Earlier this week I published a tongue-in-check piece which has suddenly become one of my most popular texts on this blog. Today I want to switch back to more serious tone and try to answer a simple question:
“When should we take CBCT of the orthodontic patient?”
How many times online or during the conference we have seen a practitioner advocating for the routine use of CBCT? To justify this the orthodontist would often show the images of scanned airways or primary dentition before and after. “3D images helped me to diagnose airway constriction and crowding, I can’t even imagine how I would now practice without this marvellous technology!” – such specialist would say. This, of course, are strong statements, and looking closer you will likely find an affiliation of the practitioner with the manufacturer of diagnostic equipment.
Let’s now throw away all the possible speculations and draw our attention to the current research data.
Does CBCT affect clinical decisions?
First, I want to look at a study in which 24 orthodontists were asked to evaluate six patients cases with classic diagnostic records and then CBCT records were added to the whole picture.
Ryan J Hodges et al., Am J Orth, 2013 May;143(5):665-74
Indeed, some treatment plans had been changed, however only in these particular situations:
- Discovery of unexpected aspects of the location of unerupted teeth
- Severe root resorption related to contact of the crown of an unerupted tooth with an erupted tooth
- Severe skeletal discrepancies
CBCT records haven’t affected the clinical decisions regarding airway or crowding.
The authors concluded:
“We propose that CBCT scans should be ordered only when there is clear, specific, individual clinical justification.”
Of course, it is a slightly dated and small study, however more recent and extensive studies only reinforce its findings. For example, I advice you to look at this comprehensive systematic review from 2018:
Annelore De Grauwe et al., EJO, Vol 41, Issue 4, Aug 2019
It has been very detailedly analysed by Kevin O’Brien in this blog post of him, so here I would just point out the advantages of CBCT over 2D imaging proposed by the authors:
- Diagnosis of root resorption
- Evaluation of root fractures
- Imaging of complex craniofacial problems
Is CBCT a reliable method to diagnose airway problems?
Here is another relevant study that looks particularly at the airway assessment:
Daniel Patrick Obelenis Ryan et al., Am J Orth, 2019;156:53-60
Despite an unambiguous message of the AAO white paper on sleep apnea, some practitioners still use CBCT pictures to illustrate the efficacy of their treatment modalities in enhancing breathing.
The issue with this approach is the fact that the airway is not static. It constantly changes during the breathing cycle and a radiographic image depicts just a particular stage of the process.
In their study the authors included 27 CBCT scans of non-growing patients taken with 4-6 months intervals. All measurements were done by one trained operator.
The authors concluded:
“Different CBCT exams with equal scanning and patient positioning protocols can result in different 3D pharyngeal airway space readings.”
In other words, every time you take a CBCT scan the airway volume measurements would be different.
Low dose CBCT?
Certainly one of the most critical issues of CBCT is its radiation dose. To the day, the effective dose of CBCT scans produced by most machines is many times greater than of conventional panoramic examinations.
However some adepts of routine CBCT examinations state that there is also an option to take low dose CBCT which would be comparable to panoramic radiographs.
After a PubMed search, I found a paper where the authors indeed claim one particular model of CBCT machine is capable to produce extremely low doses.
John B. Ludlow, Cameron Walker, Am J Orth, 2013 May;144(6):802-817
The issue with this study is that the authors were paid a “honorarium” by the manufacturer – the exact sum is not disclosed. Moreover, despite the potential positive bias the authors’ conclusion was still not very persuasive:
“QuickScan+ effective doses are comparable to conventional panoramic examinations. Significant dose reductions are accompanied by significant reductions in image quality. However, this trade-off may be acceptable for certain diagnostic tasks such as interim assessment of treatment results.”
In other words, we probably could limit the dose using an expensive new equipment, however no guarantee we will be happy with the images produced.
When should we take CBCT of the orthodontic patient?
Overall, there is no data in the literature to support the indiscriminate use of CBCT in orthodontic diagnosis. We certainly know that CBCT has greatly expanded our abilities in visualisation, but we also have to consider the potential harm of the radiation.
Given the current research data and my clinical experience, here are the situations I take a CBCT scan:
- Impacted and supernumerary teeth
- Root resorption evaluation
- Placement of TADs
- Visualisation of TMJ structures if problems suspected
- Midpalatal suture maturation assessment
- Surgical cases
No doubt in the future we will have new CBCT machines with proven low radiation doses, but until then we have not put our interests above the patient’s safety.
Here is this blog post in the form of a YouTube video: