CASE REPORT

Protraction of mandibular second and thirdmolars assisted by partial corticision andminiscrew anchorage

Hiroshi MimuraTokyo, Japan

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A woman, aged 47 years 6 months, with an anterior open bite and a left-shifted mandible was treated with amandibular right first molar extraction and without orthognathic surgery. However, her mandibular second molardid not movemesially during treatment because of the dense lamina dura; therefore, corticision was applied onlyon the mesial aspect of the mandibular second molar, and a miniscrew was inserted simultaneously. Corticisionwas introduced as a supplemental dentoalveolar surgery in orthodontic therapy to achieve accelerated toothmovement with minimal surgical intervention. In this technique, a reinforced scalpel was used as a thin chiselto separate the interproximal cortices transmucosally without a flap. This techniquewas applied not to acceleratetooth movement, but to protract the mandibular molars. One miniscrew was inserted on the mesiobuccal side ofthe mandibular right molar for protraction and intrusion. In addition, 2 miniscrews were inserted in the buccalsides of the maxillary first and second molars and the palatal side of the maxillary first molar to intrude themfor correction of the mandibular shift and the cant of the occlusal plane. Excellent occlusion and correction ofthe anterior open bite were achieved without surgery. At the 2-year follow-up examination, the patient had agood occlusion and showed good stability with no opening of the extraction space. A partial corticision is aneffective option for facilitating movement of mandibular molars. (Am J Orthod Dentofacial Orthop2013;144:278-89)

If the third molar is present, extraction of themandibular first molar is a possible alternative tocorrect an anterior crossbite and a severe Class III

molar relationship.1,2 The mandibular molars aredifficult to move mesially compared with the maxillarymolars because the mandible comprises thick corticalbone connected by coarse trabecular bone. The molarroots are extremely wide buccolingually, so sometimesthe edentulous space cannot close.3

Roberts et al4,5 used a rigid endosseous implant in theretromolar area for mesial movement of the mandibularmolars. Recently, miniscrews, which are more convenientand simple and can be placed anywhere, have becomepopular for absolute anchorage. Several case reportshave illustrated protraction of the mandibular secondand third molars with miniscrews.6-9

e practice, Tokyo, Japan.uthor has completed and submitted the ICMJE Form for Disclosure oftial Conflicts of Interest, and none were reported.t requests to: Hiroshi Mimura, 2-15-11-6, Yato-cho, Nishi-Tokyo, Tokyo001, Japan; e-mail, mimura@m-ortho.com.itted, July 2012; revised and accepted, August 2012.5406/$36.00ight � 2013 by the American Association of Orthodontists./dx.doi.org/10.1016/j.ajodo.2012.08.030

On the other hand, there are many approaches toshorten the time for orthodontic tooth movement,such as alveolar corticotomies, which produce a regionalacceleratory phenomenon.10 This phenomenon is char-acterized by a burst of localized remodeling that acceler-ates healing, particularly after the surgical wounding ofcortical bone. Kim et al11 reported a new procedurecalled “corticision” to accelerate tooth movement. Thistechnique produces a minimal surgical injury to thegingiva, cortical bone, and trabecular bone around thetarget teeth, thereby initiating the regional acceleratoryphenomenon.

This case report describes an orthodontic treatmentwith a partial corticision to protract the mandibular mo-lars with a miniscrew for anchorage. With this technique,a reinforced scalpel was used as a thin chisel to separatethe interproximal cortices transmucosally without a flap.Corticision was applied to only 1 aspect, not to accel-erate tooth movement but to protract the mandibularmolars.

DIAGNOSIS AND ETIOLOGY

The patient was a 47-year-old woman who com-plained of amaxillary anterior crossbite and amandibular

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lateral shift. Her father also had an anterior crossbite. Herface was asymmetric, and her chin and mandible wereshifted to the left. Her lips were inclined, and the leftcorner was positioned higher than the right. On the smil-ing photo, her occlusal plane was canted (Fig 1). Hermaxillary dental midline was almost aligned with thefacial midline, but the mandibular midline was posi-tioned 6 mm to the left because of the mandibular shift.The left side was in crossbite except for the second mo-lars. Her anterior teeth were in an end-to-end relation-ship (0 mm of overbite), and she had a mild anterioropen bite. She had a mandibular right third molar thatoccluded with the maxillary second molar. Her molarrelationships were Class I on the left side and Class III(6 mm) on the right side. Overbite was 0 mm (Fig 2).Her lateral facial view showed a prominent chin andexcessive lower anterior facial height (Fig 1). Cephalo-metric analysis showed a skeletal Class III relationship(ANB, 1.0�) with a mesially positioned maxilla (SNA,84.0�) and a forward-positioned mandible (SNB,83.0�). The maxillary incisors were inclined labially (U1-FH, 119�), and the mandibular incisors were inclinedslightly lingually (FMIA,74.0; L1-APo, 4.5 mm) (Figs 3and 4, Table). The soft-tissue analysis showed a slightprotrusion of the lower lip (lower lip to E-line, 1.5 mm).

The panoramic radiograph showed that the roots ofthe mandibular right first molar were widely divertedand thick, with a dense lamina dura around the roots.The mandibular right third molar had divergent and nar-row mesial and distal roots (Fig 3, C).

A functional assessment showed no remarkablediscrepancy between centric occlusion and centric rela-tionship, and no temporomandibular joint problems.The mandible was shifted skeletally.

TREATMENT OBJECTIVES AND PLAN

I planned to maintain the anteroposterior position ofthe maxillary incisors since there was no significant facialprofile problem, except for the slight protrusion of thelower lip. The main treatment objectives consisted of re-tracting themandibular incisors to correct the incisor rela-tionship and obtain a normal overbite. Midline correctionconsisted of reciprocal protraction of themandibular rightsecond and thirdmolars andmandibular incisor retractionafter extraction of the mandibular right first molar. Afterclosure of the edentulous space, I tried to improve thecanted occlusal plane with intrusion of the maxillary andmandibular right molars using miniscrews.

TREATMENT ALTERNATIVES

The first treatment of choice was to correct the skel-etal discrepancies, the mandibular lateral shift, and the

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canted occlusal plane with a combination of orthog-nathic surgery and orthodontic treatment. The patient,however, was fearful of surgery and the associated risks,and rejected it. The next alternative proposal was to usetemporary anchorage devices for distal movement of themandibular right molars after extraction of the thirdmolar to correct the anterior crossbite and the shift ofthe mandibular dental midline to correct the mandibularasymmetry. However, the roots of the mandibular rightfirst molar were widely divergent and surrounded by adense lamina dura. If possible, it was desirable to intrudethe right molars to correct the mandibular shift and thecanted occlusal plane during the treatment. However,the retromolar miniscrew could not be implanteddeep enough to intrude the mandibular molars withdistalization.

The next treatment option was an unusual extractionof only the mandibular right first premolar and recip-rocal retraction of the mandibular incisors and protrac-tion of mandibular right molars to establish a Class IIImolar relationship. However, with a Class III molar rela-tionship it is difficult to establish a stable occlusion.Therefore, the mandibular right first molar was ex-tracted, the second and third molars were protracted,and the mandibular incisors were retracted reciprocallyto establish the Class I relationship between themaxillaryright first molar and the mandibular right second molar.

TREATMENT PROGRESS

First, a transpalatal arch was placed for torque con-trol of the molars and to prevent extrusion of the molars.Then the mandibular right first molar was extracted. Allmaxillary teeth and the mandibular right segment werebanded, bonded, and leveled, and the mandibular rightsecond premolar and second molars were moved recip-rocally. Then all mandibular teeth were bonded. After8 months of leveling, Class III elastics were worn to cor-rect the midline deviation and the anterior crossbite. Onthe panoramic radiograph at this time, the radiopaquesocket of the extracted mandibular first molar wasobserved clearly.

After 16 months, the anterior open bite was cor-rected, and the right canine relationship was Class I;however, the mandibular second molar did not moveforward, and the mandibular right edentulous space re-mained at 8 mm. Therefore, I decided to apply corticisionto the mesial aspect of the mandibular second molar toprotract the mandibular second and third molars moreefficiently. At this time, a 0.016 3 0.022-in beta-titanium wire was used as a working wire (Fig 5, A).

After local anesthesia, corticision was performed onlyon the mesiobuccal aspects of the mandibular second

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Fig 2. Pretreatment dental casts.

Fig 1. Pretreatment facial and intraoral photographs.

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Fig 4. Pretreatment cephalometric tracing.

Fig 3. Pretreatment radiographs.

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molar; it was a simplified version of the original tech-nique of Kim et al.11 A reinforced surgical blade (num-ber15; Feather Safety Razor, Mino, Japan) was used tomake a surgical incision on the cortical bone. The bladewas positioned on the interradicular attached gingiva atan inclination of 90� to the molar and inserted graduallyinto the bone marrow under the overlying gingiva,cortical bone, and cancellous bone (Fig 5, B). The surgi-cal injury originated at the papillary gingival margin topreserve the alveolar crest and extended 1 mm beyondthe mucogingival junction because of the narrow zoneof attached gingiva around the molar region. The bladewas pulled out without a swing motion because of fearof injury to the lips. This procedure was modified fromthe original technique of Kim et al.11 They recommendedpulling out the blade with a swing motion to extend theincision area. On the dental radiograph just after the par-tial corticision, a thick and dense lamina dura sur-rounded the mandibular first molar socket andinhibited mesial movement. The supra-alveolar cleftmade by the incision of the scalpel was observed onthe mesial side of the second molar (Fig 5, C).

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Fig 5. Corticision: A, intraoral photograph before the partial corticision; B, a reinforced scalpel wasused as a thin chisel to separate the interproximal cortices transmucosally without a flap; C, dentalradiograph at the corticision; D, intraoral photograph just after the partial corticision and placementof the miniscrew.

Table. Cephalometric measurements

Measurement Japanese standard Pretreatment Posttreatment Two years postretentionSNA angle (�) 82.3 84 84 84SNB angle (�) 78.9 83 84 84ANB angle (�) 3.4 1 0 0MP-FH (�) 28.8 27 24.5 25.5Y-axis (�) 65.4 62 61 61FMIA (�) 54.9 74 74 74L1-MP (�) 96.3 79 81.5 80.5L1-APo (mm) 3 4.5 3 2.5U1-FH (�) 111.1 119 122 120U1-SN (�) 104.5 110 113 112Interincisal angle (�) 124.1 135 132 134

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At the same time, a miniscrew (8.0 mm long, 1.6 mmin diameter; Jeil Medical, Seoul, South Korea) was in-serted into the interradicular attached gingiva betweenthe canine and the first premolar. An elastomeric chainwas worn from the miniscrew to the second molar forimmediate protraction (Fig 5, D).

Two months after the partial corticision, the denselamina dura of the distal root of the extracted first molardisappeared, and the second molar moved forward by 1mm. The bone density of the mesial-cervical region ofthe mandibular second molar seemed less dense (Fig 6,A). Three months after the partial corticision, the secondmolar had moved a third of the way (Fig 6, B); 4 monthslater, half of the space was closed (Fig 6, C).

Four months after the partial corticision, the mini-screw loosened, the head of the screw inclined distally,

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and a 2-mm space appeared between the canine andthe first premolar. Therefore, a new screw was reinserted3 mm from the initial position on the apical side. Twoadditional screws were simultaneously inserted in theright alveolar process on both the buccal (8.0 mmlong, 1.6 mm in diameter; Jeil) and palatal (6 mmlong, 2.0 mm in diameter; Jeil) sides around the maxil-lary first molar. These 2 screws were placed to correctthe canted occlusal plane by intruding the maxillaryright molars. The apically repositioned mandibular mini-screw was used not only for protraction, but also tointrude the mandibular molars and improve the mandib-ular deviation. Three elastomeric chains were worn fromeach screw.

After 31 months of treatment, a good occlusion wasestablished. Then all brackets and bands were removed,

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Fig 6. Radiographs after the partial corticision: A, 2 months; B, 3 months; C, 4 months.

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and fixed retainers were bonded on the lingual sides ofthe mandibular incisors and also between the mandib-ular right second molar and second premolar. A circum-ferential retainer was used only in the maxillary arch.

TREATMENT RESULTS

After 2 years 7 months of treatment, a Class I idealocclusion was obtained, and ideal overjet and overbitewere also achieved (Figs 7 and 8). On the right side,the Class I molar relationship was between the maxillaryfirst molar and the mandibular second molar. The maxil-lary and mandibular arches were well aligned, and thedental midlines were aligned. However, the maxillaryarch was slightly skewed to obtain a normal overjet ofthe shifted mandible. The posttreatment facial photo-graphs showed an acceptable balanced profile, and thefacial asymmetry and the occlusal cant were improved(Fig 7).

The cephalometric analysis showed an increased SNBangle with a counterclockwise rotated mandible,whereas the SNA angle was 84.0�. The FMA was closedfrom 27� to 24.5�. The ANB angle decreased from 1�

to 0� (Figs 9 and 10; Table). The skeletal pattern wasnot corrected; however, the labially inclined maxillaryincisors and the lingually inclined mandibular incisorswere compensated. Both maxillary and mandibular mo-lars were intruded, and the anterior open bite and theend-to-end incisor relationship were corrected withautorotation of the mandible and no extrusion of themandibular incisors. The mandibular incisors were re-tracted; this contributed to correcting the anterioropen bite and obtaining a normal overjet.

On the posttreatment dental radiograph, the denselamina dura of the extracted first molar almost disap-peared, and no root resorption on the protracted secondmolar was observed (Fig 9, D). The posttreatment pano-ramic radiograph showed good root parallelism. All teethhad good alveolar bone height. The probing depths were2.0 to 3.0 mm around the mandibular right second andthird molars.

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Two years after treatment, the occlusion was wellmaintained (Figs 11-14). Comparison of theposttreatment and 2-year retention facial and oralphotos and the cephalometric superimposition showedonly minor dental changes (Fig 15; Table).

DISCUSSION

The typical treatment for facial asymmetry with ashifted mandible and a canted occlusal plane is surgicalrepositioning of the maxilla and the mandible to a morenormal relationship. However, this patient rejected thatoption, so I abandoned correcting the asymmetric facialappearance. The deviation of the dental midline and theanterior open bite were corrected orthodontically.

Previous reports have described the correction of pa-tients with implants to intrude the posterior teeth toallow the mandible to rotate upward and forward, thusreducing the anterior face height.12-14 Therefore, Itried to correct the canted occlusal plane withintrusion of the overerupted posterior teeth usingminiscrews. However, her asymmetric face could notbe corrected completely.

In this patient, the unilateral mandibular first molarwas extracted strategically to correct the mandibularmidline deviation and the right-side Class III molar rela-tionship. After 14 months of reciprocal traction of theanterior teeth and the second and third molars, the ante-rior crossbite was corrected. The canine relationshipbecame Class I, but the second and third molars did notmove mesially, and the edentulous space still remainedopen. The panoramic radiograph showed that the laminadura that surrounded the extracted mandibular molarsocket was still radiopaque, and the dense cortical boneof the lamina dura resisted mesial movement.

Orthodontic tooth movement resulted from the me-chanical force applied to the teeth that evokes cellularresponses in the teeth and their surrounding tissues,including the periodontal ligament, alveolar bone, andgingiva. In 1983, Frost10 demonstrated that regionalnoxious stimuli of sufficient magnitude can result in

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Fig 8. Posttreatment dental casts.

Fig 7. Posttreatment facial and intraoral photographs.

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Fig 10. Posttreatment cephalometric tracing.

Fig 9. Posttreatment radiographs.

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markedly accelerated reorganizing activity in theosseous and soft tissues. He termed this physiologichealing process the regional acceleratory phenomenon.It is characterized by a burst of the localized remodelingprocess, which accelerates healing, particularly after thesurgical wounding of cortical bone.

Recently, many clinical trials to accelerate toothmovement have been reported with a corticotomy afterflap opening.15-20 Germec et al19 showed that a single-sided partial corticotomy in the mandible appeared tobe sufficient to stimulate rapid tooth movement. Surgi-cal injury is a potentiating factor for the induction of theregional acceleratory phenomenon. For rapid canineretraction, Liou and Huang21 proposed periodontal lig-ament distraction. They initiated distraction just afterthe premolar extraction, so that their trials could bedone without discomfort and complications. When Idecided to use corticision, the mandibular molar hadalready been missing for 18 months. Therefore, I couldnot injure the alveolar bone without elevation of a flap.

Kim et al11 reported the new procedure, named “cor-ticision,” and it was performed to accelerate the toothmovement. This technique also produces the regionalacceleratory phenomenon. This method accelerated

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Fig 11. Two-years postretention facial and intraoral photographs.

Fig 12. Two-years postretention dental casts.

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Fig 13. Two-years postretention radiographs.

Fig 14. Two-years postretention cephalometric tracing.

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tooth movement, with a minimally invasive periortho-dontic procedure without flap elevation. In this casereport, I have tried to be clinically expedient with asound biologic foundation and to render the orthodon-tic outcome more stable and less prone to complications.

In the original technique of Kim et al,11 the cortici-sion was performed on the mesiobuccal, distobuccal,and distopalatal aspects of a maxillary canine for canineretraction. However, it was difficult to work around thetongue, so the surgical incision was limited only onthe buccal aspect. Also, the surgical blade could reachonly the mesial aspect of the second molar. Furthermore,removing the scalpel with a swing motion could not beperformed for fear of injuring the lips. However, a mesio-buccal surgical incision was enough stimulus for pro-traction of the mandibular second molar.

Previous reports stated that corticision can activatecatabolic remodeling in the direction of tooth movementwith less hyalinization and more rapid removal of hyali-nized tissues.11 On the dental radiograph of this patient2 months after the corticision, the cortical bone disap-peared. This might have been due to the same

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Fig 15. Superimposed cephalometric tracings before (black line) and after (red line) treatment, and 2years postretention (green line).

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undermining resorption. Kim et al11 monitored the cats'corticisions for only 28 days, but the effect of the accel-erated bone resorption continued for 2 months on thefollow-up dental radiographs.

In the original technique, it was suggested that thesurgical injury should be 2 mm from the papillarygingival margin to preserve the alveolar crest in thecat.11 My surgical injury was performed as deep aspossible. However, the patient's lips and buccal mucosawere obstacles for the incision in the mandibular molarregion. The width of the attached gingiva was not suffi-cient for the surgical blade, so the scalpel had to incisethe oral mucosa, resulting in considerable bleeding. Inaddition, the marks of the scalpel were observed onthe alveolar crest, but there was no alveolar bone lossnear the incisive area.

It has been reported that corticision accelerated theanabolic remodeling activity as well. On day 28, themean apposition area of the mineralized bone was3.5-fold higher in the corticision group.11 Surely, boneapposition on the tension side was observed on thedental radiograph at the follow-up evaluations. Nospace appeared in the extraction area with the assistanceof the fixed retainer.

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Before the partial corticision, the canine relationshipand the anterior incisor relationship were already cor-rected, so the edentulous space was closed entirely byprotraction of the second and third molars. Robertset al4,5 used endosseous implants placed in theretromolar area to close the missing first molar spacesby mesial movement of the mandibular molars.Furthermore, some articles have reported 10 mm ofmesial movement of the mandibular molars withminiscrews.7-9 Therefore, a miniscrew was placed atthe same time as the corticision. Four months afterinsertion, the miniscrew loosened and tipped distallytoward the second molar side, creating a spacebetween the canine and the first premolar.

There are many reports discussing the factors associ-ated with the stability of miniscrews.22-24 Miyawakiet al22 concluded that immediate loading was possibleif the applied force is less than 2 N. Owens et al23

concluded that the timing of force application did notinfluence the success rate of miniscrews, and peri-implant inflammation alone did not predispose mini-screws to failure.

However, Wu et al24 found that biomechanical stabil-ity and both maximum torque and maximum pullout

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load increased with healing time, but they increasedsignificantly only after 4 weeks. They also mentionedthat miniscrew healing is a continuous process, withweek 4 a critical time point. They recommended thatloading is safe after 4 weeks. They reported that even af-ter 1 week of healing, inflammatory cells, mainly macro-phages, were observed on the implant-bone interfaces.In my patient, the miniscrew was placed immediately af-ter the corticision; therefore, inflammation around thescrew from the corticision might have caused the screw'sfailure. I recommend that the miniscrew should beimplanted at least 4 weeks before the corticision.

The miniscrew was reinserted into an apical site inthicker buccal cortical bone. Deeper positioning of theminiscrew achieved mandibular molar intrusion duringthe protraction. Two additional miniscrews placedbuccally and palatally to the maxillary right first molarwere also effective for intrusion of the maxillary rightposterior segment and correction of the canted occlusalplane.

CONCLUSIONS

Corticision is effective for protracting mandibularsecond and third molars into the mandibular first molar'sedentulous space. The effect of the corticision continuedfor 2 months without tissue damage.

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10. Frost HM. The regional acceleratory phenomenon: a review. HenryFord Hosp Med J 1983;31:3-9.

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14. Mimura H. Treatment of severe bimaxillary protrusion with mini-screw anchorage: treatment and complications. Aust Orthod J2008;24:156-63.

15. Duker J. Experimental animal research into segmental alveolarmovement after corticotomy. J Maxillofac Surg 1975;3:31-4.

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20. Mostafa YA, Fayed MMS, Mehanni S, ElBokle NN, Heider AM.Comparison of corticotomy-facilitated vs standard tooth-movement techniques in dogs with miniscrews as anchor units.Am J Orthod Dentofacial Orthop 2009;136:570-7.

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