Retention Durability of Posterior Cantilever RBFDPs with Different Designs
Objectives: To evaluate the effect of different preparation/framework designs on the retention of monolithic zirconia posterior cantilever RBFDPs replacing molars.
Methods: Extracted caries-free human premolars and third molars were embedded in auto-curing resin to create models with an edentulous space of molar width (10.5 mm). Abutment teeth were prepared according to four groups (n=16), each design have 2 separated RBFDPs (premolar side and molar side) touching in the middle of the missing molar space with interlocking: narrow rest with 1 (N1W) or 2 wings (N2W); wide rest with 1 (W1W) or 2 wings (W2W). RBFDPs were milled from monolithic zirconia (KATANA Zirconia HT), and adhesively bonded using Panavia V5 with the corresponding primers. RBFDPs underwent dynamic loading (98 N, 1,200,000 cycles, 0.3 mm horizontal movement). The loading point was located at the 30°-buccal slope, 1 mm from the buccal cusp, 2 mm from the central fissure on the margin between the 2 RBFDPs. Debonding was performed with 2 wire loops applied proximally between the teeth and the pontic basis in a universal testing machine at a crosshead speed of 2 mm/min. The tensile force required for the failure (debonding or fractures) was recorded. Failure modes were evaluated using a microscope.
The data was statistically analyzed by three-way ANOVA followed by two-way ANOVA if necessary because of interaction.
Results: Survival rate after chewing simulation was 87.5% for N1W group, 93.75% for W1W group and 100% for all other groups. There was a significant influence of the number of wings on debonding force as well as of the type of rest for premolar side and of the side for narrow rest (p≤0.05).
Conclusions: Although posterior cantilever RBFDPs with the modified design did not show an increase in the bond strength, designs with two wings remain preferable because they show a survival rate of 100% after chewing simulation.