Hyperplasia of gingival tissues without inflammation may occur in response to various medications.
Medications that particularly cause gingival hyperplasia include the following (1):
Valproate
High-dose oral contraceptives
Hyperplasia is characterized by diffuse, relatively avascular smooth or nodular enlargement of the gingiva, which may almost cover some teeth. The hypertrophied tissue can often be excised. If possible, substitutions are made for the offending medications. Scrupulous oral hygiene may minimize recurrence.
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Oral squamous cell carcinoma can also originate in the gingiva, causing apparent enlargement of gum tissue.
General reference
1. Hassell TM, Hefti AF: Drug-induced gingival overgrowth: Old problem, new problem. Crit Rev Oral Biol Med 2(1):103-37, 1991. doi: 10.1177/10454411910020010201