The effects of force magnitude on a sutural model: A quantitative approach

Abstract

In an effort to quantify the biologic effects of an orthodontic tensile force, the rat interpremaxillary suture was investigated as model for the periodontal ligament and expanded in vivo with a helical spring across the maxillary incisors. Three levels of force were used: light (50 to 75 g), medium (150 to 175 g), and heavy (250 to 300 g). Thymidine labeling and histologic studies after 12 hours and 1, 2, and 4 days of force delivery are described (n = 48 rats), as are biochemical studies after 2 and 4 days, including a 6-hour organ culture (n = 32). The percentage of labeled cells increased significantly in all force groups at 1 day, followed by a rapid decline at 2 days, to a value at 4 days not significantly different from the controls. Biochemical studies showed significant increases in proline incorporation and alkaline phosphatase activity after 2 days of heavy force application. Histologic examinations showed obvious tissue changes beginning by day 1 and involving increases in suture width, vascularity, size and number of cells, amount of osteoid production, and changes in suture morphology. The experimental system was convenient, inflammation-free, and appeared to be reliable as evidenced by characteristic, synchronous tissue and autoradiographic changes in all experimental sutures through 4 Clays.