Pathological evaluation of the effects of intentional disocclusion and overloading occlusion in odontogenesis disorders in N-methylnitrosourea-treated hamsters

This study compares the: effects of disocclusion and overloading occlusion on dental lesions. Ten-day-old Syrian hamsters were divided into 4 groups: group I, untreated animals; group II, animals whose hemilateral incisors we re disoccluded; group III, N-methylnitrosourea (MNU)-treated animals; and g roup IV, MNU-treated animals whose hemilateral incisors were disoccluded. T he ipsilateral maxillary and mandibular incisors were repetitively cut with diamond discs. The hamster is easier to anesthetize. Animals received a 0. 2% solution of MNU (10 mg/kg body weight) intragastrically twice a week for 16 wk. All the cut mandibular incisors and the MNU-treated uncut mandibula r incisors showed lack of iron deposition on the enamel surface. The erupti on rate was significantly higher in the cut disoccluded incisors of groups II and TV (p < 0.05) and significantly lower in the uncut overloaded inciso rs of groups IV and IV (p < 0.05). In the cut mandibular incisors of group IV, the degree of the disturbance of odontogenesis and the atypical prolife ration of odontogenic epithelium were more prominent (p < 0.02), and the de ntal lesions occurred earlier. Histologically, the disturbed Hertwig's epit helial sheath and the Hertwig's epithelial sheath-like transformed U-shaped part and enamel organ seemed to lead to disturbances of amelogenesis and d etinogenesis as well as to atypical proliferation of odontogenic epithelium nests. Thus, this method of disocclusion of the incisors of rodents may re present a useful model for the investigation of the effects of various agen ts on tooth formation over a short experimental period.