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Cathepsin D: ultra-immunohistochemical localization in dentinogenesis.

Cathepsin D was purified from rat liver using a new affinity chromatographic method, based on the coupling to the specific inhibitor pepstatin. This preparation was used for the production of specific antibodies from rabbit. The purified IgG fraction was conjugated to horseradish peroxidase in a two-step coupling procedure and used for electron microscopic immunohistochemistry of the odontoblast-predentine region of the rat incisor. Precipitates, indicating the presence of cathepsin D, were seen in the odontoblast, odontoblast process, and in the extracellular unmineralized matrix, the predentine. The observations are discussed in relation to proteoglycan degradation at the mineralization front simultaneous with crystal formation, and in relation to the function of lysosomal enzymes in the turnover of connective tissue.

Animals↗

Bone sialoprotein-induced reparative dentinogenesis in the pulp of rat's molar.

Bone sialoprotein (BSP), an osteogenic protein (OP), mixed with a carrier, was implanted in the pulp of rat first upper molars (OP group). Cavities were prepared with dental burs and pulp perforation was carried out by pressure with the tip of a steel probe. After 8, 14, and 30 days, the rats were killed and the pulps of the OP group were compared with (1) a sham group (S group), (2) a group where the carrier was implanted alone (C group), and (3) capping with calcium hydroxide (Ca group). After 8 days, a few inflammatory cells were seen, mostly located at the pulp surface near the perforation. In the Ca group, a dentin bridge started to form, in contrast to the other groups. After 15 days, globular structures were seen in the pulps of the S and C groups. A reparative osteodentin bridge isolated the pulp from the cavity in the Ca group. Variable reactions were seen in the OP group, with some evidence of cell and matrix alignments or plugs of osteodentin in continuity with an inner layer of reparative dentin. After 30 days, irregular osteodentin formation was observed in the pulps of the S and C groups, with a tendency for globular structures to merge, but with interglobular spaces filled by pulp remnants. In the Ca group, osteodentin was observed in the mesial part of the pulp chamber. In the BSP-implanted group, the osteogenic protein stimulated the formation of a homogeneous dentin-like deposit occupying most of the mesial part of the pulp. Apparently, BSP stimulates the differentiation of cells which secrete an organized extracellular matrix more efficiently than any other capping material used so far. Altogether, the results reported here support that bone sialoprotein displays novel bioactive properties and is capable of stimulating in 1 month's time the development of a thick reparative dentinal tissue in the pulp, occluding the perforation and filling the mesial third of the pulp chamber.

Animals↗

Comparison of the effect of colchicine and vinblastine on the inhibiton of dentinogenesis in rat incisors.

The quantitative effect of vinblastine, colchicine and lumicolchicine on the rate of dentine formation was determined by chronologically-labelling dentine with the lead salt of EDTA, before and after the intravenous administration of the test drug. Colchicine and vinblastine produced a dose-dependent inhibition of dentine formation. Lumicolchicine had no adverse effect. Although the log dose-response lines of colchicine and vinblastine were parallel, the effect of vinblastine was more potent. The relative potency ratio of vinblastine to colchicine was 1.25-1.70. These results suggest that both colchicine and vinblastine may act at the same site i.e. microtubules, thereby inhibiting the secretion of new dentine matrix.

Animals↗

Ontogeny of circadian dentinogenesis in the rat incisor.

Periodic growth increments are found universally in the dentine of animals. The goal here was to determine when and how circadian dentine growth increments develop ontogenetically. A total of 97 rat pups, obtained from 13 mothers of the Wistar strain, were injected with nitrilotriacetato lead at appropriate intervals to chronologically label the dentine. Labelled rat pups were killed 5-50 days after birth. Histological transverse sections of the demineralized dentine were obtained from the maxillary incisors of the pups and stained with haematoxylin. Two types of increments were observed in the circumpulpal dentine. The first type was a deeply stained circadian band which appeared at intervals of about 16-24 microns. The other was a faintly stained, narrow, ultradian increment, at intervals of approx. 6-8 microns. The circadian increments were first detected during the second to third week after birth and were observed consistently afterwards. Before the circadian increments developed, the ultradian increments were predominant. These two rhythms seemed to be independent of each other and sometimes coexisted in one section. Thus, the two types of dentine increments may be due to two independent mechanisms.

Activity Cycles↗