Cell kinetics of the initial response to orthodontically induced osteogenesis in rat molar periodontal ligament

Abstract

Initial cell kinetics (15 min-20 h) of mechanically induced osteogenesis was studied with 3H-thymidine (3H-Tdr) autoradiography. Continuous orthodontic force elicited a three-stage cell proliferative reaction within rat molar periodontal ligament (PDL): (a) brief, generalized response, characterized by a burst of mitotic activity from 75 min to 2 h and a cyclic change (decrease, increase and return to control levels) in percent labeled cells from 15 to 2 h; (b) transient, generalized response, involving an increased mitotic index (MI) from 2 to 13 h, associated with elevated labeling index (LI) from 6 to 12 h; and (c) sustained, localized osteogenic response (12 h to several days) in which cell proliferation was confined primarily to the immediate area of new bone formation. These results suggest that the initial effect of mechanical perturbation on relatively quiescent adult bone progenitor cells is a generalized, transient release of G1 and G2 blocked cells. This response may correlate clinically with the regional acceleration phenomenon (RAP), which follows bone trauma, fracture, or surgical injury.

Effect of Mechanical Loading On Periodontal Cells

“…Figure 1. F the rat model (Smith and Roberts, 1980;Roberts dento-alvec and Chase, 1981;Roberts and Morey, 1985;King of orthodoi et al, 1991b), demonstrate that proliferation and osteoblasts recruitment of osteoblast precursors is an heads), whi important step in osteogenesis on periosteal and periodontiu endosteal alveolar bone surfaces. However, in a uniform s the light of our recent studies on mechanical orthodontic induction of osteoblast markers described below, it became clear that the proliferation and recruitment account for only a small part of the increase in bone matrix synthesis by mechanical stress, the largest portion of which is achieved by an enhancement of osteoblast differentiation on the bone surface.…”

“…Rats were the most widely used animal model for orthodontic tooth movement. In this model, the molar teeth were moved by insertion of a compressed elastic material between the teeth (Waldo and Rothblatt, 1954;Smith and Roberts, 1980;Yen et al, 1987;Soma et al, 1999;Terai et al, 1999), palatal expansion (Lilja et al, 1981), or by application of protractive force by either an elastic ring (Yen et al, 1992;Brudvik and Rygh, 1993) or a coil spring (Brudvik and Rygh, 1993;Soma et al, 1999).…”

“…(a) Recruitment and proliferation of osteoblasts Investigators have used the rat model to determine proliferation rates of periodontal cells by measuring the rate of DNA synthesis (Smith and Roberts, 1980;Roberts and Chase, 1981), to define a differentiation pathway of osteoblast precursors using nuclear size markers (Roberts et al, 1982), and to measure the rate of collagenous matrix synthesis by metabolic labeling with radioisotopes in intact animals (Koumas and Matthews, 1969;Diaz, 1978) and in cultured alveolar bone explants (Duncan et al, 1984). There were earlier attempts to use the mouse tooth movement model to exploit the advantages of a smaller animal, such as the presentation of larger areas of paradental tissues and teeth on the same microscopic slide.…”

Effects of Gradually Increasing Force Generated by Permanent Rare Earth Magnets for Orthodontic Tooth Movement

“…The initial phases of tooth movement are considered to be important because major environmental changes occur. 10 The present animal experimental model was designed to exert light or heavy force in initial phases according to magnet distance. Light forces induce the smooth progression of tooth movement by frontal resorption.…”

Modulation of RANKL and Osteoprotegerin in Adolescents Using Orthodontic Forces

“…The increase in RANKL expression by osteoblasts may occur much sooner after the initiation of orthodontic force. Smith and Roberts (1980) reported a rapid acceleration of mitotic activity and DNA synthesis within two hours of application of a continuous force to rat teeth. Uematsu, Mogi and Deguchi (1996) reported an increase in GCF expression of IL-1β, IL-6, tumor necrosis factor (TNF)-α, epidermal growth factor (EGF), and β₂-microglobulin in as little as one hour.…”