Effect of thermal cycling on the shear bond strength of different orthodontic adhesives to enamel

Objective: The aim of this study was to assess the influence of thermal cycling on the shear bond strength of three types of adhesives used for orthodontic brackets to human enamel. Methods: Sixty six human premolars were used in this study. Two groups of dental resin composite adhesives (ED; G) and one compomer (TP) were thermal cycled from 5 up to 55 °C at 4000 cycles for 45 s in an artificial saliva solution. Then, samples were assessed by shear bond tests and inspected by optical and scanning electron microscopy. The resulting enamel surfaces were then evaluated according to the adhesive remnant index (ARI). Results: One resin composite adhesive (group G) showed the highest shear bond strength values. Thermal cycling negatively affected the bond strength of the compomer-based adhesive although results showed clinically acceptable adhesion values after thermal fatigue for such cycles. ARI showed significant amount of residual material on the tooth surface with the adhesives that indicated strong bonding to enamel. Different adhesion mechanisms were noticed at both adhesive-enamel or adhesive-bracket interfaces. Conclusion: The orthodontic adhesives revealed proper bond strength to enamel for clinical applications considering thermal conditions assessed in this study although the compomer- based adhesive was negatively affected by thermal cycling. The high remnant adhesive amount on enamel indicated high bond strength leading to enamel damage during debonding.