Distance and time effect on shear bond strength of brackets cured with a second-generation light-emitting diode unit.
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OBJECTIVE: The aims of this study were to evaluate increasing exposure times and distance between source (light-emitting diode) and adhesive composite on the shear bond strength (SBS) of stainless steel brackets. MATERIALS AND METHODS: Stainless steel maxillary incisor brackets (3M Unitek, Monrovia, Calif) were bonded to the facial surfaces of 120 bovine incisors. The bond of each specimen in eight randomly divided groups was tested to failure using an Instron Universal Testing Machine (Instron Corp, Canton, Mass). The mode of failure was evaluated using the adhesive remnant index (ARI). RESULTS: There were significant SBS differences between exposure times; 5-second exposures were significantly less than at 20-and 40-second exposures; SBS increased in a curvilinear fashion. Significant differences were recorded neither in the frequencies of ARI scores nor the SBS in relation to distance. Significant differences in the frequencies of ARI scores were observed when comparing the 5-second cure time to other time periods, indicating incomplete polymerization in the bracket base. CONCLUSIONS: SBS increased with increasing time periods in a curvilinear fashion, with no difference between the distances evaluated from source to specimen.
