Arrest of rat molar tooth development by lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin

The interference with tooth development by 2,3,7,8-tetrachlorodibenzo-p-dio xin (TCDD) was studied in dioxin-resistant Han/Wistar rats. Lactating dams were given a single dose of 50 or 1000 mug TCDD/kg body wt 1 day after deli very and the pup heads were analyzed radiographically or histologically at postnatal days 9 and/or 22. Of 19 animals studied histologically, 10 lacked one or more third molars, which were at the bud stage at the start of the experiment. A higher proportion of pups exposed to the higher dose (9/13) l acked third molars than those exposed to the lower dose (1/6) (27/52 and 2/ 24 teeth missing, respectively). Missing upper third molars (19/38) were mo re frequent than were lower (10/38). The development of the third molars pr esent was retarded. The root tips of the more advanced first and second mol ars were prematurely closed and root formation was arrested, but eruption w as not affected. Dentinogenesis of the continuously erupting lower incisor teeth was preeruptiveIy arrested because of pulpal cell death. All the teet h of the control rat pups developed normally. In contrast to the control pu ps, none of the 11 experimental pups examined radiographically (6 exposed t o the higher dose and 5 to the lower) showed mineralization of their third molar cusps. The results show that the effects of TCDD on rat tooth develop ment depend on not only the dose but also the tooth type and developmental stage. Inasmuch as early tooth development is under the control of inductiv e interactions between the epithelium and the mesenchyme, the interference by TCDD with tooth morphogenesis with the consequent arrest of development is likely to involve epithelial-mesenchymal signaling. (C) 2001 Academic Pr ess.