EXPOSURE TO 2,3,7,8-TETRACHLORODIBENZO-PARA-DIOXIN LEADS TO DEFECTIVEDENTIN FORMATION AND PULPAL PERFORATION IN RAT INCISOR TOOTH

A single dose of 1000 mug 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)/k g body weight was given to TCDD-resistant (Han/Wistar) young adult mal e rats. Changes in the skulls and the continuously erupting incisor te eth were evaluated 16 weeks after the administration of TCDD. The skul ls of the experimental rats (N = 11) were significantly smaller than t hose of the control rats (N = 11), and the upper and lower incisor tee th of all experimental rats were significantly thinner than the contro l rat teeth. The pulps of the lower incisors of all experimental rats were lingually exposed to the oral cavity at their incisal ends. Also in 3 cases the pulps of the upper incisors were exposed, but never in the control rats. Whereas the labial surfaces of the incisors of the c ontrol rats were brown, those of the experimental rat teeth appeared g reyish and mottled. Histological examination revealed that the pulp ch ambers in the incisal halves of the affected teeth were larger than no rmal, at the expense of the thickness of dentin. Towards the incisal t ooth ends, odontoblasts gradually lost their polarity and the pulp tis sue became necrotic. A dentin zone next to the pulp chambers was irreg ular. Lingual tapering of the teeth was pronounced, which gave them a mesiodistally flattened appearance. The superficial zone of the otherw ise regular enamel was poorly pigmented. In conclusion, a single injec tion of TCDD was shown to impair normal growth of the skull and inciso r tooth formation in rats. The small size of the incisors, their aberr ant shape and the defective dentin (and enamel) formation could be med iated by vitamin A metabolism, known to be interfered with by TCDD.