Search

Enamel defects resulting from environmental conditions and way of life are public health concerns because of their high prevalence. Because their etiology is unclear, the aim of this study was to analyze the various forms of enamel hypomineralization, and to characterize the genes involved in this process to determine the mechanisms involved in disruptions of amelogenesis. We used bisphenol A (BPA) and fluoride as models; both are commonly encountered in human populations and utilized in dentistry. Wistar rats were chronically exposed to 5 μg/kg/day BPA from day 1 of gestation to day 65 after birth (P65) and 5 mM fluoride from P21 to P65. Resulting enamel defects were comparable to the human enamel pathologies molar incisor hypomineralization (MIH) and dental fluorosis (DF) respectively, and were more severe in rats exposed to both agents than to each agent alone. Large-scale transcriptomic analysis of dental epithelium showed a small group of genes the expression of which was affected by exposure to BPA or NaF. Among the most modulated, many are directly involved in amelogenesis (Amelx, Enam, Klk4, Mmp12, Slc26a4, and Slc5a8), and can be regrouped as forming the "hypomineralization enameloma." Each of these gene expression perturbations may contribute to enamel defects. Exposure to BPA weakens enamel, making it more prone to generate frequent mineralization defects MIH and DF. Our study identifies hypomineralization genes that may enable the use of dental enamel as an early marker of exposure to environmental toxicants because of its unique ability to retrospectively record ameloblast pathophysiology. © 2016 American Society for Bone and Mineral Research.

Enamel defects resulting from environmental conditions and ways of life are public health concerns because of their high prevalence. These defects result from altered activity of cells responsible for enamel synthesis named ameloblasts, which present in enamel organ. During amelogenesis, ameloblasts follow a specific and precise sequence of events of proliferation, differentiation, and death. A rat continually growing incisors is a suitable experimental model to study ameloblast activity and differentiation stages in physiological and pathological conditions. Here, we describe a reliable and consistent method to micro-dissect enamel organ of rats exposed to environmental toxicants. The micro-dissected dental epithelia contain secretion- and maturation-stage ameloblasts that may be used for qualitative experiments, such as immunohistochemistry assays and in situ hybridization, as well as for quantitative analyses such as RT-qPCR, RNA-seq, and Western blotting.

L’email est le tissu le plus visible de la dent. Il lui donne sa blancheur, sa brillance et fait l’objet de toutes les attentions d’un point de vue esthetique. Malheureusement, il n’est pas rare d’observer des alterations de cet email, que ce soit de simples taches discolorees localisees, ou des pertes de substances plus etendues. Les etiologies sont alors multiples : toxicite durant la mineralisation du germe, hyperthermie ou anomalie genetique. Comment poser ce diagnostic etiologique et rassurer les parents, voila un enjeu quotidien auquel nous devons repondre en tant que professionnel.

Endocrine-disrupting chemicals (EDCs) that interfere with the steroid axis can affect amelogenesis, leading to enamel hypomineralization similar to that of molar incisor hypomineralization, a recently described enamel disease. We investigated the sex steroid receptors that may mediate the effects of EDCs during rat amelogenesis. The expression of androgen receptor (AR), estrogen receptor (ER)-α, and progesterone receptor was dependent on the stage of ameloblast differentiation, whereas ERβ remained undetectable. AR was the only receptor selectively expressed in ameloblasts involved in final enamel mineralization. AR nuclear translocation and induction of androgen-responsive element-containing promoter activity upon T treatment, demonstrated ameloblast responsiveness to androgens. T regulated the expression of genes involved in enamel mineralization such as KLK4, amelotin, SLC26A4, and SLC5A8 but not the expression of genes encoding matrix proteins, which determine enamel thickness. Vinclozolin and to a lesser extent bisphenol A, two antiandrogenic EDCs that cause enamel defects, counteracted the actions of T. In conclusion, we show, for the first time, the following: 1) ameloblasts express AR; 2) the androgen signaling pathway is involved in the enamel mineralization process; and 3) EDCs with antiandrogenic effects inhibit AR activity and preferentially affect amelogenesis in male rats. Their action, through the AR pathway, may specifically and irreversibly affect enamel, potentially leading to the use of dental defects as a biomarker of exposure to environmental pollutants. These results are consistent with the steroid hormones affecting ameloblasts, raising the issue of the hormonal influence on amelogenesis and possible sexual dimorphism in enamel quality.

Enamel defects resulting from environmental conditions and way of life are public health concerns because of their high prevalence. Because their etiology is unclear, the aim of this study was to analyze the various forms of enamel hypomineralization, and to characterize the genes involved in this process to determine the mechanisms involved in disruptions of amelogenesis. We used bisphenol A (BPA) and fluoride as models; both are commonly encountered in human populations and utilized in dentistry. Wistar rats were chronically exposed to 5 μg/kg/day BPA from day 1 of gestation to day 65 after birth (P65) and 5 mM fluoride from P21 to P65. Resulting enamel defects were comparable to the human enamel pathologies molar incisor hypomineralization (MIH) and dental fluorosis (DF) respectively, and were more severe in rats exposed to both agents than to each agent alone. Large-scale transcriptomic analysis of dental epithelium showed a small group of genes the expression of which was affected by exposure to BPA or NaF. Among the most modulated, many are directly involved in amelogenesis (Amelx, Enam, Klk4, Mmp12, Slc26a4, and Slc5a8), and can be regrouped as forming the "hypomineralization enameloma." Each of these gene expression perturbations may contribute to enamel defects. Exposure to BPA weakens enamel, making it more prone to generate frequent mineralization defects MIH and DF. Our study identifies hypomineralization genes that may enable the use of dental enamel as an early marker of exposure to environmental toxicants because of its unique ability to retrospectively record ameloblast pathophysiology. © 2016 American Society for Bone and Mineral Research.

There has been increasing concerns over last 20 years about the potential adverse effects of endocrine disruptors (EDs). Bisphenol A (BPA), genistein (G) and vinclozolin (V) are three widely used EDs having similar effects. Tooth enamel has recently been found to be an additional target of BPA that may be a causal agent of molar incisor hypomineralization (MIH). However, populations are exposed to many diverse EDs simultaneously. The purpose of this study was therefore to assess the effects of the combination of G, V and BPA on tooth enamel. Rats were exposed daily in utero and after birth to low doses of EDs mimicking human exposure during the critical fetal and suckling periods when amelogenesis takes place. The proportion of rats presenting opaque areas of enamel hypomineralization was higher when rats were treated with BPA alone than with a combination of EDs. The levels of mRNAs encoding the main enamel proteins varied with BPA treatment alone and did not differ significantly between controls and combined treatment groups. In vitro, rat ameloblastic HAT-7 cells were treated with the three EDs. BPA induced enamelin and reduced klk4 expression, G had no such effects and V reduced enamelin expression. These findings suggest that combinations of EDs may affect enamel less severely than BPA alone, and indicate that enamel hypomineralization may differ according to the characteristics of the ED exposure.

International audience; Bisphenol A (BPA) is a widespread endocrine disrupting chemical (EDC) strongly suspected to have adverse health effects. Numerous tissues and cells are affected by BPA, and we showed recently that BPA targets include ameloblasts and enamel. We therefore investigated the effects of BPA on ameloblasts and the possible involvement of the estrogen signaling pathway. Rats were exposed daily to low-dose BPA, and developed enamel hypomineralization similar to human molar incisor hypomineralization (MIH). BPA increased ameloblast proliferation in vivo and in vitro. The proliferation of the rat dental epithelial cell line HAT-7 was also increased by estrogen (E2). Ameloblasts express ER alpha but not ER beta both in vivo and in vitro. The ER antagonist ICI 182,780 was used to inactivate ER alpha and abolished the effects of E2 on cell proliferation and transcription, but only partially reduced the effects of BPA. In conclusion, we show, for the first time, that: 1) BPA has ER-dependent and ER-independent effects on ameloblast proliferation and gene transcription; 2) the estrogen signaling pathway is involved in tooth development and the enamel mineralization process; and 3) BPA impacts preferentially amelogenesis in male rats. These results are consistent with the steroid hormones having effect on ameloblasts, raising the issues of the hormonal influence on amelogenesis and possible differences in enamel quality between sexes.

WOS:000321403600012 ; http://ajp.amjpathol.org; International audience; Endocrine-disrupting chemicals (EDCs), including bisphenol A (BPA), are environmental ubiquitous pollutants and associated with a growing health concern. Anecdotally, molar incisor hypomineralization (MIH) is increasing concurrently with EDC-related conditions, which has led us to investigate the effect of BPA on amelogenesis. Rats were exposed daily to BPA from conception until day 30 or 100. At day 30, BPA-affected enamel exhibited hypomineralization similar to human MIH. Scanning electron microscopy and elemental analysis revealed an abnormal accumulation of organic material in erupted enamel. BPA-affected enamel had an abnormal accumulation of exogenous albumin in the maturation stage. Quantitative real-time PCR, Western blotting, and luciferase reporter assays revealed increased expression of enamelin but decreased expression of kallikrein 4 (protease essential for removing enamel proteins) via transcriptional regulation. Data suggest that BPA exerts its effects on amelogenesis by disrupting normal protein removal from the enamel matrix. Interestingly, in 100-day-old rats, erupting incisor enamel was normal, suggesting amelogenesis is only sensitive to MIH-causing agents during a specific time window during development (as reported for human MIH). The present work documents the first experimental model that replicates MIH and presents BPA as a potential causative agent of MIH. Because human enamel defects are irreversible, MIH may provide an easily accessible marker for reporting early EDC exposure in humans.

MIH for Molar Incisor Hypomineralization is a recently described pathology affecting around 18% of six year old children. Although a number of putative factors have been hypothesized, etiology of MIH remains unknown. The parallel increase of exposure to endocrine disruptors (EDs) and the prevalence of MIH led us to investigate a possible relationship between both events. Rats were orally exposed daily to low dose of bisphenol A (BPA), genistein, vinclozolin, alone (for BPA) or in combination, from the conception to the sacrifice, mimicking human environmental exposure. Macroscopic observation of male rat incisors showed that the phenotype induced by BPA was the most evident with 75% of rats presenting random opaque white spots comparable to those observed in human MIH, whereas only 50% of GEN and VINCLO treated rats shared similar phenotype. Human MIH and BPA treated rat teeth were analyzed in parallel by scanning electron microscopy (SEM) - Energy dispersive X-ray (EDX) and histology. Both of them exhibited the same hypomineralization phenotype. BPA targeted specifically the expression of two major enamel genes, enamelin and kallikrein 4 (Klk4) at the transcriptional level. Rat ameloblastic HAT-7 cells were stably transfected with plasmids containing KLK4 promoter, and treated with 1 nM BPA, 1 nM GEN, 1 nM VINCLO. BPA decreased both KLK4 mRNA level and KLK4 promoter activity. Conversely, GEN increased KLK4 expression whereas VINCLO had no effect on this gene, a possible reason for the lesser effect on enamel hypomineralization. Our data strongly support a role for EDs acting as BPA in MIH pathology. In conclusion, MIH teeth may represent a much needed early biomarker, easily accessible, for ED exposure in humans.

Enamel is the most visible tissue of the tooth. It gives the tooth its whiteness, its brilliance and is the main focus of our attention from an esthetic point of view. Unfortunately, it is not uncommon to see alterations in this enamel, whether they are simple localized discolored spots, or more extensive loss of tooth substance. The etiologies, then, are multiple: toxicity during the mineralization of the bud, hyperthermia or a genetic abnormality. As professionals, making an etiological diagnosis and reassuring the parents is a challenge that we must address on a daily basis.

Objectif : Étudier l’incidence de l’éducation thérapeutique du patient (ETP) sur la prise en charge de la maladie parodontale. Méthodes : Une revue systématique de la littérature a été conduite dans PUBMED et COCHRANE, visant à déterminer l’impact de l’ETP et de la maintenance parodontale sur l’évolution de la maladie. Puis, un questionnaire anonyme a permis d’évaluer si les patients étaient suffisamment informés sur les moyens de prévention et les recommandations. Résultats : Sur 4566 articles, 22 ont été retenus. Neuf évaluaient l’effet d’un programme d’ETP, qui semble améliorer les principaux paramètres cliniques (indice de plaque, indice de saignement et gingival). Treize études évaluaient la maintenance, et soulignaient l’importance d’une bonne observance, puisque la perte dentaire moyenne était significativement moins importante chez les patients observants que chez les patients non compliants (-1,15 IDC 95 % [-2,18 ; -0.11], p=0,006). Le questionnaire auprès de 278 patients a montré que 69 % ignoraient ce qu’est une parodontite, 62 % n’ont jamais bénéficié d’une séance dédiée à l‘hygiène buccodentaire, et qu’environ 50 % ne pratiquaient pas un brossage adapté. Conclusion : L’ETP influence positivement l’évolution de parodontopathies, mais est insuffisamment appliquée en pratique, possiblement à cause des contraintes de gestion du cabinet. Le développement de la profession d’hygiéniste dentaire ou d’approches comme l’entretien motivationnel pourraient pallier ces limites.