[Type 1 allergy to formaldehyde in root canal sealant after dental treatment: two case reports and review of the literature].

Two cases of generalized urticaria after the dental treatment were reported. These cases had clearly positive RAST to formaldehyde, whereas skin prick testings were negative. We diagnosed them as type I allergy due to formaldehyde. Immediate type formaldehyde allergy is not widely recognized as a major allergic complication of dental treatment. Previous reports of immediate allergy to formaldehyde in dental treatment were reviewed. The characteristics are the followings, first, it tends to represent severe symptom like anaphylaxis, second, the symptom often appears a few hours later than usual cases of anaphylaxis. Allergen tests show highly positive ratio to formaldehyde RAST, whereas skin prick test often shows false negative. Assessment of specific IgE to formaldehyde is a useful and a diagnostic measurement, and is recommended in patients at risk.