Thermal, microstructural and physicochemical effects of nanosecond pulsed Nd:YAG laser irradiation on dentin

The effects of nanosecond pulsed Nd:YAG irradiation on crown and root dentin susceptibility to artificial de- and remineralization were investigated. Laser-induced heating and structural effects were also determined. Thirty caries-free extracted human molar teeth were used. One group of 12 teeth was bisected longitudinally, and each surface covered with acid resistant varnish, leaving 4 windows on the cut dentin surface. Using a Q-switched nanosecond pulsed Nd:YAG laser (1064 nm), one half of each tooth was irradiated at one of the following parameters: 3 mm spot size, a fluence of 1.0 J/cm2. The other half of each tooth served as (non-irradiated) control. All samples were then subjected to a 4 day, thrice daily de- and remineralization cycle. Prior to and after each demineralization, microhardness measurements were taken. After 4 days, samples were again bisected, and the other sample halves used for SEM. Microhardness in the irradiated samples did not differ significantly (p < 0.01) compared with controls; SEM results showed some laser-induced alterations on crown and root dentin surfaces. Thermometric measurements on 18 teeth at energy densities of 1.0-4.1 J/cm2 revealed intrapulpal temperature increases of approximately 2°C at a dentin thickness of 2 mm during irradiation. No consistent effect of Q-switched nanosecond pulsed Nd:YAG laser irradiation on microstructure and de- and remineralization of dentin was determined (p < 0.01). but SEM results showed some surface alterations on the irradiated samples