Objectives: Phenytoin (PHT) is well known to induce gingival overgrowth in humans. The mechanism of PHT-induced gingival overgrowth, however, is not well understood. In order to evaluate the mechanism of the PHT-induced gingival overgrowth, the replication of gingival overgrowth by the animal model is important. The purpose of this study was to establish a rat model of drug-induced gingival overgrowth by measuring overgrowth with the Charge Coupled Device (CCD) laser displacement sensor. Methods: 14-day-old rats were randomly divided into 3 groups (5 rats/group). Control rats received vehicle only. The low dose PHT treated rats (group L) received 50 mg/kg/day of PHT and high dose PHT treated rats (group H) received 100 mg/kg/day. The rats received subcutaneous injection twice a day for 42 days. The dose of PHT increased every week and the final dose of PHT in group L and group H were 100 and 150 mg/kg respectively. The CCD laser displacement sensor was used for the measurement of severity of gingival overgrowth of mandibles. Results: There was no significant difference in growth of rats between PHT-injected and control groups. Blood levels of PHT was increased dose-dependently. There was a significant extension of buccal gingival of the molar in group L and H. Histologicaly, the region of gingival overgrowth consisted of bundles of collagen fibers. The surface epithelium was markedly hyperplastic and showed long epithelial ridge extending into the underlying connective tissue. Conclusions: The CCD laser displacement sensor used in this study can measure minute changes of the gingival overgrowth in rats. Using this sensor, it is possible to quantify the change of gingiva under the precise control of the dose of PHT. The results indicated that gingival overgrowth was severe in correlation with the dose of PHT.

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