The present study tested the shear bond strength (SBS) of orthodontic brackets bonded to teeth using flowable resins. A total of 105 human teeth were divided into seven groups. The brackets in each group were bonded to the tooth substrates using a Transbond XT adhesive and six other different flowable resins, respectively. Each adhesive resin was light-cured using a quartz-tungsten-halogen (QTH) light for 40 seconds. The brackets were debonded in shear mode using a universal testing machine. The brackets bonded using Tetric Flow and Grandio Flow showed slightly greater SBS values (13.0±1.8 and 12.2±1.2 MPa, respectively) than the Transbond XT adhesive (12.1±1.2 MPa). However, the SBS values of Transbond XT, X-flow, Tetric Flow, Grandio Flow, and Filtek Z350 flow were not significantly different. As for Admira Flow and Aelite Flow, they scored significantly lower SBS values (7.0±2.1 and 9.2±1.3 MPa, respectively) than the other groups. On bracket failure mode, statistical analysis revealed a similar failure mode among all the seven test groups.

This study evaluated the polymerization shrinkage, flexural and compressive properties of low-shrinkage resin composites. For the study, four methacrylate-based and one silorane-based resin composites were light cured using three different light-curing units (LCUs) and their polymerization shrinkage, flexural (strength (FS) and modulus (FM)) and compressive (strength (CS) and modulus (CM)) properties were evaluated. Data were statistically analyzed using ANOVA and a post-hoc Tukey test. The polymerization shrinkage ranged approximately 7.6-14.2 μm for 2-mm thick specimens depending on the resin product and LCU. Filtek LS showed the least shrinkage while the rest shrank approximately 13.2-14.2 μm. However, Filtek LS showed the greatest shrinkage difference for the used LCUs. FS and CS of the tested specimens ranged 96.2-152.1 MPa and 239.2-288.4 MPa, respectively, depending on the resin product and LCU. The highest and lowest FS and FM were recorded for the methacrylate-based resin composites. Among the specimens, Filtek LS showed the lowest CS and CM.

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