Effect of Er:YAG laser parameters on dentin microhardness

Objective: This study investigated the influence of Er:YAG laser parameters settings on microhardness of dentin cavity walls. Methods: Seventeen crowns of molars were sectioned in four fragments, providing 68 samples. Sixty-five specimens were selected and grounded until expose dentin surfaces. The irradiated site (3 mm-diameter) was delimited and specimens were randomly assigned to 13 groups of equal size. Twelve groups received Er:YAG laser irradiation on focused mode (12 mm) for 1 minute, with different energies (200, 250, 300 or 350 mJ) and pulse repetition rates (2, 3 or 4 Hz), and one group (control) was prepared using carbide bur. Specimens were bisected in half, fixed in a matrix with their subsurfaces up-faced and polished. The microhardness test was performed in 5 depths (30, 60, 90, 120 and 150 µm) and 7 regions (six in the edges of the cavity preparation and one in a non-irradiated area). Data were analyzed by 3-way ANOVA and Tukey test. Results: It was observed that the lased-irradiated groups presented higher microhardness values than those recorded for the bur-prepared group (p<0.05), specially when the specimens were irradiated with 300mJ/3Hz, 300mJ/4Hz, 350mJ/3Hz and 350mJ/4Hz. The highest microhardness mean were founded in the deeper regions of the cavities and only in a depth of 30µm (p<0.05). Non-irradiated areas in the lased-specimens were similiar to the control group (p<0.01). Conclusion: Er:YAG laser irradiation increased microhardness in deeper regions of dentin cavities until 30 µm. This increase was more evident employing higher parameters settings. Grant sponsor:FAPESP 03/03780-5.