Background: The factors associated with initial periodontitis are not well understood and cannot be identified by cross-sectional studies.
Aim: To identify the factors associated with the initiation of chronic periodontitis using ante-dependence modelling.
Material and methods: A 26-year longitudinal study of the natural history of periodontitis served as the basis for the study. In 1969, 565 Norwegian men aged 16-34 years were surveyed. Subsequent surveys were performed in 1971, 1973, 1975, 1981, 1988 and finally in 1995, with 223 remaining subjects. Plaque (PlI), gingival (GI) and calculus indices (CI) and loss of attachment (LoA) were recorded. Ante-dependence modelling using a Markov chain enabled the results of this sequence of examinations to be analysed longitudinally, taking into account serial dependence, describing temporal changes in patients' levels of disease and allowing for both progression and regression between disease categories.
Results: With age, the rate of disease regression decreased. Increasing calculus accumulation and smoking increased the rate of disease progression, while increasing GI increased the rate of regression.
Conclusions: Increased mean CI and smoking were significant predictive covariates for progression, while increased mean GI and younger age predicted regression of initial periodontitis.