Retention of Posterior RBFDPs With Different Designs After Chewing Simulation

Objectives: To evaluate the effect of different preparation and framework designs on retention of posterior RBFDPs made from monolithic zirconia.
Methods: Forty-eight caries-free upper premolars and forty-eight upper third molars were used in this study. The teeth were randomly divided into six main groups (n = 8 each) according to the preparation design of the two RBFDP abutments (1 mm rest/no retainer wing, 3 mm rest/no retainer wing, 1 mm rest/one retainer wing, 3 mm rest/one retainer wing, 1 mm rest/two retainer wings, 3 mm rest/two retainer wings). All RBFDPs were milled from monolithic zirconia (KATANA Zirconia ML/HT). RBFDPs were bonded using Panavia V5 with its corresponding primers. RBFDPs underwent thermodynamic loading (10 kg, 1,200,000 cycles). Retention was evaluated using a universal testing machine in tension at a crosshead speed of 2 mm/min. Failure modes were evaluated using a microscope. Data was statistically analyzed by Kruskal-Shapiro-Wilk followed by Mann-Whitney with Bonferroni’s correction.
Results: Survival rate after chewing simulator were 75% (group 1), 62.5% (group 2) and 100% (the other groups). The mean initial retention was 31 N(±42), 70 N(±64), 286 N(±139), 302 N(±257), 748 N(±290), 766 N(±268) for groups 1-6, respectively. Designs with two wings (1 and 3 mm rest) showed significant higher bond strength than designs with no or one wing only (p<0.05).
Conclusions: RBFDPs with the modified design exhibited promising bond strength. Designs of two additional wings should be preferred over designs with rest but without retainer wing or only one additional retainer wing.