Aim:The purpose of this study was to compare the shear bond strength of orthodontic brackets bonded to teeth with conventional halogenbased light curing units and commercially available LED curing units. LED light curing unit (Apoza) and halogen-based light curing unit (Q-Lux) were tested.
Materials and methods:Specimens consisted of one hundred twenty human maxillary premolar on which stainless steel brackets were bonded with a light-cured adhesive system (Transbond XT; 3M Unitek). The specimens were divided into 6 groups of 20 teeth each. Three groups were exposed to halogen light for 10, 20, 40 seconds and the other three groups were cured with the LED light for 10, 20, 40 seconds respectively. The specimens were stored in water at 37°C for 24 hours and then tested for shear bond strength with an Instron universal testing machine at a cross head speed of 1 mm/min until the bracket debonded. The results were subjected to Kaplan meier survival analysis (p = 0.0001 sig).
Results:The findings indicated no significant differences in the shear bond strength between the conventional halogen light and the commercially available LED-curing unit when the exposure time was 20 and 40 seconds. However, both halogen and LED lights displayed inadequate bond strength when the curing time was 10 seconds. Chi-square analysis detected no difference in the adhesive remnant index scores of the 6 groups (p = 0.0996).
Conclusion:The result of this study showed promise for the orthodontic application of LED as light curing units and 20 seconds of exposure time is adequate for both LED and Halogen light, since increasing the curing time to 40 seconds showed no significant difference.
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