The effect of vitamin D on the dentine of the incisor teeth and on the alveolar bone of young rats maintained on diets deficient in calcium or phosphorus

Importance of Dietary Phosphorus for Bone Metabolism and Healthy Aging

Inorganic phosphate (Pi) plays a critical function in many tissues of the body: for example, as part of the hydroxyapatite in the skeleton and as a substrate for ATP synthesis. Pi is the main source of dietary phosphorus. Reduced bioavailability of Pi or excessive losses in the urine causes rickets and osteomalacia. While critical for health in normal amounts, dietary phosphorus is plentiful in the Western diet and is often added to foods as a preservative. This abundance of phosphorus may reduce longevity due to metabolic changes and tissue calcifications. In this review, we examine how dietary phosphorus is absorbed in the gut, current knowledge about Pi sensing, and endocrine regulation of Pi levels. Moreover, we also examine the roles of Pi in different tissues, the consequences of low and high dietary phosphorus in these tissues, and the implications for healthy aging.

Formation and mineralization of murine molar roots with hypocalcaemia induced by a low-calcium diet and the changes after returning to a normal diet

The purpose was to examine the formation and mineralization of molar roots in rats with hypocalcaemia, induced by a low-calcium diet and the changes after returning to a normal diet. Two-week-old male Wistar rats were fed a low-calcium diet (0.03% calcium) during the period when the first molar roots form and then a diet containing normal amounts of calcium (1.83% calcium) was restored. The blood calcium, the length and mineralization of the first upper molar roots, and the density of surrounding alveolar bone were measured, and the morphological and histological features of the roots examined. While the rats were fed the low-calcium diet, they had a significantly lower blood calcium than normal controls. Morphologically, the upper first molar roots were shorter and the predentine layer was thicker. The mineralization of dentine and the surrounding alveolar bone was significantly less than in the controls and no mineralization was detected in the thickened predentine. After a normal calcium diet had been restored, the blood calcium, thickness of dentine, alveolar bone density, and length of the roots caught up with the normal. In addition, hypomineralized dentine and interglobular dentine were observed. Subsequently, the mineralization of the dentine increased and the amount of interglobular dentine gradually decreased. These results suggest that in rats a low-calcium diet induces hypocalcaemia, causing the formation of interglobular dentine and hypomineralization of the dentine of the roots. Most physiological variables recovered completely with the return to a normal-calcium diet, although some hypomineralization of the dentine remained.

Morphological analysis of dentine formation in young rat molars during the recovery phase with calcium alone or combined with xylitol following a low-calcium dietary regimen

The effects of dietary calcium deficiency and subsequent replenishment of the diet with calcium alone or with xylitol were studied. Thirty 3-week-old Wistar rats were labelled with an i.p. tetracycline injection. Twenty rats were fed a diet with 0.026% calcium (Ca-deficient); 10 received a 0.5% Ca diet (controls). After 3 weeks the tetracycline labelling was repeated. Replenishment of the diet was introduced for Ca-deficient rats, and 10 received additional 5% xylitol in the diet. After 4 weeks the labelling was repeated and the animals were decapitated. Dentine formation was measured by the tetracycline stripes in the lower first and second molars. Calcium deficiency during the first 3 weeks reduced dentine formation. In the control and xylitol groups, a much smaller amount of dentine was formed during the recovery period. With Ca alone, dentine formation was faster than in the controls or Ca-xylitol group and did not differ from the Ca-deficient period. These results indicate that in rat molars the odontoblasts can accelerate the rate of dentine formation when calcium is restored to the diet, at least during primary dentinogenesis. This effect was not seen when 5% xylitol was added to the replenishment diet.

Influence of masticatory muscle function on craniofacial growth in hypocalcemic rats

The aim of this study was to investigate the influence of low masticatory function on the craniofacial growth pattern in rats fed a low calcium and vitamin D deficient diet. Male growing rats were divided randomly into three groups: the Normal Hard Diet group, the Deficient Soft Diet group, and the Deficient Hard Diet Group. Lateral cephalograms were taken at days 0, 14 and at the end of the experiment, day 28. The craniofacial growth pattern was altered by an upwards rotation of the viscerocranium (orthocranialization) in the Deficient groups and, the total skull lengths were shorter than in the Normal Hard Diet group. The viscerocranium in the Deficient Soft Diet group was in an even more orthocranial position than in the Deficient Hard Diet group and the antegonial notch was shallower. This indicates that an induced disturbance of craniofacial morphology due to metabolic bone disease during growth is accentuated by a low masticatory function.

Differential expression of calbindin-D 28 kDa in rat incisor ameloblasts throughout enamel development

Calbindin-D 28 kDa (CaBP 28 kDa), a vitamin D-dependent calcium-binding protein, has been associated with calcium handling by cells. We have investigated the expression of this protein in the rat incisor enamel organ, an epithelium interposed between a mineralizing matrix and connective tissue rich in blood vessels, by radioimmunoassay (RIA), Western blotting, and quantitative protein A-gold immunocytochemistry with antibodies to rat kidney CaBP 28 kDa. RIA of cytosolic extracts showed that enamel organs contained relatively high concentrations of CaBP 28 kDa (compared to kidney; see review by Christakos S., C. Gabrielides, and W.B. Rhoten 1989 Endocr. Rev., 10:3-25). Immunoblotting of proteins extracted from enamel organ strips revealed an intensely-stained band near 28 kDa throughout amelogenesis following ameloblast differentiation. Immunocytochemically, CaBP 28 kDa was localized exclusively within ameloblasts. The density of labelling increased from the presecretory stage to the secretory stage and fluctuated across the maturation stage in relation to ameloblast modulation. Ruffle-ended ameloblasts consistently showed the most intense immunoreaction. Gold particles were present throughout the cytoplasm and nuclei of ameloblasts but regions rich in rough endoplasmic reticulum or cell webs showed a higher immunolabelling. Some gold particles were also associated with the external face of the rough endoplasmic reticulum. Multivesicular bodies in maturation stage ameloblasts were occasionally immunoreactive. These data suggest that the intracellular concentration of CaBP 28 kDa is regulated throughout amelogenesis reflecting a stage-specific control of calcium homeostasis in ameloblasts.

Effects of a low calcium maternal and weaning diet on the thickness and microhardness of rat incisor enamel and dentine

The deposition and mineralization of incisor hard tissues have been studied in rat pups nursed by mothers on a low calcium diet or weaned with the maternal diet. Animals were killed at 30 days (control and low calcium diets; maternally fed) or 60 days (after 30 days weaning on maternal diet). The degree of mineralization of enamel and dentine was evaluated by a microhardness method on thick transverse sections. The enamel and dentine thickness, and the diameters of the incisor sections and pulp cavity were measured on microradiographs from the sections. Microhardness values of enamel were similar in groups killed after 30 days maternal feeding, but the microhardness of root enamel was 73-74% less in the low calcium-diet weaned group. Peripulpar dentine had mean microhardness values lower than controls in the group fed maternally for 30 days, whereas the whole root dentine appeared significantly less hard in the low calcium-diet weaned group than in the controls. A significant reduction of the incisor bucco-lingual diameter was observed only in this last experimental group. Enamel thickness was significantly lower in the roots of both experimental groups and in the necks of the low calcium weaned group. The reduction in dentine thickness was greater (from -30 to -56%); in the root it was more evident on the lingual aspect. Thus calcium deficiency in the mother's diet did not influence either the deposition or the mineralization of the pup's incisor enamel and dentine. However, when the offspring were weaned with the maternal calcium-deficient diet, mineralization of the tooth hard tissue was retarded.

Effects of diphenylhydantoin on teeth in rabbit

The drug diphenylhydantoin (DPH) is well known to affect the gingiva of humans. Among other known unwanted effects is that on calcified tissues. The initial purpose of our study was to examine the effect of chronic administration of DPH on the continuously erupting incisors of the rabbit. While studying the dentin a second investigation was undertaken when it was noticed that the pulps in DPH-treated rabbits were apparently more vascular than those in the control rabbits. After a treatment period of from 5-6.5 weeks the rabbits were killed, the jaws decalcified, sectioned and stained. The results presented here show that the animals treated with DPH developed less dentin. The pulps from the DPH-treated animals showed a greater area occupied by blood vessels. These experimental results are of interest in view of reported clinical findings that some patients treated with DPH develop smaller teeth with blunted apices. The vessel changes remain unexplained.

Effects of calcium and phosphate on secretion of enamel matrix and its subsequent mineralization in vitro

We examined the effects of various calcium (Ca) and phosphate (P) levels on enamel matrix synthesis, secretion, and its subsequent mineralization in vitro. Second maxillary molar tooth germs of three-day-old hamsters were cultured for nine days in vitro in media containing low (0.9 mmol/L), moderate (2.6 mmol/L), or high (4.5 mmol/L) medium levels of Ca, with either moderate (1.65 mmol/L) or high (3.65 mmol/ L) medium levels of P. Explants were then examined histologically. For examination of matrix synthesis and mineralization, explants were labeled during the last 24 hr of culture with a triple label of 3H-proline, 45Ca, and 32PO4.

At low Ca levels, tooth germs failed to deposit enamel matrix and dentin, and no mineralization took place, regardless of the levels of P. Low levels of Ca, however, did not prevent deposition of pre-dentin. At moderate and high levels of Ca, considerable amounts of enamel and dentin were deposited in vitro, and both matrices mineralized. At high Ca levels, however, the forming enamel hypermineralized, was more irregular, and tended to be thinner. Increasing P concentrations at moderate and high Ca levels resulted in formation of a more regular enamel and dentin and a better-controlled mineralization. Biochemically, high levels of Ca tended to decrease enamel matrix secretion but significantly enhanced the uptake of 45Ca. This Ca-stimulated increase of 45Ca uptake could be reduced to below control levels by increases in P medium levels.

We conclude that: (1) a minimum medium Ca concentration is required to induce enamel matrix deposition and mineralization of both enamel and dentin; (2) high levels of medium Ca induce hypermineralization of enamel and give rise to deposition of a more irregular enamel than at moderate Ca levels; and (3) high levels of P are not able to induce mineralization when Ca levels are low but seem to moderate effects of moderate and high levels of Ca.

Nuclear uptake of 1,25-dihydroxyvitamin D3 in developing rodent teeth: an autoradiographic study

Target cells for 1,25(OH)2 vitamin D3 metabolites are identified in developing rodent teeth by the use of thaw-mount autoradiography. Following the injection of [26, 27-3H]-1,25(OH)2 vitamin D3 into 18-day- and 20-day-old fetal rats and neonatal mice, nuclear concentration of radioactivity is found in different cell types. In incisors of both animal groups, strong nuclear labeling is present predominantly in pulp cells, while relatively weakly labeled cells are found in the layers of odontoblasts, ameloblasts, and stratum intermedium. In molars, nuclear labeling is absent in fetal rats, but is present in 2-day-old neonates in pulp cells and cells in the layers of stratum intermedium of the first molars, but not in the second molars. The absence of labeled pulp cells in the progenitor regions of incisors and in molars of 20-day-old fetal rats, and differential ontogenic appearance of labeled pulp cells in molars, indicates that there is a critical period of receptor emergence. The finding that labeled pulp cells exist in the regions of incisors and molars where secretory odontoblasts are present suggests that nuclear uptake of 1,25(OH)2 vitamin D3 is related to cell maturation and differentiation, and topographically related to the formation of dentin. The results further suggest that, in contrast to bone, the predominant effect of 1,25(OH)2 vitamin D3 is not on tooth cells which are directly involved in the formation of calcified tissue, i.e., ameloblasts and odontoblasts, but rather on supporting tissues such as pulp cells and stratum intermedium.

The effects of parathyroid hormone, calcitonin, and vitamin D metabolites on calcium transport in the secretory rat enamel organ

The effects of parathyroid hormone (PTH), calcitonin (CT), 1,25(OH)2D3, and 24,25(OH)2D3 on calcium transport through the secretory stage enamel organ were studied on developing rat molars in vitro. 24,25(OH)2D3 increased 45Ca uptake by the explants. 24,25(OH)2D3 plus PTH further enhanced 45Ca uptake and resulted in an increase in net calcium uptake by the developing enamel.

The effect of toxic doses of 1,25-dihydroxycholecalciferol on dental tissues in the rat

Vitamin D-depleted rats 4-weeks old were divided into three groups and given daily for 5 weeks cholecalciferol (0.25 microgram) or 1,25(OH)2D3 (0.075 microgram). The third group received no treatment with vitamin D sterols. A fourth control group was fed a diet containing vitamin D. The animals were killed after 5 weeks, plasma was prepared for calcium analysis, and incisors and molars were taken for histology. Growth was monitored throughout. Plasma calcium, body weight and the physical condition of the 1,25(OH)2D3-treated animals indicated that they were toxemic. The pulp-dentine complex of their incisors showed premature aging of fibroblasts and odontoblasts, disturbances in the dentinal matrix and osteodentine formation. That of molars was not affected. There was hypercementosis and bone-like tissue formation in the periodontal-ligament which in the incisors was considerably enlarged; some molars were ankylosed. The pulp-dentine complex of the incisors and molars of the rats in the remaining three groups appeared normal except for zones of hypomineralization in incisors of the third group. The supporting tissues of the teeth of the rats in the other three groups were within normal limits. Thus toxic doses of 1,25(OH)2D3 affected the dental tissues of both developing and mature teeth.

Histologic and microradiographic observations on teeth during calcium deprivation in rats

Adult female rats were subjected to severe calcium deprivation by feeding them a calcium-deficient diet containing oxalate (Group a). Furthermore, pregnant and lactating animals were subjected to the same diet (Group b). The mandibular teeth were examined by histologic, microradiographic and fluorescence microscopic techniques. The incisor enamel was found to be nearly unaffected by the experimental regimen; the dentin formed and mineralized during the experimental period was abnormal only in Group b. Characteristic features were reduced thickness, increased width of predentin and numerous globular defects. Both ameloblasts and odontoblasts were seemingly normal. No obvious differences could be observed between the molars from the controls and the test groups (a,b). "Cementolysis" seemed to be present to the same extent in all groups. In some of the animals of Group b some carious or erosional defects were observed in the molars. These may at least partially account for a small reduction in molar ash content observed in this group.

Odontoblast metabolism in rats deficient in vitamin D and calcium. II. Changes in activities of alkaline phosphatases

Rats were fed a low calcium diet deficient in vitamin D for 14 days. Changes in alkaline phosphatase activities in odontoblasts dissected out from incisor teeth were studied biochemically. A strong increase in pNPP-ase, PPi-ase, total ATP-degradation and Ca2+- ATPase was observed in the deficient animals compared with animals fed a control diet.

Odontoblast metabolism in rats deficient in vitamin D and calcium I: A histochemical survey

Different rat diets, deficient in calcium and/or vitamin D, were tested for varying experimental periods to obtain changes in serum calcium values, body weight gain and odontoblast-predentine morphology. One diet, R 25, used during a 14-day period, was found to induce lowered serum calcium values and an increased predentin width in incisor teeth. Rats fed this diet demonstrated an increase in alkaline phosphatase and ATP-splitting enzyme activity in dentinogenically active incisor odontoblasts. No other metabolic changes in these cells were demonstrated by the histochemical methods employed.

The effect of vitamin D in rats maintained on diets with different mineral content but with the same calcium to phosphorus ratio of unity

1. Eight groups of ten weanling rats were maintained for 60 d on diets containing calcium and phosphorus in the ratio 1:1 (w/w) at four different levels of mineral, namely 0.08, 0.12, 0.24 and 0.36% Ca, with and without the addition of ergocalciferol.

2. Provision of vitamin D increased final body-weight except at the highest level of mineral intake. Similarly, increasing the mineral intake increased final body-weight except at the highest level.

3. Vitamin D raised the serum Ca concentration at all levels of mineral intake but in the experiment as a whole had no significant effect on serum P concentration. Serum Ca concentration was significantly higher at the two higher levels of mineral intake than at the two lower levels. Increasing dietary mineral caused a progressive increase in serum P concentration, except at the highest level of intake.

4. In general, the addition of vitamin D to the diets had no effect on the fresh or dry weights of the humeri; there was an indication, however, that at the two lower levels of mineral intake, vitamin D reduced the fresh weight of bone. The addition of the vitamin caused a reduction in bone volume, and an increase in bone length, bone ash and the ratio of the weight of ash to the weight of organic matter in dry, fat-free bone. With increasing dietary mineral there was an increase in the value of all the bone measurements except bone volume, which was decreased.

5. The addition of vitamin D and increasing dietary mineral both caused an increase in tooth mass and ash content.

6. The ratios of tooth mass to bone mass, and tooth ash to bone ash were unaffected by vitamin D, but decreased with increasing mineral intake.

7. Histological examination of the bones showed that the animals receiving 0.08 % of Ca and P were markedly rachitic although the presence of vitamin D ameliorated the condition. When the dietary mineral intake was raised to 0.12% Ca and P the animals were less severely rachitic and in the presence of vitamin D the bones appeared normal.

8. The incisor teeth were abnormal at the two lower levels of mineral intake, but when vitamin D was provided, the histological appearance was improved. When the Ca and P level in the diet was 0.24%, the incisal dentine appeared normal but the apical predentine was slightlywider thannormal; addition of vitamin D produced teeth of normal appearance. The incisor teeth were normal in appearance in the remaining groups.

9. These results are compared with those obtained in two previous studies where the Ca to P ratios were 1:10 and 10:1 (Harrand & Hartles, 1968, 1969).

A study on the effect of vitamin D in rats maintained on diets with different calcium and phosphorus content but with the same high ratio of calcium to phosphorus

1. Eight groups of ten weanling rats were maintained for 60 days on diets containing calcium and phosphorus in the ratio 10:1 at four different levels of mineral, namely 0.8, 1.19, 2.29 and 3.33% Ca.

2. At the two lower levels of mineral intake the provision of vitamin D reduced final body-weight. Increasing the mineral intake increased final body-weight except at the highest level.

3. Increasing the dietary mineral content had no effect on serum Ca, but serum P was higher in the groups receiving the two higher levels of dietary mineral. Vitamin D raised the serum Ca level in the rats receiving the two lower levels of mineral, and serum P was raised by the vitamin at all levels of mineral intake.

4. Provision of vitamin D at the two lower levels of mineral intake decreased the fresh weight, dry weight and volume of the humerus but had no significant effect on the absolute amount of mineral ash in the bone. Consequentially there was an increase in percentage of ash, overall density and the ratio of weight of ash to organic matter in dry fat-free bone (A:R value). With increasing mineral intake there was an increase in all the bone measurements except volume.

5. The presence of vitamin D had no effect on tooth mass or ash content. Increasing the mineral intake caused an increase in tooth mass and ash except at the highest level of intake.

6. The ratio of tooth ash to bone ash was very much greater at the lower levels of mineral intake than at the higher levels.

7. In the animals on the two lower levels of mineral intake the bones were frankly rachitic, and the presence of vitamin D ameliorated the condition. With increase in mineral intake histological signs of rickets were reduced, but even at the highest level of dietary mineral the epiphyseal discs appeared slightly wider than normal.

8. The incisor teeth of animals on the two lower levels of dietary mineral had wide predentine, and the presence of vitamin D reduced the amount of predentine. At the two higher levels of mineral intake the dentine appeared normal when vitamin D was present in the diet.

9. Quantitatively, the bones were much more affected than the teeth by a low intake of mineral at a Ca to P ratio of 10:1.

A study of the effect of vitamin D in rats maintained on diets with different mineral content but with the same low ratio of calcium to phosphorus

1.Eight groups of weanling rats were maintained for 60 days on diets containing calcium and phosphorus in the ratio 0·1 at four different levels of mineral, namely 0·08, 0·12, 0·23 and 0·32% Ca, and in the presence and absence of added ergocalciferol.

2. Provision of vitamin D increased final body-weight, whereas at the highest mineral intake body-weight was reduced.

3. At each level of dietary mineral the serum Ca concentration was raised by vitamin D, whilst the serum P concentration was lowered except when the mineral intake was lowest.

4. With increasing mineral intake the serum Ca increased until at the highest intake it declined. Serum P was increased only at the highest mineral intake.

5. Measurements were made of bone weights, ash content and volume. Provision of vitamin D increased the fresh weight of bone at all levels of dietary mineral, and the dry weight and ash content were increased except at the lowest level of mineral intake. In general, the higher the dietary mineral the greater was the bone weight and its ash content.

6. The presence of vitamin D resulted in an increase in tooth mass and ash content at each level of mineral intake. Tooth mass and ash increased with increasing dietary mineral except at the highest level when there was a decline.

7. At the lower levels of mineral intake the ratio of tooth mass to bone mass was greater than at the higher levels of intake.

8. Histological examination of the bones revealed no increase in the width of the epiphyseal cartilage in any group. In the group with the lowest levels of Ca and P without vitamin D (0·08% Ca, 0·8% P) the shafts of the femurs appeared thinner and porotic, and the trabeculae were thin; in the group fed the same diets supplemented with vitamin D the shafts were even thinner but less porotic; in all other groups the histological appearance of the bone was within normal limits.

9. Changes in the appearance of the dentine were demonstrated in all groups.

A study in the rat of the interaction between the effects of calcium and phosphorus content of the diet at two different levels and the presence or absence of vitamin D

1. Four groups of weanling rats were maintained on diets containing either 0.12% or 0.24% of both calcium and phosphorus, in the presence and absence of added ergocalciferol. 2. Increase in mineral intake or the provision of vitamin D increased the final body-weight, with a significant interaction between the two factors. 3. Serum Ca and P concentrations were raised significantly by both the vitamin and the increase in mineral intake without signi ficant interaction. 4. Measurements were made of bone and tooth weights and ash values and of the length of the humeri. For only two measurements was there any interaction between the effect of vitamin D and increase in mineral intake, namely the length of the humeri, and their ash values expressed as a percentage of the dry fat-free weight. 5. It is concluded that in relation to the amount of mineral deposited, the incisor tooth is more resistant to nutritional stress than is the bone.