Longitudinal evaluation of the Treatment Priority Index (TPI).

The Treatment Priority Index (TPI) is an epidemiologic tool used to rank malocclusions and assess the need for orthodontic treatment. The purpose of this study was to (1) evaluate the predictability of the TPI as an indicator of malocclusion severity, (2) evaluate the effect of orthodontic treatment on TPI values, and (3) compare the results with a national survey of American children aged 6 to 11 years and 12 to 17 years conducted by the United States Public Health Service. The TPI was recorded annually in a young student population of Juniata County, Pa., from 1975 to 1979, and later in 1985. The mean values of the TPI did not reflect the range of severity in the population. For this reason the Malocclusion Severity Scale (Burlington Growth Center) was used to identify four groups in 1985. Each group was tracked back to 1975. Further evaluation investigated the role of individual factors contributing to malocclusion over time (tooth displacement and occlusal factors). The conclusions are as follows: (1) the TPI is a valid epidemiologic indicator of malocclusion but does not predict the severity of individual malocclusions in the permanent dentition, (2) TPI values decrease with orthodontic treatment, and (3) the average TPI values for this population were higher than the national average between 6 and 11 years of age and slightly lower in late adolescence, but lie within a treatment-need range of slight to elective. A characterization of treatment need relative to malocclusion severity that is different from the available scale is suggested.