Chemical and Morphological Changes of Primary Teeth Irradiated with Nd:YAG Laser: An Ex Vivo Long-Term Analysis

Objective: The aim of this study was to assess any long-term chemical and morphological Nd:YAG laser modifications on irradiated primary enamel. Background data: Previous studies on irradiated primary human enamel employed methodologies that evaluated the short-term effects only. Methods: One hundred and eighty-six irradiated (with and/or without fluoride) primary enamel teeth from high-caries-risk children, which were exfoliated over a 1-year period, were collected, and the sample surface area was submitted for scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray energy-dispersive spectrometry (EDS). The subsurface was analyzed by Knoop microhardness and light microscopy (LM). Data were analyzed by one way ANOVA and Tukey tests (alpha=0.05) and Kruskall-Wallis and Tukey tests (alpha=0.05). Results: FTIR analysis revealed a higher concentration of phosphate and carbonate in the irradiated (0.987 +/- 0.064) and lower concentration in the control groups (1.477 +/- 0.310). SEM analysis showed that the control samples exhibited a slightly smoother surface than the irradiated groups. The EDS analysis did not show any differences in the amount of calcium, phosphorus, or fluoride among the groups. The microhardness analysis revealed that sealant (249.86 +/- 7.15) and laser irradiation (262.44 +/- 22.69) led to higher hardness values than the negative control group (128.35 +/- 25.19). LM indicated significantly reduced caries formation in the laser (5.35 +/- 5.38%) and the laser plus acidulated phosphate fluoride (APF) groups (10.35 +/- 0.88%) compared with the negative control group (72.56 +/- 12.86%). Conclusions: Even with the limitations of the present study, these results suggest that Nd:YAG irradiation clinically modified the chemical composition of the enamel surface regardless of fluoride concentration, which successfully inhibited demineralization of primary tooth enamel over a 1-year period without significant morphological changes.