Effects of orthodontic forces on the morphology and diameter of Sharpey fibers of the alveolar bone of the rat.

There is little information available concerning the effects of functional and therapeutic forces on Sharpey fibers and adjacent bone matrix. In the present study, springs were placed between the left first and second maxillary molar teeth of rats and retained for 1, 2, 3, 4, or 5 days. The right side served as a control. Tissues from sham-operated, untreated animals were also studied. Maxillae were removed, fractured, rendered anorganic with sodium hypochlorite, and then examined by scanning electron microscopy (SEM). Some tissues were demineralized and examined by high-voltage electron microscopy (HVEM). Sharpey fibers were studied at the alveolar wall and at the midline of the interdental septum (intra-septal Sharpey fibers). In 5-day experimental tissues, SEM showed intra-septal Sharpey fibers had either a reduced number of, or lacked, unmineralized cores. Unit collagen fibrils in 5-day tissues viewed by HVEM were densely packed into Sharpey fibers which had no afibrillar areas. Sharpey fibers at the alveolar wall demonstrated no observable changes in morphology or in pattern of mineralization. After 5 days of spring placement, the mean diameters of intra-septal fibers were significantly less than those at the alveolar wall (p less than 0.001). The disparity in Sharpey fiber diameters of treated and untreated control animals suggests that untreated controls are essential to the design of studies of rodent tooth movement. This study suggests that orthodontic tooth movement produces changes in the morphology and mineralization patterns of Sharpey fibers which might affect the mechanical strength of the periodontium.