NEWSLETTERS

Obstructive impaction of a central incisor

Published: June 2013

Bulletin #23 June 2013

Obstructive impaction of a central incisor.

Pediatric dentists may see the full range of dental conditions in the offspring of a dentally-aware and sophisticated local population for whom dental health is important. Nevertheless, these youngsters do not comprise a truly random group for studying prevalence as a part of anything other than a typical or atypical “patients-attending-dental-office” sample. The most common reason for non-eruption of the maxillary central incisor is the presence of a supernumerary tooth in the midline area (mesiodens). Perhaps because the age at which this is first noticed by the parent is usually between 7 and 8 years of age, the first professional “port of call” for the parent is the pediatric dentist and the treatment may often be stage managed by him/her, rather than by the orthodontist. Moreover and because they see more of these cases than anyone else, most prevalence studies have been carried out by pediatric dentists and many of these do not appear in the specialist orthodontic literature. The more the practitioner sees, the more interesting the subject becomes and, by collecting them into the patient base, these cases inject an even greater bias in the above-mentioned “patients-attending-dental-office” sample, resulting in wide-ranging and probably exaggerated figures for its occurrence in what has often been mistaken for the general population.

In this website, I have published several newsletter essays devoted to aspects of the treatment of dilacerate (bulletin #10 April 2012, bulletin #11 May 2012) and traumatically intruded incisors (bulletin #9 March 2012). In contrast to these, the principles involved in the treatment of impacted incisors obstructed by one or more supernumerary teeth are relatively simple and straightforward and, yet, failure to achieve a good result is common. Failure may be absolute, as in the case of non-eruption, or it may be relative, due to surgical damage, partial eruption, ectopic eruption or a poor periodontal result.

If the principles are uncomplicated, one is entitled to ask why failure should loom so large on the horizon. It may be due to an unfounded and optimistic conservative approach of merely removing the cause and awaiting positive results. If active orthodontic treatment is undertaken, then it may be that the answer lies in the orthodontic prerequisites (space) and preparation of the dentition (anchorage) needed to accomodate the impacted tooth, or perhaps in the ingenuity of the operator to provide efficient traction to enhance the eruptive potential of the tooth and, finally, the ability to align, level and orient its long axis appropriately.

Treatment methods

Let us start with the optimistic conservative approach. We were probably all taught that, to treat a pathologic condition, we must first remove the cause. From the clinical examination, one may see the over-retained deciduous central incisor which, by the time the permanent lateral incisors erupt, should not be there. From the radiograph, the presence of the supernumerary tooth will also be diagnosed and this, too, should not be there. But, even in the months prior to their eruption, the lateral incisors will be seen to be in an inverse vertical relationship to the impacted central incisor insofar as they are much more inferiorly located in the alveolus than the impacted central incisor, indicating that something is wrong.aaa.Fig.1

Fig. 1. The initial panoramic radiograph at age 8 years shows 2 supernumerary teeth interfering with central incisor eruption. The practitioner extracted the deciduous incisors only.

The pediatric dentist now has a dilemma. Should he/she start by extracting only the deciduous tooth with follow-up arranged for the next year or so (Fig. 1)? After all, this is easy-to-deliver advice and simple treatment and does not involve a surgeon’s expertise. This line of treatment is manifestly illogical, since the deciduous incisor is only there because the permanent incisor has not advanced towards it to initiate resorption of its root. The deciduous tooth is not the cause of the failure – that distinction belongs strictly to the supernumerary tooth because it has prevented the incisor from advancing. Nevertheless, extracting the deciduous incisor only is the easiest line of advice to suggest, since neither the practitioner nor the parent is keen on the idea of oral surgery for this young child.

In the present context, it follows that the logical approach is to recommend extracting the over-retained deciduous central incisor and then surgically removing the supernumerary tooth or odontome, in one single surgical episode. If the surgeon stops there and leaves the impacted incisor untouched, it remains surrounded by an intact follicle and the extraction site is left to heal over. An intact dental follicle in contact with alveolar bone has been shown to be the initiator and promoter of bony resorption ahead of an erupting tooth, leading to the normal and spontaneous eruption of the tooth.1 Therefore and at least in theory, this should present the ideal situation for the autonomous eruption of the impacted tooth.

In the subsequent months following the surgery, the incisor may or may not improve its position by beginning to move down, within the alveolus, under its own steam. Sadly, the most common scenario is to witness the eruption of the two lateral incisors, adjacent to the fully erupted, single, unaffected, central incisor, but the affected incisor does not erupt. On the contrary, the adjacent lateral incisor tips mesially and the contralateral central incisor crosses the midline, towards one another, to reduce the space required for the unerupted tooth. Even in the small percentage of cases in which the impacted incisor erupts successfully, without professional assistance, this occurs very slowly and the child may be without a front tooth/teeth for as much as 2-3 years.

Perhaps the surgeon should alternatively perform an open surgical “window” procedure, directly over and fully exposing the tooth, with the aim of preventing the tissues from rehealing over the tooth. This approach is to be discouraged, since the tooth will have been displaced to a very superior position, high on the anterior aspect of the labial sulcus by the presence (usually) of a palatally-located supernumerary tooth. In this position, it is covered only with mobile and loose oral mucosa which will later form a non-keratinized gingival cuff for the erupted tooth. Performing an apically repositioned full thickness periodontal flap would leave a large area of alveolar bone exposed to the oral environment. A partial thickness flap raised from the attached gingiva of the labial gingiva of the deciduous tooth would circumvent this, but the post-treatment appearance of the gingival area around the aligned tooth will leave much to be desired and will usually require subsequent periodontal reparative procedures and, certainly, a considerable period of time to make it comparable to the untreated side. The fact that the incisor has been displaced to the labial side by the physical presence of the supernumerary tooth will almost always mean that the final result will show a longer clinical crown by whichever surgical method is used. However, experience has shown that a closed procedure will minimize the worst of this negative feature, which is so important in the esthetic zone, at the front of the mouth.

According to a recent study from the Department of Pediatric Dentistry in Tel Aviv University, in which the supernumerary teeth were removed and the situation left without further treatment, failure to erupt was reported in 64% of the cases in their sample and a further 9% only partially erupted. Ectopic eruption was seen in 17%. Taken together, therefore, 90% of the sample showed unsatisfactory outcomes,2 leaving the child effectively toothless in all but 10% of the cases! Clearly, this protocol cannot be declared a successful treatment strategy and belief in its efficacy is not scientifically supported. A much more reliable, predictable and proactive line of action needs to be adopted.

Without question surgical removal of the impeding supernumerary tooth or odontome is an essential part of the treatment. However, removing it is by no means an emergency situation and the surgical episode should be relegated to a time when extrusive force may be conveniently applied to the tooth, preferably immediately at the surgeon’s chairside. This means that an orthodontic appliance, capable of aligning and leveling the teeth and re-opening the space in the arch, needs to be placed. The appliance must be adequate to provide the anchorage needed to make it suitable as a base from which to apply the traction forces, by spreading the load to several teeth through the medium of a thick slot-filling archwire and by incorporating the resistance of the palatal tissue. Alignment, leveling and space opening will usually take several months of active orthodontics, before the heavy base arch may be placed in the orthodontic brackets to maximize the resistance of the appliance to the reactive forces of the traction. Only then should surgery be undertaken.

Case report

The aim of the present bulletin is to describe an overall approach to the treatment of obstructed impacted central incisors and it is illustrated here using a single case as the main theme. Several “wrinkles” will be described, which help to streamline the achievement of a good result and are here exemplified using illustrations from this and a second case.

According to the Merriam-Webster dictionary, a wrinkle is a small ridge or furrow especially when formed on a surface by the shrinking or contraction of a smooth substance, often referring to old age. In abstract terms, it describes an innovative device, trick, strategy or aspect, especially one that is new or different and most definitely related to age and longtime experience. Within the restricted meaning as it is used in our field, it refers to simple ways of achieving a result which are the outcome of years of clinical experience and yet not the sort of thing one might expect to read in a learned journal.

The patient was an 8 year old boy in the early mixed dentition stage, who had complained to his pediatric dentist that his baby teeth had not fallen out and that his front teeth had not erupted. The panoramic radiograph (Fig. 1) showed the presence of the deciduous incisor, with 2 unerupted supernumerary teeth superimposed on the impacted central incisors. The lateral incisors were more inferiorly located and appeared to have resorbed most of the roots of their deciduous predecessors and were about to erupt. The pediatric dentist extracted all four deciduous incisors, making the child embarrassingly toothless, and advised the patient to wait to see if the central incisors would thus be influenced to erupt autonomously.

aaa.Fig.2

Fig. 2. The condition seen a year later, showing erupted lateral incisors, over-erupted mandibular incisors occluding with and blanching the upper gingivae.

When I saw the child a year later, he presented with fully erupted first permanent molars, 4 mandibular incisors and 2 maxillary lateral incisors (Fig. 2). The maxillary central incisors had not erupted. The posterior deciduous and permanent teeth showed a mildly class 2 tendency, with an end-on relation of the deciduous second molars. The mandibular incisors were over-erupted and contacted the maxillary anterior gingiva.

aaa.Fig.3aaaa.Fig.3b

Fig. 3a. A CBCT 3-D view of the anterior maxilla shows the supernumerary teeth to be palatal and inferior to the central incisors which have been displaced superiorly and horizontally.

Fig. 3b. A transaxial cut shows the relative positions of the anterior teeth.

From the original panoramic and periapical views of the area, it was noted that both central incisors were present in an advanced state of root development and that 2 unerupted supernumerary teeth were obstructing their eruption path. The cephalometric film showed mild skeletal class 2 relations. Accurate localization in 3-D was established with the help of CBCT imaging (Fig. 3).

A phase 1 orthodontic treatment plan was considered appropriate for this case, due to the advanced development of the unerupted incisors and in order to restore a degree of normalcy to the child’s marred appearance. The aims of phase 1 of this treatment were

1. to level and slightly procline the maxillary anterior teeth and to create space in the incisor region.

2. to surgically extract the offending supernumerary tooth, to expose the crown of the unerupted central incisor and to bond an eyelet attachment to in

3. to apply extrusive traction to the tooth, to erupt and align it

4. to improve the alignment of the mandibular incisors and to level the mandibular occlusal plane, thereby distancing the incisors from the palatal mucosa.

5. to retain

aaa.Fig.4

Fig. 4. The Modified Johnson’s twin-wire (2-by-4) appliance prior to cementation.

a. The composite archwire comprises 2 long round buccal tubes of 0.020” internal diameter , with a light 0.014” steel anterior functional wire. Later this wire was substituted by a more rigid 0.018” sectional wire.

b. The archwire has been slotted into the 0.036” round soldered tubes on the first molar bands.

aaa.Fig.5

Fig. 5. Right side and front views of the appliance in place, with the composite archwire held into place by being pinned into a simple Begg bracket on each of the lateral incisors.

Over the years I have favored the use of a modified Johnson twin-arch (Fig. 4, 5) in these cases and the rationale for this was explained in bulletin #10 April 2012 and bulletin #11 May 2012 on this website and elsewhere.3, 4 It is an excellent appliance, but I have seen many of my former students abandoning it and using inferior methods because of their lack of skill/ability or perhaps due to inertia in setting up the soldered palatal arch and round buccal tubes. Accordingly and in this era of “preformed everything”, I have recommended using standard pre-welded molar bands and bonding regular brackets to the deciduous teeth, as advocated by Prof. Hermann van Beek of Amsterdam, but still with the addition of a rigid soldered palatal arch to reinforce the anchorage. This permits the early use of plain NiTi archwires, with little worry of distortion or dislodgement, while maintaining desirable force levels and a broad range of action.

aaa.fig.6a__b

aaa.Fig.6c

Fig. 6a. In a different patient with poor oral hygiene (!!) a simple archwire had been tied into brackets placed on each of the deciduous teeth. Note the soldered palatal arch.

b. The deciduous first molar has shed and swings on the archwire.

c. The dentine within the crown of the deciduous tooth can be seen to have been totally resorbed, leaving only its enamel shell.

Perhaps the only serious concern with this latter appliance comes when deciduous teeth have been extracted and a long span may then exist between first molar and the lateral incisor. Alternatively, if treatment starts later in the mixed dentition period or treatment takes too long, the bracketed deciduous teeth become loose and shed, with the result that the tooth or teeth then swing out of control on the archwire (Fig. 6). It should be remembered that phase 1 treatments are only efficacious for limited aims and provided that the phase is completed quickly. There is rarely much advantage in permitting a phase 1 treatment to spill over into the permanent dentition and to then become continuous with the phase 2 treatment.

The appliance was placed in May 2009 (Fig. 5) and space was created by June 2009 at which point a more rigid 0.018” steel labial archwire was inserted into the long buccal tubes that were themselves slotted into the soldered round tubes on the molar bands. This had the effect of adding a degree of rigidity to the appliance, which was to be used together with the soldered palatal arch as an anchor base from which traction force would be applied to the impacted teeth.

aaa.fig.7a_1 aaa.Fig.7b__c

Fig. 7a. Access for the extraction of the supernumerary teeth was through a palatal flap.

b. Access to the central incisors was obtained using a labial flap. Note the height of the teeth relative to the adjacent teeth and the minimal degree of exposure of the facial surface of the crown. No attempt has been made to remove more of the dental follicle and additional bone removal has been avoided.

c. An eyelet has been bonded to the facial surface of each incisor, oriented in line with the long axis of the tooth. A twisted 0.012” dead soft stainless steel ligature trails down to lie passively on the archwire.

dThe surgical removal of the supernumerary tooth and the exposure of the incisor were carried out with the orthodontist in attendance, in late June 2009 (Fig. 7). A palatal flap was raised from the crest of the ridge, the palatally placed supernumerary teeth were identified and then extracted. A labial flap was then raised from the same line on the crest of the ridge and bluntly dissected high into the labial sulcus, up to its reflection. The two impacted incisors were identified under their thin labial cover of alveolar bone, which was easily cut away with a scalpel. Only a small entry was made into the follicle, sufficient for placement of the small eyelet attachment and under the surgeon’s watchful eye to maintain hemostasis. No additional bone was removed - neither to free the incisal corners of the crowns nor to clear a direct path that the teeth would be traveling over the next few months.

aaa.Fig.7d_f

Fig. 7d. Before the labial flap was sutured, the twisted steel ligatures were curled around the raised archwire, which had been freed from the vertical slot Begg bracket by releasing the lock pins.

e. The archwire was then fully engaged into the bracket slot by drawing down the two lock pins, thereby exerting extrusive force. Although any bracket type could have been used here, the advantage of a vertical slot bracket can be clearly seen.

f. The palatal and labial flaps is finally resutured, to fully seal off the surgical wound from the oral environment.

An eyelet was bonded to each of the teeth, close to the incisal edge and a twisted dead soft steel ligature drawn from it and through the sutured edges of the fully closed and carefully re-sutured labial and palatal flaps. Vertical traction was applied immediately, by hooking the twisted ligatures around the flexed labial portion of the main archwire.

What about the brackets that we need to place on the remaining teeth in the dentition? These are the anchor teeth that will be set up to resist the reactive forces that are brought to bear on the unerupted teeth, to resolve their impaction. The aim in a phase 1 treatment is not to produce the definitive final alignment of the teeth, as is to be expected at the end of the phase 2 treatment. On the contrary, it should be remembered that between the time the lateral incisors erupt and until the final eruptive movements of the canines, there are natural changes in the alignment and 3-dimensional orientation of the incisors. For this reason, the drive for a so-called “ideal” alignment at age 9 is counter-productive and unnecessarily extends phase 1 treatment time by several more months. Moreover, it also requires a long term period of retention to maintain the child’s smile, to avoid disappointing but physiologic changes, which the parents will interpret as deterioration.

Prescription brackets of the various types are large and bulky, with sharp corners and should not be bonded to the teeth at surgery. These will cause unnecessary irritation and inflammation of the gingiva, as the tooth emerges through the delicate gingiva during its active eruption. Moreoever and aside from extrusion and rotation, no other movements of the tooth are possible until the tooth is fully erupted and ligated into the archwire. For this reason, I have encouraged the use of small, rounded, low-profile eyelets for the early post-surgical stage. An eyelet oriented in the long axis of the tooth can be used to great effect to extrude and rotate a tooth. Once the crown has emerged through the gingiva to a sufficient degree, a regular bracket may be substituted for the last couple of visits prior to debonding, to achieve a more acceptable result.

Needless to say, brackets are used in accordance with the operator’s preference or, perhaps, stock inventory. However, it should be remembered that the first attachment needs to be bonded at the time of surgical exposure and under the difficult circumstances that pervade in the operating theatre. Thus, bonding a bracket at the appropriate height and orientation on the impacted tooth at the time of surgery is very difficult, even for a trained orthodontist. I would argue that a surgeon, working alone, would be clinically ignorant of the finer points of bracket placement and technically ill-equipped to bond the bracket correctly – a procedure he/she has never learned and rarely called upon to perform.

Horizontal channel orthodontic brackets have been shown over the years to be the best for producing ideal results in the treatment of erupted teeth requiring leveling and aligning, tipping, rotation, uprighting and torqueing movements – almost everything that the orthodontic profession has to contend with - and a vertical channel bracket is at a disadvantage. Nevertheless, the single movement for which the horizontal channel bracket has a lesser answer is the vertical movement that is required in the resolution of an impacted incisor tooth. The vertical slot bracket comes into its own when extrusive forces are needed over a long range of movement, for which it is more highly suited, as seen in fig. 7.

aaa.Fig.8

Fig. 8    Leveling of the mandibular incisors

a. The composite archwire of a similar mandibular 2x4 appliance in the passive state before ligation

b. With the wire pinned into the brackets, a continuous intrusive component is introduced to level the curve of Spee.

In the present case, a similar modified Johnson twin-arch was placed in the mandibular arch (Fig. 8) to level the occlusal plane and relatively intrude the incisors to provide the possibility of achieving a normal overbite.

aaa.Fig.9

Fig. 9. Begg brackets have been substituted for the eyelets once the teeth have erupted adequately, for the final finishing.

It is recommended in this phase 1 treatment that the impacted teeth should be brought into alignment with the adjacent erupted teeth, uprighted and torqued to an acceptable degree for the stage of dental development (Fig. 9). Careful regard should be accorded to the location of the unerupted canine teeth and their proximity to the lateral incisors. Clinical research has shown that there is an increased prevalence of aberrant eruption of a canine adjacent to an impacted central incisor.5 Frequently, the canine will overlap the root of the lateral incisor and cause its root to be displaced lingually. To attempt to labially torque the root of this incisor, at this early stage and before canine eruption, is to court the possibility of resorption of its root.

aaa.Fig.10

Fig. 10. The final alignment at the end of phase 1. Note that the left maxillary lateral incisor appears to need labial root torque. This was deliberately avoided in this early treatment.

10. Post-tx pan_110._Post_tx_pa__22

Fig. 11     Radiographs taken at the time of appliance removal.

a. The panoramic view shows a degree of overlap of the left unerupted canine on the root of the left lateral incisors.

b. Periapical views emphasize the need to wait for canine eruption and phase 2 treatment before attempting to torque the roots of the lateral incisors.

Orthodontic treatment approached in this manner has a reliable outcome in terms of the relative speed with which it may be attained and in relation to the periodontal health and alveolar bone level of the outcome (Fig. 10, 11). In this case, the initial appliance was placed at the end of May 2009, surgical exposure was performed in July 2009 and the appliances were removed at the end of August 2010, for a total of 15 months of treatment. Since the impacted incisor teeth began to be visible in February 2010, as they were erupting through the gingivae, this child was edentulous for only 7 months following the removal of the supernumerary teeth. This contrasts with the 2 or 3 years or more that would have been the case in the most favorable of circumstances had we waited for autonomous eruption in the absence of proactive appliance therapy.

References

1. Marks SC Jr, Cahill DR. Regional cntrol by the dental follicle of alterations in alveolar bone metabolism during tooth eruption. J Oral Path. 1987,1:164-9

2. Ashkenazi M, Greenberg BP, Chodik G, Rakocz M. Postoperative prognosis of unerupted teeth after removal of supernumerary teeth or odontomas. Am J Orthod Dentofac Orthop 2007;131:614-9.

3. McKeown HF, Sandler J. The two by four appliance: a versatile appliance. Dental Update 2001;28:496-500.

4 .Becker A. Orthodontic Treatment of Impacted Teeth. 3rd ed. Wiley Blackwell, Oxford, 2012.

5. Chaushu S, Zilberman Y, Becker A. Maxillary incisor impaction and its relation to canine displacement. Am J Orthod Dentofac Orthop 2003,124:144-150