THE EFFECT OF ARF-EXCIMER LASER IRRADIATION OF THE HUMAN ENAMEL SURFACE ON THE BOND STRENGTH OF ORTHODONTIC APPLIANCES

This study investigated enamel laser conditioning as an alternative to acid etching in bracket therapy. In preliminary experiments optimal l aser parameters for achieving a bond strength of 6-10 N/mm(2) were def ined. Enamel surface morphology was assessed and the ablation depth wa s measured on serial enamel sections. Thirty human molars were exposed to 193 mn ArF-excimer laser radiation (energy density: 260 mJ/cm(2)) by single pulse application of 23 nanoseconds. Thirty molars were etch ed with phosphoric acid (37 %) for 60 seconds. The brackets from the t reated molars and 30 untreated molars were debonded vertically for ten sile bond strength measurement. Roughened enamel surfaces were attaine d by 450 and 900 laser pulses with a mean ablation depth of 10.13 +/- 4.84 mu m. After 1-10 laser pulses, the enamel surface appeared intact . The tensile bond strength was 6.63 +/- 2.18 N/mm(2) in the laser-tre ated group (1 pulse), 8.75 +/- 3.61 N/mm(2) in the acid-etched group, and 4.61 +/- 3.15 N/mm(2) in the untreated group. We conclude a laser- selective ablation of the membranous enamel pellicle. Since the irradi ated area can be adapted to bracket base and the enamel surface remain s morphologically intact, pulsed ArF-excimer laser treatment seems to be superior to the acid etching technique.