The study is aimed at analyzing in the Beagle dog if dental plaque is the major etiological factor not only in gingivitis but also in progressive periodontal disease as characterized by (1) loss of fiber attachment, (2) gingival pocket formation and (3) marginal alveolar bone loss. The objective also includes a detailed analysis, on a light and electron microscopic level, of the cellular, fiber and matrix composition of normal and inflamed gingivae and normal and inflamed marginal periodontal ligaments. In this analysis a morphometric method will be applied. Thus it will be possible to define and express in quantitative terms the characteristics of the developing gingival and periodontal lesion. In one group of dogs soft and mineralized plaque will be allowed to accumulate. In another group dogs a plaque-control regimen will be carried out including by two daily toothbrushing procedures. The gingival and periodontal conditions will be registered regularly by clinical and histological methods.