Evaluation of a New Photoinitiator on Dentin by Nd:YAG Laser

Objective: The aim of this study was evaluate the effect of the association of potassium nitrate and varnish fluoride as photoinitiator on exposed dentin structure irradiated with the Nd:YAG laser. Methods: Seventy-six radicular human dentin samples was used and divided in four groups: Group 1 – phosphoric acid at 37% (control group); Group 2: phosphoric acid + photoinitiator; Group 3: phosphoric acid + Nd:YAG laser; Group 4: phosphoric acid + photoinitiator + Nd:YAG laser. The photoinitiator was applied for 5 minutes and the parameters of irradiation were: 30mJ, 10 Hz, 0.3 W, 42.46J/cm² , 60 seconds, scanning contact mode, 1mm/second. Power and temperature were measured before and after each irradiation for standadization. The samples were submitted to microhardness analysis, SEM and EDS. Results: After data and statistical analysis (ANOVA and Studentxs), group 3 (54.9±20.1) showed the highest microhardness (p<0.05), followed by groups 1 (45.1±5.9), 4 (37.4±16.1) and 2 (36.0±23.6). Group 4 showed no statistical difference (p>0.05) compared with group 1. Electronmicrographies of Group 4 showed an amorphous and irregular layer suggesting melting and resolidification of the photoinitiator on dentin. EDS showed an increase of phosphorus and calcium in Group 3. No evidence of changes were observed in groups 1, 2 and 4. Conclusion: The results suggested that the new photoinitiator associated with laser irradiation can obliterate the dentin tubules without interfering in the microhardness and the composition of dentin.