Effect of the combined use of resin infiltration and bioactive glass on the surface properties of white spot lesions with or without sodium hypochlorite pretreatment: an in vitro study

Background To evaluate the effect of the combined use of resin infiltration and the subsequent bioactive glass (BAG) remineralization, with or without 5.25% sodium hypochlorite (NaOCl) pretreatment, on the surface properties of artificial enamel white spot lesions (WSLs) under toothbrushing cycles. Methods One hundred and twelve enamel blocks (4 mm × 4 mm × 2 mm) were cut from the buccal surfaces of the intact human premolars and demineralized to establish artificial enamel WSLs. All enamel blocks were then randomly allocated into four groups: RI/FF, resin infiltration + fluoride-free toothpaste suspension; RI/BAG, resin infiltration + 6% BAG solution; N/RI/FF, 5.25% NaOCl pretreatment + resin infiltration + fluoride-free toothpaste suspension; N/RI/BAG, 5.25% NaOCl pretreatment + resin infiltration + 6% BAG solution. After resin infiltration, one half of the buccal surface was covered as the self-control side, with the other half serving as the experimental side. All specimens were then immersed in the corresponding suspensions and subjected to 55,000 toothbrushing cycles. Surface morphology, elemental analysis, crystal characteristics, surface roughness and surface microhardness of the experimental and control sides were assessed by scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS) observation, X-ray diffraction (XRD), integrated white-light confocal microscope and microhardness tester, respectively. Results The calcium to phosphate ratios (mean [± standard deviation]) were 2.12 [± 0.18], 2.28 [± 0.12], 2.20 [± 0.14] and 2.32 [± 0.10] for groups RI/FF, RI/BAG, N/RI/FF and N/RI/BAG respectively ( p  = 0.038). XRD revealed apatite formation in all groups. The mean surface roughness (Ra and Sq) of the groups were as follows: Ra values (nm): 1104 [± 114], 433 [± 52], 1050 [± 177] and 381 [± 33] respectively ( p  < 0.001); Sq values (µm): 7.7 [± 1.0], 4.3 [± 0.3], 7.5 [± 0.4] and 3.9 [± 0.4] respectively ( p  < 0.001). The mean surface microhardness (kg/mm 2 ) of the groups were 245 [± 24], 336 [± 29], 336 [± 29] and 355 [± 22] for groups RI/FF, RI/BAG, N/RI/FF and N/RI/BAG respectively ( p <  0.001). Conclusions The combined use of resin infiltration and BAG remineralization seems to be a potential treatment method for enhancing the surface properties of enamel WSLs.