Abstract
It is believed that penetration of dentinal fluid into natural enamel caries (NEC) is negligible because of the barrier created by underlying sclerotic dentine, but there are conflicting evidences on whether dentine subjacent to NEC is sclerotic or demineralized. This study aimed at investigating the relationship between NEC, subjacent dentine reactions, modification of dentinal fluid, and composition of cariogenic biofilm formed on the NEC surface. Proximal NEC (PNEC) lesions of human permanent posterior teeth were included in five experiments. Histologically, microradiographic analysis with contrast solution (MRC) in dentine revealed a decreased proportion of sclerotic dentine and an increased proportion of deep dentine demineralization compared to the classical stereomicroscopic histological analysis based on dentin color and translucency. Real-time MRC and 3D optical profilometry, and 3D microtomographic analysis evidenced a facilitated transport of modified dentinal fluid towards PNEC lesions. Cariogenic biofilm formed in vitro on the PNEC surface presented lower amounts of insoluble and soluble matrix polysaccharides when 2% chlorexidine was inserted in the pulp chamber. In conclusion, this study evidenced that dentine subjacent to PNEC is mostly demineralized, providing facilitated pathway for dentinal fluid to penetrate into PNEC and alter the composition of the biofilm formed on the PNEC surface.
Highlights
It is believed that penetration of dentinal fluid into natural enamel caries (NEC) is negligible because of the barrier created by underlying sclerotic dentine, but there are conflicting evidences on whether dentine subjacent to NEC is sclerotic or demineralized
Using real-time 2D microradiographic analysis, a facilitated transport of dentinal fluid from the pulp chamber towards the Proximal NEC (PNEC) was detected in 42.86% of the lesions, being statistically different from the expected proportion of 20% (p = 0.0081) with a medium effect size (Cohen H of 0.51), and power of 84.3%
Correlation between enamel and dentine reactions to caries was high when using SM for analyzing dentine reactions (Spearman r of 0.654, 95% CI of 0.74–0.54, p < 0.0001), but decreased when microradiographic analysis with contrast solution (MRC) was used for analyzing dentine reactions (0.238, 95% CI of 0.39–0.07, p = 0.02) (Supplemental Material Fig. 6)
Summary
It is believed that penetration of dentinal fluid into natural enamel caries (NEC) is negligible because of the barrier created by underlying sclerotic dentine, but there are conflicting evidences on whether dentine subjacent to NEC is sclerotic or demineralized. Transport of materials into NEC lesion from underlying dentine is believed to be negligible This is based on evidences suggesting that, even before enamel demineralization reaches the enamel-dentine junction, dentine subjacent to NEC forms mineral crystals obliterating its main transport pathways (dentinal tubules), creating sclerotic dentine close to the enamel-dentine junction[5,6]. In cavitated natural dentine caries lesions, it was reported that tubules in sclerotic dentine are partially obliterated and that the surrounding intertubular dentine (another pathway for materials transport in dentine[3]; Shellis 2000) is demineralized[15] Those evidences suggest the existence of facilitated transport pathways for dentinal fluid in dentine underlying NEC. This study aimed at testing, in PNEC, the relationship between enamel and dentine reactions caries, dentinal fluid transport, and the composition of cariogenic biofilm formed in vitro on the PNEC surface
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