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BACKGROUND: Gingival recession is a common manifestation of periodontal disease, but it is also associated with other risk factors. A few studies have investigated the epidemiology and risk factors of this condition. This study describes the epidemiology of gingival recession in a representative, urban Brazilian population and assesses various risk indicators. METHODS: A representative sample of 1,460 subjects was selected using a multi-stage, probability, cluster sampling strategy. The subjects were interviewed using a structured questionnaire and had a full-mouth clinical examination in a mobile examination center. RESULTS: More than half (51.6%) and 22.0% of the individuals and 17.0% and 5.8% of teeth per individual showed gingival recession > or = 3 mm and > or = 5 mm, respectively. The prevalence, extent, and severity of recession correlated with age. Recession showed a nonlinear relationship with age, with 25 to 50 year olds showing the highest level of recession. Males aged > or = 30 years showed significantly higher prevalence and extent of gingival recession than females. The percentage of teeth with recession was significantly higher in the lower socioeconomic groups irrespective of age, and in subjects > or = 30 years of age with irregular dental care than in subjects with regular care. Using a multivariable model, cigarette smoking and presence of supragingival calculus were the factors most significantly associated with localized and generalized recession, whereas gender, dental visits, and socioeconomic status were not significant risk indicators. CONCLUSIONS: The high level of gingival recession in this Brazilian population may be primarily related to destructive periodontal disease and is significantly associated with a high level of supragingival dental calculus and cigarette smoking. Population-based programs aimed at the prevention of periodontal diseases may reduce the prevalence of severe gingival recession in this and similar populations.

In this article, numerical solutions of the generalized weak turbulence equation [P. H. Yoon, Phys. Plasmas 7, 4858 (2000)] are carried out. In the generalized weak turbulence theory, the generation of the 2pe-harmonic Langmuir mode is treated as a fundamental process in turbulent beam-plasma interaction process, in addition to, and concomitant to, the well-known nonlinear processes such as Langmuir and ion-sound mode coupling and wave-particle interactions. The present numerical analysis shows that the harmonic mode, which is a solution to a nonlinear dispersion equation, hence a “nonlinear” eigenmode, grows primarily due to an induced emission process, which is a “linear” wave-particle interaction process. The harmonic Langmuir mode generation has been observed since the late 1960s in laboratory experiments, simulations, and in space. However, adequate and quantitative theoretical explanation has not been forthcoming. The present work represents a step toward an understanding of such a phenomenon.