Validity of CPITN's hierarchical scoring method for describing the prevalence of periodontal conditions

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Abstract
CPITN has been a frequently used index in periodontal epidemiology during the last decade. It was originally designed to describe treatment needs in populations. For this purpose, it was decided to record only the worst periodontal condition around each index tooth. Such a recording procedure can be regarded as a hierarchical scoring method. Recently, CPITN has been used and recommended for describing the prevalence of periodontal conditions. For this purpose, the index should give a valid estimate of the true periodontal conditions of the index tooth, and not only a recording of the worst condition. The aim of the present study was to test whether the hierarchical assumption of CPITN concerning treatment needs was valid for describing the prevalence or periodontal conditions in a Scandinavian population. The study population comprised 3330 persons from a rural and an urban area in the county of Trondelag, Norway. The clinical recording was carried out so that it was possible to analyze the indicators both hierarchically and non-hierarchically. The results showed that nearly all the CPITN indicators scored hierarchically gave a correct estimate of the prevalence of bleeding in the population. CPITN codes 3 and 4 overestimated the prevalence of calculus. The degree of overestimation varied by age and tooth type. Most overestimation of calculus occurred on molar teeth with pockets 3.5-5.5 mm and for individuals 13-14 yr of age. There was almost no overestimation of calculus for those aged 65 yr and above. The distribution of the different combinations of the indicators was fairly similar for all index teeth for codes 2,3 and 4, with the exception of the mandibular incisor.