From 2D to 3D: an algorithm to derive normal values for 3-dimensional computerized assessment

Abstract

Objective: To test the accuracy of a mathematical model (algorithm) that corrects measurements made on conventional lateral head films to corresponding dimensions observed in a cone beam computed tomography (CBCT) scan in human subjects. Materials and Methods: Thirteen subjects had lateral cephalograms taken with a conventional cephalometric machine as well as a CBCT scan. Measurements of midface length, mandibular length, and lower anterior face height (LAFH) from both examinations were calculated. Two other groups of measurements were derived mathematically from the dimensions directly quantified on the lateral cephalogram: the magnification correction group and the algorithm correction group. The data were analyzed statistically, using repeated measures analysis of variance (ANOVA). Results: All measurements from the lateral cephalogram were significantly different from the corresponding measurements derived from the CBCT. Simply taking into account the image magnification did not correct the 2-dimensional (2D) linear measurement obtained from a conventional cephalogram into a 3-dimensional (3D) linear measurement made on a CBCT scan, unless the structures from which the distance will be measured are located on the midsagittal plane. When the algorithm was used to correct the 2D measurements, however, there were no statistically significant differences between the CBCT group and the algorithm group. Conclusions: Using the mathematical formula presented herein, 2D cephalometric measurements from landmarks both on and off the midsagittal plane can be corrected into a 3D CBCT measurement with accuracy. By applying this algorithm to other existing cephalometric longitudinal growth studies, control groups and standards for CBCT images could be derived without exposing untreated subjects to radiation. (Angle Orthod. 2011;81:3-10.)

A radiographic study of external apical root resorption in patients treated with single-phase fixed orthodontic therapy

“…In addition, trained radiologists are often required for the interpretation of CT images, which further reduces its use in routine orthodontic practice. 11,12 Any flaws in predictability, prevention and early diagnosis of this condition, especially in cases of extensive RR, can cause drastic consequences to both orthodontic treatment and patient's health. It is therefore important to determine the magnitude and prevalence of RR in various populations, as well as related risk factors.…”

Comparison of linear measurements between CBCT orthogonally synthesized cephalograms and conventional cephalograms

“…Thus, its values of Co-A, Co-Gn equal the projection of each 3D measurement on the midsagittal plane. 6 It was found that the distances of this type were comparable between them as well, after adjustment by the specific magnification. Generally, these comparative results of both Types 1 and 2 are consistent with those of our study.…”

“…In the light of trigonometric functions, the values of Co-A, Co-Gn on the conventional cephalogram equal the projection of each 3D measurement on the midsagittal plane multiplying the midsagittal magnification. Based on this principle, Gribel et al 6 rectified the measurements made on conventional lateral films to corresponding dimensions observed in CBCT scans in human subjects.…”

“…However, a few studies stated that direct comparison of 2D and 3D cephalometry was infeasible. 6,8,9 Gribel et al 6 stressed that 2D cephalometric norms could not be readily used for 3D measurements. Van Vlijmen et al 8 recommended that 3D tracings were not suitable for longitudinal research in cases where there were only 2D records from the past.…”

“…12,13,15 However, comparison regarding common linear measurements in longitudinal research, such as mandibular corpus length (Go-Me), mandibular ramus height (Co-Go) and posterior facial height (Go-S), was less involved in previous investigations. The related landmarks were located at different sagittal planes, leading to disproportionate enlargement distortion on the traditional lateral radiographs, 6,21 and the amount of distortion was determined by the respective focus-radiograph and midsagittalradiograph distances. The study by Oz et al 16 showed that linear measurement (Go-Me) differed significantly between conventional cephalograms and orthogonally The most anterior median point on the frontonasal suture 2.…”