Method: 90 human enamel samples with artificial WSLs created using a bi-layer protocol, were assigned to 3 WSL surface pre-conditioning groups (n=30); a: air-abrasion with BAG-polyacrylic acid (PAA-BAG) powder, b: acid-etching using 37% phosphoric acid gel (positive control), c: unconditioned (negative control). Each group was further divided into 3 subgroups according to the subsequent remineralisation therapy (n=10); I: BAG paste (39 wt.% BAG), II: BAG slurry (100 wt.% BAG) and III: de-ionised water (negative control). The average surface roughness (Sa) and the lesion step height compared to intra-specimen sound enamel references were analysed using non-contact profilometry. Optical changes within the lesion subsurface compared to baseline scans were assessed using optical coherence tomography (OCT). Knoop microhardness evaluated the WSLs’ mechanical properties. Raman micro-spectroscopy measured the v-(CO3)2-/v1-(PO4)3- ratio. Structural changes in the lesion were observed using confocal laser scanning microscopy (CLSM) and scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDX). Data was analysed statistically using linear modelling and one-way ANOVA tests (p=0.05).
Result: PAA-BAG air-abrasion and acid-etching removed 5.1µm and 2.2µm respectively from the lesion surface, increasing the WSL surface roughness. Pre-conditioning WSLs with PAA-BAG air-abrasion reduced the subsurface light scattering, increased their Knoop microhardness and the mineral content of the remineralised lesions (p<0.05). SEM-EDX micrographs revealed mineral depositions covering the lesion surface containing silicon traces of reacted BAG particles. BAG slurry surface pre-conditioning resulted in a superior remineralisation rate measured with Raman and SEM analyses, when compared to BAG paste.
Conclusion: Pre-conditioning WSL surfaces with PAA-BAG air-abrasion modified the lesion surface physically by removing an ultra-thin surface layer and increasing the lesions’ surface area and consequently enhanced the remineralisation effect using BAG 45S5 therapy.