The effect of thermocycling and debonding time on the shear bond strength of different orthodontic brackets bonded with light-emitting diode adhesive (In vitro study)

Abstract

Background: Thermocycling simulates the temperature dynamics in the oral environment. This in vitro study done tomeasure and compare the effect of thermocycling on the shear bond strength of stainless steel and sapphirebrackets bonded to human enamel teeth using light cured orthodontic adhesive and debonded at various time,and to measure adhesive remnant index after debonding.Materials and Methods: one-hundred-twenty extracted upper first premolars for orthodontic reason were used in thisstudy; depending on weather thermocycled or not, the sample was divided into two main groups, then within eachgroup 30 teeth were used for stainless-steel brackets (Bionic®) and for sapphire brackets (Pure®). Both groups weresubdivided into three groups (n = 10) according to the debond times: I: debond after 24 hour, II: debond after 7 daysand III: debond after 30 days. Within 24 hr, half of the sample was thermocycled manually for 500 complete cyclesbetween 5/55°C and the remaining sample was stored in distilled water at room temperature and water waschanged daily until debond time for each group was performed. The adhesive remnant index was tested under 20Xmagnification lens using stereomicroscope.Results and Conclusions: Both bracket types demonstrated high shear bond strength values before thermocycling(P≤0.05), whereas after 500 thermocycles, there were significant changes in shear bond strength resulted in markedreduction in the stainless steel brackets than in the sapphire brackets (P≤0.05). Shear bond strength values increasedwith time for both stainless steel and sapphire brackets with and without thermocycling (P≤0.05). The tendency ofbond failure was increased at the bracket/adhesive interface rather than enamel/bracket interface in the stainlesssteel brackets whereas at the enamel/bracket interface rather than bracket/adhesive interface in the sapphirebrackets.