Use of Non-Contact Three-Dimensional Surface Measurements to Evaluate the Accuracy of Plaster Facial Models

Abstract

Although often used in planning orthodontic surgery, facial plaster models from alginate impressions do not always express the true image of the patient owing to depressions created in the soft tissues by the impression material. In order to determine where these depressions occur, we compared plaster models of the face made from alginate impressions with the actual face using non-contact three-dimensional shape measurements.
      Facial plaster models were made of six subjects from alginate impression material. These models and the actual faces were then scanned by a three-dimensional shape measuring system. Data of the two measurements for each subject were fitted by the least squares method and processed by image analyzer software.
      By use of computergraphics we could observe depressions made in the contour by the impression material.
      These depressions were most pronounced running laterally and caudally from the ala to the mandibular gonion. These results suggest that alginate impression material tends to distort those areas of the face covering fat tissues.