Effect of flexural strength of orthodontic resin cement on bond strength of metal brackets to enamel surfaces.

Three types of experimental resin cements with different curing systems, dual, light, and chemical, were designed. The relationship between the flexural strengths of the three experimental and five commercial (Beauty Ortho Bond, Transbond™ XT, Light Cure Bond, Kurasper® F, and Super Bond) orthodontic resin cements on the tensile bond strength (TBS) and shear bond strength (SBS) of metal brackets to enamel was determined. Seven specimen bars of each resin were prepared for measuring the flexural strengths of the resins. Bonded specimens of each resin were prepared, seven for measuring TBS and seven SBS for after bonding of a metal bracket to a maxillary central human labial anterior tooth using experimental and commercial resin cements. The results were analysed by one-way analysis of variance and Scheffé's multiple comparison tests. The level of statistical significance was set at 0.05. Increases in the flexural strength of the resin cements were related to increases in the TBS and SBS of the metal bracket. While the light-curing cements exhibited a strong linear correlation between flexural strengths and TBS or SBS, the dual- and chemical-curing cements exhibited a different flexural strength effect on both TBS and SBS. This was a result of the adhesive layer under the metal bracket, which could be chemically cured, in contrast to the light-curing cement. To control setting time and to obtain higher initial TBS and SBS by polymerizing the resin cement under the bracket, a dual-curing system, that combines both light- and chemical-curing systems, is essential.