Fluoride Effect on Orthodontic Cement Bonding and Enamel Hardness

Objectives: To test the hypothesis that fluoride application methods would have no effect on the mean micro-shear bond strength and on the surface Vickers micro-hardness of enamel.
Methods: Sixty extracted teeth were mounted and polished to a flat enamel surface to 600 grit. Group [C] (control), group [FB] was treated with fluoride toothpaste (fluoride content <600 ppm), and group [FE] was treated with 5% sodium fluoride varnish (22,600 ppm) according to manufacturer's instructions. The teeth were placed in distilled water for 24 hours following treatment. Micro-shear strength and Vickers Hardness 1,000 g load were performed for the control group [C] first. After treatment with fluoride for both groups [FB] and [FE], Micro-shear strength and Vickers Hardness were tested. For micro-shear bonding strength test, a cylinder of orthodontic light-cured resin cement (2mm in diameter and 2mm in height) was applied to the treated groups prior to testing with the UltraTester device.
Results: For micro-shear bond strength, there was no significant difference (p>0.05) compared to the control, [C] 23.98 ±4.96, [FB] 24.75 ±7.60, and [FE] 19.67 ±7.18 MPa. There was also no significant difference (p>0.05) between the groups [FB] and [FE].
For the HV1.0, there was a significant difference (p<0.05) between the fluoride groups compared to the control [C] 338.92 ±26.71, [FB] 284.01 ±62.72, and [FE] 276.19 ±29.74 HV1.0. However, there was no significant difference (p>0.05) between the groups [FB] and [FE].
Conclusions: Within the limitations of the study, it was determined that fluoride application methods did not significantly affect shear bond strength, but it did affect the enamel surface microhardness. Therefore, the first null hypothesis was accepted, and the second null hypothesis was rejected.