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Factors controlling anterioC-implants depend on enwithout posterior applianctherapy type II technique

Sung-Seo Mo,a Seong-Hun Kim,b Sang-Jin Sung,c Kyu-Rhand Gerald Nelsong

Seoul, Korea, and San Francisco, Calif

Introduction: Our objective was to evaluate the factorsanterior retraction by using intrusion overlay archwireexclusive sources of anchorage without posterior bondewere constructed from a dental study model. No bracketstition during retraction. Different heights of the anterior retraferent intrusion forces with an overlay archwire placed in the

trolingtheuse

by directly placing the wire into the hole of themini-implant.1,2,7,8 When retracting against dental

biocreative therapy type I technique, demonstrating

aAsso

President, Korean Society of Speedy Orthodontics, Seoul, Korea.eProfessor and chairman, Division of Orthodontics, Department of Dentistry,

0889-5406/$36.00Copyright 2011 by the American Association of Orthodontists.

ONLINE ONLYanchorage, or against indirect miniscrew anchorage,actual intrusion vectors on the anterior teeth are hardto achieve without unwanted reactive forces affectingthe posterior dental units. With the biocreativeapproach, true intrusion vectors without side effectsare possible, since the osseointegrated C-implant orthe C-plate is secure against rotational moments.1,2

The posterior teeth can be left intact. We reportedprevious nite element analysis (FEA) studies using the

Ehwa Womans University Mokdong Hospital, Seoul, Korea.fProfessor and chairman, Division of Orthodontics, Department of Dentistry,Catholic University of Korea, Seoul, Korea.gClinical professor, Division of Orthodontics, University of California at SanFrancisco.The authors report no commercial, proprietary, or nancial interest in the prod-ucts or companies described in this article.Supported by a grant from Kyung Hee University in 2010 (KHU-20100696).Reprint requests to: Seong-Hun Kim, Department of Orthodontics, College ofDentistry, Kyung Hee University, #1 Hoegi-dong, Dongdaemun-gu, Seoul130-701, Republic of Korea; e-mail, [email protected], April 2010; revised and accepted, September 2010.partially osseointegrated mini-implants or plates caneasily endure multi-directional heavy forces even whenthey support orthodontic archwires.3-6 In C-therapy, itis possible to retract the anterior segment independently

University of Korea, Seoul, Korea.bAssociate professor, Department of Orthodontics, College of Dentistry, KyungHee University, Seoul, Korea.cAssociate professor and chairman, Division of Orthodontics, Department ofDentistry, University of Ulsan, College of Medicine, Asan Medical Center, Seoul,Korea.ddoi:10the canine.Results: The height of the anterior retraction hook and the amount of intrusion force had a combinedeffect on the labial crown torque applied to the incisors during en-masse retraction. The difference of anteriorretraction hook length highly affected the torque control and also induced a tendency for canine extrusion.Conclusions: Three-dimensional en-masse retraction of the anterior teeth as an independent segment canbe accomplished by using partially osseointegrated C-implants as the only source of anchorage, an intrusionoverlay archwire, and a retraction hook (biocreative therapy type II technique). (Am J Orthod DentofacialOrthop 2011;139:e183-e191)

In biocreative therapy (C-therapy), torque conrequires special consideration, since one is retractthe anterior teeth in a segment unattached toposterior teeth.1,2 This concept was developed becaciate professor, Division of Orthodontics, Department of Dentistry, Catholicto generate torque on the anterior segment of the teeth. The amount of tooth displacement after nite elementanalysis was exaggerated 70 times and compared with tooth axis graphs of the central and lateral incisors and.1016/j.ajodo.2010.09.023r torque with-masse retractiones: Biocreative

im Chung,d Youn-Sic Chun,e Yoon-Ah Kook,f

that affect effective torque control during en-masseand partially osseointegrated C-implants as thed or banded attachments. Methods: Base modelsor bands were placed on the posterior maxillary den-ction hooks to the working segment archwire and dif-0.8-mm diameter hole of the C-implant were applied3-dimensional (3D) anterior retraction with gable

e183

, intrry shay Nr trea

e184 Mo et albends and an anterior retraction hook (ARH).9 For patientswith a deepbite tendency in the anterior segment, we haveaddressed aweak point of the type I technique by an apply-ing intrusion force with an overlay archwire applied to theanterior segment. We called this the biocreative therapy

Fig 1. Biocreative therapy type II technique: Aapplication on the segmented archwire with a vement; C, intraoral photograph of intrusion overlwith a long hook (woman, age 26 years); D, aftetype II technique. This is an improved method of applyingthe segmented intrusion arch technique of Burstone.10

Two common orthodontic biomechanical systems to-day are the use of a continuous archwire (eg, straight-wire appliance) and segmented archwires (Burstonessegmented arch technique).10-12 Straight-wire appliancetechniques are not technique sensitive but have limited ap-plications for some toothmovements. Segmented archwiretechniques enable more effective and accurate toothmovements by using mechanically determinate forcesystems by separating the anterior and posterior segments.These systems require a better understanding of thebiomechanics involved. Problems of anchorage loss in seg-mented arch systems are resolved with temporary skeletalanchorage devices.13 Chung et al1,2,7,8 introduced thetechnique that uses minimum orthodontic hardware andminimizes side effects by replacing the posteriorappliance segments with the partially osteointegratedC-implant. This benecial protocol is only possible if themini-implant will not loosen in response to the heavy ordynamic forces that would be necessary. The C-implant(sandblasted, large-grit, acid-etched mini-implant) willallow the application of a nickel-titanium (NiTi) reversecurve of Spee overlay archwire, which will apply a momentto the mini-implant but not loosen the screw.1,2 This

February 2011 Vol 139 Issue 2 Americanintrusion overlay wire produces forces that control boththe torque and the vertical position of the incisorsegment (Fig 1). The size of overlay NiTi archwire can bechanged easily. To date, there are no studies of the factorsinvolved in the control of anterior torque by this technique.

aoral photograph of intrusion overlay NiTi wireort hook (woman, age 22 years); B, after treat-iTi wire application on the segmented archwiretment.Clinical studies and case reports have described the tech-nique.2 In this study, we constructed a 3D nite elementmodel of the maxillary teeth, periodontal ligament (PDL),and alveolar bone after extracting the rst premolars.After placement of the orthodontic mini-implant withthe 0.8-mm hole between the second premolar and therst molar, and 8 mm apical to the expected bracketposition, we applied an intrusion force using a reverse-curved NiTi archwire from a C-implant head to the pointbetween the central incisors to the segmented archwireof the 6 anterior teethusing themini-implant as a posteriororthodontic tube. We simulated the effect on torque con-trol using different heights of retraction hooks locatedbetween the lateral incisor and the canine, and differentamounts of intrusion force on the NiTi overlay archwire.

MATERIAL AND METHODS

For the nite-element model, we obtained the toothoutline forms through the 3D laser scanning of amaxillaryright dentition from a dental study model (base model)(model-i21D-400G, Nissin Dental Products, Kyoto,Japan) of an adult with normal occlusion. Using themicro-arch bracket (Tomy, Tokyo, Japan), we alignedand leveled using a broad arch form (Ormco, Glendora,Calif) and referred to previous studies for inclination and

Journal of Orthodontics and Dentofacial Orthopedics

Mo et al e185angulation.11,12,14 We did not add a curve of Spee ora curve of Wilson (Fig 2, A), and the thickness of the PDLwas assumed to be uniform (0.25 mm) (Fig 2, B).15,16

The alveolar bone crest was constructed to followthe cementoenamel junction curvature 1 mm apicalto the cementoenamel junction.17 The 3D nite elementmodel included 12 teeth, a space for the missing rstpremolars periodontal space, and alveolar bone, andwas bilaterally symmetrical (Fig 2, C). In the base model,

Fig 2. Three-dimensional nite element mesh: A and B,lateral views of the maxillary dentition and the PDL;C, lat-eral views of teeth, PDL, alveolar bone of the maxillarydentition, and C-implant head;D, lateral views of intrusionforce application.

American Journal of Orthodontics and Dentofacial OrthopedTable I. Mechanical properties of each material

Youngs modulus (MPa) Poissons ratioPeriodontal ligament 5.0E-02 0.49Alveolar bone 2.0E103 0.30Teeth 2.0E104 0.30Stainless steel 2.0E105 0.30

Table II. Comparison of ARH length and intrusionforce on z-axis displacement

Intrusion force (g)

Hookthe distance from the incisal edge of the maxillary centralincisor to the bracket slot (perpendicular to the occlusalplane) was 4.5 mm, 11 mm labial to the cementoenameljunction, and 11.8 mm to the labial alveolar crest. In thenite element model, teeth, alveolar bones, brackets,periodontal spaces, the C-implant, and the archwirewere constructed with ne tetrahedron solid elements;the teeth and brackets were connected without interfer-ence, and each tooth contacted the next at the contactpoint as individual elements (Fig 2,D). In this study, teeth,alveolar bones, and periodontal spaces were assumed tobe isoparametric and homogeneous linear elastic bodies;the material properties of the elements were Youngsmodulus and Poissons ratio according to previous studies(Table I).18-20 In the system studies, we construct the

Tooth length 70 80 90Central

incisor1 mm Root apex 2.78E-02 2.69E-02 2.60E-02

Incisal edge 1.89E-03 7.91E-03 1.39E-024 mm Root apex 2.70E-02 2.64E-02 2.57E-02



Incisal edge 5.63E-02 6.23E-02 6.83E-02Lateral

incisor1 mm Root apex 1.91E-02 1.91E-02 1.91E-02




Incisal edge 1.46E-02 1.73E-02 2.00E-02Canine 1 mm Root apex 1.95E-02 1.89E-02 1.83E-02




Incisal edge 8.07E-02 8.03E-02 7.98E-02Positiveguresmean tooth intrusion; negativeguresmean extrusion.

ics February 2011 Vol 139 Issue 2

e186 Mo et alx-axis as the in-out direction, the y-axis as the labiolin-gual direction, and the z-axis as the upper-lower direc-tion, and dened 1x as the left central incisor direction,1y as the labial direction, 1z as the apical direction,and x-y as the occlusal plane of the teeth.

The anterior segmented archwire was modeled byusing a 3D beam element (ANSYS beam 4, SwansonAnalysis System, Canonsburg, Pa) with the cross sectionof 0.016 3 0.022-in stainless steel. The archwire hook(0.019 3 0.025-in stainless steel) was set at the mid-point between the lateral incisor bracket and thecanine bracket bilaterally. The osseointegration-basedC-implant with an 0.8-mm diameter hole on the headpart (Cimplant, Seoul, Korea) was placed between themaxillary rst molar and the second premolar, and8 mm apically to the expected bracket position.

Fig 3. Changes of the axes of the maxillary anterior ttude of the intrusion force. Solid line, before; dotted linsor;,, lateral incisor;O, mandibular canine end meroot apex); IF, intrusion force; ARH, anterior retraction70 times. Themovement of themaxillary central incisoWhen a longer hook was used, more root movement,extrusion of a canine were observed.

February 2011 Vol 139 Issue 2 AmericanWe assumed that there were no gaps between thebracket and the archwire at the central incisor, lateralincisor, and canine and carried out the nonlinear analy-sis, allowing the gap element between the archwire andthe 0.8-mm diameter hole of the C-implant head. Theintrusion force can be applied to 1 point between thecentral incisors or 2 points between a central incisorand a lateral incisor; in this study, we applied the intru-sion force to 1 point between the central incisors. The re-traction force was applied via ARH between a lateralincisor and a canine. The retraction force was 150 g be-tween the ARH and the C-implant head, and the lengthsof hooks were 1 mm (very short), 4 mm (short), 7 mm(standard), and 10 mm (long). We measured the intru-sion forces by using 3 curved NiTi wire sizes (0.016 30.022-in, 0.017 3 0.025-in, and 0.019 3 0.025-in)

eeth according to the length of ARH and magni-e, after the applicatioin of force;B, central inci-an midincisal point or cusp tip, upper end meanhook. The displacement of teeth was magniedr was controlled tipping with a short hook (1mm).and proclination of the anterior teeth, and more


Mo et al e187(G&H Wire, Franklin, Ind) according to the intraoralcondition of patients and obtained 70, 80, and 90 g, re-spectively. The intrusive force was applied between theright and left central incisors in the 1z direction as ina 1-piece intrusion archwire. The boundary conditionfor holding the maxillary model was the top of the modelbase connected to the maxilla. There was signicantclearance in the 0.8-mm hole of the C-implant head,so friction for all 3 wires was low. The differences in fric-tion between the wire sizes were not signicant. Thegraphs are labeled with the forces produced as measuredon the physical models (Fig 3). The tooth displacementswere marked by applying the x, y, and z coordinates atthe midpoint of the incisal edges of the central incisorand lateral incisor, the cusp tip of canine, and eachtooths root apex.

For the FEA, ANSYS (version 11, Swanson AnalysisSystem), the universal nite element program, was

Fig 4. Comparison of the vertical effects (z-axis) of thment model (mm); IF, intrusion force; ARH, anterior rpositive value, mean intrusion. When longer ARH andclination or less linguoversion of the maxillary centralof the maxillary central incisor was increased.

American Journal of Orthodontics and Dentofacial Orthopedused on a workstation (HP XW6400, Hewlett-Packard,Palo Alto, Calif).

RESULTS

We observed the tooth displacement pattern on thez-axis (Table II, Figs 3 and 4) based on the movementof the maxillary central incisal edges. The amount ofintrusion increased as the intrusion force increasedand the length of the hook increased. Because theforce system introduces a slight counterclockwisemoment to the anterior dental segment, we noticedsome canine extrusion, which decreased witha heavier intrusion force and increased with a longerhook arm.

For the tooth displacement pattern on the y-axis(Table III, Fig 5), when we applied 70 g of force, the max-illary central incisors tipped lingually with the 1-mmhook group, moved almost bodily in the 4-mm group,

e ARH and intrusion forces in the 3D nite ele-etraction hook; negative value, mean extrusion;greater intrusion forces were applied, more pro-incisor was observed. Accordingly, the intrusion


-axi

e188 Mo et alTable III. Comparison of ARH length and intrusion on y

ToothHooklength

Central incisor 1 mm Root apexIncisal edge

4 mm Root apexIncisal edge



Lateral incisor 1 mm Root apexIncisal edge




Canine 1 mm Root apexIncisal edge

4 mm Root apexIncisal edgeand displayed a root-retraction pattern in the 10-mmgroup. As the intrusion force increased, the amount ofcoronal retraction decreased, and root retraction in-creased. The canine crown tipped distally, and thistipping pattern increased as the hook length increased.

DISCUSSION

In en-masse retraction after the usual extraction ofpremolars, adjustment of the retraction hook length isrecommended to control loss of torque from linguo-version of the anterior teeth during their retraction,and thick wires are recommended to minimize bitedeepening and torque loss from vertical bowing ofthe main archwires.21,22 But improvement of bitedeepening and control of torque loss can beobtained with restriction in a patient having en-masse retraction.

C-therapy, which is the subject of this study, has ad-vantages that can minimize unwanted tooth movementin the posterior teeth and maintain the occlusal relation-ship of the posterior area and good oral hygiene byminimally bonding braces to molars and premolars. Onthe other hand, more effort to control anterior toothmovement is needed with C-therapy.1,2,7,8



Positive gures mean tooth proclination; negative gures mean retraction.

February 2011 Vol 139 Issue 2 Americans displacement

Intrusion force (g)

70 80 901.33E-02 1.74E-02 2.14E-024.31E-02 3.75E-02 3.19E-022.45E-02 2.83E-02 3.23E-022.64E-02 2.12E-02 1.59E-023.55E-02 3.95E-02 4.34E-021.27E-02 7.39E-03 2.06E-034.65E-02 5.05E-02 5.45E-021.82E-03 7.15E-03 1.25E-021.44E-03 8.40E-04 3.12E-03

3.98E-02 3.64E-02 3.31E-029.81E-03 1.21E-02 1.43E-022.29E-02 1.96E-02 1.63E-022.03E-02 2.26E-02 2.48E-026.03E-03 2.71E-03 5.98E-043.08E-02 3.30E-02 3.52E-021.13E-02 1.46E-02 1.79E-028.62E-03 7.75E-03 6.88E-03

4.45E-02 4.22E-02 3.98E-021.39E-02 1.30E-02 1.22E-02

5.42E-02 5.17E-02 4.92E-02Unlike mechanical locked mini-implants,23,24 theC-implant used in C-therapy can resist the rotationalforce and be removed easily because of its partialosteointegration.3-6 With this feature, biocreativetherapy type II mechanics can be used after completionof anterior intrusion and decrowding.1,9 Instead of anintrusion arch, a 0.016 3 0.022-in stainless steelutility archwire is placed from the anterior segmentinto the implant tube, and distinct gable bends areused to generate an anterior torque moment on theanterior segment of the teeth to provide bodilymovement during en-masse retraction. Biocreative ther-apy type II can be the other method to control the ante-rior teeth.2 This technique allows application of bodilyretraction and early intrusion even in a patient withdeepbite. Since the length of the ARH affects the qualityof the tooth-movement pattern, the ARH can be ad-justed to t the goals of retraction. That is, we can usethe 1-mm ARH for controlled tipping in ared incisors,the 4-mm ARH for bodily movement, and the 7-mm or10-mm ARH for root retraction. A longer ARH allowsa little more extrusion of the canine during retraction.

Biocreative therapy type II shows features of the3-piece intrusion archwire. Biocreative therapy type II

1.88E-02 1.80E-02 1.71E-026.15E-02 5.90E-02 5.66E-022.35E-02 2.26E-02 2.17E-02

6.79E-02 6.54E-02 6.30E-02


Mo et al e189can control various patterns of tooth movement throughthe combination of intrusion force, retraction force, andlength of the ARH. In this study, intrusion forces of 70,80, and 90 g generated by 0.016 3 0.022-in, 0.017 30.025-in, and 0.019 3 0.025-in reverse-curved NiTiwires for patients various intraoral conditions were ap-plied, retraction forces were xed to 150 g, and thelength of the ARH was 1, 4, 7, or 10 mm. The tooth-movement patterns for the anterior 6-tooth segmentwere evaluated in these conditions. A recent studyshowed the center of resistance to be located 13.5 mmposteriorly and 9 mm superiorly from the center of thearchwire, similar to the estimation of Melsen et al.25-28

In another study, the center of resistance of the 6maxillary anterior teeth is known to be located 13.5mm apically and 14 mm posteriorly from the centralincisal edge.22 If retraction and intrusion force are ap-plied to the 1-mm ARH, the result is controlled lingualtipping of the segment (Fig 6, A) because the clockwise

Fig 5. Comparison of the sagittal effects (y-axis) of thment mode (mm); IF, intrusion force; ARH, anterior rposterior movement; positive value, mean labial or anintrusion force were applied, less linguoversion andwere observed.

American Journal of Orthodontics and Dentofacial Orthopedmoment that is equal to the magnitude of the retractionforce multiplied by the perpendicular distance of the lineof action of the force to the center of resistance exceedsthe counterclockwise moment that is equal to the mag-nitude of the intrusion force multiplied by the perpen-dicular distance of the line of action of the force toa center of resistance. When a retraction force is appliedto the 4-mm ARH, the clockwise and counterclockwisemoments are neutralized, and bodily movement occurs(Fig 6, B). When retraction forces are applied to hookswith arms longer than 4 mm, the sum of the momentsrotates the segment counterclockwise so that incisor tor-que and intrusion are increased, and the canines extrude(Fig 6, C). In the C-therapy type II technique, 1 to 4 mmARH are recommended for anterior retraction in a patientwho needs maxillary rst premolar extractions. Althoughthe retraction forces were uniform in this study, a forcesimilar to that of the 3-piece intrusion archwire of Bur-stone10 will occur if the retraction forces are decreased;

e ARH and intrusion forces in the 3D nite ele-etraction hook; negative value, mean lingual orterior movement. When longer ARH and greaterfurther proclination of the central incisor crown


e190 Mo et althis might be suited for intrusion of the anterior seg-ment. Therefore, further study seems necessary. Thetechnique described here resulted from several years ofexperience and observation of the clinical application

Fig 6. Schematic representation of the biocreative ther-apy type II technique. A black dot indicates the center ofresistance (CR). Dotted lines indicate intrusion force(blue line) and retraction force (red line). Solid arrows ex-press the moments (force times the distance betweenforce and CR) that originated from 2 forces. A, 1-mmhook (short): when the intrusion force and its moment(blue) are constant, the clockwise moments generatedfrom the distance between the red dotted line and theCR are greater, so that the group of 6 anterior teethinclines lingually. B, 4-mm hook: the distance betweenthe red dotted line and the CR is shorter than for the1-mm hook, and the decreased clockwisemoment is neu-tralized with a counterclockwise moment, so that thegroup of 6 anterior teeth translates.C, 7 and 10mmhooks(long): the retraction force nearly passes by the CR, anda clockwise moment is not generated as a result, sothat the group of 6 anterior teeth ares, and a canineextrudes.

February 2011 Vol 139 Issue 2 Americanof temporary skeletal anchorage devices. When usingthis technique, one must consider the center of resis-tance of the anterior segment to retraction in each pa-tient. Root length, bone levels, pretreatment incisorinclination, and close monitoring of the effects of forceapplication are all important considerations.

CONCLUSIONS

Based on the ndings of this study, we concluded thefollowing.

1. Finite element studies demonstrated that variationsof the height of the ARH and the amount of intru-sion force produced measurable effects on the incli-nation and vertical position of the incisors duringen-masse retraction.

2. With a 70-g intrusion force and a 1-mm high hook,the maxillary central incisors displaced lingually ina controlled tipping pattern. Increasing the hookheight to 4 mm produced almost bodily movement,and, in the 10-mm group, root retraction wasproduced ahead of the crowns. As intrusion force in-creased, the amount of coronal retraction decreased,and root retraction increased. Higher intrusionforces and longer retraction hooks also causedincreased incisor intrusion and canine extrusion.

3. Three-dimension controlled en-masse retraction ofthe 6 anterior teeth as an independent unit can beaccomplished by using partially osseointegratedC-implants as the only source of anchorage, a NiTiintrusion overlay archwire, and a retraction hook(biocreative therapy type II technique).

We thank Ki-Joon Lee, Department of Orthodontics,Youn-Sei University, for FEM model construction andJin-Kyung Lee, Division of Orthodontics, Departmentof Dentistry, Catholic University of Korea, Yoido St.Marys Hospital, for editing the manuscript.

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Factors controlling anterior torque with C-implants depend on en-masse retraction without posterior appliances: Biocreative ...Material and methodsResultsDiscussionConclusionsReferences

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