• Zahoui, Abbas
• Carvalho, Laura F. De
• Coelho, Paulo G.
• Bergamo, Edmara T. P.
• Bonfante, Estevam A.
• Jalkh, Ernesto B. Benalcázar
• Gierthmühlen, Petra C.
• Witek, Lukasz
• Gouvea, Marcus V. R.
• Lopes, Adolfo C. O.
• Araújo-Júnior, Everardo N. S. De
• Cardoso, Karina B.
• Campos, Tiago M. B.

Abstract

<p>Objective: Evaluate the effect of aging using two different methods on the three-dimensional fit of zirconia abutments at the implant-abutment connection and estimate the probability of survival of anterior crowns supported by straight and 17-degree angled abutments. Materials and methods: Two different zirconia abutment designs, straight and 17-degree angled abutments (n = 63/group), were evaluated in the current study. The abutments were randomly allocated into three experimental groups according to laboratory aging condition (134°C, 2.2 bar, 20 h): (i) control, (ii) autoclave aging, and (iii) hydrothermal reactor aging. Crystalline content was determined by X-Ray diffraction (XRD) and Raman spectroscopy, and microstructure was analyzed using field-emission gun scanning electron microscope (FEG-SEM). Implant-abutment volume misfit was determined in the straight abutments by micro-computed tomography using the silicone replica technique. For fatigue testing, abutments were torqued to the implants and connected to standardized maxillary incisor zirconia crowns. The assemblies were subjected to step-stress accelerated life testing (SSALT) in water until fracture or suspension. The use level probability Weibull curves and probability of survival for a mission of 50,000 cycles at 50, 100, 150 and 200 N were calculated and plotted. Fractured samples were analyzed using a stereomicroscope and scanning electron microscope. Results: The crystalline spectra depicted a zirconia system primarily composed of the tetragonal phase. Laboratory aging yielded a 20%- and 37%-increase in the monoclinic content for abutments aged in autoclave and hydrothermal reactor relative to control, respectively. A fully crystalline matrix with a regular grain size was observed in the FEG-SEM for control abutments, with a considerable presence of intergranular defects. While autoclave aging triggered no significant alteration to the microstructure, defect population was reduced after hydrothermal reactor aging. Control abutments presented a significantly higher volume misfit (2.128 ± 0.54 mm³) relative to aged abutments using autoclave (1.244 ± 0.48 mm³) or hydrothermal reactor (1.441 ± 0.41 mm³). The beta (β) values indicated that failures were predominantly controlled by material strength rather than fatigue damage accumulation for all groups, except for straight control abutments. Irrespective of aging, the probability of survival of straight and angled zirconia abutments was up to 95% (95–100%) at 50 and 100 N. A 50N-increase in the load resulted in wider range of survival estimate, with straight autoclave abutments percentage significantly lower probability of survival (77%) than angled hydrothermal reactor abutments (99%). At 200N, angled hydrothermal reactor (97%) or autoclave (82%) aged abutments demonstrated the highest probability of survival, angled control (71%) and straight hydrothermal reactor (69%) abutments intermediate values, and straight autoclave (23%) and control (7%) abutments the lowest estimate. The failure mode predominantly involved abutment and/or abutment screw fracture for both straight and angled abutments. Conclusions: Hydrothermal aging significantly influenced volume misfit, as well as the probability of survival of zirconia abutments at higher loads for both angled and straight abutments.</p>

Topics

• grain
• grain size
• phase
• scanning electron microscopy
• x-ray diffraction
• tomography
• strength
• fatigue
• defect
• aging
• Raman spectroscopy
• fatigue testing
• aging