Vitamin C deficiency (scurvy) impairs collagen synthesis, which is essential for maintaining the integrity of connective tissues, including the gums. This leads to fragile capillaries, resulting in swollen, bleeding gums and ultimately loose teeth due to weakened periodontal support. These oral manifestations are hallmark signs of scurvy. The other options (atrophic glossitis, oral leukoplakia, pigmented macules) are not specifically related to vitamin C deficiency but to other nutritional or pathological conditions.

Reference: Oral Pathology, Neville et al., 4th Edition.