Toxicological Sciences 69, 482-489 (2002)
Copyright © 2002 by the Society of Toxicology
SYSTEMS TOXICOLOGY |
Response of the Incisor Tooth to 2,3,7,8-Tetrachlorodibenzo-p-dioxin in a Dioxin-Resistant and a Dioxin-Sensitive Rat Strain
,¶,1
* Department of Pedodontics and Orthodontics, Institute of Dentistry, University of Helsinki, Helsinki, Finland;
Department of Oral Pathology, Institute of Dentistry, University of Helsinki, Helsinki, Finland;
Department of Environmental Health, National Public Health Institute, Kuopio, Finland; and
Department of Oral and Maxillofacial Diseases, Helsinki University Central Hospital, Helsinki, Finland; and
¶ Department of Pathology, Helsinki University Central Hospital, Helsinki, Finland
Dioxins are ubiquitous environmental pollutants that afflict developing teeth. To find out if the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the continuously erupting rat incisor is associated with the sensitivity to TCDD acute lethality and to see the histological basis for any macroscopic findings, we exposed 25 resistant Han/Wistar (Kuopio; H/W) and 20 sensitive Long-Evans (Turku/AB; L-E) female rats to total doses of 0.17, 1.7, 17, and 170 (only H/W rats) µg/kg TCDD. Each dose group comprised five animals. The treatment was started when the rats were 10 weeks old and continued for 20 weeks. The exposure time covered two life cycles of the incisor. Stereomicroscopic examination of the dissected mandibles showed color defects and pulpal perforation of the lower incisors at 17 and 170 µg/kg TCDD. Tissue sections revealed odontoblastic and pulpal cell death and the consequent arrest of dentin formation at the incisal tooth end at the same doses. H/W rat incisors were affected closer to the germinative tooth end at 170 than at 17 µg/kg TCDD, resulting in a larger perforation. In accordance with the enamel discoloration, the postsecretory enamel organ underwent, albeit inconsistently, precocious squamous metaplasia with pronounced proliferation. Thus, both the mesenchymal and, to a lesser extent, epithelial elements of the forming tooth were affected dose-dependently at relatively high doses of TCDD. Similar responses in both strains implied that the impaired formation of the incisor tooth, at least of its mesenchymal elements, is not associated with the differential resistance of H/W and L-E rats to TCDD acute lethality.
Key Words: dioxins; 2,3,7,8-tetrachlorodibenzo-p-dioxin; rat incisor; dentin; enamel; odontoblasts; enamel organ; dental defect; dose response; aryl hydrocarbon receptor.
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