J Oral Laser Applications 6 (2006), No. 1 (20.03.2006)
Influence of Different Er:YAG Laser Energies and Frequencies on the Surface Morphology of Dentin and Enamel
Delmé, Katleen I. M./Deman, Peter J./De Bruyne, Mieke A. A./De Moor, Roeland J.G.
Purpose: This study evaluated the micromorphology of Er:YAG-lased enamel and dentin surfaces at different energy outputs (EO) and repetition rates (RPR), and determined the depth of tooth substance ablation with these different parameters.
Materials and Methods: A total of 35 central incisors and 35 molars were collected for determination of the ablation depth. The laser parameters were: EO: 100 mJ, 150 mJ, 200 mJ, 250 mJ, 300 mJ, 350 mJ, and 400 mJ; RPR: 5 Hz and 10 Hz, 5 and 10 MVS over enamel (incisor) and dentin (molar) surfaces. This resulted in 56 experimental groups, each with 5 surfaces to be investigated. Depths of the tracks were measured after perpendicular sectioning. Micromorphological effects were evaluated on enamel surfaces of 28 central incisors and on dentin surfaces of 28 molars by SEM (2 x 7 groups of 4 teeth, separate groups per EO and per substrate).
Results: Three comparisons were made: (1) enamel vs dentin with identical EO, RPR and number of MVS; (2) difference in RPR with identical EO within the enamel and within the dentin groups; (3) difference in number of MVS with identical RPR and EO within the enamel and dentin groups. Statistically significant differences were found for all groups in (2) and (3) (p < 0.01), and for comparisons of enamel vs dentin (a) at 10 Hz and 10 MVS, (b) at 10 Hz and 5 MVS for 100 mJ, 300 mJ, 350 mJ, 400 mJ, (c) at 5 Hz and 5 MVS at 100 mJ, 150 mJ, 200 mJ, 250 mJ, 300 mJ, 350 mJ. SEM evaluation showed the typical characteristics of Er:YAG-lased enamel and dentin surfaces. Vitrification was seen at 300 mJ for dentin and 200 mJ for enamel.
Conclusion: Er:YAG cavity preparation without vitrification is recommended at energy outputs of 200 mJ for enamel and 300 mJ for dentin. At these energies, a 10 Hz RPR is more effective, and will not result in earlier and/or more signs of vitrification.
Keywords: ablation, dentin, enamel, energy output, Er:YAG laser, morphology, SEM