Reproducibility of bone height measurements made on serial radiographs.

The objective of this study was to determine the reproducibility of alveolar bone height measurements made on digitized images of serial radiographs using 3 different alignment systems for taking serial radiographs: 1) XCP Rinn System, 2) XCP Rinn System modified to include an alignment pin, and 3) I/EGAD system (impression based-electronically guided alignment device). Eighty duplicate films taken 1 hour apart of randomly selected anterior or posterior sites for alignment systems 1 and 2 were taken on 40 subjects. Thirty-eight duplicate films were taken of posterior and anterior sites on 19 subjects with alignment system 3. Cemento-enamel junction alveolar crest measurements were made on digital images using the side-by-side technique. Image pairs of serial radiographs were dichotomized into well-matched and poorly matched groups based on subjective evaluation of the geometric likeness. Of those taken with system 1, 47% were well matched; with system 2, 62%; and with system 3, 98%. The measurement error of change in radiographic bone height, defined as twice the standard deviation of difference (mm), was determined. This varied between 1.03 mm for poorly matched radiographic pairs taken with alignment system 1 and 0.52 mm for all radiographic pairs taken with alignment system 3. These results can be used together with power calculations to select an alignment system for a particular study. For example, power calculations indicate that detecting a bone change of 0.5 mm using the I/EGAD system would require one-third of the subjects needed when using the XCP Rinn method.