| Objective:The aim of this study was to evaluate the microshear bond strength(MSBS) of indirect and direct restoration of Bisco resin composite.Materials and Methods:Twelve noncarious human molars, extracted in 3 months, were stored in 1% Tosylchloramide Sodium at 37℃. They were divided into 2 groups by random. First, Superficial occlusal enamel was removed and dentin was exposed with the help of Isomet Low Speed Saw under copious water spray. Then ground the teeth flat with 180,400,600 grit sandpapers.Then a crown using Bisco blue composite resin directly and indirectly bonded with Super Bond C&B adhesive according to the manufacture's instructions. The teeth were stored in water for 24 h, under the room temperature and then sectioned both mesial-distally and buccal-lingually along their long axis into 1.0mm×1.0mm sticks. The indirect group was divided into Group A&B, the direct one was divided into Group C&D. Group B&D were thermocycled 1000 times(5-55℃).Finally,shear bond strength values were determined 24h later using a microshear bond test machine. Student's T Test was used to determine whether significant differences(p=0.004) existed among the indirect and direct groups. Results:Although no significant difference was found in Group A(5.53±1.13) MPa and Group C (4.92±1.13) MPa, Group B (6.64±2.19) MPa resulted in statistically higher bond strength than Group D (4.50±1.47) MPa (P=0.004< 0.05).Conclusion:The microshear bond strength of indirect and direct Light-core composite is similar in 24h,but after being thermocycled, the microshear bond strength of indirect composite is higher than direct composite.
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