Temperature generation and transmission in root dentin during Nd:YAG laser irradiation for preventive purposes

Abstract

High-intensity lasers are widely used in dental procedures and the heating produced on the surface is necessary to ensure protective activity against the development of caries and erosion lesions. However, caution should be exercised regarding the spread of heat to the pulp, periodontal tissue and alveolar bone, which can cause harm to these tissues. This study sought to evaluate the generation and transmission of heat in the root dentin and adjacent tissues during irradiation with Nd:YAG laser for preventive activity. For that, 15 lower incisor human teeth had an area of 9 mm2 of root dentin irradiated with Nd:YAG laser (λ=1.064 μm, 10 Hz, 60 mJ/pulse, 84.9 J/cm2) for 30s. During irradiations, pulpal temperature was evaluated by fast-response thermocouples, while surface temperature and heat distribution on surrounding tissues were measured by infrared thermography. It was observed a mean surface temperature increase of 293.48±30.6° C in root dentin surface, and 15.85 ± 39.6° C below the irradiated area, 11.72 ± 8.7° C above the irradiated area, 19.77 ± 4.9° C at 1 cm laterally and 7.03 ± 2.7° C at 2 cm laterally to the irradiated area. The mean pulpal temperature augment registered was 6.5±1.4° C. It can be concluded that Nd:YAG laser irradiation promoted surface temperature rises that suggest chemical changes on dentin; however, the temperature increases generated in the adjacent tissues (region of periodontal ligament) and in the pulp chamber may be dangerous in future clinical application considering the irradiation time of 30 s made in this study. Therefore, this laser protocol can be used as long as the irradiation time is reduced in future studies.