INFLUENCE OF THERMOCYCLING FOLLOWING APPLICATION OF FLUORIDE-RELEASING RESIN ON SHEAR BOND STRENGTH OF METAL BRACKETS

Objectives: To assess the influence of thermocycling following application of fluoride resin agent on shear bond strength (SBS) of metal orthodontic brackets bonded with two self-etching primers (SEPs).
Materials and methods: Eighty extracted upper premolars were randomly divided into 4 equal groups (n=20) and stainless steel brackets were bonded to their buccal surfaces as follows: group 1, teeth were conditioned with Transbond Plus SEP (3M Unitek, Monrovia, Calif), then brackets were bonded with Transbond XT adhesive (3M Unitek) and no fluoride resin applied; group 2, teeth were bonded as in group 1, and subsequently a fluoride-releasing resin (Ortho-Coat, Pulpdent, Watertown, Mass) was applied ; group 3 teeth were conditioned with Clearfil Protect Bond antimicrobial SEP (Kuraray Medical, Osaka, Japan), then brackets were bonded with Transbond XT adhesive and no fluoride resin applied; and in group 4, the same protocol for brackets bonding as in group 3 was used followed by an application of Ortho-Coat. All specimens were stored in distilled water (24 h., 37oC) then, half of each group (n=10) subjected to SBS debonding and the other half (n=10) were thermocycled before debonding. The adhesive remnant index (ARI) score was also recorded after debonding. The data of SBS and ARI scores were statistically analyzed by using 3-way ANOVA and Chi-Square test, respectively
Results: The application of Ortho-Coat had no significant effect on SBS values of both SEPs, either before or after thermocycling. SBS values of both SEPs were not significantly changed by thermocycling whether Ortho-Coat was applied or not. No significant difference was noted between the two SEPs in any application condition. No significant differences were found in the ARI scores.
Conclusions: The application of fluoride-releasing resin had no negative effect on SBS of metal brackets bonded with the two SEP systems. Thermocycling had no effect on SBS of the both SEPs either with or without fluoride-releasing resin application.