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The purpose of this study was to evaluate the histopathologic tissue change in the interradicular area induced by the orthodontic elastic hands in eight dogs. Orthodontic elastic bands were placed around the crowns of upper third and fourth premolars for day of 0, 3 and 1,2,4,8,12,14 weeks and the experimental periodontitis were produced. After the clinical and radiographic observations were recorded, block biopsies were taken in each group and prepared with hematoxylin-eosin stain for microscopic study. The results were as follows: 1. Clinically, the swollen gingiva with redness and the bleeding upon probing appeared at 3 day, and the suppurative exudate was seen at 14 week. In addition, grade III, IV according to Glickman´s classification could be observed at 12 week. 2. Radiologically, the loss of alveolar bone in furcation area appeared at 2 week, increased with time and triangular-shaped radiolucency could be seen at 14 week. 3. Acute inflammatory reaction was induced at 3 day and converted to plasma cell-rich chronic state with time and inflammatory cell infiltration extended to the supracrestal connective tissue and alveolar bone. 4. Microscopically, rapid destruction of the interradicular bone at 1 week was the consequence of highly active osteoclast associated with the inflammatory reaction and increased in the course of the experimental periods. 5. Microscopically, the epithelium with ulceration was migrated at 1 week, and completely covered in furcation area at 12 week.
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