[Rheological study of hard resin for crown and bridge].

Purpose: For the purpose of evaluating the flow properties influencing the formativeness of commercial hard resin pastes used in the construction of crowns and bridges, we examined the behaviors of various resin pastes and their temperature dependence during manipulation.

Methods: Five types of hard resins currently in use for the construction of crowns and bridges in the clinical setting, namely, New Meta Color INFIS, Solidex, Ceramage, Gradia, and Estenia C&B, were examined. The components and flow properties of each resin paste were investigated in relation to the dentine and enamel colors. The viscosities of the resin pastes before curing were measured by a cone-plate viscometer.

Results: Each resin paste demonstrated a non-Newtonian flow, and the flow curve showed a hysteresis loop, in which the upward and downward curves were different. When the shear stress at the beginning of the holding time of the flow curve (20 degrees C, 25 degrees C, 30 degrees C) of each resin paste was measured, the shear stress at 20 degrees C was found to be significantly higher than that at 25 degrees C and 30 degrees C, and the shear stress at 25 degrees C was found to be significantly higher than that at 30 degrees C. The viscosity was found to be higher at lower temperatures than at higher temperatures. Comparison of the shear stresses at the beginning and at the end of the holding time revealed that the stress at the beginning of the holding time was significantly higher than that at the end of the holding time for all except the Estenia C&B resin paste.

Conclusions: Each of the resin pastes used in the present study showed temperature dependence of its characteristics in the temperature range examined (20-30 degrees C) and thixotropic fluidity. However, the flow characteristics of these resin pastes differed significantly, suggesting that the flow characteristics may affect the manipulation of resin formativeness.