Objective: The purpose of this study was to compare the micro-shear bond strength to enamel affected by Amelogenesis Imperfecta (AI) and normal enamel of two composite materials. Materials and Method: Four central incisor, four premolar and two molar teeth affected by AI (Hypoplastic type) were extracted due to periodontal disorder. Additionally, ten normal human teeth were used in this study. The teeth were divided into four groups according to the teeth types and composite resins (Prime Bond NT, Esthet-X; Pekabond, Pekalite). After the teeth were thermocycled 1000 times between 5 and 55 oC. Specimens were cut perpendicular to tooth axis to obtain micro-sticks. The sticks were stressed in shear at a speed of 1 mm/min by a micro-shear test apparatus. After failure, the fracture surfaces were examined under a stereo microscope. Results of the micro-shear test and failure modes were analyzed with Kruskal-Wallis and the Mann-Whitney U test. A tooth was also prepared to observe under SEM for each experimental group. Results: The mean bond strength of Prime Bond NT was 11.43±5.34 MPa for normal enamel, and 5.95±2.92 MPa for enamel affected by AI. Pekabond showed 9.85±4.54 MPa for normal enamel, 2.29±0.89 MPa for enamel affected by AI. The difference of the mean micro-shear values between teeth types was statistically significant (P<0.05). Adhesive mode of failure was the most prevalent in all samples (P>0.05). Conclusion: It can be concluded that human enamel affected by AI showed significantly lower micro-shear bond strength when compared to normal enamel of human.

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