A Study of Microleakage in Orthodontic Direct Bonding Adhesive Systems

Abstract

If orthodontic direct bonding adhesives are to be successful, they must withstand the destructive influences of the oral environment and form a durable bond with enamel. Investigators have noted that moisture may be the greatest deterrent to an adhesive bond and water may have the ability to penetrate the adhesive-enamel interface, destroying this bond. An in vitro investigation was undertaken to determine whether moisture and other oral debris can penetrate this adhesive-enamel interface. Four commercially available orthodontic direct bonding systems were tested for microleakage using radioisotope45 calcium chloride (45Ca). Adhesives tested included Orthomite IIS, Directon, Unitek, and Genie. Polycarbonate brackets were bonded to freshly extracted human premolar teeth using the respective adhesive systems. Specimens were stored in 37.5°c water baths for periods of thirty days and ninety days before being tested. All specimens were thermal cycled 2500 cycles to provide a more heroic test. The thermal stressing was carried out at 15°c and 45°c with a 30 second dwell at each temperature. A total of eighty specimens were evaluated. The results of this study suggest that two of the orthodontic adhesives evaluated are susceptible to amounts of microleakage. Storage in water did affect the rate of leakage among the specimens. Generally, more specimens in the groups tested at ninety days showed leakage than at the thirty-day testing period. This study suggests that orthodontic adhesives may be susceptible to microleakage and that this may present problems clinically. However, long-term, well controlled investigations must be undertaken before more definite conclusions can be drawn concerning the effect on bond strength and enamel integrity.