Objectives: The purposes of this in vitro study were to investigate the water uptake characteristics and color changes between condensation- and addition-silicone-based soft liners, and if there were differences, to clarify the reasons for those differences. Methods: The materials used for this study were Evatouch (EVA, condensation type, Base: Lot No. FG02, Catalyst: No. FI01) and Evatouch Super Normal (EVA/SN, addition type, Lot No. 031211). Seven specimens (20mm x 18mm x 1.5mm) were made using specially constructed plaster molds and vulcanized according to the manufacturer's instructions. Water uptake measurements were determined gravimetrically at 37°C in distilled water and were compared after 1 day and 14 days. The specimens were weighed on an analytical balance A-200 (Denver Instrument Co.) to the nearest .0001g. Color changes were evaluated on specimens that were stored in testing solutions (saline, instant coffee, and olive oil mix with beta-carotene). The color was measured with a spectrophotometer CM 1000 (Minolta Camera Co.) and the specimens were evaluated with a white background made of ceramics (No. 1633368: Minolta Camera Co.). Permeability for SiOH (condensation type) and vinyl base (addition type) was measured using Infrared Reflection Absorption Spectroscopy (FTIR-8400S, Shimadzu Co.) and ATR attachment (Dura Sample IR II, ASI Co.). Results: Huge water uptake and severe color changes were observed in EVA (condensation type) (p<0.01). The permeability(%) of EVA is less than EVA/SN and at 10 minutes permeability is 18% in EVA/SN versus 1% in EVA. Conclusions: The results suggest the following: (1) severe water uptake and color change took place in condensation-silicone-based soft liners; (2) the permeability(%) of their reaction products was completely different; and (3) the differences of water uptake and color change depended on their chemical reaction and permeability.

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