Junctions between fibroblasts in mouse periodontal ligament

Quantitative evaluation of the distribution of intercellular junctions between fibroblasts in the incisor and molar periodontal ligament of the mouse indicated that structures resembling gap junctions are more frequent on the tooth side of this tissue than on the bone side. The difference was particularly evident for the ligament of the continuously erupting incisor. Here, the numerical density of gap junction‐like structures was estimated to be approximately 20 per fibroblast in the connective tissue adjacent to the cementum and 4 per fibroblast in the tissue along the alveolar bone. With regard to the distribution of adhaerens‐type junctions less variation was observed between the various zones of the incisor and molar ligament. For the incisor the average number of adhaerens‐type junctions was calculated to be in the order of 30 junctions per cell in the tooth‐related compartment and 20 junctions per cell in the alveolar compartment. Although in the molar intercellular junctions were observed throughout the entire width of the ligament, in the incisor they were confined to the two main connective tissue compartments, i.e. the one of the tooth side which moves with the erupting tooth in the direction of the oral cavity, and the one of the bone side which remains stationary with respect to the alveolar wall. In the transitional area between the two latter compartments junctions were very sparse. It is suggested that the distribution pattern of intercellular junctions between fibroblasts in mouse periodontal ligament reflects functional differences among the cells in the various regions of the tissue, differences that are possibly related to processes involving the movement of cells and the metabolism of collagen.