Abstract: Objective To compare the effect of Er:YAG laser etching on the surface of enamel with the phosphoric acid etching. Methods A total of 104 extracted premolars were collected from 26 orthodontic patients. The four premolars of each patient were randomly divided into 4 groups (26 teeth/group),and the enamel etching were done respectively with different methods or at different parameters: group A 35% phosphoric acid etching and three Er:YAG laser groups (group B 200 mJ, 30Hz, 6/8 water; group C 250 mJ,30 Hz, 6/8 water; group D 300 mJ, 20 Hz, 6/8 water). Scanning electron microscope (SEM) was used to observe the morphology of enamel surface, and atomic force microscope (AFM) was used to measure the roughness of enamel. The shear bond strength (SBS) and adhesive remnant index (ARI) were surveyed after bracket bonding on the enamel surface. Results The enamel surface of four groups showed a pattern in which there was a distinct hollowing of prism centers, called typeⅠetching pattern, with a generalized roughening enamel surface. The honeycomb border of group C was the clearest. The roughness value was raised with increasing laser parameters, and the significant statistical difference (P <0.01) existed among the four groups. The highest peak-peak values of enamel surface were in group D. Group A showed lowest peak-peak values. Group C has the most similar enamel-bonding interface morphology to that of group A. The highest SBS was measured in group A, group C has no statistically significant difference with group A (P >0.05). No statistical difference of ARI scores were found in the four groups (P >0.05). Conclusion YAG laser etching with appropriate parameter can achieve the similar enamel surface morphology and SBS to phosphoric acid etching.

Key words: Er:YAG laser, etching, shear bond strength (SBS), scanning electron microscope (SEM), atomic force microscope (AFM), surface roughness