The role of local factors in the etiology of periodontal diseases.

Early concepts of periodontal disease were derived primarily from histopathological observations. Prominent pathologists interpreted the histopathology in various ways and produced somewhat divergent theories on the nature and causes of periodontitis (see Loe in this volume). Some scientists contended that periodontitis was the result of trauma from occlusion that produced excessive forces on the connective tissue and bone. Others believed that the disease had a systemic origin and was closely linked with systemic diseases. Some argued that certain forms of periodontitis were degenerative in nature and were therefore similar to other degenerative processes in the body. And for thousands of years, Egyptian, Hebrew and Chinese writings had spoken of individuals who were “long of tooth” as a reference to individuals of old age. Some therefore argued that periodontitis was a natural consequence of aging. The accumulations of hard and soft material, including microorganisms, on tooth surfaces had been associated with periodontal disease for many years and, beginning in the late 1800s, various periodontologists and microbiologists contended that parasites, protozoa, streptococci, spirochetes and certain black-pigmented anaerobes were responsible for periodontal disease. The presence of these various theories and their very vocal proponents resulted in varying concepts of therapy and very unpredictable treatment outcomes. If a patient with periodontitis presented for treatment to one of the proponents of trauma from occlusion, the patient might receive an occlusal adjustment and new dental crowns and bridges. Since some of these therapists would secondarily clean the teeth and others would not, the outcomes of this particular therapy were inconsistent. During the first half of this century, with limited scientific evidence, multiple local factors were introduced as possible causes of periodontal pathology. There were really no means available at the time to develop a clear understanding of the importance of any specific factor or the relative influence of multiple factors. The period that followed, beginning in the late 1950s and early 1960s, used the scientific method and hypothesis testing to clarify the dominance of primary correlations with disease, that is, plaque and age, which led to the demonstration that bacterial accumulation is essential to disease initiation. Although sophisticated experimental methods were rapidly applied to studies of periodontal diseases, experimental design and data analysis techniques were limited in their ability to evaluate the interaction of multiple factors. Such techniques for the study of the relative importance of multiple factors in chronic diseases have emerged only in recent years and are still under development. These limitations, as well as the normal dialectic thought process, have produced somewhat different concepts of the role of local factors in periodontal disease at different times. A unifying concept began to emerge in 1965 when the experimental gingivitis model (79, 141) and extensive corroborating studies led to the clear demonstration that plaque was essential for the initiation of periodontal inflammation and disease. The principal concept was that plaque was the primary and essential disease-initiating factor that resulted in a transition from health to gingivitis, and if the gingivitis were untreated it might progress to adult periodontitis. Several other factors that had previously been considered important in the initiation of periodontal disease became relegated to a secondary role or were almost completely disregarded as having any role in the disease process. Given the single-factor hypotheses that were routinely used, it was easy to demonstrate that factors other than plaque and age were not the primary determinants of disease. These studies served a critical purpose of clarifymg which factors primarily influenced disease and which were secondary factors. However, the experimental designs and analytical approaches used at that time were inadequate for evaluating the true role of many