Non-destructive assessment of inhibition of demineralization in dental enamel irradiated by a λ=9.3-μm CO2 laser at ablative irradiation intensities with PS-OCT

Background and Objective: Polarization sensitive optical coherence tomography (PS-OCT) has great promise for the non-destructive assessment of the efficacy of anti-caries agents such as fluoride and thermal laser treatments on enamel surfaces. The purpose of this study was to demonstrate that PS-OCT can be used to measure demineralization in craters/incisions prepared in enamel by a CO2 laser operating at the high irradiation intensities required for cavity preparations. Materials and Methods: Incisions in bovine enamel surfaces were produced by a CO2 laser used with a water spray. The laser was operated at lambda = 9.3 mu m with a pulse duration of 15 ps and an incident fluence of 20 J/cm(2). The laser treatments were also combined with topical fluoride treatments. A PS-OCT system operating at 1,310 nm was used to acquire polarization resolved images of six areas including sound and laser-ablated+topical fluoride treated zones on each sample. After imaging the teeth, they were sectioned and the thin sections were examined with polarized light microscopy (PLM) and transverse microradiography (TMR). The integrated reflectivity and lesion depth derived from the PS-OCT scans, the integrated mineral loss and depth measured using TMR and the lesion depth measured with PLM were acquired for each area on the fifteen samples for comparison. Results: The integrated reflectivity and depth in the areas treated by the laser and fluoride were significantly lower (P<0.05) than for the untreated enamel. Similar results were observed for TMR and PLM. Conclusions: These results suggest that PS-OCT has great potential for the non-destructive in vivo assessment of the inhibition of demineralization by lasers at ablative irradiation intensities with and without topical fluoride application.