Journal of Dental Research, Vol 75, 1388-1395, Copyright © 1996 by International & American Associations for Dental Research Online Journals
The threshold effects of Nd and Ho: YAG laser-induced surface modification on demineralization of dentin surfaces
J. H. Kinney, D. L. Haupt, M. Balooch, J. M. White, W. L. Bell, S. J. Marshall and G. W. Marshall Jr
Chemistry and Materials Science Department, Lawrence Livermore National Laboratory, California 94551, USA.
Laser irradiation alters the structure of dentin and produces surface
layers that give the appearance of being more enamel-like. The
laser-modified surface may be more resistant to demineralization; hence,
many investigators are proposing continued development of the laser as a
possible preventive treatment for caries. The purpose of this study was to
explore the morphological changes that occur in dentin when treated at
threshold illuminance with two clinically interesting laser wavelengths,
and to evaluate the effectiveness of the laser-treated surface at resisting
demineralization in an acid-gel solution. The Nd: YAG laser (wavelength
1060 nm) produced significant recrystallization and grain growth of the
apatite, without the formation of second phases such as beta-tricalcium
phosphate. This recrystallized surface layer showed resistance to
demineralization; however, the layer did not provide protection of the
underlying dentin from demineralization because of cracks and macroscopic
voids that allowed for penetration of the demineralizing gel. The Ho: YAG
laser-treated surface (wavelength 2100 nm) did not show significant
evidence of recrystallization and grain growth, and only a trace amount of
an acid-resistant layer was observed with demineralization. It is
speculated that the Ho:YAG laser is coupling with absorbed water, and that
the heat transfer from the water to the mineral phase is inefficient. For
the purposes of creating a demineralization-resistant layer, threshold
illuminance with both Nd: YAG and Ho: YAG was ineffective.
