ISSN 1054-660X, Laser Physics, 2009, Vol. 19, No. 7, pp. 1463–1469. © Pleiades Publishing, Ltd., 2009. Original Russian Text © Astro, Ltd., 2009. 1463 1 INTRODUCTION Laser irradiation is a technology that is widely used in dentistry. Since the development of the first Ruby laser by Maiman in 1962, lasers were severely tested to improve the traditional procedures used in dentistry, mainly with respect to caries removal [1] and detection [2], cavity preparation [3, 4], adhesion [3], root canal treatment [5], periodontics [6], caries prevention [7– 14], surgeries [15] and other applications. Nd:YAG lasers have been suggested as a potential tool for caries prevention because of the heating effects on enamel surface [12, 13, 16–18], speculated as being the main factor in inducing crystallographic and com- positional changes that favor an increase in enamel resistance to subsurface demineralization in vitro [19, 20]. However, as opposed to what happens with pig- mented tissues, the wavelength of Nd:YAG laser (λ = 1064 nm) is not effectively absorbed by dental enamel (absorption coefficient is less than 4 × 10 –2 cm –1 ) [20, 21]; therefore, the use of photoabsorbers before Nd:YAG laser irradiation on dental hard tissues is reported [22,23]. The aim of applying a dark dye before laser irradia- tion is to increase the absorption of the laser beam at 1 The article is published in the original. the surface of the enamel. In this case, the heat pro- duced due to laser absorption by the coating material is transmitted into the adjacent enamel. This tech- nique certifies the deposit of a short laser pulse energy to a small volume of tissue, avoiding excessive penetra- tion of the laser beam into deeper dental structures, and consequently, less risk of damage to dental pulp. The waterproof India ink is the dye most used as a photoabsorber for Nd:YAG pulsed laser [22–26]. However, the esthetics of treated teeth can be harmed because of it is difficult to remove, particularly from pits and fissures. A dye for application before Nd:YAG laser irradiation should have the following characteris- tics: biocompatibility, low surface tension, be easy to remove and help to promote enamel surface melting. Enamel surface melting requires heating up to 1200°C [17, 19, 20]. When this temperature range is reached, it is speculated that several chemical changes have occurred [19, 20] in the enamel microstructure, which can favor the clinical use of Nd:YAG lasers for preventive purposes. Conversely, with the purpose of choosing an irradiation condition for the purpose of clinical applications, the fluences used must be safe for ensuring the vitality of the pulp and periodontal tissues [27]. Increases of over 5.6°C can be considered poten- tially aggressive to the vitality of the pulp and temper- LASER METHODS IN CHEMISTRY, BIOLOGY, AND MEDICINE Absorption and Thermal Study of Dental Enamel when Irradiated with Nd:YAG Laser with the Aim of Caries Prevention 1 H. G. D. Boari a , P. A. Ana a , C. P. Eduardo b , G. L. Powell c , and D. M. Zezell a, * a Centro de Lasers e Aplicações—IPEN/CNEN-SP, Av. Prof. Lineu Prestes, 2242, ZIP 05508-900, São Paulo, Brazil b Departamento de Dentística, FOUSP, Av. Prof. Lineu Prestes, 2229, ZIP 05508-000, São Paulo, Brazil c School of Medicine, University of Utah Health Sciences Center, 15 North Medical Drive East, ZIP 84132, Salt Lake City, Utah, USA *e-mail: zezell@usp.br Received February 9, 2009 Abstract—It is widely recognized that Nd:YAG can increase enamel resistance to demineralization; however, the safe parameters and conditions that enable the application of Nd:YAG laser irradiation in vivo are still unknown. The aim of this study was to determine a dye as a photoabsorber for Nd:YAG laser and to verify in vitro a safe condition of Nd:YAG irradiation for caries prevention. Fifty-eight human teeth were selected. In a first morphological study, four dyes (waterproof India ink., iron oxide, caries indicator and coal paste) were tested before Nd:YAG laser irradiation, under two different irradiation conditions: 60 mJ/pulse and 10 Hz (84.9 J/cm 2 ); 80 mJ/pulse and 10 Hz (113.1 J/cm 2 ). In a second study, the enamel surface and pulp chamber temperatures were evaluated during laser irradiations. All dyes produced enamel surface melting, with the exception of the caries indicator, and coal paste was the only dye that could be completely removed. All irra- diation conditions produced temperature increases of up to 615.08°C on the enamel surface. Nd:YAG laser irradiation at 60 mJ/pulse, 10 Hz and 84.9 J/cm 2 promoted no harmful temperature increase in the pulp chamber (ANOVA, p < 0.05). Among all dyes tested, the coal paste was an efficient photoabsorber for Nd:YAG irradiation, considered feasible for clinical practice. Nd:YAG laser at 84.9 J/cm 2 can be indicated as a safe parameter for use in caries prevention. PACS numbers: 81.40.-z, 87.15.-v, 87.63.Hg, 87.64.Ee DOI: 10.1134/S1054660X09070160