orthodontic uprighting of severely impacted mandibular ...edgewise appliance (mbt prescription with...

CASE REPORT

Orthodontic uprighting of severely impactedmandibular second molars

Catherine K. Lau,a Claudia Z. Y. Whang,b and Dirk Bisterc

London, United Kingdom

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The prevalence of impacted second molars is low, varying from 0% to 2.3%. The etiology of an impaction caninvolve systemic, local, and periodontal factors, as well as a developmental disruption of the tooth germ. A num-ber of surgical and orthodontic treatment options have been suggested in the literature, including leaving thetooth in situ, removing the impacted second molar, orthodontic uprighting, and autotransplantation. Removalof third molars has been suggested as an adjunct for space creation. This article presents the treatment ofa girl with bilateral severely impacted mandibular second molars as well as an ectopic maxillary left canineand severe crowding affecting both the maxillary and mandibular arches. Her treatment was successfully com-pleted with fixed preadjusted edgewise appliances (0.0223 0.028-in slot size) and MBT prescription (APC pre-coatedGemini Brackets; 3MUnitek, St. Paul, Minn), along with the removal of 4 first premolars. Themaxillary leftcanine and the mandibular second molars were surgically exposed. The treatment mechanics show that evenseverely impacted second molars can be uprighted by routine straight-wire techniques, which are easy to apply.The center of rotation of the second molar lies in the bifurcation of the roots of this tooth, and this biomechanicalproperty was used to its full advantage. The techniques applied comprised bracket repositioning, bypass ofbrackets, conversion of molar tubes to brackets, thermoelastic copper-nickel-titanium archwires, and a push-coil spring. Other orthodontic treatment mechanics, which require complex sectional or segmental techniques,auxiliaries, or artistic wire bending, that have been suggested in the literature were not used here. The third mo-lars were not removed. (Am J Orthod Dentofacial Orthop 2013;143:116-24)

Impaction of permanent teeth is a relatively commonoccurrence that can involve any tooth in the dentalarch. The frequency of impaction is highest for man-

dibular and maxillary third molars, followed by maxillarycanines and mandibular second molars.1 The eruption ofthe permanent molars differs from that of other perma-nent teeth, since there are no preceding deciduous teeth.For permanent molars, the tooth germ develops from thebackward extension of the dental lamina.2 Unilateralimpaction of the mandibular second molar is more com-mon than bilateral impaction. It occurs more frequentlyin the mandible, among male patients, and on the right

trar in Oral & Maxillofacial Surgery, Department of Oral & Maxillofacialry, Royal London Hospital, London, United Kingdom.ialist Registrar in Orthodontics, Department of Orthodontics, Guy's and Stas' Dental Hospital, London, United Kingdom.ultant orthodontist, Department of Orthodontics, Guy's and St Thomas'l Hospital, London, United Kingdom.uthors report no commercial, proprietary, or financial interest in the prod-r companies described in this article.t requests to: Dirk Bister, Consultant Orthodontist, Department of Ortho-cs, Guy's Hospital, Great Maze Pond, London SE1 9RT, United Kingdom;l, [email protected], December 2010; revised and accepted, September 2011.5406/$36.00ight � 2013 by the American Association of Orthodontists./dx.doi.org/10.1016/j.ajodo.2011.09.012

side of the jaw. Impacted second molars are most oftenmesially inclined.3 The 3 main causes of second molardisturbances are an ectopic position of the follicle, ob-stacles in the path of eruption, and failure of the erup-tion mechanism.4 It is important to diagnose thiscondition early so that treatment can begin at the opti-mal time. It is thought to be ideal to treat this conditionduring early adolescence, when second molar root for-mation is still incomplete and before complete develop-ment of the mandibular third molars. Treatment at thistime has been found to improve the outcome.5

The indications for treatment of impacted secondmo-lars include prevention of pericoronitis, increased risk ofcaries and periodontal disease, risk of resorption of adja-cent teeth by the follicle, and cystic development of thefollicle.6 Treatment modalities for impacted mandibularsecond permanent molars include orthodontic (with orwithout removal of third molars) and surgical reposition-ing (autotransplantation). Removal of the second molarsto allow eruption of the third molars and autotransplan-tation of the third molars after extraction of the secondmolars have also been described in the literature.

Surgical repositioning of mesially impacted teeth,however, can be associated with unwanted side effects,such as ankylosis, replacement resorption, and loss of

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http://dx.doi.org/10.1016/j.ajodo.2011.09.012

Fig 1. Panoramic radiograph on referral showing the un-erupted maxillary left central incisor and the crowding inthe maxillary labial segment.

Lau, Whang, and Bister 117

tooth vitality. In a recent study, autotransplantation ofthird molars was successful in 11% of the patients.5 Or-thodontically assisted guided eruption is thought to bethe treatment of choice for impacted second molars,with a success rate of 70%.5 This procedure might be dif-ficult if the tooth is caudal to the occlusion or horizon-tally positioned.

Several orthodontic treatment modalities have beensuggested to guide the eruption of impacted secondmolars, including diverse spring designs often encom-passing sectional or segmental mechanics.7 Other treat-ment mechanics such as the use of temporary corticalanchorage devices (mini-implants) in the retromolarregion have also been suggested.8 Surgical treatment isoften required as an adjunct; this can involve exposureof the second molars or removal of the third molars.Alignment of the impacted molar can sometimes be ob-tained without surgical assistance because the ortho-dontic uprighting involves a distal tipping movement,which creates space for the impacted molar. However,interference with the third molar cannot be excluded.

Fig 2. Panoramic radiograph showing the impactedmax-illary left canine and the mandibular second molars.

DIAGNOSIS AND ETIOLOGY

A 9-year-old female patient was referred to the or-thodontic department of Guy's and St Thomas' NHSDental Hospital Trust, London, United Kingdom,because of delayed eruption of the maxillary left centralincisor. She was diagnosed with a Class I incisor relation-ship in the early mixed dentition with crowding affectingboth the maxillary and the mandibular arches. Bothmaxillary deciduous canines were removed to relievethe crowding in the labial segment (Fig 1). On review 6months later, the maxillary left central incisor had erup-ted, and both maxillary permanent canines were palpa-ble high in the buccal vestibule. The crowding in botharches was confirmed, but orthodontic interventionwas thought unnecessary at this stage.

Further review appointments confirmed the above di-agnosis and did not lead to further intervention. Reevalu-ation at age 11 confirmed severe crowding in both arches,and a radiograph showed the ectopic position of themaxillary left canine and the mesial impaction of bothmandibular second molars, with the left one horizontallyimpacted (Fig 2). All 4 first premolars were subsequentlyextracted to create space to allow for spontaneousalignment of the anterior teeth and improvement of theeruption path of the impacted maxillary left canine.

Six months later, the patient complained of “gaps inthe front” of her teeth (Figs 3 and 4). A detailed clinicalexamination confirmed a Class I incisor relationship(British Standards Institute classification) on a mild ClassII skeletal base with average vertical facial proportions.

American Journal of Orthodontics and Dentofacial Orthoped

The position of the ectopic maxillary left canine hadnot improved, and the position of both mandibular sec-ond molars was also unchanged. There was spacing inthe maxillary and mandibular arches with potentialcrowding in the maxillary arch; the maxillary right ca-nine was short of space but in a favorable position forspontaneous eruption. The left canine was still ectopic.Overbite was increased, and the mandibular centerlinewas deviated to the left by 1 mm. The incisors appearedslightly retroclined on clinical examination. There wasa buccal crossbite of the maxillary right first molar,and the first molar relationship was nearly Class II onthe left and complete Class II on the right. The maxillaryleft canine was subsequently surgically exposed, anda gold chain was attached. The canine was buccal, anda surgically repositioned flap design was chosen forthe best possible outcome of the gingival margin.

The cephalometric analysis (Table) confirmed theclinical findings of a mild Class II skeletal base relation-ship with an increased ANB angle (5�). The Wits ap-praisal, however, suggested a moderate Class II skeletalpattern (13.5 mm). The maxillary-mandibular plane an-gle of 27� and the lower facial height proportions (55%)

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Fig 3. Pretreatment photographs.

118 Lau, Whang, and Bister

were within normal limits; this confirmed the clinicalfindings. The maxillary incisors were retroclined (100�).The mandibular incisor inclination (87�) was at the lowerlimit of the normal range. Although the incisors weretechnically Class I according to the British Standard Insti-tute's classification, they showed some features of a ClassII Division 2 incisor relationship. The panoramic radio-graph (Fig 5) showed a complete permanent dentition,except for the 4 previously extracted first premolars.

Relevant radiographic findings included the ectopicposition of the maxillary left canine with the attachedgold chain and a maxillary right canine that lackedspace. In addition, the mandibular left second molarwas horizontally impacted against the first molar,whereas the mandibular right second molar was mesiallyimpacted against the first molar.

TREATMENT OBJECTIVES

The objectives of the orthodontic treatment were to(1) align the impacted teeth (ectopic maxillary left canine

January 2013 � Vol 143 � Issue 1 American

and mandibular second molars), (2) level the arches, (3)correct the crossbite, (4) reduce the overbite while main-taining the overjet, (5) improve the maxillary incisor in-clination, (6) close the residual extraction spaces, (7)correct the molar relationship, and (8) coordinate thearches.

The orthodontic treatment mechanics includedexposure of the ectopic maxillary left canine and attach-ment of a gold chain. In addition, the mandibularsecond molars were exposed, and maxillary and man-dibular preadjusted edgewise appliances (MBT prescrip-tion: APC precoated Gemini Brackets; 3M Unitek, StPaul, Minn) were placed with headgear for anchoragereinforcement.

TREATMENT ALTERNATIVES

Treatment modalities for impacted mandibular sec-ond permanent molars include orthodontic alignmentand surgical repositioning. In view of the patient's ageand the early stage of third molar development,

Journal of Orthodontics and Dentofacial Orthopedics

Fig 4. Pretreatment dental casts.

Table. Pretreatment and posttreatment cephalometric analysis

Variable Pretreatment Normal Posttreatment ChangeSNA 85� 82� 6 3� 84� 11�

SNB 80� 79� 6 3� 80� 0�

ANB 5� 3� 6 1� 4� 11�

SN to maxillary plane 7� 8� 6 3� 7� 0�

Wits appraisal 3.5 mm 0 mm 5 mm 11.5 mmMaxillary incisor to maxillary plane angle 100� 108� 6 5� 112� 112�

Mandibular incisor to mandibular plane angle 87� 92� 6 5� 90� 13�

Interincisal angle 148� 133� 6 10� 134.5� �13.5�

Maxillary-mandibular angle 27� 27� 6 5� 27� 0�

Upper anterior face height 55 mm 56 mm 11 mmLower anterior face height 66 mm 70 mm 14 mmFace height ratio 55% 55% 56% 11%Mandibular incisor to APo line �1 mm 0-2 mm 1 mm 12 mmLower lip to Ricketts' E-plane 0 mm �2 mm �2 mm �2 mm


autotransplantation of the third molar after extractionof the second molar was not thought to be a good alter-native. Surgical repositioning of the mesially impactedmolar could be complicated by ankylosis, resorption,and loss of tooth vitality. Orthodontically assistedguided eruption would most likely be associated withthe best outcome and could be achieved with several dif-ferent biomechanical possibilities. The decision wasmade to use relatively simple orthodontic treatment me-chanics: bracket repositioning, thermoelastic (heat acti-vated) copper-nickel-titanium archwires (35�C; Ormco,


Orange, Calif), bypass of brackets, push-coil springs,and conversion of the molar tubes to brackets. Other me-chanics, which require the use of sectional or segmentaltechniques, complex auxiliaries, and artistic wire bend-ing, were not used.

TREATMENT PROGRESS

At the start of treatment, the impacted and ectopicmaxillary left canine was exposed (surgically reposi-tioned flap with gold chin attached). A fixed preadjustededgewise appliance (MBT prescription with a 0.022 3


Fig 5. Pretreatment radiographs.


0.028-in slot size) was placed in the maxillary arch withconvertible bands fitted on all first molars (3M Unitek).Posterior pull headgear with a force of 300 g per sidewas worn a minimum of 12 hours per day. The maxillaryleft lateral incisor was not bonded until 6 months afterthe start of treatment to prevent contact of its rootwith the impacted canine. The maxillary left lateral inci-sor was bonded after the maxillary left canine wasmoved into a more favorable position with the attachedgold chain.

Nine months into treatment, the mandibular teethwere bonded, and a 0.016-in nickel-titanium archwirewas placed. At the same time, an 0.018-in nickel-titanium wire was placed in the maxillary arch alongwith bonding of the now more favorably positionedmaxillary left canine.

Even after surgical exposure of the mandibular sec-ond molars, there was only a limited tooth surface


available for bonding on the left. However, the molartubes were placed at about 90� to the respective occlu-sal plane of the second molars to aid uprighting. Anactive nickel-titanium push-coil spring was placed be-tween the mandibular left first and second molars toencourage distal tipping of the impacted teeth. Toplace the push coil, the first molar tube was convertedto a bracket. These mechanics were also helpful insimultaneously creating space by pushing the molarsdistally.

Bracket repositioning became necessary as the posi-tion of the mandibular second molars improved.Bracket placement in the appropriate position wasnot possible in the beginning because of the positionof the second molar and its residual soft-tissue cover-ing. The decision was made for the wire to bypass themandibular left first molar bracket. This increased theflexibility of the archwire and decreased the force, pre-venting unwanted side effects such as root resorptionand bracket failure. The bite was temporarily openedby adding composite material to the posterior maxillaryteeth to allow the mandibular teeth to rotate withoutocclusal interference.

Two months before debonding, it was necessary touse cross-elastics from the lingual aspect of the mandib-ular left second molar to the buccal aspect of the maxil-lary left second molar to correct the scissors-bitetendency. At the end of active treatment, circumferentialretainers were used to maintain the tooth positions.

TREATMENT RESULTS

Overall, the orthodontic treatment achieved theplanned occlusal and facial esthetic goals (Figs 6-8,Table). All impacted teeth, including the horizontallyimpacted mandibular left second molar, were broughtsuccessfully into occlusion. The alignment of the man-dibular second molars did not necessitate removal ofthe third molars, and there was a slight overcorrectionof the previously impacted mandibular left second mo-lar. Both arches were well aligned with good incisaland buccal segment relationships and a mutually pro-tected functional occlusion.

The overjet has been maintained, and the increasedoverbite corrected. The MBT torque prescription forthe maxillary labial segment led to an improved inclina-tion of the maxillary anterior teeth. The chances of oc-clusal stability have been improved by establishinggood incisal and buccal segment relationships.

The maxillary left canine, which had been surgicallyexposed and brought into occlusion with traction viathe attached gold chain, showed a higher gingival mar-gin than the contralateral canine.


Fig 6. Posttreatment photographs.


The overall superimposition of the cephalometricradiographs (Fig 9) showed downward and someforward growth of the maxilla and the mandible dur-ing treatment. Local superimposition on Bj€ork's struc-tures9 (Fig 10) suggests that the maxillary molars haveremained in their position during treatment, andthat the maxillary incisor inclination was correctedas planned. The mandibular superimposition showsmesial movement of the mandibular molars into theextraction space; this corrected the molar relationship.There was some mild proclination of the mandibularincisors that contributed to the improvement of the in-terincisal angle, which measured 134� at the end oftreatment.

The mandibular incisal edges occlude anterior to thecentroids of the maxillary incisors. Circumferential re-tainers with acrylic labial segments were fitted to allowfinal occlusal settling but at the same time trying to pre-vent relapse of the maxillary left canine. The patient waspleased with the improvement in her appearance and is


aware of the need to comply with the retention regimenand maintain excellent oral hygiene.

DISCUSSION

Various methods of molar uprighting have been de-scribed in the literature. When the molar is severely dis-placed, such as the ones described here, a continuouswire that uprights the molar is often thought to causeundesirable movement of the anchorage teeth such astipping, rotation, intrusion, or extrusion of the adjacentteeth. Segmented mechanics have been advocated toprevent such side effects (T-loop spring10), and sectionaluprighting springs have been designed for this specificpurpose: eg, the Sander spring.11 The placement of theseadjuncts can be demanding on the operator and thepatient. Trauma can occur to the mucosa of the buccalsulcus, depending on the anatomy of the patient'svestibular depth. In our patient, we used an activenickel-titanium push-coil spring without showingany unwanted biomechanical side effects on the


Fig 7. Posttreatment dental casts.


surrounding dentition. We made use of the center of ro-tation of the mandibular second molars, which is locatedat the bifurcation of the roots. Pushing the molars dis-tally resulted in tipping, simultaneously creating spaceby moving the molars distally. To easily place thenickel-titanium push-coil spring between the first andsecond molars, the first molar attachments (tubes) hadto be converted: ie, the buccal cover had to be removed.

Most practitioners use banded attachments on sec-ond molars, but more recently posterior molar teethare also often bonded, although bond strength for thelatter is thought to be less than that for bands.12 It canbe difficult to band posterior teeth, particularly whenthey are only partially erupted or are impacted. Bandsare also thought to be disadvantageous from a periodon-tal point of view, when compared with bonds. Fitting ofbands on the second molars was not possible for ourpatient after uncovering, because of the horizontal posi-tion of the second molars and the limited amount oftooth surface available. This problem was overcome byprogressive repositioning of the bracket as the mandib-ular second molar became more accessible. We alsorefrained from removing the third molars, and the sec-ond molars uprighted without interference.

Aside from the above techniques, we initially alsobypassed the archwire from the mandibular left firstmolar; this allowed us to use a rectangular wire thatwas annealed at the end and bent down posteriorly(cinched back). The force (F) delivered by the wire is


expressed by the formula: F z dr4/l3, where d is deflec-tion of the wire, r is radius of the wire, and l is length.Therefore, bypassing a bracket results in increasing theeffective length of the archwire, and the applied forcelevels subsequently decrease by the power of three.Conversely, the force levels increase as the diameterof the wire increases. As a result of bypassing the firstmolar bracket we were able to use a rectangularthermally activated archwire (0.016 3 0.022-incopper-nickel-titanium, 35�C; Ormco). The use ofa long rectangular archwire instead of a short roundwire served several purposes. It saved on the numberof archwires used and the chair time. The first wirethat was engaged into the second molar bracket wasrectangular, and it bypassed the first molar. On thenext appointment, this same archwire was then en-gaged into the first molar bracket, thereby saving theremoval of an archwire, if a smaller wire had been used.

Bypassing the first molar bracket led to the reductionof the force levels and hence reduced the risk of inadver-tent debonding of the second molar bracket, simulta-neously allowing for some torque control duringuprighting of the second molars. The use of a thermo-elastic 0.016 3 0.022-in wire also eliminated the riskof permanent deformation during insertion of the arch-wire. A small round wire could have been used as an al-ternative here, but it would have been difficult to placebecause it had to be fully ligated into all brackets to beeffective. Complete ligation would most likely lead to


Fig 10. Cephalometric superimposition of the maxillaand the mandible on Bj€ork's structures9: black, Pretreat-ment; red, posttreatment.

Fig 8. Posttreatment radiographs.

Fig 9. Cephalometric superimposition on SN: black, Pre-treatment; red, posttreatment.



permanent deformation of the wire, rendering it ineffec-tive. An archwire of a smaller diameter would also haveneeded replacement at later appointments. Furthermore,the use of an annealed and cinched 0.016 3 0.022-inrectangular archwire prevented displacement of thewire during mastication.

This case report demonstrates that second molaruprighting can be undertaken by using routinestraight-wire mechanics without creating unwantedbiomechanical side effects. Segmented and sectionalmechanics were not used, nor were auxiliary springs.No wire-bending skills were required for this technique,and orthodontic assistants could carry out all of thesedetailed procedures, thus contributing to an efficientteam approach for patient management.

CONCLUSIONS

The management of impacted second molars is anorthodontic challenge. Although many orthodontictreatment mechanics encompassing different levels of



complexity have been described in the literature, routinestraight-wire mechanics as presented here are a usefulalternative.

REFERENCES

1. Aitasalo K, Lehtinen R, Oksala E. An orthopantomographic study ofprevalence of impacted teeth. Int J Oral Surg 1972;1:117-20.

2. Ten Cate AR. Oral histology, development, structure and function.3rd ed. St Louis: C. V. Mosby; 1989. p. 275-98.

3. Wellfelt B, Vaprio M. Disturbed eruption of the permanent lowersecond molar: treatment and results. J Dent Child 1988;55:183-9.

4. Andreasen JO, Petersen JK, Laskin DM. Textbook and color atlas oftooth impactions. Copenhagen, Denmark: Munksgaard; 1997. p.199-208.

5. Magnusson C, Kjellberg H. Impaction and retention of second mo-lars: diagnosis, treatment and outcome. A retrospective follow-upstudy. Angle Orthod 2009;79:422-7.


6. Raghoebar GM, Boering G, Vissink A, Stegenga B. Eruption distur-bances of permanent molars: a review. J Oral Pathol Med 1991;20:159-66.

7. Roberts WW, Chacker FM, Brustone CJ. A segmental approachto mandibular molar uprighting. Am J Orthod 1982;81:177-84.

8. Giancotti A, Muzzi F, Santini F, Arcuri C. Miniscrew treatment ofectopic mandibular molars. J Clin Orthod 2003;37:380-3.

9. Bj€ork A. Variations in the growth pattern of the human mandible:longitudinal radiographic study by the implant method. J DentResearch 1963;42:400-11.

10. Proffit WR, Fields HW Jr, Sarver DM. Contemporary orthodontics.4th ed. St Louis: Mosby; 2007. p. 636-85.

11. Sander FG, Wichelhaus A, Schiemann C. Intrusion mechanics ac-cording to Burstone with the NiTi-SE-steel uprighting spring. J Or-ofac Orthop 1996;57:210-23.

12. Banks P, Macfarlane T. Bonded versus banded first molar attach-ments: a randomized controlled clinical trial. J Orthod 2007;34:128-36.


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