Fluoride penetration from three orthodontic adhesives: an experimental study

Release of fluoride from orthodontic adhesives and penetration into enamel

OBJECTIVE

The purpose of this work was to compare fluoride release from three orthodontic adhesives and fluoride penetration into the enamel surface.

MATERIALS AND METHODS

A total of 156 extracted human premolar teeth were randomly assigned to three experimental groups and one control group (without bonding) with 39 teeth per group. Brackets were bonded to teeth using Fuji Ortho LC^®, Illuminate^®, or Light Bond^®. The amount of fluoride released (ppm) into artificial saliva was measured by a fluoride ion-selective electrode connected to an ion analyzer on days 1, 3, 7, and 30. Fluoride penetration was investigated after 1, 2, and 3 months; 13 teeth of each group were randomly selected at every period of study and sectioned across the center of the bracket. The surface of the cross-section was studied under the scanning electron microscope, and the fluoride concentration (weight%) at 1, 2, and 3 µm below the outer enamel surface was determined by energy-dispersive X-ray microanalysis.

RESULTS

On days 1, 3, 7, and 30, the mean cumulative fluoride release from the three orthodontic adhesives were significantly different (p < 0.05). Illuminate^® released the greatest fluoride, followed by Fuji Ortho LC^® and Light Bond^®. After 1, 2, and 3 months, fluoride penetration into enamel was only found from Fuji Ortho LC^®. The fluoride concentration decreased with depth but there were no significant differences (p > 0.05) over time at all depths.

CONCLUSIONS

The in vitro study indicated that fluoride release is a common property of the three fluoride-releasing orthodontic adhesives: Illuminate^®, Fuji Ortho LC^®, and Light Bond^®. However, detectable fluoride penetration is a specific property of Fuji Ortho LC^®. Further clinical studies should be undertaken to investigate the benefit of the two adhesives Illuminate^® and Fuji Ortho LC^® on protection of enamel demineralization.

Modification of surface pretreatment of white spot lesions to improve the safety and efficacy of resin infiltration

Objective

A low-viscosity resin (infiltrant) was used to inhibit the progression of white spot lesions (WSLs) and resolve associated esthetic issues. An alternative pretreatment was explored to increase the pore volume of the surface layer of the WSLs. Also, the penetration effects of the infiltrant were evaluated for various pretreatments.

Methods

Sixty two artificial lesions were fabricated on bovine teeth. As a positive control, 15% HCl gel was applied for 120 seconds. Further, 37% H₃PO₄ gel was applied for 30 seconds using three methods. The samples were divided as follows: H₃PO₄ only group, H₃PO₄ sponge group, and H₃PO₄ brush group. The acid was gently rubbed with the applicators (i.e., a sponge or brush) throughout the application time. To compare the effects of resin infiltration, twenty paired halves of specimens were treated with an infiltrant (ICON®).

Results

Thicknesses of the removed surface layers and infiltrated areas were evaluated by confocal laser scanning microscope. The positive control and the 37% H₃PO₄ brush group failed to show significant differences in the removed thickness (p > 0.05); however, the mean percentage of the infiltrated area was higher in the 37% H₃PO₄ brush group (84.13 ± 7.58%) than the positive control (63.51 ± 7.62%, p < 0.001). Scanning electron microscope observations indicate higher pore volumes for the 37% H₃PO₄ brush group than for the positive control.

Conclusions

Application of 37% H₃PO₄ with a brush for 30 seconds increased the pore volume of WSL surface layers and the percentage of infiltrated areas in comparison to the use of 15% HCl for 120 seconds.