One of the most important innovations in dento-alveolar diagnostics has been the advent of 3D cone beam computed tomography (CBCT), which has proven effective for a number of applications in oral healthcare. With more affordable systems being introduced into the market, practitioners are investing in their own systems thereby gaining immediate access to accurate 3D images of anatomical structures, enabling more precise diagnoses and treatment planning.
However the rapid growth in the install base of dental CBCT systems has given rise to concern about the level of radiation dose used by these systems and therefore the justification in their use.
Carestream Dental (manufacturer of Kodak Dental Products) has always maintained that use of ionizing radiation should conform to the principle of 'as low as reasonably achievable', and that every precaution should be taken to minimize radiation exposure.
Nigel Rosenbaum, principal of Peak Implant Clinic in Matlock, Derbyshire and clinical teacher in implant dentistry at Sheffield University, is a specialist in prosthodontics with over 10 years' experience in implantology. Until recently, when necessary to acquire a 3D view, he would refer his patients to one of the local medical centres for a CT scan. However this was never totally satisfactory for a number of reasons, as he explains: 'As the dose from a medical CT scan is relatively high I considered very few cases were justifiable.'
Nigel frequently found the radiographer administering the CT scan would not be totally conversant with the dental requirement, sometimes resulting in a scanned image that did not provide the information needed.
The advances in on-site CBTC 3D systems gave him the opportunity to invest in his own system. He commented, 'By having my own 3D system in house I now have total control and can ensure I get the image that I want.'
More important was the significantly lower levels of radiation involved in dental CBCT scans compared to medical CT scans, while at the same time they delivered much clearer and more informative images.
Peak Implant Clinic decided on the Kodak 9000 3D system (supplied and installed by Henry Schein). This device exposes a selected field of view capturing a volume equivalent to a quadrant view, thus the dose is kept to a minimum while the image resolution is maximised. Nigel explains it is not necessary to expose a larger volume: 'Where possible I get the information that I need from a quadrant view, were I to capture a larger field of view then I am obliged to analyse all of the areas in that view. I may then find myself having to report on areas of the anatomy that I consider being outside of my expertise.'
X-ray radiation dose is most often quoted as effective dose which allows for the effects of the radiation in different parts of the body. It is measured in micro sieverts (uSv). A guide to the dose delivered from the Kodak 9000 3D local field of view is in the region of 9-22 uSv depending on the area being exposed. A 2D panoramic scan can deliver between 4-30 uSv while a periapical intraoral between 1- 8 uSv. Medical CT scans limited to cover the jaw can operate anywhere in the region of 100-3300 uSv. So in general the local field of view 3D scan will be approximately 1.5 times that of 2D panoramic and 3.5 times that of an intraoral (however in such cases more than one intraoral may be required while a single 3D scan is usually sufficient).
The dose delivered from the Kodak 9000 3D is at a level that expands the justifiable indications of taking a 3D scan, but Nigel still undertakes a strict discipline of considerations before deciding on taking a 3D scan. Not every implant requires one. Currently Nigel is finding about 30 per cent of implant placements will benefit from having a 3D view. When deciding on a 3D scan for implant therapy particular consideration is given to:
- Proximity of proposed sites to important anatomical structures
- Pre-operative assessment of maxillary sinus (prior to augmentation)
- For bone grafts the harvest site would be scanned.
The opportunity to show a patient anatomical restrictions when treatment planning greatly enhances understanding, reinforces consent and consequently increases case acceptance.
The Health Protection Agency has recently been involved in providing guidance in the use of this CBCT to ensure this new technology follows the existing regulations and that users can sensibly apply the technology to obtain better diagnosis leading to faster, more accurate and improved patient treatment.