Computed Tomography (CT)
- CT scanning adds X-ray images with the aid of a computer to generate cross-sectional views of a patient's anatomy.
- For missing single teeth the use of CT imaging the cost-benefit analysis renders it inappropriate.
- CT scanning can identify vital structures and be used to guide procedures, including accurate implant placement.
- Multislice computed tomography, represented a fundamental evolutionary step in the development of imaging techniques.
Conventional bi-dimensional imaging of the maxillofacial region is limited due to the overlap of anatomical structures, making visualization of the area of interest very difficult. Computerized (or computed) tomography (CT) scan, also referred to as computerized axial tomography (CAT), is an X-ray procedure that combines several X-ray images to build three-dimensional (3D) images of the internal organs and structures of the body, able to generate cross-sectional views. Since its introduction in the early 1970s, CT has undergone tremendous improvements in terms of technology, performance and clinical applications. The introduction of Multidetector computed tomography (MDCT), also known as multislice computed tomography (MSCT), represented an important step in the development and evolution of CT imaging techniques. In MDCT, a two-dimensional (2D) array of detector elements replaces the linear array of detector elements used in typical conventional and helical CT scanners. The 2D detector array permits CT scanners to acquire multiple slices or sections simultaneously and greatly increase the speed of CT image acquisition. The development of MDCT has also resulted in high resolution CT.
In the field of oral rehabilitation , CT scan provides 3D data, offering information on craniofacial anatomy for diagnosis and treatment planning, as well as an objective method for the classification of the bone quality and quantity, and can be used to differentiate tissues and characterize bone quality. The diagnosis of density changes is based on the darkness and brightness of images, expressed with Hounsfield Unit (HU) in a CT scan and with gray scale in cone-beam computed tomography CBCT. HU is a standard scheme for measuring CT values in CT scan. Some studies have shown a strong linear relationship between HU and gray scale. However, gray scale is different due to higher noise levels, more scattered radiation, high heel effect and beam hardening artifacts. Gray scale has many applications in determining the origin of lesions and tissues and density changes, but gray scales are not the same in various devices. So far, CBCT manufacturers have not introduced a standard system for displaying gray scale.
Rapid development of computer technology, improved performance, accessibility and lower cost have paved the way for digital and advanced imaging modalities. Computed tomography images provide important information regarding the individual characteristics of pathological lesions, information which is particularly useful for diagnoses and treatments. CT was used for imaging the temporomandibular joint, evaluating dental-bone lesion, assessing maxillofacial deformities, and preoperative and postoperative evaluation of the maxillofacial region.
The main disadvantage of medical CT is higher radiation dose than CBCT. Today, there still existed numerous disadvantages-radiation exposure and availability, like small increased risk of cancer in future from exposure to ionizing radiation (X-rays) and the uses higher doses of radiation than plain X-ray, so the risks are greater than for the other imaging types.