A critical comparison of three methods for measuring dental models.

A critical comparison of three methods for measuring distances between various fiducial points on orthodontic plaster casts is presented. The first method consisted of using a vernier caliper by which direct measurements (Dv) of the distances were recorded. The second method consisted of measuring the same casts using a reflex metrograph (Dm), where the co-ordinates of the points relative to two axes were recorded and the distances between various points were calculated. In the third method, reflection holograms of the casts were made, and the same distances were measured on the holographic images (Dh) using the reflex metrograph. The Wilcoxon sign rank test indicated no significant differences (p greater than 0.1) between measurements made by the various techniques. The means of the different distances scored varied within less than 0.5 mm (Dv-Dh), 0.5mm (Dv-Dm) and 0.2mm Dm-Dh). This study indicated that holograms can provide sufficiently accurate representations of orthodontic study models. Their retention as case records may solve the problem of the storage of orthodontic plaster casts.