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Pathological Evaluation of the Effects of Intentional Disocclusion and Overloading Occlusion in Odontogenesis Disorders in N-Methylnitrosourea-Treated Hamsters

Department of Oral Pathology, Hokkaido University, School of Dentistry, Kita 13, Nishi 7, Kita-Ku, Sapporo (060), Japan

T. Zuka

Department of Oral Pathology, Hokkaido University, School of Dentistry, Kita 13, Nishi 7, Kita-Ku, Sapporo (060), Japan

M. Shindoh

Department of Oral Pathology, Hokkaido University, School of Dentistry, Kita 13, Nishi 7, Kita-Ku, Sapporo (060), Japan

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 were disoccluded; group III, N- methylnitrosourea (MNU)-treated animals; and group IV, MNU-treated animals whose hemilateral incisors were disoccluded. The 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 mandibular incisors showed lack of iron deposition on the enamel surface. The eruption rate was significantly higher in the cut disoccluded incisors of groups II and IV (p < 0.05) and significantly lower in the uncut overloaded incisors of groups II and IV (p < 0.05). In the cut mandibular incisors of group IV, the degree of the disturbance of odontogenesis and the atypical proliferation of odontogenic epithelium were more prominent (p < 0.02), and the dental lesions occurred earlier. Histologically, the disturbed Hertwig's epithelial sheath and the Hertwig's epithelial sheath-like transformed U-shaped part and enamel organ seemed to lead to disturbances of amelogenesis and detinogenesis as well as to atypical proliferation of odontogenic epithelium nests. Thus, this method of disocclusion of the incisors of rodents may represent a useful model for the investigation of the effects of various agents on tooth formation over a short experimental period.

Key Words: Disturbances in odontogenesis • eruption rate • incisor • odontogenic tumor • occlusion • hamster • N-nitrosomethylurea

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