[Validity of partial systems of periodontal examination in epidemiological studies].

The purpose of the present study was to determine the representativeness of partial examination in the assessment of the average severity and the prevalence of periodontal disease. 343 subjects aged 7, 12 and 15-19 years were examined for the presence or absence of gingival bleeding after gentle probing, supra or subgingival calculus and pocket depths of 4-5 mm., or 6 mm. and over, of each tooth. Three sets of average severity and prevalence scores were prepared: based on the full mouth examination, on observations made from the index teeth of the P.D.I., and on the six teeth utilized for the C.P.I.T.N. in this age group. Partial indices tended to underestimate the real prevalence of the different signs, and slightly overestimate severity, being these observations statistically significant. Average severity scores were obtained more accurately with the six Ramfjord teeth, while real prevalence rates were better determined with the C.P.I.T.N. teeth. From an epidemiological point of view, the real significance of the differences observed should be further determined.