Impact of polyethylene fiber-reinforced composite resin and thermomechanical cycling on dentin bond strength.

This study evaluated the microtensile bond strength (μTBS) and fracture pattern of direct composite resin reinforced with polyethylene fiber (Ribbond®) on dentin substrate after thermomechanical cycling (TMC). Dentin blocks (dentin thickness=2 mm) were obtained from forty human third molars and randomly divided into four groups (n=10) according to type of restoration (composite resin with or without Ribbond®) and to whether they were or were not subjected to TMC (100,000 cycles of 50 N / 2 Hz / 1-minute baths of 5 and 55ºC). The 1-mm-thick square-shaped specimens were submitted to μTBS testing in a universal testing machine at 0.5 mm/min. The fracture patterns were assessed by stereoscopic magnifying glass (30X magnification). The μTBS (in MPa) and failure pattern data were subjected to the generalized linear model and G tests (a=0.05). Neither the polyethylene fiber nor TMC had any statistically significant effect (p=0.196 and p=0.136, respectively) on the μTBS of the composite resin to dentin. Adhesive failures were more prevalent in the composite resin group compared with the Ribbond-containing group when subjected to TMC. Additionally, the composite resin containing Ribbond® showed a higher proportion of cohesive failures in composite resin than the resin groups not containing this fiber, irrespective of TMC. It was concluded that reinforcing the direct layer of composite resin with Ribbond® polyethylene fiber did not influence the adhesive resistance to dentin, even when subjected to TMC. However, its incorporation did result in a higher frequency of cohesive failures in resin after TMC.