Effects of soft-start irradiation on the depth of cure and marginal adaptation to dentin

Marginal adaptation of four resin composites, Clearfil APX, Estelite, Silux Plus and Z-100 cured with two irradiation methods (soft-start or high-power start) of a commercial soft-start halogen lamp unit (Elipar Highlight) were evaluated by measurement of the wall-to-wall contraction gap width. One-hundred and sixty cylindrical cavities, 3 mm in diameter and 1.5 mm in depth, were prepared in extracted human molars. The 80 cavity walls were treated with the Megabond system and each 20 cavities were filled with one of four resin composites. Then, each 10 fillings were irradiated by the soft-start method (soft-power light for 10 seconds followed by high-power light for 30 seconds) or high-power light for 40 seconds. The other 80 cavity walls were treated with an experimental bonding system consisting of 0.5M EDTA as a conditioner, 35% glyceryl mono-methacrylate as a primer and Clearfil Photo Bond as a bonding agent. The cavities were restored wtih the four resin composites and two irradiation methods, the same as the Megabond group. The contraction gap was measured with a light microscope and expressed in % of the cavity diameter. In addition, the curing capability of these two light sources was evaluated by measurement of the curing depth of the four resin composites using a split Teflon mold 4 mm in inner-diameter and 8 mm in height. Marginal gap formation of Clearfil APX, Estelite and Silux Plus with the experimental bonding system was completely prevented regardless of the kind of irradiation methods used. The deterioration of marginal adaptation caused by the Megabond system could not be improved by use of the soft-start method programmed in Elipar Highlight.