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

Fibroblast Growth Factor 2 High Molecular Weight Isoforms in Dentoalveolar Mineralization

Transgenic mice overexpressing human high molecular weight fibroblast growth factor 2 (HMWFGF2) isoforms in osteoblast and odontoblast lineages (HMWTg) exhibit decreased dentin and alveolar bone mineralization, enlarged pulp chamber, and increased fibroblast growth factor 23 (FGF23). We examined if the alveolar bone and dentin mineralization defects in HMWTg mice resulted from increased FGF23 expression and whether an FGF23 neutralizing antibody could rescue the hypomineralization phenotype. HMWTg and VectorTg control mice were given subcutaneous injections of FGF23 neutralizing antibody twice/week starting at postnatal day 21 for 6 weeks. Since Calcitriol (1,25D) have direct effects in promoting bone mineralization, we also determined if 1,25D protects against the defective dentin and alveolar bone mineralization. Therefore, HMWTg mice were given subcutaneous injections of 1,25D daily or concomitantly with FGF23 neutralizing antibody for 6 weeks. Our results showed that HMWTg mice displayed thickened predentin, alveolar bone hypomineralization, and enlarged pulp chambers. FGF23 neutralizing antibody and 1,25D monotherapy partially rescued the dentin mineralization defects and the enlarged pulp chamber phenotype in HMWTg mice. 1,25D alone was not sufficient to rescue the alveolar bone hypomineralization. Interestingly, HMWTg mice treated with both FGF23 neutralizing antibody and 1.25D further rescued the enlarged pulp chamber size, and dentin and alveolar bone mineralization defects. We conclude that the dentin and alveolar bone mineralization defects in HMWTg mice might result from increased FGF23 expression. Our results show a novel role of HMWFGF2 on dentoalveolar mineralization.

A Cross-Sectional Cohort Study of the Effects of FGF23 Deficiency and Hyperphosphatemia on Dental Structures in Hyperphosphatemic Familial Tumoral Calcinosis

Hyperphosphatemic familial tumoral calcinosis (HFTC) is a rare autosomal recessive disorder caused by mutations in FGF23, GALNT3, KLOTHO, or FGF23 autoantibodies. Prominent features include high blood phosphate and calcific masses, usually adjacent to large joints. Dental defects have been reported, but not systematically described. Seventeen patients with HFTC followed at the National Institutes of Health underwent detailed clinical, biochemical, molecular, and dental analyses. Studies of teeth included intraoral photos and radiographs, high-resolution μCT, histology, and scanning electron microscopy (SEM). A scoring system was developed to assess the severity of tooth phenotype. Pulp calcification was found in 13 of 14 evaluable patients. Short roots and midroot bulges with apical thinning were present in 12 of 13 patients. Premolars were most severely affected. μCT analyses of five HFTC teeth revealed that pulp density increased sevenfold, whereas the pulp volume decreased sevenfold in permanent HFTC teeth compared with age- and tooth-matched control teeth. Histology revealed loss of the polarized odontoblast cell layer and an obliterated pulp cavity that was filled with calcified material. The SEM showed altered pulp and cementum structures, without differences in enamel or dentin structures, when compared with control teeth. This study defines the spectrum and confirms the high penetrance of dental features in HFTC. The phenotypes appear to be independent of genetic/molecular etiology, suggesting hyperphosphatemia or FGF23 deficiency may be the pathomechanistic driver, with prominent effects on root and pulp structures, consistent with a role of phosphate and/or FGF23 in tooth development. Given the early appearance and high penetrance, cognizance of HFTC-related features may allow for earlier diagnosis and treatment. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Effects of Active Vitamin D or FGF23 Antibody on Hyp Mice Dentoalveolar Tissues

Mutations in the PHEX gene lead to X-linked hypophosphatemia (XLH), a form of inherited rickets featuring elevated fibroblast growth factor 23 (FGF23), reduced 1,25-dihydroxyvitamin D (1,25D), and hypophosphatemia. Hyp mutant mice replicate the XLH phenotype, including dentin, alveolar bone, and cementum defects. We aimed to compare effects of 1,25D versus FGF23-neutralizing antibody (FGF23Ab) monotherapies on Hyp mouse dentoalveolar mineralization. Male Hyp mice, either injected subcutaneously with daily 1,25D or thrice weekly with FGF23 blocking antibody from 2 to 35 d postnatal, were compared to wild-type (WT) controls and untreated Hyp mice. Mandibles were analyzed by high-resolution micro-computed tomography (micro-CT), histology, and immunohistochemistry. Both interventions maintained normocalcemia, increased serum phosphate levels, and improved dentoalveolar mineralization in treated versus untreated Hyp mice. 1,25D increased crown dentin volume and thickness and root dentin/cementum volume, whereas FGF23Ab effects were limited to crown dentin volume. 1,25D increased bone volume fraction, bone mineral density, and tissue mineral density in Hyp mice, whereas FGF23Ab failed to significantly affect these alveolar bone parameters. Neither treatment fully attenuated dentin and bone defects to WT levels, and pulp volumes remained elevated regardless of treatment. Both treatments reduced predentin thickness and improved periodontal ligament organization, while 1,25D promoted a more profound improvement in acellular cementum thickness. Altered cell densities and lacunocanalicular properties of alveolar and mandibular bone osteocytes and cementocytes in Hyp mice were partially corrected by either treatment. Neither treatment normalized the altered distributions of bone sialoprotein and osteopontin in Hyp mouse alveolar bone. Moderate improvements from both 1,25D and FGF23Ab treatment regimens support further studies and collection of oral health data from subjects receiving a newly approved anti-FGF23 therapy. The inability of either treatment to fully correct Hyp mouse dentin and bone prompts further experiments into underlying pathological mechanisms to identify new therapeutic approaches.

Dentoalveolar Defects in the Hyp Mouse Model of X-linked Hypophosphatemia

Mutations in PHEX cause X-linked hypophosphatemia (XLH), a form of hypophosphatemic rickets. Hyp (Phex mutant) mice recapitulate the XLH phenotype. Dental disorders are prevalent in individuals with XLH; however, underlying dentoalveolar defects remain incompletely understood. We analyzed Hyp mouse dentoalveolar defects at 42 and 90 d postnatal to comparatively define effects of XLH on dental formation and function. Phex mRNA was expressed by odontoblasts (dentin), osteocytes (bone), and cementocytes (cellular cementum) in wild-type (WT) mice. Enamel density was unaffected, though enamel volume was significantly reduced in Hyp mice. Dentin defects in Hyp molars were indicated histologically by wide predentin, thin dentin, and extensive interglobular dentin, confirming micro-computed tomography (micro-CT) findings of reduced dentin volume and density. Acellular cementum was thin and showed periodontal ligament detachment. Mechanical testing indicated dramatically altered periodontal mechanical properties in Hyp versus WT mice. Hyp mandibles demonstrated expanded alveolar bone with accumulation of osteoid, and micro-CT confirmed decreased bone volume fraction and alveolar bone density. Cellular cementum area was significantly increased in Hyp versus WT molars owing to accumulation of hypomineralized cementoid. Histology, scanning electron microscopy, and nanoindentation revealed hypomineralized "halos" surrounding Hyp cementocyte and osteocyte lacunae. Three-dimensional micro-CT analyses confirmed larger cementocyte/osteocyte lacunae and significantly reduced perilacunar mineral density. While long bone and alveolar bone osteocytes in Hyp mice overexpressed fibroblast growth factor 23 (Fgf23), its expression in molars was much lower, with cementocyte Fgf23 expression particularly low. Expression and distribution of other selected markers were disturbed in Hyp versus WT long bone, alveolar bone, and cementum, including osteocyte/cementocyte marker dentin matrix protein 1 (Dmp1). This study reports for the first time a quantitative analysis of the Hyp mouse dentoalveolar phenotype, including all mineralized tissues. Novel insights into cellular cementum provide evidence for a role for cementocytes in perilacunar mineralization and cementum biology.

The rachitic tooth

Teeth are mineralized organs composed of three unique hard tissues, enamel, dentin, and cementum, and supported by the surrounding alveolar bone. Although odontogenesis differs from osteogenesis in several respects, tooth mineralization is susceptible to similar developmental failures as bone. Here we discuss conditions fitting under the umbrella of rickets, which traditionally referred to skeletal disease associated with vitamin D deficiency but has been more recently expanded to include newly identified factors involved in endocrine regulation of vitamin D, phosphate, and calcium, including phosphate-regulating endopeptidase homolog, X-linked, fibroblast growth factor 23, and dentin matrix protein 1. Systemic mineral metabolism intersects with local regulation of mineralization, and factors including tissue nonspecific alkaline phosphatase are necessary for proper mineralization, where rickets can result from loss of activity of tissue nonspecific alkaline phosphatase. Individuals suffering from rickets often bear the additional burden of a defective dentition, and transgenic mouse models have aided in understanding the nature and mechanisms involved in tooth defects, which may or may not parallel rachitic bone defects. This report reviews dental effects of the range of rachitic disorders, including discussion of etiologies of hereditary forms of rickets, a survey of resulting bone and tooth mineralization disorders, and a discussion of mechanisms, known and hypothesized, involved in the observed dental pathologies. Descriptions of human pathology are augmented by analysis of transgenic mouse models, and new interpretations are brought to bear on questions of how teeth are affected under conditions of rickets. In short, the rachitic tooth will be revealed.

Osteopetrosis, osteopetrorickets and hypophosphatemic rickets differentially affect dentin and enamel mineralization

Osteopetrosis (OP) is an inherited disorder of defective bone resorption, which can be accompanied by impaired skeletal mineralization, a phenotype termed osteopetrorickets (OPR). Since individuals with dysfunctional osteoclasts often develop osteomyelitis of the jaw, we have analyzed, if dentin and enamel mineralization are differentially affected in OP and OPR. Therefore, we have applied non-decalcified histology and quantitative backscattered electron imaging (qBEI) to compare the dental phenotypes of Src(-/-), oc/oc and Hyp(-/0) mice, which serve as models for OP, OPR and hypophosphatemic rickets, respectively. While both, Src(-/-) and oc/oc mice, were characterized by defects of molar root formation, only oc/oc mice displayed a severe defect of dentin mineralization, similar to Hyp(-/0) mice. Most importantly, while enamel thickness was not affected in either mouse model, the calcium content within the enamel phase was significantly reduced in oc/oc, but not in Src(-/-) or Hyp(-/0) mice. Taken together, these data demonstrate that dentin and enamel mineralization are differentially affected in Src(-/-) and oc/oc mice. Moreover, since defects of dental mineralization may trigger premature tooth decay and thereby osteomyelitis of the jaw, they further underscore the importance of discriminating between OP and OPR in the respective individuals.

Ablation of systemic phosphate-regulating gene fibroblast growth factor 23 (Fgf23) compromises the dentoalveolar complex

Fibroblast growth factor-23 (FGF23) is a hormone that modulates circulating phosphate (P(i)) levels by controlling P(i) reabsorption from the kidneys. When FGF23 levels are deficient, as in tumoral calcinosis patients, hyperphosphatemia ensues. We show here in a murine model that Fgf23 ablation disrupted morphology and protein expression within the dentoalveolar complex. Ectopic matrix formation in pulp chambers, odontoblast layer disruption, narrowing of periodontal ligament space, and alteration of cementum structure were observed in histological and electron microscopy sections. Because serum P(i) levels are dramatically elevated in Fgf23(-/-), we assayed for apoptosis and expression of members from the small integrin-binding ligand, N-linked glycoprotein (SIBLING) family, both of which are sensitive to elevated P(i) in vitro. Unlike X-linked hypophosphatemic (Hyp) and wild-type (WT) specimens, numerous apoptotic osteocytes and osteoblasts were detected in Fgf23(-/-) specimens. Further, in comparison to Hyp and WT samples, decreased bone sialoprotein and elevated dentin matrix protein-1 protein levels were observed in cementum of Fgf23(-/-) mice. Additional dentin-associated proteins, such as dentin sialoprotein and dentin phosphoprotein, exhibited altered localization in both Fgf23(-/-) and Hyp samples. Based on these results, we propose that FGF23 and (P(i)) homeostasis play a significant role in maintenance of the dentoalveolar complex.

Expression and distribution of SIBLING proteins in the predentin/dentin and mandible of hyp mice

OBJECTIVES

Human X-linked hypophosphatemia (XLH) and its murine homologue, Hyp are caused by inactivating mutations in PHEX gene. The protein encoded by PHEX gene is an endopeptidase whose physiological substrate(s) has not been identified. Dentin matrix protein 1 (DMP1) and dentin sialophosphoprotein (DSPP), two members of the Small Integrin-Binding LIgand, N-linked Glycoprotein (SIBLING) family are proteolytically processed. It has been speculated that PHEX endopeptidase may be responsible for the proteolytic cleavage of DMP1 and DSPP. To test this hypothesis and to analyse the distribution of SIBLING proteins in the predentin/dentin complex and mandible of Hyp mice, we compared the expression of four SIBLING proteins, DMP1, DSPP, bone sialoprotein (BSP) and osteopontin (OPN) between Hyp and wild-type mice.

METHODS

These SIBLING proteins were analysed by protein chemistry and immunohistochemistry.

RESULTS

(1) Dentin matrix protein 1 and DSPP fragments are present in the extracts of Hyp predentin/dentin and bone; (2) the level of DMP1 proteoglycan form, BSP and OPN is elevated in the Hyp bone.

CONCLUSIONS

The PHEX protein is not the enzyme responsible for the proteolytic processing of DMP1 and DSPP. The altered distribution of SIBLING proteins may be involved in the pathogenesis of bone and dentin defects in Hyp and XLH.

Aberrant cementum phenotype associated with the hypophosphatemic hyp mouse

BACKGROUND

Cementogenesis is sensitive to altered local phosphate levels; thus, we hypothesized a cementum phenotype, likely of decreased formation, would be present in the teeth of X-linked hypophosphatemic (Hyp) mice. Mutations in the phosphate-regulating gene with homologies to endopeptidases on the X chromosome (Phex) cause X-linked hypophosphatemia, characterized by rickets, osteomalacia, and hypomineralized dentin formation, a phenotype recapitulated in the Hyp mouse homolog. Here, we report a developmental study of tooth root formation in Hyp mouse molars, focusing on dentin and cementum.

METHODS

Light and transmission electron microscopy were used to study molar tissues from wild-type (WT) and Hyp mice. Demineralized and hematoxylin and eosin-stained tissues at developmental stages 23 to 96 days postcoital (dpc) were examined by light microscopy. Immunohistochemistry methods were used to detect bone sialoprotein (BSP) distribution in Hyp and WT mouse molar tissues, and transmission electron microscopy was used to study similar molar tissues in the non-demineralized state.

RESULTS

Dentin in Hyp mice exhibited mineralization defects by 33 dpc, as expected, but this defect was partially corrected by 96 dpc. In support of our hypothesis, a cementum phenotype was detected using a combination of immunohistochemistry and transmission electron microscopy, which included thinner BSP-positive staining within the cementum, discontinuous mineralization, and a globular appearance compared to WT controls.

CONCLUSION

Mutations in the phosphate-regulating Phex gene of the Hyp mouse resulted in defective cementum development.

The PHEX transgene corrects mineralization defects in 9-month-old hypophosphatemic mice

Hypophosphatemia is an X-linked dominant disorder resulting from a mutation in the PHEX gene. While osteoblast-specific expression of the PHEX transgene has been reported to decrease the phosphate wasting associated with the disease in male hypophosphatemic (HYP) mice, there are reports that the mineralization defect is only partially corrected in young animals. To test the hypothesis that osteoblast-specific expression of the PHEX gene for a longer time would correct the mineralization defect, this study examined the bones of 9-month-old male and female HYP mice and their wild-type controls with or without expression of the transgene under a collagen type I promoter. Serum phosphate levels, alkaline phosphatase activity, and FGF23 levels were also measured. Mineral analyses based on wide-angle X-ray diffraction, Fourier transform-infrared (FT-IR) spectroscopy, and FT-IR imaging confirmed the decreased mineral content and increased mineral crystal size in male HYP humerii compared to wild-type males and females with or without the transgene and in female HYP mice with or without the transgene. There was a significant increase in mineral content and a decrease in crystallinity in the HYP males' bones with the transgene, compared to those without. Of interest, expression of the transgene in wild-type animals significantly increased the mineral content in both males and females without having a detectable effect on crystallinity or carbonate content. In contrast to the bones, based on micro-computed tomography and FT-IR imaging, at 9 months there were no significant differences between the HYP and the WT teeth, precluding analysis of the effect of the transgene.

Phosphate: known and potential roles during development and regeneration of teeth and supporting structures

Inorganic phosphate (P(i)) is abundant in cells and tissues as an important component of nucleic acids and phospholipids, a source of high-energy bonds in nucleoside triphosphates, a substrate for kinases and phosphatases, and a regulator of intracellular signaling. The majority of the body's P(i) exists in the mineralized matrix of bones and teeth. Systemic P(i) metabolism is regulated by a cast of hormones, phosphatonins, and other factors via the bone-kidney-intestine axis. Mineralization in bones and teeth is in turn affected by homeostasis of P(i) and inorganic pyrophosphate (PPi), with further regulation of the P(i)/PP(i) ratio by cellular enzymes and transporters. Much has been learned by analyzing the molecular basis for changes in mineralized tissue development in mutant and knock-out mice with altered P(i) metabolism. This review focuses on factors regulating systemic and local P(i) homeostasis and their known and putative effects on the hard tissues of the oral cavity. By understanding the role of P(i) metabolism in the development and maintenance of the oral mineralized tissues, it will be possible to develop improved regenerative approaches.

Dentin structure in familial hypophosphatemic rickets: benefits of vitamin D and phosphate treatment

OBJECTIVE

To evaluate the outcome of 1-(OH) vitamin D and oral phosphate treatment on dentin structure in patients with familial hypophosphatemic rickets, and expression of SIBLINGs (a family of non-collagenous proteins involved in dentinogenesis) and osteocalcin.

PATIENTS AND METHODS

Seven patients with familial hypophosphatemic rickets (age 3-16 years) were studied before or during treatment. Deciduous and permanent teeth were prepared for scanning electron microscopy (SEM) analysis and immunohistochemistry.

RESULTS

Untreated or inadequately treated patients had necrotic teeth with impaired dentin mineralization including unmerged calcospherites and accumulation of non-collagenous proteins in wide interglobular spaces. Most of the primary incisors analyzed displayed fissures linking enamel subsurface to pulp horn. These elements may explain the bacterial penetration and dental abscesses despite the absence of carious lesions. Well-treated patients had healthy teeth with good dentin mineralization and little evidence of calcospherites.

CONCLUSION

Treatment of hypophosphatemic children with 1-(OH) vitamin D and oral phosphate insures good dentin development and mineralization, and prevents clinical anomalies such as the dental necrosis classically associated with the disease. Starting treatment during early childhood and good adherence to the therapy are mandatory to observe these beneficial effects.

Dentin alteration of deciduous teeth in human hypophosphatemic rickets

Familial hypophosphatemic rickets is in most cases transmitted as an X-linked dominant trait and results from mutation of the PHEX gene, predominantly expressed in osteoblast and odontoblast. Patients have been reported to display important dentin defects, and therefore, we explored the dentin structure, composition, and distribution of extracellular matrix (ECM) molecules in hypophosphatemic human deciduous teeth. Compared to age-matched controls, the dentin from hypophosphatemic patients exhibited major differences: presence of large interglobular spaces resulting from the lack of fusion of calcospherites in the circumpulpal dentin; defective mineralization in the interglobular spaces contrasting with normal Ca-P levels in the calcospherites on X-ray microanalysis; abnormal presence of low-molecular weight protein complexes recognized on Western blots by antibodies against matrix extracellular phosphoglycoprotein (MEPE), dentin sialoprotein, osteopontin, and reduced osteocalcin (OC) level; and accumulation in the interglobular spaces of immunolabeling with antibodies against DSP, dentin matrix protein, bone sialoprotein, MEPE and OC, while chondroitin/dermatan sulfate glycosaminoglycans were exclusively located inside calcospherites. Alterations of the post-translational processing or partial degradation of some ECM appear as key factors in the formation of the defective hypophosphatemic dentin.

Dentinal defects in Hyp mice not caused by hypophosphatemia alone

The Hyp mouse is a murine homolog of human X-linked hypophosphatemic rickets and displays hypo-mineralization in bone and dentin due to a defect of the phosphate-regulating gene with homology to endopeptidase on the X chromosome (Phex) gene. It has long been considered that the bone and dentin defects in Hyp mice are caused by hypophosphatemia alone, however, several recent studies have indicated the possibility that intrinsic defects are present in Hyp mice osteoblasts. Further, we previously found a hyper-expression of osteocalcin (OC) mRNA in Hyp mouse odontoblasts and suggested the possibility of the presence of intrinsic defects. In the present study, we evaluated morphological features and OC mRNA expression levels in tooth germs of Nor mice with a normal phex gene and a low concentration of serum phosphate, and compared them to those in Hyp and wild-type mice. Nor mice exhibited low serum phosphate levels, however, did not show the characteristic features of dentin defects seen in Hyp mice, such as widened predentin and hyper-expression of OC mRNA. These results suggest that the hypo-mineralization of dentin in Hyp mice is not dependent on serum phosphate level, but rather is affected by intrinsic defects in odontoblasts.

PHEXdb, a locus-specific database for mutations causing X-linked hypophosphatemia

X-linked hypophosphatemia (XLH) is a dominant disorder of phosphate (Pi) homeostasis characterized by growth retardation, rachitic and osteomalacic bone disease, hypophosphatemia, and renal defects in Pi reabsorption and vitamin D metabolism. The gene responsible for XLH was identified by positional cloning and designated PHEX (formerly PEX) to depict a Phosphate regulating gene with homology to Endopeptidases on the X chromosome. To date, 131 mutations in the PHEX gene have been reported. We undertook to centralize information on mutations in the PHEX gene by establishing a database search tool, PHEXdb (http://data.mch.mcgill.ca/phexdb). This site is dedicated to the collection and distribution of information on PHEX mutations, and is accessible to the scientific community. PHEXdb provides a submission form to allow the addition of newly identified mutations in the PHEX gene. Users can search the database by mutation, phenotype, and authors who have published or submitted mutations. The PHEXdb home page includes links to information pages, which refer to recent publications on PHEX, XLH, and murine Hyp and Gy homologues, and to other web pages relevant to XLH. This resource will facilitate the identification of PHEX structure-function relationships and phenotype-genotype correlations.

The occurrence of interglobular dentin in incisors of hypophosphatemic mice fed a high-calcium and high-phosphate diet

The incisor dentin of hypophosphatemic (Hyp) mice was examined histopathologically to determine whether the multiple occurrences of interglobular dentin would be influenced by the serum phosphate level. Both normal and Hyp mice (12 weeks of age) were divided into two groups. The mice in one group were given a control diet (1.42% Ca, 1.16% P) and the other a high-calcium and high-phosphate diet (2.00% Ca, 3.00% P) for 30 days. Blood was collected from the mice every fifth day for measurement of the calcium and phosphate concentrations in serum. Both ground and decalcified cross-sections were prepared from incisors from the mandible and maxilla for microscopic examination. The levels of serum Ca and P were almost constant in normal mice, regardless of diet. On the other hand, serum P levels in Hyp mice fed the control diet were significantly lower than those in normal mice. The ten days' feeding of the high-Ca/-P diet significantly elevated the serum P level in Hyp mice, and it reached a level similar to that of the normal mice. However, histopathological examination showed no significant changes in incisor dentin of Hyp mice fed the high-Ca/-P diet, and interglobular dentin still occurred. These results suggest that the multiple formations of interglobular dentin, which is the most outstanding feature of X-linked hypophosphatemic vitamin-D-resistant rickets, are not influenced in Hyp mice by the short-time normalization of the serum phosphate level.

Physical examination of caffeine's effects on the enamel surface of first molar in new-born rats

Samples of the first molars of offspring whose dams were fed a diet supplemented with caffeine were examined by scanning electron microscopy, X-ray diffractometry and electron microprobe analysis. Scanning microscopy of the enamel surface of the caffeine group revealed a consistently rougher surface than in the non-caffeine controls, both before and after acid exposure. X-ray diffraction analysis of the pulverized whole tooth in the caffeine group showed broader diffraction peaks for the lattice plane reflections (202) and (300), indicating smaller crystallites. Pure enamel samples of the caffeine group examined with a Gandolfi X-ray camera also revealed more diffuse diffraction lines than in the non-caffeine controls, further indicating smaller crystallites in the enamel. The calcium and phosphorus contents of the acid-exposed samples in both control and caffeine groups were lower than the non-acid exposed control and caffeine groups by electron microprobe analysis. After exposure to acid, the calcium and phosphorus contents of the outer surface of the enamel in the caffeine group were greatly reduced as compared to that of the non-caffeine controls. Thus various methods consistently indicate that caffeine ingestion during early growth affects the enamel surface of the first molars, resulting in impaired mineralization. Caffeine intake may therefore have a negative effect on amelogenesis and possibly increases susceptibility to dental caries.