NEWSLETTERS

Impacted mandibular second premolars

Published: February 2012

Bulletin #8 February 2012

Impacted mandibular second premolars

Probably the most common cause of mandibular second premolar impaction is local and environmental, i.e. the early extraction of its deciduous predecessor. Although caries has been markedly reduced in the developed world, we still find children who lose the deciduous tooth well before the second premolar is developed enough to erupt rapidly into its place, with the result that the adjacent teeth tip into the extraction space. This then causes the tooth to become impacted in the line of the arch to a greater or lesser extent, or to erupt ectopically (usually on the lingual side).

In either case, the treatment is relatively straightforward with just 3 options presenting:-

  1. In a non-extraction case, the space is regained using a fixed multibracketed appliance. With space available, an unerupted premolar will almost invariably erupt spontaneously and a lingually displaced premolar will improve its alignment within a short space of time. In both cases, minor routine finishing may be necessary.
  2. In an extraction case, this tooth may be chosen along with a similar tooth in the other 3 quadrants or
  3. one of the adjacent teeth sacrificed, along with a tooth in the other 3 quadrants, to permit the premolar to erupt normally.

However, this type of second premolar impaction is not the subject of this month’s bulletin.

Fig_1aFig_1b

Fig. 1a An unerupted, distally-tipped, mandibular right second premolar is very late developing in a 13 year old girl. All other permanent teeth are erupted and apices closed.

Fig. 1b The same patient 3 years later showing the eruptive “progress” of the premolar! There has been resorption of the distal root and crown of the over-retained second deciduous molar and severe resorption of the entire mesial portion of the crown and root of the first permanent molar.

The focus here is on the more unusual, most likely genetically-determined, type of impaction in which the tooth has typically developed with a distinct distal inclination and its eruptive movement is expressed distally, rather than occlusally. In its simpler form, the end result may find its occlusal surface jammed against the mesial surface of the mesial root of the first permanent molar. In its more serious form, however, it may be discovered on a periapical or panoramic view superimposed on the roots of the molar, usually on the lingual side. Suffice it to say that the tooth is in an extremely inaccessible location. By and large, its deciduous predecessor is still in place with an unresorbed mesial root, while the degree of resorption of the distal root is dependant on the relative height and angulation of the unerupted premolar successor. Resorption of the roots of the permanent molar is an infrequent finding (Fig. 1) but, when it does occur and until it reaches a very advanced stage, it is difficult to diagnose because it occurs on the lingual surface of the molar roots and, as such, will escape detection on routine plane film radiographs until much tooth tissue has been lost.

Fig. 2a_7Fig. 2b_3

Fig. 2a A 12 year old female patient with late developing mandibular second premolars. The right premolar has not yet completed crown formation and it is tipped distally.

Fig. 2b Orthodontic treatment for the same patient involving the extraction of maxillary first premolars, has been completed. All the teeth are aligned and twistflex wire splints hold the anterior alignment, but the mandibular premolar has been deliberately left untreated, with the deciduous molar in place. The tooth is almost horizontal, its apex is ideally placed, but the crown proceed lingually and distally past the mesial root of the molar, adjacent to the furcation.

Fig. 3_1

Fig. 3 Intra-oral views of the completed case at the time of referral to the author. The yellow arrow indicates a draining sinus tract traced to the deciduous molar.

Mandibular second premolar anomaly & other linked anomalies

Abnormality in development and location of the mandibular second premolar has many anomalies associated with it. It is well known that, in most population studies, its congenital absence is more frequent than any other tooth with the possible exception of the maxillary lateral incisor. In common with the maxillary lateral incisor, its development is sometimes retarded in relation to the development of the rest of the dentition and commonly seen in company with agenesis of its antimere1-4. When it is late developing, it will frequently exhibit a distal tip5 (Fig. 2) and, at the same time, is seen with increased frequency accompanied by maxillary impacted canines5,6. It is also seen together with late development of the dentition as a whole, a condition in which the prevalence of canine impaction is also increased7-12. Furthermore and in common with late developing dentitions, the teeth are generally small and fairly normally aligned, with spacing rather than crowding a recurrent feature.

So, the upshot is that it is often to be found in a dentition which is well aligned, with normally related jaws and which may otherwise not require orthodontic treatment. Yet there is a permanent tooth in a very inaccessible location, on the lingual side of the ridge, at or below the level of the floor of the mouth. Motivation on the part of the patient may therefore be low and there may be an unwillingness to wear braces. Accordingly, it may be important to devise a partially bracketed system, specifically excluding the teeth in the esthetic zone. This presents 3 essential problems13, namely:-

1. establishing a sufficiently resistant anchor base which will not compromise the existing alignment

2. offering strategic sites on this anchor base from which traction may be applied to resolve the impaction and then to align the impacted tooth.

3. developing a spring device or system that will resolve the impaction, erupt the tooth and bring it close enough to its intended location in the arch for routine orthodontic treatment to finish the job.

This type of single tooth orthodontic movement is very demanding on anchorage and the anchor units should certainly involve a large number of teeth, including some on the opposite side of the arch, as well as teeth in the incisor/canine area. But, how can one do this without placing unsightly brackets on the anterior teeth?

The case reported here will be used as an illustration of how this can be achieved successfully (Figs. 1-7).

The anchor base

In my practice, I have adopted customized variations on the following appliance set-up to achieve a solid anchor base:-

1. On a plaster cast, a lingual twistflex splint is prepared in the laboratory extending the wire to the labial side at both distal ends and then incorporating the labial extension into a self-curing acrylic locating jig.14 The splint is transferred to the mouth and bonded in the normal way. The locating jig is then cut at the most distal end on the lingual side and discarded. Normally, the splint extends from canine to canine but, in this case, it is advantageous to continue it on the side of the impacted premolar to include the occlusal surface of the first premolar.

2. On the same visit, a separating elastic is placed to open the interproximal contact between the first and second permanent molars on the affected side. A few days later, a band is placed on the second molar, carrying a double rectangular buccal tube attachment. Brackets are then bonded to the first molar, first premolar and canine on that side only.

3. A sectional rectangular archwire is prepared, slotted into a tube on the second molar and is made to lie passively in the other three brackets, to which it is ligated in the normal manner.

This presents a substantial anchor base which includes all the teeth from second molar to canine or premolar of the opposite side, with the lower canine and first premolar providing the link between the lingual anterior splint and the buccal sectional archwire. In deference to the demands of the patient, there are no anterior brackets.

Radiography

From the radiographs and/or CBCT of the area of the impacted second premolar, it is incumbent on the orthodontist to pinpoint the exact mesio-distal, bucco-lingual and vertical location of the tooth. For the present exercise, we shall assume the worst i.e. that its root apex is in its normal location, while its crown proceeds distally and horizontally on the lingual side of the molar roots. The crown itself is at or slightly below the level of the oral mucosa of the floor of the mouth.

Shall we assume a modicum of root resorption on the lingual aspect of the molar roots, facing the horizontal premolar? Yes, why not?! The tooth is extremely difficult to access and there is no direct line between it and its intended final destination in the dental arch. Two-dimensional planning for the needed orthodontic traction offers no salvation for this tooth.

Fig._4a___b

Fig. 4a, b Immediately prior to surgery, with intra-oral views of orthodontic attachments on the mandibular right canine, first premolar, first molar, with a cemented band on the second permanent molar. A heavy sectional base arch, fashioned to lie passively, is ligated into the tube and brackets. N.B. the canine and first premolar are linked also on the lingual side by the twistflex splint. A light wire auxiliary spring slots into the second molar tube, proceeds to the mesial of the first molar bracket and is then bent in a double anti-roll bend (arrow) before turning vertically upwards and terminating in a helix.

The active spring

The active eruption device that is needed must have the capacity to apply force in three dimensions, in an occlusal, mesial and lingual direction, in order to circumvent the molar roots and evade a clash with the broad molar crown. A simple ballista type of mechanism may be constructed from 0.019”x0.025” stainless steel wire, which slots into a second rectangular buccal tube on the molar band, passes mesially to the premolar area and is then bent across the occlusal plane before being turned down lingually and terminating in a simple loop. In its passive posture the terminal portion stands vertically upwards, above the occlusal surface. Round cross-section wire may also be used (Fig. 4), provided that a suitable anti-rotation loop is incorporated in it to prevent its rotating in the buccal tube. The ballista device is removed and stored safely until the surgical stage of the treatment.

Surgery and interdisciplinary collaboration

Given that the impacted tooth is at or below the level of the floor of the mouth, bound by highly mobile and delicate oral mucosa, any form of open surgical exposure will be extremely uncomfortable for the patient for a very long time. 15

Only a closed surgical exposure should be attempted and this is a difficult task to perform, largely due to the poor accessibility of this area. It cannot be sufficiently emphasized how important it is for the orthodontist to take an active part in this procedure – to help the surgeon and to be helped by the surgeon to successfully place an attachment on the tooth and to apply immediate traction, while the anesthetic is still effective. In these technically difficult scenarios, interdisciplinary cooperation is likely to make the difference between a “make or break” situation.

Fig._5a_c

Fig. 5a At surgery, a full lingual flap is reflected from the gingival margins of the premolar and molar teeth.

Fig. 5b an eyelet attachment is bonded by the orthodontist, with the surgeon’s and assistant’s aid in maintaining a dry field. The twisted soft steel wire ligature extends upward prior to suturing.

Fig. 5c direct and mirror image to show the flap sutured back into its former place, leaving a narrow slit into which the ligature is held and stabilized by a suture. The auxiliary spring has been shortened to suit the circumstance pertaining and ensnared in the ligature wire, which is turned over to form a hook. This hold the spring in its activated position. Extrusive force, with a mesial and a minimal lingual components, is now acting on the tooth in order to erupt it away from interference with the crown of the molar. The range of this spring is extremely long and its force is light and easily measurable.

The surgeon should then extract the deciduous second molar and proceed to reflect a full lingual flap from the sulcus gingiva of the second molar, first molar, deciduous molar (or crest of the edentulous ridge) and first premolar, followed by blunt dissection down on the lingual side, until the crown of the second premolar is reached (Fig. 5). No attempt should be made to dissect out the follicle of the tooth, but a small area of crown enamel should be exposed and the area isolated as well as possible with good use of high power suction and pressure packs. Once hemostasis is achieved, the orthodontist should be on hand to bond a small eyelet on the exposed, etched and dried area of exposed crown, while the surgeon and assistant maintain a dry field.

A soft steel (0.011” or 0.012”) ligature wire is inserted into the eyelet prior to placement and twisted to form a long tight pigtail. A fresh package of light-cure bonding material should be used to ensure the reliability of the bond and, once completed, the surgeon should fully close the flap to its former place, re-covering the exposed and attachment-bonded tooth, with only the twisted pigtail ligature projecting superiorly. It is important to request the surgeon to draw the ligature through a small vertical slit in the flap and to suture it securely in a position slightly lingual to the line of the dental arch (Fig. 5c).

The orthodontist should now re-insert and ligate the prepared ballista spring device in the buccal tube with its free end in its passive position high above the occlusal surface (Fig. 5a, b). With light finger pressure, the terminal loop is pushed gently downward and lingually, over the occlusal plane and close to the tissues in the recently vacated second deciduous molar gap. The terminal loop is then ensnared on the lingual side by the twisted ligature, which is hooked over it to ensure a secure, but easily adjustable connection (Fig. 5c).

The ballista spring will provide traction in an occlusal, but also in a mesial direction, depending on the degree of mesial deflection pre-adjusted into the spring – and it is extremely easy to adjust. It may now be left for a month or more to do its work without the need for adjustments during the highly sensitive period of post-surgical discomfort, while the entire area is healing. The range of action of this spring is extremely wide and the only thing that may be needed for the subsequent 2 or 3 visits is to roll the twisted ligature over the terminal loop, to keep it close to the tissues in the extraction space.

Fig._6a__b

Fig. 6a The premolar has erupted through the attached gingiva and needs to be erupted further, but with a stronger mesial component.

Fig. 6b With the auxiliary extrusive spring re-activated and re-ligated, an elastic thread is drawn under tension from the same eyelet to a convenient interproximal location on the bonded lingual splint.

Within a few short weeks, the premolar will be seen to bulge the lingual mucosal surface of the mandible at or slightly above the level of the floor of the mouth and it may be deduced that its proximity to the roots of the molar has been overcome. Given the continuous light occlusal force and its wide range, a more mesial component of traction may become necessary within a relatively short time. This may be achieved while still using the ballista spring. An elastic ligature tie may be made between the hooked end of the pigtail ligature and one of the interproximal spaces of the bonded twistflex splint on the lingual side of the anterior teeth (Fig. 6a, b). Directional control of occlusal and mesial traction is very easy to manage and is continued until the premolar tooth stands on the lingual side of its final target site in the arch. At this point, a light elastic tie to the buccal rectangular section wire will provide the third dimension of traction control to bring the tooth into alignment. 

Fig._7a__b

Fig. 7a, b The final stages of treatment.

Fig._7c

Fig. 7c Panoramic view to check for root parallelism before appliance removal.

Needless to say (and as Murphy’s law will have it), the tooth is very likely to be rotated. In this case, the eyelet should be relocated to the anatomical mid-buccal surface of the tooth before direct elastic traction to the arch is made, in order for the traction to generate a positive rotatory effect on the tooth.

References

1. Garn SM, Lewis AB, Vicinus JH. Third molar polymorphism and its significance to dental genetics. J Dent Res 1963; 42: 1344–63.

2. Sofaer JA. Dental morphologic variation and the Hardy-Weinberg law. J Dent Res 1970; 49 (Suppl): 1505–8.

3. Baccetti T. A controlled study of associated dental anomalies. Angle Orthod 1998; 68: 471–4.

4. Shalish M, Peck S, Wasserstein A, Peck L. Malposition of unerupted mandibular second premolar associated with agenesis of its antimere. Am J Orthod Dentofacial Orthop. 2001;121:53-55.

5. Shalish M, Chaushu S, Wasserstein A. Malposition of unerupted mandibular second premolar in children with palatally displaced canines. Angle Orthod. 2009;79:796-9.

6. Distally displaced premolars: A dental anomaly associated with palatally displaced canines. Baccetti T, Leonardi M, Giuntini V Am J Orthod Dentofacial Orthop. 2010 Sep;138(3):318-22.

7. Becker A. Etiology of maxillary canine impactions. Am J Orthod 1984; 86: 437–8.

8. Zilberman Y, Cohen B, Becker A. Familial trends in palatal canines, anomalous lateral incisors and related phenomena. Eur J Orthod 1990; 12: 135–9.

9. Newcomb MR. Recognition and interception of aberrant canine eruption. Angle Orthod 1959; 29: 161–8.

10. Becker A, Sharabi S, Chaushu S. Maxillary tooth size variation in dentitions with palatal canine displacement. Eur J Orthod 2002; 24: 313–18.

12. Becker A, Chaushu S. Dental age in maxillary canine ectopia. Am J Orthod Dentofacial Orthop 2000; 17: 657–62.

13. Becker A. The orthodontic treatment of impacted teeth. 3rd edition. Oxford: Wiley Blackwell Publishers, to be published March 2012

14. Becker A, Goultschin J. The multistrand retainer and splint. American Journal of Orthodontics 85:470-474, 1984.

15. Chaushu S, Becker A, Zeltser R, Branski S, Vasker N, Chaushu G. Patients' Perception of Recovery After Exposure of Impacted Teeth: A comparison of Closed versus Open-Eruption Techniques.
Journal of Oral and Maxillofacial Surgery 2005;63:323-329.