Assessment of microcracks and shear bond strength after debonding orthodontic ceramic brackets on enamel priorly etched by different Er,Cr:YSGG and Er:YAG laser settings without acid application: An in vitro study.

ABSTRACT

BACKGROUND DATA Enamel microcrack formation has a high incidence after mechanical debonding of ceramic brackets. This may be due to high delivered shear bond strength values when enamel is priorly etched by phosphoric acid. It is still not well elucidated in the literature if laser etching affects enamel the same way. The aim of the research was to analyze different Er,CrYSGG and ErYAG laser etching settings as an alternative to phosphoric acid, in an attempt to prevent enamel microcrack formation during laser etching and mechanical debonding, while reducing the shear bond strength to the minimal clinical acceptable value. MATERIALS AND METHODS: One hundred and thirty-three teeth were randomly divided into 7 experimental groups according to their etching modalities. Settings used for enamel etching were in Er,CrYSGG groups Er,CrYSGG (1.5Watt, W/20Hertz, Hz); Er,CrYSGG (1.5W/15Hz) and Er,CrYSGG (2W/20Hz) and settings used for enamel etching in ErYAG groups were ErYAG (60 millijoules, mJ), ErYAG (80mJ) and ErYAG (100mJ). Group C etched with 37% phosphoric acid served as control. Microscopic analysis was performed to assess presence of enamel microcracks. Shear bond strength was evaluated after thermocycling using Weibull survival analysis. RESULTS: All groups showed a reduction in additional microcracks after debonding when compared to control, but only group ErYAG (60mJ) exhibited a statistically significant difference. Groups ErYAG (80mJ), control and ErYAG (100mJ) showed respectively the highest probability of survival at various stress levels followed by groups ErYAG (60mJ); Er,CrYSGG (1.5W/15Hz); Er,CrYSGG (2W/20Hz) and Er,CrYSGG (1.5W/20Hz) that presented a relatively considerable risk of failure, even at low stress levels. CONCLUSIONS: When considering reduction of enamel microcrack formation and clinical acceptable shear bond strength, none of the groups succeeded both. Etching by ErYAG (60mJ) and Er,CrYSGG (1.5W/15Hz), showed the least overall microcrack incidence between groups, but ErYAG (60mJ) displayed significant reduction compared to phosphoric acid. However, etching by ErYAG (80mJ) had the most predictable results in term of shear bond strength.