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The effect of thermocycling and dentine pre-treatment on the durability of the bond between composite resin and dentine.

The high bond strength between restorative resin and dentine plays an important role in long-term performance of restorations in the oral environment. A variety of treatment techniques have been described to enhance the bond strength of composite resin to dentine. Unfortunately, few studies have reported available bond durability of adhesive resins to dentine. The purpose of this research was to study the shear bond strength of composite resin to dentine pre-treated with phosphoric acid, self-etching agent or Nd:YAP laser irradiation. The durability of bond strength between resin and dentine stored in the artificial saliva thermocycling between 5 and 55 degrees C was also evaluated. The scanning electron microscope was used to assess the treated-dentine surfaces. The mean value of the shear bond strength in the acid-etching group (18.2 +/- 4.9 MPa) was the highest among the three dentine treatments (self-etching system: 12.6 +/-3.0 MPa, Nd:YAP laser: 13.4 +/- 3.3 MPa) prior to thermocycling. After thermocycling, shear strength values of all treated dentines decreased with increasing number of the cycles. When subjected to 3000 thermocycles, the mean bond strengths of these pre-treated samples to composite resin became 9.1 +/- 1.4, 7.8 +/- 1.8, and 8.1 +/- 1.7 MPa for acid-etching, self-etching and laser-irradiation, respectively, with a significant reduction of 38-50%.