Lack of bacterial invasion in experimental periodontitis

The present study in the beagle dog was performed to analyze whether micro‐organisms from a subgingival microbiota could be translocated into or had the potential to invade the pocket epithelium and the gingival connective tissue during a phase of rapid breakdown of the attachment apparatus. An attempt was also made to assess whether tetracycline therapy suppressed the subgingival microbiola and changed the size and quality of the lesions in the gingival tissue. 5 inbred beagle dogs were used. Throughout the period of experimentation, the animals were fed a soft diet permitting gross accumulation of plaque and calculus. No mechanical plaque control measures were performed during the course of the study. On day 0, a 120‐day period of periodontal tissue breakdown was initialed at the right mandibular 3rd and 4th premolars by tying cotton floss ligatures around the neck of these teeth. The process of tissue breakdown at the mandibular left 3rd and 4th premolars was started 3D days later. The ligatures were replaced once every 2 weeks during the subsequent 4‐month period. On experimental day 120, the first biospy was performed and gingival tissue sections prepared for light and electron microscopic assessment of a series of histometric characteristics. On day 120, a 30‐day period of tetracycline (per os) administration was initiated. Each dog was given a dose of 500 mg tetracycline twice daily. On day 150, the biopsy procedure was repeated in the mandibular left premolar regions. The results failed to demonstrate that bacteria from the subgingival microbiota penetrated the pocket epithelium and the gingival tissues of dogs, showing signs of advanced breakdown of the attachment apparatus. The data furthermore disclosed that tetracycline, administered via the systemic route in dogs with gingivitis and advanced loss of alveolar bone, markedley reduced the size of the inflammatory cell infiltrate of the gingiva and reduced the number of neutrophils and macrophages in the pocket epithelium. Tetracycline therapy however, failed to aller the connective tissue attachment level and failed to affect clinical parameters of gingivits.