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Dentin evaluation after Nd:YAG laser irradiation using short and long pulses.

OBJECTIVE
Several reports have demonstrated the advantages of using the Nd:YAG laser to reduce dentin permeability by melting the dentin surface. A comparative study using different pulse durations can be useful to obtain further information about the laser-hard tissue interaction.


MATERIALS AND METHODS
The present study pursues the evaluation of the morphological and chemical changes in human dentin surface resulting from Nd:YAG laser (lambda = 1064 nm) irradiation, with a total energy of 0.9 J distributed in 1, 2, 3, and 6 pulses with different pulse durations to promote surface melting and dentinal tubule occlusion. After irradiation, the samples were submitted to scanning electron microscopy (SEM) analysis for morphological study and energy-dispersive spectrometry (EDS) analysis for evaluation of the concentration of calcium and phosphorous in the melted layer.


RESULTS
SEM analysis of the irradiated dentin surface showed surface structural changes due to laser irradiation, where the morphological changes are dependent on the laser pulse duration. EDS analysis showed an increase of calcium and phosphorous concentrations after Nd:YAG laser exposure, but no correlation with the number of pulses or pulse duration was found.


CONCLUSION
Our results suggest that longer interaction times resulted in more evident effects with more melted substrate than shorter pulses, and in both cases the resultant melted layer contains a greater concentration of inorganic substances than non-irradiated dentin.