational feature of the Ti-6Al-4V alloy insert,and Hackle lines were noticeable, propagating fromthe intaglio surface under stereomicroscopic and SEMimaging for groups RC and LD (Figs. 7, 8). For groupLD, beach marks were identified, and hackle linesthat portrayed crack direction and stress accumulationwere observed. For group ZR, failures occurred withina load range of 250 to 310 N. Deformation of theabutment assembly occurred at the interface betweenthe Ti-6Al-4V alloy insert and zirconia abutment

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instead of fragmentation fracture of the zirconia part(Fig. 9).

DISCUSSION

The null hypothesis of this study, that no differenceswould be found in the reliability of implant abutmentsfor conical connections fabricated with different CAD-CAM tooth-colored materials, was rejected. GroupZR specimens demonstrated significantly higher reli-ability (b=2.59) and were shown to be less sensitive toload increase, with a statistically significant longer 90%

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Figure 7. A, Brittle fracture of CAD-CAM lithium disilicate abutmentspecimen after 30 103 cycles at 160-N failure load. B, Note detachment offacial and lingual fragments in macroscopic view with crack branchingand propagation toward facial zone (compressive area). Crack originshown in scanning electron micrograph (magnification ×16) (A) andmacroscopic view ([B] O). C, Hackle lines (H) correspond to crackinitiation noticeable in A, high-magnification scanning electronmicrograph view (original magnification ×100) of tooth-colored materialcemented to loading cap. D, Semielliptical marks ([B] known as “beachmarks”) are seen running perpendicularly to crack direction in fragmentsattached to Ti-6Al-4V alloy insert (original magnification ×30). CAD-CAM,computer-aided design and computer-aided manufacture.

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survival time under both 150-N and 200-N loads(Figs. 5, 6). Fatigue testing for group ZR resulted in thefracture of the Ti-6Al-4V alloy insert as opposed to theadhesive failures observed in the static compressivetesting between the abutment and Ti-6Al-4V alloyinsert, which was also reported by Kim et al.9 Thishighlights not only the fact that resin bonding betweenthe 2 components is not a factor dictating fatigue failurebut also how different results can be obtained for the 2testing modalities (static compressive testing versuscyclic fatigue loading). In addition, the axial walls of theTi-6Al-4V alloy insert were designed to maintain aminimum 0.5-mm thickness. In group ZR, this mightexplain the plastic deformation of the Ti-6Al-4V alloyinserts rather than the fatigue fracture of zirconiaabutment at higher loads.

In groups RC (b=0.30) and LD (b=0.58), brittle frac-tures of CAD-CAM tooth-colored materials occurred.Both of the groups presented with b<1, which, in Weibullcumulative damage analysis, is indicative that fatigue isnot the accelerating factor but that strength is the mainfactor dictating failure.29 From the use level probabilityplot calculations, a dramatic decrease in survival times forboth groups was seen with the increase in load (Table 4).This illustrates that, for both groups regardless of the

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materials used, failures were dictated by the strength ofthe tested materials and not fatigue damage accumula-tion. The low fracture resistance for groups LD and RCmight be related to high bending moments and the Ti-6Al-4V alloy insert design. Following ISO standard14801 for testing implant abutments with the simulationof 3 mm of bone loss, the simulation of a central incisorwith a 10.5 ±0.5-mm length in the clinical crown portion,combined with a platform-switching restoration, gener-ates relatively higher bending moments than those inother studies.2,9 By evaluating crack branching andintersection (Figs. 7B, 8B), the fragmentation patternsseen in both the CR and LD groups showed that crackinitiation was perpetrated at the interproximal area, morespecifically in the area of the antirotational features(Figs. 7A, 8A). One possible explanation is that the in-clusion of such features in the Ti-6Al-4V insert mightlead to higher tension and stress accumulation in thespecific area, leading to crack initiation and prematurefailure of the specimens in these groups. As a result,conclusions about the fracture resistance should beavoided from the data interpretation of the present study.A worst-case scenario was simulated and might under-estimate the full potential fracture resistance of eachgroup. In agreement with previous reports about the

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Figure 8. Cohesive fracture of CAD-CAM resin-based compositeabutment specimen after 45 888 cycles at 190-N failure load, withorigin of fracture at interproximal area shown in SEM ([A] originalmagnification ×18) and macroscopic view (B) marked by O.Macroscopic view shows branching of crack and propagation towardfacial zone (compressive area). Hackle lines (H) are noticeable in highermagnifications. C, SEM (×95 magnification). D, SEM image(×30 magnification) shows crack initiation at antirotational features andpropagating from intaglio of abutment. CAD-CAM, computer-aideddesign and computer-aided manufacture; SEM, scanning electronmicrograph.

Figure 9. Specimen of CAD-CAM zirconia abutment demonstratingplastic deformation of Ti-6Al-4V alloy insert after 110 000 cycles at 310-Nfailure load. A, Scanning electron micrograph (×85 magnification). B,Macroscopic view.

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clinical performance of 2-piece zirconia abutments,11,31

group ZR specimens have reliability and can beexpected to perform adequately in a clinical situation.For groups RC and LD, further clinical and in vitrostudies are necessary before safe clinical recommenda-tions can be made.

The limitations of this in vitro study include the testingapparatus used in cyclic fatigue loading. Test specimenswere cyclically loaded with a flat indenter and unidirec-tional vertical load cell, which does not allow simulation ofpotential multidirectional loading that can occur in vivo.Different surface conditioning methods and adhesivesystems were applied, according to the manufacturers’recommendations. However, the potential effects of thesetreatment protocols on reliability outcomes have not beenconsidered in the present study. Future studies looking atthe correlation between Ti-6Al-4V insert design and per-formance of hybrid abutments might be valuable toestablish better guidelines for the laboratory fabrication ofsuch abutments. With a multitude of different Ti-6Al-4Vinsert designs available, it would be clinically relevant tounderstand the influence of certain variables such as theinsert height, the inclusion of antirotational features, andthe positioning of such features. Although variations tothe insert height have been shown to improve fractureresistance of heat-pressed LD hybrid abutments, this

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feature has not been investigated for any of the CAD-CAM materials evaluated in the present study. Last, thecomparison between the more studied pressed LD andCAD-CAM LD hybrid abutments could help cliniciansmake more informed decisions about the selection ofthese materials for different clinical scenarios.

CONCLUSIONS

Within the limitations of this in vitro study, the followingconclusions were drawn:

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Gu

1. CAD-CAM customized zirconia abutments demon-strated higher maximum load capacity under staticload and significantly higher reliability for both150-N and 200-N cyclic loading stress levels at100 000 cycles.

2. CAD-CAM customized resin-based composite andCAD-CAM customized lithium disilicate abutmentsdemonstrated no statistically significant differences(P>.10) in reliability in terms of 10% failure time.

3. Differences were found in failure characteristics ofCAD-CAM customized zirconia abutments betweenstatic and fatigue loading.

4. Failure modes after fatigue loading were similar forCAD-CAM resin-based composite and CAD-CAMlithium disilicate customized abutments but differentfrom CAD-CAM zirconia customized abutments.

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Corresponding author:Dr Kwok-Hung ChungDepartment of Restorative DentistryUniversity of Washington1959 NE Pacific Street, D-770 HSCBox 357456Seattle, WA 98195-7456Email: akchung@uw.edu

AcknowledgmentsThe authors thank 3M ESPE and Ivoclar Vivadent AG for providing materials;NobelBiocare for providing implant components; Issaquah Dental Lab for CAD-CAM support; and Elisa Quintana for assistance in preparing the manuscript.

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