In vitro fracture resistance of fiber reinforced cusp-replacing composite restorations.

Objectives: To assess the fracture resistance and failure mode of fiber reinforced composite (FRC) cusp-replacing restorations in premolars.

Methods: Forty-five extracted sound upper premolars were randomly divided into three groups. Identical MOD cavities with simulated buccal cusp fracture and height reduction of the palatal cusp were prepared. In Group A two layers of resin impregnated woven continuous FRC (EverStick Net) were applied. In Group B one layer of unidirectional continuous FRC (EverStick) was used. In Group C no fibers were applied (control). Subsequently, all teeth were restored with resin composite (Clearfil Photo Posterior), subjected to thermocycling (6000 x 5-55 degrees C) and static load tests. Load until fracture was registered for each tooth. Simultaneously, fracture propagation was monitored using acoustic emission analysis (AE). Failure modes were visually assessed.

Results: Weibull analysis revealed a characteristic strength and Weibull modulus (m) at 2364.8 N for Group A (m=8.9), 2437.9 N for Group B (m=5.9) and 2160.3N for Group C (m=13.6). Fracture loads were not significantly different (ANOVA, p>0.05). Teeth with FRC showed less fractures below the cemento-enamel junction (CEJ) (38% and 23% for Groups A and B, respectively) than teeth without FRC (93%) (chi-square, p<0.05). The control group showed the least AE energy signals.

Significance: The results suggest that glass FRC does not increase fracture load of premolars with cusp-replacing restorations. However, FRC has a beneficial effect on the failure mode. Woven fibers give more consistent results than unidirectional fibers.