It is well-known that the anticonvulsant drug, phenytoin (PHT), induces gingival 
overgrowth as a side effect. The mechanism of PHT-induced gingival overgrowth, 
however, is not well understood. One reason for this is the lack of an adequate 
animal model for the PHT-induced gingival overgrowth. The purpose of this study 
was to establish a rat model of the drug-induced gingival overgrowth. 
Fourteen-day-old rats were randomly divided into 3 groups (5 rats/group). The 
control rats received only the vehicle. The rats in the experimental group were 
injected with 50 mg/kg per day (group L) and 100 mg/kg per day (group H) of PHT. 
They received a subcutaneous injection of vehicle or PHT twice a day for 42 
days. A charge-coupled device (CCD) laser displacement sensor was used for 
measurement of the severity of gingival overgrowth of the mandibles. There was 
no significant difference in the growth of rats between the PHT-injected and the 
control groups. The CCD laser displacement sensor can measure minute changes in 
the gingival overgrowth in rats, and a significant extension of the buccal 
gingiva was observed in groups L and H. Using the CCD sensor, it is possible to 
quantify the change in the gingiva under precise control of the PHT dose.