Delayed (Type 4) allergic reactions are surprisingly common in the oral cavity. They may represent a lichenoid drug reaction to systemic medications or, occasionally, drug induced erythema multiforme, but the reactions associated with DG are usually of contact allergy nature.22,30,57,74,96 This means the soft tissue changes indicative of a hypersensitivity reaction usually occur exclusively in tissue that directly contacts the allergen. Such reactions may be seen in individuals who have received dental restorative materials to which they are sensitive (silver amalgam, cast metal-containing crowns, non- metallic restorative materials, cements, stainless steel orthodontic appliances, etc).75,76 Normally hypersensitivity reactions to dental materials create a localized DG.21 Generalized DG occurs when the individual is allergic to an ingredient of oral hygiene products such as toothpastes or mouthrinses, or in other oral products such as breath mints, dry mouth mints, chewing gum, colas, etc.29,30,37,75,77 These oral reactions are consistent with those found in contact dermatitis reactions except that oral reactions usually require a longer period of contact time before they become evident. We postulate this may be because saliva dilutes or removes the antigen or serves as a buffer or neutralizer to it. The superficial vascularity of oral mucosa also may induce rapid absorption and dispersion of the antigen. Since allergens in dental hygiene products have broad generalized gingival contact, lesions mimicking DG may be created. Saliva definitely plays a role in host defense against such allergens and there is an increased incidence of oral reactions in individuals with salivary hypofunction.20
For reasons that are not clear, our data and that of others suggests women are far more susceptible to these types of reactions than men (4:1 females versus males).60,74 DIF is not indicated because it is routinely negative.75 Toothpaste may be the most common oral contact allergen. Signs and symptoms of toothpaste hypersensitivity may include generalized or localized DG often occurring in the anterior maxillary gingiva. The lesions may be accompanied by mucositis, glossitis or cheilitis. Lips may be edematous and perioral dermatitis is an occasional finding.29,30,37 Dentifrice ingredients usually include flavoring agents, coloring agents, abrasives, detergents and preservatives.20,60 Although one may be sensitive to any of these components, the flavoring agents, especially cinnamic aldehyde and preservatives such as sodium benzoate or methylparaben, are the most common sensitization components.28,29,37 As mentioned, many patients are allergic to cinnamic aldehyde but other flavoring agents such as cinnamon oil, menthol, mint/spearmint/peppermint or oil of wintergreen have been increasingly found to cause such reactions.42 The reason for this is presently undetermined, but one theory suggests the increase in therapeutic agents in toothpastes (tarter control, whitening, anti-dental hypersensitivity products, antimicrobials, etc.) may require a significant increase in the flavoring agents used in order to sustain a pleasant taste.20 Allergens may also be found in chewing gum, candies, mints, colas and mouthrinses, again resulting in a generalized or localized DG, with or without involvement of other oral mucosa.30,75 Allergy to dental restorative materials usually causes localized desquamation in gingival tissues directly contacting the restoration.52,67,68,76,93
On occasion, patch testing may be required to identify the specific antigen inducing a contact reaction and biopsy may provide histologic evidence supporting the diagnosis.71,93 DIF is not indicated because it is routinely negative.75 It should be noted, however, diseased tissue such as found in DG may be especially susceptible to contact allergic reactions and one should remain alert to the possibility of two simultaneous etiologic factors contributing to the severity of the lesion.
Treatment of hypersensitivity reactions involves identification and discontinuance of the causative allergen. During the diagnostic phase, the dental practitioner is often asked to provide advice concerning a bland alternative to a toothpaste suspected causing hypersensitivity. Children’s or even infant’s toothpaste or dry mouth toothpastes are often acceptable alternatives. Patients should be requested to discontinue use of chewing gum, mints, dark colas, and mouthrinses during the diagnostic phase. Once the causative agent is determined, other products can be gradually added back into the patient’s customary routine one at a time in order to quickly determine whether or not a contact allergen is present in the product being added.