Validation of Align Technology's Treat III digital model superimposition tool and its case application

An assessment of the efficacy and accuracy of three-dimensional computer-based predictive orthodontic systems requires that new methods of treatment analysis be developed and validated.

Invisalign is a digitally fabricated, removable orthodontic appliance that has been commercially available since 1999. It is made up of two main components: 1) computerized graphical images of a patient's teeth moving through a series of stages from initial to final position; 2) pressure formed clear plastic appliances made from stereolithography models of the images in the first component.

The manufacturer of Invisalign (Align Technology, Inc.) has created a software tool that can be used to superimpose digital models to evaluate treatment outcomes in three dimensions. Using this software, research was conducted to determine if a single operator could repeatedly superimpose two identical digital models using 12 selected points from the palatal rugae over 10 trials. The tool was then applied to one subject's orthodontic treatment. EXPERIMENT VARIABLES: The output from this tool includes rotations, translations and morphological changes. For this study, translations and rotations were chosen.

The results showed that the digital superimposition was reproducible, and that after multiple trials, the superimposition error decreased. The average error in x, y, z, Rx, Ry and Rz after 10 trials was determined to approach approximately 0.2 mm in translation and less than 1 degree in rotation, with a standard deviation of 0.15 mm and 0.7 mm, respectively. The treatment outcome from a single Invisalign-treated bicuspid extraction case was also evaluated tooth-by-tooth in x, y, z, Rx, Ry and Rz dimensions.

Using the palate, as a stable reference seemed to work well and the evaluation of the single case showed that many, but not all, of the planned movements occurred.