Flexural and thermal cycling of resins for veneering removable overlay dentures

Objectives: This investigation compared the effect of flexural and thermal cycling upon resins, bonded via adhesive primers to cobalt–chromium alloy to identify appropriate materials for veneering overlay dentures which may flex in function. Methods: The resins investigated were an acrylic resin, a crown and bridge resin, a urethane dimethacrylate and a hybrid composite resin systems. The first three were bonded via an adhesive primer/opaque system based upon 4-methacryloxyethyl trimellitate anhydride (4-META) and the last via one based on 10-methacryloxyldecyl dihydrogen phosphate (MDP). Cast alloy beams 30×4×0.8 mm with 2 mm resin veneers were stored in H2O for three days or three months, and subjected to 1000 thermo-cycles between 4 and 60°C, and/or 5000 flexural cycles to a displacement of 0.1 mm. Three-point bend testing was carried out in an Instron 4505 UTM. The increase in the flexural moduli of the cast beams, due to the addition of the resin spines, together with the displacements and loads at yield were recorded. Results: The adhesive resin systems varied in their abilities to withstand conditioning stresses, this appeared to reflect the rigidity of the resin component as well as the performance of the adhesive bond. Conclusions: While the composite/MDP system maintained the highest bond strength throughout the conditioning, its low displacement at yield indicates that it may be more suitable for rigid areas of a removable partial denture. Acrylic resin, with its high load and displacement at yield, make it the material of choice for veneering the more flexible saddle areas of partial dentures.