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News Bulletin : ADA News Bulletin March 2011
18 MARCH 2011 INTRODUCTION • Orofacial cone beam (CB) systems produce 3-D images of parts of the head and neck, including the jaws. • All dental, oral and maxillofacial clinicians must be familiar with the role of this technique. • It does not replace other imaging modalities. Instead, it complements plain 2D radiography, panoramic radiography ('OPG'), multislice computed tomography (MCT) and other techniques including MRI, ultrasound and nuclear medicine. RADIATION DOSE LEVELS • Not all CB units are 'low dose'. CB radiation doses range widely, largely depending on the unit used. • Some CB units can deliver higher radiation dose levels than MCT scans of the jaws (when appropriate low dose MCT protocols are employed). • Some CB units are able to deliver lower dose levels than low dose MCT scans for the same volume (3D data scanned). • Small field of view (FOV) CB units do not necessarily deliver doses that are lower than some larger FOV CB units. • Some CB units are capable of delivering doses comparable to some panoramic (OPG) units and some intraoral 2D series (number of projections, technique and detector dependent). • Comparing available data is difficult and the limitations in the measurement of the dose levels delivered are recognised. • Like most imaging technology, CB machines continue to evolve quickly. IMAGE QUALITY • Cone beam units produce images with higher spatial resolution than MCT although this benefit can be negated as a result of the weaknesses of CB, including scatter, beam hardening, imaging time and patient position. • Soft tissues are not sufficiently well examined with CB technique. MCT is far superior in this regard, which can be critical. It should be noted that many soft tissue lesions are best examined with MRI. • Measurements made on images from MCT and CB data have been shown to be similarly accurate. APPLICATION • There is some evidence for the use of CB imaging in many areas of dentistry, including pain diagnosis, endodontics, periodontics, implant planning, ectopic and impacted teeth, orthodontics and orofacial surgery, including image guided surgery. Caries diagnosis seems promising although further clinical studies are required. While the advantages of being able to evaluate structures in 3D and high resolution are obvious, it remains necessary that further clinically based studies are carried out to confirm the benefits of CB imaging, especially the advantages of CB over plain 2D radiography and how CB compares with MCT and MRI. These investigations are complex and involve extended time periods. This limitation of research on extremely fast evolving equipment is recognised. It is therefore essential that, when used in place of panoramic and/or intraoral 2D imaging, ultra low dose CB units should be used and appropriate low dose protocols employed. • MCT is a much more powerful and flexible modality and presently remains the technique of choice over CB imaging in several instances, especially complex cases (including dentoalveolar related inflammatory disease) and in the evaluation of more serious disease, e.g., severe infection and where a tumour is suspected. Low dose MCT protocols can be employed. • The use of intravenous contrast media with MCT examinations is sometimes essential for appropriate diagnosis. The value and practicality of post-contrast CB studies is not known although questionable, since soft tissues are poorly visualised. CONE BEAM IMAGING; the essential considerations committee report "...it remains necessary that further clinically based studies are carried out to confirm the benefits of CB imaging... These investigations are complex and involve extended time periods."
ADA News Bulletin February 2011
ADA News Bulletin April 2011