Effects of Erbium:Yttrium-Aluminum-Garnet Laser Irradiation on Bovine Dentin Contaminated by Cariogenic Bacteria.

Objective: This study was performed to determine the bactericidal effects of erbium:yttrium-aluminum-garnet (Er:YAG) laser irradiation and the morphological and chemical composition changes in bovine dentin. Methods: Dentin slabs were prepared from bovine incisors, and then cultured with Streptococcus mutans to produce bacteria-infected dentin samples. The samples were randomly divided into five groups with Er:YAG laser irradiation energy densities of 0, 6.37, 12.73, 19.11, and 25.47 J/cm(2). After irradiation, samples were stained and observed by confocal laser scanning microscopy. The bactericidal abilities were measured using live/dead staining. The morphology and chemical components were investigated by scanning electron microscopy and energy-dispersive spectrometry. Results: After irradiation, the elimination of bacteria and the smear layer were significantly better in the high energy density groups (19.11, 25.47 J/cm(2)) than in the low energy density groups (6.37, 12.73 J/cm(2); p< 0.001). On morphological examination, the group with minimum energy density (6.37 J/cm(2)) showed superficial melting. In the high energy density groups (12.73, 19.11, and 25.47 J/cm(2)), laser-irradiated dentin showed a clean surface with open orifices. Significant increases were observed in the weight percentages of calcium (from 19.75 +/- 0.69 to 34.47 +/- 2.91, p < 0.001) and phosphate (from 8.58 +/- 0.43 to 15.10 +/- 1.81, p < 0.001), whereas significant decreases were observed for oxygen (from 49.84 +/- 0.69 to 36.39 +/- 2.86, p < 0.001) and carbon (from 26.06 +/- 3.58 to 12.80 +/- 2.26, p < 0.01) with increasing energy density. Conclusions: This study confirmed that Er:YAG laser irradiation has bactericidal and dentin conditioning effects.