Etiology of Enamel Hypoplasia and Interglobular Dentin: The Roles of Hypocalcemia and Hypophosphatemia

X-Linked Hypophosphatemia: Does Targeted Therapy Modify Dental Impairment?

X-linked hypophosphatemia is a rare, hereditary disorder that significant influences teeth and alveolar bone. The first clinical sign leading to the diagnosis of X-linked hypophosphatemia is often dental impairment with dental abscesses and dentin mineralization defects. Genetic analysis helped find the responsible gene and therefore opened up new ways of therapeutically managing X-linked hypophosphatemia. The human monoclonal antibody Burosumab represents a milestone in the targeted therapy of this hereditary disease by directly addressing its pathophysiology. Targeted therapy has been shown to improve skeletal impairment, pain, and phosphate metabolism. However, the influence of this new therapy on dental impairment has only been addressed in a few recent studies with varying results. Therefore, in this review, we aim to summarize the dental phenotype and analyze the different treatment modalities with a focus on dental impairment.

The Oral Health of a Group of 19th Century South Australian Settlers in Relation to Their General Health and Compared with That of Contemporaneous Samples

The aims of this study are to determine the oral health status of a rare sample of 19th-century migrant settlers to South Australia, how oral conditions may have influenced their general health, and how the oral health of this group compares with contemporaneous samples in Australia, New Zealand, and Britain. Dentitions of 18 adults and 22 subadults were investigated using non-destructive methods (micro-CT, macroscopic, radiographic). Extensive carious lesions were identified in seventeen adults and four subadults, and from this group one subadult and sixteen adults had antemortem tooth loss. Sixteen adults showed evidence of periodontal disease. Enamel hypoplastic (EH) defects were identified in fourteen adults and nine subadults. Many individuals with dental defects also had skeletal signs of comorbidities. South Australian individuals had the same percentage of carious lesions as the British sample (53%), more than other historic Australian samples, but less than a contemporary New Zealand sample. Over 50% of individuals from all the historic cemeteries had EH defects, suggesting systemic health insults during dental development were common during the 19th century. The overall oral health of the South Australian settlers was poor but, in some categories, (tooth wear, periapical abscess, periodontal disease), better than the other historic samples.

Health effects of European colonization: An investigation of skeletal remains from 19th to early 20th century migrant settlers in South Australia

The British colony of South Australia, established in 1836, offered a fresh start to migrants hoping for a better life. A cohort of settlers buried in a section of St Mary’s Anglican Church Cemetery (1847–1927) allocated for government funded burials was investigated to determine their health, with a focus on skeletal manifestations associated with metabolic deficiencies. Findings of St Mary’s sample were compared with those published for contemporary skeletal samples from two British cemeteries, St Martin’s, Birmingham, and St Peter’s, Wolverhampton, to explore similarities and differences. To investigate the changing economic background of the St Mary’s cohort, which may have influenced the location of their burial within the cemetery, the number and demographic profile of government funded burials and those in privately funded leased plots were compared. The study sample consisted of the skeletal remains of 65 individuals (20 adults, 45 subadults) from St Mary’s Cemetery ‘free ground’ section. The bones and teeth of individuals in this cohort showed evidence of pathological manifestations, including areas of abnormal porosity in bone cortices in 9 adults and 12 subadults and flaring of metaphyses (one subadult) and costochondral junctions of the ribs (one subadult). Porous lesions of orbital roof bones (Types 3 to 4) were seen on three subadults. Macroscopic examination of teeth identified enamel hypoplastic defects and micro-CT scans showed areas of interglobular dentine. Comparison of St Mary’s findings with the British samples revealed that prevalences of manifestations associated with vitamin C deficiency were higher at St Mary’s and manifestations associated with vitamin D deficiency were lower respectively. The location of burial pattern at St Mary’s Cemetery, from the mid-1840s to1860s, showed differences in the economic status of migrants. This pattern changed from the 1870s, which reflected improvements in the local economy and the economic recovery of the colony.

The rachitic tooth: Refining the use of interglobular dentine in diagnosing vitamin D deficiency

PURPOSE

This study provides guidelines on how IGD can be differentiated from other microstructures that naturally occur in dentine. Interglobular dentine (IGD) has recently been linked to disruption in vitamin D, calcium, and phosphorous pathways offering a valuable method to investigate vitamin D deficiency in archaeological individuals, but not all dentine defects are IGD.

METHODS

A detailed review of dental literature and dental histology cases gathered from known living and archaeological individuals were incorporated into interpretations.

RESULTS

Investigation of tooth dentine revealed that there can be instances where IGD is not linked to vitamin D deficiency. Information on how to differentiate different forms of defects in dentine were identified.

CONCLUSIONS

We conclude that caution is required when evaluating low-grade IGD, as it may be misidentified.

CONTRIBUTION TO KNOWLEDGE

Information reviewed and assimilated contributes to refining the role of IGD to act as a biological marker, particularly in less severe cases of vitamin D deficiency through provision of clear guidance.

LIMITATIONS OF THIS STUDY

Information from earlier experimental work is limited and until recently understanding of vitamin D and deficiency of this pro-hormone was restricted.

SUGGESTIONS FOR FURTHER RESEARCH

Further data could be gathered from living individuals with known biological/medical information.

Dental Findings in Patients With Non-surgical Hypoparathyroidism and Pseudohypoparathyroidism: A Systematic Review

Background: Dental aberrations have been mentioned in relation to non-surgical hypoparathyroidism (Ns-HypoPT) and pseudohypoparathyroidism (PHP). However, a systematic review of dental characteristics have not been performed. The present systematic review describes the dental findings in patients with Ns-HypoPT and PHP.

Methods: Studies on Ns-HypoPT and PHP reporting dental features were eligible. A systematic literature search was conducted using four bibliographic databases (Web of Science, Scopus, Pubmed, and Embase) and was limited to studies written in English. Reviews, meta-analyses and letters were excluded. Both the research and reporting of results were based on PRISMA (preferred Reporting Items for Systematic Reviews and Meta-Analysis) guidelines.

Results: Of 88 studies included, nine were cross-sectional, one was a prospective cohort study, 26 were case series, and 52 were case reports. The most frequently reported findings in patients with Ns-HypoPT were enamel opacities, enamel hypoplasia, hypodontia, and eruption disturbances. In patients with PHP, enamel hypoplasia, eruption disturbance, and deviation of the root morphology were the most frequently reported findings.

Conclusion: An association between enamel hypoplasia and Ns-HypoPT and PHP is likely. The results should, however, be interpreted cautiously due to the limited number of high-quality studies. The present review confirms the need of further well-designed studies, such as large-scale studies, e.g., multicenter studies, to conclude on the reported associations between Ns-HypoPT/PHP and enamel hypoplasia.

Deletion of serotonin 2B receptor provokes structural alterations of mouse dental tissues

Rampant caries and periodontal diseases occur in patients treated with antidepressants such as serotonin reuptake inhibitors (SRIs; e.g., Prozac) which target the serotonin transporter (SERT). As the serotonin 2B receptor (5HT2BR) regulates SERT functionality and capacity to recognize SRIs, we investigated the potential role of 5HT2BR on dental tissues by exploiting 5HT2BR knockout (KO) mice. Compared to wild-type (WT) mice, several structural differences were identified in the teeth of KO mice. In the molar of KO mice, rod curvatures and twisting were altered compared to WT mice, suggesting involvement of 5HT2BR at early stages of enamel formation. The volume of the KO enamel layer was also reduced, and larger porosities were observed in the prismatic enamel, with smaller crystallite thickness. Crystallite pattern disorganization and occlusal abrasion were enhanced in female KO mice, indicating a sexual dimorphism. In the incisor, no difference was detected in the width of the enamel layer between KO and WT mice; however, enamel maturation differed in absence of 5HT2BR. Specifically, the outer aprismatic enamel border was 1.5- to 2-fold larger in KO compared to WT mice, together with a decreased etching pattern. Finally, although no noticeable difference was observed in dentin, the micro-CT three-dimensional pulp reconstruction evidenced a decrease in both length and width of dentin formation in the root canals of the KO versus WT mice. These data provide evidence that 5HT2BR-mediated signaling pathways are involved in enamel formation and dentinogenesis.

Obesity and dental caries in children: a systematic review and meta-analysis

OBJECTIVES

Obesity and dental caries have become increasingly prevalent challenges to public health. Research results into the relationship between obesity and dental caries in children have been mixed and inconclusive. The aim of this review and meta-analysis was to provide evidence to quantify the relationship between obesity and dental caries in children using a systematic approach.

METHODS

A systematic search for papers between 1980 and 2010 addressing childhood obesity and dental caries was conducted and a random effects model meta-analysis applied.

RESULTS

Fourteen papers met the selection criteria. Overall, a significant relationship between childhood obesity and dental caries (effect size = 0.104, P = 0.049) was found. When analysed by dentition type (primary versus permanent), there was a nonsignificant association of obesity and dental caries in permanent and primary dentitions, yet on accounting only for standardized definitions for assessment of child obesity using body mass index, a strong significant relationship was evident in children with permanent dentitions. Moderating for study country of origin (newly 'industrialized' versus industrialized) showed a significant relationship between obesity and dental caries in children from industrialized but not newly industrialized countries. Cofactors such as age and socioeconomic class were significant moderators.

CONCLUSIONS

Future analysis should investigate these confounding variables, helping shape the future of obesity management programmes and oral health interventions, through determining common risk factors.

Development of enamel defects in rat mandibular incisor after thyro-parathyroidectomy

Previous studies with scanning electron microscopy (SEM) demonstrated the presence of small hypoplastic defects in the incisal third of incisors and deep hypoplasia in the apical third of the incisors after thyro-parathyroidectomy in the rat. These studies provided a morphological description of the defects, but uncertainty remained concerning their development throughout amelogenesis. The aim of the present investigation was to study, with SEM operated in the backscattered mode, the development of the hypoplastic defects, from the beginning of the secretion to the end of the maturation zone of the enamel, in the lower incisor of thyroparathyroidectomized rats. The results of the present study showed that the large and small defects developed are separate entities that do not develop into the other. The distribution of large defects might be linked to a reduction of the eruption rate in these rats. The pathogenesis of these defects needs further investigation.

The dentino-enamel junction revisited

The dentino-enamel junction is not an simple inert interface between two mineralized structures. A less simplistic view suggests that the dentino-enamel junctional complex should also include the inner aprismatic enamel and the mantle dentin. At early stages of enamel formation, fibroblast growth factor (FGF)-2 is stored in and released from the inner aprismatic enamel, possibly under the control of matrix metalloproteinase (MMP)-3. The concentration peak for MMP-2 and -9 observed in the mantle dentin coincided with a very low labeling for TIMP-1 and -2, favoring the cross-talk between mineralizing epithelial and connective structures, and as a consequence the translocation of enamel proteins toward odontoblasts and pulp cells, and vice versa, the translocation of dentin proteins toward secretory ameloblasts and cells of the enamel organ. Finally, in X-linked hypophosphatemic rickets, large interglobular spaces in the circumpulpal dentin were the major defect induced by the gene alteration, whereas the mantle dentin was constantly unaffected. Altogether, these data plead for the recognition of the dentino-enamel junctional complex as a specific entity bearing its own biological characteristics.

Mepe, the gene encoding a tumor-secreted protein in oncogenic hypophosphatemic osteomalacia, is expressed in bone

The MEPE (matrix extracellular phosphoglycoprotein) gene is a strong candidate for the tumor-derived phosphaturic factor in oncogenic hypophosphatemic osteomalacia (OHO). X-linked hypophosphatemia (XLH) is phenotypically similar to OHO and results from mutations in PHEX, a putative metallopeptidase believed to process a factor(s) regulating bone mineralization and renal phosphate reabsorption. Here we report the isolation of the murine homologue of MEPE, from a bone cDNA library, that encodes a protein of 433 amino acids, 92 amino acids shorter than human MEPE. Mepe, like Phex, is expressed by fully differentiated osteoblasts and down-regulated by 1,25-(OH)2D3. In contrast to Phex, Mepe expression is markedly increased during osteoblast-mediated matrix mineralization. Greater than normal Mepe mRNA levels were observed in bone and osteoblasts derived from Hyp mice, the murine homologue of human XLH. Our data provide the first evidence that MEPE/Mepe is expressed by osteoblasts in association with mineralization.

SEM study of the development of rat incisor enamel hypoplasia under hypocalcemia induced by thyro-parathyroidectomy

Several clinical studies have reported the presence of enamel hypoplasia in congenital hypoparathyroidism or hypocalcemia. In previous studies we showed that thyroparathyroidectomy (TPTX) induced perturbations of the ameloblast morphology and secretion, of the rod pattern and of the enamel surface at late secretory stage and beginning of maturation, and limited hypoplasia in the erupted enamel of rat incisor. The aim of the present study was to evaluate by SEM, the extent and evolution of the enamel alterations of thyro-parathyroidectomized rats during the maturation stage. Wistar rats were thyro-parathyroidectomized and sacrificed 57 days later. The incisors were dissected out and processed for SEM. The surface of the incisor was observed from the end of secretion/beginning of maturation to its incisal erupted end. Transverse sections were prepared to study the structural defects and the prism pattern at different stages. The results showed that the surface of the TPTX incisors presented large hypoplastic defects at the end of secretion/beginning of maturation and only small defects in the erupted part. Transverse sections showed that, at the transition from secretion to maturation, the enamel defects extended to the mid-thickness of the tissue. At the incisal end the defects were limited to the outer enamel. As it is difficult to understand how the large apical defects could recover to appear as small hypoplasia at the incisal end, these results raise new questions concerning: (1) the effect of a long term calcium deficiency upon the cellular activity of the ameloblasts, and (2) the capacity of the enamel organ to compensate structural abnormalities.

Morphological and immunocytochemical analyses on the effects of diet-induced hypocalcemia on enamel maturation in the rat incisor

During the maturation stage of amelogenesis, the loss of matrix proteins combined with an accentuated but regulated influx of calcium and phosphate ions into the enamel layer results in the "hardest" tissue of the body. The aim of the present investigation was to examine the effects of chronic hypocalcemia on the maturation of enamel. Twenty-one-day old male Wistar rats were given a calcium-free diet and deionized water for 28 days, while control animals received a normal chow. The rats were perfused with aldehyde and the mandibular incisors were processed for histochemical and ultrastructural analyses and for postembedding colloidal gold immunolabeling with antibodies to amelogenin, ameloblastin, and albumin. The maturation stage enamel organ in hypocalcemic rats exhibited areas with an apparent increase in cell number and the presence of cyst-like structures. In both cases the cells expressed signals for ameloblastin and amelogenin. The content of the cysts was periodic acid-Schiff- and periodic acid-silver nitrate-methanamine-positive and immunolabeled for amelogenin, ameloblastin, and albumin. Masses of a similar material were also found at the enamel surface in depressions of the ameloblast layer. In addition, there were accumulations of glycoproteinaceous matrix at the interface between ameloblasts and enamel. In decalcified specimens, the superficial portion of the enamel matrix sometimes exhibited the presence of tubular crystal "ghosts." The basal lamina, normally separating ameloblasts and enamel during the maturation stage, was missing in some areas. Enamel crystals extended within membrane invaginations at the apical surface of ameloblasts in these areas. Immunolabeling for amelogenin, ameloblastin, and albumin over enamel was variable and showed a heterogeneous distribution. In contrast, enamel in control rats exhibited a homogeneous labeling for amelogenin, a concentration of ameloblastin at the surface, and weak reactivity for albumin. These results suggest that diet-induced chronic hypocalcemia interferes with both cellular and extracellular events during enamel maturation.

Scanning electron microscopy and energy-dispersive X-ray analysis of defects in mature rat incisor enamel after thyroparathyroidectomy

The surface and the structure of the erupted enamel of the continuously growing rat incisor were studied by scanning electron microscopy (SEM) to analyse the effect of thyroparathyroidectomy on enamel formation. Ten male 21-day-old Wistar rats were thyroparathyroidectomized and five sham-operated rats were used as controls. Two months after surgery the rats were perfused with 1% glutaraldehyde and their mandibles dissected. The erupted ends of the incisors were cut off and routinely processed for SEM. An energy-dispersive analysis of X-rays (EDX analysis) was performed for the calcium:iron ratio of the enamel surface defects. Thyroparathyroidectomy induced surface defects and structural abnormalities in the outer layer of the mature erupted enamel. It was established that the surface and structural defects were related. The EDX analysis of the outer enamel showed that the enamel defects were associated with an abnormal elevation of the iron content. The SEM appearance and the EDX analyses indicated that these defects were hypomineralized and rich in iron. The reddish colour of the enamel is due to the high concentrations of iron.

Aspects of teeth from archaelogic sites in Sweden and Denmark

The purpose of this study was to examine ground sections of primary second molars and permanent first molars from the same jaws. Teeth from 11 individuals were collected from archaeologic sites in Sweden and Denmark. Longitudinal buccolingual sections were examined in a polarization light microscope and in a Philips scanning electron microscope (SEM). The seven teeth from Sweden appeared to have been subjected to environmental influences at their burial site, which had affected both the dentin and the enamel. The teeth from the Danish sites had a normal color, and no disintegration of the dentin was seen. The general morphologic appearance was normal in all primary and permanent teeth. The position of the neonatal line indicated a normal full-term gestational age. The observed accentuated incremental lines in both the primary and permanent enamel suggested periods of dietary changes, possibly related to periods of illness. SEM images of the surface area of the Swedish teeth showed an extremely porous enamel surface with severe changes in the prism structure as an effect of acid penetration. The Danish teeth did not show any marked changes in the enamel.

Osteotropic factor-stimulated synthesis of thrombospondin in rat dental pulp cells

The amount of thrombospondin (TSP) mRNA in confluent clonal rat dental pulp cells was increased by transforming growth factor-beta (TGF-beta), 1 alpha-25-dihydroxyvitamin D3 (1,25(OH)2D3), and phorbol 12,13-didecanoate (PDD), with maximal levels 6, 36 and 2 h, respectively, after stimulation. These increases were accompanied by enhanced syntheses of TSP proteins which were found in the different forms in cell layer/matrix fraction (198 and 165 kDa TSP) and the culture medium (180 kDa TSP). These three factors also raised the mRNA level of osteopontin, which is thought to play an important role in mineralization in dentin and bone. The order of effectiveness of these factors was PDD > TGF-beta > 1,25(OH)2D3 for all the stimulations described above. These results suggest that the osteotropic factors enhance TSP synthesis at the pretranslational level and that TSP produced by dental pulp cells participates in formation of reparative dentin.

Enamel incremental lines as recorders for disease in infancy and their relation to the diagnosis of SIDS

The sudden infant death syndrome (SIDS) is a major diagnosis of post-neonatal mortality in the industrialised countries. The cause of death is, however, still elusive. The development of complementary diagnostic methods widening the possibility to analyse the postmortem findings is therefore important. The aim of this study was to histologically examine the enamel of teeth from children dying suddenly and unexpectedly in order to disclose if the presence of enamel disturbances corresponded to neo- or postnatal disorders. During enamel formation ameloblasts are susceptible to local and systemic disturbances which may be reflected in the fully formed enamel as hypoplasia, hypocalcification or accentuated incremental lines. Nineteen consecutive cases of deaths in infants between 1-19 months of age were investigated at the Department of Forensic Pathology, Stockholm, Sweden. The analyses of anamnestic and postmortem data and the analyses of incremental lines were done independently without knowledge of the conclusion of the other part. The results show a good agreement between enamel changes on one hand and the antemortem history and the autopsy findings on the other. This type of investigation may be a valuable complement to the ordinary postmortem investigations of a child who has suddenly and unexpectedly died.

Clinical and histologic appearance in enamel of primary teeth from children with neonatal hypocalcemia induced by blood exchange transfusion

This investigation was undertaken to study the clinical and histologic appearance of deciduous enamel from 11 infants who were subjected to blood exchange transfusions (ET) during the first days of life. As a result of the treatment they had a mean of 3 consecutive hypocalcemic days. At the age of 5 years a dental examination of their primary teeth was performed. Four of the children had clinically recorded enamel aberrations correlated with the neonatal period. Exfoliated teeth were then examined histologically. All had a normal major enamel morphology, and the neonatal line was present in all teeth. Histologically investigated teeth with enamel hypoplasia had the aberrations located close to the neonatal line. The conclusions drawn from this study are that hypocalcemia caused by ET in the newborn period did not affect the width of the neonatal line or the major enamel morphology to any extent. Enamel aberrations occurred only when four or more ETs were performed.

Prevalence and distribution of developmental enamel defects in primary dentition of Chinese children 3-5 years old

A total of 1344 children, 3-5 yr old, from two rural counties, Haidian and Miyun, close to Beijing, China, were examined in 1992. A modified DDE Index was employed in this study, and a pre-designed formula was used to calculate an enamel defect score (EDS) for each individual in the study. Oral examination was performed by one dentist under natural light using a standard mouth mirror and dental probe. Developmental enamel lesions were diagnosed without drying or cleaning the teeth prior to examination. Results from this study showed that primary teeth with defective enamel were seen in 23.9% of the children examined, opacity in 1.6%, and hypoplasia in 22.2%. Among the teeth, maxillary central and lateral incisors were affected by enamel hypoplasia most often (40.8% and 39.2%), followed by maxillary canines (25.7%), maxillary 1st molars (22.1%), and mandibular 1st molars (18.5%). The enamel defects occurred more frequently on the buccal surfaces of teeth than on any other surface. The study did not find a significant association of the children's age, family socioeconomic status, and anthropometric measurements with the distribution of enamel defects. However, there was a significantly higher prevalence of teeth with defects in males compared to females (P < 0.001), as well as mean tooth surfaces with defects (P < 0.05), and mean EDS (P < 0.05). Children born prematurely were shown to have four times more enamel lesions than children who were full term (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in the plasma electrolytes and metabolites of the rat following acute exposure to sodium fluoride and strontium chloride

Acute exposure of rats to strontium or fluoride by i.p. injection of sodium fluoride or strontium chloride resulted in a systemic response in which changes occurred in the plasma electrolytes and metabolites. Strontium resulted in a rapid but temporary hypercalcaemia while fluoride produced a temporary hypocalcaemia. There was no significant hypophosphataemia after fluoride and only a transient hypophosphataemia with strontium. There was some indication of kidney damage and a general stress response following fluoride injection. These results do not support the hypothesis that interglobular dentine is associated with hypophosphataemia or hypoplastic enamel with hypocalcaemia and are in conflict with the observation that the formation of interglobular dentine following the injection of lead acetate is associated with hyperphosphataemia and hypercalcaemia.

Effects of thyro-parathyroidectomy and parathyroidectomy upon dentinogenesis: Part I: Light microscopy

In order to determine the differential effects of the thyroid hormones and the parathyroid hormone upon dentinogenesis in the rat incisor one control group (C) and four groups of surgically treated rats were studied: parathyroid autotransplanted (PTT), thyroidectomized (TX), parathyroidectomized (PTX), and thyro-parathyroidectomized group. One month after surgery the incisors were dissected and the tissues were prepared for light microscopy and morphometric measurements. This study revealed modifications in the TPTX rats as well as in the PTX rats: an enlargement of the predentin, alterations in the predentin appearance and the presence of mineralization defects. These results confirm that the effects observed are probably due to a PTH deficiency and/or hypocalcemia and suggest that their occurrence is associated with a determined stage of dentinogenesis in the rat.

Effect of hypocalcemic state on enamel formation in rat maxillary incisors

Several authors have proposed that hypocalcemia can interfere with amelogenesis, resulting in enamel aberrations. Therefore, the purpose of this investigation was to study the effects of a diet-induced hypocalcemic state in young rats on enamel formation of the maxillary incisors. The experimental rats were fed a special diet, free from vitamin D and very low in calcium. The control rats were fed a normal diet. The experimental period was 3 wk. After termination, the blood analysis showed that the experimental rats had developed hypocalcemia with very low values of both total and ionized blood calcium. The experimental rats were smaller than their controls after 3 wk, with smaller skulls and teeth. At the light microscope level, the enamel and the ameloblasts did not seem to be affected, except in one rat, the smallest, which showed enamel hypoplasias in both maxillary incisors and a delayed increase of the mineral content during the maturation stage process. It is concluded that the hypocalcemic state induced did not greatly affect enamel formation. However, occasional enamel aberrations may occur.

Clinical and histologic appearance in enamel of primary teeth in relation to neonatal blood ionized calcium values

The purpose of this investigation was to study the relationship between low values of blood ionized calcium measured in the first days of life postpartum and the clinical and histologic appearance of enamel of primary teeth. Twenty-five healthy children selected on the basis of optimality with known blood values of ionized calcium from the first days of life participated in a dental examination at the age of 5 yr. Twenty-four of the children contributed one exfoliated tooth each, which was histologically examined. The infants had lower mean values of ionized blood calcium on days 1 and 3 than day 5 postpartum. Thirteen of the 25 children had enamel aberrations, mainly on one tooth each. The histologic examination showed normal overall enamel morphology. The neonatal line was present in all teeth, and these lines were mostly thin. The registered findings about the enamel morphology could not, in any case, be correlated with the measured values of neonatal blood ionized calcium.

The effects of hypocalcemia/hypophosphatemia on porcine bone and dental hard tissues in an inherited form of type 1 pseudo-vitamin D deficiency rickets

The effects of Vitamin D deficiency rickets on the formation of mineralized dental tissues were studied in a breed of pigs which had moderate and marked hypocalcemia because of an inherited defect in the renal production of the biologically-active Vitamin D metabolites. Affected piglets developed classical symptoms of rickets which were fatal unless Vitamin D supplements were given. The dissected mandibles of homozygous (rickets) and heterozygous (normal) pigs were photographed and radiographed. Compared with those of normal pigs, the mandibles of homozygous pigs demonstrated slowed development/eruption of permanent teeth, under-mineralized bone, underdeveloped dentin (enlarged pulp chambers), interglobular dentin, and enamel hypoplasia. Enamel defects in rachitic pig teeth were difficult to observe radiographically, but could be detected visually and by SDS-PAGE analysis of the enamel protein components of developing and maturing enamel. There was significant retention of amelogenins in the enamel maturation zones of developing molars taken from rachitic pigs, but there was no obvious difference in the patterns of amelogenin processing.

Pulp narrowing in renal end stage and transplanted patients

A comparison of relative dental pulp size in chronic renal disease patients with dental pulp size in healthy controls revealed a significant pulp narrowing in the kidney disease group (n = 44). A strong correlation between the chronicity of the renal disease and the pulp narrowing was found in the premolar and molar teeth of the tested group. A review of the literature concerning pulp narrowing is also presented.

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.

Familial renal hypophosphatemia, minor facial anomalies, intracerebral calcifications, and non-rachitic bone changes: apparently new syndrome?

We report on two brothers with renal hypophosphatemia, intracerebral calcifications, minor facial anomalies, and short distal phalanges. The children presented with recurrent dental abscesses; one had premature closure of the anterior fontanelle. Biochemical findings included hypophosphatemia and elevated serum alkaline phosphatase with normocalcemia. Blood levels of parathyroid hormone, 1,25(OH)2 and 25(OH) vitamin D levels were normal; TRP (the fractional tubular reabsorption of PO4) and TmP/GFR (the tubular maximum rate of PO4 reabsorption in relation to GFR) were low. Both parents had a normal serum phosphate and brain CT scan without evidence of calcifications. This apparently new syndrome of renal hypophosphatemia associated with intracerebral calcifications appears to be inherited as either an autosomal recessive or an X-linked trait.

Microscopic and crystallographic examinations of the teeth of the X-linked hypophosphatemic mouse

Teeth from the C57BL/6J-Hyp mouse (Hyp mouse) were examined histologically, radiographically, and crystallographically. Microscopic examinations of the ground sections, the decalcified and H-E-stained sections, and the contact microradiograms of molars and incisors from the Hyp mouse showed several abnormalities--such as large pulp chamber, wide predentin, thin dentin at the pulp floor, and multiple occurrences of interglobular dentin. Powder and microbeam x-ray diffraction analyses showed that the crystallinity of hydroxyapatite in incisor globular dentin from the Hyp mouse was higher than that in incisor dentin from the normal mouse. On the other hand, the findings of transmission electron microscopy demonstrated that the sizes of hydroxyapatite crystals of globular dentin in the Hyp incisor were larger than those in normal incisor dentin. These results demonstrated that the findings in Hyp mouse teeth were in accord with those of human XLH teeth.

Hypocalcification and hypoplasia in permanent teeth of children from different ethnic groups in South Africa assessed with a new index

A new descriptive index, the HHI (hypocalcification-hypoplasia index), is described for comparing enamel defects in groups of people. The index was used in a study completed in 1986, in which 1251 11-year-old children from different ethnic groups resident in South Africa were examined: 210 rural black, 203 urban black, 206 urban colored, 426 urban Indian, and 206 urban white. The index can be used as a screening examination, and the results from these different ethnic groups are presented.

Developmental enamel defects in primary teeth in children with cerebral palsy, mental retardation, or hearing defects: a review

Developmental enamel defects in primary teeth have been found at least twice as frequently in children with cerebral palsy or mental retardation as in control children, and frequently also in children with sensori-neural hearing deficits. The developing tooth germ is sensitive to a range of systemic disturbances, some of which may also affect neurologic development. Because the enamel cannot recover once it is damaged, it may provide a repository of information on the timing and nature of insults potentially affecting other ectodermally derived structures, including the brain. This paper reviews the literature on developmental defects of enamel in primary teeth, asking whether these might be useful as biological markers of the timing and in some cases the nature of insults. Among systemic factors related to development of enamel that might also have implications for neurologic development are certain genetic disorders including tuberous sclerosis, premature birth, neonatal nutritional disturbances (especially hypocalcemia), viral infections (such as rubella and cytomegalovirus during gestation), thyroid disorders, and maternal diabetes. It is concluded that further research is warranted concerning whether developmental defects of dental enamel can be useful markers for the timing of intra-uterine or perinatal events associated with certain neurologic and sensory disorders of children.

The crystallinity of human deciduous teeth in hypophosphataemic vitamin D-resistant rickets

Five teeth were obtained from three patients with hypophosphataemic vitamin D-resistant rickets (HVDRR) and five corresponding sound teeth from five healthy children. According to powder X-ray diffraction analysis, the half-peak breadths of (310) and (002) reflections of HVDRR dentine were smaller than those of normal dentine. Splitting fractions obtained from i.r. spectral analysis of HVDRR dentine powder were larger than those of normal. Microbeam X-ray diffraction analysis showed that the relative half-peak breadths of globular dentine in ground sections of HVDRR teeth were smaller than those of normal circumpulpal dentine. Transmission electron microscopy demonstrated that the hydroxyapatite crystals of globular dentine in HVDRR teeth were larger than those of normal dentine. Thus the crystallinity of deciduous tooth dentine in HVDRR was greater than that of normal dentine, mainly because of the large hydroxyapatite crystals in HVDRR globular dentine.

Dentin in chronic renal failure: an ultrastructural study

Disturbances in the mineralization of hard tissues in patients suffering from chronic renal failure and in patients undergoing chronic hemodialysis are a well-established phenomenon. These disturbances are the result of complex pathophysiologic alterations in calcium and phosphorus metabolism. Disturbances in the dentin of teeth, analagous to those occurring in bone, were not recognized until 1983 when it was reported that a significantly thicker predentin layer was present in the teeth of patients with chronic renal failure and in patients being treated with chronic hemodialysis (1). The aim of the present study was to conduct a comparative ultrastructural (SEM) analysis of dentin in this group of patients. A wide spectrum of changes was detected, ranging from mild disturbances with increasing tubule irregularity and focal obliteration of tubule lumens, to widespread formation of dysplastic dentin exhibiting numerous mineralized, largely atubular globules with only occasional large, irregular tubules. In general, these changes appeared to reflect the type and effectiveness of treatment rendered (renal transplant or hemodialysis therapy). The findings suggest that dentin exhibits significant ultrastructural alterations when the underlying homeostatic regulation of calcium and phosphorus metabolism is disturbed in systemic disorders such as chronic renal failure.

Structural deformities of deciduous teeth in patients with hypophosphatemic vitamin D-resistant rickets

Structural deformities of deciduous teeth from patients with hypophosphatemic vitamin D-resistant rickets (HVDRR) (1 male and 2 female patients) were examined by means of transmitted light microscopy, contact microradiography, and x-ray microanalysis. Freshly extracted teeth were fixed in formalin and subsequently hemisected longitudinally through the midline. One half was prepared for ground sections and the other half for decalcified sections. Neither gross nor microscopic abnormalities were present in enamel of patients with HVDRR. The concentration of calcium and phosphorus and the calcium/phosphorus ratio of the enamel of patients with HVDRR were nearly equal to those of normal teeth, although the degree of radiopacity was less in HVDRR. On the other hand, numerous microscopic abnormalities in the dentin of patients with HVDRR were found, such as interglobular dentin, wide predentin zones, and tubular defects. The concentration of phosphorus in the dentin of a patient with familial HVDRR was extremely low. Furthermore, formation of reparative dentin was observed at the pulp horn of teeth in patients with HVDRR that had been subjected to definite attrition at the corresponding dentin site.

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.

Histology and microradiography of early post-natal molar tooth development in vitamin-D deficient rats

The role of vitamin D on tooth-germ development was studied. The molars of vitamin D-deficient rats were compared with those of vitamin D-replete controls. The deficiency disturbed enamel and dentine mineralization and decreased their matrix secretion. Morphogenesis was affected; teeth were flattened and the whole of the epithelio-mesenchymal junction rippled. Where this irregularity was maximal, the inner dental epithelium and stratum intermedium were intermingled and the adjoining sub-odontoblast cells were mixed with poorly polarized odontoblasts. The cytodifferentiation of both central and sub-odontoblastic cells was inhibited. Thus vitamin D has a role in the early events of tooth development: morphogenesis, histodifferentiation and cytodifferentiation of pulp cells as well as in enamel and dentine mineralization.

Effects of orthodontic force on enamel formation in normal and hypocalcemic rats

Maxillary incisors of young rats fed a diet deficient in calcium and vitamin D for 4 weeks developed hypoplastic enamel surfaces. In the enamel of maxillary incisors of deficiently fed rats as well as in normal rats, an orthodontic force (50 gm) acting on their incisors for 3-7 days induced foldings in the enamel, globular projections from the surface and marked hypoplastic defects. However, the orthodontic force produced clusters of free-lying enamel matrix only in the nutritionally deficient rats. In view of these observations, it might be concluded that disturbances in enamel formation which cause hypoplasias can be caused both by mechanical trauma and hypocalcemia. Furthermore, it seems that hypocalcemia increases the susceptibility to mechanical trauma of ameloblasts in their secretory stage. Whether the changes in enamel formation noted in the hypocalcemic rats is a direct effect of lowered serum calcium or due to the increase in parathyroid hormone is not known at present.

Syndrome of amelogenesis imperfecta, nephrocalcinosis, impaired renal concentration, and possible abnormality of calcium metabolism

We describe a brother and sister with amelogenesis imperfecta, nephrocalcinosis and impaired renal concentrating ability. This is the second sibship reported, further substantiating autosomal recessive inheritance of this condition. There is lack of enamel, lifelong nocturnal enuresis, progressive punctate nephrocalcinosis, and decreased calcium and phosphate excretion over 24 hours and after an acute load. Increased serum osteocalcin and decreased urine delta-carboxyglutamic acid suggest involvement of vitamin K-dependent calcium binding proteins, although this may represent a secondary finding. No other evidence of abnormal calcium metabolism was found. Renal function is stable in the early teens, but the previously reported patients went on to renal failure.

Calcium distribution in freeze-dried enamel organ tissue during normal and altered enamel mineralization

Energy dispersive X-ray microanalysis was applied to freeze-dried blocks of enamel organ tissue to determine levels of calcium in various cellular regions. The tissue blocks were dissected free from adjacent forming enamel following injection of cobalt or fluoride ions, both of which temporarily inhibit enamel mineralization. In all control and experimental specimens there was an increasing gradient of calcium from the stratum intermedium cells to the distal ends of the ameloblasts. Calcium levels were significantly reduced near the distal ends of the ameloblasts following cobalt or fluoride injection as compared with controls. It is suggested that evidence of an intercellular buildup of calcium near the distal ends of the ameloblast supports a controlling function of these cells. The changes in calcium levels are correlated with alterations in mineralization known to occur in the adjacent enamel of the model systems employed.

Microscopic study of enamel defects in deciduous teeth of infants of diabetic mothers

Ground sections of deciduous teeth from infants of diabetic mothers were examined in polarized light and by microradiography. Widened neonatal lines and subsurface lesions were the main findings in the enamel. Three teeth showed enamel hypoplasia in connection with the neonatal line. The widening of the neonatal line and the hypoplasias are related to the more frequent and more pronounced neonatal hypocalcemia occurring among infants of diabetic mothers.

Enamel structure in deciduous teeth from low-birth-weight infants

Ground sections of deciduous teeth from 64 infants with birth weights below 2000 g and from 43 healthy full-term infants were examined in polarized light and by microradiography. The deciduous enamel displayed various changes, which were more frequent and pronounced in the low-birth-weight group. The main findings were diffuse areas of increased porosity and distinct subsurface lesions in the postnatal enamel. Five teeth with enamel hypoplasia from the low-birth-weight group were also examined. The hypoplasias were all located along the neonatal line. The postnatal enamel seemed to be more susceptible to disturbances in the mineralization than the prenatal enamel. The subsurface lesions showed an arrest in the very late stages of enamel maturation, which frequently occurred in the cervical deciduous enamel. Enamel hypoplasia is considered to be a result of severe neonatal hypocalcemia.

Predentin changes in patients with chronic renal failure

Morphometric studies were carried out on teeth extracted from normal human patients and compared with those extracted from patients suffering from chronic renal failure and patients being treated by chronic hemodialysis. The findings revealed that the predentin layer in patients suffering from chronic renal failure and patients undergoing chronic hemodialysis was significantly thicker than normal. These findings suggest that predentin is the metabolic equivalent of osteoid in bone and that increases in the predentin thickness may therefore be a reliable indicator of osteomalacia. It is suggested that the term odontomalacia be used to describe the changes occurring in the dentin of these patients.

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.

Hypoparathyroidism and pseudohypoparathyroidism in childhood

Although relatively uncommon, the conditions of hypoparathyroidism and pseudohypoparathyroidism in childhood provide an exciting diagnostic and therapeutic challenge. Knowledge of calcium-phosphate homeostasis has progressed rapidly over the past few years so that our understanding of the basic pathophysiological mechanisms has increased tremendously. However, further clinical and basic scientific research will, no doubt, unravel further variations of the various disease entities described.

Role of organic phosphate in mineralization of bone in vitro

Calvarial periostea were dissected from 17-day-old embryonic chicks and folded with the osteogenic cells in apposition. The folded explants were cultured for up to six d on serum and plasma clots or in serum-free hormone-supplemented completely-defined medium. Osteoid consistently formed in such cultures in both types of media, and this osteoid mineralized when appropriate levels of beta-glycerophosphate were added to each type of medium. The data presented suggest that the levels of organic phosphates as a limiting factor in the initiation of mineralization of bone in vitro.