DCA02AR Allergic Reactions in Dental Patients _ _________________________________________________
TYPE III REACTIONS Type III hypersensitivity reactions are immune complex medi- ated [13]. The unique feature of these reactions is the formation of antigen-antibody complexes in the blood vessels or tissues. Examples of disorders associated with type III hypersensitivity reactions include systemic lupus erythematosus, rheumatoid arthritis, serum sickness, and glomerulonephritis. These dis- eases are chronic in nature, and patients may be taking immu- nosuppressive medications that can predispose them to the development of opportunistic infections. In addition, patients with these disorders may develop complications of xerostomia (dry mouth) and keratoconjunctivitis sicca (dry eyes). TYPE IV REACTIONS Type IV hypersensitivity reactions do not involve the immuno- globulins. Unlike type I hypersensitivity reactions, the clinical manifestations of type IV reactions are delayed for 48 to 72 hours following exposure to a given antigen [14]. These reac- tions are the result of the antigenic response of T-lymphocytes, monocytes, and macrophages. Contact dermatitis is a classic example of a type IV hypersensitivity reaction. Contact Dermatitis The most common triggers of contact dermatitis are rubber products, metals, and medications that are applied directly to mucosal or cutaneous tissues. There are two main forms: irritant contact dermatitis and allergic contact dermatitis. Irritant contact dermatitis represents approximately 80% of the cases of contact dermatitis. It is characterized by a general- ized inflammatory reaction to substances that come in direct contact with the skin [15]. Among dental professionals, irritant contact dermatitis may occur as a reaction to the chemicals in latex gloves, as will be discussed in detail later in this course [16]. Irritant contact dermatitis is limited to the area affected by the specific substance (e.g., the hands after wearing latex gloves) [17]. Treatment of irritant contact dermatitis involves identification and avoidance of the triggering substance. Oral antihistamines and topical corticosteroids may promote heal- ing and alleviate symptoms. Allergic contact dermatitis and irritant contact dermatitis have similar clinical presentations, but their pathogenesis differs considerably. The first phase of allergic contact dermatitis is hapten binding. Haptens are low-molecular-weight molecules capable of reacting with protein and peptide molecules recog- nized as antigens [18]. Hapten-specific T-cells develop in some individuals and produce a hypersensitivity response that results in cutaneous inflammation [19]. It is this specific T-cell medi- ated response that causes the tissue damage associated with allergic contact dermatitis.
The development of allergic contact dermatitis occurs over a period of time. There is a sensitizing (afferent) phase lasting weeks to months, during which repeated exposure to a par- ticular substance stimulates the development and maturation of the hapten-specific T-cells. This is followed by the efferent or elicitation phase, during which the clinical manifestation of allergic contact dermatitis will recur with continued exposure to the same substance [20]. Identification of the substance causing allergic contact der- matitis requires patch testing. This involves the application of potential allergens to the patient’s skin, usually on the back. The testing sites are evaluated after two days, and a positive reaction, characterized by swelling, redness, and blistering, identifies the offending substance(s). Healing of allergic contact dermatitis can take several weeks. Severe cases may require the short-term use of oral corticoste- roids (e.g., prednisone) to reduce the inflammation and the associated symptoms.
ALLERGIES TO MEDICATIONS USED IN DENTISTRY
Analgesics, antibiotics, and local anesthetics are the medica- tions most commonly used in dental treatment, and allergic reactions, though infrequent, can occur with any of these. LOCAL ANESTHETICS Many dental procedures require the use of local anesthetics. Although these medications are generally very safe, allergic reactions can occur to any component of the formulations. Local and topical anesthetics are chemically classified as either amides or esters. The most frequently used injectable local anesthetics today, including lidocaine, mepivacaine, and bupi- vacaine, are all amides. Articaine is also classified as an amide but has the unique feature of the inclusion of an ester group. Allergies to amide local anesthetics have been very rare; most allergic reactions occur in response to ester types. Ester-type local anesthetics are metabolized to para-aminobenzoic acid, which has allergenic properties [21]. While the ester anesthetic procaine is no longer used in North America, benzocaine is a widely used ester topical anesthetic applied to the oral mucosa prior to the injection of a local anesthetic. An allergic reaction to benzocaine is usually limited to the site of its application and can manifest as an area of erythema or ulceration. It is important to remember that most adverse reactions to local anesthetics are not allergic reactions. More commonly, inadvertent intravascular injection of a local anesthetic can occur and is toxic to cerebral tissues. This can cause dizziness, slurred speech, seizures, and nausea. When a patient indicates
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