November 12, 2018

When should we take a Cone Beam CT? Careful with that radiation, Eugene Part 3

There is no doubt that CBCT has revolutionised orthodontic imaging. But when are we justified to take a CBCT?

I think that CBCT imaging is great. It certainly enables us to see the things that we could not see on conventional radiographs.  However, we need to consider whether the additional radiation exposure is justified. I have posted about this several times before and this generated a lot of discussion.  It is, therefore, relevant to see this update paper in the EJO.


Annelore De Grauwe et al

EJO: on line:  doi:10.1093/ejo/cjy066

The EJO have made this open access and this means that you can access it without being a member of the EOS. This is great news!

They started the paper with a nice literature review. Importantly, they pointed out that the dose from a CBCT is still higher than conventional 2D radiographs. They also emphasised that there are three fundamental principles of radiation protection. These are justification, optimisation and dose limitation. Finally, they mentioned that the SEDENTEXCT guidelines stated that it is not possible to differentiate between safe and harmful exposure because of stochastic effects. So we need to be careful.

What did they ask?

They wanted to find information on the diagnostic efficacy of CBCT in pre-orthodontic treatment children.

What did they do?

They did a systematic review with the following PICO

Participants: Paediatric patients

Intervention: CBCT

Control: 2D radiography

Outcome: Treatment change caused by the availability of CBCT images

They searched for papers that described diagnosis, therapeutics and efficiency when comparing CBCT and conventional imaging.

They did a standard systematic review with two independent assessors carrying out the paper search, data extraction, and paper identification. Finally, they assessed risk of bias and quality.

What did they find?

Following their extensive search and planned exclusions, they obtained a final sample of 37 articles.  They assessed the quality of the studies using the Quality Assessment of Diagnostic Studies (QADAS). This tool is used to assess the quality of diagnostic studies. You can find further information here.

They presented a narrative of their main findings and divided them up into several sections. I thought that the most relevant were:

Root resorption

CBCT showed better detection rates than 2D images. For example, 63% more root resorption was detected with CBCT than with 2D views.


They only found three papers on this area.  These showed that CBCT was better than 2D imaging in detecting root fractures.

CLP and other craniofacial problems

CBCT was clearly superior to 2D views in rendering cleft volume, root morphology, the outcome of bone grafting and imaging complex problems.

They summarise their main findings by suggesting that CBCT had advances over 2D imaging in the:

  • Diagnosis of root resorption
  • Evaluation of root fractures
  • Imaging of complex craniofacial problems.
What did I think?

This is an important area of our practice, as we can cause harm by over exposing children to unnecessary radiation. I thought that it was important when they related their findings to the SEDENTEXT guidelines and the DIMITRA position statement. 

Both these documents clearly state that CBCT was not recommended for detection of cysts, periapical lesions, periodontal assessment and periapical disease.

In fact, SEDENTEXT is very specific. They could not recommend CBCT as a standard method of diagnosis and treatment planning in orthodontic practice. Finally, SEDENTEXT sets out this bold statement.

“Where health professionals change their practice to adopt a diagnostic technique where there are radiation risks to young patient groups, the onus is on them to demonstrate significant improvements in patient outcomes”.

I thought that this statement was very relevant when I looked at the supplementary data on radiation doses in the studies that they included in this paper. (Table 2 in this link)This showed that the dose from CBCT ranged from 26 uSV to 194 uSV. Whereas the dose from a paediatric panoramic view is 5 uSv.  These comparative dosages look pretty high to me!


I cannot help thinking that this is a complex area of our care, or is it just confusing to me?  It appears there are some clear indications for using CBCT and these are outlined in this paper and the advisory documents from SEDENTEXT and DIMITRA. Importantly, they do not suggest that CBCT should be routinely used in an orthodontic patient population. Yet, we seem to be starting to use CBCT in this way. Surely, it is clear that CBCT is not necessary for most of our patients when we consider the possible risks and the potential harm that we may cause.

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Have your say!

  1. Kevin, I think it’s probably best to NOT group all CBCT’s into the same pot. While some are still more exposure than 2D radiographs, some are not. To group them all together would be misleading. I find a comfort in “knowing” where teeth are relative to other teeth, particularly in mixed dentition and I can better diagnose relative jaw widths (ala Miner, et al) and it allows me to surmise the most likely location of an airway problem when there is one. Moreover, by having before and after CBCT, we can superimpose much more completely and accurately than 2D to determine exactly what we’re doing. Whenever prescribing a radiograph, it’s appropriate to balance the benefit vs the cost. When the “cost” in exposure is less than 2D and the benefits are huge, it makes sense. In fact, if the difference is small, it still may be justified.

  2. It is very confusing the more you think about it. I should know probably but are stochastic effects dose related? ie the higher the dose the greater the likelyhood or number of stochastic effects or is it impossible to relate dose to this. I know that there is no safe threshold but this is not quite the same thing.
    There is no doubt that CBCT gives you alot more info but the question is does this have any effect on treatment success? It may alter your treatment plan (ie you may take out more resorbing laterals than before because you can find more resorption) but are these decisions correct? Some resorption presumably is ok and will stop.
    There is also no doubt that if you have a CBCT machine then you will want to use it.
    All together I’m not sure what the question is regarding CBCT, never mind the answers. I’m pretty sure it’s not needed for most canine cases but not sure when it is needed.

    • The first issue we have in orthodontics and medicine is to “Do no Harm”. Until we as a specialty start looking at the bone thickness that a patient has or does not have we can potentially do harm. The 2d images do not show this dimension. I have gone back and looked at many patient that I did exceed the biological limit of the patient’s bone thickness. It is incumbent upon us as a specialty to do this. Its actually less radiation with more information. It changes how I treatment plan daily. I trust this does improve the the patient’s final outcome and stability.

  3. It seems to me that even in those three scenarios additional clinical and dental/medical history would also be needed to justify the need of a CBCT. This should be obvious but worth stating. Not in every syndromic patient every time imaging is required implies CBCTs.

    Based on what is presented CBCT is better in detecting root resorption but does it clinically matter in most cases? It is likely more important the degree of root resorption and the location of it than the fact that we have a tool that allows us to better identify it. Would it change treatment? An argument can be made that if it is not fully known how can we question if different treatment is required? The point I am raising it that we need to plan and execute better studies that do actually answer the fundamental question if a better visualization tool implies better treatment outcome. There are only a handful studies in this regard.

    Regarding root fractures there is no major argument. The only point to raise is that a small filed of view would suffice in those cases. So really the need of a full filed of view in every orthodontic case is another point to question. Personally I indicate CBCTs after I have taken 2D radiographs that do not provide me enough information to make an informed treatment decision. Hence I seldom ly take a full filed of view. It usually is a request for a medium filed of view (TMJs, multiple impactions, etc.) or a small field of view (single tooth impaction, trauma, etc.)

    Finally a CBCT was adequately justified during the treatment planning stage. Is there really always the need fo another one later in treatment? Would then not 2D imaging suffice?

  4. For me CBCT is not first choice, nor should it be unless you are managing CLP/root trauma etc. ie specic areas of practice
    IMHO for assessing the vast majority of ortho, canines an OPG +/- Ceph is good enough.

  5. The use of CBCT is no longer a radiation issue. The newer softwares with the machines can take an Ultra Low / Low dose that delivers only approximately 14 Micro Ceiverts effective dose.
    A 2 d pan is approximately 35 MC. That is less information with more radiation. Read the article published by Dr. Ludlow from the Univ. of North C. He concluded the the image quality for the Plan Meca Mid ultra low, low settings was adequate for orthodontic diagnosis. An orthodontic practice that uses the same brackets on all patients and does not look the the thickness of the alveolar housings do not need to take scans. The use of CBCT for impacted cuspids is not really needed unless the orthodontist uncovers his own impacted teeth. If the orthodontist is also focused on looking at airways on their patients then a cbct is warranted. There are many other reasons. So to say that CBCTs are not warranted on all patients is not taking into considerations that our specialty has morphed into about 5 or 6 different types of practices. To practice the way we choose to practice warrants a scan on all of our patients. We do to necessary do a full scan on all patients. The field of view may vary. Less radiation with more information. The world is not Flat.

  6. I would like to hear my colleagues’ opinions more on the use of cone beam in light of the fact that we can take relatively low dose images with images from machines like the ICAT FLX; I think the radiation can be much lower than multiple traditional x-rays, and they have the ability to view airway and the TMJ’s, which traditional imaging does not do as well. Obviously these lower dose images are not good at detecting caries like bite wings do, but also keep in mind that I believe there is quite a bit more unnecessary radiation exposure done in retaking images where the head and cone position are not ideal due to technique issues. I am sure that these retakes are way under reported. What do you all think???? do I make some valid points???

  7. What does looking at the airway do? What is the implication? Teeth will still need extraction for orthodontic reasons. No data to support a connection between extraction and sleep apnea. This “looking at airway” stuff seems to be a hammer looking for nails.

  8. Kevin,
    We have no current financial interest in any CBCT company, although both of us have spoken with compensation on behalf of the company in the past. Although your summary of most reviews seems accurate, we must say that we read this post with some dismay, noting two very significant omissions.
    First, any post or review such as this that still includes data from the Hitachi Mercuray is suspect. The Mercuray was not a dental CBCT scanner as we know it, but rather a combination of helical CT and CBCT with radiation levels orders of magnitude higher than other machines, old or new. In addition, the Mercuray is no longer available, and very few were ever sold. To the best of our knowledge, none of the Mercuray units are currently in operation. It is purely a red herring, and in our opinion added only to inflate the levels of radiation associated with CBCT. We question if the authors had an agenda to suggest that CBCT should not be used as a routine superior substitute for the traditional orthodontic radiology series.
    Second, none of the studies by Oral and Maxillofacial Radiologist Dr. John Ludlow from the University of North Carolina were included. This exclusion is puzzling, given Dr. Ludlow is widely considered a leading expert in radiation dosimetry. Excluding Dr. Ludlow’s papers, most significantly his 2013 paper (Ludlow JB, Walker C., Assessment of phantom dosimetry and image quality of i-CAT FLX cone-beam computed tomography, Am J Orthod Dentofacial Orthop. 2013 Dec;144(6):802-17.) which concluded that the iCAT FLX “QuickScan+ effective doses are comparable to conventional panoramic examinations” leads us to believe the entire point of the commentary was to discourage routine use of CBCT rather than an objective review of available information. It seems a bit disingenuous to compare the high-resolution CBCT dosages they used with a pan/ceph combination dosage when most orthodontists we have spoken to do not use such high-resolution doses. In fact, we did not see the typical and widely used 4.8 seconds, 300-micron scan included anywhere in the dosage comparisons.
    If we look at international agencies that monitor medical and dental radiation, the amount of radiation we are discussing (less than 100 uSv) is magnitudes below any amount even referenced by these agencies, and by inference, should be extremely safe.
    The American Association of Physicists in Medicine (AAPM) issued the following position statement in December 2011: “risks of medical imaging at effective doses below 50,000 uSv for single procedures or 100,000 uSv for multiple procedures over short time periods are too low to be detectable and may be nonexistent.” Dezarn. W, A. et al. Recommendations of the American Association of Physicists in Medicine on dosimetry, imaging, and quality assurance procedures. Medical physics 38. 48244845 (20”).
    The ICRP recommends we keep non-occupational exposure levels less than 1,000 uSv pt./ year. ICRP, 2007. 2007 Recommendations of the International Commission on Radiological Protection (Users Edition). ICRP Publication 103 (UsersEdition). Ann. ICRP 37 (2-4).
    The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) report of 2012 states that no discernible effects of exposures below 0.1 Sv (100,000 uSv) appear to exist, which is compatible with known cellular-repair mechanisms. Bertin. D. M. [2012 report of UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation)]. 1-21 (2012).
    Finally, the few uSv difference between the most common CBCT scans used (and we remind the readers no such low dosage scans were included in this study) and the uSv exposure for a pan and ceph combination (we can debate which has more radiation if you add data not included in the current review) it is less than the daily exposure from background radiation. We can accept that any orthodontist may not choose to spend the money to purchase a 

    CBCT machine as a practice management decision. What we have an issue with is when we hear of orthodontists who hide behind bad data and claim they are protecting their patients by sticking with a pan/ceph for diagnostic records. Granted many patients can be treated with a pan/ceph if we are only looking at teeth. When we consider that for the same level of radiation we can generate a pan and ceph, look at root position and tooth eruption patterns in 3D, view sinus and nasal structural anomalies, corrected tomograms of the temporomandibular joints, airway measurements (critical data points for airway assessment), skeletal and dentoalveolar asymmetries in all three planes of space, PLUS the ability of our patients to understand diagnostic findings visually, in our opinion, it is utterly inappropriate for all orthodontists NOT to use CBCT routinely.

  9. Why use it “routinely”? What benefits does it provide in every case? Other than the financial benefits to the manufacturer and the KOLs who push this concept, it seems quite ludicrous to make this recommendation. If one is going to make such tall claims, then perhaps they can provide evidence to support such an untenable position? How does looking at the airway change our treatment plan? Is such intervention supported by the science? Routine CBCT is certainly not supported by the data. Opinions are not facts and cannot be viewed as such, especially when the proponents have past or present financial conflicts of interest with the proposed technology. Claims made by such individuals must be looked at critically.

  10. You can not know which one is the last drop or does it matter if it was the last drop or not when it overflowed. While we try to keep away from even a periapical radiograph. I think we should be so careful while using this ‘knife’ Sedentexct is a useful guideline for this purpose. I would like to thank everyone who took attention to this topic. My best wishes.

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