Fatigue resistance of removable orthodontic appliance reinforced with glass fibre weave.

The aim of this study was to measure the fatigue resistance of fibre-reinforced composite (FRC) reinforced polymeric parts of a removable orthodontic appliance beside the clasp. The effect of quantity and position of FRC-reinforcement were investigated. In addition, the influence of water storage on the fatigue properties was determined. The test specimens for eight groups (n=6) were manufactured from autopolymerizing acrylic resin. Polymethylmethacrylate pre-impregnated woven glass fibre was used as reinforcement of acrylic resin specimens at the region of steel wire clasp. The test specimens of the control group were not reinforced. In the second group, the test specimens were reinforced with one fibre layer (thickness: 0.06 mm) on the tension side, and in the third and fourth group with two fibre layers. Fatigue resistance was measured by applying repeated bending force to the clasp. The highest fatigue resistance values were achieved when the test specimens were fibre-reinforced with two fibre layers. The lowest fatigue resistance values resulted when the test specimens were not reinforced (P=0.046, anova). Water storage had a tendency to decrease the fatigue resistance in all fibre reinforced test specimen groups. The results suggest that use of the woven polymer pre-impregnated glass FRC-reinforcement increases the fracture resistance of orthodontic appliance made of acrylic polymer.