In vitrocomparison of contemporary radiographic imaging techniques for measurement of tooth length: reliability and radiation dose

OBJECTIVES: To measure the reliability of tooth length measurements taken using dental pantomograms (DPT), long cone periapical radiographs (PR), and cone beam computed tomography (CBCT) and to compare their effective radiation dose. SUBJECTS AND METHODS: A model containing sixteen anterior teeth was used to simulate a patient undergoing fixed appliance treatment. PRs were taken at standardized vertical angulations to the occlusal plane (0, 5, 10, 15, and 20°) using conventional and digital techniques. DPT and CBCT images were also taken. Measurements of radiation dosages were used to estimate a risk benefit analysis for each of the techniques. RESULTS: DPT consistently overestimated tooth lengths by 2 mm or more [mean: 2·34 mm; 95% confidence interval (CI): 1·4-3·3 mm]. CBCT consistently underestimated tooth length (mean: -0·89 mm; 95% CI: -0·44 to -1·33 mm). PRs taken at 90° angulation closely resembled the actual tooth length (mean: -0·14 mm; 95% CI: -0·64 to 0·37 mm), but overestimation occurred with increasing PR film angulation. The radiation dosages ranged widely: DPT plus eight PRs that would be necessary to assess all teeth and root length of the upper and lower labial segments amounted to 23 μSv. Radiation dose from CBCT ranged from 17·8 to 60 μSv, depending on equipment and settings.