Marginal Microleakage Of Composite-Restored Cavity Prepared By Means Of Air-Abrasive System Satoh Kaori, Komori Yuriko, Yanagihara Tamotsu, Send Akira (Professor&Chair) (Department Of Operative Dentistry, School Of Dentistry, Aichi Gakuin University 2-11 Suemori-Dori, Chikusa-Ku, Nagoya (464-8651), Japan) Previous experiments have revealed peripheral margin loss on air-abraded cavities and the breadth was related to distance between the nozzle and tooth surface. This particular peripheral margin loss on cavities may affect sealability when cavities are restored with adhesive materials, such as composite resins.   Therefore, the present study aimed to compare microleakage in composite-restored cavities prepared using an air-abrasion system at different distances from the surface.   40 extracted human incisors were used in this study, and were embedded in plastic molds. These specimens were divided into two groups at random. In Group 1 cavities were prepared (air-abraded) using 1mm-abrasive distance, and in Group 2 3mm- abrasive distance was used. After air-abrasion, specimens of both Group 1 and 2 were divided into two experimental groups (A and B). In Group A cavities were treated with only prime-bond agents. In Group B cavities were etched, and then prime-bond agents were applied. Then, cavities were restored with composite materials in Group A and B. All restorations were properly finished, and specimens were load-cycled (800g) for 10,000 cycles. All surfaces of specimens were coated with nail vanish except for the cavity margins, and were placed in 1% methylene blue solution for 24 hours. Each specimen was sectioned through the center of the air-abraded cavity, and the depth of dye-penetration at the intersurface between the restoration and the cavity wall was evaluated.   The results show that higher microleakage occurs in specimens prepared with 3mm-abrasive distance, and indicate that acid-etch may be required when air-abrasion is performed for adhesive restorations.