In addition, the reducible intermolecular covalent cross-links of the collagen are partly BMS-777607 manufacturer shifted to the precursor form, thus leading to decreased cross-links—but this change is reversible [22], and the 67-nm cross-bands of the collagen fibrils remain [23]. These results support the idea that caries-affected dentin is remineralizable. On the other hand, the secondary structure of collagen is slightly altered by the carious process [15], and the distribution of antigenically intact collagen fibrils and proteoglycans is significantly lower in normal dentin [24]. Reductions in antigenicity
from the organic matrix of sclerotic dentin under caries lesions raise concern about the potential Selleckchem GPCR Compound Library of interfibirillar remineralization [24]. Under a caries process, continuous
deposition of minerals occurs within the tubule lumen (Fig. 2). In fact, most of the dentinal tubules in caries-affected dentin are occluded by mineral crystals [25]. The crystals in the tubule lumen render the refractive index of the lumen similar to that of the intertubular dentin, making the transparent layer. In these mineral deposits, Mg was identified although Mg was barely present in intertubular caries-affected dentin [9]. Therefore, intratubular minerals consist of large rhombohedral crystals of Mg-substituted β-TCP (whitlokite) [26], which is less soluble than hydroxyapatite. As mineral is lost from the dentin matrix during the carious process, Tyrosine-protein kinase BLK its volume is replaced by water. The water content of normal dentin is approximately 10%, whereas that of caries-affected dentin shows a higher value, which varies from 14% to 53% [27]. On the other hand, permeability of caries-affected dentin decreases due to occlusion of the tubules. Tagami et al. [28] found young carious molars were only 14% as permeable as young normal dentin and suggested that the transparent layer would be effective in decreasing
permeability. Caries-affected dentin is softer than normal dentin, with about half the hardness, even though mineral depositions occlude dentinal tubules [2], [7], [11], [25], [29], [30] and [31]. In addition, ultimate tensile strength (UTS) of caries-affected dentin is also lower than that of normal dentin, and there is a positive correlation in caries-affected dentin between the UTS and the Knoop hardness number [6]. On the other hand, Nishitani et al. [32] reported that the matrix of demineralized caries-affected dentin was as strong as that of normal demineralized dentin. These results would indicate that lower UTS and hardness of caries-affected dentin are due to loss of mineral in intertubular dentin. Marshall et al. [29] reported that the mean elastic modulus (18.2 GPa) and nanohardness (0.8 GPa) of intertubular dentin on the transparent layer were slightly, but significantly lower than those of the unaffected intertubular dentin (20.6 and 1.0 GPa, respectively).