Nothing to smile about: Drug-induced tooth discolouration

Tooth discolouration is usually described as extrinsic or intrinsic, based on the location of the stain.1'2 Extrinsic stains are typically superficial and occur after teeth have erupted into the oral cavity. Generalized intrinsic or permanent discolouration is indicative of a disruption of normal tooth development, whereas localized intrinsic staining of 1 or 2 teeth can occur before or after teeth have erupted.2,3 Dental stains can be attributed to many factors (Table 1). Although not common, some medications are associated with tooth discolouration (Table 2). Each tooth has an exposed portion or crown, root(s) that extend into the alveolar bone of the mandible or maxilla, and a neck where these 2 structures meet. The tooth is comprised of enamel, den tin, pulp, and cementum - the first 3 of these are found in the crown.4 Any structural changes involving the crown can affect the transmission and reflection of light by the tooth and result in a colour change.1 Enamel, the outermost exposed layer, is the hardest tissue in the human body and does not regenerate once the tooth has erupted and is fully formed. Normally, enamel consists of minerals (96%), water (2%), protein (1%), and other materials ( 1%). Any changes to these components can affect the strength and appearance of the enamel. The strength and resistance of enamel is due to the presence of crystallite formations consisting of carbonate-substituted hydroxyapatite molecules. One-third of children treated with tetracycline experienced tooth staining.2 The drug diffuses into the tooth and binds irreversibly with calcium ions, forming a stable complex in the hydroxyapatite crystals located in the dentin and the enamel.1"3 The degree of discolouration is related to the dose and duration of exposure to tetracycline.1,3,6 It also occurs more frequently when cumulative doses exceed 3 g or the length of treatment extends beyond 10 days.2 Newly erupted teeth will usually present with a bright yellow band.3 On exposure to sunlight, the tetracycline crystals in the teeth undergo a photochemical reaction and gradually darken to a grey or red-brown colour.1,3,7 Other tetracycline derivatives are associated with different colour changes.