Operational performance of the Reflex Metrograph and its applicability to the three-dimensional analysis of dental casts.

The purpose of the present study was to investigate the applicability of a new instrument (the Reflex Metrograph) to the three-dimensional analysis of dental casts. In this system, a dental cast, placed in front of a semireflecting mirror, creates an identical image behind the mirror. The measurement of a point is made by aligning a light source behind the mirror in coincidence with the image of a specific point on the object. The light source is carried on a three-dimensional slide system, and coordinates are digitized for sampling by the computer. Measurement accuracy of the instrument was evaluated for three measuring points determined on a maxillary dental cast placed in six different locations. In addition, differences in the performance skills of ten operators were evaluated. The results indicate that digitization of a point in three planes of space can be undertaken without direct contact of the object and that a consistent measurement accuracy can be obtained, regardless of differences in the location of the cast relative to the mirror or in the anatomic shape of the measured areas. In addition, operators with no previous experience can determine specific points to an accuracy of +/- 0.1 mm, with a minimal amount of training. Finally, measurement by the same operator for a pooled sample is recommended in order to avoid interoperator measurement error when determining linear distances.