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PubMed1983

Structural organization of calcospherites in normal and rachitic human dentine.

The structure of human dentine affected by familial hypophosphataemic rickets was investigated by polarized light and electron microscopy. Within the calcospherites both radially-orientated and collagen-orientated crystals were present, in approximately equal numbers. This was so, but less distinctly, in the calcospherites of normal dentine. It is concluded that dentine mineralizes entirely by formation of calcospherities which coalesce. It is proposed that matrix vesicles are probably responsible for the initiation of mineralization, and that growth of the calcospherites may depend on scavenging of inorganic pyrophosphate by the first-formed crystals. Growth of these crystals is thus poisoned but the resulting removal of inhibition allows deposition of further crystals by precipitation and by nucleation on collagen. The rachitic structure of dentine appeared to be due to slow calcospherite growth, probably as a result of the depressed serum phosphate characteristic of the disease.

Adult↗
PubMed1984

Organ culture study of effect of vitamin-A-deficiency on rat third molar development.

A culture procedure for rat third molars suitable for nutritional-developmental studies is described. Unerupted third molars from 12-day-old rats were cultured in BGJb media containing 20 per cent rat serum and supplemented with 25 mM HEPES buffer, 25 mg ascorbic acid, 20 mg L-glutamine, 12 mg penicillin G and 10 mg streptomycin sulphate per 100 ml of media. Molars were cultured at the liquid-gas interphase using a 50 per cent O2, 45 per cent N2, 5 per cent CO2 gas mixture at 10 lb-psig (pounds per square inch guage). Molar cultures were maintained successfully for 9-14 days without evidence of necrosis, although they developed at a slower rate than in vivo. Molars cultured in 50 per cent O2 compared to those cultured in 21 per cent O2 for periods of 2, 4, 6 and 8 days had higher values for protein, alkaline phosphatase (AP), Ca, P and Ca/P. Vitamin-A-deficiency gave lower values for AP, Ca, P, Ca/P, 45Ca, 35S and [14C]-proline uptake. Histologically, A - molars had atrophic ameloblasts, some foci of squamous metaplasia and abnormal keratin formation. Thus, deficiency of vitamin A imposed during in-vitro development of rat third molars retarded dentinogenesis and interfered with early mineralization of enamel and dentine.

Aging↗
PubMed1987

Light and transmission electron microscopy of the effects of calcium, magnesium and phosphate on dentine and enamel formed by rat molars in vitro.

The effect of addition of eight different combinations of Ca, Mg and P supplements (control, Ca, Mg, P, CaMg, CaP, PMg and CaMgP) on three-day-old rat maxillary second molars, explanted at the premineralizing stage and cultured for two weeks, was studied. Light-microscopy sections, cut parallel to the occlusal plane, were divided into four sectors and given a score according to an ordinal scale for dentine and enamel depending on the regularity of these matrices. An analysis of variance on these scores revealed a significant favourable effect of Mg, CaMg and CaMgP and an adverse effect of Ca on enamel. A favourable effect on dentine regularity was obtained after addition of Ca or Mg. Ultrastructurally, enamel changes such as amorphous enamel matrix, voids and disturbance in rod-interrod pattern were seen after addition of Ca, P, CaP. Thin enamel with less tight packing of crystals was observed after CaMg addition. A thick layer of enamel with highly-organized rod-interrod pattern was seen with Mg, PMg and CaMgP addition. It is suggested that Mg plays an important role in the interaction with Ca and P for the harmonious development of enamel and dentine in vitro.

Animals↗
PubMed1987

Effect of aluminium on mineralization of rat third molar in vitro.

Crl: COBS rat third-molar explants were cultured for 12 days in either 0.6 X 10(-2), 4 X 10(-2) or 6 X 10(-2) mM aluminium, or for 12 days with exposure to 13 X 10(-2) mM Al at different 6-day intervals. Total protein, alkaline phosphatase, calcium and phosphorous were measured to evaluate cell viability and the degree of mineralization. Al in concentrations above 4 X 10(-2) mM significantly reduced the Ca and P content of explants cultured for 12 days. Explants exposed to 13 X 10(-2) mM Al for the first 6 days had less Ca and P than those exposed for the last 6 days of culture. Haematoxylin and eosin-stained sections of explants showed no gross abnormalities.

Alkaline Phosphatase↗
PubMed1990

Effects of single doses of 1-hydroxyethylidene-1,1-bisphosphonate on the mineralizing front of rat incisor enamel: a microradiographic and scanning electron microscopic study.

The effects of a single dose of HEBP were examined by injecting rats subcutaneously with various doses (0.5, 1, 2.5, 5 and 10 mg P/kg body wt) and killing them either 2 or 9 days after injection. The maxillary incisors were processed for microradiography and the mandibular incisors for scanning electron microscopy after enzymatic digestion of the enamel organ remains. All doses resulted in a hypomineralized incremental band corresponding to the position of the mineralizing front at the time of injection. At 5 and 10 mg P/kg body wt, a hypomineralized lesion was found throughout the whole thickness of the enamel in an area which corresponded to the stage of late enamel secretion at the time of injection. The surface layer covering this lesion was elevated or disrupted. By scanning electron microscopy, there were three different types of lesions along the enamel surface: a "demarcation groove" corresponding to the initial enamel formation at the time of injection; an "area containing mineral globules" and a "bright band" corresponding to the stages of late secretory and final enamel formation, respectively, at the time of injection. A single injection of HEBP thus interferes with different stages of enamel formation. The findings may be explained as of the physico-chemical effects of HEBP on the mineral phase alone, but a direct effect of the drug on ameloblast function cannot be excluded.

Amelogenesis↗