Orthodontic adhesives incorporated with strontium-containing fluorapatite for improved remineralizing effect

This study aimed to develop novel orthodontic adhesives with remineralization effect to prevent white spot lesions (WSLs) by adding strontium-containing fluorapatite (Sr-FAp), fluorapatite (FAp), and strontium-containing hydroxyapatite (Sr-HAp).

The particles were synthesized and characterized. The experimental groups consisted of a commercial control (CC), control (30 wt % resin matrix + 70 wt % glass filler), and experimental groups with 17.5 wt % of filler replaced by Sr-FAp, FAp, or Sr-HAp. The brackets were bonded to the enamel surface and the shear bond strength (SBS) and adhesive remnant index were tested. The release of calcium (Ca), phosphorus (P), strontium (Sr), and fluoride (F) ions from adhesive specimens in distilled water was evaluated after 15, 30, 60 days. The remineralization effect was observed the microhardness and surface morphology using scanning electron microscopy with energy dispersive spectroscopy.

Except for the FAp, no significant differences in SBS were observed (p > 0.05). Ion release results showed Ca, P, Sr, and F ions were detected in the Sr-FAp group up to 60 days. The Sr-FAp group showed the highest microhardness (p < 0.05), and the largest amount of fluorapatite-like layer (Ca/P: 1.69) was formed after 60 days of immersion.

The Sr-FAp group showed acceptable SBS while exhibiting the highest microhardness and the most pronounced formation of a fluorapatite-like layer, indicating its effectiveness in preventing WSLs during orthodontic treatment.

The orthodontic adhesive containing Sr-FAp offers potential clinical benefits by preventing demineralization and promoting remineralization of the enamel surface surrounding orthodontic brackets.