Control of maxillary dentition with 2 midpalatal ...buttons to provide a retraction force to the...

CLINICIAN'S CORNER

Control of maxillary dentition with 2 midpalatalorthodontic miniscrews

Yoon-Goo Kang,a Ji-Young Kim,b and Jong-Hyun Namc

Seoul, Korea

Fromsity, SaAssisbPostcAssisThe aor comReprinHospidong-Subm0889-Copyrdoi:10

The midpalatal area has no critical anatomic structures and has thick cortical bone. These conditions are favor-able for miniscrew implantation. Also, there is no concern that damaging a dental root in this area would causefailure of the miniscrew. Although these advantages can decrease the failure rate of miniscrews, midpalatalminiscrews have not been as popular as interdental miniscrews. Because the midpalatal area is far from theteeth, the utility of midpalatal miniscrews has been considered to be limited. This article describes a newmethodfor controlling the maxillary dentition with 2 midpalatal miniscrews. (Am J Orthod Dentofacial Orthop2011;140:879-85)

There is little controversy regarding whether tem-porary anchorage devices or skeletal anchoragedevices have widened and expanded the horizons

of orthodontic tooth movement limitations. Thepossibilities of an orthodontic regimen as a tool to solvedental and skeletal problems have expanded, andorthognathic surgery can even be minimized in certaincases.1,2

Miniscrews are the most popular and simplest type ofskeletal anchorage device with a simple procedure forimplantation and removal. They have a screw part thatis implanted into the bone and an upper part that is pro-jected into the oral space that can accommodate a varietyof orthodontic devices, including elastics and springs. Themost preferred site forminiscrew implantation is the inter-dental alveolar bone between the secondpremolar and thefirst molar because miniscrews are commonly used as an-chorage devices to retract the anterior teeth. In addition,this site is favored because of its ample interradicular spacefor miniscrew placement.3,4 However, many studies havereported that miniscrews implanted in the interdentalarea can fail for a variety of reasons, including root

the Department of Orthodontics, College of Dentistry, Kyung Hee Univer-eoul, Korea.stant professor.graduate student.tant professor.uthors have no commercial, proprietary, or financial interest in the productspanies described in this article.t requests to: Jong-Hyun Nam, Department of Orthodontics, Dentaltal, Kyung Hee University Hospital at Gangdong, 149 Sangil-dong, Gang-gu, Seoul, Korea; e-mail, [email protected], January 2010; revised and accepted, February 2010.5406/$36.00ight � 2011 by the American Association of Orthodontists..1016/j.ajodo.2010.02.040

proximity to the miniscrews.5-7 Root contact ofminiscrews is considered a main reason for their failurewhen placed in the interdental area.

Although many methods have been developed toprevent miniscrews from coming in contact with dentalroots, and to decrease the failure rate, these proceduresare either tedious or require specially designed equip-ment. In addition, for patients with congenitally narrowinterradicular spaces, touching the roots while implant-ing the miniscrews is sometimes unavoidable, andadditional procedures are needed.

To prevent root contact of miniscrews and decreasefailure rates, nondental bearing areas, such as the retro-molar area of the mandible and the midpalatal area ofthe maxilla, have been reported to be good sites forminiscrew implantation.8-12 These areas also havethick cortical bone that can reduce the failure rates ofminiscrews compared with miniscrews placed ininterradicular areas.8,12,13 However, the increasedsuccess rate has come at the cost of biomechanicalconvenience. Other mediating devices are requiredbecause these nondental bearing sites are far from theteeth that the clinician aims to move.

Several methodologies for miniscrews implanted inthe midpalatal area have been proposed, but more bio-mechanical considerations and methodologies areneeded to fully use midpalatal miniscrews to controlthe maxillary dentition.9,11 This article introducesa new method for controlling the maxillary dentitionwith 2 midpalatal miniscrews.

MATERIAL AND METHODS

Two miniscrews (DualTop JD, Jeil, Seoul, Korea) witha 0.215 3 0.250-in rectangular slot were used for each

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Fig 1. Miniscrew used in the patients reported in thisarticle.

880 Kang, Kim, and Nam

patient (Fig 1). Among the various sizes, 6-mm lengthand 1.60-mm diameter screws were used preferably.The rectangular slot can accommodate orthodonticarchwires up to 0.215 3 0.250 in. The implanted mini-screws are connected to a 0.2153 0.250-in rectangularstainless steel wire bent to fit the slots. Steel ligature tiesare needed to secure the wire to the miniscrews.

Two miniscrews were implanted in the midpalatalarea. The implant site was approximately 1 to 2 mmfrom the midpalatal suture transversely, and the antero-posterior position was determined according to thetreatment objectives. However, the position of the mini-screws is not of great importance because the force is notapplied directly to them but to the miniscrew-connecting wire. Even if the miniscrews are implantedin an unintended place, this can be overcome by adjust-ing the miniscrew-connecting wire. After a mucosaldisinfection treatment and the application of local anes-thestic, a mucosal incision was made with a number 15surgical blade. The bone surface was exposed witha small periosteal elevator, and a perforation of thecortical bone was made with a drill bur mounted ona low-speed hand piece (Fig 2, A). The miniscrew wasimplanted by using a low-speed contra-angle hand piece

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(Fig 2, B). Cortical perforation and miniscrew implanta-tion were performed under saline-solution irrigation.After most of the screw part implantation had beenachieved, the miniscrews were turned for a half to 1more turn to parallelize the slots (Fig 2, C and D).

After implanting the miniscrews, a rubber impressionwas taken by using a light-body injection-type vinyl pol-ysiloxane impression rubber material and a heavy-bodyputty vinyl polysiloxane impression rubber material.First, light-body rubber was injected over the miniscrewsand surrounding mucosa with care not to capture airbubbles (Fig 3, A). After initial polymerization of thelight-body rubber, heavy-body putty was applied overthe light-body putty covering more of the palatal muco-sal surface (Fig 3, B). After polymerization of the rubbermaterial, they were removed from the oral cavity andexamined carefully for any air bubbles captured in theminiscrew impressed area (Fig 3,C). Two additionalmini-screws were fitted to the miniscrew impressed area of theimpression body and secured with cyanide adhesive(Fig 3, D). These miniscrews were used as analogs forthe midpalatal miniscrews. The miniscrew-impressionbody complex was then placed in the bottom of a hollowopen cylinder, and mixed stone was poured on the com-plex (Fig 3, E and F). After the stone had hardened, thestone and impression body were separated, leaving theminiscrew analogs incorporated in the stone (Fig 3, G)This stone model and miniscrew analog complex isa precise replica of the palate and the miniscrews.

A 0.2153 0.250-in rectangular stainless steelwirewasbent to fit the 2 minscrew slots passively (Fig 3, H). Thiswire connects the 2 miniscrews tightly and enables themto withstand the moments created from an orthodonticforce thatmight loosen theminiscrews. This iswhy 2mini-screws are needed. The wire also works as a support whereorthodontic forces are applied or extended and come indirect contact with the dentition to exert the orthodonticforces. By adjusting the position of the wire, the forceapplication points can be optimized in various situationsof tooth movement without needing to relocate the screwposition. Clinical applications are described as follows.

For the intraoral delivery of the miniscrew connectingwire, the laboratory fabricated connecting wire is usuallywell fit to the intraoral real miniscrews. Mostly only mi-nor adjustments are needed to passively place the wire.However, if major adjustments are required, it mightbe better to repeat the laboratory procedure witha new rubber impression than to adjust the wire directlyin the intraoral space. After the connecting wire was pas-sively fit, its terminal ends of were generally bent to ob-tain a suitable position and shape to admit or exertorthodontic forces. The connecting wire was then se-cured to the miniscrews by tight wire ligation.

Journal of Orthodontics and Dentofacial Orthopedics

Fig 2. Miniscrew implantation procedure:A, cortical bone drilling;B,miniscrew implantation with a low-speed device;C, anotherminiscrew is implanted on the contralateral side;D, completion of implanting 2miniscrews, with the slots parallelized.

Kang, Kim, and Nam 881

To provide absolute anchorage for retraction of the 6anterior teeth (Fig 4), a miniscrew-connecting wire canbe fabricated to extend to the appropriate height accord-ing to the treatment objective (if bodily tooth movementis required, then height can be one third to two thirds ofthe root height) with the hooks bent distally. The 6anterior teeth were splinted to a large tooth witha figure-8 tie ligature wire, and lingual buttons werebonded to the palatal side of the canines. Coil springor elastomers were connected to the hooks and lingualbuttons to provide a retraction force to the anteriorteeth.

Distalization of the maxillary dentition was accom-plished (Fig 5). Bilateral or unilateral distalization ofthe maxillary molars or the whole maxillary dentitioncan be obtained by using these biomechanics. Normally,the molars are distalized first, followed by the premolarsand the anterior teeth. For bilateral distalization of themolars, a lingual arch with anterior hooks was used. Aminiscrew-connecting wire was extended to the appro-priate height with the distally opened hooks bent ateach end. The anterior hooks of the lingual arch andthe hooks of the connecting wire were connected witha coil spring or elastomers to provide a distalization forceto the molars. Another method is simply to connect theconnecting wire and lingual buttons bonded to thepalatal side of the premolars or the canines.

For unilateral distalization of the maxillary molar,a segment wire (usually 0.032 in) was inserted in the lin-gual sheath and extended anteriorly with a hook at its

American Journal of Orthodontics and Dentofacial Orthoped

end. The segment wire hook and the connecting wirehook were connected to a coil spring or an elastomerto exert a distalizing force on the maxillary molar.

Bilateral or unilateral mesial movement of the maxil-lary molar (Fig 6) is possible by using midpalatal mini-screws. The miniscrew-connecting wire was extended inthe occlusal direction to the appropriate height and thenextended anteriorly. For bilateral mesial movement ofthe molars, a transpalatal arch was placed and connectedto the hook of the miniscrew-connecting wire with a coilspring or an elastomer. As an alternative, segment wireswith a distally opened hook inserted in the lingual sheathof the molars can be used instead of a transpalatal archdepending on the clinical situation. For unilateral mesialmovement of a molar, a segment wire with a distallyopened hook was engaged in the lingual sheath of thecorresponding molar. The segment wire and miniscrew-connecting wire were connected to coil springs orelastomers to deliver a mesial force to the molar.

To intrude the maxillary molars (Fig 7), the transpa-latal arch was used to prevent palatal inclination of themolars. The miniscrew-connecting wire was extendedshortly to place the hooks in a deep position. A deepposition of the hooks ensures a long action range ofthe intrusion action components. These hooks and lin-gual sheathes of the molar bands were connected withsprings or elastomers to provide an intrusive force tothe molars.

Bilateral or unilateral expansion or constriction of themaxillary dentition (Fig 8) is frequently needed in daily

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Fig 3. Procedures for fabricating miniscrew-connecting wire: A and B, light-body followed by heavy-body rubber impression was taken; C, impression body with 2 miniscrew impressions; D, placementof theminiscrews in the impression body (cyanide adhesive can be used to immobilize theminiscrews);E, impression body placed in the bottom of the hollow cylinder; F, pouring stone in the cylinder;G, finalstone model with 2 miniscrew analogs; H, fabrication of passively fitting 0.215 3 0.250-in miniscrew-connecting wire.


orthodontic practice. Burstone’s precision lingual archbrackets, 0.215 3 0.250 in, with a rectangular slotwere welded to the palatal side of the first molar bands.A miniscrew connecting wire was fabricated and ligateddirectly to the lingual arch brackets with expansion orconstriction activation. For unilateral activation, 1 armof the miniscrew connecting wire was engaged to thelingual bracket with the other arm cut off. Loops or he-lixes can be added to increase the range of action anddecrease the magnitude of the force.


DISCUSSION

Two midpalatal screws with a connecting wire sys-tem are versatile. By modifying the connecting wire,which is removable, most of the required tooth move-ment can be achieved without additional miniscrewsor relocating them. Moreover, using 2 miniscrews andconnecting them provides good stability that can en-dure multiple forces at various directions with increasedamounts of force. Each miniscrew can resist force mo-ment of loosening direction on the other. Therefore, it is


Fig 5. Distalization of the maxillary molars: left, Lingual arch was used for bilateral distalization of themolars;middle, unilateral distalization of the maxillry molar; right, unilateral distalization of the maxillarymolar. A lingual arch with a swivel joint was used to minimize molar rotation.

Fig 4. Retraction of the anterior teeth. Height of the miniscrew-connecting wire hooks can bemodified.

Fig 6. Mesial movement of the maxillary molars: left, Bilateral mesial movement of the molars; right,unilateral movement of the molar.


possible to perform multidirectional tooth movementssimultaneously, such as intrusion and distalization.According to the features of this system, we called thesystem a midpalatal screw connected versatile device.The midpalate is a good place for miniscrew implanta-tion with few failures. We implanted more than 120miniscrews in midpalatal areas from 2006 to 2009,and none failed.

This method is not recommended for patients whoneed simple anterior retraction requiring absoluteanchorage because of the additional laboratory proce-dures. For those patients, conventional positioning ofminiscrews between the buccal sides of the secondpremolar and the first molar would be simple and


convenient for both the patient and the clinician. How-ever, this method is useful for complex cases requiringmolar control or the correction of 2 or more dimensionalproblems including the sagittal, transverse, and verticaldimensions. The midpalatal area is recommended forsuccessful miniscrew implantation in patients witha narrow interradicular space that cannot accommodateminiscrews and in those who have experienced failure ofminiscrews without an identifiable reason.

Interdental miniscrews can act as a mechanical inter-ference that limits adjacent tooth movement. Toothroots cannot move through miniscrews. Therefore,removal and replantation of miniscrews are required incertain cases. This aspect should be considered,


Fig 7. Intrusion of the maxillary posterior teeth. A transpalatal arch was used to prevent palatal tippingof the posterior teeth: left, intrusion with a slight distal vector; right, intrusion with a slight mesial vector.

Fig 8. Simultaneous bilateral expansion and intrusion of the maxillary posterior teeth: upper, initial sta-tus of narrow maxillary arch with anterior open bite; middle, intrusion and expansion activatedminiscrew-connecting wire was directly engaged into the lingual bracket of the maxillary first molars;lower, completion of maxillary posterior tooth control. Intrusion was obtained with closure of the anterioropen bite, and maxillary arch expansion was achieved simultaneously.


particularly when total distalization of the dentition isneeded. Sites for miniscrews should be carefully selectedto minimize root movement interference and the num-ber of replantation procedures. However, the midpalatalarea has no dental roots, and the limitation of toothmovement is not a matter of consideration.

Creative connecting wire designs other than the de-sign introduced in this article can be used to obtain


the required tooth movement in a range of clinical situ-ations. Loops or helixes also can be added to control theaction range and the force magnitude. For example, dis-talization of the molars can be achieved by directly en-gaging a distally activated miniscrew connecting wireto the lingual bracket welded to the palatal side of themolar bands. The loops can be added like the designof the pendulum appliance arm. The clinician’s



understanding of the biomechanical principles of toothmovement are applied to the design of the miniscrewconnecting wire, and a range of tooth movements invarious clinical situations can be achieved. By keepingthe palate plaster model with the miniscrew analogs,the clinician can promptly fabricate several designs ofminiscrew connecting wires with different tooth move-ment objectives. Therefore, various tooth movementsare possible without the need for additional miniscrewsor relocating them by only changing the design of theminiscrew connecting wire.

The most unique use of this system is unilateral ex-pansion or constriction of the maxillary dentition. Inconventional orthodontics, expansion and constrictionof the dental arch is usually obtained by using a transpa-latal or lingual arch. They produce good results for bilat-eral or unilateral expansion cases. Regardless how muchthe clinician deliberately controls the anchorage, un-wanted expansion or constriction of the contralateralpart of the dentition is generally inevitable with conven-tional orthodontic biomechanics. Absolute unilateralexpansion or constriction of the dental arch is possibleby using our method.

Occasionally, mucosal swelling occurs around thepalatal miniscrews, but the miniscrews still do not failin those circumstances. Swollen mucosa can be treatedwith dental laser eradication. We encountered 3 suchcases in 55 patients and reached the conclusion thatmucosal swelling is not a common condition and notserious. The mucosal swelling disappears when theminiscrews are removed in a month. In addition, themidpalatal area lacks critical anatomic structures, suchas large blood vessels and nerves, substantially reducingthe risk of damage during miniscrew implantationor removal. The incisive canal can be considereda dangerous structure. However, there is minimal riskwhen miniscrews are implanted distal to the first premo-lar because the incisive canal is mostly anterior to thefirst premolar.8

Sometimes, miniscrews are not placed at the samesagittal level, or the slots are not parallelized. Thesesituations need a more complicated wire-bending


procedure to fabricate the miniscrew connecting wirebut do not require replantation of miniscrews.

CONCLUSIONS

Two midpalatal miniscrews with a connecting wiresystem is a versatile method for controlling the maxillarydentition with a low failure rate.

REFERENCES

1. Ko DI, Lim SH, Kim KW. Treatment of occlusal plane canting usingminiscrew anchorage. World J Orthod 2006;7:269-78.

2. Lee HA, Park YC. Treatment and posttreatment changes followingintrusion of maxillary posterior teeth with miniscrew implants foropen bite correction. Korean J Orthod 2008;38:31-40.

3. Lee KJ, Joo E, Kim KD, Lee JS, Park YC, Yu HS. Computed tomo-graphic analysis of tooth-bearing alveolar bone for orthodonticminiscrew placement. Am J Orthod Dentofacial Orthop 2009;135:486-94.

4. Deguchi T, Nasu M, Murakami K, Yabuuchi T, Kamioka H,Takano-Yamamoto T. Quantitative evaluation of cortical bonethickness with computed tomographic scanning for orthodonticimplants. Am J Orthod Dentofacial Orthop 2006;129:721.e7-12.

5. Kang YG, Kim JY, Lee YJ, Chung KR, Park YG. Stability ofmini-screws invading the dental roots and their impact on the pa-radental tissues in beagles. Angle Orthod 2009;79:248-55.

6. Kuroda S, Yamada K, Deguchi T, Hashimoto T, Kyung HM,Takano-Yamamoto T. Root proximity is a major factor for screwfailure in orthodontic anchorage. Am J Orthod Dentofacial Orthop2007;131(Suppl):S68-73.

7. Moon CH, Lee DG, Lee HS, Im JS, Baek SH. Factors associated withthe success rate of orthodontic miniscrews placed in the upper andlower posterior buccal region. Angle Orthod 2008;78:101-6.

8. Kim SJ, Lim SH. Anatomic study of the incisive canal in relation tomidpalatal placement of mini-implant. Korean J Orthod 2009;39:146-58.

9. Kyung SH, Hong SG, Park YC. Distalization of maxillary molarswith a midpalatal miniscrew. J Clin Orthod 2003;37:22-6.

10. Kyung SH, Lee JY, Shin JW, Hong C, Dietz V, Gianelly AA. Distal-ization of the entire maxillary arch in an adult. Am J Orthod Den-tofacial Orthop 2009;135(Suppl):S123-32.

11. Lee JS, Kim DH, Park YC, Kyung SH, Kim TK. The efficient use ofmidpalatal miniscrew implants. Angle Orthod 2004;74:711-4.

12. Kyung SH. A study on the bone thickness of midpalatal suture areafor miniscrew insertion. Korean J Orthod 2004;34:63-70.

13. Kim HJ, Yun HS, Park HD, Kim DH, Park YC. Soft-tissue andcortical-bone thickness at orthodontic implant sites. Am J OrthodDentofacial Orthop 2006;130:177-82.


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