Dentin caries activity status related to hardness and elasticity

This research tested the hypothesis that active and arrested carious dentin lesions have distinct structural characteristics and differ in atomic force microscopy-based nano-mechanical properties of the identifiable zones found in hydrated coronal carious lesions. Eight carious molars were used in this study. After longitudinally bisecting all the samples through the centers of carious lesions, they were divided into two subgroups: moderately active caries and arrested caries. The samples were highly polished and stained by caries detector, which allowed identification of four zones: pink, light pink, transparent and apparently normal. The mechanical properties were studied wet using atomic force microscopy. The results show that both groups contained the same zones, regardless of activity status, and different zones have different mechanical properties. Generally, the more demineralized outer zones (pink, light pink) were larger and the mechanical properties of the zones were lower for moderately active caries. For arrested caries, the transparent zone occupied a larger portion of the lesion and the reduced elastic modulus was not significantly different from the underlying normal zone, although its hardness was lower than the apparently normal zone.