Viscoelastic Properties and Durability of Photo-activated Soft Lining Materials for Denture Base

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1. On study plan in 1997. Pour commercial soft lining materials (CMs : CS, LN, SL, TS) were stored in each solution (DW : distiied water ; SC : isotonic sodium-chloride solution (0.9%) ; AS : artificial saliva) for 8 weeks at 37"*"C, with cleaning by using seven denture base cleansers in accordance with manufacture's instruction. And viscoelastic property and degradation of four CMs were investigated. The results obtained were as follows.(1) Before immersion the hardness(Hex) of the CMs ranged from 21.1 to 44.7 and these values increased up to 104.6-132.7% after storage in each solution for 2 weeks.(2) Before immersion the light reflectivity of the CMs ranged from 20 (none glossy surface to 70 (high glossy surface). The values of the CM (GS) were apt to decrease with increasing storage period and however the values of other CMs (LN, SL, TS) showed insignificant change.(3) Before immersion the contact angle of the CMs ranged from 35 to 40"*". After I day of storing in the DW and SC.the … More values of two CMs (CS, SL) were slightly lower than those before immersion. However, the values of all CMs showed insignificant change between 3 days and 8 weeks stored in each solution.(4) Before immersion the surface roughness of the CMs ranged from about 2' to 8 mum. These values increased with increasing storage period.(5) Many hollows on the specimen surface of three CMs (CS, LN, TS) were observed within 3-7 days from start of immersion.2. On study plan in 1998. On the basis of the data obtained in 1997. the nine experimental photo-activated soft lining materials (EPMs) were produced, which the powder as a main component was polyethylmethacrylate (PEMA) and the liquid consists of di-n-butyl phthalate (DBP) as plasticizer, ethylmethacrylate (EMA), photo-sensitizer, reducing agent and ethanol(Et), and the powder-to-liquid ratio was 1.38. in this study, four EPMs (M1D8E0, M1DSE0.5, M1D8E1, M1D8E1.5), which the hardness valus were almost equal to those of the CMs, were selected out among the nine EPMs. A formation of the liquid with four EPMs was EMA : DBP in the ratio 1 : 8 and Et added within 0-14.3wt%. Measurements were performed by means of the same as that described for the CMs. Although no conclusion has been reached because the change of viscoelastic property with the EPMs is now being continued, the results obtained till now are as follows. Namely it could be seen that the EPMs (MID8E0, M1D8E0.5) with lower percentage of Et exhibited an excellent durability Less