Chronic fluoride toxicity: dental fluorosis

Defense Mechanisms Against Acid Exposure by Dental Enamel Formation, Saliva and Pancreatic Juice Production

The pancreas, the salivary glands and the dental enamel producing ameloblasts have marked developmental, structural and functional similarities. One of the most striking similarities is their bicarbonate-rich secretory product, serving acid neutralization. An important difference between them is that while pancreatic juice and saliva are delivered into a lumen where they can be collected and analyzed, ameloblasts produce locally precipitating hydroxyapatite which cannot be easily studied. Interestingly, the ion and protein secretion by the pancreas, the salivary glands, and maturation ameloblasts are all two-step processes, of course with significant differences too. As they all have to defend against acid exposure by producing extremely large quantities of bicarbonate, the failure of this function leads to deteriorating consequences. The aim of the present review is to describe and characterize the defense mechanisms of the pancreas, the salivary glands and enamel-producing ameloblasts against acid exposure and to compare their functional capabilities to do this by producing bicarbonate.

Er:YAG laser for the aesthetic treatment of developmental enamel defects in frontal teeth: a case report

Background and aims

Several studies highlighted how the ameloblasts, secretory cells responsible of the tooth enamel formation, are highly sensitive to changes in their environment. Due to enamel maturation, their dysfunctions during a limited period of tooth development may lead to permanent morphological consequences, namely Developmental Enamel Defects (DED). The aim of this study was to show the advantages of Er:YAG laser for DED treatment.

Subjects and methods

The case report presented describes the treatment, by Er:YAG laser, of some DED lesions present in the upper incisors of a young patient. The settings used were: 1W power, 100mJ energy, 10 Hz frequency corresponding to a Fluence of 0.318 J/cm² per pulse or 3, 18 J/cm².

Results

The patient, even in absence of local anesthesia, did not feel any pain or discomfort during and after intervention. Follow-up at 2, 6 and 12 months did not show any problems in an aesthetic point of view as well as regarding hypersensitivity.

Conclusions

The use of Er:YAG laser for the treatment of developmental enamel defects in frontal teeth is a safe, painless and minimally invasive; moreover, it is able to assure a good aesthetic result.

The antibacterial effects of coffee extract, chlorhexidine, and fluoride against Streptococcus mutans and Lactobacillus plantarum: An in vitro study

BACKGROUND

The aim of the present study was to compare the antibacterial effects of coffee extract with those of 0.2% sodium fluoride and chlorhexidine (CHX) mouthrinses on Streptococcus mutans and Lactobacillus plantarum in vitro.

MATERIALS AND METHODS

In this experimental in vitro study, the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and disk diffusion method were determined for different concentrations of coffee extract, 0.2% CHX, and 0.2% fluoride against S. mutans and L. plantrum. Data were analyzed using Kruskal-Wallis analysis. Statistical significance level was established at P < 0.05.

RESULTS

The MIC of coffee was achieved at 62.5 and 500 mg/mL against S. mutans and L. plantarum, respectively. The MBC against S. mutans was 125 mg/mL. The diameter of the zone of inhibition around S. mutans for pure coffee extract (100%), CHX (0.2%), and fluoride was 19.8 mm, 9.92 mm, and 0, respectively. At a concentration of 6.25%-100%, coffee had a significantly larger zone of inhibition compared to CHX and fluoride) P = 0.01). The MBC of coffee and fluoride was 0 against L. plantarum. The lowest inhibitory concentration belongs to CHX (MIC: 0.624 mg/ml for L. plantarum and 0.125 mg/ml for S. mutans).

CONCLUSION

The coffee had an antibacterial effect against S. mutans on 62.5-1000 mg/ml concentrations. The zone of inhibition around S. mutans for higher concentrations of coffee (6.25%-100%) was significantly higher than that of CHX and fluoride 0.2%. Bacteriostatic effect of coffee against L. plantarum was obtained at 500-1000 mg/ml. However, coffee and fluoride did not show any bactericidal effects against L. plantarum.

Smile Makeover by Veneers – Case Report

Ceramic veneers have evolved in the last few years as an aesthetic restoration in the field of aesthetic dentistry. It is a conservative option as compared to full coverage crowns for improving the patients smile. Ceramic veneers are widely used for smile designing in patients with fluorosis, midline diastema, hypoplastic teeth, and peg shape laterals. Clinical relevance: This article highlights the smile designing of a young patient with fluorosis using ceramic veneers, which not only improves the smile of the patient but has positive psychological benefits.

Prevalence of dental fluorosis in regions supplied with non-fluoridated water in the Brazilian territory: a systematic review and meta-analysis

This systematic review and meta-analysis aimed to estimate and compare the prevalences of dental fluorosis in Brazilian cities supplied with non-fluoridated water and in locations that uses groundwater. In December of 2016, cross-sectional studies were searched in eight databases, including the "grey literature". The prevalences were estimated through a mixed random effects model considering the locations as subgroups. The heterogeneity among the studies was assessed with I2 statistics and the Cochran's Q test. A total of 1038 records were found, from which only 18 articles met the inclusion criteria and were subjected to analysis. The meta-analytic model estimated a prevalence of dental fluorosis of 8.92 % (95 % CI: 5.41 % to 14.36 %) in cities supplied with non-fluoridated water, and of 51.96 % (95 % CI: 31.03 % to 72.22 %) in cities supplied by artesian wells. The heterogeneity among the studies was high: I2 = 95 % (p < 0.01) in the first subgroup of cities and I2 = 98 % (p < 0.01) in the second subgroup. The prevalence was significantly higher (p < 0.001) in populations exposed to artesian well water, indicating that the presence of natural fluoride at high concentrations represents a risk factor for the occurrence of dental fluorosis.

Polish School Nurses' Opinion and Knowledge towards Topical Fluoride Treatment

Aim

The aim of this study was to evaluate the Polish school nurses’ opinion on the topical fluoride treatment and their knowledge about fluoride safety.

Methods

A cross-sectional study with the use of a self-administered questionnaire was conducted on 164 school nurses. The questionnaire concerned previous training in caries prevention, action taken at schools with regard to caries prevention, cooperation with dentists, opinion on the topical fluoride application program and nurses’ knowledge about fluoride safety.

Results

93.9% of nurses included oral health in their duties and 81.7% accomplished the topical fluoride treatment. 52.1% never attended any training concerning dental issues. Nurses from cities and villages more often than those from towns provided lectures on caries prevention and fluoride topical applications (respectively p= 0.033 and p=0.021, chi2 test). The nurses had a positive opinion on the effectiveness and safety of topical fluoride application. Only a half of respondents knew the fluoride probable toxic dose and one fifth of them did not know the concentration of fluoride in gel. The knowledge was statistically dependent on the level of nurses’ education (p=0.019, Kruskal-Wallis test). Nurses with a low level of knowledge were not aware of a potential harm effect of fluoride and they had negative opinion about the effectiveness of fluoride program at school.

Conclusion

Polish school nurses had a positive opinion on topical fluoride treatment. However, there are gaps in their knowledge and the institutional training is needed.

Disrupted Iron Storage in Dental Fluorosis

Enamel formation and quality are dependent on environmental conditions, including exposure to fluoride, which is a widespread natural element. Fluoride is routinely used to prevent caries. However, when absorbed in excess, fluoride may also lead to altered enamel structural properties associated with enamel gene expression modulations. As iron plays a determinant role in enamel quality, the aim of our study was to evaluate the iron metabolism in dental epithelial cells and forming enamel of mice exposed to fluoride, as well as its putative relation with enamel mechanical properties. Iron storage was investigated in dental epithelial cells with Perl’s blue staining and secondary ion mass spectrometry imaging. Iron was mainly stored by maturation-stage ameloblasts involved in terminal enamel mineralization. Iron storage was drastically reduced by fluoride. Among the proteins involved in iron metabolism, ferritin heavy chain (Fth), in charge of iron storage, appeared as the preferential target of fluoride according to quantitative real-time polymerase chain reaction, Western blotting, and immunohistochemistry analyses. Fluorotic enamel presented a decreased quantity of iron oxides attested by electron spin resonance technique, altered mechanical properties measured by nanoindentation, and ultrastructural defects analyzed by scanning electron microscopy and energy dispersive x-ray spectroscopy. The in vivo functional role of Fth was illustrated with Fth+/-mice, which incorporated less iron into their dental epithelium and exhibited poor enamel quality. These data demonstrate that exposure to excessive fluoride decreases ameloblast iron storage, which contributes to the defective structural and mechanical properties in rodent fluorotic enamel. They raise the question of fluoride’s effects on iron storage in other cells and organs that may contribute to its effects on population health.

Brick tea consumption is a risk factor for dental caries and dental fluorosis among 12-year-old Tibetan children in Ganzi

Brick tea contains high concentration of fluoride. The aim of the present work was to explore whether and how the brick tea is a risk factor for dental caries and dental fluorosis among Tibetan children in Ganzi. A cross-sectional study was conducted with 368 12-year-old Tibetan children in Ganzi. Dental caries was measured by DMFT index, and dental fluorosis severity was measured by Dean's Index. Community Fluorosis Index was used to estimate public health significance of dental fluorosis. Oral health-related behaviors and awareness, dietary habits and socioeconomic status were determined by a questionnaire. Bivariate and multivariate analyses were used to determine risk factors associated with dental caries and dental fluorosis. Dental caries prevalence was 37.50%, mean DMFT was 0.84 ± 1.53, while dental fluorosis prevalence was 62.23%. Community Fluorosis Index was 1.35, indicating a medium prevalent strength of dental fluorosis. Dental fluorosis was associated with mother's regular consumption of brick tea and residence altitude, and dental caries was associated with mother's regular consumption of brick tea. Mother's regular consumption of brick tea was a risk factor for both dental fluorosis and dental caries among children. Reducing mother's brick tea consumption during pregnancy and lactation may improve oral health status of their children.

Long term spatial-temporal dynamics of fluoride in sources of drinking water and associated health risks in a semiarid region of Northern China

There is a concern about the increasing prevalence of health problems related to the ingestion of fluoride (F^-) in the developing world. Drinking water is one important source of F^-, and the concentration of F^- needs to be known to ensure the safety of drinking water. In this study, F^- levels in drinking water were investigated across Taiyuan in Shanxi Province, China. Spatial-temporal distribution characteristics and potential associated health risks were analyzed using GIS. We collected 485 samples from shallow wells without any defluoridation treatments between 2008 and 2016. After analyzing the samples of F^- content we found that mean F^- levels of urban areas (0.61 ± 0.39 mg L^-1), suburban areas (0.70 ± 0.87 mg L^-1) and for all of Taiyuan city (0.63 ± 0.56 mg L^-1) were in optimum range based on the recommendation by USEPA. However, individual locations within industrial areas (e.g. Gujiao District) had higher F^- levels (1.06 mg L^-1). A concerning result showed that 12.37% of tested locations had F^- concentrations larger than 1.0 mg L^-1. We calculated F^- Health Risk Indices (HRIs_F) and found that highest were associated with suburban areas, especially in the year 2009 and 2010. However, from 2008 to 2016, overall F^- levels and HRIs_F of the sampled groundwater in Taiyuan City showed a decreasing trend. HRIs_F in suburban areas was higher than urban areas, possible due to the heavily prevalent coal mining industry in those areas. Specific policies should be formulated to address HRIs_F.

Hipomineralização molar incisivo em odontopediatria: considerações gerais

Hipomineralização molar incisivo (MIH) engloba a hipomineralização do esmalte que aflige um ou mais primeiros molares permanentes e que pode acometer também incisivos permanentes. Segundos pré-molares e caninos permanentes também podem mostrar-se envolvidos, assim como alguns decíduos, entre os quais cita-se os segundos molares. O objetivo do presente artigo foi averiguar as manifestações clínicas ocasionadas pela hipomineralização molar incisivo sob o enfoque da odontopediatria. Realizou-se estudo de revisão bibliográfica com busca nas bases de dados LILACS e Google Acadêmico. Na base LILACS empregou-se a expressão de busca: hipomineralização molar incisivo and odontopediatria. Na base de dados Google Acadêmico utilizou-se a expressão de busca: hipomineralização molar incisivo and odontopediatria. É importante que se proceda ao diagnóstico precoce e correto da MIH, baseando-se na realização de anamnese detalhada, que seja capaz de investigar a existência de possíveis doenças no período da infância e que se proceda concomitantemente ao feitio de exame clínico para que se estabeleça um prognóstico adequado. Concluiu-se que uma abordagem com cunho preventivo é capaz de minimizar eventuais danos, evitando tratamentos com maior complexidade.

Developmental dental anomalies and their potential role in establishing identity in post-mortem cases: a review

Teeth may provide useful forensic evidence owing to features like uniqueness, stability and comparability. Moreover, the human dentition is heterodont, i.e. all the teeth have different morphology - incisors, canines, premolars and molars. There are sometimes deviations from normal morphology, such as the presence of extra teeth, variation in their shape and size eg the presence of an extra cusp, fractured crown/root, Carabelli's cusp, peg laterals, transpositions, fusion, etc. These differences can help forensic personnel identify bodies, especially where other methods of identification like facial features, fingerprints or DNA typing cannot yield satisfactory results as in cases of badly decomposed bodies, burnt remains, mass disasters, etc. Identification from dentition is based on the direct comparison of post-mortem dental profiles with ante-mortem dental records of the deceased. This article aims to review these developmental and morphological dental traits and their role in post-mortem identification.

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.

Enamel Microabrasion and Dental Bleaching on Teeth Presenting Severe-pitted Enamel Fluorosis: A Case Report

The present clinical case report describes the clinical steps of enamel microabrasion associated with dental bleaching to restore severely-pitted fluorosed teeth. The process of removing the fluorotic superficial stains started by using macroabrasion with a water-cooled fine tapered 3195 FF diamond bur. Rubber dam isolation of the operative field was used to remove the remaining enamel stains and superficial irregularities with the Opalustre microabrasive compound (6.6% hydrochloric acid associated with silicon carbide particles) followed by polishing using fluoridated paste and subsequent 2% neutral fluoride gel topical application. After one month, dental bleaching was performed using 10% carbamide peroxide in custom-formed acetate trays for two hours/day for 42 days. The association of enamel microabrasion with dental bleaching was effective for reestablishing the dental esthetics of a patient with severe dental fluorosis.

Aesthetic treatment of dental fluorosis in a 9-year-old girl: Case report

Background/Aim: Dental fluorosis is a specific disturbance of tooth formation caused by excessive intake of fluoride. The discoloration of teeth is the most common reason for parents to seek treatment. The purpose of this paper is to describe the therapeutic management performed in a 9-year-old girl with fluorosis. Case report: A clinical case of a 9-year-old girl diagnosed with fluorosis is reported. The treatment of this clinical case was achieved using microabrasion, which is a minimally invasive method. This technique improves the aesthetics of the teeth without causing significant loss of dental tissue; a characteristic making microabrasion applicable to children as well. Its implementation involved the combined use of 18% hydrochloric acid and pumice on the enamel surface of upper incisors. The improved appearance of the teeth was aesthetically pleasing and, consequently, the patient gained in self-confidence. Conclusions: In the literature, several treatment choices are proposed, depending on the severity of the fluorosis. In our case, microabrasion was applied and the aesthetic outcome satisfied both the patient and the dentist.

Sodium fluoride induced skeletal muscle changes: Degradation of proteins and signaling mechanism

Fluoride is a well-known compound for its usefulness in healing dental caries. Similarly, fluoride is also known for its toxicity to various tissues in animals and humans. It causes skeletal fluorosis leading to osteoporosis of the bones. We hypothesized that when bones are affected by fluoride, the skeletal muscles are also likely to be affected by underlying molecular events involving myogenic differentiation. Murine myoblasts C2C12 were cultured in differentiation media with or without NaF (1 ppm-5 ppm) for four days. The effects of NaF on myoblasts and myotubes when exposed to low (1.5 ppm) and high concentration (5 ppm) were assessed based on the proliferation, alteration in gene expression, ROS production, and production of inflammatory cytokines. Changes based on morphology, multinucleated myotube formation, expression of MyHC1 and signaling pathways were also investigated. Concentrations of NaF tested had no effects on cell viability. NaF at low concentration (1.5 ppm) caused myoblast proliferation and when subjected to myogenic differentiation it induced hypertrophy of the myotubes by activating the IGF-1/AKT pathway. NaF at higher concentration (5 ppm), significantly inhibited myotube formation, increased skeletal muscle catabolism, generated reactive oxygen species (ROS) and inflammatory cytokines (TNF-α and IL-6) in C2C12 cells. NaF also enhanced the production of muscle atrophy-related genes, myostatin, and atrogin-1. The data suggest that NaF at low concentration can be used as muscle enhancing factor (hypertrophy), and at higher concentration, it accelerates skeletal muscle atrophy by activating the ubiquitin-proteosome pathway.

Changes of DNA repair gene methylation in blood of chronic fluorosis patients and rats

To investigate the relationship between DNA repair gene methylation and chronic coal-burning fluorosis. The methylation rates of O⁶-methylguanine-DNA- methyltransferase gene MGMT, a DNA repair gene and mismatch repair gene MutL homolog 1 (MLH1) were analysed by methylation of specific PCR (MSP), and the levels of mRNA in the blood of the chronic fluorosis rats and the patients in the region of endemic coal-burning fluorosis were determined by real-time PCR. The levels of mRNA and protein of MGMT and MLH1 in the liver tissue of the chronic fluorosis rats were determined by real-time PCR and Western blot respectively. The results showed an increased methylation of the MGMT and MLH1 genes in the blood of the patients in the fluorosis region that correlated positively with the severity of fluorosis. The mRNA levels of MGMT and MLH1 genes from the patients in fluorosis region were lower than those of a control group, and also showed a positive correlation with the severity of fluorosis. Both the protein and mRNA levels of MGMT and MLH1 genes from the blood of rats and liver tissue in a fluoride-treated group were lower than those of a control non-fluoride treated group. These results indicate that the degree of methylation of MGMT and MLH1 genes is altered in fluorosis disease, the resulting changed expression of these repair genes may play a role in the liver damage caused by fluoride.

NaF Reduces KLK4 Gene Expression by Decreasing Foxo1 in LS8 Cells

Decreased expression and increased phosphorylation of Forkhead box o1 (Foxo1) in ameloblasts were observed both in vivo and in vitro when treated by fluoride. The present study aims to investigate the possible relationship between Foxo1 and enamel matrix proteinases, matrix metalloproteinase 20 (MMP20), and kallikrein 4 (KLK4), in NaF-treated ameloblasts. Ameloblast-like cells (LS8 cells) were exposed to NaF at selected concentration (0/2 mM) for 24 h. Gene overexpression and silencing experiments were used to up- and down-regulate Foxo1 expression. The expression levels of Foxo1, MMP20, and KLK4 were detected by quantitative real-time PCR and western blot. Dual luciferase reporter assay was performed to evaluate the regulation of Foxo1 on the transcriptional activity of KLK4 promoter. The results showed that KLK4 expression was decreased in LS8 cells treated by NaF, while MMP20 expression was not changed. Foxo1 activation led to significantly up-regulation of KLK4 in LS8 cells under NaF condition. Knockout of Foxo1 markedly decreased klk4 expression in mRNA level, and intensified inhibition occurred in LS8 cells when combined with NaF treatment. However, the variation trend of MMP20 was not clear. Dual luciferase reporter assay showed that Foxo1 activation enhanced the transcriptional activity of KLK4 promoter. These findings suggest that the decrease of Foxo1 expression induced by high fluoride was a cause for low KLK4 expression.

Power bleaching enhances resin infiltration masking effect of dental fluorosis. A randomized clinical trial

OBJECTIVES

Patients with moderate dental fluorosis often feel esthetically compromised. Aim of this RCT was to evaluate the objectively and self-assessed masking effect of resin infiltration alone or in combination with in-office bleaching on dental fluorosis in adults.

METHODS

Twenty-seven patients (9 male, 18 female, 24.81 ± 3.7 yrs) with 410 fluorotic teeth (TF 1-4) were randomly assigned to a treatment (BLI) or control group (NBLI). Patients underwent in-office bleaching (25% H₂O₂) in the BLI or a placebo bleaching (ACP gel) in the NBLI group followed by resin infiltration after two weeks. Standardized digital photographs were obtained at baseline; after bleaching; before and after resin infiltration and after 1, 3, and 6 months. Color differences (ΔE) between sound and fluorotic areas were calculated and patient satisfaction was evaluated using a VAS (1-10).

RESULTS

Statistical analysis revealed significant differences in the mean ΔE values 6 months after resin infiltration between the BLI (ΔE = 1.41) and the NBLI group (ΔE = 4.33) (p = 0.024). VAS values increased after resin infiltration (p < 0.05) in both groups. After 3 months patients in the BLI group had higher VAS values than in the NBLI group (p = 0.029).

CONCLUSIONS

Findings of this study suggest that resin infiltration alone can effectively mask mild to moderate dental fluorosis in young adults. In-office bleaching with 25% H₂O₂ before resin infiltration provides significantly better masking effects.

CLINICAL SIGNIFICANCE

Resin infiltration is a safe and efficient treatment option for masking fluorotic opacities. A priori in-office bleaching with 25% H₂O₂ enhances the masking effect. This controlled clinical trial is registered in the German Clinical Trials Register #DRKS00010465.

Dental hypomineralization treatment: A systematic review

INTRODUCTION

Defects in the maturation stage of amelogenesis result in a normal volume of enamel but insufficient mineralization, called hypomineralization. Molar-incisor hypomineralization (MIH), amelogenesis imperfecta and dental fluorosis (DF) are examples of such defects.

OBJECTIVE

To evaluate the effectiveness of the treatments applied to the different forms of dental hypomineralization.

MATERIALS AND METHODS

PubMed, Scopus, Cochrane Library, Web of Science, and Embase were screened. The research was limited to studies published in English, Spanish, and Portuguese, until May 30, 2018. The research question was formulated following the Population, Intervention, Comparison, Outcome strategy. The quality of the methodology of each article was evaluated employing the Cochrane Handbook for Systematic Reviews.

RESULTS

From the initial research, 7895 references were obtained, of which 33 were included in the systematic review. The following treatments were reported: desensitizing and remineralizing products, resin infiltration, restorations, fissure sealants, tooth bleaching, enamel microabrasion and calcium, and vitamins supplements.

CONCLUSIONS

Although the results are suggestive, there is a clear need for a greater uniformity of the methodologies, thus allowing for the development of clinical guidelines. Nevertheless, it was possible to identify several effective treatments for teeth with MIH (arginine pastes or fluoride varnishes) and DF (tooth bleaching and/or enamel microabrasion).

CLINICAL SIGNIFICANCE

Because MIH, amelogenesis imperfecta, and DF are commonly seen in dental daily practice, it is extremely important to analyze the literature regarding its treatment.

Chronic Exposure to Fluoride During Gestation and Lactation Increases Mandibular Bone Volume of Suckling Rats

We aimed to investigate the effect of maternal exposure to NaF on mandibular bone microarchitecture and phosphocalcic plasma parameters of the offspring. For this purpose, 10-, 15-, and 21-day-old pups (n = 6-8 per group) from two groups of mothers, control and NaF 50mg/L treated dams, were used. Plasma calcium (Ca) and phosphorus (P) levels and alkaline phosphatase activity (ALP) were measured. Fluoride concentration (F^-) in bone and in stomach content was measured using potentiometry after isothermal distillation. Morphometric, histological, and histomorphometric analyses of the jaw bones were performed. Plasma Ca and P levels and ALP activity increased in 10-day and decreased in 21-day-old pups from NaF-treated mothers. Fluoride concentration in stomach content samples of 15- and 21-day-old nursing pups from mothers exposed to NaF in their drinking water was higher compared to that observed in control dam offspring. Mandibular F^- content was higher in 21-day-old pups born to F^--exposed dams compared to those observed in age-matched control pups. Mandibular area increased in 21-day-old pups born to treated mothers as compared to controls. Mandibular bone volume BV/TV (%) was higher in offspring from NaF-exposed dams than in controls at all the studied times. The increase in bone volume after exposure to F^- was concomitant with the increase in trabecular thickness and the decrease in trabecular separation. Altogether, our results showed that exposure to NaF during gestation and lactation increased mandibular area and bone volume of pups, with concomitant changes in phosphocalcic parameters associated with the bone modeling process.

Association of Hypertension, Body Mass Index, and Waist Circumference with Fluoride Intake; Water Drinking in Residents of Fluoride Endemic Areas, Iran

Hypertension is becoming a global epidemic for both rural and urban populations; it is a major public health challenge in Iran. Fluoride can be a risk factor for hypertension. Cross-sectional analysis was conducted in two study areas to assess the relation of fluoride with blood pressure prevalence, BMI, waist circumference, and waist-to-hip ratio (WHR) among different age groups in both sexes. The mean value of fluoride concentration in the drinking water from the four study villages varied from 0.68 to 10.30 mg/L. The overall prevalence of HTN and prehypertension in all subjects was 40.7%. The prevalence of isolated systolic hypertension, isolated diastolic hypertension, systolic-diastolic hypertension, and prehypertension in the total sample population was 1.15, 0.28, 9.53, and 29.76%, respectively. The odd ratio of hypertension in residents who drank water with high fluoride levels was higher than that in residents who drank water with lower level of fluoride (OR 2.3, 1.03-5.14). Logistic regression results showed that age (P < 0.001), sex (P = 0.018), BMI (P = 0.015), and the fluoride level in drinking water (P = 0.041) had a significant relationship with increased blood pressure. There were no statistically significant correlations between fluoride and BMI, hip circumference, and waist to hip ratio (WHR). The findings of this study are important for health care personnel and policymakers.

How pH is regulated during amelogenesis in dental fluorosis

Amelogenesis is a complicated process that concerns the interaction between growing hydroxyapatite crystals and extracellular proteins, which requires the tight regulation of pH. In dental fluorosis, the balance of pH regulation is broken, leading to abnormal mineralization. The current review focuses on the electrolyte transport processes associated with pH homeostasis, particularly regarding the changes in ion transporters that occur during amelogenesis, following exposure to excessive fluoride. Furthermore, the possible mechanism of fluorosis is discussed on the basis of acid hypothesis. There are two main methods by which F^- accelerates crystal formation in ameloblasts. Firstly, it induces the release of protons, lowering the pH of the cell microenvironment. The decreased pH stimulates the upregulation of ion transporters, which attenuates further declines in the pH. Secondly, F^- triggers an unknown signaling pathway, causing changes in the transcription of ion transporters and upregulating the expression of bicarbonate transporters. This results in the release of a large amount of bicarbonate from ameloblasts, which may neutralize the pH to form a microenvironment that favors crystal nucleation. The decreased pH stimulates the diffusion of F^- into the cytoplasm of amelobalsts along the concentration gradient formed by the release of protons. The retention of F^- causes a series of pathological changes, including oxidative and endoplasmic reticulum stress. If the buffering capacity of ameloblasts facing F^- toxicity holds, normal mineralization occurs; however, if F^- levels are high enough to overwhelm the buffering capacity of ameloblasts, abnormal mineralization occurs, leading to dental fluorosis.

Influence of Fluoridated Groundwater and 1,100 Ppm Fluoride Dentifrice on Biomarkers of Exposure to Fluoride

Abstract This research aimed to determine the influence of fluoridated groundwater and 1,100 ppm fluoride dentifrice on biomarkers of exposure to fluoride in preschoolers. A cross-sectional study was performed on thirty preschoolers recruited from naturally fluoridated and non-fluoridated areas (n=15). Total Daily Fluoride Intake (TDFI) from diet and dentifrice, and Daily Urinary Fluoride Excretion (DUFE) was measured over 24 h. Nails samples were collected twice during 30 days. Fluoride analyses were performed using a fluoride-ion-specific electrode. Data were evaluated using the Student and paired t-test, Pearson correlation analysis, multiple linear regression analysis (α≤0.05). Fluoridated groundwater and dentifrice were the dominant sources (r2 > 0.83) of TDFI in children from a naturally fluoridated and a non-fluoridated area, respectively. A positive correlation between TDFI and DUFE (r=0.50), and between [F] in fingernails and toenails (r=0.60) were found in children from a naturally fluoridated area. The [F] in nails of finger and toe were not correlated to TDFI. The consumption of fluoridated groundwater influenced the fluoride concentration in urine. In addition, the use of 1,100 ppm fluoride dentifrice did not influence the fluoride concentration in urine and fingernails.

Caries-arresting effects of silver diamine fluoride and sodium fluoride on dentine caries lesions

OBJECTIVES

To investigate the remineralising effect and bacterial growth inhibition of 38% silver diamine fluoride (SDF) solution and 5% sodium fluoride (NaF) varnish on artificial dentine caries lesions.

METHODS

Demineralised dentine blocks were treated with SDF + NaF (Group 1), SDF (Group 2), NaF (Group 3) and water (Group 4) and subjected to a Streptococcus mutans biofilm challenge. Lesion depth, precipitates' characteristics and matrix (collagen)-to-mineral ratio were evaluated by micro-computer tomography (micro-CT), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), respectively. The biofilm kinetics, viability and topography were assessed by counts of colony forming units (CFUs), confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM), respectively. Data were analysed by two-way ANOVA test.

RESULTS

The lesion depths of Groups 1-4 were 170 ± 28 μm, 160 ± 32 μm, 353 ± 38 μm and 449 ± 24 μm, respectively. The addition of NaF to SDF did not show better remineralisation than SDF (p = 0.491). Metallic silver and silver chloride were found in Groups 1 and 2. The amide I-to-hydrogen phosphate ratios of the four groups were 0.14 ± 0.02, 0.14 ± 0.01, 0.29 ± 0.05 and 0.49 ± 0.16, respectively, and the addition of NaF to SDF did not offer better protection against collagen exposure than SDF (p = 0.986). The Log₁₀ CFUs of Groups 1-4 were 5.75 ± 0.56, 4.49 ± 0.57, 6.55 ± 0.39 and 6.40 ± 0.38, respectively. The presence of NaF reduced the antibacterial effect of SDF (p < 0.001). The SEM and CLSM images supported the findings.

CONCLUSION

Application of SDF with or without NaF reduced the demineralisation of dentine caries, but SDF exerted stronger inhibition of biofilm growth than SDF with NaF.

CLINICAL SIGNIFICANCE

NaF varnish affects the antibacterialeffects of SDF, the adjunctive application of SDF solution and NaF varnish is not recommended to arrest dentine caries in clinic.

Potential Co-exposure to Arsenic and Fluoride and Biomonitoring Equivalents for Mexican Children

BACKGROUND

Mexico is included in the list of countries with concurrent arsenic and fluoride contamination in drinking water. Most of the studies have been carried out in the adult population and very few in the child population. Urinary arsenic and urinary fluoride levels have been accepted as good biomarkers of exposure dose. The Biomonitoring Equivalents (BE) values are useful tools for health assessment using human biomonitoring data in relation to the exposure guidance values, but BE information for children is limited.

METHODS

We conducted a systematic review of the reported levels of arsenic and fluoride in drinking water, urinary quantification of speciated arsenic (inorganic arsenic and its methylated metabolites), and urinary fluoride levels in child populations. For BE values, urinary arsenic and fluoride concentrations reported in Mexican child populations were revised discussing the influence of factors such as diet, use of dental products, sex, and metabolism.

RESULTS

Approximately 0.5 and 6 million Mexican children up to 14 years of age drink water with arsenic levels over 10 μg/L and fluoride over 1.5 mg/L, respectively. Moreover, 40% of localities with arsenic levels higher than 10 μg/L also present concurrent fluoride exposure higher than 1.5 mgF/L. BE values based in urinary arsenic of 15 μg/L and urinary fluoride of 1.2 mg/L for the environmentally exposed child population are suggested.

CONCLUSIONS

An actual risk map of Mexican children exposed to high levels of arsenic, fluoride, and both arsenic and fluoride in drinking water was generated. Mexican normativity for maximum contaminant level for arsenic and fluoride in drinking water should be adjusted and enforced to preserve health. BE should be used in child populations to investigate exposure.

Aesthetic Rehabilitation of a Severe Dental Fluorosis Case with Ceramic Veneers: A Step-by-Step Guide

The selection of an appropriate treatment plan for cases of dental fluorosis depends on the severity of the condition. Ceramic veneers are considered the treatment of choice for moderate to severe cases of fluorosis given the optimum aesthetics, wear resistance, biocompatibility, and long-term results of these veneers. This case report describes a step-by-step rehabilitation of fluorosed teeth, using ceramic veneers in a 26-year-old Yemeni male. The patient presented at the restorative dentistry clinics at King Saud University complaining of an unpleasant smile and generalized tooth discoloration.

Dental Fluorosis Treatment Can Improve the Individuals' OHRQoL? Results from a Randomized Clinical Trial

This study aimed to evaluate the effect on oral health-related quality of life (OHRQoL) of two treatment protocols for dental fluorosis in individuals enrolled in a randomized clinical trial. Seventy volunteers, who lived in a fluorosis endemic area in Brazil, and had at least four maxillary anterior teeth showing fluorosis with a Thylstrup and Fejerskov index from 1 to 7, were randomized into two treatment groups (n= 35): GI- enamel microabrasion; or GII- microabrasion associated with at-home bleaching. Microabrasion was performed using 37% phosphoric acid and pumice, and at-home tooth bleaching with 10% carbamide peroxide in a tray. Volunteers completed a questionnaire at baseline and 1-month post treatment to assess changes in OHRQoL, using the Oral Impact on Daily Performance (OIDP). Differences in overall impact scores between and within treatment groups were analyzed with Wilcoxon (within) and Mann-Whitney (between) tests. Changes in performance scores were analyzed using Wilcoxon tests (a< 0.05). One month after treatment, subjects reported improvement in OHRQoL. Both groups showed lower OIDP scores (p< 0.001), but there was no difference between them. Eating, cleaning teeth, smiling and emotional state performance scores were lower after treatment for the whole sample. In conclusion, the treatment with microabrasion improved the OHRQoL in this sample of individuals living in a fluorosis endemic area regardless of the addition of at-home bleaching.

Overview of Calcium Phosphates used in Biomimetic Oral Care

Background:

The use of biomimetic agents is an emerging field in modern oral care. Promising biomimetic substances for such applications are calcium phosphates, because their chemical composition is very similar to that of the mineral phase in human teeth, especially of natural enamel. Examples for their application include the remineralization of early caries lesions and repair of small enamel defects.

Objective:

This review provides an interdisciplinary view on calcium phosphates and their applications in biomimetic oral care. The aim of this work is to give an overview of in vivo and in situ studies comparing several calcium phosphates in preventive dentistry that can be used as a knowledge base for the development of innovative alternative oral care concepts.

Methods:

Books, reviews, and original research papers with a focus on in vivo and in situ studies were included. The databases PubMed^® and SciFinder^® were used for literature search. Calcium phosphates that are frequently utilized in oral care products are covered in this review and were used as search terms alone and together with the following key words: in vivo, in situ, caries, clinical study, and remineralization. From 13,470 studies found, 35 studies complied with the inclusion criteria and were used for this review.

Results:

Published in vivo and in situ studies demonstrate calcium phosphates’ potential in enamel remineralization. However, more studies are needed to further substantiate existing results and to extend and refine the application of calcium phosphates in modern oral care.

Conclusion:

Calcium phosphates represent an innovative biomimetic approach for daily oral care because of their high similarity to natural enamel that will broaden the range of future treatments in preventive dentistry.

Comparison of total ionic strength adjustment buffers III and IV in the measurement of fluoride concentration of teas

Background:

Tea is the second most consumed drink in the UK and a primary source of hydration; it is an important source of dietary fluoride (F) for consumers and also abundant in aluminium (Al). Varying ranges of F concentrations in teas have been reported worldwide which may be, in part, due to differences in analytical techniques used to measure this ion.

Aim:

The effect of using total ionic adjustment buffers (TISAB) III or IV when measuring F concentration of black teas available in the UK was investigated and compared. Based on this evaluation, the effects of three different infusion times, 1 min, 10 min and 1 h, caffeine content and tea form on the F contents of the tea samples were investigated.

Methods:

The F concentrations of 47 tea samples were measured directly using a fluoride ion-selective electrode (F-ISE), TISAB III and IV and infusion times of 1 min, 10 min and 1 h.

Results:

Mean (SD) F concentration of tea samples for all infusion times was statistically significantly higher (p < 0.001) measured by TISAB IV (4.37 (2.16) mg/l) compared with TISAB III (3.54 (1.65) mg/l). A statistically significant positive correlation (p < 0.001) was found between Al concentration (mg/l) and differences in F concentration (mg/l) measured using the two TISABs; the difference in F concentration measured by the two TISABs increased with the magnitude of Al concentration.

Conclusion:

Due to higher concentrations of F and Al in teas and their complexing potential, use of TISAB IV facilitates more accurate measurement of F concentration when using an F-ISE and a direct method.

Micro-dissection of Enamel Organ from Mandibular Incisor of Rats Exposed to Environmental Toxicants

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.

Effect of chronic exercise on fluoride metabolism in fluorosis-susceptible mice exposed to high fluoride

The present study investigated the effect of chronic exercise on fluoride (F) metabolism in fluorosis-susceptible mice exposed to high-F and explored the relationship between F concentrations in bone and plasma. Thirty male mice were randomised into three groups: Group I (No-F, No-Exercise), Group II (50 ppmF, No-Exercise), Group III (50 ppmF, Exercise). Body weight and physical performance of all mice were measured at baseline and end of experiment. F concentrations of plasma and bone were measured at the end of experiment. Mean plasma F concentration was significantly higher (p < 0.001) in Groups II and III compared with Group I. Mean bone F concentration was also significantly higher (p < 0.01) in Groups II and III compared with Group I. There was a significant correlation (p = 0.01, r = 0.54) between F concentration of plasma and bone. Mean body weight of Group I mice was significantly higher than Group II (p < 0.001) and Group III (p = 0.001) mice at the end of the experiment. This study, which provides the first data on the effect of chronic exercise on F metabolism in fluorosis-susceptible mice, suggests no effect of chronic exercise on F in plasma and bone. However, exposure to high-F resulted in lower body weight and exercise capacity in mice.

Foxo1 Attenuates NaF-Induced Apoptosis of LS8 Cells through the JNK and Mitochondrial Pathways

Fluoride-induced ameloblast apoptosis is a key event in dental fluorosis development. Forkhead box o1 (Foxo1) is a transcription factor involved in cell apoptosis. The present study aims to investigate the effect of Foxo1 on ameloblast apoptosis induced by fluoride in vitro and to explore its possible mechanism. Ameloblast-like cells (LS8 cells) were exposed to various concentrations of NaF for up to 48 h. Foxo1 activation was modulated using lentiviral vectors, and cell apoptosis was measured by flow cytometry. The expression levels of Foxo1, c-Jun N-terminal kinase (JNK), and some well-known regulators of the mitochondrial pathway of apoptosis (cytoplasmic cytochrome c, cleaved caspase-9, cleaved caspase-3, Bcl-2, and Bax) were detected by quantitative real-time PCR, western blot, and immunofluorescence assay. The results showed significantly decreased expression and increased phosphorylation of Foxo1 in NaF-treated LS8 cells. Further investigation revealed that forced Foxo1 activation with lentiviral vectors attenuated NaF-induced apoptosis of LS8 cells, markedly decreasing protein levels of cytoplasmic cytochrome c, cleaved caspase-9, and cleaved caspase-3 while increasing the Bcl-2/Bax ratio and JNK expression level. These findings suggest that Foxo1 attenuated NaF-induced apoptosis of LS8 cells via inhibiting the mitochondrial pathway and activating JNK.

Influence of Toothpaste pH on Its Capacity to Prevent Enamel Demineralization

Aim:

This study evaluated in vitro the remineralization capacity of commercial toothpastes with different fluoride (F) concentrations and their effectiveness when they are acidified.

Materials and Methods:

One hundred and twelve caries-free teeth were used to prepare enamel specimens, and the specimens were divided into 16 groups (n = 7). Baseline surface Vickers microhardness was measured for all the specimens and all the tested groups were subjected to the pH-cycling regime involved five demineralization challenges each day for 10 days, and surface Vickers microhardness was then measured. Once daily, specimens were exposed for 30 min after last demineralization challenge of the day to the slurry of each toothpaste containing 1450 ppm F, 1000 ppm F, 450 ppm F, and 0 ppm F. The slurry was in original pH or acidulated on 6.5, 6.0, or 5.5 pH. The difference among tested group was assessed by analysis of variance and Newman–Keuls test (P < 0.05).

Results:

The highest increase in microhardness was detected after treatment with toothpaste containing 1450 ppm fluoride (percentage of increase in microhardness was 6.20%), and the biggest loss was detected after treatment with toothpaste containing no fluoride (percentage of decrease was 6.82%), but there was no significant difference between tested groups.

Conclusions:

The highest increase in microhardness was detected after treatment with toothpaste containing more fluorides (1450 ppm F) regardless of the acidity.

Effect of brief periodic fluoride treatments on the virulence and composition of a cariogenic biofilm

The present study investigated the effect of periodic 1-min fluoride treatments on Streptococcus mutans biofilms and then determined the relationship between anti-biofilm activity, treatment frequency, and fluoride concentration using a linear-fitting procedure. S. mutans biofilms were periodically treated (1-min/treatment) with fluoride during biofilm formation and analyzed using microbiological methods, confocal microscopy, and real-time PCR. The results indicated that reductions in the dry weight and acidogenicity of biofilms due to periodic fluoride treatment occurred in a concentration dependent manner. The reduction in dry weight without affecting bacterial cell viability was observed mainly due to the inhibitory effect of fluoride on gtfB and gtfC gene expression, which suppresses EPS production and avoids reduction of the pH below the critical point on the tooth surface. This study suggests that brief periodic exposure to appropriate fluoride concentrations through mouthwashes and toothpastes may affect the virulence and composition of cariogenic biofilms and subsequently prevent dental caries.

Proteomic Mapping of Dental Enamel Matrix from Inbred Mouse Strains: Unraveling Potential New Players in Enamel

Enamel formation is a complex 2-step process by which proteins are secreted to form an extracellular matrix, followed by massive protein degradation and subsequent mineralization. Excessive systemic exposure to fluoride can disrupt this process and lead to a condition known as dental fluorosis. The genetic background influences the responses of mineralized tissues to fluoride, such as dental fluorosis, observed in A/J and 129P3/J mice. The aim of the present study was to map the protein profile of enamel matrix from A/J and 129P3/J strains. Enamel matrix samples were obtained from A/J and 129P3/J mice and analyzed by 2-dimensional electrophoresis and liquid chromatography coupled with mass spectrometry. A total of 120 proteins were identified, and 7 of them were classified as putative uncharacterized proteins and analyzed in silico for structural and functional characterization. An interesting finding was the possibility of the uncharacterized sequence Q8BIS2 being an enzyme involved in the degradation of matrix proteins. Thus, the results provide a comprehensive view of the structure and function for putative uncharacterized proteins found in the enamel matrix that could help to elucidate the mechanisms involved in enamel biomineralization and genetic susceptibility to dental fluorosis.

No Change in Bicarbonate Transport but Tight-Junction Formation Is Delayed by Fluoride in a Novel Ameloblast Model

We have recently developed a novel in vitro model using HAT-7 rat ameloblast cells to functionally study epithelial ion transport during amelogenesis. Our present aims were to identify key transporters of bicarbonate in HAT-7 cells and also to examine the effects of fluoride exposure on vectorial bicarbonate transport, cell viability, and the development of transepithelial resistance. To obtain monolayers, the HAT-7 cells were cultured on Transwell permeable filters. We monitored transepithelial resistance (TER) as an indicator of tight junction formation and polarization. We evaluated intracellular pH changes by microfluorometry using the fluorescent indicator BCECF. Activities of ion transporters were tested by withdrawal of various ions from the bathing medium, by using transporter specific inhibitors, and by activation of transporters with forskolin and ATP. Cell survival was estimated by alamarBlue assay. Changes in gene expression were monitored by qPCR. We identified the activity of several ion transporters, NBCe1, NHE1, NKCC1, and AE2, which are involved in intracellular pH regulation and vectorial bicarbonate and chloride transport. Bicarbonate secretion by HAT-7 cells was not affected by acute fluoride exposure over a wide range of concentrations. However, tight-junction formation was inhibited by 1 mM fluoride, a concentration which did not substantially reduce cell viability, suggesting an effect of fluoride on paracellular permeability and tight-junction formation. Cell viability was only reduced by prolonged exposure to fluoride concentrations greater than 1 mM. In conclusion, cultured HAT-7 cells are functionally polarized and are able to transport bicarbonate ions from the basolateral to the apical fluid spaces. Exposure to 1 mM fluoride has little effect on bicarbonate secretion or cell viability but delays tight-junction formation, suggesting a novel mechanism that may contribute to dental fluorosis.

Optimization of Adhesive Pastes for Dental Caries Prevention

Dental caries prevention products available on the market contain only remineralizing agents or antibacterial agents. This study aimed to develop adhesive pastes containing calcium phosphate and α-mangostin for dental caries prevention using the optimization technique. Calcium phosphate was used as a remineralizing agent, and extracted α-mangostin was used as an antibacterial agent. The effect of the independent variables, which were fumed silica, Eudragit^® EPO, polyethylene glycol, and ethyl alcohol, on the responses was investigated. The drying time, erosion rate, calcium release rate, and α-mangostin release rate were established as the measured responses. An equation and a model of the relationship were constructed. An optimal formulation was obtained, and its effect on dental caries prevention was investigated using the pH-cycling model. The quadratic equation revealed that the drying time, calcium release rate, and α-mangostin release rate tended to decrease when increasing the fumed silica and decreasing other factors. The erosion rate tended to increase when decreasing Eudragit^® EPO and increasing other factors. The observed responses of the optimal adhesive pastes were not significantly different from the predicted responses. This result demonstrated that optimization is an efficient technique in the formulation development of the adhesive pastes. In addition, the optimal adhesive pastes could enhance acid resistance activity to the tooth enamel.

Biomarkers of chronic fluoride exposure in groundwater in a highly exposed population

This study examined the relation between fluoride (F-) concentrations in fingernail clippings and urine and the prevalence and severity of enamel fluorosis (EF) among Ethiopian Rift Valley populations exposed to high levels of F- in drinking water. The utility of fingernail clippings as a biomarker for F- exposure and EF was also assessed for the first time in a high-F- region. The study recorded the EF status of 386 individuals (10 to 50years old), who consume naturally contaminated groundwater with widely varying F- concentration (0.6-15mg/L). The mean F- concentrations among residents of communities with primary reliance on groundwater were 5.1mg/kg (range: 0.5-34mg/kg) in fingernails and 8.9mg/L (range: 0.44-34mg/L) in urine. We show strong positive correlations between F- in drinking water and 12-hour urinary excretion (r=0.74, p<0.001, n=287), fingernail F- content (r=0.6, p<0.001, n=258), and mean individual measures of EF severity as measured using the Thylstrup and Fejerskov (TF) Index (r=0.42, p<0.001, n=316). The data indicate that both fingernail and urine measures are good biomarkers for F- exposure and EF outcomes, the latter being slightly more sensitive. Cases of moderate/severe EF were significantly more common among younger subjects (10 to 15years old) than older subjects (mostly >25years old) (p<0.001), consistent with their greater exposure to F- during early childhood, which is the only period of life the enamel is at risk of fluorosis. In this younger population, EF may be useful as a biomarker for identifying individuals with other potential health effects that depend on a specific age window of susceptibility. The finding of exceptionally high F- concentrations in water, fingernail clippings and urine in this region should motivate further investigations of other potential health consequences such as bone disease and abnormalities in the function of the neurological and endocrine systems.

Importance of bicarbonate transport in pH control during amelogenesis - need for functional studies

Dental enamel, the hardest mammalian tissue, is produced by ameloblasts. Ameloblasts show many similarities to other transporting epithelia although their secretory product, the enamel matrix, is quite different. Ameloblasts direct the formation of hydroxyapatite crystals, which liberate large quantities of protons that then need to be buffered to allow mineralization to proceed. Buffering requires a tight pH regulation and secretion of bicarbonate by ameloblasts. Many investigations have used immunohistochemical and knockout studies to determine the effects of these genes on enamel formation, but up till recently very little functional data were available for mineral ion transport. To address this, we developed a novel 2D in vitro model using HAT-7 ameloblast cells. HAT-7 cells can be polarized and develop functional tight junctions. Furthermore, they are able to accumulate bicarbonate ions from the basolateral to the apical fluid spaces. We propose that in the future, the HAT-7 2D system along with similar cellular models will be useful to functionally model ion transport processes during amelogenesis. Additionally, we also suggest that similar approaches will allow a better understanding of the regulation of the cycling process in maturation-stage ameloblasts, and the pH sensory mechanisms, which are required to develop sound, healthy enamel.

The MMP-9/TIMP-1 System is Involved in Fluoride-Induced Reproductive Dysfunctions in Female Mice

A total of 84 healthy female mice were kept with various concentrations of sodium fluoride (F) (0, 50, 100, 150 mg F^-/L in drinking water for 90 days) and were then mated with healthy male mice for 1 week to study the effect of excessive fluoride on female reproductive function, particularly in embryo implantation. The rate of pregnancy, litter size, and the birth weight of female mice were evaluated. Ultrastructural changes of uteri tissues were observed by transmission electron microscopy (TEM). The mRNA expression levels of MMP-9 and TIMP-1 were determined by quantitative real-time PCR. The protein expression levels of MMP-9 and TIMP-1 were analyzed by western blotting. Results showed a significant decrease of litter size in mice exposed to fluoride. TEM images of uteri tissue of mice that underwent a 150 mg/L F^- treatment for 90 days showed a vague nucleus, reduced microvilli, increased lysosomes, a dilated endoplasmic reticulum, and a vacuolization mitochondrion when compared with the control group. Following the damage of the structure, the expression levels of MMP-9 and TIMP-1 in uteri tissues were significantly unregulated in the F 150 group. These results show that MMP-9/TIMP-1 system disturbance and changes of histological structure in uteri tissue are involved in fluoride-induced reproductive dysfunctions.

Enzymatic Activity of Glutathione S-Transferase and Dental Fluorosis Among Children Receiving Two Different Levels of Naturally Fluoridated Water

This study was conducted to measure the activity of the enzyme glutathione S-transferase (GST) in saliva and to compare the activity of this enzyme in children with and without dental fluorosis in communities with different concentrations of naturally fluoridated water. A total of 141 schoolchildren participated in this cross-sectional study. Children were selected from two communities: one with a low (0.4 ppm) and the other with a high (1.8 ppm) water fluoride concentration. Dental fluorosis was evaluated by applying the Thylstrup and Fejerskov Index (TFI) criteria. Stimulated saliva was obtained, and fluoride concentration and GST activity were measured. The GST activity was compared among children with different levels of dental fluorosis using multinomial logistic regression models and odds ratios (OR). The mean age of the children was 10.6 (±1.03) years. Approximately half of the children showed dental fluorosis (52.5 %). The average GST activity was 0.5678 (±0.1959) nmol/min/μg. A higher concentration of fluoride in the saliva was detected in children with a higher GST activity (p = 0.039). A multinomial logistic regression model used to evaluate the GST activity and the dental fluorosis score identified a strong association between TFI = 2-3 (OR = 15.44, p = 0.007) and TFI ≥ 4 (OR = 55.40, p = 0.026) and the GST activity level, compared with children showing TFI = 0-1, adjusted for age and sex. Schoolchildren with higher levels of dental fluorosis and a higher fluoride concentration in the saliva showed greater GST activity. The increased GST activity most likely was the result of the body's need to inactivate free radicals produced by exposure to fluoride.

Impact of Dental Fluorosis, Socioeconomic Status and Self-Perception in Adolescents Exposed to a High Level of Fluoride in Water

Objective: To identify adolescents' self-perception of dental fluorosis from two areas with different socioeconomic levels. Methods: A cross-sectional, descriptive study was conducted with 15-year-old youths by applying a questionnaire designed and validated to assess self-perceptions of dental fluorosis in two areas with different socioeconomic statuses (SESs). Fluorosis was clinically evaluated by applying the Thylstrup and Fejerkov (TF) index on the upper front teeth. Results: A total of 308 adolescents were included in the study. The medium-SES population, which was exposed to 2.5 ppm of fluoride in water, and the low-SES population, which was exposed to 5.1 ppm, presented the following levels of dental fluorosis: TF 2-3 (50%), TF 4-5 (45.6%) and TF 6-7 (4.4%) for medium SES and TF 2-3 (12.3%), TF 4-5 (67.1%) and TF 67 (20.6%) for low SES. A significant association was found between self-perception and dental fluorosis in those with medium and low SESs (p < 0.05). The multiple regression model found differences between TF levels and self-perception, with a 6-7 TF level for concerns about color (OR = 1.6), smile (OR = 1.2) and appearance (OR = 3.36). Conclusions: Self-perceptions of dental fluorosis affect adolescents such that adolescents with a medium SES have more negative perceptions than those with a low SES. Such perceptions increase as the TF index increases.

High-Dose Fluoride Induces Apoptosis and Inhibits Ameloblastin Secretion in Primary Rat Ameloblast

The objectives of this study are to establish the in vitro culture system for rat primary ameloblast and to investigate the effects of fluoride on cell viability, apoptosis, and ameloblastin (AMBN) secretion of primary rat ameloblast in vitro. Ameloblast was isolated from the tooth germ of the maxillomandibular molar and cultured in vitro. Cells were treated with NaF at 0.4, 0.8, 1.6, 3.2, and 6.4 mM for 24, 48, and 72 h, respectively. Cell viability was measured by MTT assay and apoptosis was tested by flow cytometry. The activation of Fas ligand (FasL)/Fas pathway was detected using immunoblotting for FasL, Fas, cleaved caspase-8, cleaved caspase-3, and cleaved PARP. Secretion of AMBN in culture medium was measured using ELISA. Primary rat ameloblast was successfully isolated and cultured. The effects of low-dose fluoride on cell viability were bi-phasic, while high-dose fluoride resulted in decreased cell viability uniformly. Fluoride induced ameloblast apoptosis via activation of FasL/Fas signaling pathway and diminished secretion of AMBN by ameloblast. Fluoride could decrease ameloblast viability, induce ameloblast apoptosis via activating FasL/Fas signaling pathway, and reduce AMBN secretion.

Sodium fluoride induces hypercalcemia resulting from the upregulation of both osteoblastic and osteoclastic activities in goldfish, Carassius auratus

The influence of sodium fluoride (NaF) on calcium metabolism was examined in goldfish (fresh water teleost). At 2days after administration of NaF (500ng/g body weight; 5μg/g body weight) (around 10(-5) to 10(-4)M in goldfish), we indicated that plasma calcium levels upregulated in both doses of NaF-treated goldfish. To examine the mechanism of hypercalcemia by NaF treatments, therefore, direct effects of NaF on osteoblasts and osteoclasts in goldfish were investigated by an original assay system using teleost scale which has osteoblasts, osteoclasts and bone matrix. Alkaline phosphatase activity in the scales increased with the treatment of NaF (10(-6) and 10(-5)M) during 6h of incubation. Also, tartrate-resistant acid phosphatase activity increased after exposure to NaF (10(-5)M) at the 6h of incubation. To investigate the osteoclastic activation, the mRNA expression of osteoclastogenesis related factors were examined. The receptor activator of the nuclear factor-κB ligand (RANKL) which is known as a factor for osteoclastogenesis, increased in the NaF-treated scales after 6h of incubation. The ratio of RANKL/osteoprotegerin (osteoclastogenesis inhibitory factor) significantly increased after 6h of incubation. Resulting from the increase of RANKL mRNA level, the expression of transcription-regulating factors was significantly increased. Furthermore, the expression of functional genes, cathepsin K and matrix metalloproteinase-9 mRNA, was significantly increased. In our knowledge, this is the first report concerning the effects of NaF on osteoblasts and osteoclasts in teleosts. We concluded that NaF influences calcium metabolism via osteoclastic activation in goldfish.

Urinary and plasma fluoride levels in pregnant women from Mexico City

BACKGROUND

There is need to assess the developmental neurotoxicity of fluoride. Our knowledge of prenatal fluoride exposure is challenged as few population-based studies have been conducted and these generally date back several decades, provide incomplete data on sociodemographic variables, and have methodological limitations.

OBJECTIVE

To measure urinary and plasma fluoride levels across three time points in pregnant mothers who were enrolled in the Early Life Exposures in Mexico to Environmental Toxicants (ELEMENT) birth cohort study.

METHODS

Fluoride levels were characterized in archived urine and plasma from 872 pregnant mothers sampled from the ELEMENT cohort. Various statistical methods were used to analyze the fluoride data with particular consideration for changes across three stages of pregnancy and against sociodemographic variables.

RESULTS

All samples had detectable levels of fluoride. The mean urinary and plasma fluoride levels were 0.91 and 0.0221mg/L respectively, and these were not statistically different across three stages of pregnancy. Fluoride levels correlated across the stages of pregnancy studied, with stronger correlations between neighboring stages. Urinary fluoride changed as pregnancy progressed with levels increasing until ~23 weeks and then decreasing until the end of pregnancy. For plasma fluoride, there was a decreasing trend but this was not of statistical significance. Creatinine-adjusted urinary fluoride levels did not associate consistently with any of the sociodemographic variables studied.

CONCLUSIONS

This study provides the most extensive characterization to date of fluoride exposure throughout pregnancy. These results provide the foundation to explore exposure-related health outcomes in the ELEMENT cohort and other studies.

LS8 cell apoptosis induced by NaF through p-ERK and p-JNK - a mechanism study of dental fluorosis

OBJECTIVE

To investigate the possible biological mechanism of dental fluorosis at a molecular level.

MATERIAL AND METHODS

Cultured LS8 were incubated with serum-free medium containing selected concentrations of NaF (0 ∼ 2 mM) for either 24 or 48 h. Subcellular microanatomy was characterized using TEM; meanwhile, selected biomolecules were analysed using various biochemistry techniques. Transient transfection was used to modulate a molecular pathway for apoptosis.

RESULTS

Apoptosis of LS8 was induced by NaF treatment that showed both time and concentration dependency. The activity of caspase-3, -8, -9 was found to be increased with NaF in a dose-dependent manner. Western blot revealed that the protein expression of p-ERK and p-JNK were decreased, while the expression of p-P38 was increased. Inhibition of the p-ERK and p-JNK pathways resulted in a similar decrease for caspase-3.

CONCLUSION

During NaF-induced apoptosis of LS8, p-ERK and p-JNK were closely associated with induction of apoptosis, which might be a mechanism of dental fluorosis.

Refractive Errors in Northern China Between the Residents with Drinking Water Containing Excessive Fluorine and Normal Drinking Water

The purpose of this study was to evaluate the refractive errors and the demographic associations between drinking water with excessive fluoride and normal drinking water among residents in Northern China. Of the 1843 residents, 1415 (aged ≥40 years) were divided into drinking-water-excessive fluoride (DWEF) group (>1.20 mg/L) and control group (≤1.20 mg/L) on the basis of the fluoride concentrations in drinking water. Of the 221 subjects in the DWEF group, with 1.47 ± 0.25 mg/L (fluoride concentrations in drinking water), the prevalence rates of myopia, hyperopia, and astigmatism were 38.5 % (95 % confidence interval [CI] = 32.1-45.3), 19.9 % (95 % CI = 15-26), and 41.6 % (95 % CI = 35.1-48.4), respectively. Of the 1194 subjects in the control group with 0.20 ± 0.18 mg/L, the prevalence of myopia, hyperopia, and astigmatism were 31.5 % (95 % CI = 28.9-34.2), 27.6 % (95 % CI = 25.1-30.3), and 45.6 % (95 % CI = 42.8-48.5), respectively. A statistically significant difference was not observed in the association of spherical equivalent and fluoride concentrations in drinking water (P = 0.84 > 0.05). This report provides the data of the refractive state of the residents consuming drinking water with excess amounts of fluoride in northern China. The refractive errors did not result from ingestion of mild excess amounts of fluoride in the drinking water.