الفهرس 
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Abstract
Objective: This study was designed to evaluate the shear bond strength (SBS) of metal orthodontic brackets rebonded to enamel and composite surfaces utilizing four different adhesive systems. Materials and methods: This study was carried out on 80 extracted upper human premolars and 80 composite discs (Filtek Z350). Metallic orthodontic brackets were bonded to all teeth and composite discs utilizing four adhesive systems. Either the teeth and the composite discs were equally divided into four groups (A, B, C and D) according to adhesive used (n=20). In group (A): phosphoric acid + Transbond XT primer and adhesive (Transbond XT) were used. In group (B): Transbond Plus self-etching primer + Transbond XT adhesive (SEP) were used. In group (C): one-step self-adhesive RelyX Unicem was used. In group (D): one-step self-adhesive Vertise Flow was used. All adhesives systems were applied according to the manufacturer’s instructions. After thermocycling, the SBS was measured using a universal testing machine and the adhesive remnant index (ARI) scores were evaluated using a stereomicroscope. The data was collected and statistically analyzed using Wilcoxon’s Signed Ranks, Kruskal-Wallis H, Pairwise comparisons and Chi-square test. Results: In enamel group, Transbond XT and SEP provided the significantly highest initial SBS values (11.1 & 9.6 MPa) and secondary SBS values (9.3 & 8.5 MPa), (p<0.05), with no significant difference between them (p>0.05). Vertise Flow provided the significantly lowest initial and secondary SBS values (2.6 & 1.2 MPa). RelyX Unicem provided initial and secondary SBS values of (6.0 & 4.7 MPa). In composite group, RelyX Unicem provided the significantly highest initial and secondary SBS values (6.9 & 8.5 MPa), while Vertise Flow provided the significantly lowest initial and secondary SBS values (4.2 & 6.2 MPa), (p<0.05). Transbond XT and SEP provided initial SBS values of (5.6 & 5.5 MPa) and secondary SBS values of (7.5 & 8.0 MPa), with no significant difference between them (p>0.05). Conclusion: Transbond XT and SEP provided higher initial and secondary SBS values to enamel surface in a comparison with RelyX Unicem and Vertise Flow. Vertise Flow obtained the lowest and undesired SBS to enamel and composite surfaces, while RelyX Unicem obtained an acceptable SBS to the both surfaces. Rebonding procedure had a pronounced negative effect to enamel surface and positive effect to composite surface.