THE PERIODONTAL TISSUES IN HEALED DEGREE-III FURCATION DEFECTS - AN EXPERIMENTAL-STUDY IN DOGS

The aim of the present study was (i) to describe the periodontal tissu e that formed in degree III furcation defects in mandibular molars of dogs following GTR therapy and (ii) to compare this healed periodontiu m to the corresponding tissue of pristine furcations. The study was pe rformed in 10 mongrels dogs. In 6 of the dogs (group A), the 2nd and 4 th premolars in both sides of the mandible were extracted 2 months pri or to the start of the study. The 4 remaining dogs (group B) were used as normal untreated controls. In the dogs of group A, a furcation def ect was produced in the 3rd mandibular premolars and reconstructive su rgery was later performed in accordance with the GTR technique. 5 mont hs after reconstructive surgery, all 10 animals (groups A+B) were sacr ified and perfused with a solution of 10% neutral, buffered formalin t hrough the carotid arteries. Tissue blocks containing the experimental teeth were excised, demineralized in EDTA, embedded in paraffin. Seri al sections were cut in the mesiodistal plane and parallel with the lo ng axis of the roots. The microtome was set at 7 mu m. The sections we re stained in hematoxyline and eosin or Van Gieson's connective tissue staining. From each biopsy, 3 sections, 14 mu m apart, and representi ng the central part of the furcation, were selected for light microsco pic examination. In the healed furcation sites. histometric and morpho metric measurements were performed at different levels (zones), either at the mesial or distal root surfaces; (zone 1) immediately apical of the notch; (zone 2) coronal to the notch where the newly formed alveo lar bone was in continuity with the reduced bone crest; (zone 3) coron al to the notch; representing the most coronally positioned area of ne w bone formation; (zone 4) coronal to the notch; representing areas wi th no alveolar bone present. In the pristine furcation sites, the meas urements were made at zones which corresponded to the location of the zones in the healed furcations. The present data demonstrated that all furcation sites in group A after 5 months of healing exhibited compre hensive de novo cementum formation in the previously exposed parts of the intraradicular root surfaces, and that collagen fibers invested in the newly formed cementum. Comparisons between the pristine and the h ealed furcations disclosed that the periodontal ligament of the healed furcations was poorly organised, and that bone formation was frequent ly incomplete.