Reliability and failure modes of internal conical dental implant connections Freitas jr et al. vs astra


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Reliability and failure modes of internal conical dental implant connections Freitas jr et al. vs astra

  1. 1. ´Amilcar C. Freitas-Junior Reliability and failure modes ofErika O. AlmeidaEstevam A. Bonfante internal conical dental implantNelson R.F.A. Silva connectionsPaulo G. CoelhoAuthors’ affiliations: Key words: fractography, implant-supported prostheses, internal conical interface connection, ´Amilcar C. Freitas-Junior, Postgraduate Program in step-stress accelerated life testing, WeibullDentistry, School of Health Sciences, PotiguarUniversity - UnP, Natal, RN, BrazilErika O. Almeida, Department of Dental Materials Abstractand Prosthodontics, Sao Paulo State University, ˜Aracatuba School of Dentistry, Aracatuba, Sao ¸ ¸ ˜ Objective: Biological and mechanical implant-abutment connection complications and failures arePaulo, Brazil still present in clinical practice, frequently compromising oral function. The purpose of this studyEstevam A. Bonfante, Postgraduate Program in was to evaluate the reliability and failure modes of anterior single-unit restorations in internalDentistry, UNIGRANRIO University–School ofHealth Sciences, Duque de Caxias, RJ, Brazil conical interface (ICI) implants using step-stress accelerated life testing (SSALT).Nelson R.F.A. Silva, Department of Prosthodontics, Materials and methods: Forty-two ICI implants were distributed in two groups (n = 21 each):New York University College of Dentistry, New group AT–OsseoSpeedTM TX (Astra Tech, Waltham, MA, USA); group SV–Duocon System Line,York, NY, USAPaulo G. Coelho, Department of Biomaterials and Morse Taper (Signo Vinces Ltda., Campo Largo, PR, Brazil). The corresponding abutments wereBiomimetics, Director for Research, Department of screwed to the implants and standardized maxillary central incisor metal crowns were cementedPeriodontology and Implant Dentistry, New York and subjected to SSALT in water. Use-level probability Weibull curves and reliability for a missionUniversity College of Dentistry, New York, NY,USA of 50,000 cycles at 200 N were calculated. Differences between groups were assessed by Kruskal– Wallis along with Bonferroni’s post-hoc tests. Polarized-light and scanning electron microscopesCorresponding author: were used for failure analyses.Estevam A. Bonfante ´Rua Prof. Jose de Souza Herdy, 1160 - 25 de Agosto, Results: The Beta (b) value derived from use level probability Weibull calculation was 1.62 (1.01–Duque de Caxias, RJ, Brazil 25071-202. 2.58) for group AT and 2.56 (1.76–3.74) for group SV, indicating that fatigue was an acceleratingTel.: 55-14-8153-0860 factor for failure of both groups. The reliability for group AT was 0.95 and for group SV was 0.88.Fax: 55-14-3234-2566e-mail: Kruskal–Wallis along with Bonferroni’s post-hoc tests showed no significant difference between the groups tested (P > 0.27). In all specimens of both groups, the chief failure mode was abutment fracture at the conical joint region and screw fracture at neck’s region. Conclusions: Reliability was not different between investigated ICI connections supporting maxillary incisor crowns. Failure modes were similar. Since the definition and widespread applica- (Binon 1996; Khraisat et al. 2002, 2004). Clin- tion of the osseointegration principles, sev- ically, biological and mechanical implant- eral designs for dental implant-abutment abutment connection complications and fail- connection have been available for clinical ures have been reported(Rangert et al. 1995; use. Historically, the external hexagon con- Esposito et al. 1998; Cardoso et al. 2010) and nection was designed to provide an engage- are of concern as they frequently compromise ment method for implant placement and oral function and the psychosocial well being anti-rotational feature for single-unit prosthe- of patients. sis, and is likely the functioning system with As to the commonly observed mechanical longest clinical follow-up (Priest 1999; Scho- failures, loosening and/or fracture of fixation lander 1999; Wannfors & Smedberg 1999). screws or abutments have been related to the The prerequisite for assembling an external type of implant–abutment connection (Quek hexagon abutment to an implant is the exis- et al. 2008). Also of interest, from a biologi- tence of a minimum space between engaging cal perspective, is, that the microgap between lateral walls of the implant connecting part implant and abutment may serve as a septicDate: and abutment internal surfaces. The resulting reservoir that initiates and perpetuates anAccepted 29 January 2012 horizontal and rotational misfits under load- inflammatory response with the potential toTo cite this article: ing, especially in single-unit restorations trigger peri-implantitis and play an important ´Freitas-Junior AC, Almeida EO, Bonfante EA, Silva NRFA,Coelho PG, Reliability and failure modes of internal conical lacking cross-arch stabilization, may present role in the multifactorial process of periim-dental implant connections. as a hindrance to the long-term stability and plant bone loss.(Hartman & Cochran 2004) InClin. Oral Impl. Res. 00, 2012, 1–6doi: 10.1111/j.1600-0501.2012.02443.x success of the implant-supported restoration addition, micromovements of the implant© 2012 John Wiley & Sons A/S 1
  2. 2. ´Freitas-Junior et al Á Fatigue of internal conical interface implantsand/or abutment, and periimplant vascular tube, leaving the top platform in the same ated life-testing profiles were determined foralterations might contribute to the influence level of the potting surface. the remaining 18 specimens of each groupof microbial contamination on the biologic Following connection of the corresponding which were assigned to a mild (n = 9), mod-width over time (Hermann et al. 2001; King proprietary cement-retained abutment (group erate (n = 6), and aggressive (n = 3) fatigueet al. 2002). Therefore, improving the AT–Abutment TiDesignTM 4.0, Ref. # 24285; profiles (ratio 3 : 2 : 1, respectively) (Nelsonimplant–abutment connection is of great Astra-Tech Inc.; and group SV–Anatomical 1990; Nelson 2005; Coelho et al. 2009b).interest for clinical longevity (Jung et al. Abutment, Ref. # 03111; Signo Vinces®) to Step-stress loading profiles are named based2008). the bearing housing, the titanium alloy abut- on the step-wise load increase that the speci- In an attempt to reduce the incidence of ment screws (group AT–Abutment Screw men will be fatigued throughout the cyclesmechanical failures while improving the DesignTM 4.0, Ti-alloy, Ref. # 24449; Astra- until a certain level of load, which meansinterface between soft tissue and implant- Tech Inc.; and group SV–Screw, Ti-alloy, Ref. that specimens assigned to a mild profile willabutment junction, internal conical interface # 05306; Signo Vinces®) (Fig. 1) were tight- be cycled longer to reach the same load leveljoint design (ICI connection) was developed. ened with a torque gauge (Nobel Biocare, of a specimen assigned to the aggressive pro-Different from external hexagon, the conical Goteborg, Sweden) according to the manufac- file (Fig. 2) (Abernethy 2006).interface results in a relatively tight junction turer’s instructions (20 A maxillary The prescribed fatigue method was SSALTdue to friction between implant and abut- central incisor crown was waxed to its close under water at 9 Hz with a servo-all-electricment (Bozkaya & Muftu 2003). It has been anatomical state and cast in a cobalt-chrome system (TestResources 800L; Shakopee, MN,proposed to be more biomechanically stable metal alloy (CoCr partial denture alloy, Wiro- USA) where the indenter contacted thethan external or internal hexagonal implant– bond® 280; BEGO, Bremen, Germany) with crown surface, applied the prescribed loadabutment connection.(Merz et al. 2000; Nor- its cementation surface designed to fit the within the step profile and lifted-off theton 2000; Steinebrunner et al. 2008) In the abutments from the first group (AT). To crown surface. Fatigue testing was per-ICI connections, the form lock and friction reproduce the anatomy of the first crown, an formed until failure (bending or fracture ofare the basic principles and this mechanism, impression was taken from the first waxed the fixation screw and/or abutment) or sur-referred to as positive or geometric locking, pattern and used by the technician as a guide vival (no failure occurred at the end of step-is assumed to be responsible for shielding the during waxing of crowns for the second group stress profiles, where maximum loads wereabutment and fixation screw from loading (SV). The cementation surface of the crowns up to 800 N) (Nelson 1990; Nelson 2005;(Merz et al. 2000). Thus, the reduced micro- was blasted with aluminum oxide (particle Coelho et al. 2009b). Use level probabilitymovement of ICI connection should provide size 40lm, using 276 KPa compressed air Weibull curves (probability of failure versussuperior strength and joint stability (Merz pressure), cleaned with ethanol, dried with cycles) with a power law relationship foret al. 2000). These potential mechanical air free of water and oil, and cemented (Rely damage accumulation were calculated (Altaadvantages of internal conical joint design X Unicem, 3M ESPE; St. Paul, MN, USA) on Pro 7; Reliasoft, Tucson, AZ, USA) (Zhaoover internal and external hexagonal design the ICI abutments. 2005). The reliability (the probability of anwere previously reported in in vitro (Merz item functioning for a given amount ofet al. 2000) and in vivo (Levine et al. 1999; Mechanical testing and reliability analysis time without failure) for a mission ofMangano et al. 2009, 2011) studies. However, For mechanical testing, the specimens were 50,000 cycles at a 200 N load (Freitas et is still unclear how the keying mechanism subjected to 30º off-axis loading. Three speci- 2011)(Paphangkorakit & Osborn 1997) (two-of ICI connections responds to fatigue test- mens of each group underwent single-load-to- sided 95% confidence intervals) was calcu-ing, which was previously reported as an in fracture (SLF) testing at a cross-head speed of lated for comparison between SV and AT.vitro method able to reproduce clinical fail- 1 mm/min in a universal testing machine As the sample size utilized in the presentures (Coelho et al. 2009a). Thus, the purpose (INSTRON 5666; Canton, MA, USA) with a investigation was small and the softwareof this study was to evaluate the reliability flat tungsten carbide indenter applying the utilized considers a z distribution for confi-and failure modes of anterior single-unit res- load on the lingual side of the crown, close dence bound construction, Kruskall–Wallistorations for ICI connection implants using to the incisal edge. Based upon the mean load along with Bonferroni’s post-hoc test atstep-stress accelerated life testing (SSALT) in to failure from SLF, three step-stress acceler- 95% level of significance was performedwater. based on the load to failure of all samples tested under accelerate fatigue.Materials and methodsSample preparationForty-two Ti-6Al-4V ICI connection implants(~4.0 mm diameter by 11.0 mm length) weredistributed in two groups (n = 21): group AT–OsseoSpeedTM TX (Ref. # 24942; Astra TechInc., Waltham, MA, USA); group SV–DuoconSystem Line, Morse Taper (Ref. # 21223;Signo Vinces®, Campo Largo, PR, Brazil). Allimplants were vertically embedded in acrylic Fig. 2. This chart shows the mild, moderate, andresin (Orthoresin, Degudent, Mainz, Ger- Fig. 1. Diagram depicting the internal conical interface aggressive load profiles used for accelerated fatigue test-many), poured in a 25-mm-diameter plastic angle for both implant systems. ing of the internal conical interface implant systems.2 | Clin. Oral Impl. Res. 0, 2012 / 1–6 © 2012 John Wiley & Sons A/S
  3. 3. ´ Freitas-Junior et al Á Fatigue of internal conical interface implantsFailure analysis (Table 1). The calculated reliability with 95% Table 1. Calculated reliability of anterior sin-Macro images of failed samples were taken gle-unit restorations for groups AT and SV confidence intervals for a mission of 50,000 given a mission of 50,000 cycles at 200 N loadwith a digital camera (Nikon D-70s; Nikon, cycles at 200 N showed that the cumulative Output (50,000 Astra Tech SignoTokyo, Japan) and utilized for failure mode damage from loads reaching 200 N would cycles @ 200 N) (AT) Vinces (SV)classification and comparisons between lead to implant-supported restoration survival Upper 0.98 0.95groups. To identify fractographic markings in 95% of cemented restorations over AT Reliability 0.95 0.88and characterize failure origin and direction implants, whereas 88% would survive in Lower 0.86 0.75of crack propagation, the most representative group SV when considering the given mis-failed samples of each group were inspected sion. Kruskal–Wallis along with Bonferroni’s the opposite tensile side) (Quinn 2007) andfirst under a polarized-light microscope (MZ- post-hoc tests showed no significant differ- beach marks (microscopic semielliptical linesAPO stereomicroscope; Carl Zeiss MicroI- ence between the groups tested (P > 0.27). running perpendicular to the overall directionmaging, Thornwood, NY, USA) and then by of fatigue crack propagation and marking suc-scanning electron microscopy (SEM) (Model Failure Modes cessive positions of the advancing crackS-3500N; Hitachi, Osaka, Japan) (Parrington All specimens failed after SLF and SSALT. front) (Parrington 2002), which allowed the2002; Manda et al. 2009). When component failures were evaluated identification of flaw origin and the direction together, failures comprised the combination of crack propagation.Results of screw bending or fracture, and abutment bending or fracture. Failure modes for groupsSLF and Reliability AT and SV are presented in Table 2. DiscussionThe SLF mean ± standard deviation values Screw fracture at neck’s region and abut-for group AT were 430.17 N ± 50.22 N, and ment fracture at the conical joint region were Considering the relevance of a fatigue resis-468.8 N ± 25.15 N for group SV. the chief failure mode after SSALT for both tant implant-abutment connection for the The step-stress derived probability Weibull groups (Fig. 4). In group AT, all the abut- long-term clinical success, the present studyplots and summary statistics at a 200 N load ments presented complete fractures after evaluated the reliability and failure modes ofare presented in Fig. 3 and Table 1, respec- SSALT, whereas the abutments were par- maxillary central incisor crowns restoredtively. The Beta (b) values and associated tially fractured in group SV. All implants with ICI implant abutments that are com-upper and lower bounds derived from use were intact after mechanical testing. mercially available. The scenario simulatedlevel probability Weibull calculation (proba- Observation of the polarized-light and SEM in the present study represented a commonbility of failure vs. number of cycles) of 1.62 micrographs of the fractured surface of clinical situation for single-tooth replace-(1.01–2.58) and 2.56 (1.76–3.74) for groups AT screws (Fig. 5) and abutments (Fig. 6) allowed ments in anterior region of maxilla providingand SV, respectively, indicated that fatigue the consistent identification of fractographic insight into the fatigue failure mechanisms(damage accumulation) was an accelerating markings, such as compression curl (the involved in ICI connections. Thus, all speci-factor for failure in both groups. curved lip before total fracture of a body, mens were subjected to step-stress acceler- The step-stress accelerated fatigue permit indicating the existence of a strong bending ated fatigue test in water, which has beenestimates of reliability at a given load level component and that the fracture origin is on suggested as an important service-related cause of failure in metals (Parrington 2002). Our results showed that fatigue accelerated the failures of the two designs of ICI connec- tions, as evidenced by the resulting b value (also called the Weibull shape factor): 1.62 (1.01–2.58) for group AT, and 2.56 (1.76–3.74) for group SV. The b value describes failure rate changes over time (b < 1: failure rate is decreasing over time, commonly associated with “early failures” or failures that occur due to egregious flaws; b ~ 1: failure rate that does not vary over time, associated with fail- ures of a random nature; b > 1: failure rate is increasing over time, associated with failures related to damage accumulation) (Coelho et al. 2009b; Reliasoft 2010). Given a mission of 50,000 cycles at 200 N load, our results showed no difference of fati- gue endurance for both systems (AT and SV). In the present study, the region most suscep- tible to fracture was consistent (fracture at neck’s region of the fixation screw, and frac- ture at the conical joint region of the abut-Fig. 3. Use Level Probability Weibull for groups AT and SV showing the probability of failure as a function of num-ber of cycles (time) given a mission of 50,000 cycles at 200 N. Note that for each of the groups tested, the lowest ments) regardless of the system used. In alldata values tended to increase the slope of the Weibull fit. AT, Astra Tech; SV, Signo Vinces. specimens, the fractures were characterized© 2012 John Wiley & Sons A/S 3 | Clin. Oral Impl. Res. 0, 2012 / 1–6
  4. 4. ´Freitas-Junior et al Á Fatigue of internal conical interface implantsTable 2. Failure modes after mechanical testing [single-load-to-fracture (SLF) and step-stress accel- properly take into account the cumulativeerated life-testing (SSALT)] according to the used failure criteria effect of exposure at successive stresses and, Groups Astra Tech (AT) Signo Vinces (SV) consequently, the weakest point of ICI con- SLF (n = 3) Screw: 3 bending Screw: 3 bending nections could be identified (Nelson 1990; Abutment: 3 bending Abutment: 3 bending Nelson 2005). On the other hand, another Implant: 3 intact Implant: 3 intact SSALT (n = 18) Screw: 18 fracture Screw: 18 fracture mechanical study (Perriard et al. 2002) com- Abutment: 18 fracture Abutment: 18 fracture pared a ICI connection with an octagonal Implant: 18 intact Implant: 18 intact internal key using the staircase technique to(a) (b) (c)Fig. 4. Representative failure modes of single-unit implant-supported restorations observed in abutments and fixation screws after SSALT depicting: (a and b) A fracture occur-ring at the conical joint region of the abutments in groups AT and SV, respectively. (c) A fracture occurring at the screw’s neck region in all tested specimens. SSALT, step-stress accelerated life-testing; AT, astra tech; SV, signo vinces.(a) (b) (c)Fig. 5. (a and b) SEM micrographs of the upper and lower parts of fixation screw shown in Fig. 4c. (c) is a SEM micrograph of the fractured surface shown in (b). The whitearrows show a compression curl, which evidences fracture origin at the opposing tensile side (larger black arrow). It is representative of flexure failures, and results from a trav-eling crack changing direction as it enters a compression field. Beach marks (yellow arrows), which are semielliptical lines running perpendicular to the overall direction of fati-gue crack propagation and marking successive positions of the advancing crack front, are also observed indicating that crack propagated from lingual (fracture origin) to buccal(compression curl’s region). SEM, scanning electron material tearing and exhibited gross plastic et al. 2004) in which the materials were fati- fatigue the specimens (maximum cycle num-deformation, suggesting ductile fractures (Par- gued under a constant load, no failures were ber of 106) and observed that the location ofrington 2002). The ductile fractures as the observed in ICI connections (abutments and the failure sites in ICI implant abutmentresult of stresses exceeding the material yield implants) after 500,000 cycles of 75 N. Con- group was distributed randomly across thestrength left marks indicating crack propaga- versely, in the present study, the materials structures (implant, abutment and fixationtion from lingual to buccal, where occlusal were subjected to step-stress test to quickly screw), thereby indicating the absence offorces naturally occur. In a study (Cehreli yield failures. Thus, the tested model could locus of minor resistance on this connection.4 | Clin. Oral Impl. Res. 0, 2012 / 1–6 © 2012 John Wiley & Sons A/S
  5. 5. ´ Freitas-Junior et al Á Fatigue of internal conical interface implants(a) (b) assumed to be favorable in terms of long- term success and esthetics (Levine et al. 1999; Mangano et al. 2009, 2011), further evaluations of the implant-abutment stability combined with fatigue testing are warranted for this connection design and its variations. Fatigue testing in the posterior area with loading applied in more than one force vector is also warranted to assess the reliability of ICI connections. Furthermore, standardiza- tion of parameters adopted in mechanical tests is suggested to allow the comparison ofFig. 6. (a) is a SEM micrograph of the lower part of internal conical interface abutment shown in Fig. 4a. (b) is a reliability between different designs of ICIhigher magnitude (709) of sample shown in (a) illustrating the fracture origin (black arrow) and beach marks (yellow connections.arrows) indicating direction of crack propagation from lingual to buccal. SEM, scanning electron microscopy. Conclusion As observed in maps of stress distribution centration in the abutment screw thanfrom previous finite element analyses (Pessoa internal or external hexagon (Pessoa et al. No differences in reliability values wereet al. 2010), the higher levels of stress are 2010). observed for the two tested designs of inter-concentrated in the conical joint region of Considering that the replacement of single- nal conical interface connection. Fatigueabutments when using ICI connection unit edentulous spaces in the anterior region (damage accumulation) was an acceleratingimplant. These findings are in accordance of maxilla with implant-supported restora- factor for failure in both groups, and the chiefwith the chief failure mode observed in the tions is a challenging scenario, it is crucial to failure mode was abutment fracture at thepresent study. In addition, when compared acknowledge the functional and mechanical conical joint region and screw fracture atwith other connection designs, ICI connec- limitations of the implant-abutment connec- neck’s region.tions present considerably lower stress con- tions. As the ICI connections have beenReferencesAbernethy, R. (2006) The New Weibull Handbook, Implants Research Epub Ahead of Print. doi: ter retrospective analysis of the iti implant sys- 5th edition. North Palm Beach: Dr. Robert B. 10.1111/j.1600-0501.2011.02269.x. tem used for single-tooth replacements: results Abernethy. Hartman, G.A. & Cochran, D.L. (2004) Initial of loading for 2 or more years. The Interna-Binon, P.P. (1996) Evaluation of three slip fit hexag- implant position determines the magnitude of tional Journal of Oral & Maxillofacial Implants onal implants. Implant Dentistry 5: 235–248. crestal bone remodeling. Journal of Periodontol- 14: 516–520.Bozkaya, D. & Muftu, S. (2003) Mechanics of the ogy 75: 572–577. 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