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This bulletin is dedicated to the memory of our esteemed colleague and my friend, Dr. Karl York ז"ל, who passed away suddenly and tragically at age 73 in his home in Netanya, Israel. He practiced orthodontics in his private practice to a high standard, with a warm and caring manner and was loved by his patients. Over the period of several decades, he devoted much of his professional time on a regular weekly basis as the orthodontic member of the orthognathic surgery team in Poriyah Hospital in Tiberius. Karl was an enthusiastic participant in outdoor sports and, only 10 days earlier, had returned from a kayaking holiday in Norway with the other members of his club. Our hearts go out to his wife Tzilla and to his children and grandchildren, as they strive to restructure their lives following such a deep and painful loss. May his memory be for a blessing.

Bulletin #78 August 2018

Impacted canines in a dentition with missing teeth and teeth with poor prognosis

In this bulletin, I shall present a dilemma that arose in the orthodontic treatment planning for a 12 year old girl with a mild class II skeletal relation, who was referred to me by a colleague. The patient attended the first visit armed with a panoramic film, a lateral cephalogram and CBCT of both jaws, together with facial and intraoral photographs. The facial profile and soft tissue morphology were pleasing.

There was good alignment of the teeth in the maxilla with no crowding and only slight intercanine crowding of the mandible. The dentition was in the late mixed dentition stage, but with over-retained deciduous lateral incisors and canines in the maxilla, disproportionately large second deciduous molars and a right deciduous canine in the mandible. The four second permanent molars were fully erupted.

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Fig. 1. In the panoramic view, the mandibular right impacted canine is seen to cross over the midline, with an enlarged dental follicle. The maxillary impacted canines are seen to be in close relation to the converging apices of the deciduous lateral incisors, deciduous canines and distally tipped first premolars. Their bucco-lingual locations cannot be diagnosed on this film. Permanent lateral incisors are congenitally absent. The mandibular third molars show very early calcification of their cusps and show early signs of rotation and tipping.

The panoramic radiograph revealed bilateral maxillary canine impaction (Fig 1). The other anomalies included congenitally absent maxillary lateral incisors and mandibular second premolars and an impacted mandibular right canine. The locations of the two maxillary canines were virtually mirror images of one another in all three planes of space. 

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Fig. 2. The lateral cephalogram of the patient shows the 2 superimposed impacted maxillary canines, the impacted mandibular canine in the bone of the chin and the absence of mandibular second premolars.

The mandibular right canine was severely displaced. Its root apex was ideally located but the tooth was lying at more than 90 degrees to the vertical, with the crown close to the mandibular lower border, having crossed the midline to within a few millimetres of the canine on the opposite side. The full length of the tooth was located below the root apices of the four incisors. By combining the information from the panoramic view with that from the lateral cephalogram (Fig. 2), it was confirmed that the tooth was lying slightly labial to the lingually inclined roots of the incisors. It would seem that adequate information was present on these planar radiographs that made CBCT imaging unnecessary for this specific tooth.

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Fig. 3. The height, angulation and long axis orientation of the impacted left canine is clear to see on (3a) the 3D screen shot and (3b) the longitudinal slice, from the CBCT images. Note the converging long axis of the deciduous canine, lateral incisor and the first premolar.

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Fig. 4. In these cross-sectional CBCT slices in (4a) the deciduous canine and (4b) first premolar regions, the left canine may be diagnosed as mildly deviated to the palatal side, with an enlarged dental follicle.

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Fig. 5, 6. These same 3D screen shots and longitudinal slice views of the right side canine, together with the same cross-sectional cut show identical location, orientation and relations vis-à-vis the left side in Figs. 3, 4.

The maxillary first premolar roots were tipped mesially, although the crowns of these teeth were correctly placed. Because of this unusual orientation of their long axes, the premolar root apices were in close relation to the unerupted canines and were clearly complicit in their impaction (Figs. 3-6). Third molars were present in the maxilla in the early stages of root formation, while in the mandible only the third molar cusp tips were calcified.

Based on the presence of fully apexified roots of the incisors, premolars and canines, together with almost complete closure of the second molar apices, the dental age of the patient was assessed at 13-14 years (see Bulletin #75, March 2018 for a method of assessing a child’s dental age). This calculation is quite independent of the fact that deciduous teeth were present in both jaws. The relatively advanced dental development in a dentition with impacted canines and missing teeth is unusual.1 Accordingly, optimal timing for commencement of treatment was considered to be at hand.

When planning orthodontic treatment in a child or adolescent, most orthodontists take it for granted that the prognosis of the individual teeth is good and, in an extraction case, will often choose the teeth to be sacrificed solely on strategic considerations. However, when there is a single permanent tooth severely destroyed by caries, such as a permanent molar, the criteria for making this choice must change.2 The most important aim in orthodontics is to undertake a concentrated realignment of the teeth with the view to obtaining a good overall functional and esthetic result that will be stable and in which the individual dental elements will be lasting.

The patient presented here was caries free with excellent periodontal health, but there were concerns regarding the longevity of certain individual teeth:-

1. Four deciduous teeth had no successors and the permanent successor of a fifth was too distant to be considered salvageable.

2. There were two maxillary impacted canines.

3. The form and location of the mandibular third molars did not promise a favourable future.

If we had decided to hold on to the (thus far) long rooted deciduous teeth, we would need to ask ourselves if the necessity for their orthodontic movement would contribute to an early demise, due to an exaggerated resorption of the roots or to a mechanotherapy-induced infraocclusion? By pre-empting their extraction we may create a much greater problem in terms of space closure in what must otherwise be a non-extraction case. The price for this may be paid in a much longer treatment and an adverse alteration in the patient’s profile.

There is no foolproof answer to all of these questions. While for some of the teeth the choice is clear, for others we are playing a game of chance in our search for statistical prognosticative data, most of which does not exist.

We are therefore obliged to identify those teeth which have a potentially compromised prognosis. In the present case with their large number, if we were to extract them, we would leave the patient with an unacceptably reduced dentition. Accordingly, we must try to assess how high the individual risk for a poor post-treatment prognosis is for each tooth – let’s arbitrarily call this a Coefficient-Of-Prognosis Index (COPI).

1. Mandibular right permanent canine - The crown of this tooth is displaced a long distance from its normal location. The prognosis of most displaced teeth is measured by the location of their apices. A correctly located apex is usually an indication of a good prognosis for its relocation and periodontal outcome. However, this is not so in the anterior part of the mandible, with its semi-circular archform. For this canine to move to its place, it would need to be tipped labially, superiorly (occlusally) and distally in a wide semi-circular movement, to avoid contact with the incisor roots. It is well below the reflection of the oral mucosa in the depth of the labial vestibule and it cannot be pushed back along its long axis, a distance of about 25-30 mms of horizontally intrusive movement. Can it be brought to its place? How long will this take? Will it cause unnecessary discomfort and distress to the patient? In what periodontal state will it be when it gets there? Will it cause periodontal deterioration of the adjacent incisors? The answers to these questions are strongly negative and must affect treatment planning.                                                                                             Verdict – extract.

2. Mandibular right deciduous canine – This tooth has a long unresorbed root and, given the fact that orthodontic treatment in the mandible could be minor and of short duration (see above), its prognosis is considered good.                                                     Verdict – retain as an integral element of the final occlusal scheme.

3. Mandibular deciduous second molars – These two molars are very broad and have long unresorbed roots. Neither is infraoccluded and both are in full occlusal function. Their expected longevity appears very favorable. Extracting them and closing the very broad extraction space by orthodontic means would be unnecessarily long and would require TAD’s to avoid adverse effects on the anterior teeth and the patient’s profile. Verdict – retain as an integral element of the final occlusal scheme.

4. Mandibular third molars – While these would not normally be a factor, adopting the possible extraction line of treatment mentioned in item #3 above would increase the concern for attempting to bring these teeth into the dental arch in the long term. They are small and very late in their development, which may limit their eventual value. Either way, their fate should not be decided at this point, in relation to a possible future role. Verdict – ignore for the present and re-evaluate in late adolescence.

5. Maxillary first premolars – As noted above, these two teeth are identically situated, with the crowns in their correct places in the arch, but their apices displaced mesially directly into the intended path of the unerupted canines. Left uncorrected, these teeth will continue to compromise the unerupted maxillary canines by arresting or deflecting their eruption. Verdict – move the apices away from the eruption paths of the permanent canines.

6. Deciduous lateral incisors – Since these teeth have long and intact roots, their continued presence is highly desirable in the long term. They will preserve alveolar bone and could delay artificial substitution indefinitely. Accordingly, every effort should be made to avoid factors that would cause resorption of their roots. Verdict – retain as a long term integral element of the final occlusal scheme.

7. Permanent maxillary canines - The location of these teeth is directly above the converging root apices of the deciduous lateral incisor, the deciduous canine and the first premolar on each side. The canines are only mildly palatally displaced and, given an unobstructed path by appropriate orthodontic root uprighting and deciduous canine extraction, their outlook could improve autonomously, possibly even to erupt naturally in the fullness of time. Verdict (alternative #1)– retain as an integral element of the final occlusal scheme.

8. Deciduous maxillary canines – The deciduous canines have long unresorbed roots and their potential for long term retention would be fair, in the absence of the impacted permanent maxillary canines.                                                                             Verdict (alternative #1) – ignore, but extract the permanent canines. Verdict (alternative #2) – extract to clear the eruption paths of the canines.

It is clear that there are many cases for which there are multiple treatment options and, as in this case, it is often difficult to choose the best solution for the malocclusion and for the patient. Several of the alternatives are viable and the end result may be good regardless of the choice. The real test is in the longevity of the outcome, but longevity cannot be accurately predicted with more than a modicum of scientific support, before treatment is commenced. The rest may be common sense, but mostly it will be clinical experience garnished with luck because, at present, we have no reliable means to estimate prognosis. It would be helpful if there were a scientifically-based system to evaluate it

Quantifying prognosis

Can we establish a Coefficient-Of-Prognosis Index (COPI) for the individual teeth and then build up an assessment of the long term prognosis for a particular dentition as a whole? For example, we could arbitrarily declare a value of 10 positive prognostic points for an erupted permanent tooth, unaffected by caries or periodontal disease and requiring minimal tooth movement. A full permanent dentition (second molar to second molar) comprising 28 healthy teeth and requiring only minimal alignment would give that dentition the maximum coefficient of 280 positive prognostic points. Perhaps an erupted deciduous molar which has no caries, no infraocclusion, no permanent successor, but has good roots, would warrant a value of 6 points i.e. a 60% chance of surviving as a functioning unit far into adulthood. On the other hand and in a malocclusion requiring the extraction of teeth, a high caries incidence, the presence of teeth with large restorations, root canal treatments, poor periodontal health and, on occasion, a malformed crown or severe displacement and/or impaction would all reduce the COPI value and raise the likelihood that such a tooth should be considered as a candidate for extraction. Food for thought?!

References

1. Becker A, Chaushu S. Dental age in maxillary canine ectopia. American Journal of Orthodontics and Dentofacial Orthopedics,2000;17:657-62.

2. Penchas J, Peretz B, Becker A. The dilemma of treating severely decayed first permanent molars in children: To restore or to extract. Journal of Dentistry for Children, 1994; 61:199-205.