[Collagen as a basic element of the periodontium: immunohistochemical aspects in the human and animal.  1.  Gingiva and alveolar bone]. 
The connective tissue (CT) is responsible for stability and function of the whole periodontium.  It consists of cells, which are embedded in the extracellular matrix.  Collagen plays the main role for the function of the periodontal unit.  Collagen types I, III, IV, V and VI are distributed in a different pattern in all periodontal tissues, as has been here demonstrated in the gingiva and alveolar bone.  Collagen type I, as a characteristic collagen type of the hard tissues, has been demonstrated by thick collagen fibers in the alveolar bone and in the gingival connective tissue.  It can be differentiated from the thinner collagen type III fibers, which are localized in the gingiva (especially under the basement membrane of the epithelium) as well as only in the bone marrow stroma.  The epithelium, blood vessels and nerves contain the characteristic collagen type IV in their basement membrane Filamentous (collagen type V) and microfibrillar (collagen type VI) components demonstrate different patterns of distribution, especially around the bone cells and in contrast to the other collagen types of fibrillar networks in the gingival CT.  This morphological differentiation of the extracellular matrix components of the periodontium allows conclusions in the pathological and inflammatory processes as well as in the regenerative and reparative procedures.