Using MATLAB (The Mathworks, Inc.) and its included programming tool GUIDE (Graphical User Interface Development Environment) it was comparatively easy to write a macro which would:

• Read in a picture file of teeth obtained from a flatbed scanner set at a fixed resolution (600 dots per inch in this case).
• Enlarge the picture so the appropriate morphological features of the individual teeth could be selected with accuracy.
• Accept computer mouse input to specify measurement points along the edge of the tooth in the picture.
• Calculate the length of the curve through the measurement points to determine the total length of the distal edge of the tooth as well as the length of the unserrated tip.
• Determine the ratio (unserrated tip length)/(total edge length) for the distal edge of each tooth and save this as well as the distal edge length in a file.

The measuring program uses the pixels in the picture file for its coordinate system. Thus one unit in the coordinate system is one pixel in the picture. Since the resolution of the scans was 600 pixels/inch, the program had the theoretical accuracy of 1/600 inches/pixel = .04 mm/pixel. However, tooth details generally could not be resolved down to a pixel level but the measurement techniques were more than adequate for the present purpose. Scans of a precision ruler verified that the method indeed had an accuracy to at least a tenth of a millimeter. Of 10 measurements of a marked 1 cm distance on the ruler, the errors ranged between –0.0303 mm and +0.0869 mm.

Pictures of teeth were obtained from an Epson Perfection 1200 flatbed scanner with a scanning density of 600 pixels per inch. The teeth were aligned horizontally on the scanner bed, scanned one row at a time (so that the picture file size would be relatively small), and the scan saved in a TIFF file. Variations in tooth orientation would have no effect on measurement accuracy because distances were calculated using standard Euclidean geometric methods on the pixels of the picture. The picture files were next opened in a picture editing program and a number label was inserted below each tooth: the left-most tooth was assigned number 01, and the sequence continued left to right.