PDF: Orthodontic treatment plan changed by 3D images

Conventional (or medical) computed tomography (CT) was developed in 1972 by the English engineer Hounsfield and the American physicist Comark. It represented great progress, and for this reason, its creators were recognized with the Nobel Prize for Medicine in 1979.

Despite the advances, conventional CT has been applied in dentistry with restrictions due to high radiation doses, excessive size of the device, the need for the patient to be in supine position during the shot and its cost. Towards the end of the 90's, technological advances led to a new version that met the needs of dental and maxillofacial regions, and became known as Cone-Beam Computed Tomography (CBCT).

As the name suggests, the CBCT produces radiation in the shape of a cone that rotates around the patient to acquire volumetric data. A specific amount of absorbed X-rays corresponds to a three-dimensional cuboid structure, called voxel-corresponding to the pixel in the two-dimensional images. The computer volumetric reconstruction is obtained by using software algorithms to reproduce the three dimensional image (3D) in high resolution.

The radiation dose emitted by CBCT depends on the desired field of view, exposure time, kilovoltage and milliamperage, but it has been reported that it corresponds to approximately 20% of a conventional CT and it is equivalent to the complete exposure of periapical radiographs. The differential in the CBCT is also the possibility of shooting in real size in all three planes of space, unlike the two-dimensional X-rays that project the image of the structures in one plane, often distorted and overlapped.

The literature is rich in clinical applications for the CBCT.13 In orthodontics, it allows for the visualization of impacted teeth, detection of root resorption, ankylosis and dentoalveolar fracture, assessment of height and bone volume, investigation of temporomandibular joint and upper airway, accurate determination of bone-tooth discrepancies in non-erupted teeth10 and diagnosis of pathologies.

The aim of this paper was to evaluate the influence of 3D exams in redirecting the orthodontic treatment plan. For this, two clinical situations were described, in which the clinical examination and/or conventional radiographic exams suggested complementation with tomographic images. In both cases, images were acquired by the tomograph i-CAT® (Imaging Sciences International, Hatfield, USA) whose data were exported to Xoran software version. (Xoran Technologies, Ann Arbor, USA) for 3D reconstruction.

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