Impact of adhesive system generation and light curing units on orthodontic bonding: In vitro study

Objective > We aimed to compare adhesive performance of fourth, fifth and seventh generation adhesive systems (GASs) and the effect of two different light curing units on shear bond strength (SBS). Materials and methods > One hundred and twenty extracted human upper premolars were divided in four groups. Bonds were assessed as following: group 1 using 4th GAS, group 2 using 5th GAS, group 3 and 4 using 7th GAS with two different light curing units (1500 and 800mw/cm(2)). Adhesive remnant index (ARI) scores were counted. Results > Group 1 and 2 showed similar SBSs (P = 0.7) which were significantly higher than group 3 (P = 0.0002). Group 4 exhibited significantly the weakest SBS with mean = 2.15 +/- 0.25. Applying shear forces less than 15 MPa on group 3 bonds led to the release of almost all of the of brackets. Whereas, applying the same forces on group 2 bonds leads to the release of 66.7% of brackets. Notably, only 40% of brackets in group 1 were debonded. Group 4 brackets were totally debonded when applying shear forces less than 10 MPa. While ARI = 0 was the most frequent in group 1, ARI = 3 was the most frequent in group 3. Conclusion > Fourth and fifth GASs showed similar SBS higher than seventh GAS. Fourth GAS bonds were able to resist longer against traction forces than those set up by fifth generation. Seventh GAS bonds offered the least efficient resistance. ARI = 0 was the highest in group 1. However, Group 4 showed the highest ARI = 1 and ARI = 2 revealing cohesive failure. We also found that the adhesive power is proportional to the power of the lamp used. In fact, we concluded that 1500 mw/cm(2) units light curing during 30 seconds generated an ideal energy to enhance orthodontic bracket adhesion.