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Follicular enlargement, peg-shaped incisors and canine-driven resorption

Published: November 2016


Bulletin #60 November 2016

Follicular enlargement, peg-shaped incisors and canine-driven resorption

Introducing the problem

The 9 year old female patient came to see me initially in April 2014 and was accompanied by her mother, who complained of the poor appearance of her anterior dental display. The anterior teeth were widely spaced, due in part to two newly-erupting peg-shaped maxillary lateral incisors and a shift of 2-3 millimeters of the maxillary dental midline. Her dentition comprised four permanent molars, four maxillary and four mandibular incisors, but also included all four second and the right maxillary primary molars. The mandibular permanent canines were just erupting. From the dental history, it was learned that the other 3 deciduous first molars had earlier been extracted due to caries, while all four deciduous canines had shed spontaneously.

There was a mild degree of crowding in the mandibular dentition. The overjet and overbite were 4-5mms and the two maxillary canines were still unerupted, although the right canine could be palpated on the palatal side of the incisors. Mother also produced a panoramic radiograph that had been taken in November 2013, which was prior to the eruption of the left lateral incisor (Fig. 1).

November_2016._Fig._1._November_2013_pan

Fig. 1. Panoramic radiograph of November 2013. Note the normal location of the unerupted maxillary canines and the relation between the crown tip of the right canine with the developing apex of the right lateral incisor.

In my initial discussion with mother at that first visit, I explained the necessity for future orthodontic treatment and that there would likely be a problem with the canine that might require surgery. Based on the panoramic view taken only 4-5 months earlier, I advised that the last remaining deciduous first molar be extracted with the intention of facilitating rapid eruption of the first premolar and, thereby, permitting the right canine to undergo some degree of spontaneous positional improvement. I then requested that I see the child again in the Spring of 2015 with a new panoramic film to be taken at that time, in order to re-evaluate the dental development and positional changes that will have occurred.

What were the factors that were taken into account to justify this decision?

Due to early shedding of the deciduous canines and the extraction of 3 of the deciduous first molars, I viewed the extraction of the 4th primary first molar to be the realization of a prophylactic protocol proposed by Alessandri Bonetti and co-workers.1 This protocol involves the prophylactic extraction of the maxillary deciduous canines and first primary molars and has been shown to improve the fortunes of potentially impacting maxillary canines and to result in their spontaneous eruption in a large proportion of the cases.

The child’s dental age was assessed at 8½ -9 years, with open apices in the permanent molars and incisors and with premolar roots less than ¼ developed. Together with the fact of so many unerupted teeth, actively initiating orthodontic mechanotherapy was contraindicated. Nevertheless, the crown-to-apex orientation of the right lateral incisor was not apically convergent with the central incisors, as would be expected at this age and the developing apex appeared to be in close proximity to the unerupted and normally-located right canine in the mesiodistal plane. On the left side, the unerupted and peg-shaped lateral incisor shows a more normal orientation, characteristic of this early stage.2 It may be argued that a proactive environmental alteration, in the form of re- orientation (mesial over-uprighting) of the right lateral incisor root3 would improve the chances for normal eruption of the right canine. This protocol was well illustrated in a lecture I presented at the AAO Annual Session earlier this year,4 although its efficacy has yet to be tested in a large patient sample.

Follow-up of the case

November_2016._Fig._2._September_2015_pan

Fig. 2. Panoramic radiograph of September 2015. Note the presence of an enlarged follicle surrounding the right canine and the enlargement of the image of the canine crown and its superimposition on the root of the peg-shaped lateral incisor.

The parents of this child work full time and, because of the distance between their home and my office, they decided to see another orthodontist locally and a new panoramic film was commissioned in September 2015 (Fig. 2). This showed the presence of an enlarged follicle surrounding the crown of the unerupted maxillary right canine but some progress in the descent of both canines, which showed mild overlap of the lateral incisor root on the left side and complete overlap on the right side.

The projected image of the crown of a tooth in a panoramic film may be enlarged, depending on the distance of the tooth from the film. The projected image of the crown of the right canine was much enlarged and, by direct mesio-distal measurement on the film, appeared to be 19% wider than that of the adjacent central incisor. This is despite that, in reality, the incisor has the larger mesiodistal width. For the left side, the canine measured 15% larger than its adjacent central incisor. In this film, the right canine may be seen to superimpose on the mid-section of the root of the central and lateral incisors, while the left canine is in the coronal zone of the incisor roots. At these levels, an enlargement of the canine crown measurement of 15% or more above that of the central incisor determines that both canine are palatally displaced.5, 6

Through the partially radiolucent image of the canine crowns on the September 2015 panoramic view, the clear and undisturbed 2D outline of the roots of the superimposed lateral incisors may be clearly seen, along their full length (Fig. 2). There is no indication of resorption of these roots. However, since the canines were palatal, considerable resorption of the palatal side of the incisor root could conceivably have occurred before its extension interproximally could alter the root shape, to make it diagnosable on this or any other planar film.

November_2016._Fig._3._August_2016_p.a

Fig. 3. The periapical radiograph taken in August 2016 showing severe resorption of the root of the right lateral incisor.

November_2016._Fig._4._August_2016_pan

Fig. 4. Panoramic view of August 2016. Note the autonomously erupted left maxillary canine and the impaction of the right canine. The root of the right lateral incisor has largely disappeared, although the reader may be excused for considering the right lateral incisor to be unaffected.

The patient was only seen by the orthodontist 11 months later, in August 2016, when a single periapical radiograph revealed severe resorption of the right lateral incisor, with the disappearance of 90% of its root (Fig. 3). A new panoramic film performed at the same time (Fig. 4) confirmed this and also showed the left canine to have autonomously reached its assigned place in the dental arch and to have fully erupted. Its immediate incisor neighbor showed good and apparently healthy, completed root development. On the right side, the canine remained impacted and had migrated further down and mesially to overlap the distal side of the central incisor root. There was only the faintest outline of root visible where the canine crown was superimposed on the lateral incisor.

November_2016._Fig._5

Fig. 5. Clinical intraoral photographic views of the dentition and malocclusion in August 2016.

Realizing the seriousness of the condition and its influence on the prognosis of the right lateral incisor tooth, the parents decided to consult me once more. Having seen the new periapical and panoramic films, I considered it essential to assess the degree of resorption that the lateral incisor had undergone, in order to evaluate whether this tooth was savable, since the overall malocclusion was typically a non-extraction case (Fig. 5).

New findings of the CBCT imaging

In general, it is true to say that accurate and detailed interpretation of the CBCT can best be derived through slices made in the 3 planes of space, with cross-sectional, axial and coronal cuts. These are usually performed as a series of parallel slides at millimeter intervals or less. They may also be made longitudinally at various angles to these planes, although they are then more difficult to interpret. Creating 3D pictures or movie video clips are an excellent bonus, to complete the depiction of the location and orientation of the impacted tooth in relation to its neighbors and, as in this case, will show any resorption craters in full and easily understandable detail.

November_2016._Fig._6aFig. 6a. A series of cross-sectional CBCT slices at 0.5mm increments, showing the severity of the resorption of the right lateral incisor.

November_2016._Fig._6b

Fig. 6b. A close-up slightly angulated cross-sectional view of the same tooth showing the complete severance of the incisor root, leaving the sequestered apex unharmed.November_2016._Fig._7_cross_section_22

Fig. 7. A series of cross-sectional CBCT slices at 0.5mm increments, showing the severity of the resorption of the left lateral incisor. This could not be diagnosed from the 2D panoramic view which was taken only 1 month earlier.November_2016._Fig._8

Fig. 8. A 12 slide series of axial cuts performed with 0.5mm increments shows the differing patterns and severities of resorption of the two lateral incisors (yellow arrows), the gradual appearance of the canine in the higher cuts (green arrows) and the enlarged dental follicle (pink arrows).


The selected images shown here (Figs. 6-8) illustrate how the continued progress of the impacted canine has traversed the middle of the root of the lateral incisor, leaving the crown almost completely severed from its residual and unaffected apex. At the same time, however, it also shows an extensive resorption crater located on the lingual aspect of the left lateral incisor (Fig. 7), which was clearly the result of the final eruptive throes of the left canine prior to its successful autonomous eruption. Referring back to the August 2016 panoramic film, a careful re-examination of the image of the left lateral incisor, with the benefit of 20-20 hindsight, reveals a minor radiolucency in the distal and cervical area of the tooth at its cemento-enamel junction, which had been earlier overlooked.

Fig. 9. https://youtu.be/h-lxM-fSUDQ Please click on this video clip which has been carefully produced to show the inter-relations between the right canine and the adjacent resorbed lateral incisor. At the very end of the clip, the lesion on the palatal side of the left lateral incisor comes into view.

Fig. 10. https://youtu.be/Y-p2hsOC11I Please click to view a 3D MPR video clip which shows how the progression of the cuts in the 3 planes of space is depicted in relation to one another.

With the video clips herewith (Figs. 9, 10), we will now have a much clearer picture of the status of the maxillary anterior dentition vis-à-vis the degree of resorption of the two lateral incisors and their prognoses, the palatal location of the impacted maxillary right canine and the inadequacy of space for its alignment.

Could this have been predicted?

According to a study performed in Sweden almost 30 years ago,7 the presence of an enlarged follicle around the crown of an impacted tooth is not an etiologic factor in resorption of incisor roots. Furthermore, studies performed by our group in Israel have shown that small and peg-shaped lateral incisors are strongly associated with the occurrence of impacted canines.8 However, we have also shown that, while those with large and larger-than-normal lateral incisors are likely to be affected by root resorption, resorption is highly unusual in cases with lateral incisors that are small or peg-shaped.9

The present case paradoxically shows severe and rapid resorption despite the presence of an enlarged canine follicle and peg-shaped lateral incisors. However, it falls into line with another study from our group which has shown that the likelihood of this extreme degree of resorption severity shows a 5:1 affinity for affecting females over males.10

Certainly, a more disciplined follow-up was indicated in this case, the more so since a study of incisor root resorption associated with impacted maxillary canines11 has indicated as many as 67% of affected incisors. The reason for this very high figure is undoubtedly due to today’s use of accurate diagnostic modalities such as CBCT, through which it is possible to detect early lesions. It should nevertheless be remembered that every one of the severest and most extreme resorption cases starts life as a small and undetectable lesion!

Treatment options

It should be quite obvious in this case that the presence of extensive lesions in both lateral incisors spells their early demise. This demise will also be hastened if attempts are made to prosthodontically enhance their crown form, since the resorption front in each is at the CEJ.

In this situation, the two incisors should be extracted, taking care to remove the sequestrated apical portion of the root on the right side. The next task will be to resolve the impacted canine.

Three alternative lines of treatment are then available, as follows:-

1. Recreate the lateral incisor spaces, including correction of the midline and disperse the crowding by distal movement of the posterior teeth in both arches.

2. Bring forward the maxillary posterior teeth to close up the spaces and alter the crown form of the canines to simulate lateral incisors, finishing the posterior occlusion in a class 2 relationship.

3. Extract a mandibular premolar on each side to compensate for the missing lateral incisors and to maintain and improve the present class 1 molar relations, while closing up all spaces.

Lessons to be learned

From evidence-based studies of the phenomena described here, many associations between the presence of certain anomalies and the likelihood that certain unwanted side-effects will occur , may seem remote. Nevertheless, as orthodontists, we treat our patients on a one-by-one and a one-to-one basis and, in the end, our treatment must be tailored to the individual requirements of the patient and his/her malocclusion and not to a general statistic. In the present case, extreme root resorption of the incisor roots has unexpectedly been caused by eruption disturbance of adjacent canines, in the presence of peg-shaped lateral incisors and an enlarged canine follicle, features that clinical studies have shown to be normally unassociated with resorption. On the other hand, the existence of resorption of such extreme severity serves to emphasize the finding that it has a predilection for females.10

References

1. Alessandri Bonetti G, Zanarini M, Incerti Parenti S, Marini I, Gatto MR. Preventive treatment of ectopically erupting maxillary permanent canines by extraction of deciduous canines and first molars: A randomized clinical trial. American Journal of Orthodontics and Dentofacial Orthopedics, 2011;139:316-23.

2. Broadbent BH. Ontogenic development of occlusion. Angle Orthodontist, 1941;1:45.

3. Becker A, Chaushu S. Etiology of maxillary impacted canines: A review. American Journal of Orthodontics and Dentofacial Orthopedics, 2015;148:557-67.

4. Becker A. Lecture entitled: If impacted canines are genetically determined – prove it! From the 116th American Association of Orthodontists Annual Session, Orlando, May 2016. Published in the AAO Distance Learning Resource.

5. Chaushu S, Chaushu G, Becker, A. The use of panoramic radiographs to localize maxillary palatal canines. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endododontics 1999; 88:511-516.

6. Chaushu S, Chaushu G, Becker A. Reliability of a method for the localization of displaced maxillary canines using a single panoramic radiograph. Clinical Orthodontics and Research 1999; 2:194-199

7. Ericson S, Kurol J. Resorption of maxillary lateral incisors caused by ectopic eruption of the canines. A clinical and radiographic analysis of predisposing factors. American Journal of Orthodontics and Dentofacial Orthopedics, 1988;94:503-13.

8. Becker A, Smith P, Behar R. The incidence of anomalous lateral incisors in relation to palatally-displaced cuspids. Angle Orthodontist, 1981;51:24-29.

9. Brin I, Becker A, Zilberman Y. Resorbed lateral incisors adjacent to impacted canines have normal crown size. American Journal of Orthodontics 1993;104:60-66.

10. Chaushu S, Kaczor-Urbanowicz K, Zadurska M, Becker A. Predisposing factors for severe incisor root resorption associated with impacted maxillary canines. American Journal of Orthodontics and Dentofacial Orthopedics, 2015;147:52-60.

11. Walker L, Enciso R, Mah J. Three-dimensional localization of maxillary canines with cone-beam computed tomography. American Journal of Orthodontics and Dentofacial Orthopedics, 2005;128:418-23.