Comparative Study of the Ultrastructure and Adhesive Properties of Enamel Prepared by Er: YAG Laser and Conventional Bur.

Purpose: The objective of the study was firstly to examine the surface morphology of enamel under scanning electron microscopy (SEM), following Er:YAG laser ablation and conventional high-speed bur preparation, with and without acid etching, and secondly to investigate the adhesion of composite resin (CR) to those surfaces by means of a shear bond strength (SBS) test. Materials and Methods: The buccal surface of 42 human extracted molars were ground flat using 500-grit silica carbide paper under water. The surfaces were subjected to simulated cavity preparation treatment and placed into groups: (1) Er:YAG laser ablation (350 mJ,10 Hz, VSP), (2) Er:YAG ablation plus acid etching (37% phosphoric acid), (3) conventional bur (Diamond Fis Z10), (4) conventional bur plus acid etching. Three teeth from each group (n = 3) were examined under SEM (Philips XL 30) to determine the nature of the treated surface. The remaining teeth in each group (n = 10), except group 3, underwent an SBS test to investigate the bond strength of CR to those surfaces, using a universal testing machine (Hounsfield; Hounsfield, UK) following ISO standard TR 11405. Results: Er:YAG laser irradiation resulted in roughened, irregular whitish enamel surfaces, resembling a typical Type I or Type II acid-etch pattern. Surfaces prepared by conventional high-speed bur exhibited a diffuse smear layer that was removed following acid etching. Shear bond strength testing revealed that there was no statistically significant difference in values between acid-etched/laser-ablated (15.89 MPa ± 1.90) and conventionally prepared and etched enamel surfaces (16.55 MPa ± 3.88) (p > 0.05). However, samples of Er:YAG irradiation without acid etching produced significantly lower (p < 0.05) SBS values (10.10 MPa ± 3.57). Discussion: Er:YAG laser irradiation produced surfaces visually similar to an acid-etch pattern, although without a smear layer. Both the conventional bur- and laser-prepared samples exhibited similar surfaces following acid etching. Enamel bond strength produced by Er:YAG laser ablation is comparable to that obtained by the conventional bur. However, within the limitations of this study, Er:YAG irradiation alone cannot be recommended as a viable alternative to acid etching to increase bond strength to enamel. Conclusion: It was concluded that the Er:YAG laser compared very favourably with the conventional bur in preparing enamel surfaces for restoration with composite resin. Of clinical significance, however, is that while the surface produced by the Er:YAG laser is similar to the conventionally prepared, etched enamel surface, it still requires acid etching to obtain an equivalent bond strength. [ABSTRACT FROM AUTHOR]