Dental Fluorosis and Periodontium: an Original Research Report of In Vitro and In Vivo Institutional Studies

Effects of chronic fluorosis on the expression of VEGF/PI3K/AKT/eNOS in the gingival tissue of rats with orthodontic tooth movement

It has been reported that the force of orthodontic correction triggers periodontal tissue remodeling by affecting angiogenesis. However, the manifestation of the vascular response to orthodontic tooth movement in the setting of chronic fluorosis is unclear. The aim of the present study was to preliminarily explore the effect of orthodontic treatment on the angiogenesis of gingival tissue in rats with chronic fluorosis by monitoring changes in the expression of vascular endothelial growth factor (VEGF), phosphatidylinositol-3 kinase (PI3K), AKT (or protein kinase B) and endothelial nitric oxide synthase (eNOS) in the gingival tissue. A total of 60 rats were randomly divided equally into the orthodontic group (O group; n=30) and fluorosis orthodontic group (FO group; n=30). Each of these groups was divided into 0-, 3-, 7-, 14- and 21-day groups (n=6/group). Fluorosis and orthodontic tooth movement models were established, and rats in each group were sacrificed for tissue sampling at the corresponding time points. Tissue morphology was observed via hematoxylin and eosin (H&E) staining. The protein and mRNA expression levels of VEGF, PI3K, AKT and eNOS in gingival tissue were detected by western blotting and reverse transcription-quantitative polymerase chain reaction, respectively. The H&E staining images showed that the FO group had smaller blood vessels and reduced vascular proliferation compared with the O group. Furthermore, the mRNA and protein expression levels of VEGF, PI3K, AKT and eNOS were reduced in the gingiva of rats in the FO group compared with the O group, and certain reductions were significant during the delayed tooth movement period. In addition, with the extension of the application of orthodontic stress, the mRNA and protein expression levels of VEGF, PI3K, AKT and eNOS in the gingiva of the O and FO groups showed a trend of increasing at first and subsequently decreasing, which corresponds with the tooth movement cycle. In conclusion, chronic fluorosis may inhibit the angiogenesis and the expression of the VEGF/PI3K/AKT/eNOS pathway in gingival tissue of orthodontic tooth movement.

Prevalence of malocclusions under conditions of prolonged introduction of systemic fluorides in variable concentrations: Literature review

The pathogenesis of malocclusions, which are common among the population of  all  countries, is  well represented in the professional literature. The occurrence of  malocclusions is associated with genetic and various environmental factors. Among the latter, fluorides which affect the prevalence of some dental diseases are of particular interest. However, there are few publications reflecting the frequency of malocclusion among the population in the regions with different levels of fluoride in drinking water. This problem seems to be significant in the context of the increasing impact of fluorine compounds on human health, including dental health.

The aim of the study. To analyze the literature on the frequency of malocclusion among the population living in conditions of variable fluoride content in drinking water. A manual search of domestic and foreign literature was performed in the search databases PubMed, Medline and Google Scholar. From the initial list of publications, eighteen articles that met the inclusion criteria for the study were selected for analysis. We revealed significant variability of the research results. Some authors note a higher prevalence of malocclusions among the population under conditions of increased fluoride intake, others note a lower one, and still others did not reveal any differences between the values obtained in both samples. Most of the assessed publications did not methodologically meet modern international standards, and therefore were of little evidence.

The literature data do not provide grounds for an unambiguous assessment of fluorine compounds as an environmental factor that indirectly affects the process of occlusion formation in humans and animals.

The review did not allow to make a definitive conclusion on the possible impact of  systemic fluorides on the prevalence and pattern of malocclusion in humans and animals. It requires the implementation of studies that comply with the principles of evidence-based medicine. 

In Silico Analysis of Ferroptosis-Related Genes and Its Implication in Drug Prediction against Fluorosis

Fluorosis is a serious global public health problem. Interestingly, so far, there is no specific drug treatment for the treatment of fluorosis. In this paper, the potential mechanisms of 35 ferroptosis-related genes in U87 glial cells exposed to fluoride were explored by bioinformatics methods. Significantly, these genes are involved in oxidative stress, ferroptosis, and decanoate CoA ligase activity. Ten pivotal genes were found by the Maximal Clique Centrality (MCC) algorithm. Furthermore, according to the Connectivity Map (CMap) and the Comparative Toxicogenomics Database (CTD), 10 possible drugs for fluorosis were predicted and screened, and a drug target ferroptosis-related gene network was constructed. Molecular docking was used to study the interaction between small molecule compounds and target proteins. Molecular dynamics (MD) simulation results show that the structure of the Celestrol-HMOX1 composite is stable and the docking effect is the best. In general, Celastrol and LDN-193189 may target ferroptosis-related genes to alleviate the symptoms of fluorosis, which may be effective candidate drugs for the treatment of fluorosis.

Integrated 16S rDNA sequencing and metabolomics to explore the intestinal changes in children and rats with dental fluorosis

Dental fluorosis (DF) is a widely prevalent disease caused by excessive fluoride with limited awareness of its underlying pathogenesis. Here, a pilot population study was conducted to explore the pathogenesis of DF from the perspective of intestinal microbiome changes, and verified it in animal experiments combining intestinal microbiome and metabolomics. A total of 23 children were recruited in 2017 in China and divided into DF (n = 9) and control (n = 14) groups (DFG and CG, respectively). The SD rat model was established by drinking water containing sodium fluoride (NaF). Gut microbiome profiles of children and rats were analyzed by16S rDNA V3-V4 sequencing, and the intestinal metabolomics analysis of rats was performed by LC-MS methods. The 16 S rDNA sequencing revealed that the gut microbiome composition was significantly perturbed in children in DFG compared to that in CG. Acidobacteria and Thermi were specifically observed in DFG and CG, respectively. Besides, 15 fecal microbiotas were significantly altered at the genus level in DFG. Furthermore, only the expression of annotated genes for pentose and glucuronate interconversion pathway was significant lower in DFG than that in CG (P = 0.04). Notably, in NaF-treated rats, we also observed the changes of some key components of pentose and glucuronate interconversion pathway at the level of microorganisms and metabolites. Our findings suggested that the occurrence of DF is closely related to the alteration of intestinal microorganisms and metabolites annotated in the pentose and glucuronate interconversion pathway.

Redox and biometal status in Wistar rats after subacute exposure to fluoride and selenium counter-effects

This study aimed to investigate the effect of 150 mg/L sodium fluoride (NaF) on redox status parameters and essential metals [copper (Cu), iron (Fe), and zinc (Zn)] in the blood, liver, kidney, brain, and spleen of Wistar rats and to determine the protective potential of selenium (Se) against fluoride (F^-) toxicity. Male Wistar rats were randomly distributed in groups of five (n=5) receiving tap water (control) or water with NaF 150 mg/L, NaF 150 mg/L + Se 1.5 mg/L, and Se 1.5 mg/L solutions ad libitum for 28 days. Fluorides caused an imbalance in the redox and biometal (Cu, Fe, and Zn) status, leading to high superoxide anion (O^{2 .-}) and malondialdehyde (MDA) levels in the blood and brain and a drop in superoxide dismutase (SOD1) activity in the liver and its increase in the brain and kidneys. Se given with NaF improved MDA, SOD1, and O^{2 .-} in the blood, brain, and kidneys, while alone it decreased SH group levels in the liver and kidney. Biometals both reduced and increased F- toxicity. Further research is needed before Se should be considered as a promising strategy for mitigating F^- toxicity.