Changes in properties of short-term-use soft liners after thermocycling

The objectives of this study were to determine the influence of thermocycling on the changes of elastic modulus (EM) and colour, and to evaluate cytotoxicity after repeated elution of short-term-use soft liners. Three short-term-use soft liners [soft acrylic-based Coe Comfort (CCM), Coe Soft (CST) and Soft Liner (SFL)], and long-term-use silicone-based Tokuso Soft Liner (TSL) acting as a control were studied. EM was measured at baseline and after thermocycling at 5-55 degreesC for 500, 1000, 1500 and 2000 cycles. For the colour measurement, specimens in discs 20 mm in diameter and 1 mm in thickness were prepared, attached to a denture base resin plate, and then thermocycled as above. Colour change (DeltaE*) was measured according to the Commission Internationale de l'Eclairage (CIE) L*, a*, and b* scale on a spectrophotometer. For the cytotoxicity evaluation, specimens were eluted for 24 h in culture media repeatedly up to four times, and MTT assay (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) was performed. EM of CCM and CST increased up to 1500 and 1000 cycles of thermocycling respectively. EM of SFL gradually increased up to 2000 cycles, and that of TSL increased after 500 cycles and did not change after then. DeltaE* of soft liners after 2000 cycles except CCM were 3.68-8.65. EM increased up to 1000-1500 cycles, and perceivable colour change was observed after 2000 cycles in most materials. Therefore, short-term-use soft liners should be used within a limited time, although the cytotoxicity decreased after repeated elution.