CBCT vs conventional views in localising impacted canines. Careful with that radiation Eugene: (Revisited).
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….
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.
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.
- Is there a the difference between the modalities in the accuracy of maxillary impacted canine localization?
- What is the intermodalities agreement between information obtained by CBCT compared with conventional radiographs for the localization of maxillary impacted canines?
- What is the level of agreement between the treatment decisions made from CBCT compared with conventional radiographs?
- Are there differences between the treatment outcomes provided through these modalities?
- 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:
- The accuracy of CBCT ranged from 50-90%. Whereas the accuracy of conventional views ranged from 39-85%.
- 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).
- 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.
Summary
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.
Emeritus Professor of Orthodontics, University of Manchester, UK.
Thank you Kevin.
Just what we keep saying. Simple things first.
BOS Orthodontic Guidelines still a definitive document.
Allan
I routinely take CBCT over a conventional Pan. Time and time again the diagnostic information is remarkable. With one scan I have a Pan, a Ceph, Digital study models, the soft tissue profile, and an accurate 3D view of the developing dentition. I can also clearly see supernumery teeth, internal or external root resorption etc. etc. No one can ever fault me for over diagnosing a case.
You must always razzle dazzle the patient with new technology don’t you know
Impacted canine which failed to erupt due to lack of normal path of eruption will probably cause resorption of adjacent teeth eg upper latral incisors. Conventional xray fails to show lingual root resorption that may change the treatment plan which will consider latral incisors extraction in some cases.
CBCT is a reliable diagnostic tool that will facilitate location of impacted canine and help the clinician to establish successful mechanics.
Distortion,inability to detect resorption of adjacent teeth, superimposition
of structures, errors in projection, imagingartifacts, and variation in magnification are commonly seen with conventional xray.
there are a study showed that, linear and angular measurements on CBCT images are accurate and precise and can be used to assess the exact position of palatal displaced canines.
Impacted canine which failed to erupt due to lack of normal path of eruption will probably cause resorption of adjacent teeth eg upper latral incisors. Conventional xray fails to show lingual root resorption that may change the treatment plan which will consider latral incisors extraction in some cases.
CBCT is a reliable diagnostic tool that will facilitate location of impacted canine and help the clinician to establish successful mechanics.
Distortion,inability to detect resorption of adjacent teeth, superimposition
of structures, errors in projection, imaging artifacts, and variation in magnification are commonly seen with conventional xray.
there is a study showed that, linear and angular measurements on CBCT images are accurate and precise and can be used to assess the exact position of palatal displaced canines.
Dear Dr. O’Brien,
Is the following of interest to you:
Position statement by the American Academy of Oral and Maxillofacial Radiology (2013)
http://www.sciencedirect.com/science/article/pii/S2212440313002800
I think that Table III is helpful. I noticed that there are not too many I = Likely Indicated.
A ultra Low dose configuration of the Plan Meca Mid delivers an effective dose of around 14 to 15 micro Ceiverts depending on the head size. A traditional pan delivers around 35 micro ceiverts. Why would we deliver more radiation to get less information
About our patients. Yes we do take ULD scans on all patients.
If you use the ICAT FLX you are using 1/2 the dosage of a digital panoramic x-ray. So the argument about dosage is a thing of the past.
Hi Kevin,
Thank you for shining a light on the important subject of impacted canines in clinical practice, a subject dear to my heart. As important is the issue of radiographic hygiene for wet finger dentist. I found it interesting that the 2015 British Orthodontic Societies 4th edition of “The Guidelines for use of Radiographs in Clinical Orthodontics” shows examples of 8 radiographs with 7 of them depicting impacted canines. I think this alone points to the importance radiographs play in the accurate diagnosis and location of canines in an orthodontic practice. Your last two review articles on diagnosis of impacted canines with CBCT by Julia Naoumova (EJO) now has to be balanced on the scale of radiographic hygiene.
I don’t think anyone disputes the fact CBCT is better at locating a canine or for that matter any tooth in 3 dimensions of space. This is all well and good after the fact but the question remains “how do we prevent (minimize) canine impactions with the least amount of ionizing radiation in clinical practice.”
We should not under estimate the role of clinical observation and basic knowledge of canine eruption patterns in the diagnosis of (potential) impacting canines augmented by radiographs not the other way around. Time will tell if CBCT becomes one of the front line defenders in this day to day battle.
Thanks for your excellent reviews.
Since the radiation exposure of an ICAT FLX can be set so low and you can get multiple views at less radiation than a conventional panorex and peri-apical and occlusal films to locate a cuspid, I am not sure I understand the logic in not having a CBCT as your initial imaging. What am I missing?
Additionally, I am not aware of any documented injury to patients with routine x-rays, so I am wondering if we may be erring on the side of being overly cautious at the risk of missing important diagnostic imformation
Thank you very much for presenting this study. I’m sure some day it will be regulated by law.
Hi Kevin,
Thank you for your posts I enjoy reading them and always learn something. I think the main indications for using CBCT in canine impaction cases other than to localise the position of the impacted canines is to diagnose adjacent tooth resorption which will certainly influence my treatment decisions. The information also allows me to advise patient about damage and therefore cover myself medico-legally.
I am currently trying to prepare a paper on the incidence of lateral incisor root resorption with palatally impacted canines and predictive factors.
Thanks again.
With current CBCT scans, the exposure can be only marginally higher than an OPG. If you seek specific diagnostic information, such as locating canines, a narrow focus area can be used which is less than a single PA. I am not advocating for full mouth CBCT for every patient, but to assess each patients needs and make a clinical decision then. As you note, there is a possibility some imaging is taken and then the dose is increased if this is elevated to a CBCT as further information is needed. You noted that you would prefer to use the best practice for the patient and start with the lower dose. If the average patient will receive less radiation by having a CBCT first rather than some having and OPG and others having both, would this not change things. I would have thought that this was the point of studies. To find out which treatment or investigation is best for the average person and then decide based on their specific case whether you should deviate from that norm. By this, I mean, starting with a lower dose and then increasing it so the average patient is worse off, would not be protecting patients from further radiation and would provide less diagnostic information for some patients.
thanks for the blog post
Do we get to a point though where a modern CBCT delivers a comparable or lower dose of radiation than an old OPT machine? At what stage does some regulation tell us we have to replace old digital equipment that can’t be upgraded to be more sensitive and deliver lower doses? I presume the oldest mass produced digital OPT machines are 20 + years old now. How does that compare to a CBCT that was shrink wrapped in the factory this morning?
If the doses are the same, then likely the CBCT gives enough diagnostic info to warrant its routine use. Presumably it replaces a CEPH too (if you felt a CEPH was a benefit in the first place).
Stephen Murray
Swords Orthodontics
CBCT scans are more accurate diagnostic tools compared with Xray scans.
CBCT scans have higher dosage than all single Xray scans but lower dosage compared to 2 or more Xray scans.
CBCT scans incur higher financial burden.
Conventional preliminary Xray diagnostics for treatment planning is often insufficient diagnostic information for impacted canine treatment planning.
With experience, treatment planning can be at Standard of Care level without detailed xray/CBCT scans.
Finish Xrays are not necessary.
Records are not deemed complete unless finish Xrays are taken.
Practice audits are not survivable by clinicians without complete records.
Treatment practiced outside of historically comprehensively documented methodologies are not accepted as even the most basic level of evidence basis.
It is interesting that with the advent of the most cutting edge diagnostic tool to date, we set rules that lock us into only historically ratified practice methodologies.
My question, once radiation levels for full head scan CBCT machines are brought down to be less than single film xrays, should we petition under guidance of xray hygiene, that all practices that own Xray machines, replace them with CBCT machines?
The diagnostic problems and treatment risks associated with the alignment of impacted canines demand not only the early detection of tooth eruption disturbances but they are of special importance for the treatment planning in cases of impacted canines and the detection of root resorptions on adjacent teeth (1, 2).
At the age of 9 to 10 for most children a clinical inspection including the successful digital palpation of the permanent canines bulge on the alveolar process above the root of the deciduous canine together with an account of the general occlusal development and somatic maturity oft he child are sufficient to make an expert appraisal of the possibilities of natural tooth eruption (5, 49, 54).
In a minority of cases the bulge of the permanent canine can not be detected and supplemental imaging is necessary to determine the position of the canine to exclude eruption disturbancies and possible root resorptions on adjacent teeth (1, 2, 50, 56, 57, 59).
Due to the problem to depict a three dimensional corpse in a two dimensional image, the radiological imaging of impacted canines and their surroundings with low dose conventional radiographs like panoramic radiographs and intraoral radiographs (upper standard occlusal radiographs, paralleling technique periapicals) is limited and in certain cases does not correspond with the required accuracy and reliability.
Nevertheless panoramic imaging is indicated in course of a stepped progress (3-13).
The palatally impacted canine will be magnified (11, 13) in comparison to the contra-lateral canine or adjacent teeth but correct prediction of palatal canine impactions by using differential magnification on a dental panoramic radiograph is only possible in about 77% of cases (55).
If the impacted canine cannot be imaged seperately and is projected on the matured root of the lateral incisor, the diagnosis of palpability oft the crown of the permanent canine is not sufficient for excluding the threatening or already existing root resorption on the roots of the central or lateral incisors or first premolars and further radiographic views are needed. In the past this was done using standard occlusal radiographs (3) or paralleling technique periapicals (3, 5, 11). In many cases, especially when root resorption occured in the sagittal plane, it could not be diagnosed on low dose conventional radiography (2).
In cases of superimpositions of the crown of the canine with the roots of the adjacent teeth the prevalence of root resorptions has to be clarified. Complying to the Sedentex CT and (German) sK2-guidelines (45, 46) further radiographic views should include cbct or low dose ct-radiography for the localized assessment of an impacted tooth where the current imaging method of choice is conventional dental radiography and when the information cannot be obtained adequately by lower dose conventional radiography (14-43, 59). The taking of CBCT radiographs has become the standard diagnostic tool in such cases by scientific findings (14, 19, 26, 29, 32, 34, 36, 37, 39, 40, 42, 43, 47, 48, 49, 51, 52, 53, 59), practical experience and professional acceptance.
(For the localised assessment of an impacted tooth (including consideration of resorption of an adjacent tooth), the smallest volume size compatible with the situation should be selected because of reduced radiation dose.)
The panoramic radiograph still remains an important part of initial diagnosis with the intention to reduce the need for additional cone beam computed tomography (CBCT) imaging. It is used for determining the position of the impacted canine according to the sectors proposed by Ericson and Kurol, later modified by Lindauer.
The mesiodistal position of the tip oft he canine gives the clue for the degree of canine impaction and threatening or beginning root resorptions on adjacent teeth. The labiopalatal position of impacted canines and resorption of permanent incisors might be predicted using sector location on panoramic radiography.
Unfortunately the orthodontic community did not agree on a uniform nomenclature. The original numbering of the sectors by Ericson begins with sector 5 in canine position ending with sector 1 in mesial half of ipsilateral cental incisor. Lindauer started with sector 1 in canine postion ending with sector 5 in ipsilateral mesial cental incisor sector and Alquerban choose sector 0 to begin in canine position and ends with 4 in mesial central incisor sector.
The following discussion uses the nomenclature by Lindauer as the most frequently used.
As reported by Jung (36) labially impacted canines are often found in sectors 1, 2, and 3, mid-alveolus impacted canines were more frequent in sector 4 and palatally impacted canines were more frequent in sector 5.
According to Yan (37) proximity (<1 mm) between the impacted canine and an adjacent root is the most important predictor for root resorption. He also stressed that eruptive movement or migration of the impacted canine during its root development process is likely to increase the risk of root resorption at adjacent incisors.
Up to Chausu et al. (61) the etiology of impacted canine-associated severe incisor root resorption (SIRR) is multifactorial, including both systemic and local factors.
They suggest that the risk for SIRR is increased:
a) in female patients with enlarged dental follicles and anomalous lateral incisors.
b) Lateral incisors are affected more than central inci- sors, and the chance of bilateral occurrence is high.
c) SIRR is found in both palatally and buccally impacted maxillary canines but is associated with the more severely displaced canines, situated in the middle third of the adjacent incisor roots.
Alqerban (44) proposed a prediction model for root resorption based on radiographic variables assessed on 2D panoramic radiographs with the intention to reduce the need for additional cone beam computed tomography (CBCT) imaging.
In this prediction model, patient female gender, closed or dilacerated canine apex, vertical canine crown position less than 45 degrees to midline , and canine magnification were the strongest predictors for root resorptions.
The presence of one of these predisposing factors was considerd a helpful tool in justifying the need of additional CBCT or low dose CT examination.
Appropriate treatment measures
If the root of the canine is fully developed and the proximity is less than 1mm an immediate orthodontic treatment to align the canine or if such treatment is not possible, the extraction of the impacted canine is indicated.
When root developement oft he canine is only finished halfway interceptive treatment might be indicated. A guidance of eruption of the canine in order to avoid the need for active orthodontic treatment or to reduce it to a minimun is started by extraction of the deciduous canine (62) and the first deciduous molar (63) plus the slicing of the second deciduous molar mesially (64). The premature eruption oft he first premolar in the enabled distal direction will lead to a space gain for the crown of the impacted canine which can take a natural eruption path.
If the impacted canine requires orthodontic treatment the orthodontist should be the leader oft the team and discuss treatment objectives with the participating oral surgeon (69). Minimal exposure of the impacted canine with hard and soft tissue preservation is recommended (65, 66, 67, 68, 69) and the closed eruption technique should be preferred (70-78) with the exception of superficially palpable canines which should be left open after exposure, with or without a surgical pack as a dressing (69).
For the overriding majority of cases, there is no urgency to expose the impacted tooth. In cases with already resorbed adjacent roots or when there is no proximity the treatment should start with distancing the canine from the immediate vincinity to arrest the resorption process (69, 77).
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