What is the primary cause of gingival hyperplasia in patients taking phenytoin (Dilantin)?

Drug-induced gingival hyperplasia (DIGH) caused by phenytoin results from the drug's effect on gingival fibroblasts — it stimulates fibroblast proliferation and collagen synthesis while reducing collagenase activity, leading to excess connective tissue accumulation. The fibroblast subpopulations most susceptible to phenytoin's effects are disproportionately represented in gingival tissue. Poor oral hygiene exacerbates the condition (plaque-induced inflammation synergizes with the drug effect), but excellent oral hygiene alone does not prevent hyperplasia. Management includes meticulous oral hygiene, professional cleaning, and — in severe cases — gingivectomy or periodontal surgery. An alternative anticonvulsant should be considered if possible.