Which anatomical areas are primarily affected by gingival hyperplasia due to phenytoin?

Gingival hyperplasia is a condition characterized by an abnormal increase in the size of the gums, and it can occur as a side effect of certain medications, including phenytoin, which is commonly used to manage seizures. The areas most commonly affected by phenytoin-induced gingival hyperplasia are typically the facial papillae of the anterior teeth.

This phenomenon occurs because the anterior regions have more keratinized tissue and are exposed to the effects of the drug in a way that promotes gingival overgrowth. The facial papillae, which are the gum tissue located between the teeth on the front side, see a concentration of reactive changes due to the interplay of irritation from plaque accumulation and the pharmacological effects of phenytoin.

While other areas of the mouth can certainly be involved, the anterior facial papillae are particularly susceptible due to their anatomical exposure and the presence of more vascular tissue, making them prone to hyperplastic changes in response to the medication. Hence, the specificity of the facial papillae in the anterior region is what makes this the correct answer.