Unipolarity of fibroblasts in rodent periodontal ligament

In order to investigate whether fibroblasts in rodent periodontal ligament have a structural polarity, the position of the Golgi apparatus or the centriolar region in the cells was studied using light and electron microscopy. It appeared that, in the periodontal ligament of continuously erupting mouse and rat incisors, centrioles in fibroblasts on the tooth side of the ligament are preferably located in the anterior (occlusally directed) part of the cytoplasm. Polarity of fibroblasts in a single direction was less pronounced or absent on the bone side of the tissue. In the mouse, fibroblasts in the connective tissue adjacent to the incisor also contained an extensive system of cytoplasmic microtubules, whereas in the fibroblasts on the bone side of the ligament microtubules were less frequent. Unipolarity of fibroblasts was also observed in the periodontal ligament of the rat maxillary first molar, which is characterized by a limited eruption. Here, the Golgi region was usually situated in that pole of the cells that was directed towards the alveolar wall and the occlusal plane. It is suggested that structural polarity of fibroblasts in the periodontal ligament of rodent teeth is associated with orientation of functional activities of the cells, such as unidirectional movement or unidirectional deposition or phagocytosis of collagen.