CLINICIAN'S CORNER
Anchorage reinforcement with a fixed functional appliance during protraction of the mandibular second molars into the first molar extraction sites Aditya Chhibbera and Madhur Upadhyayb New York, NY, and Farmington, Conn
Protraction of posterior teeth into edentulous spaces is a challenge. This report describes the treatment of a 19-year-old woman with missing mandibular first molars owing to caries. A fixed functional appliance was used for anchorage reinforcement during mandibular second molar protraction. Eight millimeters of bilateral protraction was done with bodily mesial movement of the molars and no lingual tipping of the incisors. (Am J Orthod Dentofacial Orthop 2015;148:165-73)
E
ffective space management of missing posterior teeth is a great challenge in orthodontic treatment. Edentulous posterior sites are commonly seen in an adult population. The most commonly observed missing teeth are first molars, often owing to caries,1 and second premolars, which are the most common congenitally missing teeth.2 The sequel of missing mandibular first molars is usually tipping and drifting of adjacent teeth, supraeruption of unopposed teeth, poor interproximal contacts, poor gingival contours, reduced interradicular bone, and pseudopockets.3 Treatment options for missing posterior teeth commonly include fixed prosthodontic bridges or endosseous implants. Although both are viable treatment options, the use of fixed partial dentures may compromise the longevity of adjacent prepared teeth with the risk of secondary caries and mechanical failures,4 whereas endosseous implants can increase the financial burden for patients.5 Orthodontic space closure of edentulous sites is an alternative treatment option. However, attempts at space closure by protraction of posterior teeth into the edentulous sites without anchorage reinforcement bears the risk of anchorage loss, thereby leading to a compromised occlusion. a Assistant professor, Division of Orthodontics, College of Dental Medicine, Columbia University, New York, NY. b Assistant professor, Division of Orthodontics, Department of Craniofacial Sciences, University of Connecticut Health Center, Farmington, Conn. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Address correspondence to: Aditya Chhibber, College of Dental Medicine, Columbia University, 630 West 168th Street, New York, NY 10032; e-mail,
[email protected]. Submitted, October 2014; revised and accepted, February 2015. 0889-5406/$36.00 Copyright Ó 2015 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2015.02.029
Historically, extraoral appliances such as chincup and facemask have been used for protraction of posterior teeth.6 However, use of extraoral devices depends on patient compliance, and it has been reported that patient compliance is generally overestimated when similar devices are used for orthopedic purposes.7 Hemisection of deciduous teeth has also been advocated to encourage more mesial eruption of the permanent teeth into the missing-tooth regions.8 Recently, there have been case reports in the literature on the use of mini-implants for protraction of mandibular posterior teeth into edentulous sites.9-12 However, mini-implants placed in interradicular regions can cause root damage because of improper placement of the devices,13,14 which can subsequently lead to implant failure.15,16 Thus, development of alternative methods capable of providing absolute anchorage while protracting posterior teeth into edentulous sites is desirable. Fixed functional appliances have traditionally been used for Class II correction. The use of such appliances results in a combination of mild skeletal effects along with dentoalveolar changes such as retroclination of the maxillary incisors and proclination of the mandibular incisors, and distalization of the maxillary molars and mesial movement of the mandibular molars.17,18 The aim of this report was to use a fixed functional appliance for anchorage reinforcement during space closure by protraction of the posterior teeth into the edentulous spaces without Class II correction. DIAGNOSIS AND ETIOLOGY
A 19-year-old woman came to the orthodontic department at University of Connecticut Health Center 165
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Fig 1. Pretreatment photographs.
Table. Cephalometric skeletal analysis before and af-
ter treatment SNA ( ) SNB ( ) ANB ( ) SN-GoGn ( ) FMA ( ) U1-SN ( ) U1-NA ( ) U1-NA (mm) IMPA ( ) L1-NB ( ) U1-NB (mm) E-line–upper lip (mm) E-line–lower lip (mm)
Pretreatment 77 71 6 47 41 118 42 12 90 35 13 1 5
Posttreatment 77 71 6 48 42 92 19 3 92 33 11 5 2
with a chief complaint of “crooked teeth.” Her previous medical history was not significant, and no history of habits was reported. Her dental history showed that the mandibular left and right first molars were extracted because of caries approximately 4 years
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previously. She had a Class II malocclusion on an underlying Class II skeletal base with a normal sized maxilla, a short mandible, and a vertical growth pattern (Fig 1, Table). Dentally, the patient had proclined and forwardly placed maxillary incisors and normally inclined and forwardly placed mandibular incisors with U-shaped maxillary and mandibular dental arches, missing mandibular right and left first molars with 8 mm of extraction space bilaterally, mesially tipped mandibular second molars bilaterally (Fig 2), extruded maxillary left and right first molars, an end-on canine relationship, moderate crowding in both arches, an increased overjet, a 4-mm overbite, and a 3-mm curve of Spee in the mandibular arch. Facially, the patient had a leptoprosopic facial type with a convex soft tissue profile, a right angled nasolabial angle, and 100% maxillary incisor and 70% mandibular incisor display on smiling. The mandibular midline was coincident with the facial midline, and the maxillary midline was shifted 2 mm to the left, along with incompetent lips (Fig 2) and lip strain on closure.
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Fig 2. Pretreatment radiographs.
TREATMENT OBJECTIVES
The treatment objectives for this patient were to (1) improve the soft tissue profile and relieve the lip incompetence with minimal changes to the skeletal vertical dimensions, (2) manage the space of the missing mandibular first molars by protraction of the mandibular second molars into the first molar regions bilaterally, (3) achieve simulated Class II molar and Class I canine relationships by retraction of the maxillary incisors and protraction of the mandibular molars, (4) relieve the crowding in both arches, and (5) reduce the increased overjet. TREATMENT ALTERNATIVES
The alternative treatment plans that were considered entailed extraction of only the maxillary premolars with retraction of the incisors and endosseous implants, or fixed partial dentures placed for the missing mandibular first molars. Implants would increase the overall treatment cost for the patient, and she was unwilling to undergo this procedure. In addition, the use of fixed partial dentures could compromise the longevity of the prepared adjacent teeth in the long term. The use of mini-implants or miniplates for protraction of the posterior teeth into the edentulous sites could have been considered as a treatment alternative. TREATMENT PROGRESS
Treatment was initiated by bonding all teeth with a 0.022-in slot MBT (McLaughlin, Bennett, and Trevisi) prescription, which had 6 of lingual crown torque on
the mandibular anterior brackets. In the mandibular arch, initial leveling and alignment was done with 0.16-in nickel-titanium archwires from the left second premolar to the right second premolar without engaging the tipped second molars. The archwire was gradually increased to 0.021 3 0.025-in stainless steel. An uprighting spring was fabricated and placed on the tipped second molars to upright them (Fig 3, A). A seating elastic was used in the anterior segment to prevent the bite from opening during uprighting of the tipped molar. The mechanics involved in using the uprighting spring are shown more in Figure 3, B. An uprighting spring is a 1-couple system. An intrusive component of force exists in the anterior segment along with an extrusive force on the molar with a counterclockwise moment (moment of couple) to upright the tipped molar. In addition, the point of force application on the molar (buccal tube) is usually ahead of the center of resistance of the molar, thereby leading to an additional moment (moment of force) in the counterclockwise direction that can further help in uprighting the tipped molar. In the maxillary arch, the patient was referred for extraction of the maxillary first premolars. Initial leveling and alignment were performed in the maxillary arch using a 0.016-in nickel-titanium archwire. The archwires were progressively increased to 0.021 3 0.025-in nickeltitanium. Space closure was performed using loop mechanics; a 0.019 3 0.025-in T-loop archwire was fabricated for en-masse retraction of the maxillary anterior teeth (Fig 4, A). After space closure, the archwire was increased to a stiff 0.021 3 0.25-in steel archwire with the wire cinched distal to the molars to prevent any
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Fig 3. A, Placement of uprighting spring to upright mandibular second molars bilaterally; B, biomechanics during the use of an uprighting spring. Green dot, Center of resistance of molar; a, distance between the point of force application on the molar tube and the center of resistance of the molar; d, distance between the point of force application and the molar tube; Mc, moment of the couple; Mf, moment of the force; F, force applied by the uprighting spring; Fr, reciprocal force acting on the molar tube.
spaces from opening up and to create the maxillary arch as a single unit. In the mandibular arch, after the tipped second molars were uprighted, the archwires were built up to a continuous stiff 0.021 3 0.025-in steel archwire (Fig 4, B). Crimpable hooks were spot welded onto the archwire distal to the canines bilaterally. A passive Forsus appliance (size 25) was placed from the maxillary molar to the distal aspect of the mandibular canine. An elastic chain was placed from the second molar to the crimpable hooks, applying approximately 200 to 250 cN of force (Fig 4, C). The patient was recalled every 5 to 6 weeks until the space was closed by protraction of the second molar; this took 9 months. No breakage of any appliances or brackets during the molar protraction phase was observed. After space closure, a progress panoramic radiographic was taken to evaluate root movement of the second
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molars (Fig 5). No tipping of the second molars during space closure was observed. Finishing and detailing of the occlusion were performed as needed, and the patient was debonded after 28 months of active treatment. She was referred for extraction of the maxillary third molars because there were no opposing teeth in the mandibular arch. A maxillary Hawley retainer was given. In the mandibular arch, a fixed lingual retainer was placed on the anterior teeth. In addition, a bonded buccal retainer was placed between the second molar and the second premolar to minimize the risk of space reopening after treatment. TREATMENT RESULTS
After 28 months of active treatment, the patient was debonded with simulated Class II molar and Class I canine relationships bilaterally, along with ideal overjet
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Fig 4. Progress records: A, placement of the 0.019 3 0.025-in T-loop for space closure in the maxillary arch; B, continuous 0.021 3 0.025-in steel archwire in the mandibular arch after uprighting the tipped second molars; C, placement of the Forsus appliance for anchorage reinforcement during mandibular second molar protraction.
Fig 5. Progress panoramic radiograph after mandibular molar protraction.
and overbite (Fig 6). The maxillary and mandibular arches were well aligned, and the dental midlines were coincident. The posttreatment facial photographs showed a balanced profile. A slight gingival height discrepancy was observed between the 2 maxillary central incisors at the end of treatment; however, the patient was not willing to have surgical recontouring of the gingival margins. The radiographic records showed root parallelism at the end of treatment, with relief of the lip incompetence (Fig 7). A slight discrepancy in the occlusal relationship of the molars was
observed; it could be attributed to a posterior Bolton discrepancy, since the maxillary first molar was occluding with the mandibular second molar. In addition, a slight lateral open-bite tendency was also observed at the maxillary left lateral incisor that could be attributed to the torque control during space closure with the T-loop. Lateral cephalograms were taken at pretreatment and posttreatment. The cephalometric evaluation showed that the skeletal pattern was maintained with no change of the SNA and SNB angles, along with maintenance of the mandibular plane angle (Table). Reduction in the proclination of the maxillary incisors and minimal flaring of the mandibular incisors were observed. The overall superimpositions with the best-fit method and regional superimposition using the method of Bj€ ork and Skieller19 showed a slight intrusion of the extruded maxillary first molars (Fig 8). There was retraction of the maxillary incisors into the extraction spaces. In the mandibular arch, the incisors intruded with minimal flaring of the anterior teeth. The mandibular second molar underwent complete mesial movement into the missing first molar space. The soft tissue evaluation showed retraction of the maxillary lip, which led to a reduction
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Fig 6. Posttreatment photographs.
Fig 7. Posttreatment radiographs.
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Fig 8. Overall and regional superimpositions: pretreatment (black) and posttreatment (red).
in lip incompetence and an improvement in the soft tissue profile. DISCUSSION
Protraction of posterior teeth, while being a treatment option, is difficult to perform without anchorage reinforcement. Traditionally, extraoral devices such as chincup and facemask have been used for anchorage reinforcement during protraction of posterior teeth.6 There have been a few reports in the literature on the use of miniscrews for anchorage reinforcement during molar protraction.9-12 However, there is a risk of root contact when miniscrews are placed in the interradicular regions13,14 leading to subsequent implant failure.15,16 In addition, patients may not be willing to have invasive procedures during orthodontic treatment.20 Thus, there is a need to develop alternative methods for anchorage augmentation to protract posterior teeth into edentulous sites. A fixed functional appliance is commonly used for Class II correction. These appliances have a combination of skeletal and dental effects.17,18 Their use for simultaneous Class II correction and protraction of posterior teeth has been reported in the literature.21 However, we aimed to demonstrate the usefulness of a fixed functional appliance for anchorage reinforcement during protraction of the second molars into the missing mandibular first molar sites, with no
skeletal or dental Class II correction being attempted. The patient had a Class I canine relationship with optimal overjet when molar protraction was initiated (Fig 4, C). Adequate bone and gingival levels at the edentulous site may be critical factors associated with successfully protracting the second molars.22 Furthermore, it has been reported that moving teeth into an edentulous site increases the width and the height of the edentulous alveolar ridge.23,24 Mechanically, placement of an elastic chain between the second molar and the archwire hooks leads to a mesially directed force on the molar, but it also leads to a reactionary force in the distal direction on the anterior segment (Fig 9, A). We hypothesize that when the distal force on the anterior segment leads to retraction of the mandibular anterior teeth (anchorage loss), the Forsus appliance that was placed passively becomes active, thereby exerting a mesially directed force on the mandibular anterior teeth offsetting the retractive force and thereby preventing anchorage loss (Fig 9, A). In addition, since the point of force application was superior to the center of resistance of the second molar, it leads to a moment of force to tip the molar into the extraction space during protraction (Fig 9, A). However, we did not observe any tipping of the second molars after space closure in the progress panoramic radiograph (Fig 5). This perhaps may be attributed to the use of a stiff 0.021 3 0.025-in archwire during molar protraction (Fig 9, B). It has been reported that the use of rigid
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Fig 9. Biomechanics during the use of fixed functional appliance for molar protraction. A, Green dot, Center of resistance of molar; d, vertical distance between the molar tube and the center of resistance of the molar; F, force applied to the elastomeric chain on the molar; Fr, reciprocal force acting on the mandibular anterior segment; Fr0 , force applied by the fixed functional appliance on the mandibular anterior segment; a, length of the molar tube; Mc, moment of the couple; Mf, moment of the force. B, Inside of a molar tube with a 0.021 3 0025-in steel archwire: a, Length of the molar tube; f, vertical forces generated from tipping of the molar tube during protraction.
high-stiffness archwires leads to reduction of elastic deflection of the archwire during tooth movement.25 Based on beam theory, elastic deflection is inversely proportional to flexural rigidity of the archwire, EI, where E is Young's modulus and I is the moment of inertia of the cross-section. In the case of a rectangular cross-section of width b and height h, I is calculated by the equation I 5 bh3/12. Thus, the 0.021 3 0.025-in steel archwire with high flexural rigidity may have minimized the elastic deflection of the wire during molar protraction, thereby preventing tipping of the molar during space closure. It has also been reported that elastic deflection of the archwire is proportional to the amount of applied force.25 A decrease in the applied force associated with using elastomeric chains that have up to a 50% force decay26 may have led to a lesser reduction in flexural rigidity of the archwire as opposed to methods that apply a constant force such as nickel-titanium coil springs.27 Play between the archwire and the bracket with undersized archwires is often reported.28,29 Furthermore,
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it has also been shown that a full-slot archwire provides better root control during retraction of anterior teeth. It has been suggested that torsion of the archwire (moment of couple) may be completely transmitted to the bracket with full-slot archwires during incisor retraction.30,31 Similarly, perhaps a full-slot archwire for molar protraction would have led to better control of the roots during protraction (Fig 8). However, further studies would be necessary to substantiate this theory. It could be argued that the point of force application could have been lowered on the molar with power arms to ensure that the point of force application was closer to the molar's center of resistance and could be recommended for similar attempts in the future. In addition, it could also be advisable to use the fixed functional appliance during space closure in the maxillary dentition because it might provide anchorage reinforcement during anterior tooth retraction. Some possible limitations reported with a Forsus appliance are an increased risk for cheek irritation and breakage of the appliance.32 Reports on breakages
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specifically with the Forsus appliance have been variable, from as low as 1%33 to as high as 37%32; the breakages have been attributed to varying levels of operator experience or other factors. However, we did not observe any breakages during the space closure phase. This could be attributed to operator experience or patient compliance, or the fact that the fixed functional appliance was placed passively. Another possible limitation with this approach is that it may be suitable only for protraction of teeth in the mandibular arch as opposed to protraction of maxillary posterior teeth. CONCLUSIONS
This case demonstrates the effectiveness of a fixed functional appliance for anchorage reinforcement during the protraction of the mandibular second molar into the first molar extraction site. REFERENCES 1. Meskin LH, Brown LJ. Prevalence and patterns of tooth loss in U.S. employed adult and senior populations, 1985-86. J Dent Educ 1988;52:686-91. 2. Thilander B, Myrberg N. The prevalence of malocclusion in Swedish schoolchildren. Scand J Dent Res 1973;81:12-21. 3. Proffit WR. Special considerations in treatment for adults. In: Proffit WR, Fields HW Jr, Sarver DM, editors. Contemporary orthodontics. 4th edition. St Louis: Mosby; 2007. p. 635-85. 4. Tan K, Pjetursson BE, Lang NP, Chan ESY. A systematic review of the survival and complication rates of fixed partial dentures (FPDs) after an observation period of at least 5 years. III. Conventional FPDs. Clin Oral Implants Res 2004;15:654-66. 5. Kim Y, Park JY, Park SY, Oh SH, Jung Y, Kim JM, et al. Economic evaluation of single-tooth replacement: dental implant versus fixed partial denture. Int J Oral Maxillofac Implants 2014;29:600-7. 6. Kokich VG, Kokich VO. Congenitally missing mandibular second premolars: clinical options. Am J Orthod Dentofacial Orthop 2006;130:437-44. 7. Bos A, Kleverlaan CJ, Hoogstraten J, Prahl-Andersen B, Kuitert R. Comparing subjective and objective measures of headgear compliance. Am J Orthod Dentofacial Orthop 2007;132:801-5. 8. Northway W. Hemisection: one large step toward management of congenitally missing lower second premolars. Angle Orthod 2004; 74:792-9. 9. Nagaraj K, Upadhyay M, Yadav S. Titanium screw anchorage for protraction of mandibular second molars into first molar extraction sites. Am J Orthod Dentofacial Orthop 2008;134:583-91. 10. Chung KR, Cho JH, Kim SH, Kook YA, Cozzani M. Unusual extraction treatment in Class II Division 1 using C-orthodontic mini-implants. Angle Orthod 2007;77:155-66. 11. Kravitz ND, Jolley T. Mandibular molar protraction with temporary anchorage devices. J Clin Orthod 2008;42:351-5. 12. Baik UB, Chun YS, Jung MH, Sugawara J. Protraction of mandibular second and third molars into missing first molar spaces for a patient with an anterior open bite and anterior spacing. Am J Orthod Dentofacial Orthop 2012;141:783-95. 13. Kravitz ND, Kusnoto B. Risks and complications of orthodontic miniscrews. Am J Orthod Dentofacial Orthop 2007;131(4 Suppl): S43-51.
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14. Cho UH, Yu W, Kyung HM. Root contact during drilling for microimplant placement: affect of surgery site and operator expertise. Angle Orthod 2010;80:130-6. 15. Chen YH, Chang HH, Chen YJ, Lee D, Chiang HH, Yao CC. Root contact during insertion of miniscrews for orthodontic anchorage increases the failure rate: an animal study. Clin Oral Implants Res 2008;19:99-106. 16. Papageorgiou SN, Zogakis IP, Papadopoulos MA. Failure rates and associated risk factors of orthodontic miniscrew implants: a metaanalysis. Am J Orthod Dentofacial Orthop 2012;142:577-95. 17. Chhibber A, Upadhyay M, Uribe F, Nanda R. Mechanism of Class II correction in prepubertal and postpubertal patients with twin force bite corrector. Angle Orthod 2013;83:718-27. 18. Chhibber A, Upadhyay M, Uribe F, Nanda R. Long-term stability of Class II correction with the twin force bite corrector. J Clin Orthod 2010;44:363-76. 19. Bj€ork A, Skieller V. Facial development and tooth eruption. An implant study at the age of puberty. Am J Orthod 1972;62:339-83. 20. Uribe F, Padala S, Allareddy V, Nanda R. Patients', parents', and orthodontists' perceptions of the need for and costs of additional procedures to reduce treatment time. Am J Orthod Dentofacial Orthop 2014;145(4 Suppl):S65-73. 21. Davoody AR, Feldman J, Uribe FA, Nanda R. Mandibular molar protraction with the twin force bite corrector in a Class II patient. J Clin Orthod 2011;45:223-8. 22. Hom BM, Turley PK. The effects of space closure of the mandibular first molar area in adults. Am J Orthod 1984;85:457-69. 23. Eliasova P, Marek I, Kamınek M. Implant site development in the distal region of the mandible: bone formation and its stability over time. Am J Orthod Dentofacial Orthop 2014;145:333-40. 24. Zachrisson BU. Implant site development by horizontal tooth movement. World J Orthod 2001;4:266-72. 25. Kojima Y, Fukui H. A finite element simulation of initial movement, orthodontic movement, and the centre of resistance of maxillary teeth connected with an archwire. Eur J Orthod 2014;36:255-61. 26. Buchmann N, Senn C, Ball J, Brauchli L. Influence of initial strain on the force decay of currently available elastic chains over time. Angle Orthod 2012;82:529-35. 27. Miura F, Mogi M, Ohura Y, Karibe M. The super-elastic Japanese NiTi alloy wire for use in orthodontics. Part III. Studies on the Japanese NiTi alloy coil springs. Am J Orthod Dentofacial Orthop 1988;94:89-96. 28. Kang BS, Baek SH, Mah J, Yang WS. Three-dimensional relationship between the critical contact angle and the torque angle. Am J Orthod Dentofacial Orthop 2003;123:64-73. 29. Dellinger EL. A scientific assessment of the straight-wire appliance. Am J Orthod 1978;73:290-9. 30. Tominaga JY, Chiang PC, Ozaki H, Tanaka M, Koga Y, Bourauel C, et al. Effect of play between bracket and archwire on anterior tooth movement in sliding mechanics: a three-dimensional finite element study. J Dent Biomech 2012;3:1-8. 31. Tominaga JY, Ozaki H, Chiang PC, Sumi M, Tanaka M, Koga Y, et al. Effect of bracket slot and archwire dimensions on anterior tooth movement during space closure in sliding mechanics: a 3-dimensional finite element study. Am J Orthod Dentofacial Orthop 2014;146:166-74. 32. Bowman AC, Saltaji H, Flores-Mir C, Preston B, Tabbaa S. Patient experiences with the Forsus fatigue resistant device. Angle Orthod 2012;83:437-46. 33. Cacciatore G, Alvetro L, Defraia E, Ghislanzoni LTH, Franchi L. Active-treatment effects of the Forsus fatigue resistant device during comprehensive Class II correction in growing patients. Korean J Orthod 2014;44:136-42.
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