Degradation of extracellular matrices propagates calcification during development and healing in bones and teeth.

BACKGROUND: Bone, dentin, and enamel are tissues formed through calcification, a process involving deposition of calcium phosphate minerals on extracellular organic matrices. Calcification, the underlying mechanism of which is unknown, is initiated with mineral deposition followed by advancing of the deposit and subsequent maturation of the mineral crystal. HIGHLIGHT: We have reviewed the current knowledge of how calcification proceeds during bone development, bone healing, and enamel and dentin development, based on reported studies. Previous studies reported by us and by other authors have suggested that degradation of some extracellular matrix (ECM) proteins is involved in calcification during bone and dentin development and bone healing in a manner similar to that previously reported for enamel development. CONCLUSION: The ECM proteins may inhibit mineral deposition and calcification, similar to the role of amelogenin during enamel development. The candidates for the amelogenin equivalents in bone and dentin have not been identified. Further studies are required to elucidate the regulatory mechanisms of bone and dentin calcification in light of specific ECM proteins that prevent calcification and enzymes that degrade these ECM proteins.

Calcification in rat developing mandibular bone demonstrated by whole mount staining, microcomputed tomography and scanning electron microscopy with energy dispersive X-ray spectroscopy.

The study was designed to investigate calcification in developing rat mandibular bone using whole mount staining, micro-computed tomography (micro-CT) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). Wistar rats at embryonic days 16, 18, and 20 and postnatal weeks 1 and 6 were used. Rats were fixed with 4% paraformaldehyde and heads were resected, frozen and sectioned for histology, then analysed with SEM-EDX. Some of the specimens were observed with micro-CT. Other rats were fixed and stained with alcian blue and alizarin red for whole mount staining. Histology and whole mount staining showed that osteoid was deposited around Meckel's cartilage at day 15 and developed into bone at day 16. Accumulation of Ca and P was identified in the bone matrix with SEM-EDX. The area of bone expanded until week 6. The Ca/P ratio increased, whereas the C/Ca and C/P ratios decreased during development. Micro-CT demonstrated an increase in radio-opacity with bone development. The results suggest that rat mandibular bone formation is initiated around Meckel's cartilage at day 15. Deposition and maturation of the calcium phosphate mineral increase gradually with decrease in the organic component as the rat mandible develops.

Bone matrix calcification during embryonic and postembryonic rat calvarial development assessed by SEM-EDX spectroscopy, XRD, and FTIR spectroscopy.

Bone mineral is constituted of biological hydroxyapatite crystals. In developing bone, the mineral crystal matures and the Ca/P ratio increases. However, how an increase in the Ca/P ratio is involved in maturation of the crystal is not known. The relationships among organic components and mineral changes are also unclear. The study was designed to investigate the process of calcification during rat calvarial bone development. Calcification was evaluated by analyzing the atomic distribution and concentration of Ca, P, and C with scanning electron microscopy (SEM)-energy-dispersive X-ray (EDX) spectroscopy and changes in the crystal structure with X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Histological analysis showed that rat calvarial bone formation started around embryonic day 16. The areas of Ca and P expanded, matching the region of the developing bone matrix, whereas the area of C became localized around bone. X-ray diffraction and FTIR analysis showed that the amorphous-like structure of the minerals at embryonic day 16 gradually transformed into poorly crystalline hydroxyapatite, whereas the proportion of mineral to protein increased until postnatal week 6. FTIR analysis also showed that crystallization of hydroxyapatite started around embryonic day 20, by which time SEM-EDX spectroscopy showed that the Ca/P ratio had increased and the C/Ca and C/P ratios had decreased significantly. The study suggests that the Ca/P molar ratio increases and the proportion of organic components such as proteins of the bone matrix decreases during the early stage of calcification, whereas crystal maturation continues throughout embryonic and postembryonic bone development.

Analysis of calcium, phosphorus, and carbon concentrations during developmental calcification of dentin and enamel in rat incisors using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX).

OBJECTIVE: The study was designed to investigate the concentrations of calcium (Ca), phosphorus (P), and carbon (C) during developmental calcification of dentin and enamel in rat incisors. METHODS: Mandibular incisors from eight 2-week-old male Wistar rats were analyzed by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). We analyzed data on the elements in the course of developmental processes in dentin and enamel and along the vertical line of the matrix between odontoblasts and ameloblasts. RESULTS: The dentin concentrations of Ca and P and the Ca/P ratio were the lowest, while the C concentration was the highest in initial dentin. The Ca and P concentrations were the lowest, whereas the C concentration was the highest in predentin along the vertical line; the Ca/P ratio did not show any differences. The concentrations of Ca and P increased, while the C concentration decreased during early maturation and more so in late maturation in developing enamel, while the Ca/P ratio increased during late maturation. The Ca and P concentrations and the Ca/P ratio were the highest, while the C concentration was the lowest in enamel adjacent to the junction with dentin on the vertical line. CONCLUSIONS: During tooth development, the initial dentin matrix may possess distinctive mineral characteristics as compared with other parts of dentin and predentin. Elemental composition of the mineral in enamel may change during late maturation. Our results are suggestive of degradation of organic components during developmental calcification in dentin and enamel.