Which drug is most commonly associated with causing gingival enlargement as a side effect, and through what mechanism does this occur?

Gingival enlargement is a well-recognized side effect of three major drug categories: anticonvulsants (phenytoin), immunosuppressants (cyclosporine), and calcium channel blockers (nifedipine, amlodipine, verapamil). Phenytoin stimulates gingival fibroblasts to overproduce collagen. Cyclosporine causes both fibroblast stimulation and inflammatory cell infiltration. Calcium channel blockers reduce cation influx in fibroblasts, leading to altered collagen metabolism. Poor oral hygiene exacerbates enlargement for all three drug types. Phenytoin is the classic and most cited example in dental board examinations.