Enamel loss and superficial aspect during bonding and debonding of metallic brackets = Perda de esmalte e aspecto superficial durante colagem e descolagem de bráquetes metálicos

To evaluate the cumulative enamel loss during bonding and debonding procedures of orthodontic metallic brackets and to analyze the enamel superficial roughness.  Forty-seven maxillary first premolars were obtained for quantitative and qualitative analysis.  For quantitative analysis, forty premolars were weighed at each stage of treatment and the equivalent thickness of enamel loss was measured. The amount of tooth mass loss in each stage was divided by the density value to obtain the corresponding enamel volume lost. Subsequently, these volumes were divided by a circular area with a diameter of 7 mm, thus obtaining the equivalent thickness of enamel loss. They were assessed under the following conditions: as sound enamel, after acid conditioning, following the removal of residual resin composite, after final polishing with high or low-speed, and with or without water refrigeration. A rugosimeter was used to obtain a graphic registration of the enamel superficial roughness before and after acid conditioning. The data were analyzed with the Quantikov software and the Shapiro Wilk’s and Wilcoxon statistical tests were used to evaluate enamel superficial roughness. The one-way ANOVA followed by Bonferroni Post-Hoc tests were used to analyze the amount of enamel loss.  For qualitative analysis, scanning electron microscopy (SEM) of the enamel surfaces was performed on seven premolars, one in each step. Acid conditioning significantly increased enamel surface roughness (p<0.01). Based on the dental mass weighed after each stage of evaluation, enamel loss was statistically significant in all stages (p<0.01). However, when the 4 different final polishing methods were compared, no statistically significant differences were registered regarding loss of mineralized structure (p=0.72). The SEM analysis revealed that the tungsten-carbide bur with water refrigeration and low-speed rubber points caused less damage to the enamel. The greatest amount of enamel loss was due to acid conditioning. The losses relative to abrasion with composite removal or after the 4 polishing protocols were similar. Finally, none of the enamel surfaces was restored to their original aspects after bonding and debonding metallic brackets.