Viscoelastic and adherence properties of dental relining materials

The viscoelastic properties of three classes of soft relining materials (acrylic resins, silicones, and EVA copolymers) were studied comparatively. Their behaviors were investigated by in vitro tests at a frequency omega = 1 Hz, which stimulates the masticatory cycle. The experimental parameter was the temperature (T). Black graphs giving the variations of the stiffness K--proportional to the complex viscoelastic modulus Ex(T) omega--according to the phase angle delta, were used for a predictive approach to increase the comfort of removable dentures. Cole-Cole diagrams, describing the variation of the loss modulus E"(T) omega in relation to the storage modulus E'(T)omega additionally provide quantitative data. The values obtained were related to the noninteger parameter h used for modelization of the viscoelastic behavior of the materials by means of nonlinear Zener models. An attempt was made to correlate the experimental data to the viscoelastic energy loss observed when instability of the prosthetic structure occurs. This attempt takes into account the formation of "cracks" (areas of inadaptation) between the prosthetic intrados and the mucosa.