Enamel remineralization behavior under coating materials via polarized light microscopy.

Abstract

The aim was to characterize remineralization behavior of enamel lesions after a toothbrushing regimen when treated with either a rosin-based fluoride varnish or an experimental resin-modified glass ionomer, where each was applied as a coating over the lesion. Extracted human molars with artificial caries-like lesions were cut longitudinally into 100 micrometer sections, photographed in the polarizing microscope (PM) first immersed in water to (nD 1.33, showing > 5% porosity) then in Thoulet's solution (nD 1.41, showing >10% porosity). Acid-resistant varnish was applied to all surfaces, leaving only the external tooth surface with lesion exposed. Three treatments were applied: untreated control group (UNTR); lesion coated with Duraphat fluoride varnish (Colgate)( DUR); lesion coated with experimental resin-modified glass ionomer EXM-713 (EXM-OVR). The sections were stored 30 days in artificial saliva (20mM NaHCO₃, 3 mM NaH₂PO₄, 1mM CaCl₂, pH 6.7), brushed with water once daily, the acid resistant varnish removed, sections imaged in PM again. The lesion body area was quantified via computerized imaging and percent remineralization calculated from the lesion area before and after treatment. Data were analyzed by one-way ANOVA and compared with t-test (= 0.05). Mean percent remineralization (SD, n) with water imbibitions was UNTR 10.1 (7.1,9)a, DUR 2.4 (2.3,10)b, EXM-OVR 6.9 (10.1,9)a,b, with Thouldet's imbibitions, UNTR 1.5 (4.8,10)b, DUR 2.9 (2.7,10)b, EXM-OVR 30.3 (21.8,10)a. With each imbibitions set, superscript letters denote groups that are not statistically different. In conclusion, a resin-modified glass ionomer coating applied over an enamel lesion resulted in significantly enhanced remineralization versus untreated control. A conventional rosin-based fluoride varnish applied over the lesion did not change the remineralization behavior versus the control. Ion diffusion through the coating, and ion release from the coating, are proposed as ion sources for the remineralization observed under the RMGI.