NEWSLETTERS

Impaction resolution difficulty, root resorption, prognosis and appearance

Published: April 2015

Bulletin #43 – April 2015

Impaction resolution difficulty, root resorption, prognosis and appearance

The following case was referred to me by one of our former residents because of the complexity of the problem and the combination of unfavorable factors that needed to be evaluated in regard to diagnosis and for the formulation of a treatment plan. Several treatment options were considered appropriate for this case and this month’s bulletin will discuss these, together with the relative merits of each option. These were evaluated in terms of the biomechanical level of difficulty in resolving the impactions, the estimated prognosis of the individual teeth at the completion of treatment and the anticipated appearance of the outcome – the patient’s smile.

The patient was a normal, healthy 11.4 year old girl with no relevant, contributory medical history. She was first seen in my office 2 months ago, in January 2015, when the initial clinical examination was carried out. She arrived already equipped with extra-oral and intra-oral clinical photographs, a panoramic film, a lateral cephalometric film, a digitized cephalometric analysis and a CBCT series.

gg._Fig._1._initial_intraorals

Fig. 1. Initial intra-oral photographs of the patient’s dentition.


Clinical examination:

The patient had an orthognathic profile with normal antero-posterior and vertical relations, with lip competency and good lip cover. The clinical intra-oral photographs showed a class 1 molar relation with a slightly increased overbite and overjet of 2.5mm and 4.6mms respectively (Fig. 1). The most significant feature of the dentition was the large size of the teeth and the severe degree of dental crowding, which expressed itself in only a millimeter of space on either side for the unerupted, non-palpable canines and a distal angulation of the maxillary first molars. The mandibular arch was also characterized by a general crowding, although notably less than in the maxilla. The maxillary central incisors exhibited distally flared apex-to-crown orientation and a minor degree of proclination. The maxillary lateral incisors were disproportionately large and their apices were estimated to be displaced palatally, resulting in their labially flared apex-to-crown orientations. The mandibular anterior teeth were lingually retroclined. The maxillary deciduous second molars were still present and the second permanent molars were unerupted

.gg._Fig._2._Pangg._Fig._3._Ceph_annotated

Fig. 2. The panoramic radiograph of the case clearly shows the impacted canines in close association with the root apices of the four incisors in the midline area.

Fig. 3. The lateral cephalogram shows the accurate superimposition of the maxillary canines on each other. Similarly, the long axes of the lateral incisors and of the central incisor on one another, is clearly seen. The colored broken lines show the canines (orange line) on the palatal side of the central incisors (blue line) and labial to the lateral incisors (*yellow line).

Radiographic examination:

The panoramic view (Fig. 2), taken 2 month earlier, confirmed the large size of the erupted and unerupted teeth, all of which were discernible, including third molars. Using root development as a guide, the patient’s dental age was determined as being in agreement with her chronologic age. The maxillary canines were impacted with their crown tips in close relation to the root apices of the central and lateral incisors and close to the midline. The film showed the presence of the two deciduous second molars, which appeared about to shed in favor of their premolars successors. The mandibular second molars were unerupted and their locations were considered to be a cause for concern regarding their ability to erupt normally. This was because of the proximity and horizontal angulation of the third molars on each side and the mesial inclination of the right second molar. The lateral cephalogram showed the two maxillary canines superimposed in identical positions (Fig. 3). This film was particularly valuable, when combined with information obtained from the panoramic view, insofar as it showed their crown tips to be palatal to the roots of the central incisors and labial to the roots of the lateral incisors.

gg._Fig._4a_annotatedgg._Fig._4bgg._Fig._4c

Fig. 4a-c. Three different occlusally oriented views of the maxillary arch. The axial CBCT cuts (a) depict the canine interposed between the labially located root apices of the central incisors and the palatally located apices of the lateral incisors. Root resorption cane clearly be seen on the lateral incisors (arrows). The 3D screen shot (b) highlights the entanglement of the canine crowns with the incisor roots. The clinical occlusal photographic view of the maxilla (c) shows a degree of lingual tipping of the central incisors, which must be interpreted as labial tipping of their roots. In contrast, the crowns of the lateral incisor are labially tipped and their roots therefore palpable immediately under the palatal mucosa. Cause or result of the interposing unerupted canines?


Cone beam computerized tomography (CBCT) examination:

Axial cuts (parallel to the occlusal plane) of the maxillary anterior teeth at level 20 show the two canines interposed palatal to the roots of the central incisors and labial to the roots of the lateral incisors on each side. At this level, marked resorption of the labial half of the root of the lateral incisors can be clearly seen (Fig. 4a). The cone beam 3D view (Fig. 4b) shows the entanglement between the incisor apices and canines with great clarity, while the clinical occlusal view of the upper jaw shows the contrasting orientation of the incisor crowns (Fig. 4c).

gg._Fig._5

Fig. 5a-d. Cross-sectional cuts from the CBCT images show the contrasting labio-lingual relationships between impacted canines and incisor roots.

Cross-sectional cuts (Fig. 5a-d) confirm the canines as being located labial to the lateral incisor roots - which are extensively resorbed in an oblique manner (Fig. 6) - and palatal to the central incisor roots.


Overall treatment considerations:

As a case of class 1 skeletal and dental relationships with large teeth and marked crowding in the canine/premolars areas and in the retromolar areas, extraction was considered to be mandatory in both jaws. In the mandibular dentition, a premolar on each side would appear to be a reasonable choice to align the teeth mesial to the first molars. In regard to the retromolar area, it is considered unlikely that growth will provide enough additional arch length to permit a significant improvement in the chances for the third molars being incorporated in the erupted dentition and the need for their later extraction seems inevitable.

The complex inter-relations of the maxillary anterior teeth seen here provide us with food for thought regarding the influence of the choice of teeth for extraction on treatment and on quality of outcome. These aspects are

1. difficulty of mechanotherapy,

2. Incisor root resorption

3. individual prognosis of remaining teeth,

4. appearance.

Problem list

Aside from the fact of tooth size and crowding, the special problems that are faced in the present case are:-

1. the complicated nature of the relationship between the maxillary canines and the incisor roots

2. the distance of the canines from their normal location

3. the very large lateral incisors

4. the resorption of the roots of the lateral incisors

Extraction options

In the mandibular dentition, extraction of a premolar on each side is the logical way and this has to be coupled two teeth in the maxilla. Under the present circumstances, the options are as follows:-

a. maxillary first premolars:

Extracting the maxillary first premolars is the treatment of choice in most orthodontic extraction cases, but to promote this line of treatment in the present case would be a mistake, even though this proposal is possible to complete successfully. Since the maxillary canines and incisors are in virtually identical positions on either side in their 3D locations in space and in relation to each other, we shall consider them as one.

The canines are located palatal to the roots of the central incisors and this would encourage most of us to surgically expose them and subsequently apply traction to them on the palatal side. However, this is to ignore the fact that the roots of the canines are situated labial to the roots of the lateral incisors. Drawing the canines palatally would bring their roots into contact with the labial side of the roots of the lateral incisors and, the more the canines progressed on the palatal side, the greater would be the displacement of the (already palatally displaced) roots of the incisors against the palatal periosteum. The result would be a dehiscence of the palatal aspect of the roots of the lateral incisors and a transposed relationship between them and the canines – a situation which will usually spell the demise of all four teeth1 …….. and an expensive and unwinnable legal action.

The only way that these canines can be successfully treated is to approach them from the labial side and to draw them both labially and distally. The crowns of the central and lateral incisors on each side are in interproximal contact. The orientation of the long axes of the central incisors, in the crown-to-apex direction is mesial (towards the midline suture) and slightly labial (towards the labial periosteum). The same long axes of the lateral incisors is mesial (towards the midline suture) and strongly palatal (towards the palatal periosteum). This means that high up in the premaxilla there is a wide bucco-lingual space discrepancy between the apices of the central vis-à-vis the lateral incisors, which is where the canine is located. Provided the incisors are not uprighted or torqued in the early stages of orthodontic alignment and leveling, this wide bucco-lingual space, or “window of opportunity”, is the key to freeing the canine crown and, with biomechanical assistance, to permit it to escape from its confined location, in a disto-labial direction. 2, 3

When faced with cases of this type, it is strongly recommended that the initial leveling and alignment stage of treatment not include distal uprighting of the central incisor nor labial root torque of the lateral incisor. Therefore, it is recommended that the lateral incisors remain without brackets until the canine impaction has been resolved. For the central incisors, a straight-wire or any other form of horizontal channel bracket should be placed at an angle that will temporarily maintain or increase a mesial uprighting movement of the root apices. A superior alternative is the use of a Tip Edge bracket (TP Orthodontics), which will allow leveling, alignment and rotational movements to be performed without distal uprighting, because of its unique slot configuration. Moreover, only round archwires should be used. Rectangular wires of any form or variety, whether stainless steel or nickel-titanium, are strongly contraindicated until resolution of the impaction has been achieved, since these will “correctively” torque the incisor roots, close off the ”window of opportunity” and thereby further entrap the canine into an intractable position.

The risk attached to this case, in terms of damage to the roots of the two adjacent incisors during the surgical exposure of the canines, is very high. Obviously an open surgical exposure is out of the question, since this would leave the roots bare and open to the oral environment. 4 But even with a closed procedure, the proximity of the canine crown to the incisor roots will not permit sufficient surgical accuracy to avoid damaging the incisor root surfaces. Furthermore, attachment bonding will be essential and the danger of etchant damage to the root surfaces, with the likelihood of the initiation of invasive cervical root resorption, is not to be ignored.

In addition to having to deal with these very difficult conditions, the present case shows 2 other features which are problematic. In the first place, the lateral incisor roots have been markedly resorbed by their close association with the advancing canines. It has been shown that distancing the canines from the resorption area will arrest the resorption process. 5 However, in the present situation, the mechanotherapy addressing the difficult location of the canines may aggravate the resorptive process because of the initial topographical difficulty in moving the canines away from the incisor roots. It would be imprudent to build the future on an uncertain prognosis of the lateral incisor. 

The second problematic feature is the size of the crowns of the lateral incisors. The presence of such a broad lateral incisor, adjacent to a similarly-sized central incisor, will present an easily recognized flaw in the attractiveness of the patient’s eventual incisor display and “smile esthetics”. Moreover, the presence of such a large tooth will create a serious Bolton discrepancy although extensive interproximal enamel reduction will largely address both these problems.

In summary, therefore, extraction of first premolars in this case may offer a more classic dental order and a superior appearance. However, it presents a challenging surgical exposure task as well as giving the orthodontist an immensely demanding biomechanical problem regarding the canines. The already resorbed lateral incisors will then need to undergo labial root torque followed by considerable crown reduction reshaping. In the long term analysis, approaching this case in the above manner is fraught with technical difficulty and generates an outcome with an uncertain prognosis.

          b.  maxillary impacted canines:

If the decision is to extract the permanent canines, then it is essential that this be done as soon as possible. Their continued existence adjacent to the roots of the lateral incisor will certainly cause further resorption and may affect the central incisors in similar fashion. Even a skilled surgeon will not find the task easy, because of the possibility of damage to the adjacent incisors in the cramped conditions of their inter-relations. Given the detailed portrayal presented by the 3D images of the CBCT, the OMFS will need to decide whether to approach the extraction from the labial or the palatal side and whether the teeth will need to be sectioned in order to best be eliminated.

In this way converting the appearance of the first premolar into a more canine-like shape and reshaping the lateral incisor, as already described above, will not present difficulty. However, this would leave the very young patient with two lateral incisors and their markedly shortened roots and their re-shaped crowns with which to face the future.

By exercising this option, the orthodontics is very much simplified, in favor of minor prosthodontic reshaping but, here too, the patient is left with lateral incisors whose prognosis might be fairly good in the short-to-medium term, but is uncertain long term.

c. maxillary lateral incisors:

gg._Fig._6

Fig. 6. The extracted lateral incisor teeth display their resorption craters (arrows) from the interproximal and labial sides.

Extraction of maxillary lateral incisors is an unusual choice for extraction in orthodontics and the shock that is likely to be registered by the patient at the loss of two of the front teeth is not something easily understood, accepted and assuaged by any patient. However, this bold decision has several significant advantages, the most obvious of which is that it eliminates a priori the teeth which will end up being the most damaged (Fig. 6) or prosthodontically altered and with the most uncertain future. At the same time, the palatal aspect of the impacted canines becomes freed and the teeth are no longer impacted. Although the canines are located palatal to the central incisors, the chances of their spontaneous eruption are almost certainly favorable …. always provided that the orthodontist, the parents and the patient are prepared to wait! The question here is just how long will the patient be without the teeth. It should not be forgotten that the spaces that needs to be filled are not the canine locations, but the lateral incisor locations and missing front teeth adjacent to the central incisors inject a degree of urgency in resolving the impaction.

Canine teeth generally take a very long time to erupt under normal circumstances, when their eruption path is in a direct line to the space in the dental arch and there is space for them. It is sometimes more than a year between the tooth first breaking through the mucosa until it reaches its fully erupted length. One can therefore expect eruption in this case to take considerably longer. Thus, both for the small chance that spontaneous eruption will not occur and for the expected time lag if it does, biomechanically encouraged eruption of the tooth should be undertaken (Fig. 7a-d).

gg._Fig._7

Fig. 7a. Following extraction of the lateral incisors, the canines were exposed on each side, immediately palatal to the central incisors. Note the minimal degree of crown exposure and the eyelet attachment place on the disto-labial aspect of the crown of the left canine. No attempt was made to remove more of the follicle nor to remove bone on the labial or mesial sides, to avoid exposing and damaging the incisor root. Surgery by Dr. Eran Regev.

Fig. 7b. Full closure of the surgical flap in this closed exposure procedure was performed, leaving only the twisted stainless steel (0.014”) ligature visible.

Fig. 7c, d. The maxillary orthodontic appliance was placed 3 weeks after the surgery. Note the use of TipEdge brackets on the central incisors which, because of the special features of their horizontal channel, have no uprighting effect on these teeth, as seen in these anterior and left side views on the day the appliance was placed. Distal re-orientation of the incisor roots would place them in the direct path of the erupting canines. Ligation of the twisted steel connector from the unerupted canine was made immediately to this 0.014” stainless steel archwire.

One further point that is pertinent in any impaction case where there is concurrent crowding. This fear is always in the back of the orthodontist’s mind when extracting erupted teeth in the attempt to resolve the impaction of other teeth. What are the chances of ankylosis of the canines presented in this case? Ankylosis in unerupted teeth is uncommon, but it occurs much less frequently in the young patient. This patient presented here is only 11.4 years of age, which is approximately when the canines were expected to have erupted naturally. These canines have taken an abnormal and futile “eruption” path and, as such, have travelled further than for a normal eruption. They have also caused the resorption of the roots of the lateral incisors to a considerable extent. Both these factors take time. It must therefore be safely assumed that these teeth are “on the move” and that, by mechanically redirecting their eruptive movements, the prognosis for successful eruption would appear to be very good.

The active orthodontic treatment of this case has only just begun and the maxillary orthodontic appliance was placed just 2 weeks ago, which was when Fig. 7c&d were photographed. The reason for its presentation here has been to discuss different treatment options in cases where there are multiple adverse factors involved. I plan to update the reader with a progress report in due course.





References

1. Becker A. The orthodontic treatment of impacted teeth. 3rd edition. Oxford: Wiley-Blackwell Publishers, 2012: Chapter 12 (Fig. 12.17)

2. http://dr-adrianbecker.com/page.php?pageId=281&nlid=40

3. Becker A. The orthodontic treatment of impacted teeth. 3rd edition. Oxford: Wiley-Blackwell Publishers, 2012: Chapter 6 (Fig. 6.45) and Chapter 15 (Fig. 15.6)

4. Becker A, Chaushu S. Palatally impacted canines: The case for closed surgical exposure and immediate orthodontic traction. American Journal of Orthodontics and Dentofacial Orthopedics 2013;143:451-459.

5. Becker A, Chaushu S. Long-term follow-up of severely resorbed maxillary incisors following resolution of etiologically-associated canine impaction. American Journal of Orthodontics and Dentofacial Orthopedics 2005,127:650-654