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PubMed1991

The effect of lead acetate on dentine formation in the rat.

The intravenous injection of lead acetate produces a response in dentine by formation of the so-called lead line. This is associated with a rapid but temporary rise in serum calcium and phosphorus. Previous studies have suggested that lead replaces calcium and phosphorus in the apatite lattice. In this study the lead line was investigated in the scanning electron microscope using backscattered electron imaging and was shown to consist of continuous hypomineralized interglobular spaces within the dentine. Dentine formation was disrupted for at least a week after injection of lead ions. With energy dispersive analysis by X-rays, no localized concentration of lead was detectable within the 'lead line'. It is suggested that the lead line results from a direct effect of lead on the odontoblasts and other hard tissue-forming cells producing a rapid loss of intracellular calcium temporarily displaced by lead ions and a subsequent disturbance of local calcium metabolism.

Animals↗

PubMed1991

Temperature dependence of water transport into the mineralized matrix of freeze-dried human dentine.

Ten dentine sections cut perpendicular to the dentinal tubules from human mature non-carious third molars, were freeze-dried and then rehydrated by immersion in water at four temperatures, 10, 25, 40 and 70 degrees C. The uptake of water by the sections was assessed as a function of rehydration time. The data were analysed using a theoretical model in which the uptake is ascribed to two processes. The first is capillary suction of water into the dentinal tubules, the second is the diffusion of water from the two faces of the section into the mineralized matrix. By fitting theory to experiment the diffusion coefficient of water in intertubular dentine at the different temperatures was found. Using the Arrhenius relation the activation energy of diffusion of water in intertubular dentine was calculated as Ea = 29.5 +/- 2.2 kJ/mol, which is of the order of the strength of a hydrogen bond. Transport of water in the mineralized matrix during rehydration is thus most likely a hopping of water molecules along the surfaces of the collagen and/or mineral, each jump involving the breaking of one hydrogen bond.

Dentin↗

PubMed1992

Localization of glycosylated matrix proteins in secretory porcine enamel and their possible functional roles in enamel mineralization.

The present study was undertaken to investigate glycosylation of porcine enamel proteins secreted in the secretory stage of amelogenesis and to gain insight into functional roles of glycosylated proteins in enamel mineralization. Enamel proteins, isolated from various zones of the secretory enamel, were separated by SDS-PAGE and then transferred on to a nitrocellulose membrane. The transblotted proteins were visualized with either antibodies against porcine amelogenins or various biotin-conjugated lectins. The lectins used were Con-A, GS-II, STA, WGA, s-WGA, GS-I, MPA, VVA, PNA, RCA-I, DBA, SJA, UEA-I, Lotus-A and LPA. The results of the immuno- and lectin blottings revealed that most of the lectins did not bind to porcine amelogenins, while a large number of non-amelogenins having various molecular masses were stained strongly with the conjugated WGA, Con A and MPA lectins. On the basis of the binding specificity with the lectins, porcine non-amelogenins were classified into two groups: WGA (and Con A)-binding moieties at 60-90 kDa (WGA-HMW); and MPA-binding moieties at 13-17 kDa (MPA-LMW). These two groups of non-amelogenins differed distinctly in terms of their localization and stability in the secretory tissue and their adsorption properties onto hydroxyapatite. The WGA-HMW were concentrated in the outer region adjacent to the ameloblasts and disappeared (due to degradation) in the underlying inner secretory enamel. In contrast, the MPA-LMW were found in all zones of the secretory enamel and their quantity remained relatively constant. Histochemical studies using FITC-conjugated WGA and MPA showed that the fluorescence-labelling of WGA was localized in the core region of prism rods, while the fluorescence-labelling of MPA was locally limited at the rim of prism rods or at the prism sheath. In separate adsorption studies, it was found that the WGA-HMW, as well as the intact amelogenins, displayed a high adsorption affinity on to apatite crystals, whereas the MPA-LMW showed only marginal adsorption on to apatitic surfaces. The overall results indicate that part of the heterogeneity found in porcine enamel proteins can be ascribed to variations of carbohydrate moieties attached to non-amelogenins.(ABSTRACT TRUNCATED AT 400 WORDS)

Adsorption↗

PubMed1993

The distribution of cellular retinoic acid-binding protein I during odontogenesis in the rat incisor.

Retinoids are important molecules in various aspects of embryological development. Here the distribution of cellular retinoic acid-binding protein I (CRABPI) was studied in the continuously growing incisor of adult rats using an affinity-purified rabbit polyclonal antibody. CRABPI was present throughout the presecretory and secretory ameloblast layer. The protein disappeared from that layer during its maturation phase. The adjacent dental mesenchyme of the developing pulp stained positively for CRABPI, especially in the layer immediately beneath the fully differentiated odontoblasts. Little CRABPI was present in the odontoblast layer itself. The distribution of CRABPI, both in the undifferentiated basal region of the incisor tooth and associated with the cells during hard-tissue formation, suggests a role for this molecule during differentiation and hard-tissue genesis.

Ameloblasts↗

PubMed1993

The structure of dentine after the injection of strontium chloride by backscattered electron imaging in the scanning electron microscope.

The subcutaneous injection of 0.5 ml of 20% aqueous strontium chloride produced a distinct calciotraumatic response in rat incisor dentine. In both the labial and lingual dentine this consisted of an unmineralized layer comprising continuous interglobular spaces. Lingually this unmineralized layer was sharply defined and about 1-2 microns in width but labially it was more irregular, diffuse and difficult to measure. Labially and lingually the dentine formed after the unmineralized layer hypomineralized in comparison to the rest of the dentine. Within the hypomineralized labial dentine a diffuse, more intensely hypomineralized layer was often present. The appearance of the unmineralized layer probably reflects the differences in structure between labial and lingual dentine, that is, small linear calcospherites lingually and large irregular calcospherites labially.

Animals↗

PubMed1993

Fluoride-induced developmental changes in enamel and dentine of European roe deer (Capreolus capreolus L.) as a result of environmental pollution.

Using macroscopic, microradiographic and scanning electron-microscopic methods, the effects of increased fluoride exposure on enamel and dentine formation were studied in fluorosed mandibular premolars and molars of roe deer from the heavily industrialized Ruhr area, Germany. Macroscopically, fluorosed teeth were characterized by opaque and stained enamel and in more severe cases also by enamel surface lesions, reduction or loss of enamel ridges on their occlusal surfaces and increased wear. Microradiographically, fluorosed enamel exhibited different degrees of subsurface hypomineralization, in part apparently indicating a fluoride effect during enamel maturation. In some specimens, a pronounced but varying enhancement of the pattern of Retzius lines was observed throughout the enamel, denoting strongly intermittent fluoride exposure during enamel matrix secretion. This variation in exposure was also reflected histologically in dentine, by bands of interglobular dentine and marked accentuation of incremental lines. Microradiography of sections through enamel surface hypoplastic lesions showed the enamel forming the bottom and partly also the walls of the lesions to be highly mineralized. Scanning electron microscopy showed that the outer enamel along the more pronounced hypoplastic lesions consisted of stacked, thin layers of 'aprismatic' enamel, indicating that the ameloblasts in these areas had lost the distal (rod-forming) regions of their Tomes' processes. These observations demonstrate that the origin of enamel hypoplasias in deer clearly differs from that in rodents, where fluoride induces the formation of subameloblastic cysts. The differences in the degree of fluorotic alteration between the teeth of a single tooth row could be related to the developmental sequence of the dentition in roe deer. The roe deer is thus considered to be a very sensitive and useful bioindicator of environmental pollution by fluorides.

Animals↗

PubMed1994

The time-course of the induction of reparative dentine formation in monkeys by recombinant human osteogenic protein-1.

Recombinant human osteogenic protein-1 (hOP-1, BMP-7) induces cartilage and bone formation when implanted in extra- and intraskeletal sites in vivo. rOP-1 also preserves pulp vitality and stimulates reparative dentine formation when placed on partially amputated vital dental pulp tissue. The amount of dentine formed in 6 weeks was earlier found to be proportional to the total amount of rOP-1/carrier placed on the pulp and the capacity of the pulp to respond to rOP-1 appeared to be independent of the amount of coronal pulp removed. This reparative dentine was not completely mineralized after 6 weeks healing. Experiments were now made to determine the capacity of hOP-1 to preserve the vitality of and induce reparative dentine in vital radicular pulps. The extent of tissue mineralization present after 1, 2, 4 and 6 months' healing time in permanent monkey teeth was assessed. Radicular pulp vitality was maintained, reparative dentine formed, and mineralization was nearly 75% complete after 1 month and more than 95% after 4 months. The effects of irrigating the exposed pulps with EDTA, sodium hypochlorite or saline were also compared. Significantly more sodium hypochlorite-treated pulps became non-vital and the root canals of all the non-vital teeth contained bacteria at the time of sacrifice.

Animals↗

PubMed1994

Morphometric analysis of the deposition and mineralization of enamel and dentine from rat incisor during the recovery phase following a low-calcium regimen.

The administration of a low-calcium diet to pups nursed by a mother on the same diet has been shown to induce a slowing of growth. A reduction of the apposition rate of dentine, which was normally mineralized, and a dramatic reduction of the extent of mineralization of enamel, whose organic matrix was otherwise produced in an almost normal amount, was observed in the incisors of these animals. Modifications of the mineral apposition rate of dentine, measured after administration of tetracycline (10 mg/kg), and the thickness and the microhardness of the two tissues, the latter being an expression of the degree of mineralization, were now investigated when hypocalcic pups were restored to a normal-calcium diet for 10 or 60 days. Enamel microhardness was increased by more than 60% after only 10 days of restored diet and had become the same as in the control tissue after 60 days, without any significant increase in thickness. Dentine thickness and mineral apposition rate increased significantly, to become similar to those of the controls after 60 days of restored diet. In dentine there was no significant variation of microhardness between experimental pups and controls, either during the low-calcium diet or the restorative period. These results indicate that the deposition of the organic matrix of enamel is a process independent from that of its mineralization, and that the mineralization of the organic matrix happens by its replacement even a long time after its deposition. In contrast, the deposition and mineralization of dentine are strictly interdependent processes, at least in these experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Effects of xylitol and carbohydrate diets on dental caries, dentine formation and mineralization in young rats.

Female Wistar rats were weaned at the age of 3 weeks and fed for 7 weeks either a high-sucrose diet, a non-cariogenic raw potato-starch diet, a high-sucrose diet with 5% xylitol supplement, a raw potato-starch diet with 5% xylitol supplement or a non-cariogenic, commercial, powdered rat food (Ewos R3) for reference. A low xylitol concentration reduced the progression and severity of carious lesions but did not affect dentine apposition or the width of predentine in rats fed high-carbohydrate diets. Widening of the predentine zone in rats fed a high-sucrose diet might reflect disturbed mineralization, which could not be explained by serum ionized calcium or phosphate ion levels and which could not be corrected by low xylitol concentrations. It is concluded that the reduced area of dentinal carious lesions after low xylitol supplementation is not dependent on dentine formation or mineralization, but rather on direct effects in the mouth.

Animals↗

PubMed1996

A comparison of the mineral content of enamel and dentine in human premolars and enamel pearls measured by X-ray microtomography.

Mineral content gradients in two composite enamel pearls from permanent human upper molars were measured by X-ray microtomography (XMT) at a resolution of 15-30 microns. This non-destructive microscopic technique was used to make 15-microns thick XMT slices with 100-microns separation through one pearl and 250-microns separation through the other. Average mineral contents were calculated from the linear absorption coefficients determined from regions of the XMT slices assuming the inorganic component to be calcium hydroxyapatite. These values were compared with similar XMT studies of coronal enamel and dentine of upper permanent premolars. A mineral content gradient in the pearls, reducing from the enamel surface to the amelodentinal junction, was found; this was similar to that observed in the coronal enamel of the upper premolar. The mineral contents in the surface and deeper enamel regions of the pearl were similar to those observed in premolar enamel. In contrast, the mineral content for the dentine of the pearl was greatest at the amelodentinal junction, i.e. the gradient was in the opposite direction to that observed in premolar dentine. These results suggest that the process of mineralization of the pearl dentine differs from that in permanent control dentine. In addition, gradients in enamel and dentine mineral contents reducing from the tip of the pearl to the base of the pearl were found.

Bicuspid↗

PubMed1996

The relation between long-period incremental markings in dentine and daily cross-striations in enamel in human teeth.

Ground sections of human permanent teeth were chosen where fluorescent labels in the dentine, resulting from repeated doses of tetracycline antibiotic, were unambiguously associated with accentuated markings in the enamel developing at the same time. Counts of daily cross-striations in enamel were continued from one tooth to another in a developmental sequence over a period of some 1200 days such that the time interval between doses of tetracycline could be calibrated. Long-period incremental markings in the dentine, spaced on average between 15 and 30 microns apart (and first described by Andresen in 1898) were easily visible in the coronal dentine when the ground sections were viewed with polarized light. The total number of long-period incremental markings in the dentine between the consecutive fluorescent labels was also counted. A regression plot of daily incremental lines in enamel against long-period lines in dentine demonstrated a regular and consistent relation between the two (r = 0.997) over a 1200-1300-day period. These data support the hypothesis that long-period markings in dentine are in fact regular incremental markings with a constant periodicity in an individual. They also suggest that regular long-period markings in dentine can be used to reconstruct the timing of tooth growth or to retrieve developmental information about dentine formation rates in forensic, archaeological and palaeontological studies with some confidence.

Anti-Bacterial Agents↗

PubMed1966