Influence of an optically thick water layer on the bond-strength of composite resin to dental enamel after IR laser ablation

Abstract

Background and objectives: Several studies of hard tissue ablation with Er:YAG lasers have shown that the addition of an optically thick water layer ( approximately 1 mm) added to the surface of dental enamel before each incident laser pulse, profoundly influences the rate and efficiency of ablation and the resulting surface morphology. The objective of this study was the determination of laser parameters which result in clinically useful bond strengths without the need for phosphoric acid etching. The hypothesis to be tested was that laser irradiation through a relatively thick layer of water would result in a surface to which composite could be bonded with bond strength similar to surfaces etched with phosphoric acid. This hypothesis is predicated on the assumption that the water prevents the formation of non-apatite calcium phosphate phases on the enamel surface.

Materials and methods: In this study, a calibrated syringe pump and a motion control system were used to uniformly treat flat enamel surfaces using free-running Er:YAG laser pulses with and without water, and 9.6 mum CO(2) laser pulses on a dry surface for comparison. The rate of water delivery that resulted in the most efficient ablation was determined by profiling the resulting laser incisions using optical coherence tomography. In addition, enamel surfaces of 5 x 5 mm(2) were uniformly treated and the resulting surface morphology was examined using synchrotron radiation-fourier transform infrared spectroscopy (SR-FTIR), and optical and electron microscopy. The influence of the modified surface morphology on the adhesion of composite resin was investigated.

Results: The shear-bond strength of composite bonded to enamel surfaces irradiated at intensities clinically relevant for caries removal approached values measured for conventional acid etching when the water delivery rate was optimized.

Conclusions: This study demonstrates that composite restorative materials can be directly bonded to laser prepared surfaces without the necessity of further surface preparation and acid etching and that the addition of a thick water layer ( approximately 1 mm) prevents the formation of undesirable CaP phases that compromise adhesion to restorative materials. 2003.