Application of oral CT

Application of oral CT in orthodontics

Oral CT spirally collects data around a volume of the human body. The essential difference between oral CT and conventional CT is that the former obtains three-dimensional information while the latter obtains two-dimensional information. Oral CT improves the scanning speed, has a wide scanning coverage, and has no gap in the collected data, which is convenient for image reconstruction in various ways and angles, and can be reconstructed arbitrarily and retroactively. Three-dimensional reconstruction techniques of oral CT include multiplanar reconstruction (MPR), maximum density projection (MIP), surface shadow display (SSD) and volume rendering (VR). Different reconstruction methods are selected according to different sites, lesions and clinical requirements. With the help of dental CT program (DCT), oral CT can reconstruct panoramic images of jaw-mouth and sectional images in all directions. The image is clear and intuitive, and has been successfully applied to the diagnosis of diseases such as pre-implantation measurement, oral inflammation, tumor and oral maxillary sinus fistula!

The practical methods and skills of CT tooth surface imaging are discussed by using oral CT scanner and ADW4.0 image processing workstation. It is considered that oral CT dental imaging technology has important guiding significance in orthodontic treatment, and the reasonable selection of scanning reconstruction parameters and the accurate application of image post-processing methods are the keys to obtain high-quality three-dimensional images. With the help of DCT, two-dimensional images of three planes can be used to display the distance from the labial palatine cortex and the direction and position of impacted teeth. Two-dimensional reconstructed images have unique advantages in showing their relationship with adjacent structures (such as incisor canal, inferior alveolar nerve canal, maxillary sinus and adjacent roots), which can make up for many shortcomings of curved surfaces.

To summarize the significance of oral CT in the localization diagnosis of embedded teeth and supernumerary teeth: it can accurately display the number, size and shape of embedded supernumerary teeth in bone; The spatial position (labial buccal side, lingual side, height and inclination) of embedding supernumerary teeth can be determined; It can be determined whether the position of embedded supernumerary teeth is impacted by soft tissue or jaw. It can accurately display the distance or embedding relationship between embedded supernumerary teeth and adjacent tooth germs and roots. It can show whether the adjacent roots are absorbed and to what extent. Reasonable application of oral CT three-dimensional reconstruction technology in the location of impacted teeth: MIP (maximum density projection) can display the whole picture of teeth and the longitudinal arrangement of teeth; MPR (multiplanar reconstruction) shows the local relationship between apical bone and alveolar bone more clearly. SSD (Surface Coverage Display) can display the external contours and overall shapes of teeth and jaws, as well as the relationship between tooth arrangement and jaws. Therefore, it has extremely important clinical significance and development prospects for orthodontic traction treatment and jaw surgery.

Application of oral CT in orthodontics

Oral CT can simulate panoramic film and lateral head film, which will be very convenient for orthodontists. Its specific applications include: ① Image slope reconstruction. This technique generates a two-dimensional image without cross-section by crosscutting a pile of superimposed cross-section images. This method is very useful in evaluating the structure of TMJ and embedded third molar, because some features are more obvious than those on mutually perpendicular MPR images; ② Reconstruct the surface of the image. This method is useful in displaying dental arch and can provide panoramic thin-layer images, which can be obtained by arranging the long axis of the imaging plane containing specific anatomical structures. The image will not be deformed and can be used for accurate anatomical measurement, and the size and angle obtained from it have only a very small error; ③ Continuous plane reconstruction. This technique generates a series of sequentially superimposed cross-sectional images, which are perpendicular to the images of inclined planes or curved surfaces. The image is a thin sheet (for example, 1 mm thick) with a known distance (for example, the distance from 1 mm).

The final image can be used for specific morphological evaluation, such as measuring the height and width of alveolar bone to estimate the implantation position, and pathological evaluation of inferior alveolar neural tube related to mandibular impacted molars or diseases affecting jaw. Honey OB et al. [10] also studied the accuracy of CBCT measurement, and the results show that CBCT images have high reliability, and the accuracy of CBCT diagnosis is obviously higher than other two-dimensional joint areas such as linear tomography and panoramic radiography. At the same time, it is found that the two-dimensional lateral cephalogram made by CBCT is more accurate than the traditional lateral cephalogram in most linear distance measurements (sagittal plane). In a word, many scholars believe that the measurement of CBCT images of teeth, jaws and facial structures is repeatable, which is obviously more accurate and reliable than the traditional cephalometric measurement. This technology will undoubtedly expand the application of three-dimensional imaging technology in orthodontics.