Commercially available mouthguards: First time unearthing trace elements (2024)

Highlights

Novel method for detecting toxic elements in mouthguards

Identified hazardous contaminants (cadmium, lead, copper)

Highlighted the urgent need for quality control in mouthguard manufacturing

Abstract

Highlights

Novel method for detecting toxic elements in mouthguards

Identified hazardous contaminants (cadmium, lead, copper)

Highlighted the urgent need for quality control in mouthguard manufacturing

Abstract

The use of mouthguards is advocated by the American Dental Association for orofacial injury prevention and teeth protection. However, the chemical environment in the mouth may cause harmful substances within the mouthguard’s polymer material to leach out and be absorbed by the user. Considering this, the present study for the first time analyzed commercially available mouthguards and disclosed the presence of trace elements. Specifically, an analytical method was developed based on closed-vessel microwave-assisted digestion and plasma-based atomic spectrometry for determining toxic trace elements in mouthguard samples. Initially, 75 elements were assessed and, thereafter, quantified cadmium (Cd), copper (Cu) and lead (Pb) in each sample by inductively coupled plasma mass spectrometry (ICP-MS). Method validation was carried out by analyzing a certified reference material of Low-Density Polyethylene, and by addition and recovery experiments. Results for copper were further validated by ICP optical emission spectrometry (ICP-OES). While most samples exhibited elemental levels beneath the method’s limit of quantification, Cd, Cu and Pb were detected in four samples. Remarkably, one sample had Cu levels exceeding safe limits by 109 times, highlighting potential toxicity risks. This initial research underscores the need for stricter contamination control in mouthguard materials to minimize potentially health hazards.

Introduction

As a preventative solution for combating orofacial injuries sustained from practicing contact sports, high-risk competitions, as well as bruxism, the American Dental Association (ADA) has advised the use of mouthguards (AFFAIRS, 2006). Mouthguards are dental devices that cover the teeth of the user with the primary purpose of protecting them from injuries. These devices also protect the tongue, gingiva, and the jawbone from trauma. A variety of industrially manufactured polymers are used in the production of mouthguards, with the most common materials including ethylene vinyl acetate (EVA) copolymer and polyolefins, while others, such as polyvinyl chloride (PVC), polyurethanes and acrylic resins, also being used in the past (Sousa et al., 2020).

Manufacturers continuously seek to improve the polymeric material used in mouthguards, especially regarding their biocompatibility/safety, as the presence of potentially toxic contaminants in the polymer can be transferred to the user. This is particularly important because the mouthguard remains inside the user’s mouth for long periods of time, where it comes into direct contact with enzyme-containing saliva. The chemical environment of the mouth may facilitate the leaching of potentially harmful contaminants in the mouthguard, which may then be absorbed by the user’s body (Bussan et al., 2022; Chen, 1998; Corea-Téllez et al., 2008). In this context, it is of paramount importance to rigorously assess the safety of commercially available mouthguards to ensure that they are free of various contaminants, especially those associated with the manufacturing process. In recent years, compounds such as bisphenol A (BPA), phthalates, and methyl methacrylate (MMA) have been investigated as potential contaminants in commercially available materials used intraorally, including mouthguards (Sharma et al., 2016).

In addition to these harmful substances, other chemicals of concern may also be present in polymer products, including toxic elements that are often used as additives in the manufacturing process of these products (Turner and Filella, 2021a). Elements such as cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb), antimony (Sb) and titanium (Ti) can be found in products made of polymer materials similar to those used in mouthguards, as well as in dental biomaterials (Ferg and Rust, 2007; Filella et al., 2020; Mikulewicz and Chojnacka, 2018; Turner and Filella, 2021b). Cadmium, for example, is immunotoxic and carcinogenic to humans. The main factor responsible for Cd’s toxicity is its low excretion rate, resulting in an estimated biological half-life of 10–30 years. It mainly accumulates in the brain and the kidneys, which can be exacerbated by low levels of iron (Fe), so it particularly affects the elderly and pregnant women (Gumienna-Kontecka et al., 2018; Pavón et al., 2015). Lead is known for its toxicity to the nervous system, although it affects almost every human organ. Even at low levels of exposure, Pb can affect the cognitive and intellectual development of children (Pavón et al., 2015). On the other hand, Cu is an essential nutrient, which is involved in many enzymatic functions, production of neurotransmitters, and the synthesis of collagen and elastin (Gumienna-Kontecka et al., 2018; Konikowska and Mandecka, 2018). However, excess chronic exposure to Cu can result in liver damage, especially for Wilson’s disease patients and children with Indian childhood cirrhosis and idiopathic copper toxicosis (Council, 2001).

Considering the harmful effects of toxic elements potentially leaching from polymer materials, testing and monitoring these elements in mouthguards is critical for safety and quality control. To contribute to this effort, the presence of trace elements in commercially available mouthguards is being investigated for the first time. Accurate and highly sensitive (down to the parts per trillion level) inductively coupled plasma mass spectrometry (ICP-MS) was used to semi-quantitatively evaluate 75 elements, and then quantified Cd, Cu and Pb in 13 commercially available mouthguard samples. Furthermore, Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to further validate analyte concentrations found in a sample contaminated with Cu (Douvris et al., 2023; Hou and Jones, 2000).

Section snippets

Instrumentation

All elemental determinations were carried out using ICP-MS and ICP-OES. Instrumental operating conditions for the Agilent 8800 ICP-MS/MS (Agilent, Tokyo, Japan) used in this study are shown in Table 1. A SPS 4 automatic sampler, a Scott-type double pass spray chamber operated at 2 °C, and a Micromist concentric nebulizer compose the instrument’s sample introduction system. Single quadrupole mode was adopted in each analysis, using helium gas (≥ 99.999 % purity, Airgas) in the instrument’s

Exploratory semi-quantitative analysis, limit of detection and method validation

Trace element analysis of polymer materials is challenging, especially due to the difficulty in digesting polymers and converting them into a solution that is compatible with modern analytical instrumentation. Complete decomposition and low acidity of digests are some of the most important requirements for achieving accurate ICP-MS and ICP-OES determinations (Flores, 2014; Nóbrega and Donati, 2006). In this study, the mouthguard samples were subjected to closed-vessel microwave-assisted

Conclusions

For the first time, an investigation was conducted to reveal insights into the presence of toxic elements in commercially available mouthguards. An analytical method, using closed-vessel microwave-assisted digestion using diluted acid, and ICP-MS has been developed for these samples. The detection of Pb, Cd, and Cu in mouthguards raises significant health concerns. The findings of this study underscore the need for stricter quality control and regulation in the manufacturing of mouthguards to

CRediT authorship contribution statement

Jesse R. Ingham: Investigation, Formal analysis. George L. Donati: Writing – original draft, Supervision, Resources, Investigation, Formal analysis. Liliya Douvris: Formal analysis. Georgios Bartzas: Writing – review & editing, Investigation. Derek D. Bussan: Writing – review & editing, Writing – original draft, Investigation, Conceptualization. Chris Douvris: Writing – review & editing, Writing – original draft, Supervision, Resources, Methodology, Conceptualization.

Declaration of Generative AI and AI-assisted technologies in the writing process

The authors declare that no generative AI or AI-assisted technologies were used in the writing process of this manuscript.

Declaration of competing interest

There are no conflicts of interest to declare.

Acknowledgements

We are grateful to the New York Institute of Technology’s Department of Biological & Chemical Sciences for their financial support to this research. This work was also supported by the National Science Foundation’s Major Research Instrumentation Program (NSF MRI, grant CHE-1531698), and the Graduate School of Arts and Sciences at Wake Forest University. The authors would like to thank Kimberly Savaglio for her work with the graphical abstract.