The site of remodeling of collagen in the periodontal ligament of the mouse incisor.

In an attempt to localize the site of remodelling of collagen in the periodontal ligament of the continuously erupting mouse incisor a radioautographic and stereologic investigation was undertaken. Grain distributions in radioautographs for light microscopy were studied at various time intervals after administration of [3H]-proline. The distribution of rough endoplasmic reticulum cisternae in fibroblasts and the incidence of collagen phagocytosis across the ligament were studied by means of stereologic methods at the electron microscopic level. No significant differences were found in half lives of [3H]-labelled substances among the various regions across the ligament. Rough endoplasmic reticulum cisternae within fibroblasts were distributed more or less uniformly throughout the entire width of the ligament. Analysis of the distribution of collagen phagocytosis, however, revealed that in the midregion of the ligament the amount of phagocytosed collagen was approximately four times as high as in the area adjacent to the tooth and about nine times as high as in the alveolar compartment. It is concluded that synthesis and turnover of total protein occurs throughout the periodontal ligament but that remodelling of collagen predominantly takes place in an intermediate area of the ligament.