Relationship of Occlusal Force to Fracture Potential of Posterior Ceramic FPDs

Objective: 1) To test the hypothesis that no significant relationship exists between the magnitude of occlusal force and the incidence of chipping or bulk fracture of the ceramic crowns, pontics or connectors of the FPDs; 2) To test the hypothesis that there is a critical level of maximum biting force to connector height that predisposes to fracture. Methods: Baseline data were obtained for selected patients to include maximum occlusal force measurement with a gnathodynamometer. Thirty ceramic FPDs were designed and processed using the heat-pressed technique and an experimental core (EXC) ceramic. Connector heights and widths were measured for each FPD. One of two cements was selected based on a random number table (a reinforced glass ionomer cement or a dual cure resin cement). Patients were recalled one year and two years after cementation and were evaluated using eleven (11) clinical criteria. FPDs were examined by two independent clinicians and rankings for each criteria were made from 1 to 4 with 4=excellent and 1=unacceptable. Results: The mean maximum occlusal force recorded for 18 patients (17 females, 1 male) was 461 N with a standard deviation of ±246. The data were analyzed by time via logistic regression with a term for force. The results indicated that there was no statistically significant effect of maximum occlusal force on the incidence of chipping or fracture at either the first year or the second year recall exam (p = 0.445 and p = 0.230, respectively). Conclusion: Further analysis with a larger sample size is needed to evaluate the effect of occlusal force on fracture of an all-ceramic restoration. Initial results on a small sample size support the two hypotheses. This study was supported by Ivoclar Vivadent, Inc.