Journal of Dental Technology
Lee Ann Brady DMD
The adaptation of traditional CT (computed tomography) scanning by modern 3-D cone beam technology has transformed the use of advanced diagnostic imagery from the extraordinary to the ordinary. Historically only a small percentage of patients received the advantages of this type of imaging prior to having dentistry completed to restore their mouths to optimal health, function and beauty. The inherent challenges of sending a patient to a hospital or diagnostic center to obtain imaging, where the technicians and radiologists were generally unfamiliar with obtaining scans that would provide the information the dentist was seeking and the expense of doing so created a barrier to routinely obtaining this information. Fortunately as dentistry has advanced and surgical procedures and implant placement have become the standard of care for which the need to obtain advanced imaging has become more important than ever, the technology became available to make this possible.
Traditional CT imaging is obtained when an x-ray beam is collimated to produce a flat fan of very narrow secondary beams. Each beam is aimed at a receptor panel on the opposite side of a circular gantry. As the patient is slowly moved forward the gantry is rotated around the subject and they are irradiated. The receptor panel transmits to a computer not a direct image but a signal indicating the amount the x-ray was attenuated as it passed through. The raw data is processed in the computer to create an attenuation value for each small component area of the scan, these are translated into “gray-levels” and an image is created.
3-D cone beam technology uses a larger cone shaped x-ray beam to expose a scan of the entire head with one rotation of the machine eliminating the need to move the patient forward for successive slices of data. The receptor than sends the information to a computer that uses a complex set of mathematical algorithms which create the “slices” equivalent to a traditional CT. Because of these changes to the technology it is now possible to obtain these high quality diagnostic images, easily and cost-effectively in the private dental practice. Current machines have been reduced in size, with a foot-print that resembles a panoramic machine. The patient is placed in an open environment, seated, where they do not have to be moved past the point of x-ray transmission to obtain the scan. The scan can be completed in under a minute with much less radiation than either a traditional CT or a full series of radiographs and the final image is available 2 minutes after completion of the scan. Software allows unlimited manipulation of the data, the operator can view the images in varying slice thicknesses from axial, sagittal and coronal views as well as completing a three dimensional reconstruction of the scanned regions. The data can also be constructed with traditional panoramic or cephalometric views of the scanned regions.
This new technology has also improved the image quality increasing the diagnostic value of the information obtained. Image distortion resulting from scatter has been reduced increasing the accuracy of the final image and the final image is a 1:1 representation of the anatomical structures allowing for precise measurement. The ability to easily obtain these high quality diagnostic images has already changed the face of implant dentistry. We have the ability to accurately assess bony architecture, including width and height measurements of potential placement sites, as well as bone quality and location of vital anatomic features. In the planning phase it is now possible to determine if bone grafting or sinus lift surgery will be necessary for optimal success. Selection of ideal sites for implant placement, and optimal angulation, implant size and type can all be
determined before the surgeon lifts the scalpel. Additionally the imaging can be used to correlate the anatomic architecture with the proposed placement of the final restorations to obtain maximal function and esthetics.
Using an original set of mounted study models the laboratory can create a wax-up of the final restoration based on ideal tooth position and occlusal function. This wax-up can than be duplicated by the technician and a clear acrylic template of the final restoration fabricated. The dentist than adds radiopaque markers (gutta percha) to the template. The patient has two scans completed, with and without the restorative template in place. Specialized software correlates the patient’s anatomy with the proposed location of the restoration. The implant placement is than planned virtually on the computer choosing locations that place the implant fixtures within the planned restoration, and where the bone has the best quality and quantity. This virtual planning is than used by the laboratory to create the surgical guide
Over the years most dentists and technicians who collaborate on implant cases have experienced the frustrations of having to fabricate a restoration to an existing implant site by altering emergence profiles or tooth form and alignment. Using this technology we can ensure that during the restorative phase we won’t have to compromise because the fixture placement has been exquisitely planned in advance allowing both the restorative dentist and the laboratory to obtain ideal esthetic and functional results.
Everyone involved in the process of helping patients receive optimal, comprehensive care benefits from having appropriate diagnostic information in the planning phase. This information allows us to reduce or eliminate the need to compromise care when we are confronted with a previously “unknown” scenario. At The Pankey Institute one of the “unknowns” we teach dentists to understand before commencing treatment is the health of the temporomandibular joint, and the position of the condyle in the fossa, because no occlusion exists in isolation without the joints and the muscles. Obtaining imaging of the joint has become a valuable adjunct, when indicated, to completion of a comprehensive muscle and joint examination as part of patient case work-up. Imaging is used to assess the bony architecture of the condyle and the eminence, as well as their relationship. The ability to slice the data, change the view and recreate a 3-D representation allows a comprehensive understanding of the anatomy.
The future holds untapped potential for using advanced imaging. Currently we can use the data obtained in three dimensions and create a sterolithographic model of the skull. These models are used to fabricate both surgical guides and final prostheses based on scanned images that correlate the anatomical structures with the planned implant placement and proposed restoration. 3-D cone beam imaging has advanced dentistry our ability to provide our patients with long lasting, successful, optimal dentistry.