DIRECT BONDING OF POLYCARBONATE ORTHODONTIC BRACKETS - INVITRO STUDY

One hundred four polycarbonate brackets were bonded to extracted premolars with four direct bonding resins, coded N, D, G, and O. The procedures necessary for direct bonding of plastic brackets clinically were duplicated in vitro. The adhesion of a minimum of ten bracket/enamel interfaces per material was tested in shear after both 7 and 30 days' storage in artificial saliva at 37 °C. Preliminary characterization of the bond failures was performed at low-power magnification, but final characteristics of the fractured bonds were analyzed under the scanning electron microscope. Statistical analysis of the shear strength data was carried out with the exclusion of the failures attributable to defective brackets. The results were as follows:. After 7 days' storage in Ringer's solution, D and G resins showed a significantly greater shear bond strength than the N system, while system O occupied an intermediate position. D, O, and N showed a significant decrease in mean shear bond strength from 7 to 30 days, while G maintained its initial good strength through that period. In addition, it was found that EDX analysis showed only one of the four materials tested (N system) had a ceramic filler. SEM analysis revealed that most bonds which appeared to be of an adhesive nature when viewed under low magnification actually turned out to have a cohesive component when viewed under higher magnification. © 1979.