Neutrophil-Induced Physical Changes in Caries-Affected Root Dentin

Objectives: Human neutrophil enzymes have been associated with extracellular matrix degradation and tissue damage in multiple systemic diseases. Our preliminary data show that neutrophils may compromise remineralization of root caries (RC) by degradation of the demineralized dentin matrix. Here, we hypothesized that neutrophils would induce physical changes in the partially mineralized caries-affected dentin. Our goal is to show that neutrophils may alter physical properties of dentin underneath RC lesions.
Methods: For that, chemically created RC were developed on human dentin specimens (~2×4×4mm). After RC formation, half of each lesion was covered to keep the baseline lesion (initial lesion; IL). The other half was exposed to one of the following conditions (n=6): Control (DPBS buffer; negative control); Human Neutrophils; or Collagenase (100 μg/mL; positive control). Following incubation, the second half of all specimens was 8-day pH-cycled and 3-min treated with sodium fluoride (5000 ppm; 2×/day) to induce remineralization (final lesion; FL). Changes on physical properties of the caries-affected dentin were evaluated by cross-sectional microhardness (CSMH) and loss of mineral density (MD).
Results: For CSMH, Two-way ANOVA showed effects of both factors (treatments and RC depth; p<0.001) with no interaction (p=0.999). Scheffe’s test pointed significant differences (p<0.001) in hardness of the caries-affected dentin (FL) between the Neutrophils (53.65MPa) and Collagenase (56.70MPa) groups compared to the Control group (61.43MPa). After remineralization, lower hardness values were observed up to 80 μm-depth within RC lesion, suggesting sustained physical changes induced by RC, regardless group. For MD loss of the caries-affected dentin, T-test within each group (IL-FL) showed statistically significant changes for Collagenase (54 mgHA/cm³; p=0.042) and Neutrophils (148 mgHA/cm³; p=0.012) groups, with no difference for the Control group (4 mgHA/cm³; p=0.411).
Conclusions: These findings reveal that human neutrophils induced deeper physical changes in mineralized dentinal tissue, compromising not only RC remineralization but also the properties of the caries-affected dentin.