Which of the following oral conditions is LEAST likely to be infectious in origin?

An irritation fibroma is a reactive fibrous hyperplasia caused by chronic mechanical irritation, not infection. The others are infections: periapical abscess (bacterial), ANUG (fusospirochetal bacteria), and candidiasis (fungal).Other options: Periapical abscess, ANUG, and candidiasis are all microbial infections.Key exam takeaway: Fibroma = reactive/traumatic, not infectious; distinguish reactive lesions from true infections.