From Volume 14, Issue 2, April 2021 | Pages 105-107
The nature of the type of treatment carried out in orthodontics frequently exposes clinical staff to potential occupational hazards. A lesser-known risk includes hypersensitivity to composite resins and bonding materials, as well as the permeability of gloves to these materials. This article highlights the importance of care when handling composite materials, and suggests methods to reduce potential exposure.
Exposure to occupational hazards in orthodontics is a daily occurrence and includes a range of physical, biological and chemical risks.1,2 Originally proposed by Pirquet in 1906, the term ‘allergy’ describing the influence of an external factor to the immune system has evolved over time.3 Allergens are antigens that cause allergy, and it is the immune response to them that can cause damage. The prevalence of dermatoses for dental personnel has been reported to vary between 15% and 33%, with common irritants being latex, methyl methacrylate, cyanoacrylates and certain glove constituents.4,5
Despite knowledge of various occupational hazards, there has been little awareness of occupational hypersensitivity to resin composites and bonding agents in orthodontics and general dentistry. The purpose of this article is to raise awareness of this particular vulnerability and discuss clinical options that can be easily applied to daily practice to minimize potential exposure.
Four types of hypersensitivity (Table 1) were originally classified by Gell and Coombs in 19636 and remain commonly used today. The classification stems from the concept of immediate and delayed forms of allergic reaction and it is important to consider that clinical disease may involve more than one of the mechanisms.
| Allergy type | Mediators | Examples of reactions | Description |
|---|---|---|---|
|
Type I
|
IgE | Bronchospasm asthma Allergic rhinitis and conjunctivitis (hayfever) Urticaria (hives) Angioedema Anaphylaxis | Immediate response triggered by clustering of IgE receptors on mast cells and basophils through cross-linking. Subsequent mediator release occurs, which helps orchestrate a defensive acute inflammatory reaction, eg bronchoconstriction and vasodilatory effects. Diagnosis by skin prick testing or enzyme-linked immunoassay |
| Type II Antibody-dependent cytotoxic hypersensitivity | IgM, IgA or IgG Complement | Drug allergies Rhesus incompatibility Autoimmune disorders | IgM, IgA or IgG antibodies bind to antigen on a target cell. Complement pathway activated. Coombs test used for Rhesus antibody detection |
| Type III Immune complex disease | IgG Complement Neutrophils | Arthus reaction Immune complex glomerulonephritis Serum sickness | Exposure to excess antigen over a protracted period, eg persistent infection, or repeated contact with environmental agents. Union of antigens and antibodies form a complex that results in acute inflammatory reactions, eg local ischaemia |
| Type IV Cell mediated delayed-type hypersensitivity | T-cells | Contact dermatitis Inflammatory bowel disease psoriasis Lichenoid reactions | Exaggerated interaction between antigen and ordinary cell-mediated immune mechanisms. Memory T cells (following priming) and antigen-presenting cells undergo proliferation when antigen has been recognized. Cytokines mediate response. T cells produce pro-inflammatory cytokines that induce keratinocyte apoptosis. |
Developed following the introduction of the acid-etch technique,8 composite resin and bonding agents are the most commonly used substances in orthodontics for bonding of fixed appliances and bonded retainers. Following the application of an etchant on the enamel, a bonding agent, which may contain 2-hydroxyethyl methacrylate (HEMA) and other monomers, provides an interface between the micro-undercuts on the etched enamel and the composite layer.9 The composition of the uncured hydrophobic composite includes different resin methacrylate monomers. These include tri-ethylene glycol dimethacrylate (TEDGMA), urethane dimethacrylate (UDMA), bisphenol A glycidyl methacrylate (BisGMA) and inert filler particles (eg silica, quartz, barium, or strontium derivatives). The curing process to enable polymerization involves light-activation commonly with 470-nm visible blue light or dual-cured light and chemical activation (with photo initiator).
A common practice for many orthodontic professionals is to either manipulate or remove excess composite or bonding material from an instrument directly onto a gloved hand. However, there is little awareness of the cumulative effects from this seemingly insignificant habit.
Previous studies have shown permeability of various medical gloves to acrylic monomers, including nitrile and synthetic gloves.10–14 Laboratory tests have measured the breakthrough time as the time elapsing from initial contact of the glove to the time when the chemical is detected on the other side of the glove. The permeation rate of the material has been represented by the slope of the curve resulting from plotting the accumulated amount of a chemical in the collection medium against time. Munksgaard11 tested five types of latex and nitrile gloves against TEGDMA and HEMA with dilutions of ethanol and acetone. Table 2 shows the breakthrough time depending on dilution medium. The permeation rate of HEMA was shown to be generally faster than that of TEGDMA. These results highlight the short length of time needed for penetration of material through a glove during treatment.11
| NITRILE | LATEX | |
|---|---|---|
| HEMA | 9.9 min (ethanol) |
4.8 min (ethanol) |
| TEDGMA | 9.9 min (ethanol) |
4.8 min (ethanol) |
Although not widely reported, Type IV (cell-mediated) delayed hypersensitivity to dental composites and resin-bonding agents, manifesting as contact dermatitis or delayed hypersensitivity, have been published.15–18 A cross-sectional questionnaire-based study of Swedish dentists noted a prevalence of methacrylate allergy of 0.9% in those sampled, manifesting as hand eczema.19 No serious medical, social or occupational consequences were found in most cases in this study. A study by Wrangsjo and colleagues20 of dental personnel referred to the Department of Occupational and Environmental Dermatology in Stockholm found that 22% of patients tested had positive reactions to (meth)acrylates. Reactions to HEMA, EGDMA and MMA were most frequent and females were shown to be more likely to exhibit sensitivity reactions.
Furthermore, there has also been a documented case of occupational allergic contact dermatitis to light-cured hybrid glass ionomer through daily manual mixing.21 Some of those affected by contact dermatitis were reported to be unable to continue in their occupation.16
There are a variety of simple and practical methods to reduce exposures to risks of composite hypersensitivity as outlined below.
Removal of excess composite following placement of an orthodontic bracket is commonly carried out with a probe or the end of a positioning instrument. Placement of a cotton wool roll/gauze in the non-dominant hand, either held between fingers or taped on the dorsum of the hand using surgical tape (Figure 1), can provide easy access to a surface for composite deposition. Alternatively, the cotton wool roll/gauze can be held by the assistant. However, care must be taken with potential sharps injuries. This ensures that any resin or bonding material is consistently collected on a surface away from the operator or assistant.
Traditional methods of bonding orthodontic brackets commonly involve the manual application of composite material onto the bracket base. Distribution of the material may involve the use of a gloved digit, which may increase permeation. Pre-coated brackets could eliminate the need for composite loading and distribution onto the bracket by the assistant. A study has shown no significant difference in failure rate in comparison to conventional non-pre-coated brackets.22
A further development from pre-coated orthodontic brackets are flash-free brackets, which have been designed to eliminated the flash removal process between placement and curing. A fibre mat containing an adhesive formulation is incorporated on the bracket base that facilitates conformation of the bracket onto the tooth during placement with no resultant excess material. Significant reduction in chairside time, improvements in marginal integrity and potential plaque accumulation with flash-free brackets compared to conventional pre-coated brackets have also been found.23 This method further reduces contact of the operator during bracket placement.
First described by Silverman and colleagues in 1972,24 the indirect bonding technique involves placement of orthodontic brackets on plaster casts in the optimal position, ahead of the bond up appointment and subsequent construction of bonding trays for the predetermined brackets to be transferred precisely intra-orally.
Evolving technology has enabled use of 3-dimensional (3D) data capture with intra-oral scanners or model scanners and computer-aided design (CAD) software to make the bracket placement procedure completely virtual. Once the desired bracket positions have been determined, an indirect bonding tray (Figures 2 and 3) can be produced using a 3D printer.25,26 Although this technique does not eliminate contact with composite resin, it may reduce operator exposure to the material owing to the interface provided by the pre-fabricated splint. Any excess adhesive (flash) will be cured during the indirect bonding procedure resulting in the composite resin being less allergenic.
Developed by Wilson and Kent in 1972,27 glass ionomer cement (GIC) is a plastic restorative material resulting from an acid–base reaction. Composed of calcium fluoro-aluminosilicate glass particles with strontium and itaconic acid copolymer solution in water with tartaric acid, GIC has the ability to bond chemically to enamel.9 More commonly used for cementation of orthodontic bands, the benefits of GIC include the release of fluoride ions and good aesthetics.
Resin-modified GIC (RMGIC) is composed of the same substances as conventional GIC, with the addition of HEMA, bis-GMA and other photo-initiators.9 The benefit of the material is its command-set nature; however, risks of sensitivity to the uncured resin can, therefore, still apply.
As permeability is not immediate, it may be advisable to change gloves promptly following contact with composite or resin-bonding materials. Strategic glove material selection may also be considered, as evaluated by Andreasson and colleagues.13 Effective handwashing following direct skin contact of such materials should also be carried out. Should any suspicion of hypersensitivity be noted, early self-referral to occupational health and patch-testing should be sought.
Occupational hypersensitivity to composite resin and bonding agents should be a daily consideration for all staff, and it may impact on the ability to undertake clinical practice. A minimum-contact technique for uncured materials should, therefore, be widely promoted and employed to ensure safe handling of materials and reduction in occupational risk.
