Coordinated regulation of endothelial and fibroblast cell proliferation and matrix synthesis in periodontal ligament adjacent to appositional and resorptive bone surfaces

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Abstract
Little is known about the remodeling of blood vessels and soft connective tissue or the proliferation of endothelial cells in the periodontal ligament (PL) of teeth undergoing physiological drift. To determine whether there is evidence for coordinated regulation of endothelial cell and fibroblast proliferation and matrix synthesis in sites within the PL adjacent to bone‐appositional (A) and bone‐resorptive (R) surfaces, the PL in mouse mandibular molar was subdivided into A and R sectors on the basis of 3H‐proline incorporation into alveolar bone. Computer‐assisted morphometry of radioautographs showed that the number and area of blood vessels were similar in A and R sectors. Proliferation of endothelial cells and fibroblasts was assessed from radioautographs prepared from mice continuously labeled with 3H‐thymidine at times between 2 and 60 days. Significantly more labeled endothelial cells (P < .001) and fibroblasts (P < .05) were seen in the A sector. The percent of labeled endothelial cells and the percent of labeled fibroblasts increased linearly to 25 days and then formed a plateau. The rate of increase of labeled fibroblasts was higher in the A sector than in the R sector (P < .025). In addition, 3H‐proline grain counts over extracellular matrix were significantly higher in the appositional sector than in the resorptive sector (P < .025). These data suggest first that PL endothelial cell populations are in steady state despite significant cell turnover, and second, that the remodelling of blood vessels and extracellular matrix, as well as the turnover of fibroblasts and endothelial cells, occurs at a more rapid rate in A sectors of the PL than in R sectors and appear to be coordinately regulated by factors associated with the phenomenon of tooth drift.