ORIGINAL ARTICLE Effective single-charge end point of cordless light-emitting diode light-curing units Robert H. Judy, a William J. Dunn, b Arpita B. Patel, c and Timothy Swanson d Fairfield, Calif, and San Antonio, Tex Introduction: The purpose of this study was to evaluate the battery lives of cordless light-emitting diodes (LEDs) and their effect on orthodontic bracket bond strength. Methods: One hundred eighty-six metal orthodontic brackets were bonded to extracted molars. Two LED light-curing units (L. E. Demetron [SDS/Kerr, Orange, Calif] and Ortholux [3M Unitek, Monrovia, Calif]) were evaluated. Each light was used to bond 93 specimens. One bracket was bonded every 5 minutes until the battery ran out. The lights were activated for 20 seconds, then automatically turned off for 40 seconds every minute (33% duty cycle) without recharging. Bonded specimens were stored in water at 37°C for 24 hours and then subjected to shear force with a universal testing machine until bracket failure. Results: Repeated measures ANOVA detected significantly weaker mean shear bond strength and fewer consecutive cures with the Ortholux compared with the L. E. Demetron light-curing unit. However, when the first 5 time points were excluded, there were no differences between the 2 lights, demonstrating that the lights performed similarly after the first 20 minutes of operation Just before battery failure, both lights still provided the same power density as at the beginning. Conclusions: Both light-curing units provided adequate power density for up to 2 hours without recharging at a 33% duty cycle. There was no significant decrease in power in cordless LED light-curing units as the battery life approached its end point. (Am J Orthod Dentofacial Orthop 2006;130:378-84) V isible light-curing units (LCUs) play an impor- tant role in the practice of modern clinical orthodontics by providing rapid resin-based composite polymerization on command. Resin poly- merization occurs when carbon double bonds in methacrylate monomers are selectively converted into single bonds, propagating polymer growth, by free radicals created by the activation of diketone photoini- tiators by light in the blue range of the visible spectrum at approximately 468 nanometers (nm). 1 Currently, most sources of visible blue light used in orthodontic practice are quartz-tungsten-halogen (QTH) LCUs. De- spite their popularity, QTH lights have several draw- backs. Conventional units operate by heating a tungsten filament, similar to an incandescent light bulb, to generate light; they also generate a significant amount of heat, and the process in inherently inefficient be- cause only 1% of the initial energy input is actually converted into blue light for composite polymeriza- tion. 2 The heat generated from QTH light systems can cause blistering of sensitive light filters and discolora- tion of the reflectors, and the cooling fan can be noisy and disperse any bacterial aerosol in the patient’s mouth. 3 In addition, halogen bulbs last approximately 50 hours 4 and should be replaced every 6 months. 5 Studies have shown that private dental offices do not routinely service their QTH LCUs, and many LCUs have an output that is inadequate for polymerization. 6,7 Other methods for curing dental composite resins use xenon plasma arc lights and argon lasers. Although these lights dramatically reduce the curing time for dental composite resins, they are substantially more expensive and bulky. In 1995, after improvements in blue light-emitting diode (LED) semiconductor technology, LEDs were proposed as a light source for the polymerization of light-cured resins. 8,9 LEDs are solid-state light sources that convert electrical energy directly into light. 10 Because they are solid-state devices, they can be manufactured to extremely small dimensions and with- stand mechanical shock and vibration with low failure rates. LEDs are in everyday household appliances such as indicator lights and sensors, and in the dashboard instrument panels of automobiles, and they can have a lifetime of up to 10,000 hours. 11 LEDs are manufac- tured by metal-organic chemical vapor deposition of different semiconductor materials in films that are a Department of Orthodontics, Travis Air Force Base, Fairfield, Calif. b Director of Research and Biomaterials, Wilford Hall Medical Center, Lack- land Air Force Base, San Antonio, Tex. c Private practice, San Antonio, Tex. d Department of Orthodontics, Tri-Service Orthodontic Residency Program, Lackland Air Force Base, San Antonio, Tex. Reprint requests to: Dr William J. Dunn, 3701 Point Clear Dr, Ocean Springs, MS 39564; e-mail, william.dunn@keesler.af.mil; darkhorse@cableone.net Submitted, October 2004; revised and accepted, February 2005. 0889-5406/$32.00 Copyright © 2006 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2005.02.017 378