Influence of topical fluoride application on mechanical properties of orthodontic bonding materials under pH cycling

To evaluate in vitro the influence of topical fluoride application on the mechanical properties of orthodontic cements containing fluoride under pH cycling conditions.

Edgewise brackets for maxillary central incisors were bonded to 192 bovine incisors using Transbond XT (G1), Transbond Plus Color Change (G2), and Fuji Ortho LC (G3) (n  =  64 for each group). The specimens of each group were subdivided (n  =  16) into different subgroups. Subgroup A received no topical fluoride application during pH cycling, while the experimental subgroups received topical fluoride treatments as follows: B, application three times per day of fluoride dentifrice (1450 ppm F); C, application one time per day of fluoride mouth rinse (250 ppm F); and D, combination of fluoride dentifrice and fluoride mouth rinse. After 14 days of pH cycling, the shear bond strength and Adhesive Remnant Index were evaluated statistically.

Polarized light microscopy showed that pH cycling induced mineral loss in all specimens. The topical application of fluoride did not have an influence on shear bond strength, although the association of fluoride dentifrice and mouth rinse increased the shear bond strength of the resinous cement without fluoride (P < .01). Regarding the Adhesive Remnant Index, no statistical differences were found within the groups G1 (P  =  .23), G2 (P  =  .47), and G3 (P  =  .74).

Topical fluoride treatments improved the shear bond strength of resinous cement, regardless of the material's fluoride-releasing capacity, and reached the adhesive fractures.