Factors Affect Fracture Resistance of Three-unit Zirconia Posterior Bridge

Objectives: The aim of this study was to investigate the effect of connector size and position of fracture resistance of dental zirconia three-unit bridge. Method: A standard model for mandibular 3-unit bridge was prepared from dentiform model (Nissin) using polyurethane die material. Zirconia bridge cores were fabricated by using Cercon system and cerconbase30 (Dentsply) system with 9 mm2 (G1 and G2) or 12 mm2 (G3) in connector area. The pontics of G1 and G3 were placed in the default position from CAD program, but the pontic of G2 was repositioned to premolar-direction about 1 mm. After cementation (ZPC), the fracture load of zirconia bridge was obtained by loading at the center of pontic with steel ball at a cross-head speed of 1 mm/min using Instron machine. Fracture load of uncolored vs. colored zirconia core was compared with G1 and G2 configurations. Ten specimens of each group were tested and the data were statistically compared at a P<0.05 level. Results: Mean fracture loads of (uncolored and colored) for G1, G2, and G3 (uncolored) were (1271±148, 1312±92), (803±138, 827±117), and (2094±197), respectively, There were significantly differences among groups (P<0.05). No significant difference was found fracture loads between uncolored and colored cores. Conclusions: The size of connector area as well as the position of pontic significantly affects the fracture resistance of posterior three-unit mandibular zirconia bridge core. Design of zriconia bridge should be designed with considered with mechanical performce.