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cone beam international magazine of cone beam dentistry

opinion _ CBCT in orthodontics I more precise for the orthodontist to assess trans- versal plane discrepancy using 3-D data. For this purpose, one simple method is the University of Pennsylvania’s CBCT transversal analysis (Fig. 9). This transversal analysis uses CBCT to locate the points that define the maxillary and mandibular skeletal base width. For the transversal dimension of the mandible, the measurement is taken at the levelofthefurcationoftherootsofthefirstmolars. For the maxillae, the measurements are done from Mx to Mx points. The ideal difference between the width of the jaws should be 5 mm.6 _The size and position of impacted teeth In clinical practice, the predictability and the quality of the orthodontic treatment outcome are uncertain with an impacted tooth. This is because it is very difficult for the orthodontist to assess clinicallythecorrectpositionoftheimpactedtooth, both the crown and the root, and proximity to the roots of the adjacent teeth (Fig. 10). The 3-D images allow the orthodontist to analyse those aspects, as well as the eventual morphological anomalies, pathology of the impacted tooth, and resorption of the root of an adjacent tooth, and to determine the direction of the necessary orthodontic forces that will permit the recovery of the impacted tooth (extrusion, rotation, tipping, or root uprighting; Fig. 11).1 _Root resorption With CBCT images, the orthodontist can deter- mine whether root resorption has been caused by ectopia, or by orthodontic treatment. Figure 12 shows the external root resorption of a crowded central incisor. _Localisation of teeth The location of ectopic or supernumerary teeth can be determined with CBCT images. Figure 13 showsathirdpremolarimpactedbetweentheroots of the first and second premolars. _Sinuses and teeth–sinus relationship In many clinical cases, the close proximity of the roots of the posterior teeth and the maxillary sinus cortical bone cannot be properly assessed on 2-D images. When the roots are blocked by the sinus cortical bone, movements such as intrusion or mesialisation of the posterior teeth cannot be performed, or may cause external root resorption. With CBCT images, this shortcoming of 2-D images is easily overcome.7 Various incidental sinus find- ingsonCBCTimagesmaybemade,includingpolyps, sinusitis and complete opacification of the maxil- lary sinuses (Fig. 14).8 _Airway assessment On CBCT images, it is possible to measure the airway volume of the patient because the clinician can trace and analyse the contours and form of the Fig. 13_A third premolar impacted between the roots of the first and second premolars. Fig. 14_Maxillary sinusitis. Fig. 15_A mini-screw correctly placed between the canine and first premolar roots. I 19cone beam3_2014 Fig. 15 Fig. 13 Fig. 14 CBE0314_16-20_Iacob 30.09.14 14:15 Seite 4

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