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

TL;DR

Neutrophil activity prevents root caries from healing and changes the structure of affected dentin.

Contribution

This study shows that neutrophil-derived enzymes hinder remineralization and alter dentin properties during root caries progression.

Findings

Neutrophils and collagenase prevent remineralization of root caries lesions.

Neutrophils and collagenase disrupt collagen organization and reduce dentin microhardness.

Neutrophils and collagenase cause significant mineral density loss in caries-affected dentin.

Abstract

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.

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