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 reprodu ce the changes seen clinically with a view to formulating more clinica lly 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 imm ersion in distilled water using a penetrometer modified to record cree p 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. Su mmary measures were used to describe individual specimen changes in de rived values of initial and time dependent compliance and elastic reco very 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 signi ficantly 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 re duction of up to 1 mm/N in distilled water. There was a reduction in e lastic recovery for 3 out of 4 materials with 20% acetone/80% water so lution. Changes in elastic recovery were smaller than those of complia nce. Significance. The reduction in compliance with hexane immersion s uggests that this, or similar solvents, may form the basis of more cli nically relevant immersion regimes. This may contribute to the develop ment of improved temporary soft lining materials.