274 R ecent research has focused on the argon laser’s ability to achieve photopolymerization of compos- ite resins. 1-6 Photoactivated dental resins use a dike- tone initiator such as camphoroquinone and a reducing agent such as a tertiary amine to initiate polymeriza- tion. 7 This photoinitiator system is very sensitive to light in the blue region of the visible light spectrum, with the peak of activity centered around 480 nanome- ters (nm). 8 The argon laser is monochromatic and emits light over a narrow band of wavelengths in the blue green spectrum (457.9 to 514.5 nm), making it ideally suited to polymerize composite resins. Although con- ventional visible light curing units also emit energy centered around 480 nm, the energy is emitted over a much broader range. In addition, light from the argon laser is collimated, which results in more consistent This article is based on a thesis submitted by Dr. Talbot in partial fulfillment of the degree of Master of Science, Mayo Graduate School of Medicine. From the Department of Dental Specialties, Division of Orthodontics, Mayo Clinic. a In private practice, Salt Lake City, Utah. b Orthopedic Biomechanics Laboratory. c Biostatistician. d Data analyst. e Assistant Professor. * Deceased. Reprint requests to: Dr Joe Rebellato, Department of Dental Specialties, Mayo Clinic, 200 First St, SW, Rochester, MN 55905. Submitted October 1999; Revised and accepted January 2000. Copyright © 2000 by the American Association of Orthodontists. 0889-5406/2000/$12.00 + 0 8/1/l06069 doi:10.1067/mod.2000.106069 ORIGINAL ARTICLE Effect of argon laser irradiation on shear bond strength of orthodontic brackets: An in vitro study Travis Q.Talbot, DDS, MS, a Richard J. Blankenau, DDS,* Mark E. Zobitz, MS, b Amy L. Weaver, MS, c Christine M. Lohse, BS, d and Joe Rebellato, DDS e Rochester, Minn, and Omaha, Neb Argon lasers, due to their significant time savings over conventional curing lights, are being investigated for use in bonding orthodontic brackets. They are also being investigated for their ability to confer demineralization resistance on enamel. The purpose of this study was to evaluate the effects of argon laser irradiation on bond strength at 3 different laser energies (200, 230, and 300 mW) and at 3 unique time points of laser application (before, during, or after bracket placement). One hundred-fifty human posterior teeth were divided into 9 study groups and 1 control group. After debonding, the adhesive remnant index was scored for each tooth. There was no evidence of an effect of energy level on bond strength, P = .903, or of an interaction between timing of bracket placement and energy level, P = .858. When combining data across energy levels, the mean bond strength was significantly different between all 3 bracket placement groups, P < .001. In addition, the mean bond strength of teeth lased after bonding was significantly higher than the control group, P < .05. There were no statistically significant differences between adhesive remnant index scores among the 10 groups. Lasing the enamel before or after bonding does not adversely affect bond strength. Use of the argon laser to bond orthodontic brackets can yield excellent bond strengths in significantly less time than conventional curing lights, while possibly making the enamel more resistant to demineralization. (Am J Orthod Dentofacial Orthop 2000;118:274-9) power density over distance. 3 In contrast, the power density of light reaching composite from a conventional visible light curing unit decreases dramatically with distance, due to divergence of light from the source. 9 Finally, visible light curing units use bulbs, reflectors, and filters, which can degrade and decrease curing effi- ciency. 10 These factors may contribute to the increased efficiency of argon laser curing of composite resins compared with visible light curing. Since 1965, investigators have shown that exposing enamel to laser irradiation imparts some degree of protec- tion against demineralization under acid attack. 11 Yamamoto and Sato 12 embedded small pieces of lased enamel into several parts of human dentures. After 3 months, the nonlased area of the enamel showed a chalky white lesion, whereas no noticeable change was observed in the lased area. More recent studies have also shown that argon laser irradiation of enamel reduces the suscep- tibility of enamel to demineralization by up to 50%. 13-16 Westerman et al 17 showed that argon laser treatment at low energy could considerably alter the surface morphol- ogy while maintaining an intact enamel surface. Applying these principles to orthodontics, laser irra- diation has promising potential in that it may reduce the enamel decalcification that is often seen during fixed appliance treatment. The enamel surface can be lased before or after bracket placement. Alternatively, an argon laser can be substituted for the conventional cur- ing light during bracket placement. The adjacent enamel C E