The oral mucosa including the lips is constantly exposed to several noxious stimuli, irritants and allergens. However, oral contact pathologies are not frequently seen because of the relative resistance of the oral mucosa to irritant agents and allergens due to anatomical and physiological factors. The spectrum of signs and symptoms of oral contact allergies (OCA) is broad and a large number of condition can be the clinical expression of OCA such as allergic contact stomatitis, allergic contact cheilitis, geographic tongue, oral lichenoid reactions, burning mouth syndrome. The main etiological factors causing OCA are dental materials, food and oral hygiene products, as they contain flavouring agents and preservatives. The personal medical history of the patient is helpful to perform a diagnosis, as a positive history for recent dental procedures. Sometimes histology is mandatory. When it cannot identify a direct cause of a substance, in both acute and chronic OCA, patch tests can play a pivotal role in the diagnosis. However, patch tests might have several pitfalls. Indeed, the presence of metal ions as haptens and specifically the differences in their concentrations in oral mucosa and in standard preparation for patch testing and in the differences in pH of the medium might result in either false positiveegative reactions or non-specific irritative reactions. Another limitation of patch test results is the difficulty to assess the clinical relevance of haptens contained in dental materials and only the removal of dental materials or the avoidance of other contactant and consequent improvement of the disease may demonstrate the haptens’ responsibility. In conclusion, the wide spectrum of clinical presentations, the broad range of materials and allergens which can cause it, the difficult interpretation of patch-test results, the clinical relevance assessment of haptens found positive at patch test are the main factors that make sometimes difficult the diagnosis and the management of OCA that requires an interdisciplinary approach to the patient.
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