Introduction Ossification of the posterior longitudinal ligament in the spinal ligament compresses the spinal cord, causing various spinal nerve diseases. The ligament tissue is an important connective tissue in the joints, teeth, and spine, which, when torn and damaged, reduces the range of movement. Case presentation We report the treatment of periapical periodontitis and tooth preservation in a 41-year-old Japanese woman previously diagnosed with ossification of the posterior longitudinal ligament. She presented with widespread pain from the paranasal sinuses to the head caused by the onset of periapical periodontitis of the upper front tooth. Discussion The patient received an oral zinc supplement, which resolved periapical periodontitis over a 2-year follow-up period. Conclusion The findings from this case imply that, when patients with ossification of the posterior longitudinal ligament develop periapical periodontitis, they should be tested for zinc deficiency.