ANALYSING TREATMENT RESULTS BY SUPERIMPOSITION OF CBCTs
ANALYSING TREATMENT RESULTS BY SUPERIMPOSITION OF CBCTs

Summary/Abstract: The three-dimensional (3D) imaging is being widely used in all dental fields. In orthodontics one of its uses is for 3D superimposition methods. There are three methods to compare Cone Beam Computed Tomography (CBCT) scans of the same patient taken at different treatment time-points. They are landmark-based, surface-based and voxel-based methods. The superimposition allows us to analyze and compare the dental, skeletal and soft tissue changes during orthodontic treatment. Thus, allowing us to evaluate the efficiency of the treatment method and the effects of the orthodontic appliance. By using landmark-based CBCT superimposition software we aim to create clinical protocol for comparing the transversal (dental, skeletal and soft tissue) changes after using Rapid Maxillary Expansion (RME) in growing patients. Consecutive CBCT scan of the patients were made – one at the beginning of the treatment (at the stage of orthodontic treatment planning) and one after the rapid maxillary expansion had finished. Each of the CBCTs were analyzed and the obtained values and measurements were put in a table by order. The same reference bone points and planes were used. Then the superimposition method was done using the software. This superimposition method relies on localizing the landmarks on stable anatomical structures. The software offers manual placement of the landmarks using fitting tool where the user places 3 landmarks sequentially on the initial and on the final CBCT scan. It starts by placing the first landmark on the final CBCT and finishes with placing the last on the initial CBCT. For better accuracy the software allows adjusting the bone density thresholds for both CBCT scans so that the bone surface can be displayed equally. If there are any mismatches, they can be corrected by manually rotating or moving the final volume. After superimposing the volumes, the dental, skeletal and soft tissues changes can be evaluated by using different measurement tools. The landmark-based method requires knowledge of the anatomical structures and well-trained eye of the user in order to get good superimposition. The used software provides user-friendly and fast superimposition method, allowing the clinicians to perform it easily. The landmark-based method is reliable but less accurate method compared to the surface-based and voxel-based superimposition methods. It gives credible and reproducible results for the purpose of the clinical protocol and the research. The results obtained from the superimpositions are commensurable and corresponding to the difference in the measurements obtained from separate measurements made on the initial and final CBCTs. The CBCT software analysis allows the assessment of the airway volume changes with different orthodontic treatments and appliances. A disadvantage of the software is that it does not allow comparing and superimposing of the segmented jaws taken from the CBCT.

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