What is the least commonly lost tooth due to periodontal disease?

The MANDIBULAR CANINE is the tooth LEAST commonly lost due to periodontal disease because it has the LONGEST ROOT of all teeth, providing excellent bone support, favorable root-to-crown ratio, and good periodontal prognosis. The teeth most commonly lost to perio disease are upper molars (furcation involvement), lower molars, and upper incisors. Canines (especially mandibular) are the most periodontally stable. A is correct.