Fracture Strength of Posterior Crowns made of Adoro and Gradia Fiber-reinforced Composites.

Aim: The aim of this study was to assess the fracture strength of posterior crowns made of Adoro and Gradia fiber-reinforced composites (FRCs). Materials and methods: In this in vitro, experimental study, extracted sound 37 maxillary first and second premolars were selected. A celluloid index was taken from teeth and the teeth received crown preparation. Impressions were made and poured. Composite crowns were fabricated of Adoro and Gradia composite resins. After curing, the teeth were immersed in distilled water for 24 hours and thermal cycled for 6,000 cycles between 5 and 55°C. Load was applied at a crosshead speed of 1 mm/minute and the fracture strength was measured. Specimens were inspected under a stereomicroscope to determine the mode of failure. Results: The fracture strength was 1,631.77 N for Gradia and 1,569.84 N for Adoro. The difference between the fracture strength of the two groups was not significant (p > 0.05). The mode of failure was cohesive in composite in 7 specimens and adhesive between composite and fiber in 12 specimens in the Gradia group. In the Adoro group, the mode of failure was cohesive within composite in 11 specimens and adhesive between composite and fiber in 7 specimens. Complete tear of fiber did not occur in any group. Conclusion: The fracture strength of Gradia and Adoro composites is not significantly different. Clinical significance: Cohesive fracture within the fiber did not occur in any case in our study and the mode of failure was adhesive at the fiber-composite interface or cohesive within the composite in most specimens. Keywords: Composite resin, Crown, Gradia, Laboratory.