class ii malocclusion treated by combining a

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CASE REPORT

Class II malocclusion treated by combining alingual retractor and a palatal plateKyu-Rhim Chung,a Yoon-Ah Kook,b Seong-Hun Kim,c Sung-Seo Mo,d and Jae-An Junge

Gyeonggi-do, Korea

In this article, we describe the treatment of a woman, aged 25 years 8 months, with a Class II malocclusion,

severe anterior protrusion, and a high mandibular plane angle. The treatment plan consisted of extracting

both maxillary first premolars and mandibular second premolars. En-masse retraction of the 6 maxillary

anterior teeth was performed with a lingual approach combining a C-lingual retractor and a C-palatal plate

(C-plate). However, the mandibular dentition was treated with conventional labial fixed appliances. After the

maxillary anterior retraction, labial fixed appliances were placed on the maxillary dentition only during the

finishing stage. Correct overbite and overjet, facial balance, and improved lip protrusion were obtained. The

active treatment period was 17 months, and the results were stable for 13 months after debonding. This

C-lingual retractor and C-plate combined retraction method can be effective for intrusive retraction of the

anterior teeth. (Am J Orthod Dentofacial Orthop 2008;133:112-23)

Although lingual orthodontic treatment is moreesthetically appealing to patients than labialapproaches, the appliances can complicate

torque control of the maxillary anterior teeth in patientswith lip protrusion who need maximum anchorage.1-4

Sliding mechanics are preferred because of their simpledesign, but accurate retraction force calibration is madedifficult by friction.5 The C-lingual retractor (C-retrac-tor) was introduced as an alternative lingual method for

obtaining a direct controlled retraction force on themaxillary anterior teeth.6,7

Consideration of the center of resistance (CRes) isessential for anterior retraction in maximum anchoragecases.3,8 The lingual force can be directed through theCRes, making it possible to precisely control toothmovement during en-masse retraction. CRes is deter-mined by loop extension to the palatal side or complex

wire bending in conventional lingual therapy, but, if itis insufficient, uncontrolled tipping of anterior teeth andbowing can result (Fig 1). Solutions such as labialbracketing, complex archwire bending, or skeletal an-chorage might need to be considered to correct it.

Large-diameter osseointegrated implants have beenused for palatal anchorage during anterior retraction.However, these systems require a waiting period ofover 4 months, and immediate loading is impossible,

and the surgery process is more invasive due to thelarge diameter.9,10 Currently, various types of orth-odontic mini-implants are used for palatal anchor-age.11,12 These mini-implants are placed with 2 or 3miniscrews in the midpalatal suture area, and the headportions are bonded with resin for the retraction of the6 maxillary anterior teeth.

A cross-type titanium miniplate (C-plate) can standimmediate heavy force to minimize the disadvantagesof palatal implants and maximize their advantagesduring C-retractorbased en-masse retraction (Fig 2,

A).13 Its main arm has 3 holes for inserting the

miniscrews and 2 horizontal arms with holes for elas-tics or nickel-titanium (Ni-Ti) coil springs.

Effective anterior retraction can be achieved bysimple retraction in patients with severe protrusion (Fig3). The C-retractor is fabricated based on a dentalmodel in CRes position. If intrusion is needed duringthe retraction period, the length of the horizontal armscan be adjusted. For simultaneous intrusion and retrac-tion of 6 anterior teeth, orthodontic force should beapplied in the CRes area that is positioned 44.32% fromthe cervical area.14 If these combined mechanics areused during the en-masse retraction period, effective

aPresident, Korean Society of Speedy Orthodontics, Gyeonggi-do, Korea.bAssociate professor and chairman, Department of Orthodontics, CatholicUniversity of Korea, Kangnam St Marys Hospital, Gyeonggi-do, Korea.cAssistant professor, Department of Orthodontics, Catholic University of

Korea, Uijongbu St. Marys Hospital, Gyeonggi-do, Korea.dAssistant professor, Department of Orthodontics, Catholic University ofKorea, Uoido St. Marys Hospital, Gyeonggi-do, Korea.eFormer resident, Department of Orthodontics, Catholic University of Korea,Uoido St. Marys Hospital, Gyeonggi-do, Korea.Partly supported by the Korean Society of Speedy Orthodontics and the AlumniFund of the Department of Dentistry and Graduate School of Clinical DentalScience, Catholic University of Korea.Reprint requests to: Seong-Hun Kim, Department of Orthodontics, CatholicUniversity of Korea, Uijongbu St Marys Hospital, 65-1 Kumoh-dong, Ui-jeongbu, Gyeonggi-do, 480-130, South Korea; e-mail, [email protected], January 2006; revised and accepted, April 2006.0889-5406/$34.00Copyright 2008 by the American Association of Orthodontists.doi:10.1016/j.ajodo.2006.04.033

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retraction can be achieved. Because no friction isproduced, accurate tooth movements are possible.17

Ni-Ti closed-coil springs (Jinsung, Seoul, Korea) are

stretched from the retractor to the horizontal arm of theC-plate for retraction of the 6 maxillary anterior teeth.

This case report describes the application of thelingual retractor and plate combinationa usefulmethod for patients who need maximum anchorage,anterior torque control, and intrusion.

DIAGNOSIS

A woman, age 25 years 8 months, sought treatmentfor her protruded anterior teeth (Fig 4). She was healthyand had no significant temporomandibular joint symp-toms, except for a clicking sound during opening and

closing of the jaw. The pretreatment photographsshowed the facial characteristics typical of Class IIanterior protrusion, with everted lips, convex profile,and hypermentalis activity. The dental casts demon-strated Class II molar and canine relationships exceptfor the right molars, minor mandibular anterior crowd-ing, and severely protruded incisors (Fig 5). The dentalmidlines coincided with the facial midline. A pan-oramic radiograph showed no missing teeth, and theperiodontal condition was normal. Cephalometric anal-ysis showed a skeletal Class II relationship (ANB

angle, 7; maxillary incisor to NA angle, 26; maxillaryincisor to NA, 5.5 mm) with a steep occlusal plane(SN-OP angle, 24), high mandibular plane angle(FMA, 33.5), and protrusive incisors (interincisal an-gle, 108; mandibular incisor to NA angle, 40; man-dibular incisor to NB, 11.5 mm; IMPA, 101) (Fig 6,Table). The patient was diagnosed with skeletal Class IImalocclusion and bidentoalveolar protrusion.

TREATMENT OBJECTIVES

The treatment objectives based on the cephalomet-ric and dental cast analyses were to extract 2 maxillary

premolars and 2 mandibular premolars, retract andintrude the anterior teeth, improve the interincisal anglerelationship, improve lip competence, achieve a well-intercuspated bilateral Class I canine and molar occlu-sion, and improve facial balance. Near the end of theen-masse retraction, conventional labial fixed appli-ances would be used for finishing.

TREATMENT ALTERNATIVES

The patients chief concern was improvement offacial balance, and her goal was maximum retraction ofthe maxillary anterior teeth with the lingual appliance.

Fig 1. Schematic illustration of en-masse retraction

with the conventional lingual approach.

Fig 2. A, Schematic illustration of titanium C-plate and

drill-free screws; B, frontal image of palatal computed

tomography view. Median palatal suture area has thin

mucosa and thick cortical bone.

Fig 3. Schematic illustration of C-plate and C-retractor

combined retraction mechanics.

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The patient rejected a treatment plan involvingheadgear for maximum anchorage. Thus, 2 alternatives,both involving maxillary first premolar extraction anden-masse retraction of the maxillary dentition withmini-implants, were presented: (1) a conventional lin-gual approach with bonded lingual brackets and mini-

implants as anchorage to reinforce the posterior teethduring anterior retraction and (2) a C-retractor andC-plate combined approach for controlled anterior re-traction without assistance of bonded or banded poste-rior anchorage, and finishing with labial orthodonticappliances for a short time. The treatment plan includedmandibular second premolar extractions, because themandibular anterior retraction needed moderate an-chorage.

Even though finishing would be done with labialfixed appliances, the patient selected the second treat-ment plan for en-masse retraction. This plan allowed

maximum retraction of the maxillary anterior teethwithout affecting the molar occlusal relationship andperiodontal condition, and it required fewer appoint-ments. During the en-masse retraction period, thepatient would be checked only for deformation orremoval of the appliances. After en-masse retraction of

the maxillary anterior teeth, full fixed labial applianceswould be used for a short time to finish treatment.

TREATMENT PROGRESS

Treatment was started with the placement of amaxillary C-retractor and a C-plate in the maxilla andby leveling the mandibular anterior dentition. TheC-retractor, made of 0.032-in stainless steel spring wiresoldered to mesh brackets, consolidated the anteriorteeth with stiff wires, and the resultant forces wereapplied directly to the C-retractor as suggested by

Fig 4. Pretreatment intraoral and extraoral photographs.


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Burstone.15 The fabrication and clinical application ofthe C-retractor were explained previously.6,7

A C-plate with a wide horizontal arm (GebrderMartin GmbH, Tuttlingen, Germany) was placed on thecortical bone of the midpalatal suture area with thefollowing sequence (Fig 7, A-C): (1) local anesthesiawith lidocaine with 1:100,000 epinephrine on the mid-palatal suture; (2) longitudinal incision by using a #15blade from the first premolar to the first molar distalarea; (3) positioning of the C-plate after flap elevationby using a periosteal elevator; (4) 2 or 3 drill-free

miniscrews, 1.5 mm in diameter and 5 mm in length(Gebrder Martin GmbH), were fixed by using a handdriver; and (5) suture. In case of a thin mucosal flap inthe midpalatal suture area, the C-plate can be implantedwithout flap surgery (Fig 7, D-F).

The sutures were removed, and the C-retractor wasbonded on the lingual sides of the maxillary anteriorteeth 1 week after placement of the C-plate. Afterextraction of both maxillary first premolars and man-dibular second premolars, the mandibular dentition wastreated with conventional labial fixed appliances, andmaxillary anterior retraction was started with a Ni-Ti

Fig 5. Pretreatment dental casts.

Fig 6. Pretreatment lateral cephalogram.




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coil spring between the C-plate and the C-retractor. Atotal of 400 g was initially loaded on the C-plate by the2 sides of the lever arm (200 g each) (Fig 8). Themandibular first molars were banded to withstandheavy loads for the molar protraction period.

A .016 .022-in copper Ni-Ti archwire (Ormco,Glendora, Calif) with a gable bend was placed as theinitial archwire for treatment of the mandibular denti-

tion. During retraction of the mandibular anterior teeth,moderate anchorage was used. A drill-free miniscrew,1.5 mm in diameter and 7 mm in length, was placedbetween the mandibular left canine and the first premo-lar for molar key correction. A Ni-Ti coil spring wasimmediately loaded, but conventional treatment wasused when the screw became loose and fell out 2months later.

Fig 7. Surgical procedure of C-plate application: A-C, open method for thick mucosa with

longitudinal incision along the midpalatal suture; D-F, closed method for thin mucosa withoutincision.

Table 1. Cephalometric measurements before and after treatment

Average (female) Pretreatment Posttreatment

SNA angle () 81.6 83 82.5SNB angle () 79.2 76 76

ANB angle () 2.4 7 6.5PFH/AFH (%) 85.1/127.4 (66.8%) 76/126 (60.3%) 76/127 (59.8%)SN-OP () 17.9 24 25FH-UI () 116.0 118 105FMA () 24.3 33.5 34.5IMPA () 95.9 101 86FMIA () 59.8 45.5 59.5UL-E plane (mm) -0.9 1.5 0.5LL-E plane (mm) 0.6 2.5 0.0Interincisal angle () 123.8 108 135Mx 1 to NA (mm) 7.3 5.5 0.0Mx 1 to NA () 25.3 26 13Mn 1 to NB (mm) 7.9 11.5 6Mn 1 to NB () 28.4 40 28

SN to PP () 10.2 14 14


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The retraction period for the maxillary anteriordentition was 7 months (Fig 9). Intrusion and retractionwere performed with a force direction of 2 to theocclusal plane (Fig 10). The patient could return forappointments only every 6 to 8 weeks, for a total of4 visits during the retraction period. Molar protrac-tion of the mandibular dentition was achieved with a.018 .025-in stainless steel archwire with a shoe-horn loop.

After en-masse retraction, the finishing phase wasstarted by placing a .022 .028-in preadjusted fixedappliance on the maxillary posterior teeth. Because theeffect of the C-retractor on tooth movement is mainlyfocused on the controlled retraction of the maxillaryanterior segment, it is important to control the axis ofthe canines individually after en-masse retraction. Us-ing a .016 .022-in stainless steel archwire with a Tloop, bilateral canine axis control and space closure

Fig 8. Progress intraoral photographs during en-masse retraction.

Fig 9. Intraoral photographs after en-masse retraction.




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were performed (Fig 11). Detailing of the dentitiontook 10 months. Although there was some remaining

space in the band area around the maxillary leftposterior teeth and the mandibular left first molar, thepatient requested that the appliance be removed. Themaxillary C-plate was removed under local anesthesiabefore debonding. The palatal soft tissue healed withina few days. The active treatment period with a fixedappliance was 17 months. The retention was providedby a maxillary lingual fixed retainer and a mandibularcircumferential retainer.

TREATMENT RESULTS

Class I canine and molar relationships on the right

side and improved overjet and overbite were obtainedafter treatment (Figs 12 and 13). Although the anchor-age teeth were controlled, correction of the canine andmolar relationship on the left side was insufficientbecause of the severe skeletal discrepancy and poorpatient cooperation during the finishing stage. Theposttreatment facial photographs showed a dramaticdecrease of lip protrusion and improvement of facialesthetics (Fig 12). The facial midline coincided with thedental midline.

The cephalometric analysis (Figs 14 and 15)showed a slight increase of FMA (from 33.5 to 34.5).

The occlusal plane also increased slightly after treat-ment (SN to OP angle, from 24 to 25). The maxillaryincisors were remarkably retracted and intruded byC-retractor and C-plate combined mechanics compared

with normal measurements (FH-U1 angle, from 118 to105; maxillary incisor to NA, from 5.5 to 0 mm;maxillary incisor to NA angle, from 26 to 13). TheANB angle decreased a little during treatment, from 7to 6.5. The mandibular incisors were uprighted andretracted significantly, even though moderate anchor-age mechanics were used (IMPA, from 101 to 86;FMIA, from 45.5 to 59.5; mandibular incisor to NB,from 11.5 to 6 mm; mandibular incisor to NB angle,from 40 to 28). The lower lip was retracted more thanthe upper lip (upper lip to E-plane, from 1.5 to 0.5 mm;lower lip to E-plane, from 2.5 to 0 mm). The interin-cisal angle increased significantly (from 108 to 135).The posteroanterior facial height ratio decreased a littleafter treatment (from 76/126 mm [60.3%] to 76/127mm [59.8%]).

In spite of the overretracted anterior dentition, thepatient was pleased with the final results, which werestable 13 months later (Fig 16).

DISCUSSION

In lingual en-masse retraction of the 6 maxillaryanterior teeth, torque and anchor control are the mostimportant factors. Hong et al3 introduced a lever armand mini-implant system for anterior torque control

during retraction in lingual orthodontic treatment. Theysuggested that favorable torque control of the maxillaryincisors can be obtained with this approach. In addition,other reports described an additional process that uses aguide bar to select the mini-implant placement site.11,16

However, after the leveling and alignment stages, anadditional step of soldering the lever arm to the mainarchwire is required. These methods do not accuratelycontrol the 6 anterior teeth during retraction because thelever arm is connected to the main archwire, and theydo not easily control the CRes because of play betweenthe main archwire and the bracket slot. These lever-arm

systems can cause vertical changes in the posteriorteeth during retraction because a continuous wire isattached to the posterior bracket. Some authorsshowed lingual treatment of skeletal Class II maloc-clusion with palatally placed microimplants.17,18

However, several factors must be considered when 2miniscrews are placed in the midpalatal area or forceis applied directly to a mini-implant in the lateralside of palate. First, this complicated structure can bedifficult to keep clean. Second, the resin on the headof the miniscrew can irritate the palatal tissue. Thelaboratory procedures require additional cost. Fi-

Fig 10. Intrusive movement of maxillary anterior denti-

tion during en-masse retraction.


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nally, loosening or fracturing of the miniscrews canresult from increased lateral force from the thickmucosa on the lateral sides.

The C-plate is designed to be placed in the mid-

palatal area, because, in contrast to the lateral palatewith its thick soft tissue, palatal nerves, and vessels thatcannot stand force, the midpalatal suture area hasthinner soft tissues and thicker cortical bone that could

Fig 11. Finishing stage: detailing with fixed labial appliances.

Fig 12. Posttreatment intraoral and extraoral photographs.




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be ideal for skeletal anchorage (Fig 2, B).11,16

Miniplates, compared with mini-implants, have thedisadvantage of requiring flap surgery. However, im-mediate loading with heavy force is possible. TheC-plate has bendable horizontal arms that can beadjusted to allow 3-dimensional retraction of the ante-rior teeth. Various tooth movementseg, intrusion,rotation correction, and distalization of the posteriorand anterior teethcan be achieved.

Previous reports have described the retraction of the6 anterior teeth with a C-retractor.6,7 The C-retractor isfabricated on the lingual side of the maxillary anterior

teeth on a dental cast; therefore, the clinician canestimate the CRes direction of the 6 maxillary anteriorteeth as 1 segment.

This patient had a high mandibular plane angle andrequired full retraction of the anterior teeth. The 6maxillary anterior teeth were treated by using a C-plateplaced in the palatal area and without appliances on themaxillary posterior teeth. Backward and upward move-ment of the anterior teeth did not cause prematurecontact with the mandibular anterior teeth. However, aC-retractor and a palatal plate can be used for patientswith protrusion and moderate anterior crowding.

Fig 13. Posttreatment dental casts.

Fig 14. Posttreatment lateral cephalogram.


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Unlike conventional lingual treatment, the mechan-ics of the C-retractor combined with C-plate do notrequire banded or bonded brackets on the maxillaryposterior teeth during en-masse retraction.13 We in-tended to use skeletal anchorage as the major appliance

for the retraction period. The C-retractor fabricated onthe initial model has an advantage in that it does notrequire special control during this period. Due to itssimple design, periodontal damage and discomfort inthe maxillary posterior dentition were minimized.

An open surgical method was planned for thispatient because of the thick mucosa. Loosening ofminiscrews can easily occur when they directly pene-trate a thick mucosa without flap surgery. There is aheavy load on the bone in this method because there isa large moment on the plate. To withstand this heavyload, it is recommended that 2 or 3 self-drilling minis-

crews be placed, depending on bone quality, after thelongitudinal incision. However, C-plate miniscrews canbe placed directly and immediately without flap surgeryin areas of thin mucosa in which the midpalatal sutureis covered. The C-plate can withstand heavy orthodon-tic force (300-500 g) with 2 miniscrews in open-methodcases. It is necessary to place miniscrews into all 3holes in the C-plate for retention without irritating thesoft tissue in the closed method.

For successful placement of the C-plate, the bonethickness in the sagittal area of the palate must beconsidered before the miniscrews are placed.10 It was

suggested that vertical bone support should be at least2 mm higher than apparent on the cephalogram.10,19

Crismani et al20 reported that 10% of palatal implantscaused histologic fenestration of the nasal cavity, and20% of implants projecting beyond the nasal floor were

false-positive records on the lateral cephalograms in 20studies. A C-plate used with a C-retractor is fixed withmultiple miniscrews that are 1.5 mm in diameter and 5mm in length. Therefore, it is harder to perforate thenasal cavity than it is with conventional miniscrews ormini-implants, which have larger dimensions. If a slightbony perforation without penetration of the nasal mu-cosa occurs, the thick nasal mucosa will prevent anopen connection to the nasal sinus.19

After removal of the C-plate in our patient, a slightperforation in the small bony structure healed unevent-fully and did not cause any untoward postoperative

sequelae, as happened in other studies.19,21,22When 6 anterior teeth are retracted by a C-retractor,

tipping and intrusion of the maxillary canine tend tooccur. This phenomenon is caused by intrusion andretraction of the 6 maxillary anterior teeth respondingas 1 segment. To resolve this problem for the patient, abeta-titanium alloy T loop was used to control thecanine retraction, which was accomplished with theremoval of the C-retractor in the canine area beforecompleting the anterior segment retraction. Since thepatient did not return for frequent visits, conventionaltreatment was used to resolve the tipped and intruded

Fig 15. Superimposition of pretreatment and posttreatment lateral cephalograms.




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maxillary canines after the anterior retraction (Fig 9),and detailing was needed for 10 months after retraction.

Cephalometric analysis showed a slight clockwiserotation of the mandible (FMA, from 33.5 to 34.5). Itwas assumed that the mandibular posterior teeth were

extruded slightly during leveling. The patient did notcooperate with intermaxillary elastic wear during thefinishing stages. In spite of her poor compliance, theocclusal plane opened slightly (1).

CONCLUSIONS

The C-plate and C-retractor combined approach cancorrect a Class II malocclusion that requires maximumanchorage. The placement of the C-plate on the mid-palatal cortical bone can offer sufficient anchorage fora heavy retraction force immediately without damagingvital anatomic structures. This combined retraction

method can be effective for intrusive retraction ofanterior teeth.

We thank Hyung-Keun Kook for his help with theillustrations.

REFERENCES

1. Fulmer DT, Kuftinec MM. Cephalometric appraisal of patientstreated with fixed lingual orthodontic appliances: historic reviewand analysis of cases. Am J Orthod Dentofacial Orthop 1989;95:514-20.

2. Miyawaki S, Yasuhara M, Koh Y. Discomfort caused by bondedlingual orthodontic appliances in adult patients as examined byretrospective questionnaire. Am J Orthod Dentofacial Orthop1999;115:83-8.

3. Hong RK, Heo JM, Ha YK. Lever-arm and mini-implant systemfor anterior torque control during retraction in lingual orthodon-tic treatment. Angle Orthod 2004;75:129-41.

Fig 16. Extraoral and intraoral photographs after 13 months of retention.


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4. Caniklioglu C, ztrk Y. Patient discomfort: a comparisonbetween lingual and labial fixed appliances. Angle Orthod2004;75:86-91.

5. Kurz C. The use of lingual appliances for correction of bimax-illary protrusion (four premolars extraction). Am J Orthod

Dentofacial Orthop 1997;112:357-63.6. Kim SH, Park YG, Chung KR. Severe Class II anterior deep bitemalocclusion treated with a C-lingual retractor. Angle Orthod2004;74: 280-5.

7. Kim SH, Park YG, Chung KR. Severe anterior open bitemalocclusion with multiple odontoma treated by C-lingual re-tractor and horseshoe mechanics. Angle Orthod 2003;73: 206-12.

8. Vanden Bulcke MM, Burstone CJ, Sachdeva RCL, Dermaut LR.Location of the centers of resistance for anterior teeth duringretraction using the laser reflection technique. Am J OrthodDentofacial Orthop 1987;91:375-84.

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specific fixture: related study analysis. Am J Orthod DentofacialOrthop 2002;122:84-94.

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12. Kyung SH, Choi HW, Kim KH, Park YC. Bonding orthodonticattachments to miniscrew heads. J Clin Orthod 2005;39:348-53.

13. Chung KR, Kim SH, Kook YA. C-palatal plate. In: Cope JB,editor. Orthotads: The clinical guide and atlas. Dallas: TexasUnder Dog Media; 2007.

14. Lee HK, Chung KR. The vertical location of the center ofresistance for maxillary six anterior teeth during retraction usingthree dimensional finite element analysis. Korean J Orthod2001;31:425-38.

15. Burstone CJ. The segmental arch approach to space closure.

Am J Orthod 1982;82:361-78.16. Wehrbein H, Merz BR, Diedrich P, Glatzmaier J. The use ofpalatal implants for orthodontic anchorage. Design and clinicalapplication of the orthosystem. Clin Oral Implants Res 1996;7:410-6.

17. Lee JS, Park HS, Kyung HM. Micro-implant anchorage forlingual treatment of a skeletal Class II malocclusion. J ClinOrthod 2001;35:643-7.

18. Kyung HM, Park HS, Bae SM, Sung JH, Kim IB. The lingualplain-wire system with micro-implant anchorage. J Clin Orthod2004;38:388-95.

19. Wehrbein H, Merz BR, Diedrich P. Palatal bone support fororthodontic implant anchoragea clinical and radiologicalstudy. Eur J Orthod 1999;21:65-70.

20. Crismani AG, Bernhart T, Tangl S, Bantleon HP, Watzek G.Nasal cavity perforation by palatal implants: false-positiverecords on the lateral cephalogram. Int J Oral MaxillofacImplants 2005;20:267-73.

21. Meechan JG. Oro-nasal fistula occurring after a simple dentalextraction. Br J Oral Surg 1983;21:229-32.

22. Tataryn RW, Torabinejad M, Boyne PJ. Healing potential ofosteotomies of the nasal sinus in the dog. Oral Surg Oral MedOral Pathol Oral Radiol Endod 1997;84:196-202.



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