Mineralized tissues in hypophosphatemic rickets.

Hypophosphatemic rickets is caused by renal phosphate wasting that is most commonly due to X-linked dominant mutations in PHEX. PHEX mutations cause hypophosphatemia indirectly, through the increased expression of fibroblast growth factor 23 (FGF23) by osteocytes. FGF23 decreases renal phosphate reabsorption and thereby increases phosphate excretion. The lack of phosphate leads to a mineralization defect at the level of growth plates (rickets), bone tissue (osteomalacia), and teeth, where the defect facilitates the formation of abscesses. The bone tissue immediately adjacent to osteocytes often remains unmineralized ("periosteocytic lesions"), highlighting the osteocyte defect in this disorder. Common clinical features of XLH include deformities of the lower extremities, short stature, enthesopathies, dental abscesses, as well as skull abnormalities such as craniosynostosis and Chiari I malformation. For the past four decades, XLH has been treated by oral phosphate supplementation and calcitriol, which improves rickets and osteomalacia and the dental manifestations, but often does not resolve all aspects of the mineralization defects. A newer treatment approach using inactivating FGF23 antibodies leads to more stable control of serum inorganic phosphorus levels and seems to heal rickets more reliably. However, the long-term benefits of FGF23 antibody treatment remain to be elucidated.

Evaluation of the accuracy of the Nolla method for the estimation of dental age of children between 4-14 years old in Spain: A radiographic study.

The aim of this study was to estimate the age of subjects from their dental age by showing the different stages of tooth development using the Nolla method in a Spanish population sample considering the gender, age group, and the development of the two dental arches. The sample consisted of 604 orthopantomographs corresponding to Spanish children (male: 302 and female: 302) aged from 4 to 14 years old. The resulting chronological and dental ages were compared using Student's t-test. We obtained a good index of agreement between the evaluators and good internal consistency in the evaluation of the ages of the teeth. In general, the dental age estimates were lower than the chronological ages, obtaining an underestimation with the application of the Nolla method. In the male group, the average dental age of the maxillary teeth was 8.36 years and that of the mandibular teeth was 8.40 years, compared to the chronological age of 8.84 years in both cases. In the female group, the average dental age of the maxillary teeth was 7.76 years and that of the mandibular teeth was 7.88 years, compared to the chronological age of 8.70 years in both cases. On applying the Nolla method to our sample, a significant overestimation was observed only in children aged between 4 and 6.9 years. The Nolla method can be used as a complementary tool for estimating age in children of Spanish origin. The application of this method is more favourable in the case of individuals evaluated under the law applied to minors. In general, with this method, age is underestimated, but the calculations involved are reliable, and greater precision has been observed in male than in female. The data from this study can be used as a reference to determine the dental maturity of Spanish children and to estimate their ages.

Animal Board Invited Review: Sheep birth distribution in past herds: a review for prehistoric Europe (6th to 3rd millennia BC).

In temperate latitudes sheep have a seasonal reproductive behaviour, which imposes strong constraints on husbandry in terms of work organization and availability of animal products. During the last 50 years, researchers have focused on understanding the mechanisms driving small ruminants' reproduction cycles and finding ways to control them. This characteristic is inherited from their wild ancestor. However, the history of its evolution over the 10 millennia that separates present day European sheep from their Near Eastern ancestors' remains to be written. This perspective echoes archaeologists' current attempts at reconstructing ancient pastoral societies' socio-economical organization. Information related to birth seasonality may be retrieved directly from archaeological sheep teeth. The methodology consists of reconstructing the seasonal cycle record in sheep molars, through sequential analysis of the stable oxygen isotope composition (δ 18O) of enamel. Because the timing of tooth development is fixed within a species, inter-individual variability in this parameter reflects birth seasonality. A review of the data obtained from 10 European archaeological sites dated from the 6th to the 3rd millennia BC is provided. The results demonstrate a restricted breeding season for sheep: births occurred over a period of 3 to 4 months, from late winter to early summer at latitudes 43°N to 48°N, while a later onset was observed at a higher latitude (59°N). All conclusions concurred with currently held expectations based on present day sheep physiology, which, aside from the historical significance, contributes to the reinforcing of the methodological basis of the approach. Further study in this area will permit regional variability attributable to technical choices, within global schemes, to be fully reported.

Tooth Tissue Engineering: The Importance of Blood Products as a Supplement in Tissue Culture Medium for Human Pulp Dental Stem Cells.

One of the goals in using cells for tissue engineering (TE) and cell therapy consists of optimizing the medium for cell culture. The present study compares three different blood product supplements for improved cell proliferation and protection against DNA damage in cultured human dental pulp stem cells for tooth TE applications. Human cells from dental pulp were first characterized as adult stem cells (ectomesenchymal mixed origin) by flow cytometry. Next, four different cell culture conditions were tested: I, supplement-free; II, supplemented with fetal bovine serum; III, allogeneic human serum; and IV, autologous human serum. Cultured cells were then characterized for cell proliferation, mineralized nodule formation, and colony-forming units (CFU) capability. After 28 days in culture, the comet assay was performed to assess possible damage in cellular DNA. Our results revealed that Protocol IV achieved higher cell proliferation than Protocol I (p = 0.0112). Protocols II and III resulted in higher cell proliferation than Protocol I, but no statistical differences were found relative to Protocol IV. The comet assay revealed less cell damage in cells cultured using Protocol IV as compared to Protocols II and III. The damage percentage observed on Protocol II was significantly higher than all other protocols. CFUs capability was highest using Protocol IV (p = 0.0018) and III, respectively, and the highest degree of mineralization was observed using Protocol IV as compared to Protocols II and III. Protocol IV resulted in significantly improved cell proliferation, and no cell damage was observed. These results demonstrate that human blood product supplements can be used as feasible supplements for culturing adult human dental stem cells.

Characterisation of secretory calcium-binding phosphoprotein-proline-glutamine-rich 1: a novel basal lamina component expressed at cell-tooth interfaces.

Functional genomic screening of the rat enamel organ (EO) has led to the identification of a number of secreted proteins expressed during the maturation stage of amelogenesis, including amelotin (AMTN) and odontogenic ameloblast-associated (ODAM). In this study, we characterise the gene, protein and pattern of expression of a related protein called secretory calcium-binding phosphoprotein-proline-glutamine-rich 1 (SCPPPQ1). The Scpppq1 gene resides within the secretory calcium-binding phosphoprotein (Scpp) cluster. SCPPPQ1 is a highly conserved, 75-residue, secreted protein rich in proline, leucine, glutamine and phenylalanine. In silico data mining has revealed no correlation to any known sequences. Northern blotting of various rat tissues suggests that the expression of Scpppq1 is restricted to tooth and associated tissues. Immunohistochemical analyses show that the protein is expressed during the late maturation stage of amelogenesis and in the junctional epithelium where it localises to an atypical basal lamina at the cell-tooth interface. This discrete localisation suggests that SCPPPQ1, together with AMTN and ODAM, participates in structuring the basal lamina and in mediating attachment of epithelia cells to mineralised tooth surfaces.

New immature hominin fossil from European Lower Pleistocene shows the earliest evidence of a modern human dental development pattern.

Here we present data concerning the pattern of dental development derived from the microcomputed tomography (microCT) study of a recently discovered immature hominin mandible with a mixed dentition recovered from the TD6 level of the Gran Dolina Lower Pleistocene cave site in Sierra de Atapuerca, northern Spain. These data confirm our previous results that nearly 1 million years ago at least one European hominin species had a fully modern pattern of dental development with a clear slowdown in the development of the molar field regarding the anterior dental field. Furthermore, using available information about enamel formation times and root extension rates in chimpanzees, early hominins, and modern humans, we have estimated that the formation time of the upper and lower first molars of individual 5 (H5) from TD6, which had just erupted at the time of the death of this individual, ranges between 5.3 and 6.6 y. Therefore, the eruption time of the first permanent molars (M1) in the TD6 hominins was within the range of variation of modern human populations. Because the time of M1 eruption in primates is a robust marker of life history, we suggest, as a working hypothesis, that these hominins had a prolonged childhood in the range of the variation of modern humans. If this hypothesis is true, it implies that the appearance in Homo of this important developmental biological feature and an associated increase in brain size preceded the development of the neocortical areas leading to the cognitive capabilities that are thought to be exclusive to Homo sapiens.

Nerve growth factor promotes differentiation of odontoblast-like cells.

Contemporary strategies in tooth repair markedly rely on the newest findings on the cellular and biological components of dental development. Among several identified bioactive molecules, neurotrophins were recently proposed to affect tooth germ cell proliferation, differentiation, and cell-extracellular matrix interactions. The present study attempted to explore the effect of nerve growth factor (NGF) on a spontaneously immortalized dental papilla mesenchymal cell line. NGF induced differentiation of odontoblast-lineage cells with subsequent biomineralization in vitro. Here we showed that normalized transcript levels of tissue-specific markers such as DSPP and DMP1 were elevated significantly, indicating cell differentiation and maturation processes. We performed innovative gene expression analysis of TM14, a matricellular protein and novel member of the fibulin family. TM14 expression followed a pattern similar to that of DMP1, which suggests its important role in cell-matrix and intercellular interactions during dentin calcification. Alkaline phosphatase enzyme assay confirmed the extracellular matrix calcifications in NGF-supplemented groups. Thus, NGF was characterized as a potent promoter of mineralization during dentin formation. For the first time, we included TM14 in odontoblast genotype analysis and proved that NGF also promotes in vitro odontoblast differentiation. Collectively, these results highlight the importance of NGF during tooth morphogenesis, as well as urge the elaboration of complex epithelial-mesenchymal tissue cultures, where further elucidation of the signaling factor network could be completed.

The chiton stylus canal: An element delivery pathway for tooth cusp biomineralization.

A detailed investigation of the stylus canal situated within the iron mineralized major lateral teeth of the chiton Acanthopleura hirtosa was undertaken in conjunction with a row-by-row examination of cusp mineralization. The canal is shown to contain columnar epithelial tissue similar to that surrounding the mineralized cusps, including the presence of iron rich particles characteristic of the iron storage protein ferritin. Within the tooth core, a previously undescribed internal pathway or plume is evident above the stylus canal, between the junction zone and mineralizing posterior face of the cusp. Plume formation coincides with the appearance of iron in the superior epithelium and the onset of mineralization at tooth row 13. The plume persists during the delivery of phosphorous and calcium into the tooth core, and is the final region of the cusp to become mineralized. The presence of the stylus canal was confirmed in a further 18 chiton species, revealing that the canal is common to polyplacophoran molluscs. These new data strongly support the growing body of evidence highlighting the importance of the junction zone for tooth mineralization in chiton teeth, and indicate that the chemical and structural environment within the tooth cusp is under far greater biological control than previously considered.

Rapid dental development in a Middle Paleolithic Belgian Neanderthal.

The evolution of life history (pace of growth and reproduction) was crucial to ancient hominin adaptations. The study of dental development facilitates assessment of growth and development in fossil hominins with greater precision than other skeletal analyses. During tooth formation, biological rhythms manifest in enamel and dentine, creating a permanent record of growth rate and duration. Quantification of these internal and external incremental features yields developmental benchmarks, including ages at crown completion, tooth eruption, and root completion. Molar eruption is correlated with other aspects of life history. Recent evidence for developmental differences between modern humans and Neanderthals remains ambiguous. By measuring tooth formation in the entire dentition of a juvenile Neanderthal from Scladina, Belgium, we show that most teeth formed over a shorter time than in modern humans and that dental initiation and eruption were relatively advanced. By registering manifestations of stress across the dentition, we are able to present a precise chronology of Neanderthal dental development that differs from modern humans. At 8 years of age at death, this juvenile displays a degree of development comparable with modern human children who are several years older. We suggest that age at death in juvenile Neanderthals should not be assessed by comparison with modern human standards, particularly those derived from populations of European origin. Moreover, evidence from the Scladina juvenile and other similarly aged hominins suggests that a prolonged childhood and slow life history are unique to Homo sapiens.

An experimental study of the use of hyperbaric oxygen to reduce the side effects of radiation treatment for malignant disease.

Hyperbaric oxygen (HBO) has been used for more than 20 years to assist wound healing in the treatment of the more severe complications associated with the side effects of therapeutic radiation treatment. A prospective study was performed in an irradiated rat model to determine whether HBO is effective in reducing the long-term side effects of therapeutic radiation treatment on normal tissue, when given 1 week after the completion of the radiation treatment. The experimental model was designed to simulate a fractionated course of therapeutic radiation that is commonly used in the treatment of cancer of the mandible. One week following completion of the radiotherapy, the animals underwent a 4-week course of HBO treatment, and two animals from each group were killed at 8-week intervals until the end of the experiment at 36 weeks. Histological sections of tissue clearly showed continued growth of teeth and maintenance of specialized tissues, such as salivary gland and bone, in the treated group compared to the non-treated group. This experimental model demonstrated that HBO is effective in reducing the long-term side effects of therapeutic radiation treatment in normal tissue, when given 1 week after the completion of the radiation treatment.

Relative dental maturity and associated skeletal maturity in prehistoric native Americans of the Ohio valley area.

Estimation of age-at-death of subadults in prehistoric skeletal samples based on modern reference standards rests on a number of assumptions of which many are untestable. If these assumptions are not met error of unknown magnitude and direction will be introduced to the subadult age estimates. This situation suggests that an independent estimate or estimates of age-related features, free of most of the assumptions made when using modern reference standards may be useful supplements in evaluating the age of subadults in prehistoric samples. The present study provides an internally consistent, population-specific measure of maturity for prehistoric Ohio valley Native Americans based on the seriation of dental development that may be used as a supplement to age-estimation. The developing dentition of 581 subadults from eight Ohio valley prehistoric-protohistoric groups was seriated within and among individuals resulting in a sequence of tooth development and a sequence of individuals from least to most mature. Dental maturity stages or sorting categories were then defined based on exclusive, easily observable, and highly repeatable tooth-formation stages. Tooth eruption (into occlusion), bone lengths, and fusion of skeletal elements are summarized by dental maturity stage. This procedure provides maturity estimates for skeletal features ordered by dental maturity stages derived from the same sample thus making explicit the relationship between dental and skeletal maturity.

Expression of collagen XVIII and MMP-20 in developing teeth and odontogenic tumors.

Collagen XVIII is a basement membrane (BM) component, whereas MMP-20 (enamelysin) is a matrix metalloproteinase predominantly expressed in teeth. Since MMP-20 was found to degrade collagen XVIII, we studied the co-expression of these proteins in dental tissues. Collagen XVIII surrounded the developing tooth during early and late bell stages and was also present in developing enamel. Western blotting indicated that developing enamel contains collagen XVIII N-terminal fragments of the frizzled variant. Enamelysin was co-localized with collagen XVIII in the developing enamel matrix and stratum intermedium. Electron microscope analysis showed that total mineral, calcium and phosphorus contents of enamel were slightly increased in collagen XVIII null mice but the analysis revealed no visible defects in the enamel or dentin structures. In odontogenic tumors MMP-20 and collagen XVIII were co-localized in the enamel-like tumor matrix. Our results show that collagen XVIII is present in developing teeth, but its absence seems not to be critical for the development of the teeth.

Prevalence and the duration of linear enamel hypoplasia: a comparative study of Neandertals and Inuit foragers.

As a dental indicator of generalized physiological stress, enamel hypoplasia has been the subject of several Neandertal studies. While previous studies generally have found high frequencies of enamel hypoplasia in Neandertals, the significance of this finding varies with frequencies of enamel hypoplasia in comparative samples. The present investigation was undertaken to ascertain if the enamel hypoplasia evidence in Neandertals suggests a high level of physiological stress relative to a modern human foraging group, represented here by an archaeological sample of Inuit from Point Hope, Alaska. Unlike previous studies, this study focused specifically on linear enamel hypoplasia (LEH), emphasizing systemic over localized causes of this defect by considering LEH to be present in an individual only if LEH defects occur on two anterior teeth with overlapping crown formation periods. Moreover, this study is the first to evaluate the average growth disruption duration represented by these defects in Neandertals and a comparative foraging group. In the prevalence analysis, 7/18 Neandertal individuals (from Krapina and southern France) and 21/56 Neandertal anterior teeth were affected by LEH, or 38.9% and 37.5% respectively. These values do not differ significantly from those of the Inuit sample in which 8/21, or 38.1% of individuals, and 32/111, or 28.8% of anterior teeth were affected. For the growth disruption duration analysis, 22 defects representing separate episodes of growth disruption in Neandertals were compared with 22 defects in the Inuit group using three indicators of duration: the number of perikymata (growth increments) in the occlusal walls of LEH defects, the total number of perikymata within them, and defect width. Only one indicator, the total number of perikymata within defects, differed significantly between the Inuit and Neandertal groups (an average of 13.4 vs. 7.3 perikymata), suggesting that if there is any difference between them, the Inuit defects may actually represent longer growth disruptions than the Neandertal defects. Thus, while stress indicators other than linear enamel hypoplasia may eventually show that Neandertal populations were more stressed than those of modern foragers, the evidence from linear enamel hypoplasia does not lend support to this idea.

Rescue of the acetylcholinesterase knockout mouse by feeding a liquid diet; phenotype of the adult acetylcholinesterase deficient mouse.

Acetylcholinesterase (AChE, EC3.1.1.7) functions in nerve impulse transmission, and possibly as a cell adhesion factor during neurite outgrowth. These functions predicted that a mouse with zero AChE activity would be unable to live. It was a surprise to find that AChE -/- mice were born alive and survived an average of 14 days. The emaciated appearance of AChE -/- mice suggested an inability to obtain sufficient nutrition and experiments were undertaken to increase caloric intake. Pregnant and lactating dams (+/-) were fed 11% high fat chow supplemented with liquid Ensure. AChE -/- pups were weaned early, on day 15, and fed liquid Ensure. Although nullizygous animals showed slow but steady weight gain with survival over 1 year (average 100 days), they remained small at all ages compared to littermates. They demonstrated delays in temperature regulation (day 22 vs. 15), eye opening (day 13 vs. 12), righting reflex (day 18 vs. 12), descent of testes (week 7-8 vs. 4), and estrous (week 15-16 vs. 6-7). Significant physical findings in adult AChE -/- mice included body tremors, abnormal gait and posture, absent grip strength, inability to eat solid food, pinpoint pupils, decreased pain response, vocalization, and early death caused by seizures or gastrointestinal tract ileus. Behavioral deficits included urination and defecation in the nest, lack of aggression, reduced pain perception, and sexual dysfunction. These findings support the classical role for AChE in nerve impulse conduction and further suggest that AChE is essential for timely physical development and higher brain function.

Expression and localization of membrane type 1 matrix metalloproteinase in tooth tissues.

Matrix metalloproteinases (MMPs) have been detected in forming dental enamel and are thought to play an important role during enamel biomineralization. Membrane-type 1 matrix metalloproteinase (MT1-MMP) is a membrane bound member of the MMP gene family that has previously been shown to be expressed by cells associated with bone and cartilage formation (osteoclasts, osteoblasts and chondrocytes). Thus, we asked if MT1-MMP was also expressed by the cells responsible for the formation of enamel and dentin. A porcine MT1-MMP cDNA composed of 3284 bp was isolated from an enamel organ-specific cDNA library. Multiple tissue Northern blot analysis revealed that the MT1-MMP message was expressed highly in the enamel organ and pulp organ when compared to the expression levels observed in other non-mineralizing tissues. Northern blot analysis of stage-specific enamel organs (early secretory, late secretory, or maturation stage) and their corresponding pulp organs revealed that MT1-MMP expression increased as the dentin matured. In the enamel organs, however, the MT1-MMP message level became reduced only during the late secretory stage. Immunohistochemical analysis showed that MT1-MMP was present on the surface of the cells (ameloblasts and odontoblasts) responsible for dentin and enamel formation. Thus, MT1-MMP is highly expressed in developing tooth tissues and may play a role in the biomineralization of enamel and dentin.

Translocation of enamel proteins from inner enamel epithelia to odontoblasts during mouse tooth development.

The developmental problem of how dental epithelia and/or dental papilla ectomesenchyme induce and/or up- or down-regulate tooth formation are as yet unresolved issues. We have designed studies to map the synthesis and fate pathways of secreted amelogenin proteins from Kallenbach differentiation zones II-IV during in vivo and in vitro mouse mandibular first molar tooth development (M1). Tooth organs from cap, bell, and crown stages were processed for reverse transcriptase/polymerase chain reaction (RT-PCR) and high resolution Protein A immunocytochemistry using anti-amelogenin and anti-peptide antibodies. Cap stage M1 were cultured for periods ranging from 10-21 days in vitro using either serum-less, or 15% fetal calf sera-supplemented, chemically-defined medium. Amelogenin transcripts are expressed in the mouse embryonic molar from E15 through early postnatal development. Amelogenin antigens were first detected in Kallenbach's differentiation zone II. Amelogenin proteins secreted from preameloblasts were identified along cell processes and cell surfaces of odontoblasts adjacent to forming mantle dentine extracellular matrix (ECM) prior to biomineralization. Amelogenin proteins were restricted to forming endocytotic vesicles, clathrin-coated vesicles, and lysosomes within odontoblasts. At later stages (e.g. 2 days postnatal development), enamel proteins were not identified in odontoblasts or predentine matrix following mineralization. Comparable observations for stages of development were noted for in vitro cultured tooth explants. Preameloblasts synthesize and secrete amelogenin proteins which bind to odontoblast cell surfaces possibly through the process of receptor-mediated endocytosis. We conclude that amelogenin proteins secreted from preameloblasts, prior to the initiation of biomineralization, were translocated to odontoblasts to serve as yet unknown biological functions.

Efeitos da N-(Pirrolidino-Metil): tetraciclina sobre o sangue da preá (Cavia Aperea Aperea) Erxleben-1777 (Rodentia) / Effect of the pirrolidino-metil-tetracycline upon o blood of preá Cavia Aparea Aparea

Na presente pesquisa estudou-se os efeitos da tetraciclina sobre o teor de cálcio sanguíneo e a influência da droga no tempo de coagulação

Is vitamin D3 essential for mineral metabolism in the Damara mole-rat (Cryptomys damarensis)?

The Damara mole-rat (Cryptomys damarensis) leads a strictly subterranean existence in an extensive maze of plugged burrows and eats a strictly herbivorous diet. An obvious source of vitamin D3 (D3), an important hormone in mineral homeostasis, therefore is lacking in this mammal. The effects of orally ingested D3 on mineral balance were investigated. In the normal D' status group of mole-rats, the apparent fractional intestinal absorption of calcium (91.1%), magnesium (91.2%), and inorganic phosphorous (91.2%) was high and increased slightly, (calcium, 94.5%; magnesium, 93.2%; inorganic phosphorous, 92.9%) after D3 administration. The amount of element absorbed was positively correlated with the amount ingested (P less than 0.001), suggesting that absorption occurs via a nonsaturable process. This might be an adaptation to the sparseness of natural food. The observed positive retention of calcium (94%), magnesium (85%), and inorganic phosphorous (99.9%) is attributed to their evergrowing teeth. These teeth are constantly worn down during digging and it is speculated that they represent a mineral "sink," assisting in the maintenance of mineral homeostasis. It is also hypothesized that mole-rats have adapted to an environment devoid of D3 and can attain sufficient calcium for their needs via nonvitamin D3-dependent processes. Although mole-rats have the "machinery" to use D3 and D3 can affect mineral balance, this effect may be disadvantageous if invoked.

Effects of perinatal alcohol exposure and dietary calcium supplements on skeletal and dental growth in rats.

Osteoporosis, hypocalcemia and skeletal size reduction are all common correlates of perinatal alcohol exposure. The present study assesses the effects of dietary calcium supplements on reversing perinatal alcohol-induced osteopenia. One hundred and twenty-nine offspring from Fisher 344 rats received 14% v/v alcohol in tap water from conception to weaning or 3 months of age followed by dietary calcium supplements (230 mg/kg/day) to 6 months of age. Significant group effects (p less than 0.001) were noted for all 12 dental and skeletal dimensions measured. Results suggest that calcium therapy following perinatal alcohol exposure may ameliorate alcohol-induced osteopenia in exposed offspring.

Effects of zinc deficiency on dental caries in rats.

The effects of graded levels of dietary zinc on the development and mineralization of teeth and bones and on the susceptibility of teeth to dental caries were studied in young growing rats. Thirty-six weanling male Sprague-Dawley rats were randomly assigned to four dietary treatments: 1) zinc-deficient, less than 1 ppm; 2) 12 ppm zinc; 3) 36 ppm zinc, and 4) 108 ppm zinc. For treatments 2, 3 and 4, rats were pair-fed the quantity of feed consumed by their individual counterparts fed the zinc-deficient diet. After 4 weeks of treatment, growth retardation along with other clinical zinc deficiency signs were observed in rats fed the zinc-deficient diet. The zinc levels in bones and teeth of zinc-deficient rats were lower than those for rats fed supplemental zinc. Increased dietary zinc resulted in greater levels of zinc in bones and teeth, but the levels of calcium decreased. Greater incidences of enamel lesions in mandibular molars were observed in rats fed the zinc-deficient diet than in rats pair-fed zinc-supplemented diets. Furthermore, the effect of zinc deficiency on dental caries of young rats was predominantly at the smooth surfaces of the molars. Dietary zinc may be an important trace mineral in the process of post-eruptive mineralization of the enamel and may reduce the susceptibility of teeth to caries.