A 15-year-old female presents lethargic with blood pressure 80/60 mmHg, hyperpigmentation of the skin and oral mucosa, and weight loss. What is the most likely diagnosis?

Addison disease (primary adrenal insufficiency) presents with the classic triad of hyperpigmentation, hypotension, and fatigue/weakness. The bronze or brown hyperpigmentation occurs in sun-exposed areas, skin folds, scars, and notably in the oral mucosa (gingiva, buccal mucosa, lips) due to elevated ACTH stimulating melanocytes. Hypotension (low blood pressure) results from aldosterone deficiency causing sodium wasting. This is a critical diagnosis in dentistry because these patients are at risk for adrenal crisis under the stress of dental procedures and may require steroid supplementation.