Acid resistance of erbium-doped yttrium aluminum garnet laser-treated and phosphoric acid-etched enamels

Objective: To compare the effects of erbium-doped yttrium aluminum garnet (Er:YAG) laser ablation and of phosphoric acid etching on the in vitro acid resistance of bovine enamel. Materials and Methods: Teeth were polished to make the surface flat. The polished enamel was either etched with 37% phosphoric acid for 30 seconds or ablated with a single 33 J/cm(2) pulse from an Er:YAG laser. The control specimens were free from acid etching and laser ablation. Changes in crystal structure, dissolved mineral (calcium [Ca] and phosphorus [P]) contents, and calcium distribution in the enamel subsurface after a pH-cycling process were evaluated. Results: After laser treatment, poor crystal structures improved without forming any new phases, such as tricalcium phosphates. Among the tested enamels, dissolved mineral contents were significantly different (P <.05). Er:YAG laser-treated enamels had the lowest mineral dissolution (Ca, 13.78 ppm; P, 6.33 ppm), whereas phosphoric acid-etched enamels had the highest (Ca, 15.90 ppm; P, 7.33 ppm). The reduction rate and reduced depth of calcium content along the subsurface were lowest in Er:YAG laser-treated enamels. Conclusion: The Er:YAG laser-treated enamels are more acid resistant to acid attack than phosphoric acid-etched enamels.