Periodontal repair or regeneration: structures of different types of new attachment

The present study details the structural and ultrastructural features of healing events between the regenerated periodontal ligament and the root surface after experimental periodontal disease. Experiments were performed on dogs, and the concept of guided tissue regeneration was tested using resorbable polyurethane membranes. Light microscopy, scanning- and transmission electron microscopy were employed to determine if healing events involve regeneration (ie, process by which the architecture and the function are completely renewed) or periodontal repair (ie, healing of a wound by tissue that does not fully restore the architecture of a part). Regeneration occurred in parts of the roots only if some original cementum remained on the root surface after root planing. Repair was observed if peripheral dentin was removed by root planing as this layer was not reestablished. In areas remote from the base of the defect, new collagen fibrils, synthesized by fibroblasts and oriented perpendicular to the root surface, were spliced with severed ends of Sharpey's fiber bundles of original cementum. If circumpulpal dentin was exposed, intermingling between new fibrils with dentinal matrix fibrils occurred. In areas near the base of the defect, the first event was the formation of a cementoid by a cementoblast monolayer and subsequent formation of intrinsic fibrils oriented parallel to the root surface. Afterwards, the cementoblast monolayer disintegrated and extrinsic fiber bundles became anchored in the new cellular mixed fiber cementum. In these areas, linkage between new cementum and pre-existing tissues always occurred by interfacial intermingling of the fibrils, regardless of whether new attachment occurred at circumpulpal dentin or original cementum.