A comparison of three methods to accurately measure root length.

Measuring the severity of root shortening after orthodontic treatment is a common problem in the dental fields as well as in litigation, legislation, and the ethics arena. The most common method to evaluate root length shortening is by using periapical radiographs. Surprisingly, root elongation after orthodontic treatment in adult patients was reported in the past. The aims of this study were to measure the effects of angular changes between the tooth and the film on the length of the image of a tooth model, to compare three methods to accurately measure root length in different films, and to find the most accurate reference points on the tooth for calculating root lengths. Five amalgam dots were placed on an acrylic model of a maxillary central incisor: ie, most apical, most incisal, mesial CEJ, distal CEJ, and most apical CEJ on the buccal side. The tooth model was placed in a special jig and radiographed at four different film-to-tooth angulations. Root and crown lengths were measured on both the model itself and on a computer monitor displaying the image that resulted from scanning the film into the computer. The results revealed that angular changes between the tooth and the film affect the measured tooth length. The midpoint between the mesial CEJ point and the distal CEJ point (median CEJ) was the best reference point for measuring root length. This was true when the calculations were done with the rule-of-three formula.