RESEARCH AND EDUCATION

This researchaPostdoctorabPrivate praccProfessor, S

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Dental implant-abutment fracture resistance and wear inducedby single-unit screw-retained CAD components fabricated by

four CAM methods after mechanical cycling

Roberto A. Markarian, DDS, MS, PhD,a Deborah P. Galles, DVM, MS,b and Fabiana M. G. França, DDS, MS, PhDc

ABSTRACTStatement of problem. Computer-aided design and computer-aided manufacturing (CAD-CAM)methodologies allow the fabrication of custom dental implant abutments with a variety ofmaterials and techniques. Studies on the mechanical strength of such components and the wearinduced at their coupling interface during mechanical cycling are sparse.

Purpose. The purpose of this in vitro study was to measure the wear patterns at the hexagonalplatform of dental implants induced by the installation and mechanical cycling of customabutments fabricated by using 4 different CAD-CAM methods and to determine the compressivestatic resistance of the implant-abutment combinations.

Material and methods. A CAD software programwas used to design a custom abutment for a single-unit screw-retained external hexagon dental implant crown. The same design file was used tomanufacture with 4 CAM methods (N=40): milling and sintering of zirconium dioxide (ZO), cobalt-chromium (Co-Cr) sintered by selective laser melting (SLM), fully sintered machined Co-Cr alloy(MM), and machined and sintered agglutinated Co-Cr alloy powder (AM). Prefabricated titaniumabutments were used as a control (TI). Each abutment was installed onto a dental implant (4.1×11mm), and the specimens were mechanically aged (1 million cycles, 2 Hz, 100N, 37 �C). Aftermechanical cycling, the hexagonal connection of the dental implants was examined with a scanningelectron microscope (SEM), and unused dental implants (NI) were examined as a control (n=10). Theimages were analyzed with a software program to quantify the areas that showed wear. Theimplant-abutment combinations were reassembled and submitted to a compression test (1mm/min)with a universal testing machine. The data obtained were submitted to 1-way ANOVA (a=.05).

Results. The mean ±standard deviation fracture load (N) of the specimens of each group were 1005±187 (ZO), 1074 ±123 (SLM), 1033 ±109 (MM), 1019 ±149 (AM), and 923 ±129 (TI). These values werestatistically similar (P=.213). The mean ±standard deviation wear of the implants in squared-pixels were 1.1 ±0.38×105 (ZO), 2.0 ±0.29×105 (SLM), 1.0 ±0.38×105 (MM), 1.1 ±0.27×105 (AM),1.1 ±0.33×105 (TI), and 0.51 ±0.29×105 (NI). The results indicated that, although significantlyhigher than those in in the control group (NI), the wear values found in the groups TI, ZO, MM,and AM were significantly lower than in the SLM group (P<.001).

Conclusions. The CAD-CAM abutments presented the same mechanical fracture load and wearmeasurements as the TI group, except for the SLM material, which showed increased wear. The failuremode from the load bearing test was the fracture of the abutments for the ZO group. The implantspermanently deformed or fractured for the metal abutment groups. (J Prosthet Dent 2021;-:---)

Prefabricated titanium abut-ments are considered the goldstandard for connecting todental implants as they ensurean optimal implant-abutmentinterface fit.1 As a result, theimplant-abutment combina-tion has excellent mechanicalstrength as the parts wereproduced under the originalmanufacturer’s specifica-tions.2,3 Recently, however,computer-aided design andcomputer-aidedmanufacturing (CAD-CAM)techniques have been devel-oped to fabricate customdental implant abutments withvarious geometries, includinginternal and external connec-tions, by directly engaging theimplant hexagon or includinga metallic coupling titanium-based component.4 After theCAD of a dental abutment, thematerial for its fabrication canbe selected from a variety ofoptions as per the clinicalapplication.5 When high me-chanical strength is required,

did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.l fellow, Department of Implant Dentistry, São Leopoldo Mandic Institute and Dental Research Center (SLMANDIC), Campinas, Brazil.tice, São Paulo, SP, Brazil.ão Leopoldo Mandic Institute and Dental Research Center (SLMANDIC), Campinas, SP, Brazil.

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Clinical ImplicationsComputer-aided machining allowed the fabricationof abutments with different materials and methods.However, clinicians must be aware that computer-aided design and computer-aided manufacturingsingle-unit custom abutments can induce increasedwear when coupled directly to implants with ahexagon connection.

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base metal alloys, such as cobalt-chromium (Co-Cr) al-loys can be used.6-8 Because of the high hardness of thesolid crystallized Co-Cr alloys, computer numeric control(CNC) milling machines are required to shape the ma-terial.9 Although new technologies have been developedto facilitate the fabrication of Co-Cr alloy prostheticstructures, including additive selective laser melting(SLM),10,11 SLM-processed abutments have been re-ported to have poor abutment-implant adaptation andhigh surface roughness.1,12 Another strategy has beendeveloped with a softened base metal Co-Cr alloy forCAD-CAM, which allows a desktop laboratory machineto produce custom structures.13

As an alternative to metal, zirconia has been usedextensively for dental prostheses to improve es-thetics.14,15 Although the successful use of zirconiaabutments has been reported,16 the ceramic has ahardness several times higher than titanium.17,18 There-fore, a 1-piece abutment connecting with a titaniumimplant might be contraindicated because of suscepti-bility to fracture,19-24 the risk of inducing damage,25,26 orincreased implant hexagon wear21,27-31 when comparedwith a titanium-titanium connection. Furthermore, fric-tion between components during physiologic cyclicloading can eventually increase 3-dimensional damage tothe coupling surfaces that may involve deformation orloss of material.31,32

Concerns may arise regarding the precision of theadaptation and mechanical strength25 when customCAD-CAM abutments are used because the specifica-tions of these components are beyond the supervision ofthe implant manufacturer.12 The purpose of this in vitrostudy was to observe and quantify the wear of dentalimplants connected to CAD-CAM abutments subjectedto mechanical cycling with a scanning electron micro-scope (SEM) and a dedicated software program. Thestatic compressive fracture load of implants connected tothese abutments was measured by submitting the com-binations to a compressive load. The null hypotheseswere that CAD-CAM abutments would not alter implantwear over time and would resist a mechanical loadsimilar to those of titanium abutments.

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MATERIAL AND METHODS

One 4.1-mm external hexagon implant analog (AN 4100;S.I.N.) was scanned (D700; 3Shape A/S) and used as aprototype connection. By using CAD software (DentalSystem; 3Shape A/S), a single-unit custom antirotationalabutment was designed (4.1×9.6 mm) as a structure toengage the implant hexagon, requiring further porcelainlayering. The same resulting standard tessellation lan-guage (STL) file of the designed abutment was used tomanufacture structures by using 4 different CAD-CAMmethods.

Ten identical abutments were made for each group(Table 1), and titanium cylinders with antirotationhexagons (AI 4151-Q; S.I.N.) were used as controlabutments. For the specimen preparation in the ZOgroup, a CNC milling machine (Roders; RXD5) was used.The zirconia was milled in a presintered stage with di-mensions increased by 25%. The milling step was fol-lowed by the sintering of the structures in a furnace(inFire; Dentsply Sirona), with the structure shrinking tothe final dimensions. For the abutments in the SLMgroup, the structures were fabricated with an SLM ma-chine (EOSINT M270; EOS GmbH) from a Co-Cr alloypowder (EOS cobalt chrome SP2; EOS GmbH). Thespecimens were then separated from their base by usinga diamond disk (Horico, Wilcos). The Co-Cr specimensin the MM group were made at a CNC machining center(Neoshape; Neodent). The abutments were shapeddirectly from a block of dense and completely sinteredCo-Cr alloy, which needed no further treatment. Thespecimens in the AM group were prepared with labora-tory machining equipment (Ceramill Motion II; AmannGirrbach AG). The material was machined in the bondedphase (Ceramill Sintron; Amann Girrbach AG), with di-mensions increased by 10%. The abutments were thensintered in an argon gas atmosphere at 1300 �C (CeramillArgoTherm; Amann Girrbach AG). The specimens werethen attached to 50 external hexagon titanium implants(4.1×11mm) (SA411; S.I.N.).

Each implant was inserted into an aluminum block(7×7×11 mm) with a 3.5×8-mm central orifice by means ofan insertion key (CCIT 20; S.I.N.) and a manual ratchet(TMECC; S.I.N.), leaving 3 mm of the implant exposed.Then, the abutments were coupled onto the implants byusing a square-headed retaining screw (PTQ 2008; S.I.N.)and manual torque of 32 Ncm with a specific key(CQTM20; S.I.N.), manual ratchet (TMEC; S.I.N.), anddigital torque wrench (TQ-8800; Lutron). To simulatemasticatory forces, the implant-abutment assemblies weresubjected to 1million compressivemechanical cycles undera 100-N load. The specimenswere kept in saline solution at37 �C throughout the experiment, and the treatment in thecycling machine (Biocycle; Biopdi) complied with theInternational Organization for Standardization (ISO)

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Table 1. Experimental groups, strategies to fabricate CAD-CAM abutments, and mechanical properties

Material TI ZO SLM MM AM

Manufacturing method CNC Prefabricated CNC Custom Machined Selective Laser Melting CNC Custom Machined Desktop Milling Machine

Raw material Titanium Abutment(AI 4151-Q; S.I.N.)

(a) Zirconium dioxide(Z-CAD HD; Metoxit)

(b) Powdered Co-Cr(EOS cobalt chrome SP2; EOS)

(c) Dense Co-Cr(Wirobond M+; Bego)

(d) Agglutinated Co-Cr(Ceramill Sintron;Amanngirrbach)

Vickers hardness (HVN) 34017 1250* 350* 290* 270*

Elastic modulus (GPa) 11333 20033 200* 235* 200*

*Manufacturer’s specification. (a) Metoxit high tech ceramics Z-CAD smile material data sheet; (b) EOS cobalt-chrome SP2 for Eosint 270 Material data sheet; (c) Bego processing information forCAD-CAM product restorations; (d) Ceramill Sintron Dental Dialogue.

Figure 1. Implant hexagon. A, Observed under ×65 magnification. B,Under ×65 magnification, with wear areas highlighted (green). C, Alteredsurfaces selected and quantified after further image magnification.

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14801 standard (2Hz, 30-degrees).33 After mechanicalcycling, the specimens were disassembled, and the hex-agonal connections of the aluminum blocks connected tothe dental implants were inspected and photographed(Rebel T1i; Canon).

Subsequently, the implants were examined with aSEM (Quanta FEG 250; FEI). Two SEM images of theimplant hexagon were captured for each specimenat ×65 magnification and 10 degrees of angulation atdiametrically opposed locations. A group of unuseddental implants (NI) was analyzed under the sameconditions to serve as a control group for the wear test(n=10). To quantify the wear, the obtained images wereimported into a software program (Icy Bioimage Anal-ysis; Institute Pasteur) that permitted a detailed obser-vation of the implant hexagon and shoulder underfurther on-screen digital amplification. The same cali-brated observer (R.A.M.) highlighted the regions thatshowed signs of surface irregularities, scratches, debris,or marks (Fig. 1), and the sum of the selected areas wasquantified by the software program with a squared pixelscale. The mean value of the wear between the2 opposing sides of the hexagon corresponded to thevalue of the specimen. Additional SEM images weremade at a higher magnification (×400) to identifyirregularities located on the flat side and edge of thehexagon (Fig. 2). After SEM observations, the abut-ments were reattached to the implants as per the initialspecifications.

The specimens were then positioned in a test ma-chine (Emic DL-2000; Instron) by following the ISO14801 standard instructions.33 A static resistance testwas conducted by applying a 30-degree compressiveload to the occlusal portion of the abutments at the rateof 1 mm/min until fracture or permanent deformation.After the mechanical test, the implant-abutment con-nections were disassembled and inspected for thepresence of visible deformation of the components witha ×40 stereoscopic magnifier (HVS-1000; Pantec) andclassified in a qualitative analysis.

The statistical test applied to the compressive loaddata and wear quantification was the 1-way ANOVA,followed by the Tukey test for multiple comparisons. Astatistical software program (IBM SPSS Statistics, v23program; IBM Corp) was used for the analysis (a=.05).

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RESULTS

The 1-way ANOVA test indicated that the groupsdiffered statistically from each other in wear rates(P<.001). As shown in Table 2, although significantlyhigher than in the control group (NI), the wear

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Figure 2. Scanning electron microscope images. A, Group ZO overall view. B, Group ZO hexagonal flat side surface at higher magnification. C, Group ZOhexagonal edge at higher magnification. D, Group SLM overall view. E, Group SLM hexagonal flat side surface at higher magnification. F, Group SLMhexagonal edge at higher magnification. G, Group MM overall view. H, Group MM hexagonal flat side surface at higher magnification. I, Group MMhexagonal edge at higher magnification. J, Group AM overall view. K, Group AM hexagonal flat side surface at higher magnification. L, Group AMhexagonal edge at higher magnification. M, Group TI overall view. N, Group TI hexagonal flat side surface at higher magnification. O, Group TIhexagonal edge at higher magnification. P, Group NI (control) overall view. Q, Group NI hexagonal surface panoramic view. R, Group NI hexagonal flatside surface at higher magnification. R, Group NI hexagonal edge at higher magnification. Original magnifications: A, D, G, M, P, ×65; highermagnifications ×400.

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values found in the TI group or the milled groups(ZO, MM, AM) were significantly lower than those inthe SLM group. No statistically significant differences(P=.213) were found for load under compression(Table 2).

Wear was assessed from SEM images at low (×65)and higher (×400) magnification (Fig. 2). In addition,

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artifacts were identified in specimens of the MM group(Fig. 3) under further magnification (×1125). The quali-tative analysis of the specimens after the mechanical testare presented in Table 3. The mechanical cycling did notinduce fractures on the tested specimens, and all abut-ments remained stable during the test with no screwloosening detected.

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Figure 2. (Continued)

Table 2. Relative wear and fracture strength among studied groups.Mean ±standard deviation, wear (squared pixels), and compressivestrength (N), as per experimental groups

Group Wear Sq. [Pixels] Fracture Strength [N]

ZO 1.1×105 ±0.38×105 B 1005 ±187 A

SLM 2.0×105 ±0.29×105 C 1074 ±123 A

MM 1.0×105 ±0.38×105 B 1033 ±109 A

AM 1.1×105 ±0.27×105 B 1019 ±149 A

TI 1.1×105 ±0.33×105 B 923 ±129 A

NI 0.51×105 ±0.29×105 A d

Means followed by different letters indicate statistically significant difference betweengroups within each column (P<.05).

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DISCUSSION

This study analyzed the behavior of assemblies contain-ing external connection hexagon implants connected toabutments fabricated with 4 different CAD-CAM tech-niques and submitted to 2 tests: the assessment of wearat the implant hexagonal connection induced by MC andthe compressive mechanical static resistance of thespecimens (Table 1).

The CAD-CAM methodologies were developed toproduce abutments with a highly accurate implant-abutment interface.19 However, in the present study,

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Figure 3. Scanning electron microscope image of surface of milled Co-Crdense alloy implant (MM) showing small metallic beads. Originalmagnification ×1125. Co-Cr, cobalt-chromium.

Table 3. Relative frequency (%) of failure modes observed on prostheticabutment, prosthetic screw, and implant abutment

Component EventTI(%)

ZO(%)

SLM(%)

MM(%)

AM(%)

Implant Fracture 70 - 80 90 70

d Plasticdeformation

30 40 20 10 30

d No alterations - 60 - - -

Abutment Fracture - 100 - - d

d Plasticdeformation

- - - - d

d No alterations 100 - 100 100 100

Screw Fracture - - - - -

d Plasticdeformation

30 20 50 60 70

d No alterations 80 80 50 40 30

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the manufacturing process was found to influence theimplant hexagon wear after mechanical cycling of single-unit CAD-CAM abutments, and thus, the first null hy-pothesis was rejected. The images of the hexagonalsurfaces of the abutments did not reveal damage to theprosthetic abutments after mechanical cycling. However,the zirconia abutments presented some dark spotsprobably caused by titanium deposition induced by thefriction between the connecting surfaces. The method-ologies of wear quantification at the IAI has not beenstandardized,32 probably because of the small di-mensions, and the 3-dimensional nature of the phe-nomena involved. However, the methodology developedfor the present study successfully allowed qualitative(Fig. 2) and a simplified 2-dimensional indirect quanti-tative wear analysis for each specimen.

The unused implants (NI) were analyzed for surfaceundulations, marks, irregularities, and debris and werecompared with implants that underwent artificial me-chanical cycling. The unused implants showed minorirregularities inherent in the fabrication by CNC ma-chines, which as expected, were the lowest among thestudied groups. The installation and mechanical cyclingof CAD-CAM abutments induced different levels of wearamong the groups, mostly on the top hexagonal facesand edges and less on the base of the hexagon andimplant shoulders.

Although significantly higher than in the controlgroup (NI), the wear values found in groups TI, ZO, MM,and AM were significantly lower than those in the SLMgroup (Table 2). A qualitative observation of the SEMimages of the TI group revealed minor debris and irreg-ularities (Fig. 2M-O), similar to those on the images ofthe NI group (Fig. 2P-R); however, the quantitative wearanalysis showed statistically significantly greater wearamong the TI group specimens (P<.001).

Metal beads (5-30 mm) along the hexagonal surface inthe MM group (Fig. 2E, 2F) were probably released from

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the abutments during the mechanical cycling of thespecimens (Fig. 3). These beads have been related to theheat generated during the milling of the dense, fullysintered, Co-Cr alloy.1 SEM images showed that some,but not all, of the SLM and AM specimens presented anincreased deleterious wear effect at the implant hexagonas shown in Figure 2D-F, J-L. In these specimens, wearmarks, plastic deformation, carved surfaces with materialloss, and kneading at the implant hexagon face and topwere seen. However, the overall wear within the AMgroup was statistically similar to that in the ZO and MMgroups (Table 2). As the Vickers hardness of Co-Cr issimilar to that of titanium,8,17 this marked wear effect atSLM may be related to other mechanical properties, suchas the surface roughness of the abutments. Eventually,vibration and micromovements between componentsunder mechanical cycling could lead to subsurfacebreakups and loss of material29,31,32 that could be relatedto surface irregularities. Laser sintered additive Co-Cralloys11 and Co-Cr alloys particles embedded in poly-mers have been reported to increase surface rough-ness,1,9,13 which could impair the fabrication of acomponent that seats reliably onto the implant hexago-nal connection. A positive correlation between internalroughness and the inadequate seating of the abutmenthas been reported for SLM abutments.12 To overcomethe limitations of SLM Co-Cr fabrication, new ap-proaches to the fabrication of structures have been pro-posed, such as adding a secondary milling step that isrestricted to the hexagonal coupling surface.7 This novelmixed additive/subtractive fabrication of structuresshould combine the rapid production and cost-benefit oflaser sintering10 with the geometrical precision obtainedwith milling and should be further studied.

In the present study, the zirconia abutments (ZO)presented regular and well-defined shapes, edges, andangles that did not induce quantitative (Table 2) orqualitative increased wear of the implant after mechani-cal cycling (Fig. 2A-C), when compared with titanium

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abutments (Fig. 2M-O). These finding conflict with thoseof previous studies that reported more wear for engagingzirconia abutments than for titanium abutments.27,28,30,34

The mechanical test showed that all the abutments in thepresent study withstood similar static fracture loads(around 1000 N). However, the qualitative analysis ofdamage showed that the final failure modes weredifferent among the groups (Table 3). No damage wasdetected within the studied metal prosthetic abutments.Regarding the screw’s overall integrity, no fractures werefound within the studied groups, but some screws weredeformed during the test. At the fracture point, all thespecimens mounted with Co-Cr abutments showedfailures at the implant structure, with plastic deformationor an incomplete fracture at the implant neck. Similarimplant deformation patterns have been reported forinternal connection4 or external connection implants2

and with 1-piece or 2-piece abutments.2 The reason forthis deformation may be that the implant neck corre-sponded to the fulcrum of the bending moments applied,and in addition, the titanium implant material had thelowest elastic modulus of the materials in the assembly.8

The titanium abutment selected for this study wasdesigned for a cemented restoration and therefore hadthinner walls than the CAD-CAM custom abutmentsdesigned for screw-retained restorations. This differencemay explain the lower numeric static resistance values ingroup TI (Table 2). However, the final load bearing oftitanium abutments was statistically similar to those ofthe CAD-CAM abutments, and thus, the second nullhypothesis was accepted. The failure mode in the TIgroup occurred at the implant fracture in 70% of thespecimens. Most of the retention screws of titaniumabutments were also deformed plastically during theoverload test, and there were no visual signs of abutmentdamage. The ZO group presented a different behavior,as, in 40% of the tests, the implant showed some plasticdeformations after loading. Within the ZO group, all theabutments fractured during the load test at the hexagonalconnection region, consistent with previous studies.15,26

Before fracture, elastic deformation may occur withinthe implant-abutment assembly,19 but the brittleness ofthe sintered zirconia may explain this failure mode.14 Theresults in the present study are consistent with those ofprevious research that showed that the region around theabutment screw is the most critical for the stability ofceramic abutments.3,15,24 The reduced strength of zirco-nia abutments when compared with titanium compo-nents has been reported.3,20,22-24 Other studies havereported that a 2-piece ceramic abutment with a titaniumengaging component helps stabilize zirconiaabutments.4,15,16

A titanium-titanium interface should be preferredover a zirconia-titanium one, as differences in theimplant-abutment interface materials have been reported

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to damage the coupling connection and to weaken itsstability under mechanical load.21 However, the zirconiaabutments in the present study were able to withstand asimilar maximum load at fracture when compared withthe metal abutments. A probable reason is that these ZOabutments were designed for screw-retained restorationsand as such had thick walls and consequently high me-chanical strength. In contrast, the previous studiescompared cemented titanium and zirconia abutmentswhich have a thinner structure. This finding suggests thatthe mechanical strength of the zirconia abutments can beincreased by thickening the abutment walls.

Mechanical overload 26 or a high insertion torquewhen seating zirconia abutments on an external hexagonimplant has been reported to damage the couplinginterface,25 especially because the hardness of zirconia isseveral times higher than that of titanium.18 However, inthe present study, neither diminished mechanical failureload of the ZO abutments nor increased implant wearwas detected. The reasons for this improved zirconiaresult are unclear, and further studies regarding thefabrication method are indicated to verify the geometricalaccuracy of the engaging abutment connection. TheCAD-CAM milling strategy (ZO, MM, or AM) may leadto screw-retained abutments engaging external implanthexagonal connections with similar resistance to me-chanical aging as titanium abutments. As the milledCAD-CAM abutments in the present study inducedsimilar wear to that of the IAI as TI abutments, known tobe clinically successful,16 the use of such technologiesmay be encouraged.

One of the limitations of this in-vitro study is that theCAD-CAM structures did not receive the thermalexpansion and contraction induced during ceramicveneering, which could cause distortions and affect the fitof frameworks.7 In a real clinical situation, the structuremay have needed such aesthetic finishing before receivingthe occlusal loads. Another limitation is that the study wasperformed under nonclinical conditions, and therefore,the impact intraoral factors such as saliva, soft tissuecontour, and other clinical conditions were not accessed.

Further studies should be carried out to validateCAD-CAM methodologies before their clinical use,especially for an engaging coupling surface, becausethese represent a nonoriginal manufacturing method forthese precision connections.

CONCLUSIONS

Based on the findings of this in vitro study, the followingconclusions were drawn:

1. Except for the SLM material, which causedincreased implant damage, the wear induced byCAD-CAM abutments to the implants was similarto that a titanium abutment would produce.

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2. The CAD-CAM abutments withstood mechanicalcompressive loads similar to those of the titaniumabutments.

3. The failure mode with the load bearing test for thezirconia group occurred after the fracture of theabutments. However, the implants permanentlydeformed or fractured with the metal abutments.

REFERENCES

1. Markarian RA, Galles DP, França FMG. Scanning electron microscopyanalysis of the adaptation of single-unit screw-retained computer-aideddesign/computer-aided manufacture abutments after mechanical cycling. IntJ Oral Maxillofac Implants 2018;33:127-36.

2. Joda T, Bürki A, Bethge S, Brägger U, Zysset P. Stiffness, strength, and failuremodes of implant-supported monolithic lithium disilicate crowns: influenceof titanium and zirconia abutments. Int J Oral Maxillofac Implants 2015;30:1272-9.

3. Sailer I, Asgeirsson AG, Thoma DS, Fehmer V, Aspelund T, Özcan M,et al. Fracture strength of zirconia implant abutments on narrow diameterimplants with internal and external implant abutment connections: Astudy on the titanium resin base concept. Clin Oral Implants Res 2018;29:411-23.

4. Truninger TC, Stawarczyk B, Leutert CR, Sailer TR, Hämmerle CHF, Sailer I.Bending moments of zirconia and titanium abutments with internal andexternal implanteabutment connections after aging and chewing simulation.Clin Oral Implants Res 2012;23:12-8.

5. Kapos T, Ashy LM, Gallucci GO, Weber HP, Wismeijer D. Computer-aideddesign and computer-assisted manufacturing in prosthetic implant dentistry.Int J Oral Maxillofac Implants 2009;24:110-7.

6. Vigolo P, Fonzi F, Majzoub Z, Cordioli G. An in vitro evaluation of titanium,zirconia, and alumina procera abutments with hexagonal connection. Int JOral Maxillofac Implants 2006;21:575-80.

7. Svanborg P, Eliasson A, Stenport V. Additively manufactured titanium andcobalt-chromium implant frameworks: fit and effect of ceramic veneering. IntJ Oral Maxillofac Implants 2018;33:590-6.

8. Anusavice KJ, Shen C, Rawls HR. Phillips’ science of dental materials. 12thed. St. Louis: Elsevier; 2012. p. 384-454.

9. Stawarczyk B, Eichberger M, Hoffmann R, Noack F, Schweiger J, Edelhoff D,et al. A novel CAD/CAM base metal compared to conventional CoCrMoalloys: an in-vitro study of the long-term metal-ceramic bond strength. OralHealth Dent Manag 2014;13:446-52.

10. Koutsoukis T, Zinelis S, Eliades G, Al-Wazzan K, Rifaiy MA, Al Jabbari YS.Selective laser melting technique of Co-Cr dental alloys: a review of structureand properties and comparative analysis with other available techniques.J Prosthodont 2015;24:303-12.

11. Oyagüe RC, Sánchez-Turrión A, López-Lozano JF, Suárez-García MJ. Ver-tical discrepancy and microleakage of laser-sintered and vacuum-castimplant-supported structures luted with different cement types. J Dent2012;40:123-30.

12. Fernández M, Delgado L, Molmeneu M, García D, Rodríguez D. Analysis ofthe misfit of dental implant-supported prostheses made with threemanufacturing processes. J Prosthet Dent 2014;111:116-23.

13. Lee DH, Lee BJ, Kim SH, Lee KB. Shear bond strength of porcelain to a newmillable alloy and a conventional castable alloy. J Prosthet Dent 2015;113:329-35.

14. Afrashtehfar KI, Del Fabbro M. Clinical performance of zirconia implants: ameta-review. J Prosthet Dent 2020;123:419-26.

15. Sailer I, Sailer T, Stawarczyk B, Jung RE, Hämmerle CHF. In vitro study of theinfluence of the type of connection on the fracture load of zirconia abutmentswith internal and external implant-abutment connections. Int J Oral Max-illofac Implants 2009;24:850-8.

16. Borges T, Lima T, Carvalho Á, Dourado C, Carvalho V. The influence ofcustomized abutments and custom metal abutments on the presence of theinterproximal papilla at implants inserted in single-unit gaps: a 1-year pro-spective clinical study. Clin Oral Implants Res 2014;25:1222-7.

17. Rocha SSR, Adabo GL, Henriques GEP, Nóbilo MAA. Vickers hardness ofcast commercially pure titanium and Ti-6Al-4V alloy submitted to heattreatments. Braz Dent J 2006;17:126-9.

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18. Chun KJ, Lee JY. Comparative study of mechanical properties of dentalrestorative materials and dental hard tissues in compressive loads. J DentBiomech 2014;5. 1758736014555246.

19. Gehrke P, Johannson D, Fischer C, Stawarczyk B, Beuer F. In vitro fatigueand fracture resistance of one-and two-piece CAD/CAM zirconia implantabutments. Int J Oral Maxillofac Implants 2015;30:546-54.

20. Foong JKW, Judge RB, Palamara JE, Swain MV. Fracture resistance of tita-nium and zirconia abutments: an in vitro study. J Prosthet Dent 2013;109:304-12.

21. Cavusoglu Y, Akça K, Gürbüz R, Cehreli MC. A pilot study of joint stability atthe zirconium or titanium abutment/titanium implant interface. Int J OralMaxillofac Implants 2014;29:338-43.

22. Alsahhaf A, Spies BC, Vach K, Kohal RJ. Fracture resistance of zirconia-basedimplant abutments after artificial long-term aging. J Mech Behav BiomedMater 2016;66:224-32.

23. Att W, Kurun S, Gerds T, Strub JR. Fracture resistance of single-toothimplant-supported all-ceramic restorations: an in vitro study. J Prosthet Dent2006;95:111-6.

24. Mühlemann S, Truninger TC, Stawarczyk B, Hämmerle CHF, Sailer I.Bending moments of zirconia and titanium implant abutments supportingall-ceramic crowns after aging. Clin Oral Implants Res 2014;25:74-81.

25. Elias CN, Fernandes DJ, Resende CRS, Roestel J. Mechanical properties,surface morphology and stability of a modified commercially pure highstrength titanium alloy for dental implants. Dent Mater 2015;31:e1-13.

26. Basílio MA, Delben JA, Cesar PF, Rizkalla AS, Junior GCS, Filho JNA. Failuremodes of Y-TZP abutments with external hex implant-abutment connectiondetermined by fractographic analysis. J Mech Behav Biomed Mater 2016;60:187-94.

27. Tannure ALP, Cunha AG, Junior LAB, Concílio LRS, Neves ACC. Wear atthe implant-abutment interface of zirconia abutments manufactured by threeCAD/CAM systems. Int J Oral Maxillofac Implants 2017;32:1241-50.

28. Stimmelmayr M, Edelhoff D, Güth J-F, Erdelt K, Happe A, Beuer F. Wear atthe titaniumetitanium and the titaniumezirconia implanteabutment inter-face: A comparative in vitro study. Dent Mater 2012;28:1215-20.

29. Yüzügüllü B, Avci M. The implant-abutment Interface of alumina and zir-conia abutments. Clin Implant Dent Relat Res 2008;10:113-21.

30. Klotz MW, Taylor TD, Goldberg AJ. Wear at the titanium-zirconia implant-abutment interface: a pilot study. Int J Oral Maxillofac Implants 2011;26:970-5.

31. Brodbeck U. The ZiReal Post: A new ceramic implant abutment. J EsthetRestor Dent 2003;15:10-24.

32. Heintze SD, Cavalleri A, Forjanic M, Zellweger G, Rousson V. A comparisonof three different methods for the quantification of the in vitro wear of dentalmaterials. Dent Mater 2006;22:1051-62.

33. International Organization for Standardization. ISO-14801. Dentistry - Im-plants - Dynamic fatigue test for endosseous dental implants. Geneva: ISO.Available at: https://www.iso.org/store.html.

34. Cibirka RM, Nelson SK, Lang BR, Rueggeberg FA. Examination of theimplantdabutment interface after fatigue testing. J Prosthet Dent 2001;85:268-75.

Corresponding author:Dr Roberto A. MarkarianImplart Dental ClinicRua Cincinato Braga 37 cj 112, 01333-011São Paulo, SPBRAZILEmail: roberto@implart.com.br

AcknowledgmentsThe authors thank S.I.N. Implants, São Paulo, Brazil, for their support by donatingthe implants and prosthetic components and CEME/UNIFESP, São Paulo, Brazil,for the scanning electron microscopic analyses.

CRediT authorship contribution statementRoberto A. Markarian: Conceptualization, Resources, Methodology, Formalanalysis, Writing - original draft. Deborah P. Galles: Visualization, Investigation,Software, Data curation. Fabiana M.G. França: Supervision, Methodology,Validation, Writing - review & editing, Project administration.

Copyright © 2021 by the Editorial Council for The Journal of Prosthetic Dentistry.https://doi.org/10.1016/j.prosdent.2020.08.052

Markarian et al