NEWSLETTERS

What price negligent reading of radiographs?

Published: October 2012

Bulletin #15 October 2012

What price negligent reading of radiographs?

Those of us fortunate enough to have been practicing orthodontics for 10 years or more have woken up one morning during this time, to find that the CBCT era is upon us. I would guess that many are now using or beginning to use CBCT for some of our cases, while others may be employing it for a majority of their cases. The whole point is that we have come to recognize the vast superiority of this imaging modality over plane film radiography, giving us the opportunity for greatly improved diagnosis and helping us to provide better quality treatment, as the direct result. Nevertheless, a few of the cases that were started just before CBCT was included in our diagnostic armamentarium have dragged on because of mistakes made in the interpretation of inadequate plane film radiographic imaging or perhaps poor reading or mistaken interpretation of good imaging. Patients with impacted teeth are among the most likely to be affected.1,2 For some, the films that were used to localize the tooth in the 3 planes of space were not sufficiently comprehensive, while for others, solicited pre-treatment films had not been properly examined for existing evidence.

Case report

A while ago, I was consulted by an experienced and respected colleague and friend regarding a patient he had been treating, whose impacted left maxillary canine was not behaving as he had expected. During the coffee break at a local orthodontic society meeting, he showed me the radiographs of the case and then, finally, the CBCT. The case had been in treatment for just under 2 years, but with no end in sight. Surgical exposure had been performed through a full palatal flap, to place an attachment on the canine. Traction was then applied to initially distance the tooth from the adjacent roots, which showed evidence of resorption due to the juxtaposition of the canine. Over several months, resolution appeared to be very slow and atypical. New plane films were ordered and these showed a bizarre arrangement of the canine vis-à-vis the adjacent teeth and raised the question as to how this could have occurred. It was this strange orientation of the individual teeth that encouraged the orthodontist to order a CBCT examination at this late stage in the treatment.

October_2012_Fig

Fig. 1a-c Pre-treatment clinical intraoral views of the teeth in occlusion.

Let’s follow the diagnostic steps that were taken in the case and hopefully try to learn where and why mistakes were made.

Seeking orthodontic treatment for her malocclusion, the patient had been seen for an initial examination and was considered to be dentally mature enough to begin. She had a fully established permanent dentition (Fig. 1), except for a single remaining deciduous left maxillary canine, which showed no mobility and neither could the permanent canine be palpated in the buccal sulcus nor under the palatal mucosa. Accordingly and in addition to being referred for panoramic and cephalometric radiography, an anterior (oblique) occlusal view and a pair of periapical views of the left canine were ordered, by the tube-shift technique (lateral parallax method), to establish the bucco-lingual relation between the canine and the incisors.

October_2012_Fig.2

Fig. 2a Periapical view of the maxillary left incisors, to show the degree of superimposition of the canine in relation to the incisors and to the midline.

Fig. 2b Distally rotated view of the same area to show the change in the degree of superimposition of the canine and its relation to the midline.

The periapical radiographic film directed at the central incisors (Fig. 2a) shows that the crown of the impacted canine completely covers the root of the left central incisor and crosses the midline to the mesial edge of the root of the central incisor of the opposite side. The rotated view directed a few degrees to the patients left (Fig. 2b), shows the crown of the canine to be incompletely superimposed on the left central incisor and not reaching the midline. From this it was concluded that the canine was palatal to the incisors and this was later confirmed at surgery.

You, the reader, are invited to study these 2 films for a few minutes and, hopefully, you will agree with this determination. If all are in agreement with this accepted mode of diagnosis, then the next thing that would appear to be called for is to open space in the canine region between lateral incisor and first premolar, with an orthodontic appliance and surgically expose the canine from the palatal side.

This was the plan that was followed by my friend and, because it was calculated that the path of the canine from the midline immediately behind the central incisors to the intended canine location would be obstructed by incisor roots, it was decided to initially draw the canine posteriorly and away from the incisors i.e. towards the mid-palate. This was achieved by ligating the twisted pigtail ligature from the attachment on the canine to the transpalatal arch with elastic thread. After its projected eruption into the palate and with an unimpeded path to the labial archwire, it would then be drawn labially to take up its traditional place in the arch.

October_2012_Fig.3

Fig. 3a Pre-treatment anterior (oblique) occlusal view of the initial situation.

Fig. 3b Anterior occlusal view after traction, at the time of consultation. Note the rotation of the tooth around the lateral incisor root.

As noted above, the tooth did not respond as anticipated. It was drawn in a posterior direction to the soldered hook on the transpalatal arch close to the opposite molar and thus, to a degree, across the midline. At this point, it became clear from clinical intra-oral observation that its long axis showed a severely displaced horizontal and antero-posterior orientation – the crown palpably pointing towards the mid-palate and the apex palpable high in the labial sulcus. A solution to the problem of bringing it into alignment seemed beyond the scope of routine orthodontics. It was at this point that the orthodontist referred the patient for new plane film radiographs and the CBCT scan, which confirmed that the treatment provided had actually compounded the initial problem Fig. 3a, b).

Armed with the results of the CBCT scan, my friend took me aside during the coffee break at that local orthodontic meeting because, with the new information, he was hungry for answers to the following questions:-

  1. How did this bizarre degree of ectopia occur?
  2. Could it have been foreseen?
  3. Could it have been prevented?
  4. Was a palatal approach the right way to go?
  5. Was this tooth doomed from the outset?
  6. Is there a way out of this mess now?

It is probably true to say that, given only the initial plane film radiographs, orthodontists in general might have approached the initial problem in one of four possible ways. The options are as follows:-

  1. A good number would have extracted the aberrant canine and built the patient’s dental future on the over-retained deciduous canine and, in the fullness of time, an implant.
  2. Others would have approached the problem in the same way as described here - and would have failed in similar manner
  3. A good number today (but not all!) would not have been satisfied with the existing films and would have requested the CBCT from the outset and seen the complexity of the problem before making the decision in option #1.
  4. Only a small minority will have requested the CBCT, seen a way around the problem and chosen the alternative and apparently paradoxical approach.

Commentary

My orthodontist friend, committed the frequently made, elementary mistake of looking first at the most obvious piece of diagnostic evidence and ignoring other important details. On the basis of the periapical views alone, he had made his operative decision without seeking further clinical or radiographic evidence which he himself had commissioned and which was already freely available to him.

Fig._4_pan

Fig. 4. The initial panoramic film, showing the distal inclination of the incisor and its partial transposition with the canine.

Let’s begin by examining by looking at the other plane film radiographs that were available before treatment began and see what information can be gleaned from them.

1. The anterior (oblique) occlusal film (Fig. 3b) and the panoramic view (Fig. 4) could have been used together as a diagnostic vertical parallax (vertical tube-shift) pair of films, since they image the canine at different angles to the horizontal. The intraoral film is taken at a 60 degree angle to the horizontal and, thus, an object palatal to the labially-adjacent central incisor root will appear to superimpose higher on that root. In the event, the canine may be seen to obscure approximately half the root of the central incisor. The panoramic view is taken at a -7 degree angle, from below the horizontal, which has the visual effect of “drawing down” the more palatal body towards the crown of the central incisor. In the panoramic view in this case, the canine “moves down” coronally, with a tad more of unobscured root apex visible.

2. Similarly, the periapical view (Fig. 2a) which is taken at 50 degrees to the horizontal and the anterior occlusal view (Fig. 3a), at 60 degrees, also provide a diagnostic pair of vertically shifted views for this purpose.

With each of these diagnostic “tube-shift pairs”, we have shown that the crown of the impacted canine lay palatal to the root of the central incisor, close to the midline, at the beginning of treatment. The orthodontist was present at the surgical procedure, to bond the attachment and apply traction and he confirms the palatal location of the crown. So, up to this point, there can be no argument.

However, the methods described above have all been aimed at locating the crown of the tooth, with no attention paid to the position and orientation of its root, in relation to the adjacent lateral incisor. For its part, the lateral incisor is complicit in this difficult scenario and is a factor to be considered, due to the 3-D orientation of its long axis.

But let’s stop there for a few moments and re-examine the patient in a more logical and ordered manner, so that we are not also guilty of making the same elementary mistake referred to above. We must begin with a thorough clinical examination!

October_2012.Fig._5._annotated_LHS

Fig. 5. This is the same left side clinical view as in Fig. 1c, with dotted lines to indicate the apically divergent long axes of the central and lateral incisors.

At this late stage in the game, the closest that we are able to get to a clinical intra-oral examination of the initial malocclusion, as it was almost 2 years ago, is to study the pre-treatment clinical photographs of the case (Fig. 1a-c). But are these helpful? In relation to impacted teeth in general and to impacted canines in particular, I believe these to be an important aid in arriving at a diagnosis. If we study the long axis of the left maxillary central incisor, we will note that the tooth is very upright, with its root almost vertical. In contrast and if we may ignore the rotation, the adjacent lateral incisor is mildly displaced labial to the line of the dental arch. However, the inclination of the crown of this tooth indicates that the orientation of its root is in a posterior and distal direction, close to the horizontal (Fig. 5). In other words, if we study the long axes of the roots of these two adjacent incisors, with their crowns in interproximal contact, we will be able to mentally construct a strong and progressive bucco-lingual and mesiodistal divergence, leading to a very wide separation of their apices. It will also be evident that the orientation of the root of the lateral incisor has brought it in close proximity to the palatal mucosa and, as such, it will be obvious that the root of the canine could not be situated palatal to the lateral incisor. It must therefore be on the labial side. Whether the divergent roots of the incisors have encouraged a normally developing labial canine to proceed mesially towards the midline, labial to the almost horizontal lateral incisor root and palatal to the upright central incisor, or that the canine has actually caused this divergence, is a moot point.

Returning to the panoramic radiographic view, it can be seen that the lateral incisor indeed has a distinct distal orientation on this 2-dimensional view. The canine is partially transposed with this incisor and its root can be seen superimposed on the lateral incisor root apex. This degree of superimposition on the panoramic view, with its -7 degree angulation to the horizontal, shows a lesser degree of vertical coverage of the lateral incisor apex than is seen on the +60 degree angulated periapical view in figure 1b. Thus it must be concluded that, in contrast to the canine crown relation to the central incisor, the panoramic view corroborates the location of the canine root to be on the labial side of the lateral incisor root.

October_2012_Fig.6

Fig. 6a Anterior section of the cephalogram

Fig. 6b The same view indicating the long axis of the left lateral incisor (blue dotted line) and the superimposed long axes of the other incisors (yellow dotted line). The long axis of the canine (orange dotted line) shows the canine labial to the lateral and palatal to the central incisors.

The only bucco-lingual view of the anterior maxilla that can be imaged on a plane film comes from the lateral cephalogram (Fig 6a). The purpose for which this film was commissioned has, of course, nothing to do with diagnosis of canine impaction. Nevertheless, whenever such a film is available, it should be scoured for information that may be helpful and, in relation to impacted canines, there often is. This film superimposes the right and left sides on to one another and, in general in the anterior area, it is impossible to discern the outline of individual teeth. Nevertheless, when there is severe ectopia of a single tooth, such as for a dilacerate incisor, this may sometimes become the most illustrative view available.

If we now examine the photographic records of the dentition of the patient, several clinical features can be clearly seen. The two central incisors, the right lateral incisor and the right canine are all erupted in their correct places and will be seen superimposed on each other in the cephalogram and quite impossible to define individually. The only teeth that are significantly out of line are the left lateral incisor and the impacted left canine and these should be visible as distinct entities on that film.

The cephalogram had been commissioned by the orthodontist and was available at the treatment planning stage. On examination, it is not difficult to define the combined profiles of the closely superimposed central incisors and the right lateral incisor, with the orientation of their long axes marked in Fig. 6b by the yellow dotted line. The left lateral incisor can be seen to have an extreme palatal orientation, with its apex displaced far palatally and inferiorly, marked by the blue dotted line. The left canine can be seen to be “wedged” between the two, with its a-p orientation represented by the orange dotted line.

October_2012_Fig.7

Fig. 7a CBCT 3-D view showing the final resting place of the canine after the ill-fated traction attempt.

Fig. 7b The CBCT transaxial slice of the anterior ridge.

So, the 3-D orientation of the canine in space and in relation to its immediate neighbors could and should have been possible to diagnose before treatment began, using plane film radiography that was available. Certainly, the new CBCT (Fig. 7a, b) taken following the failed attempts at resolution of the impaction, now shows the bizarre location of the tooth in all its glory, making a successful resolution virtually impossible. What has occurred is that the applied traction pulled the canine crown posteriorly in the palate, while its root was levered by its contact with the lateral incisor root causing its apex to be rotated labially. This levering component had the secondary effect of torqueing the lateral incisor root still further in the palatal direction.

Given the clear picture of the canine relations that became available with the CBCT and the intractability of the situation, the tooth was extracted and the premolars and molars of that side are presently being drawn mesially, to close the canine space against a strategically placed TAD in the canine area.

The lesson to be learned, in relation to accurately locating the position of impacted teeth, is that we should study all the radiographs available for evidence and, without question, consider the use of CBCT in these cases.

In the next bulletin in this series, I plan to show a similar case and how proper directional traction planning can bring about a successful resolution of this unusual (although not rare) impaction. The case appears in the video clip that you can see rotating at all angles and in all directions on the home page of this website. You may not have noticed but it is also on the cover of the third edition of my text “Orthodontic Treatment of Impacted Teeth” where book designer laterally inverted (mirror-imaged) it to blend more harmoniously with the cover design.

References:

1. Becker A, Chaushu G, Chaushu A . An analysis of failure in the treatment of impacted maxillary canines. American Journal of Orthodontics & Dentofacial Orthopedics 2010;137:743-54.

2. Becker A, Chaushu S, Casap-Caspi N. CBCT and the Orthosurgical Management of Impacted Teeth. Journal of the American Dental Association 2010;141(10 suppl):14S-18S