The existence and distribution of melanocytes in the periodontal ligament of the mongrel dog.

The existence and distribution of melanocytes in the periodontal ligament of the mongrel dog were investigated. Melanocytes were found in the periodontal ligament of the maxillary incisor and premolar segments. Melanocytes in the periodontal ligament varied in number, and generally appeared as dendritic or elongated cells with several, long cytoplasmic processes. These melanocytes were always distributed closer to the tooth root side of the periodontal ligament than the alveolar bone side, but did not contact the cementum. Melanocytes were longitudinally distributed in the apical half of the periodontal ligament. There were no findings suggestive of a relationship between melanocytes and epithelial rests of Malassez or other cellular elements of the periodontal ligament. Although some parts of the gingival mucosa of all dogs in this study showed pigmentation, no relationship was seen between melanocytes in the periodontal ligament and those in the gingival mucosa. This is the first report of melanocytes in the periodontal ligament under normal conditions.