Factors controlling anterior torque during C-implant-dependent en-masse retraction without posterior appliances Sung-Seo Mo, a Seong-Hun Kim, b Sang-Jin Sung, c Kyu-Rhim Chung, d Youn-Sic Chun, e Yoon-Ah Kook, f and Gerald Nelson g Seoul and Suwon, Korea, and San Francisco, Calif Introduction: Our objective was to evaluate the factors that affect effective torque control during en-masse incisor and canine retraction when using partially osseointegrated C-implants (Cimplant, Seoul, Korea) as the exclusive source of anchorage without posterior bonded or banded appliances. Methods: Base models were constructed from a dental study model. No brackets or bands were placed on the maxillary posterior dentition during retraction. The working archwire was modeled by using a 3-dimensional beam element (ANSYS beam 4, Swanson Analysis System, Canonsburg, Pa) with a cross section of 0.016 3 0.022-in stainless steel. Different heights of anterior retraction hooks and different degrees of gable bends were applied to the working utility arch- wire that was placed into the 0.8-mm diameter hole of the C-implant to generate anterior torque on the anterior segment of the teeth. The amount of tooth displacement after finite element analysis was exaggerated 70 times and compared with tooth-axis graphs of the central and lateral incisors and the canine. Results: The height of the anterior retraction hook and the degree of the gable bend had a combined effect on the labial crown torque ap- plied to the incisors during en-masse retraction. By using 30 gable bends and the longest hook, lingual root movement of the 6 anterior teeth occurred. By using 20 gable bends, the 6 anterior teeth showed a translation tendency during retraction. Conclusions: Three-dimensional en-masse retraction of the 6 anterior teeth can be accomplished by using partially osseointegrated C-implants as the only source of anchorage, gable bends, and a long retraction hook (biocreative therapy type I technique). (Am J Orthod Dentofacial Orthop 2011;140:72-80) A fter Kanomi’s report 1 on this concept, published case reports with mini-implants when applying conventional orthodontic mechanics have shown new complications, such as anterior bite deepen- ing, occlusal plane canting, and posterior open bite or posterior crossbite. 2-5 When using mini-implants to re- tract the anterior teeth, it is most important to consider the location of the center of resistance (CR) relative to the location of the mini-implants. 6-13 Successful bodily translation of the anterior teeth might require additional complicated archwires or a supplementary mini-implant in the anterior segment. 13 If bilateral mini-implants are not in the same horizontal plane, as sometimes required by the anatomy of the maxilla, the clinician could see unwanted canting of the occlusal plane because of the different vectors of forces during retraction. 14 A final concern is that sliding mechanics in a full-arch appliance with mini-implant-assisted an- terior retraction might be adversely affected by friction in the bracket slots and tubes. In recent reports, a new treatment system has been de- scribed, called biocreative therapy (C-therapy), to a Associate professor, Division of Orthodontics, Department of Dentistry, Catholic University of Korea, Seoul, Korea. b Associate professor, Department of Orthodontics, Kyung Hee University, School of Dentistry, Seoul, Korea. c Associate professor and chairman, Division of Orthodontics, Department of Dentistry, University of Ulsan, College of Medicine, Asan Medical Center, Seoul, Korea. d Professor and chairman, Department of Orthodontics, Ajou University, Graduate School of Clinical Dentistry, Suwon, Korea. e Professor and chairman, Division of Orthodontics, Department of Dentistry, Ehwa Womans University, Mokdong Hospital, Seoul, Korea. f Professor and chairman, Division of Orthodontics, Department of Dentistry, Catholic University of Korea, Seoul, Korea. g Clinical professor, Division of Orthodontics, University of California at San Francisco. The authors report no commercial, proprietary, or financial interest in the products of companies described in this article. Partly supported by the Korean Society of Speedy Orthodontics and a grant from Kyung Hee University. Reprint requests to: Seong-Hun Kim, Department of Orthodontics, Kyung Hee University, School of Dentistry, #1 Hoegidong, Dongdaemungu, Seoul 130- 701, South Korea; e-mail, [email protected]and [email protected]. Submitted, July 2009; revised and accepted, September 2009. 0889-5406/$36.00 Copyright Ó 2011 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2009.09.026 72 ORIGINAL ARTICLE
Introduction: Our objective was to evaluate the factors that affect effective torque control during en-masseincisor and canine retraction when using partially osseointegrated C-implants (Cimplant, Seoul, Korea) as theexclusive source of anchorage without posterior bonded or banded appliances. Methods: Base models wereconstructed from a dental study model. No brackets or bands were placed on the maxillary posterior dentitionduring retraction. The working archwire was modeled by using a 3-dimensional beam element (ANSYS beam4, Swanson Analysis System, Canonsburg, Pa) with a cross section of 0.0163 0.022-in stainless steel. Differentheights of anterior retraction hooks and different degrees of gable bends were applied to the working utility arch-wire that was placed into the 0.8-mm diameter hole of the C-implant to generate anterior torque on the anteriorsegment of the teeth. The amount of tooth displacement after finite element analysis was exaggerated 70 timesand comparedwith tooth-axis graphs of the central and lateral incisors and the canine.Results: The height of theanterior retraction hook and the degree of the gable bend had a combined effect on the labial crown torque ap-plied to the incisors during en-masse retraction. By using 30� gable bends and the longest hook, lingual rootmovement of the 6 anterior teeth occurred. By using 20� gable bends, the 6 anterior teeth showeda translation tendency during retraction. Conclusions: Three-dimensional en-masse retraction of the 6anterior teeth can be accomplished by using partially osseointegrated C-implants as the only source ofanchorage, gable bends, and a long retraction hook (biocreative therapy type I technique). (Am J OrthodDentofacial Orthop 2011;140:72-80)
ciate professor, Division of Orthodontics, Department of Dentistry, Catholicrsity of Korea, Seoul, Korea.ciate professor, Department of Orthodontics, Kyung Hee University, Schoolntistry, Seoul, Korea.ciate professor and chairman, Division of Orthodontics, Department ofstry, University of Ulsan, College of Medicine, Asan Medical Center, Seoul,.ssor and chairman, Department of Orthodontics, Ajou University, Graduatel of Clinical Dentistry, Suwon, Korea.ssor and chairman, Division of Orthodontics, Department of Dentistry,Womans University, Mokdong Hospital, Seoul, Korea.ssor and chairman, Division of Orthodontics, Department of Dentistry,lic University of Korea, Seoul, Korea.cal professor, Division of Orthodontics, University of California at Sanisco.uthors report no commercial, proprietary, or financial interest in thects of companies described in this article.supported by the Korean Society of Speedy Orthodontics and a grant fromHee University.t requests to: Seong-Hun Kim, Department of Orthodontics, Kyung Heersity, School of Dentistry, #1 Hoegidong, Dongdaemungu, Seoul 130-outh Korea; e-mail, [email protected] and [email protected], July 2009; revised and accepted, September 2009.5406/$36.00ight � 2011 by the American Association of Orthodontists..1016/j.ajodo.2009.09.026
After Kanomi’s report1 on this concept, publishedcase reports with mini-implants when applyingconventional orthodontic mechanics have
shown new complications, such as anterior bite deepen-ing, occlusal plane canting, and posterior open bite orposterior crossbite.2-5 When using mini-implants to re-tract the anterior teeth, it is most important to considerthe location of the center of resistance (CR) relative tothe location of the mini-implants.6-13 Successful bodilytranslation of the anterior teeth might requireadditional complicated archwires or a supplementarymini-implant in the anterior segment.13 If bilateralmini-implants are not in the same horizontal plane, assometimes required by the anatomy of the maxilla, theclinician could see unwanted canting of the occlusalplane because of the different vectors of forces duringretraction.14 A final concern is that sliding mechanicsin a full-arch appliance with mini-implant-assisted an-terior retraction might be adversely affected by frictionin the bracket slots and tubes.
In recent reports, a new treatment systemhas been de-scribed, called biocreative therapy (C-therapy), to
Fig 1. Biocreative therapy type I technique: A, Omega loop-forming pliers for gable bend application;B, intraoral photograph of gable bend application on retraction archwire; C, 4 months after gable bendapplication; D, gable bend application on retraction archwire; E and F, 5 months after gable bendapplication. Yellow circles indicate amounts of gable bends generated by the pliers.
Mo et al 73
implement independent en-masse retraction of theanterior teeth while avoiding orthodontic applianceson the posterior segments during the retractionperiod.2,15-18 This concept developed because partiallyosseointegratedmini-implants or plates can easily enduremultidirectional heavy forces even when they support or-thodontic archwires.19-21 In C-therapy, it is possible toretract the anterior segment independently by directlyplacing the wire into the hole of the mini-implant.2,15,22
This mini-implant system allows light continuous forces,the ability to control complex tooth movements, mini-mum friction, and no need for patient compliance.
In the cited clinical study, mini-implants were used asthe only source of anchorage for en-masse retraction ofthe 6 maxillary anterior teeth.5 No appliances were placedin the maxillary and mandibular posterior dentition. Themini-implants were designed to accommodate archwiresthat were free to slide during retraction and could resistthe force levels necessary for a wide range of applications.Since applied orthodontic forces during anterior retractionare against the mini-implants and not against the ortho-dontic appliances fixed to the posterior teeth, no changein the posterior occlusion is expected during retraction.This beneficial protocol is only possible if the mini-implant does not loosen in response to the heavy or dy-namic forces that would be necessary. The C-implant(sand-blasted, large-grit, acid-etched mini-implant; Cim-plant, Seoul, Korea) allows the application of a gable
American Journal of Orthodontics and Dentofacial Orthoped
bend in the buccal area that will apply a moment to themini-implant, but not loosen the screw.17,19 This gablebend produces forces that control the torque and thevertical position of the incisor segment. The bend is easilyapplied with an Omega loop-forming pliers (Fig 1). Todate, there are no reviews regarding the factors involvedin control of anterior torque by this technique except clin-ical literature and case reports. In this study,we constructeda 3-dimensional (3D) finite element model of the maxillaryteeth, periodontal ligament (PDL), and alveolar bone afterextracting the first premolars. After placing orthodonticmini-implants with an 0.8-mmhole at 8mm above the ex-pected bracket position between the second premolar andthefirstmolar,weappliedautility archwire to the 6 anteriorteeth and placed the posterior ends of the archwire into theholes of the mini-implants, effectively using the mini-implant as a posterior orthodontic tube. We simulatedthe effect on torque control using different heights of re-traction hooks located between the lateral incisor and thecanine, anddifferent angles of gable bendson the archwire.
MATERIAL AND METHODS
We obtained the tooth outline forms by 3D laserscanning of a maxillary right tooth from a dental studymodel (base model) (model-i21D-400G; Nissin DentalProducts, Kyoto, Japan) of an adult with normal occlu-sion. Using the Micro-arch bracket (Tomy, Tokyo,
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Fig 2. Three-dimensional finite element mesh: A and B, lateral views of the maxillary dentition and thePDL; C, lateral view of tooth, PDL, and alveolar bone of the maxillary dentition; D, lateral view of tooth,PDL, alveolar bone of the maxillary dentition, and C-implant head and archwire.
Japan), we aligned and leveled with a broad arch form(Ormco, Glendora, Calif) and referred to the studies ofAndrews,23 Germane et al,24 and Park and Yang25 for in-clinations and angulations. We did not add a curve ofSpee or a curve of Wilson (Fig 2, A).
The thickness of the PDL was assumed to be uniform(0.25 mm) according to the studies of Coolidge26 andKronfeld27 (Fig 2, B). The alveolar bone crest was con-structed to follow the curvature of the cementoenameljunction 1 mm apical to it. The 3D finite element modelincluded 12 teeth, open space according to the missingfirst premolars, periodontal space, and alveolar bone,and was bilaterally symmetrical (Fig 2, C). In the basemodel, the distance from the incisal edge of the maxil-lary central incisor to the bracket slot (perpendicular tothe occlusal plane) was 4.5 mm, 11 mm to the labial ce-mentoenamel junction, and 11.8 mm to the labial alve-olar crest. In the finite element model, teeth, alveolarbones, brackets, periodontal spaces, C-implant, andarchwire were constructed with fine tetrahedron solidelements; the tooth and bracket were connected withoutinterference, and each tooth contacted the next at thecontact point as individual elements (Fig 2, D). In thisstudy, teeth, alveolar bones, and periodontal spaces
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were assumed to be isoparametric and homogeneouslinear elastic bodies, and the material properties of theelements were Young’s modulus and Poisson’s ratio ac-cording to the studies of Tanne et al,28 Ziegler et al,29
and Poppe et al30 (Table I). In the system studies, weconstruct the x-axis as the in-out direction, the y-axisas the labiolingual direction, and the z-axis as theupper-lower direction, and defined1x as the left centralincisor direction, 1y as the labial direction, 1z as theapical direction, and the x-y plane as the occlusal planeof the teeth (Fig 3, A and B).
The archwire was modeled by using a 3D beam ele-ment (ANSYS beam 4, Swanson Analysis System, Can-onsburg, Pa) with a cross section of 0.016 3 0.022-instainless steel. The archwire hook (0.019 3 0.025-instainless steel) was set at the midpoint between the lat-eral incisor bracket and the canine bracket bilaterally(Fig 3). The gable bend was located at the posteriorthird of the space of the extracted maxillary first premo-lar, activated toward the root (1z), and placed withbends of 0�, 10�, 20�, 30�, and 40� (Fig 3, C and D).The osseointegration-based C-implant, which hasa 0.8-mm diameter hole on the head part, was placed8 mm above the expected bracket position betweenthe second premolar and the first molar.
For convenience of analysis, we assumed that therewere no gaps between the bracket and the archwire atthe right maxillary central and lateral incisors and ca-nine, and carried out the nonlinear analysis, allowingthe gap element between the archwire and the 0.8-mmdiameter hole of C-implant head. The retraction forcewas 150 g between the anterior retraction hook (ARH)
Journal of Orthodontics and Dentofacial Orthopedics
Fig 3. Schematic representation of the coordinate system: A, lateral view; B, frontal view; C and D,gable bend application.
Table II. Comparison of ARH lengths and gable bends on Z-axis displacement
Tooth Hook length
Gable bend
0� 10� 20� 30� 40�
Right maxillary central incisor 4 mm Root apex 3.31E-02 3.22E-02 3.12E-02 3.03E-02 3.07E-02Incisal edge �2.18E-02 �1.77E-02 �1.35E-02 �9.36E-03 �5.79E-03
Positive figures mean tooth intrusion, and negative figures mean extrusion.
Mo et al 75
and the C-implant head, the lengths of hooks were 4 mm(short), 7 mm (standard), and 10 mm (long), and the an-gles of the gable bends were 0�, 10�, 20�, 30�, and 40�.The tooth displacements were marked by applying the x,y, and z coordinates at the midpoints of the incisal edgesof the 2 incisors, the cusp tip of the canine, and eachtooth’s root apex.
For the finite element analysis, ANSYS 11 (SwansonAnalysis System), which is the universal finite elementprogram, was used on a workstation (XW6400;Hewlett-Packard, Palo Alto, Calif).
American Journal of Orthodontics and Dentofacial Orthoped
RESULTS
The tooth-displacement pattern on the z-axis isshown in Table II and Figures 4 and 5.
In applying the 150-g orthodontic force between theARH and the C-implant head if the gable bend was 0�,the canine experienced the most extrusion because ofthe step-down bend of the main archwire (0.016 30.022-in). By using a midsized hook, an increase in thegable bend decreased the amount of extrusion of all teeth(rightmaxillary incisors and canine), and eventually all an-terior teeth intruded with a gable bend greater than 20�.
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Fig 4. Comparison of the effects of the ARH and the gable bends for the 0.016 3 0.022-in stainlesssteel archwires in the 3D finite element model. GB, Gable bend; ARH, anterior retraction hook (short,4 mm; standard, 7 mm; long, 10 mm).
76 Mo et al
With an increase of the length of the ARH, theamounts of extrusion of the incisors decreased. Soeven without a gable bend, intrusion occurred with thelong hook (Fig 4, A, F, and K). However, without a gablebend, the amount of extrusion of the canine increased asthe length of the ARH increased.
The tooth-displacement pattern in the y-axis isshown in Table III and Figure 6.
With an increase in the gable bend, the degree of re-traction of the teeth has a tendency to decrease, andlikewise the retraction of the crown decreased with in-creased ARH length. With the shortest hook and no gablebend, the incisors tipped lingually (the crowns retractedmore than the roots). This changed to a controlled tip-ping pattern with the increase of the gable bend. Withthe standard hook, there was translation as the gablebend was increased. By using the long hook, the qualityof retraction changed from controlled tipping to transla-tion at the 30� gable bend and gradually to increasingroot retraction with an increase in the gable bend.
The displacement pattern of the lateral incisor wassimilar with that of the central incisor. Although the re-traction of the lateral incisor’s crown decreased with theincreases of the gable bend and the ARH length, the
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retraction of the root had a tendency to increase. Withthe standard hook, the 10� gable bend produced thebest translation pattern, and an increase in the gablebend increased root retraction. Retraction of the crownof the canine decreased with the increase of the gablebend, and it was significantly a greater decrease thanin the 2 incisors. However, the longer the ARH, themore retraction of the crown of the canine without sig-nificant differences with the 2 incisors.
DISCUSSION
To maintain or control the inclination of the incisor,exaggerated anterior torque in the archwire or the use ofhigh-torque brackets can be recommended. Even if thisasymmetrical gable bend can generate favorable anteriortorque, there will always be unwanted side effects ac-cording to Newton’s law of action and reaction, includ-ing intrusion on the posterior segment and extrusion onthe anterior segment.31 Because traditional orthodonticfull fixed appliances applying incisor torque during re-traction might cause incisor extrusion or loss of posterioranchorage, the use of mini-implant anchors is recom-mended, not only to solve the anchorage problem butalso to control anterior torque.
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Fig 5. Comparison of the vertical effects (z-axis) of the ARHand the gable bends for the 0.0163 0.022-instainless steel archwires in the 3D finite element model. GB, Gable bend; ARH, anterior retraction hook(short, 4 mm; standard, 7 mm; long, 10 mm).
Mo et al 77
However, using fullfixed applianceswith conventionalmini-implants has some associated drawbacks that are re-lated to the position of the CR and friction in the sys-tem.12,13 A recent study showed the CR position to belocated 13.5 mm posteriorly and 9 mm superiorly fromthe center of the archwire, similar to the estimations ofSung et al13 andMelsen et al.32 In thefinite element anal-ysis study of Sung et al,13 even though the vector of theretraction force was applied close to the CR for the 6 an-terior teeth with an 8-mm ARH, the central and lateral in-cisors were not bodily retracted. They suggested that thecompensating curves and the additional mini-implantplaced between the incisors to add vertical forces wouldovercome the limitations of the ARH. As the authorsmen-tioned, placing an additional mini-implant to apply mid-line vertical traction might unnecessarily increasemorbidity. Canting of the occlusal plane from asymmetri-cal retraction force vectors can be avoided if the mini-implants resist the application of corrective moments.
American Journal of Orthodontics and Dentofacial Orthoped
Osseointegration can be useful in orthodontic mini-implants when the case requires resistance to rotationalforces on the mini-implant, high stability during forceapplication, and the capability of supporting heavyand dynamic forces.17-19,21 However, this does notmean that the mini-implant will be difficult to re-move.19,33 The mini-implant used in this study, theC-implant, was a sand-blasted, large-grit, acid-etched,surface-treated mini-implant. It has 2 parts: a screwand a head. The retention portion of the C-implanthas a higher osseointegration potential when comparedwith smooth titaniummini-implants and is better able toresist the rotational tendency during heavy dynamicloads.19-21,33,34 Seo et al,33 in a study of the histologicand histomorphometric findings of retrieved sand-blasted, large grit, acid-etched C-implants that werefunctionally loaded, showed 52.6% of mean bone-implant contact (%) (excluding the upper smooth-surfaced 2-mm portion of the mini-implant). These
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Table III. Comparison of ARH lengths and gable bends on y-axis displacement
Tooth Hook length
Gable bend
0� 10� 20� 30� 40�
Right maxillary central incisor 4 mm Root apex 2.57E-03 9.49E-04 �8.37E-04 �2.87E-03 �4.81E-03Incisal edge �6.62E-02 �6.22E-02 �.81E-02 �5.42E-02 �5.24E-02
Positive figures mean tooth proclination, and negative figures mean retraction.
78 Mo et al
authors described the C-implant as a "partially osseoin-tegrated mini-implant." Kim et al,19 evaluating removaltorque values, judged the C-implant’s removal torquevalue to be relatively high considering its shorter length,titanium alloy, and multiple force applications.
Biocreative therapy type I mechanics require distinctgable bends on 0.016 3 0.022-in stainless steel utilityarchwires to generate an anterior torque moment onthe anterior segment of the teeth to resist lingual tippingduring en-masse retraction.17 A 0.0163 0.022-in stain-less steel utility archwire is recommended as the main re-traction archwire because it can resist over 300 g ofvertical force without distortion during retraction pe-riods despite its smaller size than other rectangularstainless steel archwires (unpublished data).
The archwire is directly placed into the hole in thehead of the C-implant. In the tooth-displacement pat-tern on the z-axis in our study (evaluation of the verticalposition), the effects of the length of the hook were op-posite among the 2 incisors and the canine, and therewas more intrusion with an increased gable bend. Theseresults can be interpreted that it is possible to control theanterior teeth vertically by changes in the length of thehook or the gable bend. In the tooth-displacement pat-tern on the y-axis (evaluation of the horizontal retrac-tion of the anterior teeth), the patterns of the 2incisors and the canine were dissimilar. When the gablebend and the length of the hook were increased in theincisors, the retraction amount of the root was increased,whereas the retraction amount of the crown was de-creased. By changing the degree of the gable bend or
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the hook length, we could change the behavior of the in-cisors during retraction from uncontrolled tipping tocontrolled tipping to translation and then to increasedroot retraction. In the case of the canine, there werealmost no effects by the length of the hook, but thegable bend significantly influenced its tooth displace-ment. Uncontrolled tipping was changed at the 20�
gable bend, and the root retraction could increase overthe 20� gable bend. It was supposed that root retractionof the canine was possible by controlling the gable bendand the retraction force.
If the empirical tooth movement on a continuousarchwire disagrees with the schematic displacementgraph, an important consideration is that the magnifieddisplacement is not actual tooth movement, but an ini-tial reaction that does not simulate a time-dependent re-action.35 The tooth reaction from biocreative therapytype I mechanics can be analyzed by tooth displacementand stress distribution on the root by using the finite el-ement method. Therefore, harmonizing the results of thefinite element method with the clinical experience oftype I mechanics will be useful in predicting the clinicaleffects of certain mechanics compared with conven-tional labial mechanics.
From our study, the biocreative therapy type I tech-nique provides intrusion and retraction of the 6 ante-rior teeth simultaneously. The technique is simple andminimizes the unwanted side effects that are commonwhen retracting the anterior segment with full fixedappliances. The mechanics preserve the patient’s origi-nal posterior occlusion as much as possible and
Journal of Orthodontics and Dentofacial Orthopedics
Fig 6. Comparison of the sagittal effects (y-axis) of the ARHand the gable bends for the 0.0163 0.022-instainless steel archwires in the 3D finite element model. GB, Gable bend; ARH, anterior retraction hook(short, 4 mm; standard, 7 mm; long, 10 mm).
Mo et al 79
minimize iatrogenic effects on the periodontium, sincethe posterior segments are not engaged during retrac-tion of the anterior teeth. After en-masse retraction,short-term fixed appliances or clear aligners can beused as the finishing stage.5 The technique describedin this study is the result from several years of experi-ence and observation of the clinical application of tem-porary skeletal anchorage devices. Further studies areneeded to determine the treatment effects of en-masse retraction with different type of skeletal anchor-age based on retraction force, length of hook, andbracket slot size.
CONCLUSION
Based on the findings of this study, the following canbe concluded:
American Journal of Orthodontics and Dentofacial Orthoped
1. The height of the ARH and the angle of the gablebend had combined effects on the labial crown tor-que of the incisors during en-masse retraction.
2. At a gable bend greater than 20�, the 6 anteriorteeth showed translation during retraction. At a ga-ble bend greater than 30� with a long ARH, root re-traction beyond the crown retraction occurred.
3. Three-dimensional en-masse retraction of the 6 an-terior teeth can be accomplished by using partiallyosseointegrated C-implants as the only source ofanchorage, gable bends, and a long retractionhook (biocreative therapy type I technique).
We thank Jin-Kyung Lee, Division of Orthodontics,Department of Dentistry, Catholic University of Korea,Yoido St Mary’s Hospital, for manuscript editing.
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80 Mo et al
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