Introduction In this study, we compared the precision of landmark identification using displays of multi-planar cone-beam computed tomographic (CBCT) volumes and conventional lateral cephalograms (Ceph). Methods Twenty presurgical orthodontic patients were radiographed with conventional Ceph and CBCT techniques. Five observers plotted 24 landmarks using computer displays of multi-planer reconstruction (MPR) CBCT and Ceph views during separate sessions. Absolute differences between each observer’s plot and the mean of all observers were averaged as 1 measure of variability (ODM). The absolute difference of each observer from any other observer was averaged as a second measure of variability (DEO). ANOVA and paired t tests were used to analyze variability differences. Results Radiographic modality and landmark were significant at P <0.0001 for DEO and ODM calculations. DEO calculations of observer variability were consistently greater than ODM. The overall correlation of 1920 paired ODM and DEO measurements was excellent at 0.972. All bilateral landmarks had increased precision when identified in the MPR views. Mediolateral variability was statistically greater than anteroposterior or caudal-cranial variability for 5 landmarks in the MPR views. Conclusions The MPR displays of CBCT volume images provide generally more precise identification of traditional cephalometric landmarks. More precise location of condylion, gonion, and orbitale overcomes the problem of superimposition of these bilateral landmarks seen in Ceph. Greater variability of certain landmarks in the mediolateral direction is probably related to inadequate definition of the landmarks in the third dimension.
The purpose of this study was to determine if half-skull and multiplanar reconstruction (MPR) images derived from CBCT image volumes will provide more precise location of landmarks and measurements than conventional cephalometric radiographs. A population of 20 pre-treated surgical orthodontic patients was radiographed and evaluated using lateral cephalometric and CBCT techniques. Four radiographic displays were used: conventional cephalogram, right and left half CBCT cephs, and MPR. Precision was calculated for 23 landmarks, 4 modalities and 20 cases using two measures of observer variation for identifying the same landmark in the same case and modality: ODM (Observers difference from the mean) and DEO (Difference from Every other Observer). Analysis of Variance (ANOVA) was computed for ODM or DEO for all modalities, landmarks, coordinates, and cases as every effect as well as all interactions among them. Statistical significance was defined as an ⍺ level of 0.05. Paired-t Tests were also used to assess each of the two calculations of variability for each landmark and the 6 possible combinations of 4 modalities. Bonferroni correction for multiple comparisons was applied and a p threshold of 0.0036 was calculated. Landmark variability clinically important used a threshold of 2mm. iv Results indicate that overall statistically landmark variation was greater for conventional cephalogram than CBCT modalities when calculated using ODM and DEO approaches. The x and y overall modality variability were higher for conventional cephalograms than for any of the alternative modalities. Landmark variability over 2 mm was greater for conventional cephalogram for more than half of the landmarks. Only soft tissue Pogonion exceeded the 2mm for all modalities. Based on the results of this study is possible to conclude that CBCT modalities provide a more precise location of landmarks overcoming problems obtained with conventional cephalograms. v To my family, who offered me unconditional love and support throughout the course of my studies. Also, this thesis is dedicated to Brian who has been a great source of happiness, motivation and inspiration. Finally, this thesis is dedicated to Cristina, my friend, sister and colleague without her I would not be here at UNC. vi ACKNOWLEDGEMENTS Dr. John Ludlow (my mentor), for guiding me through every step of my thesis work, and for getting my ideas into focus during the process of my studies. Thank you for your patience, time and help. Dr. Andre Mol, for making your explanations crystal clear, for your constructive comments, understanding and support. Dr. Lucia Cevidanes, for your guidance, your decisive and energetic support during this project.
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