Reliability testing of indirect composites as single implant restorations

Purpose: To investigate the reliability and failure modes of indirect composites as single-unit implant crowns. Materials and Methods: Thirty-eight custom-milled titanium alloy locking-taper abutments were divided into two groups (n = 19 each), and crown build-up of a mandibular molar was accomplished using two indirect composite systems (Ceramage, Shofu, Kyoto, Japan; Diamond Crown, DRM, Branford, CT). Three crowns of each material were loaded until failure for determination of the step-stress profiles. Reliability testing started at a load 30% of the mean load to failure and used three profiles with increasing fatigue loading (step stress). Weibull curves with 300 N stress and 90% confidence intervals were calculated and plotted using a power-law relationship. Weibull modulus "Beta" and characteristic strength "Eta" were identified, and a contour plot was used (Beta vs. Eta) for examining differences between groups. Specimens were inspected in polarized light and scanning electron microscope for fracture analysis. Results: Use level Weibull probability showed fatigue being a damage factor only for the Ceramage group (β= 3.39) but not for the Diamond Crown group (β= 0.40). Overlap in the confidence bounds resulted in no statistical difference. Irrespective of composite system, fracture initiated in the region immediately below the contact between the indenter and the cusp, with the crack propagating toward the margins of cohesive failure. Conclusions: No significant differences were observed in life and Weibull probability calculations for Ceramage and Diamond Crown veneered onto Ti alloy abutments. Failure modes comprised composite veneer chippings.