[Visible light cured resin. Change of quantity of remaining double bonds in the surface low conversion layer by FT-IR method].

The quantity of the remaining double bonds (RDB) in polymerized visible light cured resins has been determined. Five trial unfilled resins, eight commercial composite resins and three commercial crown and bridge resins were investigated by Fourier transform infrared spectrophotometer with the liquid-film method. Infrared absorbance was measured before irradiation and at various times after irradiation. The quantity of RDB was determined and the data expressed as percentage of the total amount of double bonds in the unpolymerized resins. The quantity of RDB of five trial unfilled resins decreased linearly corresponding to the logarithmic time after the start of irradiation. The difference in the quantity of RDB at 5 min and decreasing rate of RDB could be seen in accordance with the kind of monomer. Among five trial unfilled resins, one with BMPEPP (BPE-200) used as monomer gave the smallest RDB, and one with 4 PN-(TF)2-(EMA)6 used as monomer gave the largest value. The quantity of RDB in the unfilled resin with Tri-EDMA at 5 min decreased in accordance with the irradiation time, but after 1 month, it showed almost the same value irrespective of the irradiation time. The quantity of RDB of commercial composite resins and crown and bridge resins decreased linearly corresponding to logarithmic time. In all commercial resins, the quantity of RDB became small when the base monomer was Bis-GMA but large when it was UDMA.