CBCT vs conventional views in localising impacted canines. Careful with that radiation Eugene: (Revisited).


One of the first posts that I did was on the use of CBCT in localising unerupted teeth.  The AJO-DDO has recently  published an investigation that looks at this subject in greater depth.  As a result, I am updating this post on this important subject.

This also allows me to return to my adolescence  and tendency to name blog posts after Pink Floyd tracks….

vervolg: CBCT vs conventional views in localising impacted canines. Careful with that radiation Eugene: (Revisited).

We are all familiar with the clarity of images that we can get from CBCT techniques. However, there is some concern that, as with all new techniques, there is a tendency for over prescription.  For example, some orthodontic practices state that they routinely use CBCT imaging for most of their patients.  This is an important area because of the increased radiation exposure with CBCT compared to conventional imaging. Furthermore, there is no safe level of exposure and we do not know the long term effects of excessive radiation exposure.

As a result, it is becoming essential to evaluate the risk/benefit balance of CBCT against conventional techniques.  This paper is a systematic review that attempts to answer this question. I thought that it was interesting but very complex! A team from California and Boston did this study.

Cone-beam computed tomography vs conventional radiography in visualization of maxillary impacted-canine localization: A systematic review of comparative studies

Ehsan Eslami et al

Am J Orthod Dentofacial Orthop 2017;151:248-58  http://dx.doi.org/10.1016/j.ajodo.2016.07.018

They aimed to find out if there was any difference in the diagnostic accuracy, agreement, treatment planning and societal efficacy between CBCT and conventional imaging in the assessment of impacted canines.

What did they do?

They took a really interesting approach and decided to base their study on the measurement of “clinical usefulness in decision making”.  In effect they asked these five questions.

  1. Is there a the difference between the modalities in the accuracy of maxillary impacted canine localization?
  2. What is the intermodalities agreement between information obtained by CBCT compared with conventional radiographs for the localization of maxillary impacted canines?
  3. What is the level of agreement between the treatment decisions made from CBCT compared with conventional radiographs?
  4. Are there differences between the treatment outcomes provided through these modalities?
  5. What is the difference between the societal costs incurred with these modalities?

They carried out a standard systematic review directed at this PICO;

Population:  Patients or still life models with an impacted canine

Intervention:  CBCT imaging

Comparison:  Conventional 2D views

Outcome: Diagnostic accuracy between methods, treatment planning, outcome efficacy and social assessment.

Two authors identified the papers. They then evaluated them for bias with the Newcaste-Ottowa Scale and the Quality Assessment of Diagnostic Accuracy Studies tool to evaluate the diagnostic criteria.

What did they find?

They identified 8 studies for inclusion. Most of these had a high risk of selection bias with the inclusion of “complex” cases.  I looked at their results and I felt that these were the main findings:

  1. The accuracy of CBCT ranged from 50-90%. Whereas the accuracy of conventional views ranged from 39-85%.
  2. The information gained from CBCT was different from conventional radiographs.  But I was not clear on this (no matter how many times I read this section of the paper).
  3. The general agreement between techniques was moderate.  Three studies looked at the therapeutic efficacy of CBCT and there was a 70-80% agreement between the techniques.


In their very wide ranging discussion they covered a large amount of information. I must admit that I found a fair amount of the discussion a little confusing.  Nevertheless, the authors clearly stated the following:

  • CBCT is more accurate than conventional techniques in localising impacted maxillary canines.
  • CBCT is more reliable than conventional techniques
  • There is no robust evidence that supports using CBCT as the first line imaging technique. We should only use it when conventional radiography does not provide sufficient information.

What did I think?

I thought that this was an interesting systematic review.  The authors used a clinically relevant technique to drive the methodology. As a result, it provides us with useful information.  However, I found the paper very complex and I hope that I have correctly interpreted the large amount of information in the paper.

It is relevant for me to point out that the authors felt that the results supported the recommendation of the SEDENTEX project, the British Orthodontic Society and the AAO guidelines (this last one is members only).  These all state that CBCT should only be used when information cannot be obtained from conventional techniques. I have always practiced this way and I shall not change.  Nevertheless, whenever I have discussed this with colleagues someone has said “but, if we start with conventional techniques then move to CBCT then we are exposing the patient to more radiation than if we just did a CBCT”.  My view is that we should consider the risk for each patient and still attempt not to irradiate too many of our patients.  I think that this is best practice because we do not know the diagnostic yield vs the risks of the extra radiation.

This brings me to the practice of routine taking CBCT views for orthodontic patients. This will be the subject of another blog post.


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