Asymmetrical Mandibular Molar Protraction with Conventional Mechanics
The technique is illustrated here in an ado-lescent male patient. After leveling and alignment, a space between the lower right first premolar and first molar required closure by means of asym-metrical molar protraction (Fig. 1A). Bidimen-sional brackets had already been bonded; at the beginning of the protraction phase, an .018" × .022" working wire was inserted, with a 300g nickel titanium closed-coil spring attached from the molar hook to an archwire hook crimped distal to the lateral incisor.
The archwire incorporates the following characteristics:
• A reverse curve of Spee on the active side to counteract the moment generated by the coil spring, which would tend to tip the molar mesi-ally (Fig. 2A). This upward curve to the archform is preferred over a gable bend because it permits easier sliding and avoids posterior stops. Posterior sliding is also encouraged by the wire play in the .022" × .028" buccal brackets.• A toe-in bend at the molar to counteract the moment produced by the closed-coil spring, which would tend to rotate the molar lingually (Fig. 2B).
Mandibular molar protraction is one of the most difficult and least predictable ortho-
dontic movements to achieve, not only because the molar roots are wide buccolingually but because the mandible is formed by thick cortical plates and dense trabecular bone.1 Anterior anchorage pres-ervation is another challenge, especially in cases requiring asymmetrical space closure.2
Many different solutions have been proposed to overcome the anchorage issue and expedite treatment, including miniscrews,3 lasers,4 electrical stimulation,5 vibration,6 corticision,7 piezocision,8 corticotomies,9 and osteotomies.10 This article demonstrates the use of traditional and self-ligating brackets for asymmetrical mandibular molar pro-traction, in a modification of a technique first described by Gianelly and colleagues.11
Technique
Bidimensional appliances with vertical slots are utilized: .018" × .025" brackets on the incisors and .022" × .028" brackets on the canines, pre-molars, and molars. An .018" × .022" stainless steel high-tempered wire (we use American Ortho-dontics* and Dentsply GAC** wires) is fully en-gaged in the anterior brackets for torque control, while sliding mechanics are used for protraction in the posterior regions.
Dr. Rinchuse Dr. P. CozzaniDr. MazzottaDr. M. Cozzani
Dr. Mauro Cozzani is a Professor, Department of Orthodontics, School of Dental Medicine, University of Cagliari, Cagliari, Italy, and President, Scientific Committee, Unità Operative Odontoiatria, IRCCS Istituto Giannina Gaslini, Genoa, Italy. Dr. Mazzotta is a resident, Department of Orthodontics, School of Dental Medicine, University of Cagliari, Cagliari, Italy. Dr. Rinchuse is Professor and Program Director, Graduate Program in Orthodontics, Seton Hill University, Greensburg, PA. Drs. Mauro Cozzani and Paolo Cozzani are in the private practice of orthodontics at 21/N Via Fontevivo, 19125 La Spezia, Italy. E-mail Dr. Mauro Cozzani at [email protected].
• 5-10° of additional labial crown torque to main-tain anterior anchorage, since the incisors would otherwise tend to move lingually (Fig. 2C). This is effective because the .018" × .022" archwire is fully engaged in the .018" × .025" slots of the inci-sor brackets.• A bow on the active side of the wire to prevent the wire and thus the archform from collapsing
lingually under the force of the closed-coil spring (Fig. 2D).• A cinchback on the passive side to anchor the entire arch against the one or two teeth being pro-tracted and to counteract the closed-coil spring, which would otherwise tend to move the wire to-ward the active side (Fig. 2E).
Fig. 1 A. 14-year-old male patient with space between lower right first premolar and first molar after align-ment phase. B. Patient after four months of asymmetrical molar protraction (case treated by Anthony A. Gianelly and published here by permission).
B
A
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In addition, an uprighting spring is inserted at the level of the canine bracket’s vertical slot on the protraction side to increase resistance to sliding12 (Fig. 2F). The spring provides a force couple that uprights the tooth until the two corners of the slot contact the wire; the consequent binding anchors the tooth to the wire. The uprighting spring and added anterior labial crown torque combine to cre-ate an anterior component of force that prevents retraction of the mandibular anterior teeth and de-viation of the midline.
Our uprighting springs are either purchased preformed or bent from .016" Australian*** wire. They are generally applied at the beginning of molar protraction and removed when protraction
is completed. A canine uprighting spring usually ends just distal to the lower first premolar; an uprighting spring applied to the first premolar ends just distal to the second premolar. The spring arm should not be allowed to interfere with molar protraction by acting as a mesial stop on the wire.
Using this technique, the space can be man-aged without losing anterior anchorage or shifting the midline, as shown in this patient after four months of protraction treatment (Fig. 1B).
Fig. 2 Bends made in .018" × .022" stainless steel archwire for asymmetrical molar protraction. A. Reverse curve of Spee on active (right) side counteracts moment generated by coil spring, which would tip molar mesially. B. Toe-in bend counteracts moment produced by coil spring, preventing lingual molar rota-tion. C. 5-10° of labial crown torque added to maintain anterior anchorage. D. Bow added in active side of wire to prevent collapse of archform under 300g of spring force. E. Wire cinched back on passive (left) side to form anchor unit. F. Uprighting spring inserted on protraction side to increase bracket resistance to sliding.
***Registered trademark of A.J. Wilcock Pty. Ltd., Whittlesea, Victoria, Australia. Distributed in North America by G&H Wire Company, Franklin, IN; www.ghwire.com.
D E F
B CA
.022"
.018".018"
.025"
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lars had been previously extracted; all four third molars were erupted.
The treatment plan involved surgically as-sisted maxillary expansion to resolve the maxillary incisor crowding and unilateral crossbite, followed by orthodontic decompensation for bimaxillary
Case 1
An adult female presented with a unilateral posterior crossbite, facial asymmetry, mandibular deviation, a tilted occlusal plane, and maxillary crowding (Fig. 3A). The upper and lower first mo-
Fig. 3 Case 1. A. Adult female patient with unilateral posterior crossbite, mandibular deviation, tilted oc-clusal plane, maxillary crowding, and previously extracted upper and lower first molars before treat-ment. B. Asymmetrical protraction of lower right second molar initiated after surgically assisted maxillary expansion, bimaxillary surgery, and chin advancement (continued on next page).
B
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surgery and chin advancement. An edgewise Bi-dimensional technique was used to level and align the teeth while controlling torque and tip. Since all four second molars were mesially angulated due to the missing first molars, they were upright-ed and mesialized to close the spaces. After sur-gery, a space remained between the lower right second molar and second premolar (Fig. 3B); this was closed in three months using the protraction technique described above. Total treatment time was 37 months (Fig. 3C,D).
Case 2
When self-ligating appliances are used, we recommend the “dual activation” concept—active
brackets on the incisors to ensure torque control13 and passive brackets on the canines, premolars, and molars to facilitate sliding.
An 11-year-old female presented with anky-losis of the lower left and the upper left and right second deciduous molars, a full-molar Class II relationship, excessive overjet and overbite, and normal transverse relations (Fig. 4A). The pan-oramic radiograph showed that both upper second premolars and the lower left second premolar were congenitally missing. Cephalometric analysis in-dicated average maxillary prognathism and a re-trusive pogonion, resulting in an increased sagittal jaw relationship, a reduced interincisal angle, and a slight posterior inclination of the mandible.
The ideal treatment plan in this case, consid-
Fig. 3 (cont.) Case 1. C. Patient after 37 months of surgical-orthodontic treatment, including three months of protraction; note asymmetrical space closure without loss of anchorage or midline deviation. D. Molar root movement during protraction.
C
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preferred a treatment plan calling for extraction of the ankylosed teeth, closure of the maxillary spac-es by anterior retraction, and asymmetrical closure of the mandibular space by protraction of the left molars. Therefore, the lower right second premolar was not extracted.
ering the patient’s chin position and profile, would be orthopedic or, if this proved unsuccessful, sur-gical. Other alternatives were to extract the lower right second premolar for symmetrical space clo-sure or to open the lower left second-premolar space for future implant placement. The parents
Fig. 4 Case 2. A. 11-year-old female patient with ankylosed lower left and upper left and right second de-ciduous molars, congenitally missing lower left and upper left and right left second premolars, Class II malocclusion, excessive overjet, and deep overbite before treatment. B. Mesial movement of lower left first molar during nine-month protraction phase; note passive mesial drift of left second molar (continued on next page).
A
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Interactive .018" × .025" T3* self-ligating brackets were bonded to the incisors and passive .022" × .028" LP* self-ligating brackets with verti-cal slots to the canines and posterior teeth. After leveling and alignment, asymmetrical protraction was initiated in the lower arch, using an .018" × .022" stainless steel wire as described above and a 300g nickel titanium closed-coil spring (Fig. 4B). Uprighting springs were placed on both the lower left canine and premolar for additional anchorage. The lower left second molar was initially unbond-ed, since the second molar generally follows the first molar’s mesial movement in these cases. The second molar was bonded and aligned after the protraction phase, which took nine months. Total treatment time was 35 months (Fig. 4C).
Discussion
Efficient and effective asymmetrical man-dibular molar protraction can be reliably achieved using the conventional mechanics shown here. No surgical procedures are required, and tooth move-ments can be controlled in three dimensions. If the technique is not working properly, a mandibular midline shift and an increase in overjet will quick-ly be observed. In that case, the protracting force (closed-coil spring) should be removed, anterior
torque increased, and asymmetrical Class II elas-tics applied. Since maximum anterior torque con-trol is fundamental to the success of this technique, full engagement of a highly tempered wire in the bracket slot (an .018" × .022" wire in an .018" × .025" bracket)14 and, when possible, the use of ac-tive self-ligating brackets15 are recommended.
This method can produce equivalent clinical results without the invasiveness of surgical tech-niques or miniscrews. It may also be just as fast, since the literature is unclear as to whether corti-cotomies actually reduce overall treatment time.16,17 When miniscrews are utilized to establish anterior anchorage, they have to be placed either between the lateral incisor and canine or between the ca-nine and first premolar. The former location is undesirable because of a lack of bone, the latter because of the difficulty of biomechanics.18 More-over, miniscrews can drift when subjected to orthodontic forces19 and therefore cannot be con-sidered absolute anchorage. Finally, we believe that the use of miniplates and miniscrews is contra-indicated in young children due to the low quality of bone. In summary, our technique represents a pragmatic solution to asymmetrical mandibular molar protraction.
Fig. 4 (cont.) Case 2. C. Patient after 35 months of treatment.
1. Roberts, W.E.: Bone physiology, metabolism, and biomechan-ics in orthodontic practice, in Orthodontics: Current Principles and Techniques, 3rd ed., ed. T.M. Graber and R.L. Vanarsdall, Mosby, St. Louis, 2000, pp. 193-257.
2. Kravitz, N.D. and Jolley, T.: Mandibular molar protraction with temporary anchorage devices, J. Clin. Orthod. 42:351-355, 2008.
3. Nagaraj, K.; Upadhyay, M.; and Yadav, S.: Titanium screw anchorage for protraction of mandibular second molars into first molar extraction sites, Am. J. Orthod. 134:583-591, 2008.
4. Cruz, D.R.; Kohara, E.K.; Ribeiro, M.S.; and Wetter, N.U.: Effects of low-intensity laser therapy on the orthodontic movement velocity of human teeth: A preliminary study, Lasers Surg. Med. 35:117-120, 2004.
5. Davidovitch, Z.; Finkelson, M.D.; Steigman, S.; Shanfeld, J.L.; Montgomery, P.C.; and Korostoff, E.: Electric currents, bone remodeling, and orthodontic tooth movement, II. Increase in rate of tooth movement and periodontal cyclic nucleotide levels by combined force and electric current, Am. J. Orthod. 77:33-47, 1980.
6. Darendeliler, M.A.; Zea, A.; Shen, G.; and Zoellner, H.: Effects of pulsed electromagnetic field vibration on tooth movement induced by magnetic and mechanical forces: A preliminary study, Austral. Dent. J. 52:282-287, 2007.
7. Kim, S.J.; Park, Y.G.; and Kang, S.G.: Effects of corticision on paradental remodeling in orthodontic tooth movement, Angle Orthod. 79:284-291, 2009.
8. Dibart, S.; Sebaoun, J.D.; and Surmenian, J.: Piezocision: A minimally invasive, periodontally accelerated orthodontic tooth movement procedure, Comp. Cont. Ed. Dent. 30:342-350, 2009.
9. Kole, H.: Surgical operations on the alveolar ridge to correct occlusal abnormalities, Oral Surg. Oral Med. Oral Pathol. 12:515-529, 1959.
10. Kişnişci, R.S.; Işeri, H.; Tüz, H.H.; and Altug, A.T.: Dentoalveolar distraction osteogenesis for rapid orthodontic canine retraction, J. Oral Maxillofac. Surg. 60:389-394, 2002.
11. Gianelly, A.A.; Smith, J.B.; Bednar, J.R.; and Dietz, V.S.: Asymmetric space closure, Am. J. Orthod. 90:335-341, 1986.
12. Cozzani, M. and Mazzotta, L.: Bidi-Self: La tecnica bidimen-sional con brackets de autoligado, Rev. Esp. Ortod. 42:240-246, 2012.
13. Archambault, A.; Lacoursiere, R.; Badawi, H.; Major, P.W.; Carey, J.; and Flores-Mir, C.: Torque expression in stainless steel orthodontic brackets: A systematic review, Angle Orthod. 80:201-210, 2010.
14. Huang, Y.; Keilig, L.; Rahimi, A.; Reimann, S.; and Bourauel, C.: Torque capabilities of self-ligating and conventional brackets under the effect of bracket width and free wire length, Orthod. Craniofac. Res. 15:255-262, 2012.
15. Badawi, H.M.; Toogood, R.W.; Carey, J.P.; Heo, G.; and Major, P.W.: Torque expression of self-ligating brackets, Am. J. Orthod. 133:721-728, 2008.
16. Uribe, F.; Janakiraman, N.; Fattal, A.N.; Schincaglia, G.P.; and Nanda, R.: Corticotomy-assisted molar protraction with the aid of temporary anchorage device, Angle Orthod. 83:1083-1092, 2013.
17. Mathews, D.P. and Kokich, V.G.: Accelerating tooth move-ment: The case against corticotomy-induced orthodontics, Am. J. Orthod. 144:5-13, 2013.
18. Poggio, P.M.; Incorvati, C.; Velo, S.; and Carano, A.: “Safe zones”: A guide for miniscrew positioning in the maxillary and mandibular arch, Angle Orthod. 76:191-197, 2006.
19. Liu, H.; Lv, T.; Wang, N.N.; Zhao, F.; Wang, K.T.; and Liu, D.X.: Drift characteristics of miniscrews and molars for anchorage under orthodontic force: 3-dimensional computed tomography registration evaluation, Am. J. Orthod. 139:e83-89, 2011.
