The influence of immersion solutions on the viscoelasticity of temporary soft lining materials

Objectives. The purpose of this study was to examine the influence of laboratory immersion in a number of solvents on the viscoelasticity of temporary soft lining materials. It was an initial attempt to reproduce the changes seen clinically with a view to formulating more clinically relevant immersion regimes for the evaluation of these materials. Methods. Changes in the viscoelasticity of four temporary soft lining materials following immersion at 37 +/- 1 degrees C in 10% acetone/90% water, 20% acetone/80% water and hexane was compared to a control immersion in distilled water using a penetrometer modified to record creep strain and strain during recovery. Testing was performed at 2 h and 24 h and then at 2, 4, 7, 14, 21 and 28 d after sample preparation. Summary measures were used to describe individual specimen changes in derived values of initial and time dependent compliance and elastic recovery from 0-7, 7-28 and 0-28 d. Results. Immersion in hexane resulted in at least a 50% reduction in compliance over 28 d. There was a significantly greater reduction in compliance for hexane immersion than for any other solvent (p < 0.01). Immersion in 20% acetone resulted in an increase in compliance of around 1 mm/N after 1 wk compared with a reduction of up to 1 mm/N in distilled water. There was a reduction in elastic recovery for 3 out of 4 materials with 20% acetone/80% water solution. Changes in elastic recovery were smaller than those of compliance. Significance. The reduction in compliance with hexane immersion suggests that this, or similar solvents, may form the basis of more clinically relevant immersion regimes. This may contribute to the development of improved temporary soft lining materials.