Bonding of clear plastic orthodontic brackets using an ultraviolet-sensitive adhesive

Abstract

Numerous investigators have been involved in attempts to develop effective materials and methods for attaching orthodontic brackets directly to tooth surfaces to eliminate some of the present clinical disadvantages and problems related to the use of metal orthodontic bands. The objectives of the present study were to (1) test the usefulness of an ultraviolet-sensitive adhesive “bracketing” system under active orthodontic conditions, (2) determine both tensile and shear strength of the system, and (3) examine fracture patterns and locations at the various interfaces by means of a scanning electron microscope. Clear polycarbonate Begg-type and acrylic edgewise orthodontic brackets were bonded to preconditioned tooth surfaces, using an ultraviolet-sensitive adhesive. Clinical, mechanical, and scanning electron microscope studies were carried out at the State University of New York at Buffalo and the University of Western Ontario, Canada. It was found that the ultraviolet bonding system was clinically effective and the esthetics of the bonded brackets were excellent. The bracket failure rate for all teeth was 13.1 per cent (8/61), and the brackets remaining have been retained from 3 to 10 months under orthodontic conditions. The mean shear strength was found to be 821 p.s.i. (57.7 Kg. per square centimeter), and the mean tensile strength was found to be 508 p.s.i. (35.8 Kg. per square centimeter); both test results followed 30 days' immersion in water. The bracket-adhesive interface and the bracket itself were found to be the weakest links in the bonding system. The scanning electron microscopic observations revealed that there was good wetting at the adhesive-tooth interface; however, there was considerably less roughening of the bracket bases, possibly accounting in part for failure at the adhesive-bracket interface. It was concluded that the ultraviolet bonding system has clinical orthodontic potential because of (1) improved esthetic qualities, (2) adequate time for bracket placement but only 20 seconds for polymerization, (3) no time delay in applying orthodontic forces to the brackets, and (4) no necessity for finishing procedures.