- Email: [email protected]
A new protocol of Tweed-Merrifield directional force technology with microimplant anchorage
CASE REPORT
A new protocol of Tweed-Merrifield directional force technology with microimplant anchorage Jong-Moon Chae Daejeon, South Korea Tweed-Merrifield directional force technology with microimplant anchorage is a useful treatment approach for a patient with a Class I or Class II dentoalveolar-protrusion malocclusion. It can create a favorable counterclockwise skeletal change and a balanced face without patient compliance. In contrast, headgear force with high-pull J-hook can obtain similar results but depends on patient cooperation. This case report presents the treatment of a patient with Class I canine and molar relationships, a convex profile with retrognathic mandible and marked lip protrusion, and excessive lower anterior facial height. Good facial balance was obtained by Tweed-Merrifield directional force technology with microimplant anchorage, which provided horizontal and vertical anchorage control in the maxillary and mandibular posterior teeth, and intrusion and torque control in the maxillary anterior teeth, resulting in a favorable counterclockwise mandibular response. (Am J Orthod Dentofacial Orthop 2006;130:100-9)
ngle1 introduced the edgewise appliance in 1928 and presented many case reports to support its efficacy. Tweed2 suggested modifications both of the appliance itself and how to use it. Anchorage preparation was the cornerstone of Tweed’s treatment mechanics. He prepared anchorage with coordinated bends in the mandibular archwire, Class III elastics, and maxillary headgear. Merrifield3 enhanced, expanded, and simplified Tweed’s concepts and treatment mechanics and developed force systems to simplify the use of the edgewise appliance. A hallmark of Tweed-Merrifield edgewise treatment is the use of directional force systems to move the teeth.4 Directional forces can be defined as controlled forces that place the teeth in the most harmonious relationships with their environment. Although headgear force with the high-pull J-hook in an appropriate direction can provide directional forces and stable anchorage, it depends on patient cooperation. To obtain absolute anchorage without patient cooperation, endosseous implants,5 miniplates,6 and screws7-11 have been used as orthodontic anchorage. Of those, screws have many advantages— eg, ease of implantation and removal, low cost, possible immediate loading,
A
Assistant professor, Department of Orthodontics and Dentistry, Eulji University; director, Korean Orthodontic Research Institute, Daejeon, South Korea. Reprint requests to: Jong-Moon Chae, Department of Orthodontics and Dentistry, Eulji University Hospital, 1306, Dunsan-Dong, Seo-Gu, Daejeon, 302-799 South Korea; e-mail, [email protected]. Submitted, July 2005; revised and accepted, October 2005. 0889-5406/$32.00 Copyright © 2006 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2005.10.020
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and possible placement in most areas of the alveolar bone. Sliding mechanics with the aid of microimplant anchorage (MIA) and its application for the treatment of Class I and Class II dentoalveolar-protrusion malocclusions have been described previously.9-11 However, its application in loop mechanics such as edgewise sequential directional force technology has not been widely discussed. This case report demonstrates the usefulness of microimplants (MIs) as an anchorage aid in directional force technology. A new protocol of directional force treatment with MIA involves 4 steps: preparation, correction, completion, and recovery. In the first step, denture preparation, the canines are retracted. During canine retraction, maintenance of the posterior tooth position has always been a major concern for the orthodontist, especially when maximum anchorage is needed.12,13 The use of MIA is most effective in maximum anchorage cases. Maxillary and mandibular posterior MIs, and elastomeric forces are used to retract the maxillary and mandibular canines and to prepare anchorage of the terminal molars (Fig 1, A). At the end of the denture preparation step, the mandibular arch should be leveled, the maxillary and mandibular canines should be retracted, all rotations should be corrected, and the mandibular terminal molars should be tipped distally into an anchorage-prepared position (Fig 1, B). During denture correction, the anterior teeth are retracted with closing loops that are supported by the
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Fig 1. A, During denture preparation, .022 ⫻ .028-in edgewise appliance and 0.17 ⫻ .022-in maxillary and .018 ⫻ .025⬙ mandibular archwires are placed. Maxillary and mandibular posterior MIs and elastomers are applied to canine brackets and mandibular archwire just mesial to omega stop loops. B, End of denture preparation: arches are leveled, rotations corrected, canines retracted, and mandibular terminal molar tipped to anchorage-prepared position. C, During denture correction, mandibular .019 ⫻ .025-in closing loop archwire and maxillary .020 ⫻ .025-in closing loop archwire are fabricated. Maxillary and mandibular posterior MIs, maxillary anterior MIs, and elastomers are attached to hooks, brackets, and archwires.
maxillary anterior MIs and elastomers attached to hooks soldered between the maxillary central and lateral incisors, and the mandibular posterior MIs and elastomers attached to omega stop loop areas of the mandibular archwire (Fig 1, C). During en-masse movement, anchorage loss of the posterior teeth can occur. To reinforce anchorage during overjet reduction, additional headgear support to the molars can be used.13 However, the maxillary and mandibular posterior MIs can prevent vertical and horizontal anchorage loss during denture correction. Anchorage bends can be supported by Class III elastics between the maxillary posterior MIs and the mandibular anterior hooks, or elastomers between the mandibular posterior MIs and the mandibular archwire just mesial to the omega stop loops. Intruding and uprighting forces are applied to the mandibular posterior teeth with this force system that can cause horizontal mandibular response by counterclockwise rotation of the mandible (Fig 2, A). At the end of mandibular anchorage preparation, the second molars, first molars, and second premolars have distal axial inclinations. During the denture completion step, ideal archwires are fabricated. Hooks for MIs and elstomers, and anterior vertical and Class II elastics, are soldered to the archwires. Supplemental hooks for vertical elastics are soldered as needed. During this step, the orthodontist repeats the systems of forces that are necessary until the original malocclusion is overcorrected (Fig 2, B). After overcorrection, the final artistic bends and cusp-seating forces that give detail and quality to the overcorrected malocclusion are added (Fig 2, C).
When all appliances are removed and the retainers are placed, the critical recovery phase occurs. Recovery, based on the concept of overcorrection, is predicated on clinical experience and research. Orthodontists not familiar with overtreatment have expressed concern about the posterior disclusion after treatment. This treatment occlusion, sometimes called the “Tweed occlusion,” but properly identified as “transitional occlusion,” is characterized by disclusion of the second molars and the distal cusps of the first molars (Fig 3, A). This concept of a transitional occlusion followed by a period of recovery is based on the belief that each patient’s oral environment will determine the ultimate position of the dentition and that overtreatment allows the greatest opportunity for maximum stability and functional efficiency (Fig 3, B). DIAGNOSIS
This 23-year-old woman’s chief complaint was lip protrusion. She appeared to be facially asymmetrical and had a convex profile because of a retrognathic mandible. The facial photographs showed a convex facial profile with marked protrusion of lips, mentalis strain, excessive lower anterior facial height, and a gummy smile. Intraorally, she had Class I canine and molar relationships with minor crowding; the maxillary and mandibular third molars were present (Figs 4 and 5). The lateral cephalogram (Fig 6) and its tracing confirmed the severe skeletal and dental problem. The Frankfort-mandibular plane angle of 32° and the occlusal plane angle of 13.5° reflected the vertical skeletal and dental problem. The SNB angle of 77.5° and the
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Fig 2. A, To prepare mandibular first molars for anchorage, .019 ⫻ .025-in mandibular archwire biases first molar bracket at 10° angle. To prepare second premolars for anchorage, compensation bend is placed mesial to mandibular first molar, and anchorage bend of 5° is placed 1 mm mesial to second premolar bracket. Mandibular anchorage preparation is supported by Class III elastics between maxillary posterior MIs and anterior hooks in mandibular archwire, or elastomers between mandibular posterior MIs and mandibular archwire just mesial to omega stop loops. B, Denture completion with Class II elastics, anterior vertical elastics, and MIs and eastomeric threads or chains used for directional force control. C, Maxillary and mandibular .0215 ⫻ .028-in archwires are fabricated. Hooks are soldered for MIs and elastomeric threads or chains, cusp seating, and anterior vertical elastics. Force system used depends on desired final tooth positions.
Fig 3. A, Denture recovery: Tweed occlusion. Note distal inclination of maxillary and mandibular second molars. Maxillary first molar occludes with its mesial buccal cusp in mesial buccal groove of mandibular first molar. Canines are in ideal Angle Class I relationship. Overjet and overbite are overcorrected. B, Denture recovery: functional occlusion. Settling places maxillary and mandibular posterior and anterior teeth in ideal occlusal relationships.
ANB angle of 5.5° reflected the horizontal skeletal problem. The Z-angle of 53° quantified the facial imbalance (Table). The posteroanterior cephalometric radiograph showed skeletal asymmetry with canting of the maxilla, a difference between the ramus heights, a longer mandibular body on the right side, and a deviation of the chin to the left. Dental asymmetry was also present with a shifting of the upper dental midline to the left of the facial midline and a 1-mm deviation of
the mandibular dental midline to the left relative to the maxillary dental midline (Fig 7). There were no significant signs or symptoms of temporomandibular disorders. TREATMENT OBJECTIVES
The treatment objectives were to (1) align and level the teeth in both arches and establish functional occlusion, (2) normalize the overjet and overbite relation-
American Journal of Orthodontics and Dentofacial Orthopedics Volume 130, Number 1
Fig 4. Pretreatment facial and intraoral photographs.
Fig 5. Pretreatment dental casts.
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Fig 6. Pretreatment lateral cephalometric radiograph.
Table.
Cephalometric measurements Pretreatment
Posttreatment
47.5 32.0 100.5 83.0 77.5 5.5 ⫺1.5 13.5
60.0 29.5 90.5 82.0 78.0 4.0 1.0 7.0
115.5 53.0 48.0 73.5 0.65
112.0 67.5 48.0 71.5 0.67
FMIA angle (°) FMA angle (°) IMPA angle (°) SNA angle (°) SNB angle (°) ANB angle (°) AO-BO (mm) Occlusal plane angle (°) Frankfort horizontal to maxillary central incisor (°) Z-angle (°) PFH (mm) AFH (mm) FHI (PFH/AFH) (%)
AO-BO, Wits appraisal; PFH, posterior facial height; AFH, anterior facial height; FHI, facial height index.
ships, (3) obtain a balanced facial profile, (4) minimize facial asymmetry, and (5) improve smile esthetics. TREATMENT ALTERNATIVES
The first alternative was orthognathic surgery. The maxillary second premolars and the mandibular first premolars would be extracted to resolve the arch-length discrepancy and upright the mandibular anterior teeth. Two-jaw surgery including counterclockwise differential impaction of the maxilla and concurrent mandibular advancement surgery would be performed to correct the skeletal asymmetry. Genioplasty would be necessary to reduce the long lower anterior facial height and advance the chin along the facial midline. However, the patient did not want surgical treatment because she was
Fig 7. Pretreatment posteroanterior cephalometric radiograph.
a nurse in an operating theater. So another treatment plan was chosen. The second alternative was orthodontic treatment with extraction of the 4 first premolars and 4 third molars, and directional force technology with MIA. I believed that MIs could provide absolute anchorage not only in the retraction of the maxillary and mandibular anterior teeth, but also in the intrusion of the maxillary anterior and posterior teeth, and the mandibular posterior teeth; this would induce a horizontal mandibular response followed by a balanced facial profile. TREATMENT PROGRESS
The treatment plan involved Tweed-Merrifield directional force technology with MIA, after the extraction of the maxillary and mandibular first premolars, and the third molars. However, the mandibular second premolars were inadvertently extracted instead of the mandibular first premolars by an oral surgeon. After the extractions, .022 ⫻ .028-in nontipped, nontorqued edgewise appliances were placed in both arches. Maxillary posterior MIs (1.2 mm in diameter, 8 mm in length; Absoanchor AX12-108, Dentos, Taegu, South Korea) were implanted into the buccal alveolar bone between the maxillary second premolars and the first molars, and mandibular posterior MIs (1.2 mm in diameter, 7 mm in length; Absoanchor ATX
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Fig 8. A, Denture preparation: retraction of maxillary and mandibular canines and first premolars with elastomeric chain, and maxillary and mandibular posterior MIs. B, Denture correction: en-masse retraction with closing loop archwires supported by maxillary posterior and anterior MIs and mandibular posterior MIs. C, Denture completion: directional force. D, Denture completion: finishing with cusp-seating elastics for good interdigitation and additional unilateral Class III elastics for correction of asymmetry.
1311-107, Dentos) were implanted into the buccal alveolar bone between the mandibular first and second molars (Fig 8, A). Elastic chain force was loaded immediately after placement of the MIs, from the maxillary and mandibular posterior MIs to the canine brackets, to retract the maxillary canines and simultaneously retract the mandibular canines and first premolars (Fig 8, B). After the retraction of the maxillary canines, mandibular canines, and first premolars, closing loop archwires were placed. The maxillary archwire was sup-
ported by the maxillary anterior MIs (1.2 mm in diameter, 6.0 mm in length; Absoanchor ATX1311106, Dentos) implanted into the labial alveolar bone between the maxillary central and lateral incisors for torque control, bodily movement, and intrusion of the maxillary anterior teeth. Intruding force was applied to the omega stop loop areas of the mandibular archwire to prevent mesial tipping and extrusion of the mandibular posterior teeth. After en-masse movement, directional force control was performed to promote mandibular response (Fig
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Fig 9. Posttreatment facial and intraoral photographs.
Fig 10. Posttreatment dental casts.
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Fig 11. Posttreatment lateral cephalometric radiograph.
8, C). The treatment was completed with ideal archwires and cusp-seating elastics; additionally, unilateral Class III elastic force was applied to the hook of the mandibular archwire from the maxillary posterior MIs to reduce the asymmetry (Fig 8, D). Twisted, 3-strand .032-in wires bonded onto the lingual sides of the 6 anterior teeth and circumferential clear retainers were placed on both arches, just before and after removal of the appliances for retention, respectively. Total treatment time was 24 months. TREATMENT RESULTS
The posttreatment facial photographs showed a nicely balanced and harmonious face by retracting the upper and lower lips, reducing the muscle strain of the mentalis, and decreasing lower anterior facial height (Fig 9). The intrusive forces used on the maxillary anterior segment successfully reduced the excessive gingival display when smiling. The posttreatment casts illustrated good interdigitation of the teeth and acceptable overjet-overbite relationship (Fig 10). The cephalometric radiographs showed significant improvement in skeletal and dental asymmetry (Figs 11 and 12). As shown on the cephalometric superimposition (Fig 13), the maxillary anterior teeth were bodily retracted with intrusion, the maxillary posterior teeth were intruded and moved distally, the mandibular anterior teeth were retracted with uprighting, and the mandibular posterior teeth were uprighted with intrusion. A good mandibular response was achieved by the counterclockwise directional forces. The chin advancement was obtained by the autorotation of the mandible, facilitated by vertical control of the dentition, resulting in a decrease of the Frankfortmandibular plane angle by 2.5°, a reduction of the ANB
Fig 12. Posttreatment posteroanterior cephalometric radiograph.
angle by 1.5°, and a decrease of the occlusal plane angle by 6.5° The mandibular incisors were uprighted from 105.0° to 90.5°. The Z-angle was improved from 53.0° to 67.5°, the Frankfort-mandibular incisor angle was increased by 12.5°, and anterior facial height was shortened by 2 mm (Table). All these changes contributed to improving the facial profile. DISCUSSION
Tweed-Merrifield directional force technology is very useful, particularly for dentoalveolar protrusion and Class II malocclusion corrections. All patients treated with the Tweed technique, however, do not finish with stable teeth, improved facial esthetics, healthy mouth tissues, and functional occlusions. Many problems can cause an unsuccessful treatment response, including mouth breathing habits, weak musculature, poor patient cooperation during anchorage preparation, lack of high-pull headgear wear to the maxillary anterior segment of the dentition, and improper diagnosis and treatment planning.14,15 The key to successful orthodontic treatment is the control of the vertical dimension through anchorage preparation. The control of the horizontal movement of the dentition depends on how the vertical dimension of the maxillomandibular complex is managed. Vertical control can make horizontal correction pos-
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Fig 13. Cephalometric superimposition.
sible.16 Successful correction of various orthodontic problems depends on control of the horizontal planes, particularly the occlusal plane. The occlusal plane is the key to upward and forward rotation of the horizontal planes. The maintenance, or the closing, of the occlusal plane depends on 2 factors: vertical control of the maxillary and mandibular molars, and control of the anterior vertical dimension, particularly the maxillary anterior segment.17 The clinician can control extrusion of the maxillary posterior teeth during mechanotherapy by applying directional force with MIs to the maxillary dentition. Mandibular posterior MIs are effective in maintaining or closing the occlusal plane and the mandibular plane angle, and inducing forward and upward movement of the chin by intruding and uprighting the mandibular molars during treatment. The most significant contribution to poor vertical control is the excessive amount of anterior facial height increase caused by poor patient cooperation, incorrect diagnostic decisions, and, perhaps most important, a growth response that made treatment more complex and difficult.15 Any increase in anterior facial height in Class II malocclusion correction is an unfavorable sequela of treatment in either an adult or an adolescent, but it has more serious consequences for the adult because there is no compensation from an increase in posterior facial height as in the adolescent. Vertical control is therefore more critical during an adult’s treatment than during an adolescent’s treatment.18 Maxillary anterior MIs or a high-pull headgear auxiliary is
absolutely essential for supporting the maxillary anterior teeth and the anterior segment of the maxilla. Control of the anterior vertical dimension during treatment inhibits the increase in anterior facial height and allows a large increase in horizontal mandibular response for Class II correction, chin enhancement, and Z-angle improvement.15 To date, clinical efficacy5-11 and stability19,20 of temporary skeletal anchorage devices have been described by many authors. This is an efficient method for solving an orthodontic problem that cannot be corrected by a conventional method. However, more studies are needed to determine the causes of failure and to improve the success rate of MIs. In many cases, especially in growing adolescents, orthopedic forces have been used to inhibit or stimulate growth of the maxillomandibular complex. Questions arise about whether MIs have the same effect as the high-pull J-hook. Further studies should be done to determine whether MIA can be used as an orthopedic appliance to control skeletal problems. CONCLUSIONS
Tweed-Merrifield directional force technology is a useful concept, particularly for the treatment of Class I and Class II dentoalveolar protrusion malocclusions. This case report shows the versatility of the directional force system by using MIA. Consequently, TweedMerrifield directional force technology with MIA not only maximizes the result of treatment but also can minimize the need for patient compliance.
American Journal of Orthodontics and Dentofacial Orthopedics Volume 130, Number 1
REFERENCES 1. Angle EH. Tweed profile: Dr. Edward Hartley Angle, the Henry Ford of orthodontics. J Charles H. Tweed Int Found 1988;16:59-76. 2. Tweed CH. Clinical orthodontics. Vols 1 and 2. St Louis: C. V. Mosby; 1966. 3. Merrifield LL, Cross JJ. Directional forces. Am J Orthod 1970;57:435-64. 4. Merrifield L. The systems of directional force. J Charles H. Tweed Int Found 1982;10:15-29. 5. Roberts WE, Nelson CL, Goodacre CJ. Rigid implant anchorage to close a mandibular first molar extraction site. J Clin Orthod 1994;28:693-704. 6. Umemori M, Sugawara J, Mitani H, Nagasaka H, Kawamura H. Skeletal anchorage system for open-bite correction. Am J Orthod Dentofacial Orthop 1999;115:166-74. 7. Creekmore TD, Eklund MK. The possibility of skeletal anchorage. J Clin Orthod 1983;17:266-9. 8. Kanomi R. Mini-implant for orthodontic anchorage. J Clin Orthod 1997;31:763-7. 9. Park HS, Bae SM, Kyung HM, Sung JH. Micro-implant anchorage for treatment of skeletal Class I bialveolar protrusion. J Clin Orthod 2001;35:417-22. 10. Chae JM. Nonextraction treatment of Class II division 2 in an adult patient using microimplant anchorage (MIA). Korean J Orthod 2005;35:485-94. 11. Park HS, Kwon TG, Kwon OW. Treatment of open bite with microscrew implant anchorage. Am J Orthod Dentofacial Orthop 2004;126:627-36.
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12. Ayala Perez C, de Alba JA, Caputo AA, Chaconas SJ. Canine retraction with J hook headgear. Am J Orthod 1980;78:53847. 13. Charles CR, Jones ML. Canine retraction with the edgewise appliance—some problems and solutions. Br J Orthod 1982;9: 194-202. 14. Gebeck TR, Merrifield LL. Orthodontic diagnosis and treatment analysis— concepts and values: part I. Am J Orthod Dentofacial Orthop 1995;107:434-43. 15. Gebeck TR, Merrifield LL. Orthodontic diagnosis and treatment analysis— concepts and values: part II. Am J Orthod Dentofacial Orthop 1995;107:541-7. 16. Ward DM. Angle Class II, Division 1 malocclusion. Am J Orthod Dentofacial Orthop 1994;106:428-33. 17. Lamarque S. The importance of occlusal plane control during orthodontic mechanotherapy. Am J Orthod Dentofacial Orthop 1995;107:548-58. 18. Vaden JL, Harris EF, Behrents RG. Adult versus adolescent Class II correction: a comparison. Am J Orthod Dentofacial Orthop 1995;107:651-61. 19. De Pauw GA, Dermaut L, De Bruyn H, Johansson C. Stability of implants as anchorage for orthopedic traction. Angle Orthod 1999;69:401-7. 20. Miyawaki S, Koyama I, Inoue M, Mishima K, Sugahara T, Takano-Yamamoto T. Factors associated with the stability of titanium screws placed in the posterior region for orthodontic anchorage. Am J Orthod Dentofacial Orthop 2003;124: 373-8.
A new protocol of Tweed-Merrifield directional force technology with microimplant anchorage Jong-Moon Chae Daejeon, South Korea Tweed-Merrifield directional force technology with microimplant anchorage is a useful treatment approach for a patient with a Class I or Class II dentoalveolar-protrusion malocclusion. It can create a favorable counterclockwise skeletal change and a balanced face without patient compliance. In contrast, headgear force with high-pull J-hook can obtain similar results but depends on patient cooperation. This case report presents the treatment of a patient with Class I canine and molar relationships, a convex profile with retrognathic mandible and marked lip protrusion, and excessive lower anterior facial height. Good facial balance was obtained by Tweed-Merrifield directional force technology with microimplant anchorage, which provided horizontal and vertical anchorage control in the maxillary and mandibular posterior teeth, and intrusion and torque control in the maxillary anterior teeth, resulting in a favorable counterclockwise mandibular response. (Am J Orthod Dentofacial Orthop 2006;130:100-9)
ngle1 introduced the edgewise appliance in 1928 and presented many case reports to support its efficacy. Tweed2 suggested modifications both of the appliance itself and how to use it. Anchorage preparation was the cornerstone of Tweed’s treatment mechanics. He prepared anchorage with coordinated bends in the mandibular archwire, Class III elastics, and maxillary headgear. Merrifield3 enhanced, expanded, and simplified Tweed’s concepts and treatment mechanics and developed force systems to simplify the use of the edgewise appliance. A hallmark of Tweed-Merrifield edgewise treatment is the use of directional force systems to move the teeth.4 Directional forces can be defined as controlled forces that place the teeth in the most harmonious relationships with their environment. Although headgear force with the high-pull J-hook in an appropriate direction can provide directional forces and stable anchorage, it depends on patient cooperation. To obtain absolute anchorage without patient cooperation, endosseous implants,5 miniplates,6 and screws7-11 have been used as orthodontic anchorage. Of those, screws have many advantages— eg, ease of implantation and removal, low cost, possible immediate loading,
A
Assistant professor, Department of Orthodontics and Dentistry, Eulji University; director, Korean Orthodontic Research Institute, Daejeon, South Korea. Reprint requests to: Jong-Moon Chae, Department of Orthodontics and Dentistry, Eulji University Hospital, 1306, Dunsan-Dong, Seo-Gu, Daejeon, 302-799 South Korea; e-mail, [email protected]. Submitted, July 2005; revised and accepted, October 2005. 0889-5406/$32.00 Copyright © 2006 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2005.10.020
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and possible placement in most areas of the alveolar bone. Sliding mechanics with the aid of microimplant anchorage (MIA) and its application for the treatment of Class I and Class II dentoalveolar-protrusion malocclusions have been described previously.9-11 However, its application in loop mechanics such as edgewise sequential directional force technology has not been widely discussed. This case report demonstrates the usefulness of microimplants (MIs) as an anchorage aid in directional force technology. A new protocol of directional force treatment with MIA involves 4 steps: preparation, correction, completion, and recovery. In the first step, denture preparation, the canines are retracted. During canine retraction, maintenance of the posterior tooth position has always been a major concern for the orthodontist, especially when maximum anchorage is needed.12,13 The use of MIA is most effective in maximum anchorage cases. Maxillary and mandibular posterior MIs, and elastomeric forces are used to retract the maxillary and mandibular canines and to prepare anchorage of the terminal molars (Fig 1, A). At the end of the denture preparation step, the mandibular arch should be leveled, the maxillary and mandibular canines should be retracted, all rotations should be corrected, and the mandibular terminal molars should be tipped distally into an anchorage-prepared position (Fig 1, B). During denture correction, the anterior teeth are retracted with closing loops that are supported by the
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Fig 1. A, During denture preparation, .022 ⫻ .028-in edgewise appliance and 0.17 ⫻ .022-in maxillary and .018 ⫻ .025⬙ mandibular archwires are placed. Maxillary and mandibular posterior MIs and elastomers are applied to canine brackets and mandibular archwire just mesial to omega stop loops. B, End of denture preparation: arches are leveled, rotations corrected, canines retracted, and mandibular terminal molar tipped to anchorage-prepared position. C, During denture correction, mandibular .019 ⫻ .025-in closing loop archwire and maxillary .020 ⫻ .025-in closing loop archwire are fabricated. Maxillary and mandibular posterior MIs, maxillary anterior MIs, and elastomers are attached to hooks, brackets, and archwires.
maxillary anterior MIs and elastomers attached to hooks soldered between the maxillary central and lateral incisors, and the mandibular posterior MIs and elastomers attached to omega stop loop areas of the mandibular archwire (Fig 1, C). During en-masse movement, anchorage loss of the posterior teeth can occur. To reinforce anchorage during overjet reduction, additional headgear support to the molars can be used.13 However, the maxillary and mandibular posterior MIs can prevent vertical and horizontal anchorage loss during denture correction. Anchorage bends can be supported by Class III elastics between the maxillary posterior MIs and the mandibular anterior hooks, or elastomers between the mandibular posterior MIs and the mandibular archwire just mesial to the omega stop loops. Intruding and uprighting forces are applied to the mandibular posterior teeth with this force system that can cause horizontal mandibular response by counterclockwise rotation of the mandible (Fig 2, A). At the end of mandibular anchorage preparation, the second molars, first molars, and second premolars have distal axial inclinations. During the denture completion step, ideal archwires are fabricated. Hooks for MIs and elstomers, and anterior vertical and Class II elastics, are soldered to the archwires. Supplemental hooks for vertical elastics are soldered as needed. During this step, the orthodontist repeats the systems of forces that are necessary until the original malocclusion is overcorrected (Fig 2, B). After overcorrection, the final artistic bends and cusp-seating forces that give detail and quality to the overcorrected malocclusion are added (Fig 2, C).
When all appliances are removed and the retainers are placed, the critical recovery phase occurs. Recovery, based on the concept of overcorrection, is predicated on clinical experience and research. Orthodontists not familiar with overtreatment have expressed concern about the posterior disclusion after treatment. This treatment occlusion, sometimes called the “Tweed occlusion,” but properly identified as “transitional occlusion,” is characterized by disclusion of the second molars and the distal cusps of the first molars (Fig 3, A). This concept of a transitional occlusion followed by a period of recovery is based on the belief that each patient’s oral environment will determine the ultimate position of the dentition and that overtreatment allows the greatest opportunity for maximum stability and functional efficiency (Fig 3, B). DIAGNOSIS
This 23-year-old woman’s chief complaint was lip protrusion. She appeared to be facially asymmetrical and had a convex profile because of a retrognathic mandible. The facial photographs showed a convex facial profile with marked protrusion of lips, mentalis strain, excessive lower anterior facial height, and a gummy smile. Intraorally, she had Class I canine and molar relationships with minor crowding; the maxillary and mandibular third molars were present (Figs 4 and 5). The lateral cephalogram (Fig 6) and its tracing confirmed the severe skeletal and dental problem. The Frankfort-mandibular plane angle of 32° and the occlusal plane angle of 13.5° reflected the vertical skeletal and dental problem. The SNB angle of 77.5° and the
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Fig 2. A, To prepare mandibular first molars for anchorage, .019 ⫻ .025-in mandibular archwire biases first molar bracket at 10° angle. To prepare second premolars for anchorage, compensation bend is placed mesial to mandibular first molar, and anchorage bend of 5° is placed 1 mm mesial to second premolar bracket. Mandibular anchorage preparation is supported by Class III elastics between maxillary posterior MIs and anterior hooks in mandibular archwire, or elastomers between mandibular posterior MIs and mandibular archwire just mesial to omega stop loops. B, Denture completion with Class II elastics, anterior vertical elastics, and MIs and eastomeric threads or chains used for directional force control. C, Maxillary and mandibular .0215 ⫻ .028-in archwires are fabricated. Hooks are soldered for MIs and elastomeric threads or chains, cusp seating, and anterior vertical elastics. Force system used depends on desired final tooth positions.
Fig 3. A, Denture recovery: Tweed occlusion. Note distal inclination of maxillary and mandibular second molars. Maxillary first molar occludes with its mesial buccal cusp in mesial buccal groove of mandibular first molar. Canines are in ideal Angle Class I relationship. Overjet and overbite are overcorrected. B, Denture recovery: functional occlusion. Settling places maxillary and mandibular posterior and anterior teeth in ideal occlusal relationships.
ANB angle of 5.5° reflected the horizontal skeletal problem. The Z-angle of 53° quantified the facial imbalance (Table). The posteroanterior cephalometric radiograph showed skeletal asymmetry with canting of the maxilla, a difference between the ramus heights, a longer mandibular body on the right side, and a deviation of the chin to the left. Dental asymmetry was also present with a shifting of the upper dental midline to the left of the facial midline and a 1-mm deviation of
the mandibular dental midline to the left relative to the maxillary dental midline (Fig 7). There were no significant signs or symptoms of temporomandibular disorders. TREATMENT OBJECTIVES
The treatment objectives were to (1) align and level the teeth in both arches and establish functional occlusion, (2) normalize the overjet and overbite relation-
American Journal of Orthodontics and Dentofacial Orthopedics Volume 130, Number 1
Fig 4. Pretreatment facial and intraoral photographs.
Fig 5. Pretreatment dental casts.
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Fig 6. Pretreatment lateral cephalometric radiograph.
Table.
Cephalometric measurements Pretreatment
Posttreatment
47.5 32.0 100.5 83.0 77.5 5.5 ⫺1.5 13.5
60.0 29.5 90.5 82.0 78.0 4.0 1.0 7.0
115.5 53.0 48.0 73.5 0.65
112.0 67.5 48.0 71.5 0.67
FMIA angle (°) FMA angle (°) IMPA angle (°) SNA angle (°) SNB angle (°) ANB angle (°) AO-BO (mm) Occlusal plane angle (°) Frankfort horizontal to maxillary central incisor (°) Z-angle (°) PFH (mm) AFH (mm) FHI (PFH/AFH) (%)
AO-BO, Wits appraisal; PFH, posterior facial height; AFH, anterior facial height; FHI, facial height index.
ships, (3) obtain a balanced facial profile, (4) minimize facial asymmetry, and (5) improve smile esthetics. TREATMENT ALTERNATIVES
The first alternative was orthognathic surgery. The maxillary second premolars and the mandibular first premolars would be extracted to resolve the arch-length discrepancy and upright the mandibular anterior teeth. Two-jaw surgery including counterclockwise differential impaction of the maxilla and concurrent mandibular advancement surgery would be performed to correct the skeletal asymmetry. Genioplasty would be necessary to reduce the long lower anterior facial height and advance the chin along the facial midline. However, the patient did not want surgical treatment because she was
Fig 7. Pretreatment posteroanterior cephalometric radiograph.
a nurse in an operating theater. So another treatment plan was chosen. The second alternative was orthodontic treatment with extraction of the 4 first premolars and 4 third molars, and directional force technology with MIA. I believed that MIs could provide absolute anchorage not only in the retraction of the maxillary and mandibular anterior teeth, but also in the intrusion of the maxillary anterior and posterior teeth, and the mandibular posterior teeth; this would induce a horizontal mandibular response followed by a balanced facial profile. TREATMENT PROGRESS
The treatment plan involved Tweed-Merrifield directional force technology with MIA, after the extraction of the maxillary and mandibular first premolars, and the third molars. However, the mandibular second premolars were inadvertently extracted instead of the mandibular first premolars by an oral surgeon. After the extractions, .022 ⫻ .028-in nontipped, nontorqued edgewise appliances were placed in both arches. Maxillary posterior MIs (1.2 mm in diameter, 8 mm in length; Absoanchor AX12-108, Dentos, Taegu, South Korea) were implanted into the buccal alveolar bone between the maxillary second premolars and the first molars, and mandibular posterior MIs (1.2 mm in diameter, 7 mm in length; Absoanchor ATX
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Fig 8. A, Denture preparation: retraction of maxillary and mandibular canines and first premolars with elastomeric chain, and maxillary and mandibular posterior MIs. B, Denture correction: en-masse retraction with closing loop archwires supported by maxillary posterior and anterior MIs and mandibular posterior MIs. C, Denture completion: directional force. D, Denture completion: finishing with cusp-seating elastics for good interdigitation and additional unilateral Class III elastics for correction of asymmetry.
1311-107, Dentos) were implanted into the buccal alveolar bone between the mandibular first and second molars (Fig 8, A). Elastic chain force was loaded immediately after placement of the MIs, from the maxillary and mandibular posterior MIs to the canine brackets, to retract the maxillary canines and simultaneously retract the mandibular canines and first premolars (Fig 8, B). After the retraction of the maxillary canines, mandibular canines, and first premolars, closing loop archwires were placed. The maxillary archwire was sup-
ported by the maxillary anterior MIs (1.2 mm in diameter, 6.0 mm in length; Absoanchor ATX1311106, Dentos) implanted into the labial alveolar bone between the maxillary central and lateral incisors for torque control, bodily movement, and intrusion of the maxillary anterior teeth. Intruding force was applied to the omega stop loop areas of the mandibular archwire to prevent mesial tipping and extrusion of the mandibular posterior teeth. After en-masse movement, directional force control was performed to promote mandibular response (Fig
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Fig 9. Posttreatment facial and intraoral photographs.
Fig 10. Posttreatment dental casts.
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Fig 11. Posttreatment lateral cephalometric radiograph.
8, C). The treatment was completed with ideal archwires and cusp-seating elastics; additionally, unilateral Class III elastic force was applied to the hook of the mandibular archwire from the maxillary posterior MIs to reduce the asymmetry (Fig 8, D). Twisted, 3-strand .032-in wires bonded onto the lingual sides of the 6 anterior teeth and circumferential clear retainers were placed on both arches, just before and after removal of the appliances for retention, respectively. Total treatment time was 24 months. TREATMENT RESULTS
The posttreatment facial photographs showed a nicely balanced and harmonious face by retracting the upper and lower lips, reducing the muscle strain of the mentalis, and decreasing lower anterior facial height (Fig 9). The intrusive forces used on the maxillary anterior segment successfully reduced the excessive gingival display when smiling. The posttreatment casts illustrated good interdigitation of the teeth and acceptable overjet-overbite relationship (Fig 10). The cephalometric radiographs showed significant improvement in skeletal and dental asymmetry (Figs 11 and 12). As shown on the cephalometric superimposition (Fig 13), the maxillary anterior teeth were bodily retracted with intrusion, the maxillary posterior teeth were intruded and moved distally, the mandibular anterior teeth were retracted with uprighting, and the mandibular posterior teeth were uprighted with intrusion. A good mandibular response was achieved by the counterclockwise directional forces. The chin advancement was obtained by the autorotation of the mandible, facilitated by vertical control of the dentition, resulting in a decrease of the Frankfortmandibular plane angle by 2.5°, a reduction of the ANB
Fig 12. Posttreatment posteroanterior cephalometric radiograph.
angle by 1.5°, and a decrease of the occlusal plane angle by 6.5° The mandibular incisors were uprighted from 105.0° to 90.5°. The Z-angle was improved from 53.0° to 67.5°, the Frankfort-mandibular incisor angle was increased by 12.5°, and anterior facial height was shortened by 2 mm (Table). All these changes contributed to improving the facial profile. DISCUSSION
Tweed-Merrifield directional force technology is very useful, particularly for dentoalveolar protrusion and Class II malocclusion corrections. All patients treated with the Tweed technique, however, do not finish with stable teeth, improved facial esthetics, healthy mouth tissues, and functional occlusions. Many problems can cause an unsuccessful treatment response, including mouth breathing habits, weak musculature, poor patient cooperation during anchorage preparation, lack of high-pull headgear wear to the maxillary anterior segment of the dentition, and improper diagnosis and treatment planning.14,15 The key to successful orthodontic treatment is the control of the vertical dimension through anchorage preparation. The control of the horizontal movement of the dentition depends on how the vertical dimension of the maxillomandibular complex is managed. Vertical control can make horizontal correction pos-
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Fig 13. Cephalometric superimposition.
sible.16 Successful correction of various orthodontic problems depends on control of the horizontal planes, particularly the occlusal plane. The occlusal plane is the key to upward and forward rotation of the horizontal planes. The maintenance, or the closing, of the occlusal plane depends on 2 factors: vertical control of the maxillary and mandibular molars, and control of the anterior vertical dimension, particularly the maxillary anterior segment.17 The clinician can control extrusion of the maxillary posterior teeth during mechanotherapy by applying directional force with MIs to the maxillary dentition. Mandibular posterior MIs are effective in maintaining or closing the occlusal plane and the mandibular plane angle, and inducing forward and upward movement of the chin by intruding and uprighting the mandibular molars during treatment. The most significant contribution to poor vertical control is the excessive amount of anterior facial height increase caused by poor patient cooperation, incorrect diagnostic decisions, and, perhaps most important, a growth response that made treatment more complex and difficult.15 Any increase in anterior facial height in Class II malocclusion correction is an unfavorable sequela of treatment in either an adult or an adolescent, but it has more serious consequences for the adult because there is no compensation from an increase in posterior facial height as in the adolescent. Vertical control is therefore more critical during an adult’s treatment than during an adolescent’s treatment.18 Maxillary anterior MIs or a high-pull headgear auxiliary is
absolutely essential for supporting the maxillary anterior teeth and the anterior segment of the maxilla. Control of the anterior vertical dimension during treatment inhibits the increase in anterior facial height and allows a large increase in horizontal mandibular response for Class II correction, chin enhancement, and Z-angle improvement.15 To date, clinical efficacy5-11 and stability19,20 of temporary skeletal anchorage devices have been described by many authors. This is an efficient method for solving an orthodontic problem that cannot be corrected by a conventional method. However, more studies are needed to determine the causes of failure and to improve the success rate of MIs. In many cases, especially in growing adolescents, orthopedic forces have been used to inhibit or stimulate growth of the maxillomandibular complex. Questions arise about whether MIs have the same effect as the high-pull J-hook. Further studies should be done to determine whether MIA can be used as an orthopedic appliance to control skeletal problems. CONCLUSIONS
Tweed-Merrifield directional force technology is a useful concept, particularly for the treatment of Class I and Class II dentoalveolar protrusion malocclusions. This case report shows the versatility of the directional force system by using MIA. Consequently, TweedMerrifield directional force technology with MIA not only maximizes the result of treatment but also can minimize the need for patient compliance.
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