A new method for analyzing change in dental arch form.

Our method was developed and subsequently computerized in a system incorporating graphics and quantitative indexes to analyze change in dental arch form as a result of orthodontic treatment and subsequent relapse. The cubic spline function was used to model the form of the dental arches. On the basis of digitized data, splines were fitted to the dental arches before treatment, immediately after treatment, and at least 2 years after removal of retention. The fit of each spline was evaluated through the use of a set of normals to the curve and their average length. The change in form between the registrations was computed, and superimposed graphics of the three records were produced to visually indicate the magnitude of the changes in addition to numeric indexes that reflected the changes. Interjudge and intrajudge reliability were examined and found to be within acceptable limits.