Characterization and in vitro estrogenicity of orthodontic adhesive particulates produced by simulated debonding

Impact of bisphenol A and analogues eluted from resin-based dental materials on cellular and molecular processes: An insight on underlying toxicity mechanisms

Dental resin systems, used for artificial replacement of teeth and their surrounding structures, have gained popularity due to the Food and Drug Administration's (FDA) recommendation to reduce dental amalgam use in high-risk populations and medical circumstances. Bisphenol A (BPA), an endocrine-disrupting chemical, is an essential monomer within dental resin in the form of various analogues and derivatives. Leaching of monomers from resins results in toxicity, affecting hormone metabolism and causing long-term health risks. Understanding cellular-level toxicity profiles of bisphenol derivatives is crucial for conducting toxicity studies in in vivo models. This review provides insights into the unique expression patterns of BPA and its analogues among different cell types and their underlying toxicity mechanisms. Lack of a consistent cell line for toxic effects necessitates exploring various cell lines. Among the individual monomers, BisGMA was found to be the most toxic; however, BisDMA and BADGE generates BPA endogenously and found to elicit severe adverse reactions. In correlating in vitro data with in vivo findings, further research is necessary to classify the elutes as human carcinogens or xenoestrogens. Though the basic mechanisms underlying toxicity were believed to be the production of intracellular reactive oxygen species and a corresponding decline in glutathione levels, several underlying mechanisms were identified to stimulate cellular responses at low concentrations. The review calls for further research to assess the synergistic interactions of co-monomers and other components in dental resins. The review emphasizes the clinical relevance of these findings, highlighting the necessity for safer dental materials and underscoring the potential health risks associated with current dental resin systems.

Cytotoxicity Evaluation of Various Composite Resin Materials: An In Vitro Study

Aim This study aimed to determine and compare the cytotoxicity of light-cured composite resin (Enlight light cure composite (Ormco, Glendora, California, USA)), light-cured acrylic resin (Orthocryl LC (Dentaurum, Ispringen, Germany)), and the self-cure acrylic (DPI RR cold cure acrylic (Dental Products of India, Bombay Burmah Trading Corporation Ltd., Mumbai, India)) material and to determine which component is best to be used for the purpose of nasal stent fabrication in the nasoalveolar molding (NAM) technique for cleft therapy. Methods Circular discs made from Enlight light cure composite, Orthocryl LC, and self-cure acrylic were submerged for 24 hours in gingival fibroblast media (three discs of each material) and control medium (three discs of each material) that were both contained in plates. After analyzing the optical densities of the plates, the cytotoxicity of the products was assessed by measuring cell viability using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The compiled data was analyzed using IBM SPSS Statistics for Windows, V. 23.0 (IBM Corp., Armonk, NY). The normality of the data was evaluated using the Shapiro-Wilk test. One-way analysis of variance (ANOVA) and pairwise comparison made with Tukey's honestly significant difference (HSD) post hoc test with a significance level (p) of 0.05 were considered. Results The percentage of cell viability was between 80% and 150%. A significant mean difference was noted in the cell viability between the three groups (p=0.009). High mean cell viability was seen in Orthocryl LC. However, there was no significant mean difference between Orthocryl LC and Enlight light cure composite material (p=0.854). Conclusion Both Orthocryl LC and Enlight light cure composite materials are less cytotoxic when compared to the self-cure acrylic resin material and can be used to fabricate the nasal stent component for infants with cleft defects, undergoing NAM procedure.

Characterization of dental dust particles and their pathogenicity to respiratory system: a narrative review

OBJECTIVES

Dental professionals are exposed to large amounts of dust particles during routine treatment and denture processing. This article provides a narrative review to investigate the most prevalent dust-related respiratory diseases among dental professionals and to discuss the effects of dental dust on human respiratory health.

MATERIALS AND METHODS

A literature search was performed in PubMed/Medline, Web of Science, and Embase for articles published between 1990 and 2022. Any articles on the occupational respiratory health effects of dental dust were included.

RESULTS

The characterization and toxicity evaluation of dental dust show a correlation between dust exposure and respiratory system injury, and the possible pathogenic mechanism of dust is to cause lung injury and abnormal repair processes. The combination use of personal protective equipment and particle removal devices can effectively reduce the adverse health effects of dust exposure.

CONCLUSIONS

Dental dust should be considered an additional occupational hazard in dental practice. However, clinical data and scientific evidence on this topic are still scarce. Further research is required to quantify dust in the dental work environment and clarify its pathogenicity and potential toxicological pathways. Nonetheless, the prevention of dust exposure should become a consensus among dental practitioners.

CLINICAL RELEVANCE

This review provides dental practitioners with a comprehensive understanding and preventive advice on respiratory health problems associated with dust exposure.

Preparation and evaluation of novel bio-based Bis-GMA-free dental composites with low estrogenic activity

OBJECTIVE

Although bisphenol Aglycidyl methacrylate (Bis-GMA) are widely used in the dental composite, its raw materials include the petroleum-based product bisphenol A (BPA) with high estrogenic activity (EA). In this study, two new BPA-free dimethacrylate monomers from bio-based material creosol were synthesized and evaluated.

METHODS

The renewable bisphenol monomer 5, 5'-methylenedicreosol (BCF) was prepared from bio-based material creosol. By the human breast cancer cells (MCF-7 cells) proliferation assay, a risk assessment of BCF was performed to determine if BCF possessed reduced EA in comparison to BPA. Then, the novel monomers 5, 5'-methylenedicreosol diglycidyl ether diacrylate (BCF-EA) and 5, 5'-methylenedicreosol diglycidyl ether dimethacrylate (BCF-GMA) were synthesized from BCF with epichlorohydrin and (meth)acrylate. All products were investigated by ¹H NMR and FT-IR spectra. The control resin was a mixture based on Bis-GMA and tri(ethyleneglycol) dimethacrylate (TEGDMA) with a weight ratio of 5:5 (5B5T). Similarly, experimental resin matrix was a mixture based on BCF-EA/TEGDMA (5E5T) and BCF-GMA/TEGDMA (5G5T). And their corresponding composites were then prepared with corresponding resin matrices and hybrid SiO₂ (5E5TC, 5G5TC and 5B5TC). The properties of these composites were investigated according to the standard or referenced methods. Each sample was evaluated for double bond conversion (DC), shrinkage stress (SS) and volumetric polymerization shrinkage (VS). Water sorption (WS), water solubility (SL), mechanical properties and cytotoxicity were also measured.

RESULTS

¹H NMR and FT-IR spectra confirmed the chemical structure of each monomer. EA test revealed that bio-based bisphenol monomer BCF as the precursor of BCF-EA and BCF-GMA showed lower EA than BPA. Cured resin matrix: Both 5E5T and 5G5T had nearly the same DC (p < 0.05), which was higher than 5B5T (p < 0.05); 5E5T and 5G5T had lower VS, SL and cytotoxicity than 5B5T (p < 0.05); mechanical properties of 5E5T and 5G5T were all better than those of 5B5T (p < 0.05). Cured composite: There was no significant difference in conversion (p < 0.05); 5E5TC and 5G5TC had significantly lower VS (p < 0.05); WS of 5E5TC and 5G5TC were similar (p < 0.05), but higher compared to 5B5TC (p < 0.05); 5E5TC and 5G5TC had the deeper depth of cure (p > 0.05); before water immersion, there was no significant difference in flexural strength between 5E5TC and 5G5TC (p > 0.05), and higher than 5B5TC (p < 0.05); 5E5TC and 5G5TC showed less cytotoxicity than 5B5TC (p < 0.05).

SIGNIFICANCE

The new BPA-free di(meth)acrylates are promising photocurable dental monomers owning to bio-based raw material, high degree of conversion coupled with low curing shrinkage and good mechanical properties. Therefore, BCF-EA and BCF-GMA has a potential to be used as the substitution for Bis-GMA to prepare Bis-GMA-free dental composite.

Characterisation of Microparticle Waste from Dental Resin-Based Composites

Clinical applications of resin-based composite (RBC) generate environmental pollution in the form of microparticulate waste. Methods: SEM, particle size and specific surface area analysis, FT-IR and potentiometric titrations were used to characterise microparticles arising from grinding commercial and control RBCs as a function of time, at time of generation and after 12 months ageing in water. The RBCs were tested in two states: (i) direct-placement materials polymerised to simulate routine clinical use and (ii) pre-polymerised CAD/CAM ingots milled using CAD/CAM technology. Results: The maximum specific surface area of the direct-placement commercial RBC was seen after 360 s of agitation and was 1290 m²/kg compared with 1017 m²/kg for the control material. The median diameter of the direct-placement commercial RBC was 6.39 μm at 360 s agitation and 9.55 μm for the control material. FTIR analysis confirmed that microparticles were sufficiently unique to be identified after 12 months ageing and consistent alteration of the outermost surfaces of particles was observed. Protonation-deprotonation behaviour and the pH of zero proton charge (pH_zpc) ≈ 5–6 indicated that the particles are negatively charged at neutral pH7. Conclusion: The large surface area of RBC microparticles allows elution of constituent monomers with potential environmental impacts. Characterisation of this waste is key to understanding potential mitigation strategies.

Cytotoxicity evaluation of dental and orthodontic light-cured composite resins

INTRODUCTION

The aim of this study was to determine the cytotoxicity of light-cured composite resins (Clearfil ES-2, Clearfil ES Flow, Filtek Supreme XTE, Grengloo, Blugloo, Transbond XT, and Transbond LR) then to assess leachable components in contact with human gingival fibroblasts (GFs) and to quantity detected bisphenol A (BPA).

METHODS

Light-cured composite resin discs were immersed for 24 hours in gingival fibroblastic medium (n = 3 for each product) and in control medium (n = 2 for each product) contained in plate. Cytotoxicity of the products (n = 95) was determined by the measure of cell viability using MTT assay after reading the optical densities of the plates. The analysis of leachable components was done by gas phase chromatography and mass spectrometry (GC-MS) and detected BPA was quantified. The limit of quantification was 0.01 μg/mL. Statistical analyses were performed by using IBM SPSS Statistics 20 and Kruskal-Wallis and Mann-Whitney U-tests were applied.

RESULTS

Cell viabilities were between 85 and 90%. Many chemical compounds including triethylene glycol dimethacrylate (TEGDMA) and BPA were identified. The average concentrations were 0.67 μg/mL ± 0.84 in the control medium and 0.73 μg/mL ± 1.05 in the fibroblastic medium. Filtek Supreme XTE presented the highest concentration of BPA with 2.16 μg/mL ± 0.65 and Clearfil ES Flow presented the lowest with 0.25 μg/mL ± 0.35. No BPA was detected with Transbond XT and Transbond LR. Clearfil ES Flow, Filtek Supreme XTE, Grengloo and Transbond LR presented residual TEGDMA.

CONCLUSIONS

Light-cured composite resins are slightly cytotoxic opposite GFs and release many components including BPA and TEGDMA. Clinical precautions should be taken to decrease the release of these monomers.

Biodegradation of orthodontic composites by Streptococcus mutans: An in vitro qualitative and quantitative assessment

Objectives:

The purpose of this study was to evaluate the degradation products of orthodontic composites (Grengloo, Blugloo, Transbond XT, and Transbond LR) by Streptococcus mutans and then to quantify the levels of released bisphenol A (BPA) using gas-phase chromatography and mass spectrometry (GC–MS).

Materials and Methods:

Orthodontic light-cured composite discs were incubated at 37°C in brain heart infusion (BHI) (control group) and in a culture of S. mutans with BHI (test group). Incubation solutions were collected every 48 h in each group and replaced with fresh solutions. These incubation solutions were accumulated and grouped. The assessment of degradation products from composites was done at 1 and 30 days. Detected BPA was then quantified. The limit of quantification was 0.01 μg/mL.

Results:

Degradation products were present at day 30. For the test group, BPA was detected in Blugloo at day 1 (0.38 μg/mL) and triethylene glycol dimethacrylate (TEGDMA) was detected in Grengloo and Transbond LR at day 1.

Conclusion:

S. mutans can hydrolyze long-term orthodontic composites. Monomers such as BPA and TEGDMA may be present in degradation products. It is possible to separate and identify leaching compounds by GC–MS technique.

Release and toxicity of bisphenol-A (BPA) contained in orthodontic adhesives: A systematic review

OBJECTIVE

The objectives of this systematic review of the literature are to search for BPA release from biomaterials used in orthodontics and to highlight their possible impact on human health.

MATERIALS AND METHODS

Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) model, digital and manual searches were conducted in February 2020 in the database of CENTRAL, MEDLINE and EMBASE. Thirteen parameters relating to the release and biological effects of BPA were identified and analysed.

RESULTS

Thirty-one non-randomized clinical trials were included. In general, the level of evidence was low, and the risk of bias ranged from moderate to high. Furthermore, although at different concentrations, most of in vitro and in vivo studies found BPA release from orthodontic adhesives. The lack of standardized protocols and the clinical and methodological heterogeneity of the studies prevented a valid interpretation of the actual results. Concerning the possible toxicity of BPA, no conclusive scientific evidence could be drawn, but it seems that orthodontic biomaterials containing BPA have potential adverse biological effects in humans.

DISCUSSION AND CONCLUSION

Until we have solid evidence from clinical trials, clinicians should consider that orthodontic adhesives containing BPA have potential short- and long-term adverse biological effects in humans. Careful consideration should therefore be given to bonding, polymerization and debonding protocols in orthodontics.

Minimizing the aerosol-generating procedures in orthodontics in the era of a pandemic: Current evidence on the reduction of hazardous effects for the treatment team and patients

The purpose of this critical review is to list the sources of aerosol production during orthodontic standard procedure, analyze the constituent components of aerosol and their dependency on modes of grinding, the presence of water and type of bur, and suggest a method to minimize the quantity and detrimental characteristics of the particles comprising the solid matter of aerosol. Minimization of water-spray syringe utilization for rinsing is suggested on bonding related procedures, while temporal conditions as represented by seasonal epidemics should be considered for the decision of intervention scheme provided as a preprocedural mouth rinse, in an attempt to reduce the load of aerosolized pathogens. In normal conditions, chlorhexidine 0.2%, preferably under elevated temperature state should be prioritized for reducing bacterial counts. In the presence of oxidation vulnerable viruses within the community, substitute strategies might be represented by the use of povidone iodine 0.2%-1%, or hydrogen peroxide 1%. After debonding, extensive material grinding, as well as aligner related attachment clean-up, should involve the use of carbide tungsten burs under water cooling conditions for cutting efficiency enhancement, duration restriction of the procedure, as well as reduction of aerosolized nanoparticles. In this respect, selection strategies of malocclusions eligible for aligner treatment should be reconsidered and future perspectives may entail careful and more restricted utilization of attachment grips. For more limited clean-up procedures, such as grinding of minimal amounts of adhesive remnants, or individualized bracket debonding in the course of treatment, hand-instruments for remnant removal might well represent an effective strategy. Efforts to minimize the use of rotary instrumentation in orthodontic settings might also lead the way for future solutions. Measures of self-protection for the treatment team should never be neglected. Dressing gowns and facemasks with filter protection layers, appropriate ventilation and fresh air flow within the operating room comprise significant links to the overall picture of practice management. Risk management considerations should be constant, but also updated as new material applications come into play, while being grounded on the best available evidence.

Particulate Production and Composite Dust during Routine Dental Procedures. A Systematic Review with Meta-Analyses

Composite dust generation is most likely a continuous and daily procedure in dental practice settings. The aim of this systematic review was to identify, compile and evaluate existing evidence on interventions and composite material properties related to the production of aerosolized dust during routine dental procedures. Seven electronic databases were searched, with no limits, supplemented by a manual search, on 27 April 2020 for published and unpublished research. Eligibility criteria comprised of studies of any design, describing composite dust production related to the implementation of any procedure in dental practice. Study selection, data extraction and risk of bias (RoB) assessment was undertaken independently either in duplicate, or confirmed by a second reviewer. Random effects meta-analyses of standardized mean differences (SMD) with associated 95% confidence intervals (CIs) were employed where applicable. A total of 375 articles were initially identified, resulting in 13 articles being included in the qualitative synthesis, of which 5 contributed to meta-analyses overall. Risk of bias recordings ranged between low and high, pertaining to unclear/raising some concerns, in most cases. All types of composites, irrespective of the filler particles, released significant amounts of nano-sized particles after being ground, with potentially disruptive respiratory effects. Evidence supported increased % distribution of particles < 100 nm for nanocomposite Filtek Supreme XTE compared to both conventional hybrid Z100MP (SMD: 1.96, 95% CI: 0.85, 3.07; p-value; 0.001) and nano- hybrid Tetric EvoCeram (SMD: 1.62, 95% CI: 0.56, 2.68; p-value: 0.003). For cytotoxicity considerations of generated aerosolized particles, both nanocomposites Filtek Supreme XTE and nanohybrid GradiO revealed negative effects on bronchial epithelial cell viability, as represented by % formazan reduction at 330-400 μg/ml for 24 hours, with no recorded differences between them (SMD: 0.19; 95% CI: -0.17, 0.55; p-value: 0.30). Effective and more rigorous management of dental procedures potentially liable to the generation of considerable amounts of aerosolized composite dust should be prioritized in contemporary dental practice. In essence, protective measures for the clinician and the practices' personnel should also be systematically promoted and additional interventions may be considered in view of the existing evidence.

Safety Considerations for Thermoplastic-Type Appliances Used as Orthodontic Aligners or Retainers. A Systematic Review and Meta-Analysis of Clinical and In-Vitro Research

Use of thermoplastic material in orthodontics, either as aligner or as retainer appliances, is common practice and is likely to increase in the years to come. However, no systematic assessment on safety considerations of these adjuncts has been implemented up to date. The aim of this systematic review was to collectively appraise the existing evidence from both clinical and laboratory studies, on whether these appliances are associated with any estrogenic/cytotoxic effects or bisphenol-A (BPA) and monomer leaching. Eight electronic databases were searched with no limits in December 22, 2019, for published and unpublished research. Eligibility criteria comprised of studies of any design, describing use of any type of thermoplastic aligner. Study selection, data extraction and risk of bias (RoB) assessment was done independently, either in duplicate or confirmed by a second reviewer. Random effects meta-analyses of weighted mean differences (WMD) with associated 95% Confidence Intervals (CIs) were planned. Quality of the evidence was evaluated with Grading of Recommendations Assessment, Development and Evaluation (GRADE). A total of 58 articles were initially identified, while 5 were included in qualitative synthesis and 2 of those contributed to the quantitative syntheses. Four studies were in-vitro, while one was a randomized controlled trial; all assessed some type of orthodontic aligner or retainer, either as-received or retrieved. Risk of bias recordings ranged between unclear and high for all studies. Proliferation induction capacity of thermoplastic appliances’ eluents on MCF-7 cells failed to be confirmed compared to beta-estradiol (2 studies: 5% v/v, WMD: −182.08; 95% CI: −198.83, −165.33; p-value < 0.001; and 20% v/v, WMD: −184.53; 95% CI: −206.17, −162.88; p-value < 0.001). No cytotoxic activity was detected as well. In addition, although evidence from in-vitro studies was indicative of no traceable detection of BPA or other monomers, the findings from a single clinical trial were allied to increased levels of BPA in whole stimulated saliva, after up to 30 days of thermoplastic retainer usage, compared to standard Hawley retainer. The quality of the evidence overall was low to medium. Current data from in-vitro research are indicative of an absence of an estrogenic or cytotoxic effect of thermoplastic aligners or retainers. Regarding BPA or monomer release, evidence from clinical and laboratory studies appear inconsistent.

Decalcification and bond failure rate in resin modified glass ionomer cement versus conventional composite for orthodontic bonding: A systematic review & meta-analysis

BACKGROUND

Demineralized white spot lesions (DWSLs) are one of the unfavourable effects of orthodontic treatment. Resin modified glass ionomer cement (RMGIC) was introduced to reduce its occurrence.

OBJECTIVE

The study aimed to determine the incidence of DWSLs as primary objective and bond failure rate in brackets bonded with RMGIC versus conventional composite (CC) as secondary objective.

MATERIAL AND METHODS

A thorough literature search was done until April 2019 on various databases including Scopus, Web of Science, PubMed, Cochrane database, CINHAL, Dental and Oral Science, and manual search. Only human clinical trials and published in English language were included. We considered the experimental group of orthodontic patients with brackets bonded with RMGIC and the control group with brackets bonded with CC. Blind and induplicate study selection, data extraction, and risk of bias assessment were undertaken. RevMan software was used for data analysis. Odds ratio with 95% confidence intervals (CIs) was used to express the effect estimate of frequency of bracket failure bonded using RMGIC and CC. The risk of bias was assessed using Cochrane risk of bias tool for RCTs and ROBINS-I tool for N-RCTs. Sensitivity analyses and subgroup analysis were performed as well.

RESULTS

Out of 2285 articles, nine met the inclusion criteria. Five were RCTs and four were N-RCTs. Out of nine, seven studies were included in the meta-analysis. A random effect model was used. No significant difference was found in the bond failure rate (risk ratio: 1.48; 95% CI: 0.57-3.87; P≤0.42). No difference was found in the occurrence of DWSLs between the two groups.

CONCLUSIONS

Due to the limited number of studies and studies with high risk of bias, no strong conclusion can be drawn. More studies need to be done to reasonably conclude that RMGIC is beneficial in reducing the occurrence of DWSLs and have comparable bond failure rate. The protocol was registered on PROSPERO (CRD42019125386) prior to the commencement of the systematic review.

Resin-modified glass ionomer cement vs composite for orthodontic bonding: A multicenter, single-blind, randomized controlled trial

INTRODUCTION

In this study, we aimed to compare the incidence of new demineralized lesions and bond failures between 2 groups of participants wearing fixed orthodontic appliances bonded with either light-cured resin-modified glass ionomer cement or light-cured composite.

METHODS

This trial was a multicenter (6 centers: 2 teaching hospitals, 4 specialist orthodontic practices), single-blinded, randomized controlled trial with 2 parallel groups. Patients aged 11 years or older, in the permanent dentition, and about to start fixed orthodontic treatment in these 6 centers were randomly allocated to have either resin-modified glass ionomer cement or light-cured composite for bonding brackets, forward of the first molars. Pretreatment and day-of-debond digital photographic images were taken of the teeth and assessed by up to 5 clinical and 3 lay assessors for the presence or absence of new demineralized lesions and the esthetic impact. The assessors were masked as to group allocation.

RESULTS

We randomized 210 participants, and 197 completed the trial. There were 173 with complete before-and after-digital images of the teeth. The incidence of new demineralized lesions was 24%; but when the esthetic impact was taken into account, this was considerably lower (9%). There was no statistically significant difference between the bracket adhesives in the numbers with at least 1 new demineralized lesion (risk ratio,1.25; 95% confidence interval, 0.74-2.13; P = 0.403) or first-time bracket failure (risk ratio,0.88; 95% confidence interval, 0.67-1.16; P = 0.35). There were no adverse effects.

CONCLUSIONS

There is no evidence that the use of resin modified glass ionomer cement over light-cured composite for bonding brackets reduces the incidence of new demineralized lesions or bond failures. There might be other reasons for using resin modified glass ionomer cement.

REGISTRATION

This trial was registered at ClinicalTrials.govNCT01925924.

PROTOCOL

The protocol is available from the corresponding author on request.

Monomer release from orthodontic retentions: An in vitro study

INTRODUCTION

The adhesives used to bond orthodontic retentions are low-loaded composite resins with a resinous matrix containing bisphenol A diglycidyl ether dimethacrylate synthesized from bisphenol A (BPA), fluidizers such as triethylene glycol dimethacrylate (TEGDMA) and hydrophilic polymers such as hydroxyethylmethacrylate. BPA disrupts the endocrine balance, and TEGDMA has high risks for human health: eg, allergies and cytotoxicity. The aim of this study was to evaluate in vitro the release of monomers from orthodontic bonded retentions.

METHODS

A reproducible model of bonded retentions was carried out using calibrated molds. We analyzed the release of monomers by gas phase chromatography coupled with mass spectrometry.

RESULTS

This model allowed us to qualitatively and quantitatively evaluate the in-vitro release of monomers from orthodontic adhesives. The quantitative and qualitative analyses showed no BPA release above the 0.02 ppm detection limit. A greater release of TEGDMA was observed with Transbond LR (31.7 μg/mL) than with Transbond XT (13.12 μg/mL) (both, 3M Unitek, Monrovia, Calif). Other toxic components (iodobenzene, iodobiphenyl, triphenyl stibine, and so on) were also identified.

CONCLUSIONS

Toxic and carcinogenic molecules not mentioned in the material safety data sheets were identified.

Adverse reactions to orthodontic materials

Adverse effects can arise from the clinical use of orthodontic materials, due to the release of constituent substances (ions from alloys and monomers, degradation by-products, and additives from polymers). Moreover, intraoral aging affects the biologic properties of materials. The aim of this review is to present the currently identified major adverse effects of the metallic and polymeric components found in orthodontic appliances and materials. Corrosion in metallic orthodontic attachments releases metal ions, mainly iron, chromium, and nickel. The latter has received the greatest attention because of its reported potential for an allergic response. The formation of an oxide layer may inhibit the outward movement of ions, thereby acting as an obstacle for release. Titanium alloys have superior corrosion resistance than stainless steel. The efficiency of polymerisation is considered an essential property for all polymers. A poor polymer network is susceptible to the release of biologically reactive substances, such as bisphenol-A (BPA), which is capable of inducing hormone-related effects. The close proximity of a light-curing tip to the adhesive, pumice prophylaxis after bonding, indirect irradiation and mouth rinsing during the first hour after bonding may decrease BPA release. The adverse effects of some orthodontic materials should be considered during material selection and throughout orthodontic treatment, in order to minimise possible undesirable implications.

The role of polycarbonate monomer bisphenol-A in insulin resistance

Bisphenol A (BPA) is a synthetic unit of polycarbonate polymers and epoxy resins, the types of plastics that could be found in essentially every human population and incorporated into almost every aspect of the modern human society. BPA polymers appear in a wide range of products, from liquid storages (plastic bottles, can and glass linings, water pipes and tanks) and food storages (plastics wraps and containers), to medical and dental devices. BPA polymers could be hydrolyzed spontaneously or in a photo- or temperature-catalyzed process, providing widespread environmental distribution and chronic exposure to the BPA monomer in contemporary human populations. Bisphenol A is also a xenoestrogen, an endocrine-disrupting chemical (EDC) that interferes with the endocrine system mimicking the effects of an estrogen and could potentially keep our endocrine system in a constant perturbation that parallels endocrine disruption arising during pregnancy, such as insulin resistance (IR). Gestational insulin resistance represents a natural biological phenomenon of higher insulin resistance in peripheral tissues of the pregnant females, when nutrients are increasingly being directed to the embryo instead of being stored in peripheral tissues. Gestational diabetes mellitus may appear in healthy non-diabetic females, due to gestational insulin resistance that leads to increased blood sugar levels and hyperinsulinemia (increased insulin production from the pancreatic beta cells). The hypothesis states that unnoticed and constant exposure to this environmental chemical might potentially lead to the formation of chronic low-level endocrine disruptive state that resembles gestational insulin resistance, which might contribute to the development of diabetes. The increasing body of evidence supports the major premises of this hypothesis, as exemplified by the numerous publications examining the association of BPA and insulin resistance, both epidemiological and mechanistic. However, to what extent BPA might contribute to the development of diabetes in the modern societies still remains unknown. In this review, I discuss the chemical properties of BPA and the sources of BPA contamination found in the environment and in human tissues. I provide an overview of mechanisms for the proposed role of bisphenol A in insulin resistance and diabetes, as well as other related diseases, such as cardiovascular diseases. I describe the transmission of BPA effects to the offspring and postulate that gender related differences might originate from differences in liver enzyme levels, such as UDP-glucuronosyltransferase, which is involved in BPA processing and its elimination from the organism. I discuss the molecular mechanisms of BPA action through nuclear and membrane-bound ER receptors, non-monotonic dose response, epigenetic modifications of the DNA and propose that chronic exposure to weak binders, such as BPA, may mimic the effects of strong binders, such as estrogens.

Release of monomers from orthodontic adhesives

INTRODUCTION

Most composite resins release both bisphenol A (BPA), which disrupts the endocrine balance, and triethylene glycol dimethacrylate (TEGDMA), which has high risks for human health: eg, allergies and cytotoxicity. The aim of this study was to characterize monomers released from orthodontic adhesives.

METHODS

We studied samples of orthodontic adhesives by associating 2 techniques: gas phase chromatography and mass spectrometry.

RESULTS

The in-vitro analysis detected significant quantities of BPA, TEGDMA, and other monomers in orthodontic adhesives used in daily practice: Transbond XT, Transbond Supreme LV (both, 3M Unitek, Monrovia, Calif), Blugloo (Ormco, Orange, Calif), and MonoLok 2 (Rocky Mountain Orthodontics, Denver, Colo).

CONCLUSIONS

Clinicians should consider that orthodontic adhesives contain BPA, an endocrine disruptor; TEGDMA, an allergic and a cytotoxic compound; and carcinogenic genotoxic compounds. These molecules are not mentioned in the material safety data sheets. Manufacturers should declare all components of dental composites to identify these substances that may result in allergic or undesirable side effects for patients and dental staff.

A systematic study of the release of bisphenol A by orthodontic materials and its biological effects

INTRODUCTION

Bisphenol A (BPA) is a synthetic chemical substance used as a starting ingredient in the manufacturing process of a number or orthodontic materials. It is a well-known endocrine disruptor with low estrogenic properties. The aim of this investigation is to present a systematic review regarding the issue of bisphenol A release by orthodontic materials and its impact in orthodontics.

MATERIALS AND METHODS

A systematic analysis was performed by electronic search (between 1936 and 2015) on several data bases. The search was limited by using several specific key-words in two languages, English and French. Two investigators selected the responses, which met the selection criteria.

RESULTS AND DISCUSSION

Of the 376 studies found, only 21 met our selection criteria: 11 of these dealt with the release of bisphenol by orthodontic materials and 10 in vitro studies described the effects of BPA leaching from orthodontic materials on human and murine cells. The rate of BPA release was well below the daily tolerable intake (DTI) (50mg/kg/day in 2006, then 50μg/kg/day in 2015) according to the European Food Safety Authority (EFSA). Theoretical exposure to BPA was 11,000 times lower than recommendations. However, other studies have shown the presence of BPA and of monomers released in large quantities at very low doses. The effects of observed BPA varied significantly (toxic and carcinogenic potential) while some studies found no effects at all. The relatively small number of studies dealing with the release of Bisphenol A by orthodontic materials, apart from orthodontic materials and their significant biological effects, has led to the absence of standard protocols and has hindered precise determination of released BPA. Moreover, the lack of coherence between the various methodological approaches and variations in the experimental protocols have resulted in a low level of proof regarding the impact of BPA by orthodontic materials.

RECOMMENDATIONS

Through this study, the authors encourage clinicians to observe the following recommendations designed to reduce the amount of BPA released by materials used in orthodontics: keep the tip of the light-curing lamp as close as possible to the composite and perform indirect rather than direct light-curing; Pumice-polish the composite after bonding so as to reduce the potential amount of BPA released; reduce exposure by brushing or rinsing with a mouthwash during the first hour after bonding; follow a standardized, reproducible and expert-validated research protocol aimed at better understanding of BPA release.

Effect of intraoral aging on the setting status of resin composite and glass ionomer orthodontic adhesives

INTRODUCTION

The aim of this study was to assess the effect of intraoral aging on the setting status of a resin composite and a glass ionomer adhesive, relative to control specimens stored in water.

METHODS

Metallic brackets were bonded with resin composite orthodontic adhesive (Transbond XT; 3M Unitek, Monrovia, Calif) or a glass ionomer cement (Fuji I; GC, Tokyo, Japan) to recently extracted premolars and kept in water for 6 months. The same materials were also bonded to the premolars of orthodontic patients. After 6 months, the teeth were carefully extracted, with the brackets intact on their buccal surfaces. All teeth were embedded in epoxy resin and sectioned buccolingually. Fourier transform infrared microscopy and Raman microscopy were used for the estimation of the degree of cure in the composite and the salt yield in the glass ionomer adhesives.

RESULTS

The control samples of the composite showed significantly lower degrees of cure than did the retrieved specimens (52.40% ± 3.21% vs 57.62% ± 1.32% by Fourier transform infrared microscopy, and 61.40% ± 2.61% vs 67.40% ± 3.44% by Raman microscopy). Raman microscopy significantly overestimated the degree of cure and failed to provide reliable information for the salt yield in the glass ionomer cement. Fourier transform infrared microscopy showed increased, but no statistically significant difference in, aluminum-carboxylate salts in the retrieved specimens.

CONCLUSIONS

Enhanced oxidation of residual carbon-carbon bonds in the composite and slightly increased dissolution of the weaker calcium-salt phase in the glass ionomer cement were the main differences in the intraorally aged specimens in comparison with the specimens stored in water.

In-vitro evaluation of an experimental method for bonding of orthodontic brackets with self-adhesive resin cements

BACKGROUND

Self-adhesive resin cements do not require the surface treatment of teeth and are said to release fluoride, which makes them suitable candidates for bonding of orthodontic brackets. The objectives of this study was to investigate the shear bond strength (SBS) of self-adhesive resin cements on etched on non-etched surfaces in vitro and to assess their fluoride release features.

MATERIALS AND METHODS

Four fluoride-releasing dual-cure self-adhesive resin cements were investigated. For SBS experiment, 135 freshly extracted human maxillary premolars were used and divided into nine groups of 15 teeth. In the control group, brackets were cemented by Transbond XT (3M Unitek, USA), in four groups self-adhesive resin cements were used without acid-etching and in four groups self-adhesive cements were applied on acid-etched surfaces and the brackets were then deboned in shear with a testing machine. Adhesive remnant index (ARI) scores were also calculated. For fluoride release investigation, 6 discs were prepared for each self-adhesive cement. Transbond XT and Fuji Ortho LC (GC, Japan) served as negative and positive control groups, respectively. The fluoride release of each disc into 5 ml of deionized water was measured at days 1, 2, 3, 7, 14, 28, and 56 using a fluoride ion-selective electrode connected to an ion analyzer. To prevent cumulative measurements, the storage solutions were changed daily.

RESULTS

The SBS of brackets cemented with Transbond XT were significantly higher compared to self-adhesives applied on non-etched surfaces (P<0.001). However, when the self-adhesive resin cements were used with enamel etching, no significant differences was found in the SBS compared to Transbond XT, except for Breeze. The comparisons of the ARI scores indicated that bracket failure modes were significantly different between the etched and non-etched groups. All self-adhesive cements released clinically sufficient amounts of fluoride for an extended period of time.

CONCLUSION

For the tested cements, the strongest bonds were obtained by enamel acid-etching prior to bracket bonding. All the self-adhesive resin cements had significant long-term fluoride release and could be recommended as suitable fluoride-releasing orthodontic bonding materials.

An investigation into bisphenol-A leaching from orthodontic materials

OBJECTIVE

To quantitatively determine the bisphenol-A (BPA) leached from orthodontic materials during simulated intraoral exposure.

MATERIALS AND METHODS

Samples of orthodontic materials were subjected to simulated abrasion, immersion in artificial saliva, thermal shock via temperature cycling, and simulated intraoral exposure. Sample aliquots were collected for up to 2 weeks after artificial saliva immersion, derivatized, then analyzed for BPA by gas chromatography/mass spectroscopy.

RESULTS

Quantifiable amounts of leached BPA were observed from a thermoformed orthodontic retainer material (7.63 µg/g of material) and an orthodontic adhesive (2.75 µg/g of material). BPA leaching was only observed within the first 3 days of artificial saliva immersion.

CONCLUSIONS

Under the test conditions, BPA was observed to leach from two orthodontic materials. While the quantities of leached BPA were below the reference dose for daily intake, existing data of low-dose effects and medical disorders associated with elevated urinary BPA levels suggest that BPA exposure, and thus the use of the leaching materials identified in this study, should be reduced or eliminated.

The Challenge for Innovation in Direct Restorative Materials

During the past 50 years, a series of key UN conferences have established a framework to minimize human health risks from environmental exposures to key chemicals. In January 2013, more than 140 countries agreed to the text of new treaty to minimize Hg effects on the environment (the Minamata Convention). Dental caries is omnipresent around the globe, affecting 60% to 90% of school children and most adults, and producing discomfort that affects quality of life. Dental amalgam is frequently used to treat carious lesions and its use releases mercury into the environment. The best way to avoid the use of dental amalgam is to emphasize caries prevention. Alternatives to amalgam are suitable in some applications, but no replacement for amalgam has been found for large posterior restorations. For any restorative material, safety and environmental impacts are part of clinical risk assessment. Safety is freedom from unacceptable risks. Risk is a combination of probability of exposure and severity of harm. Best management practices are crucial to manage dental amalgam, but these impose additional that are disproportionately more for developing countries. The Minamata Convention seeks a phase-out of all mercury-based products except dental amalgam, where a phase-down is the present goal. For dentistry, the most important focus is the promotion of caries prevention and research on new materials.