Age changes in the viscoelasticity of permanent soft lining materials.

Age-related changes in the viscoelasticity of an acrylic-based (Palasiv 62) and silicone (Molloplast-B) permanent soft lining material were evaluated in parallel clinical and laboratory longitudinal studies using a force/distance probe. Changes in the viscoelastic properties of Palasiv 62 in clinical use were characterized by a significant and continued reduction in both initial and delayed compliance. That is, the material became harder whilst still retaining the underlying pattern of viscoelasticity seen at baseline. Laboratory immersion in distilled water resulted in significant reductions in compliance values. These reductions were cumulatively similar to those seen clinically but did not occur as rapidly. There was evidence of small, continued reductions in the measured thickness of clinical linings of Palasiv 62. The clinical and laboratory compliance of Molloplast-B remained stable over time. Ageing did not affect the essential elasticity of this material.