What causes the periodontal ligament to become narrower in labially positioned mandibular canines as a person ages?

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Accumulation of cementum and bone tissueProliferation of gingival epithelial cells downwardFormation of gingival cysts originating from residual cellsChange in the function of horizontal and oblique periodontal fibers

Explanation

The narrowing of the periodontal ligament in labially placed mandibular canines with age is primarily due to the buildup of cementum and bone. Other options such as epithelial down growth, gingival cyst formation, or fiber function reversal do not contribute to this specific change.