PERIODONTAL-LIGAMENT TISSUE-REACTIONS TO TRAUMA AND GINGIVAL INFLAMMATION - AN EXPERIMENTAL-STUDY IN THE BEAGLE DOG

The aims of the present study were to analyze (i) which tissue changes may occur in the zone of co-destruction to better understand why trau ma from occlusion may induce additional attachment loss, and (ii) whet her changes occur in the periodontal ligament tissue when an inflammat ory lesion (ICT) approaches the periodontal ligament space. 16, 1-year -old beagle dogs, were selected and divided into 2 groups, group A and group B, consisting of 6 and 10 dogs, respectively. In group A, on da y 0, a bucco-lingual jiggling type movement was induced resulting in i ncreasing tooth mobility at P-3 (test tooth) by the application of an orthodontic elastic which traversed the buccal surface of the crown of the test tooth. The elastic was exchanged either in a buccal or in a lingual position 2x a week during a 3-month period. P-3 served as non- jiggled control tooth. Tooth mobility measurements were recorded on da ys 0, 30, 60, 90. A plaque control regimen was maintained until the en d of the experiment (day 90). On day 90, biopsies including P-3 and P- 3 were harvested. The dogs representing group B, were divided into 2 s ubgroups of 5 each, group BI and group BII. On day 0, a 4-month period of experimental periodontal tissue breakdown was initiated by placing cotton floss ligatures submarginally around the mandibular fourth pre molars (P-4(4)) in group BI and around the mandibular third premolars (P-3(3)) in group BII. All ligatures were exchanged, replaced Ix every month, and on day 120 permanently removed. On the same day, biopsies included P-4(4) were harvested. Following supragingival debridement P- 3(3) were allowed to accumulate plaque until the end of the study (day 225). On this occasion, biopsies including P-3(3) were harvested. The results of the histological measurements revealed that in the most co ronal portion of the periodontal ligament of teeth exhibiting increasi ng mobility, there was an increased width, a reduced % tissue volume o f collagen, and an increased volume of vascular structures and leukocy tes. Furthermore, the number of osteoclasts bordering this portion of the alveolar bone was increased and the number of collagen fibers inse rting into the root cementum and into the alveolar bone was reduced. I t was also demonstrated that in teeth with normal mobility, the positi on of the gingival ICT failed to influence the composition of the tiss ue within the coronal portion of the periodontal ligament.