Neurotoxicity of dental amalgam is mediated by zinc

Mercury abatement in the environment: Insights from industrial emissions and fates in the environment

Mercury's neurotoxic effects have prompted the development of advanced control and remediation methods to meet stringent measures for industries with high-mercury feedstocks. Industries with significant Hg emissions, including artisanal and small-scale gold mining (ASGM)-789.2 Mg year-1, coal combustion-564.1 Mg year-1, waste combustion-316.1 Mg year-1, cement production-224.5 Mg year-1, and non-ferrous metals smelting-204.1 Mg year-1, use oxidants and adsorbents capture Hg from waste streams. Oxidizing agents such as O3, Cl2, HCl, CaBr2, CaCl2, and NH4Cl oxidize Hg0 to Hg2+ for easier adsorption. To functionalize adsorbents, carbonaceous ones use S, SO2, and Na2S, metal-based adsorbents use dimercaprol, and polymer-based adsorbents are grafted with acrylonitrile and hydroxylamine hydrochloride. Adsorption capacities span 0.2-85.6 mg g-1 for carbonaceous, 0.5-14.8 mg g-1 for metal-based, and 168.1-1216 mg g-1 for polymer-based adsorbents. Assessing Hg contamination in soils and sediments uses bioindicators and stable isotopes. Remediation approaches include heat treatment, chemical stabilization and immobilization, and phytoremediation techniques when contamination exceeds thresholds. Achieving a substantially Hg-free ecosystem remains a formidable challenge, chiefly due to the ASGM industry, policy gaps, and Hg persistence. Nevertheless, improvements in adsorbent technologies hold potential.

Cytotoxic evaluation of two orthodontic silver solder materials on human periodontal ligament fibroblast cells and the effects of antioxidant and antiapoptotic reagents

OBJECTIVES

To evaluate the cytotoxicity effects of two different solder materials used for orthodontic appliances on human periodontal ligament fibroblast (HPLF) cells, and to determine whether the mechanism of toxicity may involve oxidative stress and apoptosis.

MATERIALS AND METHODS

The silver solder samples (Leone and Summit) were soldered to orthodontic stainless steel bands and exposed to HPLF cells via cell culture inserts for 48 hours. Cytotoxicity effect of the soldered materials on HPLF cells was measured via tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) colorimetric assay (n = 10/sample) and morphological observation. In addition, the mechanism of cytotoxicity of the most toxic silver solder was investigated using both a caspase inhibitor Z-VAL-Ala-Asp-flu-oromethylketone (ZVAD-fmk) and the free radical scavenger Trolox (n = 8/sample). Statistical analysis was performed using one-way analysis of variance with a Bonferroni test. P < .05 was considered statistically significant.

RESULTS

Compared to the control (no treatment, cells only), both silver solders were cytotoxic (P < .001). The bands alone were significantly cytotoxic compared to the control. There was a significant difference in cytotoxicity between the stainless steel bands alone and the Summit silver solder (P < .001), but not the Leone silver solder. The Summit silver solder was more cytotoxic than the Leone silver solder (P < .05). MTT results were supported by the microscopic morphological changes of the HPLF cells. Neither ZVAD-fmk nor Trolox provided significant protection.

CONCLUSIONS

The two silver solder materials demonstrated different levels of cytotoxicity, and neither oxidative stress nor apoptosis is involved in the mechanism of cytotoxicity.

The protective role of selenium against dental amalgam-induced intracellular oxidative toxicity through the TRPV1 channel in DBTRG glioblastoma cells

OBJECTIVE

The exposure to mercury (Hg) from dental amalgams is a suspected causative factor in neurological diseases. This study investigated the toxic effects of two different amalgam compositions related to Hg and the protective effects of selenium against the toxic effects of Hg through the TRPV1 channel in the human DBTRG glioblastoma cell line.

METHODOLOGY

Six groups of the cells were organized. Analyses of cell viability, apoptosis, caspase 3 and caspase 9 activities, mitochondrial membrane depolarization, reactive oxygen species (ROS) production, and Western Blotting for protein expression levels were performed.

RESULTS

Cell viability values were lower in amalgam with high copper (HCu) and low copper (LCu) groups independently of time but were increased by selenium and capsazepine (p<0.001 and p<0.05). Conversely, apoptosis rates, caspase 3 and caspase 9 expression, ROS formation, mitochondrial membrane depolarization, and protein expression levels were higher in the HCu and LCu groups but were decreased by selenium (p<0.001 and p<0.05).

CONCLUSIONS

Selenium combined with an amalgam of either HCu or LCu decreases the toxic effects created by Hg in human DBTRG glioblastoma cells.

A review on potential toxicity of dental material and screening their biocompatibility

OBJECTIVES

A wide range of compounds are utilized in dentistry such as dental composites, resins, and implants. The successful clinical use of dental materials relies on theirm physiochemical properties as well as biological and toxicological reliability. Different local and systemic toxicities of dental materials have been reported. Placement of these materials in oral cavity for a long time period might yield unwanted reactions. An extensive variety of materials is used in dentistry including filling materials, restorative materials, intracanal medicines, prosthetic materials, different types of implants, liners, and irrigants. The increasing rate in development of the novel materials with applications in the dental field has led to an increased consciousness of the biological risks and tempting restrictions of these materials. The biocompatibility of a biomaterial used for the replacement or filling of biological tissue such as teeth always had a high concern within the health care disciplines for patients.

MATERIALS AND METHODS

Any material used in humans should be tested before clinical application. There are many tests evaluating biocompatibility of these materials at the point of in vitro, in vivo, and clinical investigations.

RESULTS

The current review discusses the potential toxicity of dental material and screening of their biocompatibility.

CLINICAL RELEVANCE

It is essential to use healthy and safe materials medical approaches. In dentistry, application of different materials in long-term oral usage demands low or nontoxic agents gains importance for both patients and the staff. Furthermore, screening tests should evaluate any potential toxicity before clinical application.

In vitro load-induced dentin collagen-stabilization against MMPs degradation

INTRODUCTION

Teeth are continuously subjected to stresses during mastication, swallowing and parafunctional habits, producing a significant reduction of the bonding efficacy in adhesive restorations. The purpose of this study was to evaluate the metalloproteinases (MMPs)-mediated dentin collagen degradation of hybrid layers created by using different demineralization processes, previous resin infiltration, and in vitro mechanical loading.

METHODS

Human dentin beams (0.75×0.75×5.0mm) were subjected to different treatments: (1) untreated dentin; (2) demineralization by 37% phosphoric acid (PA) or by 0.5% M ethylenediaminetetraacetic acid (EDTA); (3) demineralization by PA, followed by application of Adper(™) Single Bond (SB); (4) demineralization by EDTA, followed by application of SB. In half of the specimens, mechanical loadings (100,000 cycles, 2Hz, 49N) were applied to dentin beams. Specimens were stored in artificial saliva. C-terminal telopeptide (ICTP), determinations (which indicates the amount of collagen degradation) (radioimmunoassay) were performed after 24h, 1 week and 4 weeks.

RESULTS

Load cycling decreased collagen degradation when dentin was untreated or PA-demineralized and EDTA-treated. ICTP values increased when both PA-demineralized and EDTA-treated and infiltrated with SB dentin beams were loaded, except in samples that were subjected to EDTA treatment and SB infiltration after 4w of storage, which showed similar values of collagenolytic activity than the non loaded specimens. Load cycling preserved the initial (24h) ICTP determination at any time point, in all groups of the study, except in PA-demineralized and SB infiltrated dentin which showed an increased of collagen degradation values, over time. This same trend was observed in all groups without loading.

INTERPRETATION

Mechanical loading enhances collagen's resistance to enzymatic degradation in natural and demineralized dentin. Mild acids (EDTA) lead to a lower volume of demineralized/unprotected collagen to be cleaved by MMPs. Load cycling produced an increase of collagen degradation when PA-demineralized dentin and EDTA-treated dentin were infiltrated with resin, but EDTA-treated dentin showed a constant collagenolytic degradation, over time.

Cytotoxicity of separation orthodontic elastics

OBJECTIVE: To test the hypothesis that there is no difference in cytotoxicity between separating elastics of different manufacturers. METHODS: The present article compared latex elastics (4.0 mm, 4.4 mm and 4.8 mm) of four different manufacturers. The sample was allocated to seven groups of 9 elastics: Group A (American Orthodontics, green color, modules), Groups M1 and M2 (Morelli, blue color, modules and free in pack respectively), Groups M3 and M4 (Morelli, green color, modules and free in pack respectively), Group U (Uniden, blue color, free in pack) and Group T (Tecnident, blue color, free in pack) regarding their possible cytotoxic effects on oral tissues. Cytotoxicity assays were performed using cell culture medium containing epithelioid-type cells (Hep-2 line) derived from human laryngeal carcinoma and submitted to the methods for evaluating the cytotoxicity by the "dye-uptake" test, at time intervals 24, 48, 72 and 168 h. Data were compared by analysis of variance (ANOVA) and Tukey's test (p < 0.05). RESULTS: Results showed statistically significant difference (p < 0.05) between group U and all the other Groups (A, M1, M2, M3, M 4 and T) at 24 and 48 hours. CONCLUSIONS: Uniden elastics evoked more cell lysis at 24 and 48 h, although, all brands showed biocompatibility from 72 h onwards.

Evaluation of the cytotoxicity of latex and non-latex orthodontic separating elastics

OBJECTIVE

To test the hypothesis that a difference in cytotoxicity exists between latex and non-latex orthodontic separating elastics.

MATERIAL AND METHODS

Five intra-oral separating elastics from different manufactures (four latex and one non-latex) were divided into five groups of 15 elastics each: Group MA (non-latex elastics, Masel), Group MO (natural latex, Morelli), Group DE (natural latex, Dentaurum), Group TP (natural latex, TP Orthodontics) and Group UN (natural latex, Unitek). The cytotoxicity assay was performed using cell cultures (epithelial HEp-2 cells originating from human laryngeal carcinoma) that were submitted to the cell viability test with neutral red (dye-uptake) at 24, 48, 72 and 168 h. Analysis of variance (anova) with multiple comparisons and Tukey's test were employed (p < 0.05).

RESULTS

The results showed no statistically significant differences between groups MA, DE, TP and UN in relation to Group CC (cell control) for experimental times of 24, 48 and 168 h (p > 0.05). Morelli, Dentaurum, TP Orthodontics and Unitek elastics induced a great amount of cell lyses at 72 h.

CONCLUSION

One can demonstrate that the Masel elastic induced less cell lysis compared with other elastics, but all trademarks were found to be clinically biocompatible.

CLINICAL RELEVANCE

Separating orthodontic elastics are used in the interdental subgingival region with the aim to separate the teeth for placement of orthodontic bands. However, latex has been known to cause allergy. As these materials are widely used in clinical orthodontics, care regarding the cytotoxicity of orthodontic elastics should be taken. Thus, clinically proven biocompatible materials should be acquired whenever possible.

Cytotoxicity of intermaxillary orthodontic elastics of different colors: an in vitro study

Objectives:

Natural latex does not fall into the category of materials known to be entirely inoffensive. The purpose of this in vitro study was to test the hypothesis that there is no difference in the cytotoxicity between elastics of different colors and those from different manufacturers.

Material and Methods:

Different latex intraoral elastics of different colors (5/16 = 7.9 mm, mean load) were compared. The sample was divided into 7 groups of 24 elastics each: Group T (TP Orthodontics, natural latex elastics, control); Groups U1, U2, U3, U4, U5 and U6 (Uniden, natural latex elastics and colored elastics, namely, green, pink, yellow, red and purple, respectively). Cytotoxicity assays were performed by using cell culture medium containing epithelioid-type cells (Hep-2 line) derived from human laryngeal carcinoma. The cytotoxicity was evaluated by using the "dye-uptake" test, which was employed at two different moments (0 and 24 h). Data were compared by analysis of variance (ANOVA) and Tukey's test (p<0.05).

Results:

There was statistically significant difference (p<0.05) between Group T and all other groups (U1, U2, U3, U4, U5 and U6) at 0 and 24 h. No statistically significant difference (p<0.05) was found between Groups U1 and U5, U1 and U6, U2 and U3, U2 and U4, U2 and U5, U2 and U6, U3 and U4, U3 and U5, U3 and U6, U4 and U5, U4 and U6, and U5 and U6 at 0 and 24 h.

Conclusions:

The TP Orthodontics elastics promoted less cell lysis compared to the Uniden elastics regardless of their color.

A 7-year prospective quasi-experimental study of the effects of removing dental amalgam in 76 self-referred patients compared with 146 controls

BACKGROUND

Dental amalgam has been suggested to cause long-term physical and mental problems. Claims that removal of the amalgam may lead to dramatic improvements in health have not been tested empirically in controlled studies with a long follow-up period.

PURPOSE

To investigate the long-term effects of removal of dental amalgam on physical and mental symptoms in self-referred patients who complained of multiple somatic and mental symptoms attributed to dental amalgam fillings.

METHODS

In a quasi experimental study, changes in the mental and physical symptoms in 76 patients who had their dental amalgam removed 7 years ago were compared with changes in symptoms among patients with known chronic medical disorders seen in alternative (n=51) and ordinary (n=51) medical family practices and noncomplaining patients with similar amounts of dental amalgam fillings (n=44) seen in an ordinary dental practice. The assessments included written self-reports, a 131-item somatic symptom checklist, Eysenck Personality Questionnaire (EPQ), the General Health Questionnaire (GHQ) and Toronto Alexithymia Scale (TAS).

RESULTS

Subjects who removed their dental amalgam reported reduced physical and mental symptom load compared to status prior to removal, but only to a level comparable with that reported by the other groups with chronic medical disorders. The dental control group consistently reported lower symptom load during the whole period. In a hierarchical three-step regression model, pretreatment physical symptom load (P<.01), age (P<.10) and removal of dental amalgam (ns) predicted 26% of the variance in posttreatment physical symptom load.

CONCLUSION

In a self-referred group of subjects with health complaints attributed to dental amalgam who remove their dental amalgam, the symptom load at follow-up corresponds to the level seen in chronic medical disorders despite the strong implicit placebo effect of the present quasi-experimental design. The finding does not support the hypothesis that removal of dental amalgam will reduce health complaints to normal levels and seriously questions the hypothesis that dental amalgam is an important cause of distress and health complaints.

In vitro neuronal cytotoxicity of latex and nonlatex orthodontic elastics

Although the toxicity of many dental materials has been thoroughly investigated, the toxicity of orthodontic elastic materials has not been extensively tested. We evaluated the neurotoxicity of 3 latex and 3 nonlatex orthodontic elastics in murine cerebral cortical cell cultures. Standard-sized pieces of each material from 3 manufacturers (American, Masel, and GAC) were placed on culture well inserts, allowing the material to be exposed to the culture bathing media without causing physical disruption of the cells. Cell death was quantified by assaying the release of the cytosolic enzyme lactate dehydrogenase. Exposure of cortical cultures to the nonlatex elastics did not cause significant neuronal death, but exposure to each of the latex elastics resulted in significant neuronal death. The neuronal death induced by each of the latex elastics was blocked by adding the metal chelator, EDTA (calcium disodium ethylenediaminetetraacetate). Because many latexes use zinc-containing compounds in the prevulcanization process, and the death induced had characteristics similar to zinc-induced neuronal death, it seems likely that the toxicity of latex elastics was mediated by zinc release. Because ingestion of zinc is not a health risk, the results suggest that, in spite of the finding that latex elastics have higher in vitro cytotoxicity than nonlatex elastics, the use of latex elastics in orthodontics is acceptable.