Navigating metals in the mouth – David Claridge Carestream DentalFeatured Products Promotional Features
Posted by: Dental Design 2nd June 2019
Diagnostic images remain one of the most important parts of effective patient treatment. However, even as imaging systems continue to evolve, there are some factors that can still interfere with the image taking process, one of which is restorative metals. These metals can cause metal artefacts on important diagnostic images, so it’s important for professionals to understand more about why this may happen and how to overcome it.
How many people have metals in their mouth?
Metallic components are used in a huge array of dental indications, from fillings to dental implants to fixed orthodontic appliances. It is estimated that over 80% of the UK population have fillings,[i]and although some of these are going to be composite or resin alternatives, this means that over 50 million individuals in the UK may have amalgam in their mouths. Although there have been recent efforts to move away from the material due to ongoing environmental concerns, the majority of people are likely to keep their metal restorations rather than run the risk of having them replaced. This means that metal fillings are here to stay and will continue to cause problems for the imaging process.
Metallic dental crowns are also likely to feature in the modern UK individual. Although there have been metal-free alternatives available for some time, due to the strength benefits and cheaper costs[ii]that full metal and PFM crowns can bring they remain a popular choice for treatment in posterior locations.
Overall, by compiling these numbers it’s likely that a high percentage of patients you treat will have metal in their mouths, making it an important factor to take into consideration when performing diagnostic images.
An obstacle in diagnosis
As anyone who has used a CBCT or CT machine will know, metals can sometimes create distortions or imperfections that are picked up in the final image and compromise the quality. These distortions can vary in appearance, but quite often appear as overly bright spots (cupping artefacts) or even as beams of light or darkness (metal streak artefacts), disfiguring the final image and making it harder to achieve accurate diagnoses. In these scenarios the image will need to be taken again, in which case there’s no guarantee that the same issues will not occur a second or even third time, or that synthetic data will impede the accuracy of the image as a whole. In light of these shortcomings, professionals should always look towards ways of limiting the effect that metals can have during CT or CBCT image acquisition.
So why do metal artefacts occur?
There are multiple reasons why metals in a patient’s mouth may affect image acquisition. In CT imaging, one cause of metal artefacts is thought to be beam hardening. Beam hardening is when a metallic substance hardens the beams used to create the image before they effectively reach the patient, resulting in widespread cupping artefacts that can overshadow the rest of the diagnostic image.[iii]This hardening of the X-ray beams is thought to occur when the beam made of polychromatic energies passes through the metallic substance, which results in selective attenuation of lower energy protons – i.e. the beam becomes solely high energy protons and therefore cannot function to the same standard, marring the image with artefacts.
Scatter caused by metals reflecting the beams can also be a cause of artefacts on the final image. These occur simply due to the reflective nature of metal materials and have been found to be worse when there is more than one piece of metal present.[iv]
Metals may also cause exponential edge-gradient effect (EEGE). This causes artefacts to appear whenever long, sharp edges of contrast are encountered.[v]A study[vi]that replicated the effect of metals on CT style beams found that a single metal restoration is unlikely to cause EEGE but multiple metal restorations can, meaning that these image distortions are likely to appear in patients that have more than one amalgam filling or metal crown.
A sharper image
So what can professionals do to combat these image defects? You’re probably aware of certain filters or metal artefact reduction (MAR) methods already, but these are rarely integrated into image acquisition technology. That is, unless you choose the CS 9600 from Carestream Dental. With the optional CS MAR module, the system allows professionals to drastically reduce any metal artefacts found in the image, even letting you explore the image dynamically with or without filters so that you can always achieve a confident diagnosis.
Restorative metals are so widespread it’s unlikely that we will see them disappear from patients’ mouths in the near future. Therefore, to remain confident in the diagnostic process, professionals should look towards technology that can help to abolish the image artefacts that metals in the mouth can cause.
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[ii]Dental Treatment Guide. Dental Crowns. Link: https://www.dental-treatment-guide.com/dental-crowns/metal-crowns[Last accessed November 18].
[iii]De Man, B., Nuyts, J., Dupont, P., Marchal, G., Suetens, P. Metal Streak Artifacts in X-ray Computed Tomography: A Simulation Study. Link: ftp://kumulus.uzleuven.be/pub/nuyts/publications/bdm_ieeetns99.pdf[Last accessed November 18].
[iv]De Man, B., Nuyts, J., Dupont, P., Marchal, G., Suetens, P. Metal Streak Artifacts in X-ray Computed Tomography: A Simulation Study. Link: ftp://kumulus.uzleuven.be/pub/nuyts/publications/bdm_ieeetns99.pdf[Last accessed November 18].
[vi]De Man, B., Nuyts, J., Dupont, P., Marchal, G., Suetens, P. Metal Streak Artifacts in X-ray Computed Tomography: A Simulation Study. Link: ftp://kumulus.uzleuven.be/pub/nuyts/publications/bdm_ieeetns99.pdf[Last accessed November 18].
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