ON THE DYNAMICS OF PERIODONTAL TISSUE FORMATION IN DEGREE-III FURCATION DEFECTS - AN EXPERIMENTAL-STUDY IN DOGS

The aim of the experiment was to describe the formation of periodontal tissues in degree III furcation defects following GTR therapy. The st udy was performed in 8 foxhound dogs. The 2nd and 4th premolars in bot h sides of the mandible were extracted. Furcation defects were produce d in the 3rd mandibular premolars. 3 weeks later, reconstructive surge ry was performed. The dogs were scheduled for sacrifice 2, 4, 8, and 2 0 weeks after GTR therapy. Tissue blocks containing the experimental t eeth were excised, demineralized in EDTA and embedded in paraffin. Ser ial sections were cut in the mesio-distal plane and parallel with the long axis of the roots. The microtome was set at 7 mu m. The sections were stained in hematoxyline and eosin. From each biopsy, 3 sections r epresenting the central part of the furcation, were selected for light microscopic examination. In the healed furcation sites, descriptive h istological analysis of the newly-formed tissues was performed and the relative proportions of the hard and soft tissues were determined. It was demonstrated that at 2 weeks, the furcation defect contained gran ulation tissue and cell-rich connective tissue, while at 4 weeks the f urcation was mainly occupied by connective tissue. At 8 weeks, woven b one occupied the central portion of the furcation, whereas connective tissue and cementum were observed in the lateral portions. The furcati on area at 20 weeks was comprised of newly-formed cementum, periodonta l ligament and bone. The onset of cementum formation had started as ea rly as 2 weeks after GTR therapy. The cementum formation apparently oc curred in 3 phases: organisation of collagen fibers adjacent and perpe ndicular to the root surface (phase 1), assembly of the collagen fiber s and deposition of matrix (phase 2), and addition of cells and collag en fibers organised parallel to the root surface (phase 3). Bone forma tion took place through a process that included (1) organisation of a fibrous connective tissue, (2) differentiation of this tissue into wov en bone and, (3) maturation of the woven bone into lamellar bone and b one marrow.