Evaluation of shear bond strength of metal bracket to enamel after application of primers over bracket base-an in vitro study

"nBackground and Aims: The aim of this study was to evaluate the effect of application of two types of primers over bracket bases on the shear bond strength (SBS) and mode of bond failure."nMaterials and Methods: In this study, 75 human premolar teeth were divided into three equal groups. In group 1 (control), after surface preparation of enamel by conventional method (acid etching+primer) brackets were bonded with Transbond XT composite. In group 2 (TX), brackets were bonded to enamel same as the first group but Transbond XT primer were used on bracket bases before placement of composite. In group 3 (PL), Transbond plus primer was applied on bracket bases before placement of composite. After 24 h, the SBS test was performed by universal testing machine at crosshead speed of 0.5 mm/min. Then, adhesive remnant index (ARI) scores and percentage of cohesive fracture were determined using stereomicroscopy. SBS data were analyzed by one-way ANOVA and Duncan tests. Kruskal-Wallis and Mann-Whitney tests were used to analyze ARI and cohesive fracture results."nResults: There was significant difference in SBS values among the groups (P<0.001). The highest SBS was shown in TX group and the lowest was seen in PL group. There was no significant difference between control and TX groups in ARI scores (P=0.199). No significant difference was found in cohesive fracture values between the groups (P=0.093). Both the control and TX groups showed significant difference in ARI scores and cohesive fracture compared with the PL group in all of the comparisons (P<0.001)."nConclusion: Application of Transbond XT primer over bracket base affects the bond strength and failure mode. Transbond XT primer increased the bond strength but Transbond plus primer decreased it