Microstructural changes of enamel, dentin–enamel junction, and dentin induced by irradiating outer enamel surfaces with CO₂ laser

The microstructural changes of enamel, dentin–enamel junction (DEJ), and dentin after CO₂ laser irradiation were studied. Buccal enamel surfaces of human third molars about 2 mm from the DEJ were irradiated, and the laser tip was moved 5 mm in a mesiodistal direction with 5 s of irradiation time. The output powers were 2 to 10 W in a continuous mode, and the average doses were approximately from 250 to 1,250 J/cm². All specimens were examined by a scanning electron microscope, and heat-transfer simulation was also applied to calculate temperature distribution. Surface ablation of enamel and separation of enamel and dentin along the DEJ were observed when the laser power output exceeded 3 W. Heat-transfer simulation indicated that dentin was prone to store more thermal energy than enamel. In conclusion, operation parameters of the CO₂ laser should be carefully selected to avoid thermal damage to the DEJ.