Load Fatigue Performance of Ceramic Onlays

Objective: The amount of remaining enamel influences the predictability of posterior ceramic onlay restorations. However, the amount of remaining enamel in posterior teeth is proportional to the amount of occlusal reduction required for the preparation. The purpose of this study was to evaluate the influence of different ceramic thicknesses and luting agents on the fatigue resistance of ceramic onlay restorations.

Methods: Extracted intact human third molar were prepared as followed: group NT, normal tooth with an ideal ceramic onlay preparation; group WT, worn tooth with an ideal ceramic onlay preparation.  The teeth were restored using a pressable ceramic (IPS Empress) with two different ceramic thicknesses (2 mm and 4 mm).  Two different resin-based luting agents were used (conventional resin (RelyX ARC) and self-adhesive resin (RelyX Unicem) to cement the ceramic onlays. A fatigue load of 150 N was applied on occlusal surface at a frequency of 72 cycles per minute and at an angle of 135 degrees to the long axis of the tooth. Restoration failure was indicated by a strain gauge (EA-06-062AP-120, Vishay Precision), which was cemented over the restoration margin. The independent variable recorded was the number of load cycles required to induce preliminary failure of the restorations. Significant difference in cycles to failure was analyzed using a Kruskal- Wallis test to evaluate the difference between the groups using a 95% confidence interval.

Results: Group NT cemented with conventional resin luting agent performed significantly better than all other groups (P<.05).  No significant differences were demonstrated in groups WT, irrespective of ceramic thickness or luting agent utilized.

Conclusion: Tooth preparation, ceramic thickness, and luting agent had a significant effect on the fatigue resistance of ceramic onlay restorations. The highest fatigue resistance cycle count was recorded when teeth had less amount of occlusal reduction and cemented with conventional resin cement.