Evaluation of Tensile Bond Strength of a Fluoride-Releasing Resin Adhesive with Ceramic Brackets

Abstract

The increased attention to the esthetics of orthodontic appliances has led to the popularity of ceramic brackets in the last decade. Although the bonding of ceramic brackets has become predictably successful, the extreme brittleness of ceramics coupled with higher bond strengths has caused significant clinical problems in debonding and risk of enamel damage. This study evaluated an experimental bonding resin with different levels of fluoride concentration, linking the therapeutic property of long-term fluoride release to the benefit of decreased bond strength to ceramic brackets. Four groups of 40 Transcend™ ceramic brackets each were bonded to bovine teeth, using 0, 3, 6, and 12 percent fluoride concentrations. At two weeks, one-half of each group was tested for tensile bond strength in an lnstron machine. The remaining half were tested at six months. In the groups broken at two weeks, the bond strength peaked around 6 percent fluoride, but the three top groups were not significantly different. In the groups tested at six months, peak strength was observed at 3 percent fluoride and was significantly greater than the others. The overall mean at six months than at two weeks. The study found bond strength values in the range of 25-50 kg/cm2. Although minimum values have not been established, the low values reported in this study are likely to be within acceptable clinical limits. Following debonding, the mode of bond failure was determined by viewing enamel specimens and bracket bases under a light microscope. In all but one group, 95 percent of the bond failure occurred at the bracket base/adhesive interface. No bracket failure occurred and no enamel damage could be observed under the light microscope. In a parallel study of physical properties, Knoop hardness was measured at one hour, 24 hours, and six months, and compressive strength was tested at one week and six months. While physical properties generally decreased over the period of study, bond strength was significantly greater in the six-month group. The results of this study regarding the correlation of these properties to bond strength is inconclusive. In addition, results of fluoride-release data by SISCO Inc. indicate that the 12 percent group was shown to release greater than 10 μg/g/day at six months. This was comparable to amounts known to have the clinical benefit of reducing demineralization, and equaled or exceeded other commercially available fluoride-releasing adhesives. The results of this study indicate that a fluoride-releasing resin can release clinically significant amounts of fluoride ions, and still have adequate bond strength.