Establishing malocclusion severity levels on the Dental Aesthetic Index (DAI) scale

The Dental Aesthetic Index (DAI) is an orthodontic index based on socially defined aesthetic standards. It is useful in both epidemiological surveys to identify unmet need for orthodontic treatment and as a screening device to determine priority for subsidized orthodontic treatment. An earlier study established the score of 36 on the DAI scale to identify handicapping malocclusions. The purpose of the present study was to determine decision points on the DAI scale that identify malocclusion severity levels less severe than handicapping. Two sources of data were used: 1) The frequency distribution of DAI scores on a probability sample of 1306 study models representing the untreated occlusions found in half a million adolescents. 2) The percent distribution of US youths aged 12-17 by specified case severity reported in an assessment of the occlusion of youths by the National Center for Health Statistics (NCHS). The decision points separating specific case severities on the DAI scale were determined by relating the proportions of the NCHS population with specified case severities to the cumulative percentages of the frequency distribution of DAI scores on the 1306 models. The NCHS report found 45.8 percent of the sample to have normal or minor malocclusion with no need or slight need for treatment. DAI scores 25 and below corresponded to that proportion of the sample. The NCHS report found 25.2 percent of the sample to have definite malocclusion with treatment being elective. DAI scores between 26 and 30 corresponded to that proportion of the sample. The NCHS report found 13 percent of the population to have severe malocclusion with treatment highly desirable. Fifteen percent were included in this category. DAI scores 31 to 35 corresponded to that proportion of the sample.