Infrared laser irradiation of dental enamel using submicrosecond laser pulses with and without an applied water layer: effect on bond strength to restorative materials

Abstract

Previous studies have shown that during IR laser irradiation at CO₂ and Er:YAG laser wavelengths, residual particles of fused non-apatite calcium phosphate phases accumulate that may inhibit adhesion to restorative materials. A layer of water added to the enamel surface before ablation prevents the accumulation of such phases. 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 enamel surfaces. The surfaces of bovine enamel were irradiated by three lasers systems: a 0.5-μs Er:YSGG laser. a 25-μs Er:YAG laser and a 5-μs TEA CO₂ laser operating at 9.6-μm. 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. There was no significant reduction in the shear-bond strength of enamel to composite for the shorter erbium laser pulses if a water-spray was not used, in contrast to previous results for the 200-μs free-running Er:YAG laser in which the water-spray resulted in significantly higher bond-strengths. Shear-bond strengths for both erbium laser systems were significantly higher than for the CO₂ laser irradiated samples and the negative control (no acid-etch) but significantly lower than the positive control group (phosphoric acid-etch). The application of the water-spray markedly influenced the surface morphology for all three laser systems with the most uniform surface preparation being produced by the 25-μs Er:YAG laser and the 5-μs CO₂ laser with the water-spray.