use of rhythmic wire system with miniscrews to correct occlusal … · be corrected by skeletal...

CLINICIAN’S CORNER

Use of rhythmic wire system with miniscrews tocorrect occlusal-plane canting

Yoon-Goo Kang,a Jong-Hyun Nam,b and Young-Guk Parkc

Seoul, Korea

Occlusal-plane canting is a challenging problem for orthodontists because it cannot be solved easily withoutsurgical intervention. Normally, a LeFort I osteotomy and concomitant mandibular surgery is used to correctthe problem, even in patients with mild facial asymmetry but with noticeable occlusal-plane canting. Skeletalanchorage can be used in patients with occlusal canting to reduce the need for orthognathic surgery. Thepurpose of this article was to introduce a biomechanical system—rhythmic wire— to correct occlusal-planecanting. The records of 2 patients treated with this system are shown. (Am J Orthod Dentofacial Orthop2010;137:540-7)

The cant of the occlusal plane in the frontal planecan be the result of skeletal asymmetry of thejaw bones or the asymmetric vertical position

of anterior or posterior teeth. Before the advent ofskeletal anchorage in orthodontics, the correction ofocclusal-plane canting had only limited indications,whether the origin was skeletal or dental. Therefore,surgery was considered the only method for correctingthis problem.1 However, skeletal anchorage has madepossible true intrusion of molars, which was difficultwith conventional orthodontic means.2-8 Moreover, itis now possible to correct occlusal-plane canting bycontrolling the vertical position of the molars.9,10

It was reported that all people have some craniofa-cial asymmetry, even in esthetically normal or pleasingfaces.11-13 In addition, an occlusal cant in most normalpatients might be too small to detect.14,15 Padwa et al15

reported that 4� is the threshold for recognizing an oc-clusal cant. However, they measured occlusal-planecanting from a horizontal line connecting the supraor-bital rim. In our experience, patients often recognizetheir occlusal canting as being unpleasant estheticallywhen there is a discrepancy in parallelism between thelip line and the occlusal plane. In some patients with

From the Department of Orthodontics, College of Dentistry, Kyunghee Univer-

sity, Seoul, Korea.aClinical assistant professor.bAssistant professor.cProfessor and chairman.

The authors report no commerical, financial, or proprietary interest in the

products or companies described in this article.

Reprint requests to: Young-Guk Park, Department of Orthodontics, Kyunghee

University, #1 Hoegidong, Dongdaemungu, Seoul, Korea; e-mail, ygpark@

khu.ac.kr.

Submitted, January 2008; revised and accepted, April 2008.

0889-5406/$36.00

Copyright � 2010 by the American Association of Orthodontists.

doi:10.1016/j.ajodo.2008.04.032

540

vertical asymmetry of the right and left posterior teethwithout anterior occlusal-plane canting, the occlusalcanting becomes obvious after orthodontic leveling. Fa-cial asymmetry that is too minimal for orthognathic sur-gery but accompanies recognizable occlusal canting canbe corrected by skeletal anchorage-reinforced ortho-dontic treatment. However, few biomechanical systemsuse skeletal anchorage to correct occlusal canting.

We developed a biomechanical system called‘‘rhythmic wire,’’ which consists of 2 miniscrews (onthe maxillary and mandibular teeth), intrusion wire, ex-trusion wire, transpalatal arch, and lingual arch. This re-port presents the use of this method in 2 patients forcorrecting the occlusal cant to avoid or minimizeorthognathic surgery.

RHYTHMIC WIRE

Rhythmic wire was initially developed to control thevertical position of the posterior teeth and consists of in-trusion rhythmic wire and corresponding extrusionrhythmic wire. In addition, a transpalatal arch or a lin-gual arch can be applied if there is a need to controlthe third-order torque of posterior teeth that face an in-trusion or extrusion force.16 Rhythmic wire can also bea good option for patients with palatally or lingually tip-ped posterior teeth because buccal tipping of the teethcan occur without a transpalatal or lingual arch.

The intrusion wire is formed with 0.019 3 0.025-inbeta-titanium alloy straight wire of appropriate length(usually the length between the first premolar and thesecond molar) with hooks on each end for engagementto the main archwire (Fig 1). If a decrease in the intru-sion force is required, the size of wire can be reduced,or helices can be included. There is no consensus onthe optimal force for the intrusion of teeth, but there

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Fig 1. Intrusion rhythmic wire: upper, schematicdiagram of the intrusion rhythmic wire; lower, afterplacement.

Fig 2. Extrusion rhythmic wire: upper, schematicdiagram of the extrusion rhythmic wire; lower, afterplacement.

American Journal of Orthodontics and Dentofacial Orthopedics Kang, Nam, and Park 541Volume 137, Number 4

appears to be some accord between researchers that pos-terior teeth require more force than anterior teeth. Kalraet al16 used 90 g of force per posterior tooth, Park et al6

suggested 150 to 200 g, Umemori et al7 recommended500 g, and Melsen and Fiorelli8 used 50 g buccolinguallyper posterior tooth. The intrusion wire is placed on thevestibular side of the miniscrew, which is generallyplaced between the second premolar and the first molar,and each end is activated to engage the main archwire(Fig 1). The point where the hooks of the intrusion rhyth-mic wire engage depend on the clinical need; this meansthat the clinician can choose the site to apply the forceand change the site by adjusting the intrusion wire with-out replacing the miniscrew. The miniscrew should havean undercut in its head design to place the intrusion wire,and an elastomeric ring can be used to secure the intru-sion wire to the miniscrew.

The extrusion rhythmic wire, which is placed on theopposite dentition, is made from stainless steel wire (orcobalt-chromium wire with heat treatment) in a clover-like form (Fig 2). An indentation is prepared on the tophalf circle (vestibular side) to accept the miniscrewhead, and each root (occlusal side) has a hook for attach-ment to the main archwire. Figure 2 shows its configu-ration and activation. Activation is achieved bymanipulation of the horizontal loops. A smaller forcethan for intrusion is sufficient for extrusion of the teeth.However, to prevent deformation of the wire, its sizeshould be greater than 0.016 in, and stainless steelwire is recommended. Helices or loops can be addedto reduce the force (Fig 3). The intrusion and extrusionrhythmic wires should be used simultaneously to main-tain the integrity of the occlusal contacts. In addition,the position of the hooks is determined by the clinicalsituation.

The extrusion or intrusion of molars from the buccalside can cause buccal or lingual crown tipping, which is

generally undesirable. To minimize this tipping, a trans-palatal or lingual arch can be applied with a rectangularlingual sheath to the active (extrusion or intrusion) side,and a round sheath can be applied to the other side, asdescribed by Rebellato.17 Also, full alignment, leveling,and space consolidation are recommended before ap-plying a rhythmic wire, and the main archwire shouldbe rectangular stainless steel for more predictable andeasy control of the posterior quadrant.

PATIENT 1

A 20-year-old woman was referred from a local den-tal clinic complaining of masticatory problems on theleft side. The intraoral features showed moderatecrowding of her maxillary dentition, an anterior edge-to-edge bite, and a posterior crossbite on the left side(Fig 4). The occlusal relationship was Class II molarand Class I canine on her right side, and Class III molarand canine on her left side (Fig 4). Her maxillary rightposterior teeth were positioned vertically low comparedwith the left side (Fig 4). After reviewing her condition,she was diagnosed with skeletal Class III facial asym-metry and a canted posterior occlusal plane.

Her skeletal problems were mild, and she did not re-quire facial changes. She refused surgery and also de-clined treatment accompanying the extraction of herpremolars. The treatment plan was established to distal-ize the maxillary right posterior and mandibular left

Fig 3. Modifications of the rhythmic wire: left, a helix was included in the intrusion wire to reduce theforce; right, loops were added to the extrusion wire to reduce the force.

Fig 4. Patient 1: upper row, pretreatment study model. Note the difference in the vertical heights ofthe molars between the left and right sides; middle and lower rows, application of the rhythmic wiresystem.

542 Kang, Nam, and Park American Journal of Orthodontics and Dentofacial Orthopedics

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posterior teeth with miniscrews to resolve the crowdingand correct the occlusal relationships with rhythmicwire.

After distalization of the molars, aligning and level-ing were performed. The leveling procedure unmaskedthe posterior occlusal canting and showed an apparent

difference in the gingivae between the left and rightsides while smiling (Fig 5). It was decided to intrudethe maxillary right posterior teeth because of the exces-sive gingival display on the right side. Miniscrews wereplaced between the maxillary right second premolar andmolar, and between the mandibular right second

Fig 5. Smile photos of patient 1. From left, pretreatment, midtreatment, and after debonding. Occlu-sal canting occurred at midtreatment and was corrected.

Fig 6. Pretreatment and posttreatment cephalograms and superimposed tracings of patient 1: blackline, pretreatment; red line, posttreatment. The difference in vertical height of the molars was reducedmainly by intrusion without remarkable changes in the mandibular position.


premolar and molar. An intrusion rhythmic wire wasplaced on the maxillary right posterior teeth, and an ex-trusion wire was placed on the mandibular right poste-rior teeth. In addition, a transpalatal arch and a lingualarch with a rectangular lingual sheath were applied onthe right side, and a round sheath was used on the leftto control the inclination of the teeth.

The occlusal cant was corrected by the intrusion ofthe maxillary right posterior teeth. Finishing and detail-ing of the occlusion was then performed, and the in-truded maxillary right posterior teeth were maintainedwith wire ligation to the miniscrew. After removingthe appliances, a canine-to-canine lingual bonded re-tainer was placed in the maxilla, and a wraparound re-tainer was used for the mandible. Superimposition of

pretreatment and posttreatment lateral cephalogmsshowed reductions of the difference in vertical heightof the right and left molars (Fig 6).

Distalization of the molars and leveling took 15months, correction of the occlusal cant with rhythmicwires took 9 months, and finishing took 4 months. Over-all, the total active treatment period was 28 months.

PATIENT 2

A 22-year-old woman visited the orthodontic depart-ment of Kyunghee University complaining of crowdingof her maxillary teeth and protrusion of her lips. The in-traoral examination showed maxillary and mandibularanterior crowding, and the facial examination showed

Fig 7. Patient 2: upper row, pretreatment study model; middle and lower rows, application of therhythmic wire system.


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a canted occlusal plane with asymmetric elevation of theright and left corners of the mouth during smiling thatexaggerated the occlusal canting (Figs 7 and 8). Thetreatment plan was to extract the first premolars to re-solve the crowding and lip protrusion and to apply rhyth-mic wire to correct the occlusal canting.

After the conventional aligning and leveling, and clo-sure of the extraction site with retraction of the anteriorteeth, rhythmic wire was applied to the right side of herdentition. The application side was determined by theamount of gingiva showing. Her occlusal canting was cor-rected after 4 months of rhythmic wire application. Aswith patient 1, a canine-to-canine lingual bonded retainerwas placed on the mandibular dentition, and a wraparoundretainer was used for the maxillary dentition. The totaltreatment duration was 18 months, which included 12months for aligning, leveling, and anterior retraction; 4months for correcting the canting; and 2 months for detail-

ing. Superimposition of pretreatment and posttreatmentlateral cephalograms showed reduction of the differencein vertical height of right and left molars (Fig 9).

DISCUSSION

There are many reports of intrusion of the molars;many focus on only 1 molar. Other reports on the intru-sion of more than 2 or 3 teeth required more than 1 mini-screw or used miniplates. Our method required only 1miniscrew to intrude 1 quadrant of the dentition, therebyavoiding or reducing the economic and psychologicstress to the patient from the placement of severalminiscrews.

The system introduced here was called rhythmicwire because of the smooth curvature of the intrusionwire and the subsequent change in curvature as intrusionproceeds; this is reminiscent of rhythm. The advantages

Fig 8. Smile photos of patient 2. From left, pretreatment, midtreatment, and after rhythmic wireapplication. Occlusal canting before treatment was corrected.

Fig 9. Pretreatment and posttreatment cephalograms and superimposed tracings of patient 2: blackline, pretreatment; red line, posttreatment. The difference in vertical height of the molars was reducedafter treatment.


of this system are the minimal need for miniscrewsand the continuous constant force it exerts. The forcedecreases as the intrusion proceeds, but, unlike elastics,the force does not change rapidly. Because of thisadvantage, patients can have longer times between ap-pointments. In addition, it is said that a light continuousand constant force is advantageous for the intrusion ofteeth.18 The drawbacks of this method are that consider-able handwork is required, and patients can feel discom-fort from the transpalatal arches. Fabricating anintrusion wire is quite simple, and an extrusion wiremight appear complicated but becomes simple after a lit-tle practice. Placing 4 components (intrusion wire, ex-trusion wire, transpalatal arch, and lingual arch) at the

same time takes considerable chair time, but, after place-ment, chair time is fairly short because the only neces-sary thing is to check the wires. Prefabrication of thewires is recommended to shorten the first chair time.

Instead of an extrusion rhythmic wire, up-and-downelastics can be adopted to maintain the integrity of theocclusal contact. However, elastics rely on the patient’scooperation and can interrupt the intrusion if they areconnected to teeth planned to be intruded. In addition,elastics can be engaged as a miniscrew to a tooth, butthis method can cause a sagittal force vector unlessseveral screws are placed.

There can be vertical asymmetry of tooth positionsbetween the right and left quadrants without apparent


April 2010

facial asymmetry. The most common cause of verticaltooth position asymmetry is when unilateral posteriorteeth are lost; this causes overeruption of their opposingteeth. Even when all teeth are present, there still can bea vertical asymmetric tooth position caused by a dentaldevelopmental disorder (eg, prolonged retention orearly loss of deciduous teeth or delayed eruption of per-manent teeth) or functional problems. Patient 1 hadovererupted maxillary right posterior teeth, and the con-ventional leveling procedure made the occlusal cantingapparent on the anterior teeth.

The process of determining which quadrant can beintruded or extruded is associated with dental esthetics.Maxillary incisor exposure in the lip-rest position andgingival and maxillary incisor exposure while smilingshould be considered. It was suggested that 3 to 5 mmof maxillary incisor exposure in the lip-rest positionand three quarters of incisor length to 2 mm of gingivalexposure during smiling are esthetically pleasing.19

This guideline can be a good aid for determining the ex-tent of extrusion or intrusion. The patients presentedhere were believed to have excessive gingival exposureon the right side while smiling, and treatment wasdirected to intrude the maxillary right posterior teeth.

The importance of the smile arc, and the relationshipof the curvature of the incisal edges of the maxillary in-cisors and canines with the curvature of the lower lip inthe posed smile in esthetics have been noted.20 A rhyth-mic arch on both the right and left sides can be consideredif there is a flat or steep occlusal plane and the smile arc isnot consistent with the lower lip line. The occlusal planecan be changed without apparent changes in jaw position.However, the effect of occlusal-plane inclination to oc-clusion should also be considered. Braun and Legan21 re-ported an approximately 0.5-mm change in the occlusalrelationship for each degree of occlusal-plane rotation.

Several studies on the effect of molar intrusion on thedental and paradental tissues have been reported. Kan-zaki et al22 investigated the remodeling of the alveolarbone crest when several teeth were intruded simulta-neously. Their results showed that alveolar bone crest re-sorption and remodeling occurs with tooth intrusion.They concluded that bone remodeling prevented deepen-ing of the gingival pockets. In addition, Sugawara et al23

reported that no pseudopockets were observed aftermandibular molar intrusion. Daimaruya et al24 carriedout an animal study on the effect of molar intrusion onthe nasal floor and tooth roots. They achieved 4.2 mmof intrusion after 7 months. Histology showed a thinlayer of newly formed bone covering the intranasallyprojected root without serious pathologic changes inthe pulp of the tooth. However, there was moderateroot resorption. Umemori et al7 reported open-bite

patients who had been corrected by intrusion of themandibular molars with skeletal anchorage. Theyachieved 3 to 5 mm of intrusion without serious side ef-fects. According to the above-mentioned studies, molarintrusion is a safe tooth movement and can be a good al-ternative to orthognathic surgery for the impaction ofmolars. Nevertheless, there are some limitations withthis modality because of root resorption during molarimpaction.

CONCLUSIONS

Rhythmic wire is a valuable method for the correc-tion of occlusal canting. This procedure makes it possi-ble to avoid orthognathic surgery in patients withocclusal-plane canting. However, further studies areneeded to verify the stability and functional aspect ofthe achieved occlusal canting correction.

REFERENCES

1. Burstone CJ. Diagnosis and treatment planning of patients with

asymmetries. Semin Orthod 1998;4:153-64.

2. Bae SM, Kyung HM. Mandibular molar intrusion with miniscrew

anchorage. J Clin Orthod 2006;40:107-8.

3. Park HS, Jang BK, Kyung HM. Maxillary molar intrusion with

micro-implant anchorage (MIA). Aust Orthod J 2005;21:129-35.

4. Lee JS, Kim DH, Park YC, Kyung SH, Kim TK. The efficient

use of midpalatal miniscrew implants. Angle Orthod 2004;74:

711-4.

5. Kuroda S, Katayama A, Takano-Yamamoto T. Severe anterior

open-bite case treated using titanium screw anchorage. Angle

Orthod 2004;74:558-67.

6. Park YC, Lee SY, Kim DH, Jee SH. Intrusion of posterior teeth

using mini-screw implants. Am J Orthod Dentofacial Orthop

2003;123:690-4.

7. Umemori M, Sugawara J, Mitani H, Nagasaka H, Kawamura H.

Skeletal anchorage system for open-bite correction. Am J Orthod

Dentofacial Orthop 1999;115:166-74.

8. Melsen B, Fiorelli G. Upper molar intrusion. J Clin Orthod 1996;

30:91-6.

9. Ko DI, Lim SH, Kim KW. Treatment of occlusal plane canting

using miniscrew anchorage. World J Orthod 2006;7:269-78.

10. Jeon YJ, Kim YH, Son WS, Hans MG. Correction of a canted oc-

clusal plane with miniscrews in a patient with facial asymmetry.

Am J Orthod Dentofacial Orthop 2006;130:244-52.

11. Erickson KL, Bell WH, Goldsmith DH. Analytical model surgery.

In: Bell WH, editor. Modern practice of orthognathic and recon-

structive surgery. Philadelphia: Saunders; 1992. p. 156.

12. Shah SM, Joshi MR. An assessment of asymmetry in the normal

craniofacial complex. Angle Orthod 1978;48:141-8.

13. Peck S, Peck L, Kataja M. Skeletal asymmetry in esthetically

pleasing faces. Angle Orthod 1991;61:43-8.

14. Ferrario VF, Sforza C, Miani A Jr, Serrao G. Craniofacial mor-

phometry by photographic evaluations. Am J Orthod Dentofacial

Orthop 1993;103:327.

15. Padwa BL, Kaiser MO, Kaban LB. Occlusal cant in the frontal

plane as a reflection of facial asymmetry. J Oral Maxillofac

Surg 1997;55:811-6.


16. Kalra V, Burstone CJ, Nanda R. Effects of a fixed magnetic appli-

ance on the dentofacial complex. Am J Orthod Dentofacial

Orthop 1989;95:467-78.

17. Rebellato J. Two-couple orthodontic appliance systems: transpa-

latal arches. Semin Orthod 1995;1:44-54.

18. Burstone CJ. Biomechanics of deep overbite correction. Semin

Orthod 2001;7:26-33.

19. Arnett GW, McLaughlin RP. Facial and dental planning for ortho-

dontists and oral surgeons. St Louis: Mosby; 2004. p. 51-63.

20. Sarver DM. The importance of incisor positioning in the esthetic

smile: the smile arc. Am J Orthod Dentofacial Orthop 2001;120:

98-111.

21. Braun S, Legan HL. Changes in occlusion related to the cant of the

occlusal plane. Am J Orthod Dentofacial Orthop 1997;111:184-8.

22. Kanzaki R, Daimaruya T, Takahashi I, Mitani H, Sugawara J.

Remodeling of alveolar bone crest after molar intrusion with

skeletal anchorage system in dogs. Am J Orthod Dentofacial

Orthop 2007;131:343-51.

23. Sugawara J, Baik UB, Umemori M, Takahashi I, Nagasaka H,

Kawamura H, et al. Treatment and posttreatment dentoalveo-

lar changes following intrusion of mandibular molars with ap-

plication of a skeletal anchorage system (SAS) for open bite

correction. Int J Adult Orthod Orthognath Surg 2002;17:

243-53.

24. Daimaruya T, Takahashi I, Nagasaka H, Umemori M, Sugawara J,

Mitani H. Effects of maxillary molar intrusion on the nasal floor

and tooth root using the skeletal anchorage system in dogs. Angle

Orthod 2003;73:158-66.

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