ABSTRACT
Teeth The teeth and oral cavity are inspected routinely in toxicology studies with the AP rat but, apart from the tongue, only tissues which appear abnormal are sampled for histological examination. The most common change seen in the teeth is malocclusion, which occurs in 1 per cent of animals, and broken incisors which are even less frequent. Both conditions interfere with feeding and usually necessitate sacrifice of the affected animals. Dietary fibres which penetrate the gingiva can give rise to gingivitis and periodontitis, and occasionally abscesses. Such changes have been seen rarely, except in a few studi es where the animals were fed powdered diet rather than the usual pelleted diet Similar changes were reported by Robinson (1985). The dietary pellets fed to AP rats are firm, but not hard, and probably reduce dental problems by providing appropriate wearing of the occlusal surfaces and preventing overgrowth. Very hard diets can produce a variety of problems due to abrasive loss of enamel and dentin (Bossman et al., 1981). Histological examination of teeth has been done in the AP rat in several studies which were specifically designed to examine teeth. These were short term studies and only a few minor changes were seen, including some deposition of secondary dentin and pulpal stones. In old AP rats the incisors may become discoloured due to porphyrin deposits in the enamel.
