Selective targeting of protein, water and mineral in dentin using UV and IR pulse lasers: The effect on the bond strength to composite restorative materials

Previous studies have shown that during the laser irradiation of dentin and bone, thermal damage can be minimized by using a highly absorbed laser wavelength, laser pulses shorter than the thermal relaxation time of the deposited laser energy at that wavelength, and the addition of a layer of water to the tissue surface before ablation. The objective of this study was to investigate the influence of laser pulse duration and wavelength with and without the added water layer on the bond strength of composite to laser prepared dentin surfaces. The specific hypothesis that was tested was that thermal damage to the collagen matrix in dentin compromises the bond strength to composite restorative materials. Three laser systems were employed that were tuned to water, collagen and mineral absorption with pulse durations less than the thermal relaxation time of the deposited energy. The surfaces of human dentin were irradiated by laser irradiation from free-running and Q-switched Er:YSGG lasers (2.79-mum), pulsed CO2 lasers operating at 9.6-mum and a Q-switched Nd:YAG laser operating at 355-nm. A motion control system and a pressurized spray system incorporating a microprocessor controlled pulsed nozzle for water delivery, were used to ensure uniform treatment of the entire surface. Shear bond testing was used to evaluate the adhesive strength in order to access the suitability of laser treated surfaces for bonding. All the laser groups had significantly lower bond strengths than the positive acid etch control group. The highest bond strengths were for the short (<5-mus) Er:YSGG and CO2 groups with water. Laser groups without water had significantly reduced bond strengths.