Enamel Maturation Research Articles

Clinical and Molecular Disorders Caused by COVID-19 During Pregnancy as a Potential Risk for Enamel Defects

This paper discusses the potential risk that COVID-19 generates for the development of enamel defects. This hypothesis was built based on the etiopathogenesis of enamel defects and the relationship with the symptom's characteristic of COVID-19. Pregnancy is a critical period for the child's development; exposure to pathological agents can cause systemic imbalances and risks of adverse perinatal and prenatal outcomes. The main clinical symptoms of this disease and its association with that dental outcome were considered. Fever, breathing, cardiovascular disorders, and diarrhea were related as potential etiological factors of ameloblast metabolism imbalance, which can interfere qualitatively and quantitatively in the development, maturation and mineralization of the tooth enamel. Molecular disorders derived from COVID-19, as well as their clinical symptoms, can be considered potential risk factors for the development of enamel defects. Individuals with enamel defects experienced high stress levels during pregnancy or early childhood. The approach adopted may help build new research to ensure understanding of the etiology of the development of dental enamel defects and its relationship with COVID-19. However, longitudinal studies need to be conducted to confirm the association between COVID-19 and adverse events during pregnancy.

Comparative assessment of the rate and quality of enamel mineral component maturation of human teeth with connective tissue dysplasia in the early postpartum period

Objective. It is necessary to study the human enamel prisms size at different periods of postpartum ontogenesis in connective tissue dysplasia by atomic force microscopy. Materials and methods. The study involved 150 males divided into a group with and without connective tissue dysplasia (each additionally by age: 15—20, 21—30, 31—40 years). Each examined was removed one of the low wisdom teeth (3.8 or 4.8 by ISO). Prepared thin sections of human tooth enamel samples up to grade 14, with maximum preservation of the edges of the enamel prisms within the surface layer. The Image Analysis NT-VDT software was used to analyze the number of faces, shape, length, and width of enamel prisms. Results. It was found that at 15—30 years old there is an ordered structure of enamel prisms, a large number of 5-sided forms (50—60%). A permanent form of enamel prisms at 31—40 years old, where the share of 6-sided figures is 30%. With CTD, the growth rate on the plane, which increases the width of the prism, is very similar to the growth rate of length up to 30 years, which leads to a violation of their spatial configuration relative to the organic matrix. Conclusions. The maturation of human enamel is strictly individual, depending on the connective tissue dysplasia, which has a negative effect on the rate of maturation, and after eruption can lead to pathological conditions of hard dental tissues.

Permanent Signatures of Birth and Nursing Initiation are Chemically Recorded in Teeth

In 2013 we presented a model for identifying nursing behavior from primate teeth based on rapid postnatal concentration changes in the non-essential trace element barium. Here we leverage the permanent neonatal (birth) line in the enamel of several dozen primate M1 cusps to compare pre- and postnatal trends in barium, zinc, strontium, and oxygen, as each element is believed to evince developmental patterning. Barium and zinc are the most consistent biomarkers of nursing initiation; a majority of M1 cusps show concentration increases from prenatal to postnatal enamel, whereas strontium shows no change or decreases with equal frequency. Exceptions to the pattern of barium increase occurred in cusps that had been mineralizing for less than three weeks, suggesting that subsequent enamel maturation has only a minor impact on detecting real time events. Oxygen isotope compositions (δ18O) show marked fluctuations (~ 1–2 ‰) within a few weeks of birth in 92% of M1 cusps (n = 22/24). This is likely due to measurements of hypomineralized perinatal enamel, as well as physiological changes in the body water of newborn infants. Ongoing work integrating elemental concentration gradients with isotopic variation will help establish the degree to which milk intake may cause elevated δ18O in teeth. We show that chemical identification of pre- to postnatal transitions may be robust to slight planar deviations that often obscure growth increments under light microscopy, and could help validate the identification of potential neonatal lines, making this approach a useful complement to bioarchaeological studies and public health investigations.

Effectiveness of the Application of Remineralizing Means and Methods of Early Diagnostics of the Caries in the Process of Teeth Enamel Maturation: A Review

Non-mineralized enamel in childhood is a risk factor for the development of caries in the stage of macula cariosa, therefore it is very important at this age to provide remineralizing therapy,..

IMPROVING THE EFFICIENCY OF CARIES PREVENTION DUE TO THE TIMING OF THE ERUPTION AND MINERALIZATION OF PERMANENT TEETH IN CHILDREN ENVIRONMENTAL PROBLEMS OF THE REGIONS OF THE REPUBLIC OF UZBEKISTAN

The process of mineralization or maturation of enamel occurs within 3-5 years after teething. Numerous clinical observations indicate that caries develops most intensively in the first years after teething, which coincides with the period of immature enamel. Due to the mineralization of enamel, its resistance to caries increases. The terms of eruption and mineralization of permanent teeth in school-age children with the physiological development of the child coincide with the terms of complete resorption of the roots of temporary teeth.

G protein–coupled receptor Gpr115 (Adgrf4) is required for enamel mineralization mediated by ameloblasts

Dental enamel, the hardest tissue in the human body, is derived from dental epithelial cell ameloblast-secreted enamel matrices. Enamel mineralization occurs in a strictly synchronized manner along with ameloblast maturation in association with ion transport and pH balance, and any disruption of these processes results in enamel hypomineralization. G protein-coupled receptors (GPCRs) function as transducers of external signals by activating associated G proteins and regulate cellular physiology. Tissue-specific GPCRs play important roles in organ development, although their activities in tooth development remain poorly understood. The present results show that the adhesion GPCR Gpr115 (Adgrf4) is highly and preferentially expressed in mature ameloblasts and plays a crucial role during enamel mineralization. To investigate the in vivo function of Gpr115, knockout (Gpr115-KO) mice were created and found to develop hypomineralized enamel, with a larger acidic area because of the dysregulation of ion composition. Transcriptomic analysis also revealed that deletion of Gpr115 disrupted pH homeostasis and ion transport processes in enamel formation. In addition, in vitro analyses using the dental epithelial cell line cervical loop-derived dental epithelial (CLDE) cell demonstrated that Gpr115 is indispensable for the expression of carbonic anhydrase 6 (Car6), which has a critical role in enamel mineralization. Furthermore, an acidic condition induced Car6 expression under the regulation of Gpr115 in CLDE cells. Thus, we concluded that Gpr115 plays an important role in enamel mineralization via regulation of Car6 expression in ameloblasts. The present findings indicate a novel function of Gpr115 in ectodermal organ development and clarify the molecular mechanism of enamel formation.

Synchrotron X-ray fluorescence imaging of strontium incorporated into the enamel and dentine of wild-shot orangutan canine teeth

ObjectivesDental hard tissues contain trace elements of both dietary and environmental origin. One objective was to demonstrate that a longitudinal record of synchronous Sr incorporation into enamel and dentine can be retrieved from museum specimens of once-free-living endangered species. Further objectives were to quantify sudden fluctuations in Sr concentration and estimate the extent of Sr overprinting back into dentine and enamel formed prior to the time of Sr ingestion. Materials and methodsDaily incremental markings were used to determine rates and times of tooth formation and synchrotron X-ray fluorescence of the same polished ground sections to image Sr distribution in a male and a female orangutan canine. The X-ray beam was monochromatised to 17.0 keV and focused to 500 × 500 nm2. Scans were performed at either 25.0 or 5.0 μm resolution. ResultsBaseline Sr levels ranged between 215-750 ppm. Multiple short, intense Sr labels reaching 750- 1,625 ppm occurred randomly throughout 15-22 years of tooth formation. In dentine, Sr concentration increased gradually away from the EDJ, while in enamel, it reduced towards the enamel surface. Using daily incremental markings, Sr overprinting into earlier formed dentine and enamel was estimated to be ∼12-45 days. There was no evidence of Sr overprinting by maturational ameloblasts. ConclusionsA good record of growth and trace element incorporation into tooth tissues can be retrieved from museum specimens. Short, intense Sr labels were equally well time-resolved in enamel and dentine and could be distinguished from more diffuse background levels. Enamel maturation appears to have no quantifiable effect.

Intra-tooth stable isotope profiles in warthog canines and third molars: Implications for paleoenvironmental reconstructions

Intra-tooth stable isotope variations have been used to interpret seasonality and aridity in paleoenvironmental reconstructions of paleontological and archeological sites. However, most intra-tooth datasets only permit qualitative interpretations of seasonality, because the measured signal is attenuated due to the duration of enamel mineralization process and sampling geometry. The common warthog (Phacochoerus africanus) is an ideal organism to investigate stable isotope variation in enamel. Their canines grow continuously through the life of the individual and are therefore excellent candidates for mathematical modeling of seasonal signals and of signal attenuation; further, their isotope profiles (a series of isotope measurements) can be compared to isotope profiles of third molars (M3) to provide insights into environmental reconstructions. We first obtained paired intra-tooth enamel samples from ever-growing canines and hypsodont M3s of two extant common warthog specimens from Laikipia, Kenya. Second, from a different set of specimens, we collected data on enamel growth patterns and geometry using histological thin sections and transmitted light microscopy, and enamel mineralization parameters using micro-CT scans in each tooth type. Third, we reconstructed the timeline of unattenuated seasonal δ18O signal from canine enamel using growth rate estimates and the inverse model of Passey et al. (2005). Our results demonstrate that canines, which capture ~1.5 years of time, exhibit near-constant growth rates and simple enamel maturation geometry, whereas M3s, which also represent ~1.5 years of time, exhibit linearly decreasing growth rates and more complex maturation patterns. We compare the timelines of unattenuated seasonal δ18O signal and measured M3 profiles and find an average signal reduction of ~50% in the M3s, providing interpretations of the duration of seasonal cycles that are consistent 75% of the time. We conclude that warthog canines are well suited for the inverse model approach, and we established the model parameters for the forward and inverse methods. Timeline reconstructions based on M3 histology are promising for investigating the pattern of rainfall seasonality in the past. Finally, we found an unexpected carbon isotopic spacing of ~2‰ between canine and M3 enamel, which suggests caution in interpreting δ13C results from suid canine or molar enamel alone.

Forward and inverse methods for extracting climate and diet information from stable isotope profiles in proboscidean molars

Intratooth stable isotope profiles in enamel provide time series of dietary and environmental information that if correctly interpreted, serve as archives of seasonal variability in past environments. A major challenge in interpreting these profiles arises from time averaging imparted by enamel mineralization and developmental geometry, whereby the primary (δ13C or δ18O) input signal is attenuated and shifted, which can potentially lead to incorrect interpretations of the magnitude or frequency of seasonal variability. Several forward and inverse models have been developed to reconstruct the primary input signal from intratooth profiles in continuously growing teeth. Here the models developed by Passey and Cerling (2002) and Passey et al. (2005) are extended to molars of Elephantinae, which grow over a long but finite interval of time. Proboscidean molars are particularly attractive for intratooth profiles because they may contain a decade or more of information and they are often well preserved in the fossil record because of their thick enamel and large size.Forward model parameters are established using histological analysis of molar thin sections of extant African elephants (Loxodonta africana) and a mammoth (Mammuthus columbi) and by micro-CT analysis of L. africana molar plates. The density of immature enamel is about 65% of the final density of mature enamel. The appositional length varies from approximately 35 to 55 mm, and the maturation length is about 70 mm. Histological methods are used to determine crown formation time (CFT) in elephant and mammoth molar plates. CFT for the elephant and mammoth molar plates studied in thin section are about 5–6 years and 11 years, which translate to mean growth rates of about 21 mm/year and 16 mm/year, respectively.Coeval molar and tusk profiles from a zoo elephant are compared. The tusk isotope profile serves as a proxy for the primary input signal, and thus provides an opportunity to evaluate the forward and inverse models. The results from the zoo elephant profiles demonstrate that the inverse model accurately reconstructs the amplitude and overall structure of the primary input signal. Inverse model results of mammoth molar profiles show double the range of δ13C in measured enamel profiles. Inversion model results illustrate that improved reconstruction of the primary input signal can lead to more accurate interpretations of the seasonal variability of diet and body water and by extension, vegetation and precipitation in past environments.

Chemical gradients in human enamel crystallites.

Dental enamel is a principal component of teeth.[1] It has evolved to bear large masticatory forces, resist mechanical fatigue, and withstand wear over decades of use.[2] Functional impairment or loss, as a consequence of developmental defects or tooth decay (caries), has a dramatic impact on health and quality of life, with significant costs to society.[3] While the last decade has seen great progress in our understanding of enamel formation (amelogenesis) and the functional properties of mature enamel, attempts to repair enamel lesions or synthesize enamel in vitro have had limited success.[4–6] This is partly due to the highly hierarchical structure of enamel and the additional complexities arising from chemical gradients that we are only beginning to understand.[7–9] Herein, we show, using atomic-scale quantitative imaging and correlative spectroscopies, that the nanoscale crystallites of hydroxylapatite (OHAp; Ca5(PO4)3(OH)) that are the fundamental building blocks of enamel are comprised of two nanometric layers enriched in magnesium flanking a core rich in sodium, fluoride, and carbonate ions; this sandwich core is surrounded by a shell with lower concentration of substitutional defects. A mechanical model based on DFT calculations and X-ray diffraction data predicts that significant residual stresses arise as a consequence of the chemical gradients, in agreement with preferential dissolution of the crystallite core. Further, stresses may impact the mechanical resilience of enamel. Finally, the two additional layers of hierarchy suggest a new model for biological control over crystal growth during amelogenesis and have implications for the preservation of biomarkers during tooth development.

Phosphorylated/Nonphosphorylated Motifs in Amelotin Turn Off/On the Acidic Amorphous Calcium Phosphate-to-Apatite Phase Transformation.

Amelotin (AMTN) as a matrix protein exerts a direct effect on biomineralization by modulating apatite (HAP) formation during the dental enamel maturation stage through the specific interaction of a potentially phosphorylated Ser-Ser-Glu-Glu-Leu (SSEEL) peptide fragment with calcium phosphate (Ca-P) surfaces. However, the roles of (non)phosphorylation of this evolutionarily conserved subdomain within AMTN remain poorly understood. Here, we show, by time-resolved atomic force microscopy (AFM) imaging of in situ HAP crystallization via the HPO42--rich amorphous calcium phosphate (acidic ACP), the on/off switching of the phase transformation process through a nonphosphorylation-to-phosphorylation transition of the SSEEL motif. Using high-resolution transmission electron microscopy (HRTEM), we observed that the acidic ACP phase is stabilized by the phosphorylated SSEEL motif, delaying its transformation to HAP, whereas the nonphosphorylated counterpart promotes HAP formation by accelerating the dissolution-recrystallization of the acidic ACP substrate. Dynamic force spectroscopy measurements demonstrate greater binding energies of nonphosphorylated SSEEL to the acidic ACP substrate by the formation of molecular peptide-ACP bonding, explaining the enhanced dissolution of the acidic ACP substrate by stronger complexion with surface Ca2+ ions. Our findings demonstrate direct evidence for the switching role of (non)phosphorylation of an evolutionarily conserved subdomain within AMTN in controlling the phase transition of growing enamel and designing tissue regeneration biomaterials.

The Effect of Zinc and Vitamin D Nutrition on Reducing Morphine Side Effects and Development of Dental Anomalies in Rats Newborns.

Introduction:The use of opioids such as morphine has anti-pain effects along with some side effects on body organs. Opioids such as morphine can be transferred from mother to child through the placenta and or breastfeeding. This study aimed to assess the effect of morphine on mineral content and histological changes of incisor teeth of rats born to morphine-addicted mothers.Methods:In this experimental animal study, 24 pregnant rats were randomly divided into 6 groups of control, morphine, zinc, vitamin D, morphine plus zinc, and morphine plus vitamin D. After completion of the breastfeeding period, two babies were randomly selected among the newborns of each mother rat. Mineral content was analyzed using the Rontec device. The obtained data were analyzed by Newman-Keuls multiple comparisons test in Prism 5.Results:Results showed a significant reduction in fluorine content in the experimental groups compared with the control group (P<0.05). The magnesium content in the experimental groups was significantly higher than that in the control group (P<0.05). Microscopic assessment of the slides showed a significantly less enamel maturation in the experimental groups compared with the control group (P<0.05).Conclusion:Morphine use by mothers decreased the fluorine content of tooth structure and retarded the maturity of the enamel of infants.

Dental fluorosis: The Dilemma of Therapeutic Management

Dental fluorosis is a disorder resulting in anesthetic coloration of enamel due to excessive ingestion of fluoride during enamel maturation. Disturbing the appearance, it has considerable implications on patients’ esteem and quality of life. Depending on the severity of fluorosis and the thickness of the layer of enamel involved, wide ranges of approaches of varying invasiveness are proposed. Alone or in combination, they can provide esthetic masking of the discolored enamel unless the effect of each treatment the clinical situation is well considered.

REVIEW OF MODERN APPROACHES TO DENTAL FLUOROSIS MANAGEMENT

Dental fluorosis is caused by ingesting too much fluoride while the teeth are developing. Poltava region belongs to Buchach fluorine hydrogeological province which ground waters are characterized by a high content of fluorine. Such districts as Myrgorod, Lubny, Gadyach, Globino, Mashivka, Shyshaky and Novy Sanzshary have fluoride concentration in drinking water from 2,5 tо 7 mg/l. It is known that the overdose of fluoride has deleterious effect on enamel development, generating a hypomineralized porous subsuperfacial enamel. Mild fluorosis transforms into moderate fluorosis with brown pigmentation over time and increasing the severity of fluorosis is associated with increasing the patient`s dissatisfaction.&#x0D; There are a few different ways that dental fluorosis can be treated. Local remineralisation therapy is the most careful way to reduce or eliminate fluorosis spots. Enamel microabrasion removes the outer porous enamel with pumice after it has been partly demineralized by the acid; topical fluoride that remineralized the enamel follows microabrasion. A teeth whitening can return teeth to their former glory in a single visit. Infiltration technique is the novel approach to fluorosis management which masks white spots. Veneers or crowns are the next option that restores teeth gleaming appearance. Unfortunately, previous reviews that have analyzed contemporary methods of fluorosis treatment didn’t determine their indications depending on the disease severity and the enamel maturation.&#x0D; Purpose of the study was to systematize the methods of dental fluorosis management offered last years and to determine the indications for their use depending on the severity of the disease and the maturity of the tooth enamel. Searching strategy for identification of scientific publications published between the years 2009 - May 2019 was conducted by reviewers independently through Google. The search strategy included keywords "dental fluorosis management", «teeth whitening», «teeth microabrasion», «infiltration for fluorosis treatment» and it was complementated by checking references of the relevant review articles and the eligible studies for additional useful publications.&#x0D; Over the last 10 years few articles were dealt with minerals, vitamins, adaptogens, antitoxicants prescription for fluorosis management. Such tooth pastes as «R.O.C.S» and «Novyi zhemchuh calcium» showed efficacy in local remineralisation therapy of fluorosis in children. Infiltration technique was used for mild fluorosis management and in combination with whitening for moderate fluorosis treatment in children. Different tooth whitening techniques were offered and only some of them include local remineralisation therapy that can stabilize clinical result. Carbamide and orthophosphoric acid were utilized for whitening of immature fluorosis teeth. Microabrasion in children's teeth was effective in combination with following fluoridation, for example Tooth Moose.&#x0D; Direct and indirect restorations are considered the treatment of choice for moderate to severe cases of fluorosis given the optimum aesthetics, wear resistance, biocompatibility, and long-term results. Whereas veneers and crowns are indicated in mature fluorosis teeth, choice of direct composite restorations doesn’t depend on tooth maturity.&#x0D; Treatment of fluorosis of various severities in children should include endogenous use of medicines that increase the enamel remineralisation. Local remineralisation therapy is indicated for mild fluorosis in immature teeth and for moderate fluorosis in combination with bleaching and microabrasion. Infiltration technique is recommended for mild fluorosis management and in combination with whitening for moderate fluorosis treatment in children. In the case of inefficiency of minimally invasive methods or severe fluorosis, direct or indirect restorations are conducted. Promising direction in fluorosis treatment is the development of new methods for fluorosis management, including general and local remineralization therapy, as well as infiltration technique.

Porcine keratin 75 in developing enamel

ObjectiveTo provide in vivo biochemical evidence for the isolation, identification, and characterization of porcine keratin 75 (K75) in developing enamel. MethodsImmunolocalization of K75 was observed in mandibles from mice at postnatal days 5 and 11. K75 gene expression was analyzed by quantitative reverse transcription-polymerase chain reaction using enamel organ epithelium (EOE) of incisors from pigs at 5 months of age. Enamel protein was extracted and isolated from both immature and mature enamel of second molars from 5-month-old pigs, and the K75 antibody-positive fraction was analyzed by liquid chromatography-mass spectrometry (LC-MS/MS). In vitro protease digestion of K75-antibody-positive fraction was carried out using porcine kallikrein 4 (pKLK4) or recombinant human enamelysin (rhMMP20) and their degradation patterns were characterized by both SDS-PAGE and western blotting. ResultsSpecific immunostaining for K75 was restricted to the layers of stratum intermedium and the enamel side of ameloblasts in mice at postnatal day 5, and to the papillary layer at postnatal day 11. Porcine K75 was expressed throughout enamel formation, but its transcript levels were significantly higher in the transition EOE than in the secretory- and maturation-stage EOE. Porcine K75 was extracted from the neutral soluble fraction from both immature and mature enamel. It was identified by LC-MS/MS analysis, and was found not to be degraded by either pKLK4 or rhMMP20. ConclusionWe propose that K75 is present in the developing enamel and undergoes different processing/degradation compared to other enamel proteins.

The Enamel Phenotype in Homozygous Fam83h Truncation Mice.

BackgroundTruncation FAM83H mutations cause human autosomal dominant hypocalcified amelogenesis imperfecta (ADHCAI), an inherited disorder characterized by severe hardness defects in dental enamel. No enamel defects were observed in Fam83h null mice suggesting that Fam83h truncation mice would better replicate human mutations.MethodsWe generated and characterized a mouse model (Fam83h Tr/Tr) expressing a truncated FAM83H protein (amino acids 1–296), which recapitulated the ADHCAI‐causing human FAM83H p.Tyr297* mutation.ResultsDay 14 and 7‐week Fam83h Tr/Tr molars exhibited rough enamel surfaces and slender cusps resulting from hypoplastic enamel defects. The lateral third of the Fam83h Tr/Tr incisor enamel layer was thinner, with surface roughness and altered enamel rod orientation, suggesting disturbed enamel matrix secretion. Regular electron density in mandibular incisor enamel indicated normal enamel maturation. Only mildly increased posteruption attrition of Fam83h Tr/Tr molar enamel was observed at 7‐weeks. Histologically, the Fam83h Tr/Tr enamel organ, including ameloblasts, and enamel matrices at sequential stages of amelogenesis exhibited comparable morphology without overt abnormalities, except irregular and less evident ameloblast Tomes' processes in specific areas.ConclusionsConsidering Fam83h−/− mice showed no enamel phenotype, while Fam83h Tr/Tr (p.Tyr297*) mice displayed obvious enamel malformations, we conclude that FAM83H truncation mutations causing ADHCAI in humans disturb amelogenesis through a neomorphic mechanism, rather than haploinsufficiency.

Enamel mineralization and compositional time-resolution in human teeth evaluated via histologically-defined LA-ICPMS profiles

Abstract Mammalian dental enamel is a key archive for the reconstruction of past environments. Sequentially mineralizing enamel provides continuous, several year-long records, which spatially-resolved sampling can ‘read’ at seasonal or higher time resolution. Yet it remains underexplored how much an initially incorporated compositional signal is overprinted by the two-stage enamel mineralization process, which affects the finally achievable time-resolution. We report results of a systematic investigation into histologically-defined compositional profiles from human enamel obtained by laser-ablation inductively-coupled-plasma mass spectrometry (LA-ICPMS). Sr/Ca, Zn/Ca, Ba/Ca and Pb/Ca are investigated as commonly-utilized proxies of (palaeo)diet, mineralization and/or pollution in modern and archaeological samples. Our modern human teeth are from unequivocally breast-fed and formula-fed individuals, respectively. By focusing on two profiles that are time-equivalent yet topographically different, namely the enamel-dentine junction (EDJ) vs. enamel prisms (P), we evaluate the compositional effect of enamel secretion vs. maturation on elemental proxies throughout enamel thickness. These two broadly orthogonal orientations are compared with the connecting Neonatal/Retzius (NNL/R) profiles that represent nominal isogrowth events during enamel secretion, which – if later maturation had no effect – should show invariant compositional signals across enamel. However, we find that all NNL/R profiles record systematically varying compositions across enamel, with Sr/Ca always decreasing by 30–80% and Zn/Ca increasing near-exponentially 20–35 times towards outer enamel. As such they can be used to benchmark the extent of enamel maturation. Since all prism profiles reveal signals similar to NNL/R for Sr, Zn and in part Ba, this unequivocally demonstrates that P-orientations are equally overprinted by maturation, in all cases with increasing intensity towards outer enamel. EDJ and P profiles do not match one-another despite representing coeval secretion time, and we infer that the highest degree of initial signal variability can be retrieved along the EDJ (approx. ≤ 100 μm) where maturation had the least effect. Using a simple two-component mixing model we show that during maturation only a moderate increase (1.3–1.9×) in discrimination against Sr is required to explain the Sr/Ca patterns. The Zn/Ca increase on the other hand is interpreted to reflect the Zn-binding motifs of the enzymes MMP-20 (matrix metalloproteinase-20) and KLK-4 (kallikrein-4) active during enamel secretion and maturation, which may preferentially imprint a Zn compositional signal in maturing enamel. In the case of Ba/Ca we find no systematic patterns analogous to that of Sr and Zn in modern samples. Moreover, cryptic diagenesis affecting Ba in otherwise well-preserved fossil teeth argues for caution when using Ba/Ca to infer nutritional signals without additional elemental/isotopic corroboration. Unlike all other investigated elements, Pb/Ca shows broadly similar EDJ-P profiles, and nearly invariant R-signals across enamel, which may reflect the affinity of Pb to both organic molecules and inorganic apatite during enamel mineralization. Overall our results reveal the element-specific behaviour of Sr, Zn, Ba and Pb during enamel mineralization.

Amelogenic transcriptome profiling in ameloblast-like cells derived from adult gingival epithelial cells

Dental enamel is the highly mineralized tissue covering the tooth surface and is formed by ameloblasts. Ameloblasts have been known to be impossible to detect in adult tooth because they are shed by apoptosis during enamel maturation and tooth eruption. Owing to these, little was known about appropriate cell surface markers to isolate ameloblast-like cells in tissues. To overcome these problems, epithelial cells were selectively cultivated from the gingival tissues and used as a stem cell source for ameloblastic differentiation. When gingival epithelial cells were treated with a specified concentration of BMP2, BMP4, and TGFβ-1, the expression of ameloblast-specific markers was increased, and both the MAPK and Smad signaling pathways were activated. Gingival epithelial cells differentiated into ameloblast-like cells through epithelial-mesenchymal transition. By RNA-Seq analysis, we reported 20 ameloblast-specific genes associated with cell surface, cell adhesion, and extracellular matrix function. These cell surface markers might be useful for the detection and isolation of ameloblast-like cells from dental tissues.

Mechanics of amelogenin TRAP protein in the proximity of hydroxyapatite mineral is altered by interfacial water

Enamel is a composite bioceramic that covers teeth. Here, based on molecular dynamic (MD) simulation, we seek a better understanding of the interactions between the enamel matrix proteins with hydroxyapatite (HAP) crystal surfaces. These interactions occur during enamel formation and are responsible for controlling the formation of high aspect ratio carbonated hydroxyapatite nanocrystallites, whereas, in mature enamel, they are implicated to alter the mechanical properties of mature enamel to yield a tough composite that resists fracture during chewing. We choose an archetypal matrix protein known as tyrosine-rich amelogenin peptide (TRAP), which is retained among the HAP crystallites of mature enamel. Our findings provide molecular details to the emerging blueprint needed to engineer a biologically inspired enamel restorative material.

Evaluation of genetic polymorphisms in MMP2, MMP9 and MMP20 in Brazilian children with dental fluorosis

Recent studies suggested that genetics contribute to differences in dental fluorosis (DF) susceptibility among individuals having the same environmental exposure. This study evaluated if MMP2, MMP9 and MMP20 are expressed during enamel development and assessed the association between polymorphisms in these genes with DF. Mice susceptible and resistant to DF were used to evaluate if MMPs were candidate genes for DF. The animals received fluoride and their enamels were used for immunohistochemistry. Additionally, 481 subjects from a city with fluoridation of public water supplies were recruited. Genotyping was performed using real time PCR. Allele/genotype frequencies were compared between groups. MMP2, MMP9 and MMP20 immunostaining was detected in both animal groups. DF was observed in 22.4% of the subjects. A borderline association was observed in MMP2 (rs243865), MMP9 (rs17576) and in MMP20 (rs1784418) (p = 0.06, p = 0.08 and p = 0.06 respectively). Briefly, MMPs were expressed during enamel maturation and genetic polymorphisms were not associated with DF.