Ultrastructural changes of human dentin after irradiation by Nd:YAG laser

BACKGROUND AND OBJECTIVE: The use of Nd:YAG laser has been proposed for endodontic treatment. However, its ability to reduce dentin permeability, which is important for the success of root canal treatment, remains controversial. STUDY DESIGN/MATERIALS AND METHODS: Nd:YAG laser irradiation was performed in pulsed mode on human dentin. The parameters were: pulse energy (100 mJ), rate (10 pps), and total irradiation time (4 seconds). The crystalline phases, electron diffraction patterns, morphology, and microstructure of specimens after laser irradiation were observed by dark-field emission transmission electron microscope (TEM). RESULTS: Three ultrastructural zones could be delineated in the dentin: (1) an outer zone with an ordered columnar structure composed of hydroxyapatite and beta-tricalcium phosphate, (2) an intermediate zone composed of an amorphous substance (about 40-70 nm in diameter), and (3) an inner zone of well-crystallized hydroxyapatite grains. These three zones were free of pores or voids. CONCLUSIONS: Our study demonstrated that laser-irradiation might be used to reduce dentin permeability.