Formation of multinucleated fibroblasts in the periodontal ligaments of old mice.

Multinucleated cells were observed to account for more than 17% of all cells in the periodontal ligament (PDL) of 20-month-old mice. The number of nuclei contained in sections of these cells ranged from 2 to 17, with over 50% of the multinucleated cells containing four or more nuclei within the plane of section. The multinucleated cells contained several cytoplasmic features resembling those previously described by the authors as characteristic of PDL fibroblasts. The multinucleated cells did not resemble osteoclasts or foreign body giant cells. It is suggested that fibroblasts develop a tendency to fuse and form multinucleated cells in the aged PDL. Similar cells were not observed in the PDL of young (5-week-old) mice or in the tail tendon at any age.