comparison of the effect of three led light modes and conventional qth curing light on shear bond strength of composite to dentin

objective: shear bond strength is an important property inherent to the durability of tooth-colored restorative materials namely composite resins. it has been years that halogen light sources have been used for polymerization of composite resins. in recent years light emitting diodes (led) have been introduced for this purpose. with respect to their longer bulb life, needless of a filter and no heat production, the demand for their use has increased. this study aimed to compare three different led curing-lights with conventional quartz tungsten halogen (qth) lights to assess their effects on shear bond strength of composite to dentin.   methods: in this laboratory study, 60sound caries-free premolar teeth, after disinfection with sodium hypochlorite and cleaning with a scaler, were divided into four groups of 15. after the specimens had their dentin surface exposed with a metal disc, the composite restoration was done. the restorations in each group were done using single bond bonding agent and cured with the qth light curing units and three different led curing devices. next, the strength of each bond was measured with an instron machine. the results were analyzed with one-way anova and tukey’s test.   results: analysis of the data with one-way anova revealed statistically significant differences between the groups (p<0.05). the greatest bond strength related to the led light in ramp mode with 114.68 newtons (n) or 22.94megapascals (mpa).the lowest related to the pulsed-led with a mean of 70.35n (14.70 mpa). in pair wise comparison of the 4 groups with tukey’s test, all groups with the exception of qth with a mean of 99 n (19.80 mpa) and the conventional led with a mean of 86.78n (17.35 mpa), had a significant difference (p<0.05). conclusion: our study showed that the use of led light in ramp mode had better results compared to the qth light source (control group) (p=0.38). conventional led light was comparable to the qth light as well (p=0.169).