RESUMO
Fiber reinforced composite (FRC) has been widely used in operative and prosthetic fields of dentistry and its use is expanding into the orthodontic field. The purpose of this study was to examine the changes of flexural properties of FRC reinforced with silica glass fiber (FibreKor(R), Jeneric/Pentron Inc., Wallingford, U.S.A.) according to the duration of water absorption. Specimens were grouped according to their shape as round and rectangular cross sections, and were immersed in distilled water at room temperature (23 degrees C) for 0 hour, 1 hour, 1 week, 15 days, 1 month and 3 months. The number of specimens was 5 for each duration and bending test was done using a torque tester. The flexural stiffness after 24 hour water immersion was reduced to 59% for round specimens and 25% for rectangular specimens and after 3 months of water immersion it was reduced to 29% and 19% stiffness of the 0 hour-specimen respectively. Yield flexural moment after 24 hour water immersion was reduced to 45% for round specimens and 76% for rectangular specimens and after 3 months of water immersion it was reduced to 29% and 60% stiffness of the 0 hour-specimen respectively. Ultimate flexural moment after 24 hour water immersion was reduced to 36% for round specimens and 76% for rectangular specimens and after 3 months of water immersion it was reduced to 25% and 37% stiffness of 0 hour-specimen respectively. Those results suggested that the flexural stiffness of FibreKor(R) decreased greatly after initial water immersion. Consequently, further research for the maintenance of strength against water will be necessary.