Does periodontal tissue regeneration really work?

Periodontitis is an infectious disease that causes destruction of the tooth-attachment apparatus. Untreated periodontitis results in progressive attachment loss that may eventually lead to early tooth loss. Fortunately, research has provided evidence that in most situations chronic periodontal diseases can be treated [reviewed in Ref. (29)]. There is also evidence that periodontally involved teeth have a good chance of survival, provided that therapy, patient compliance and maintenance care are appropriate [reviewed in Ref. (29)]. There are a broad range of treatment options available, but only a few may be regarded as truly regenerative procedures. According to a position paper from the American Academy of Periodontology (29), periodontal regenerative procedures include soft tissue grafts, bone replacement grafts, root biomodifications, guided tissue regeneration, and combinations thereof, for osseous, furcation and recession defects. Regeneration is defined as the reproduction or reconstitution of a lost or injured part of the body in such a way that the architecture and function of the lost or injured tissues are completely restored. The aim of regenerative periodontal therapy is to restore the structure and function of the periodontium. This means that the structure and function of the gingiva, alveolar bone, root cementum and periodontal ligament must be restored (Figs 1 and 2). By contrast, periodontal repair implies healing without restoration of the tooth-attachment apparatus and is often associated with the formation of a long junctional epithelium (Figs 3–5). Detachment of the junctional epithelium from the tooth surface (i.e. the formation of a periodontal pocket), disconnection of periodontal ligament fiber attachment to the root surface via cementum, and bone loss, are hallmarks of periodontitis. New attachment of junctional epithelium to the tooth surface and of connective tissue fibers to the root surface are very critical components of true periodontal regeneration. New connective tissue attachment requires the formation of new cementum to a previously diseased root surface that was modified following periodontal therapy. Needless to say, in order to increase the attachment function of a tooth, the periodontal connective tissue fibers also have to insert into newly formed bone (Fig. 6). While less concern exists about the new epithelial attachment, new connective tissue attachment is much more critical. Concerns include predictability and the amount of new connective tissue attachment, as well as the strength of the regenerated interface between the treated root surface and the new cementum. As formation of cementum is essential for the attachment of periodontal ligament fibers to the root surface, much research has been devoted to understanding cementogenesis (for reviews, see Refs 3, 7, 9, 26, 30, 61, 62, 81). Not all studies that claim to have achieved periodontal regeneration have utilized histological techniques. Methods of assessing periodontal regeneration have been reviewed previously (56). Clinically, the outcome of a regenerative periodontal treatment is assessed by clinical parameters (periodontal probing, radiographs and re-entry evaluations). These methods are, however, inappropriate for demonstrating true attachment gain. Histology continues to be the only reliable method of evaluating the efficacy of a therapy aimed at achieving periodontal regeneration. According to the World Workshop in Periodontics of the American Academy of Periodontology (1996), the requirements for a periodontal treatment to be considered a regenerative procedure are as follows: (i) human histology demonstrating new cementum, periodontal ligament and bone coronal to the former defect base; (ii) controlled human clinical trials demonstrating improved clinical probing attachment and bone levels; and (iii) controlled animal histological studies revealing new cementum, periodontal ligament and bone.