Neutrophil activity compromises root caries remineralization and alters caries-affected-like dentin

Root caries (RC) progression involves the dentin extracellular matrix (dECM) degradation by proteolytic enzymes. As neutrophil-derived enzymes have been systemically associated with ECM degradation, we hypothesized that neutrophil activity would: (i) inhibit RC remineralization; and (ii) alter the caries-affected-like dentin.

In vitro RC were created on human dentin specimens. Half each lesion was covered to keep the initial lesion (IL). The other half (final lesion; FL) was exposed to one of the following groups (n = 10): Control (buffer solution; C); Neutrophils (human neutrophils; N); Collagenase (positive control; Col), and then remineralized by pH-cycling and sodium fluoride. RC remineralization was calculated using rhodamine infiltration and cross-sectional microhardness (CSMH). Collagen of the fully demineralized dentin was stained with picrosirius red. The physical properties of the caries-affected-like dentin were investigated by CSMH and loss of mineral density (MD).

Two-way ANOVA and Tukey showed only remineralization in the C group (p < 0.001). N did not show any remineralization (p = 0.588) between IL and FL. The N and Col groups exhibited changes in collagen integrity and organization. The N and Col groups' caries-affected-like dentin showed significantly lower CSMH (p < 0.001) than the C group, and significant losses (IL-FL) of MD (p = 0.012 and p = 0.042, respectively). In contrast, no MD loss was observed in the C group (p = 0.411).

Neutrophil-derived enzymes compromise RC remineralization and detrimentally affect the physical properties of the caries-affected-like dentin.

Identifying proteolytic sources involved with dECM degradation during RC progression will pave new research directions.