Probing considerations in relation to susceptibility to periodontal breakdown.

Both epidemiological and clinical studies indicate that not all individuals are equally susceptible to periodontal breakdown. Therefore, the clinical differences were investigated between subjects highly susceptible and subjects insusceptible to periodontal breakdown. The highly susceptible group consisted of patients with a diagnosis of juvenile periodontitis. The insusceptible group consisted of older individuals with gross amounts of plaque and no periodontal breakdown. Results indicated that a high value of the bleeding/plaque ratio may possibly act as a prognostic indicator for periodontal breakdown. However, longitudinal data are indispensable for substantiation of this hypothesis. Since longitudinal research takes many years, the experimental gingivitis model was chosen for further investigation. 4 groups of individuals were selected on the basis of a different history of inflammatory periodontal disease: 2 younger age groups without periodontal breakdown, having either a low or a high bleeding/plaque ratio--a hypothetically susceptible and a hypothetically insusceptible group, respectively; one older age group with presence of gross amounts of plaque, no periodontal breakdown and a low bleeding/plaque ratio--an insusceptible group; and an adult group who previously suffered from severe periodontal disease--a susceptible group. Results of the experimental gingivitis studies indicated that the older insusceptible group developed only small amounts of bleeding, whereas the younger hypothetically insusceptible group developed a comparable low bleeding index. The younger hypothetically susceptible group developed a much higher bleeding index comparable to that of the susceptible group, the periodontal patients. In conclusion, comparison of the results of the experimental gingivitis studies in subjects with differing histories of inflammatory periodontal disease supports the concept that the bleeding/plaque ratio may act as a prognostic indicator for periodontal breakdown.