The effect of ArF-excimer laser irradiation of the human enamel surface on the bond strength of orthodontic appliances.

Abstract

This study investigated enamel laser conditioning as an alternative to acid etching in bracket therapy. In preliminary experiments optimal laser parameters for achieving a bond strength of 6-10 N/mm2 were defined. Enamel surface morphology was assessed and the ablation depth was measured on serial enamel sections. Thirty human molars were exposed to 193 nm ArF-excimer laser radiation (energy density: 260 mJ/cm2) by single pulse application of 23 nanoseconds. Thirty molars were etched with phosphoric acid (37%) for 60 seconds. The brackets from the treated molars and 30 untreated molars were debonded vertically for tensile bond strength measurement. Roughened enamel surfaces were attained by 450 and 900 laser pulses with a mean ablation depth of 10.13 +/- 4.84 microns. After 1-10 laser pulses, the enamel surface appeared intact. The tensile bond strength was 6.63 +/- 2.18 N/mm2 in the laser-treated group (1 pulse), 8.75 +/- 3.61 N/mm2 in the acid-etched group, and 4.61 +/- 3.15 N/mm2 in the untreated group. We conclude a laser-selective ablation of the membranous enamel pellicle. Since the irradiated area can be adapted to bracket base and the enamel surface remains morphologically intact, pulsed ArF-excimer laser treatment seems to be superior to the acid etching technique.