Effect of implant-abutment connection design on reliability of crowns: regular vs. horizontal mismatched platform.

OBJECTIVES To evaluate the reliability and failure modes of regular and horizontal mismatched platforms for implant-abutment connection varying the implant diameter. MATERIAL AND METHODS Regular (REG, n = 21, 4.0-mm-diameter implant) and horizontal mismatched (HM, n = 21, 4.6-mm-diameter implant) platform Ti-6Al-4V implants were restored with proprietary identical Ti-6Al-4V abutments and metal crowns (cobalt-chrome, Wirobond 280, BEGO, Bremen, Germany) cemented. Mechanical testing comprised step-stress accelerated-life testing, where crowns were distributed in three loading profiles for fatigue in water, producing timely and clinically relevant fractures. The probability of failure vs. cycles (95% two-sided confidence intervals) was calculated and plotted using a powerlaw relationship for damage accumulation, Weibull modulus (95% two-sided confidence intervals) and then the reliability for a mission of 50,000 cycles at 125 N load (95% two-sided confidence interval) were calculated. Fractography was performed in the scanning electron microscope. RESULTS The β-value for group REG (β = 1.37) indicated that fatigue was a factor accelerating the failure, whereas load alone dictated the failure for group HM (β = 0.71). The Weibull parameter contour plot showed no significantly different Weibull modulus for REG (10.24) compared to HM (10.20) and characteristic strength of 162.6 and 166.8 N, respectively (P > 0.91). The calculated reliability for a mission of 50,000 cycles at 125 N load was not significantly different (0.71 for REG and 0.73 for HM). Abutment screw failure was the chief failure mode. CONCLUSIONS Reliability was not significantly different between groups and failure modes were similar.