Orthodonties

Effect of protraction headgear on Class III malocclusionPeter Ngan* /Stephen H. Y Wei** /Urban Hagg*** /Cynthia K. Y Yiu**** / Daniel Merwin̂ '̂̂ '̂*̂ ^ / Brian Stickel̂ ^

Ten patients with skeletal Class HI malocclusion in the early mixed dentition who weretreated with maxillary expansion appliance and protraction headgear were comparedwith reasonably matched controls. Significant orthopedic effects were found after aslittle as 6 months of treatment. Cephalornetric analysis revealed that the correction ofClass III malocclusion was primarily a result of forward and downward movement ofthe maxilla and backward rolaUon of the mandible. The clinical result of one patienttreated with this appliance is used to demonstrate the importance of force magnitudesand directions, as well as the design of the appliance, to the success of the treatment.(Ouintessence lnt 1992:23:197-207.)

Introduction

Approximately 5% of the white population exhibitsskeletal Class III malocclusion,̂ "^ characterized byeither mandibular protrusion, maxillary retrusion, or acomhination of the two.^"" The incidenee has heen re-ported to be significantly higher in the Japanese,'"Scandinavian,'"* and Chinese'"* populations.

The treatment of Class III malocclusion dates to the1800s. Whereas '"psendo-Class III" malocclusion withforward mandibular displacement can sometimes becorrected using removable or fixed appliances, mostClass III malocclusions with underlying skeletal dis-crepancies require orthopedic intervention. Earlytreatment with chincap therapy has been shown bymany investigators to be effective ¡n treating develop-ing Class III malocclusions,'^""

* Associate Professor, Department of Orthodünlics. OhioStale University, College ot Dentislry, 305 West 12th Avenue.Columbtis, Ohio 43210,

*•• Professor and Head, Department of Children's Dentistryand Orthodontics, Faculty of Dentistry, university of HongKong, Prince Philip Dental Hospital, 34 Hospital Road,Hong Kong.

'•' Reader, Department of Children's Dentistry and Orthodon-tics, Faculty of Dentistry, University of Hong Kong.

•*•' Clinical Dental Surgeon. Department of Children's Dentis-try and Orthodonties. Faculty o( Dentistry. University ofHong Kong.

** Dental Studenl, Ohio State University.

However, many practitioners continue to avoid thistreatment modality. It is believed that developing man-dibular prognathism cannot be altered. The commonlyrecotnmended treatment for these patients at the endof the growth period is orthognathic surgery. More-over, clinicians are not always familiar with the avail-able orthopedic devices. Some of these appliances forClass III corrections can be uncomfotiahle, and thetreatment time is usually quite long. Consequently, thecooperation from these patients is poor.

In .lapan. where the incidence of Class III malocclu-sions is significantly higher, extraoral forces such aschincap therapy are often used in an attempt to cor-rect the developing skeletal Class III malocclusion.Researchers performing animal and clinical studies ofchincap treatment""^' have reported and confirmednumerous statistically significant changes in the cranio-facial complex, including a decrease in gonial andsella-nasion-point B angles, a decrease in mandibu-lar plane angle, and redirection in the downward verti-cal growth of the midface. However, a recent study bySugawara et al- has shown that Class III patientstreated early with ehineap therapy alone have latentcatch-up of mandibular displacement in a forward anddownward direction. The authors suggested that chin-cap therapy does not necessarily guarantee positivecorrection of skeletal profile after complete growth. Inaddition, this modality of treatment may not be suit-able for Class III malocclusion that is characterized bymaxillary retrusion. ̂ ''̂ ^

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Protraction headgear has been used to provide direct-ed, forward growth of the maxilla at an early age. Thisis particularly useful in treating patients with underde-velopment of the maxilla and/or overdevelopment ofthe mandible. The orthopedic force is used to protractthe maxilla, while the chincap, or mental anchorage,serves to redirect mandibular growth. The use of thisappliance was described more than 100 years ago,^''with other descriptions appearing early in this century,Tlie individual most responsible for reviving interest inthis technique is Delaire,"' Mote recently. Petit"'' mod-ified the basic concepts of Delaire by increasing theatuount of force generated by the appliance, thus de-creasing the overall treatment time. Several inves-tigators have demonstrated the dramatic skeletalchanges that can be obtained in animals with continu-ous protraction forces to the maxilla,"'*"'"' In thesestudies, not only was point A affected through forwardmovement of the incisors, but the entire maxilla wasdisplaced anteriorly, with significant effects as far pos-teriorly as the zygomaticotemporal suture.

Recently, McNamara" reported on two patients(aged 8 and 9) who received early orthopedic interven-tion for Class III malocclusions using protractionheadgear in combination with a rapid palatal expan-sion appliance. Two other patients (aged 7 and 9) weretreated by Turley,""̂ who used the same approach, ex-cept that the protraction headgear was individualized,or custom-made, for each patient to increase patientcomfort and compliance. Palatal expansion "disarticu-lates" the maxilla and initiates cellular response in thesutures, allowing a more positive reaction to protrac-tion forces,̂ ^

However, the sample size in each of those twostudies was small and without comparison to a controlgroup of patients; thus there seems to be a need toqnantify the changes in response to protraction head-gear and palatal expansion appliances. The objectiveof this prospective study was to investigate the dimen-sional changes that occur in specific areas of thecraniofacial complex in response to this treatmentmodality.

Method and materials

Treated sample

The sample consisted of ten patients who had askeletal Class III malocclusion and a retrusive maxillaas described in the section on diagnosis and treatmentplanning. All patients were treated with protractionheadgear and palatal expatision appliances by one of

the authors at Ohio State University, College of Den-tistry, All patients had tio history of any other cranio-facial anomalies and had not undergone prior orth-odontic treatment. There were three boys and sevengirls, ranging in age from 7 years 2 months to 10 years8 months (mean age of 8.06 years).

Control sample

A control sample, consisting of ten untreated Class IIIchildren obtained from Ohio State University and Uni-versity of Hong Kong Growth Studies, was used as acomparison group. These subjects were matched byage and sex to the treated sample.

Diagnosis and treatment planning

For diagnosis of Class III malocclusion in young pa-tients, cephalometric values can only provide the rela-tive contributions of skeletal and dental componentsto a malocclusion. Further, cephalometric values areoften unrehable in a young child, and neither jaw maybe identified as the obvious contributor to a Class HIcondition. Sue et al''' found that the determination ofstructural cause varied with different cephalometricanalyses. In addition, all mandibular cephalometricmeasurements must take into account the amount andthe direction of any retruded contact position-inter-cuspal position (RCP-ICP) mandibular shift on clo-sure.

Because of the variability of cephalometric analyses,other factors such as the overall facial profile, chinposition, maxillary position, and mandibular reposi-tioning were considered (Fig 1), Patients with (1) astraight or concave profile: (2) a protruded mandibleand retruded maxilla according to the method ofTur-ley"*"; and (3) a cephalometric analysis indicating aClass III skeletal pattern were included in the study.

Facial pattern considerations

Studies have shown that the direction of protractionforces can influence the repositioning of the maxillarycomplex,^' A horizontal protraction force can cause acounterclockwise rotation of the maxilla, resulting inan open bite. On the other hand, a downward forcecan produce almost translatory repositioning of thecomplex and its surrounding structure. These effectshave been demonstrated both in animal models"""*and humans,^'' Therefore, in treatment planning for aClass III patient with skeletal open bite or deep bite,the direction of protraction force shouid he taken intoaccount.

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Figs la to 1c Facial profile evaluation.

Fig la Profile is concave, suggesting maxillary retrusion. Fig 1b Blocking out lips focuses on chin to assess man-dibular prognathism.

Fig 1c Blocking out the chin and mandible focuses on themidface. Maxillary deficiency is indicated by straight verti-cal shadow from infraorbital margin, through alar base ofnose, to corner of mouth.

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Fig 2 Hyrax tapid palatal expansion appliance with bandsfitted on the maxillary pnmat̂ second molars and permanentfirst molars. An 0,045-inch wire is soldered bilaterally to thebuccal aspects of the molar bands and extended anteriorlyto the canine area for engagement to mtraoral elastics.

Fig 3 Face mask with adjustable anterior wire and hooksto accommodate a downward and forward pull to themaxilla with mtraoral elastics.

Objectives of treatment

The primary objective of the treatment was to correctthe Class III molar occlusion to a Class I occlusion,correct atiy crossbites, if present, and improve theskeletal profile of the patient. Once these objectiveswere met, a second phase of treatment with fixedappliances was to be undertaken if indicated.

Appliances and treatment procedures

The Hyrax rapid palatal expansion appliance was con-structed by using bands on the posterior teeth. Bandswere fitted on the maxillary primary second molarsand permanent first molars (Fig 2), These bands werejoined by a heavy wire (0.045-inch) to the palatalplate, which had a jack screw in the midline. Theappliance was activated twice daily (0,25 mm per ttirn)hy the patient for 1 week. In patients with a con-stricted maxilla, activation of the expansion screw wasapplied for 2 weeks. An 0,ü45-inch wire was solderedbilaterally to the buccal aspects of the molar hands,and extended anteriorly to the canine area. In addi-tion, a lingual wire could be soldered to the premolarband and extended TO the cingulum of the maxillaryincisors to increase anchorage control if needed.

The face mask was a one-piece construction with ad-justable anterior wire and hooks to accomodate adownward and forward pull of the maxilla with elastics(Fig 3), To avoid an opening of the bite as the maxillawas rotated, the protraction elastics were attachednear the maxillary canines with a downward and for-ward pull of 45 degrees to the occiusal plane. Attach-ment of elastics from the soldered buccal wire to thehooks on the face mask ran across the lip to the otherside to avoid irritation around the commissure of thehps.

Orthopedic effects require greater forces than doorthodontic movements, Maxiiiary sutural protractiongenerally requires 600 to 800 g per side, depending onthe patient. Elastics that delivered between 14 and 18oz of force (as measured by a gauge) were used, Pa-tietits were instructed to wear the headgear 12 to 16hours a day to obtain maximal skeletal effect, but min-imal tooth movement,

Cephalometric analysis

Lateral cephalograms taken before and at the comple-tion of this phase of treatment were used. All cephalc-grams were taken with the teeth in occlusion (centricocclusion) and the hps in a relaxed position to standard-ize soft tissue posture and morphology. The amountof RCP-ICP mandibular shift on closure were noted,A lateral cephalogram was taken with the patient's jawwide open, to help in locating the position of condyl-ion, to obtain an accurate measurement of condylarlength (Co-Gn) as reference, Cephalogram landmarkidentifications and constructed lines were establishedas shown in Figs 4 and 5, Cephalograms were digitizednsing a Texas Itistrumcnt digitizer, and all analyses

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Rg 4 Cephalometric landmarks, constructed lines, atid di-gitized points used: (S) sella; (N) nasion; {Co) condyiion; (Ar)articulare; {PNS] posterior nasal spine; {ANS) anterior nasalspine; {A) point A; (Go) gonion; (B) point B; (SHP) seiia-nasion perpendicular; {Pg) pogonion; {Grt) gnathion; {Me)menton.

Fig 5 Deiermjnation of changes in {A) horizontal positionof maxillary molar and centrai inoisor; {B) vertioai positionof maxillary molar and central incisor; {C) horizontai posi-tion of mandibular molar and central incisor; {D) verticaiposition of mandibuiar moiar and central incisor.

were performed on an IBM PC using OlicephOrthodontic Software (OLI Inc).

The size of the combined method error (ME) inlocating, superimposing, and measuring the changes inthe different landmarks was calculated by the formula

ME = Kd-/2nwhere d is the difference (mm) between two registra-tions of a pair and n is the number of double registra-tions. Before- and after-treatment cephalograms fromten randomly chosen subjects were traced and super-imposed with measurements recorded on two differentoccasions. The combined ME did not exceed 0.6 mmfor any variable investigated.

Statistical analysis

Comparisons of starting forms in the control andtreated groups as well as the serial changes observedbetween these two groups were analyzed using a two-sample t test. The a priori level of statistical signifi-cance was set at .05.

Equivalence of starting forms

Before serial changes observed iti the treatment group

were compared with those in the controls for the sameage range, the starting forms of the two groups werecompared. There were no statistically significant differ-ences in any maxillary mandibuiar, horizontal, or ver-tical measurements between the treated and controlgroups (Table I). However, since the sample sizeswere small, with large variances, some differences be-tween the two starting groups may not have beenstatistically supported.

Results

Cephalometric effects

The 6-month cephalometric changes in both the con-trol group and the experimental group treated withprotraction headgear and palatal expansion appliancesare shown in Table 2, For maxillary skeletal relation-ships, the treatment induced a forward movement ofpoint A by 0.81 mm, while the control group exhibitedbackward movement (hy 0.76 mm; P < .01). Similarresults were found when point A was meai,ured withreference to nasion perpendicular.

For maxillary dentai relationships, maxillary molars

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Table 1 Starting forms in control and headgear groups

Control Experimental

Mean SD Mean SD Í Sig

ANBO

Mä xilla rv skeletalSNA(°)Nasion perp

to pt A (mm)

Max molarhorizont (mm)

Max molarvert (mm)

Max incisorhorizont (mm)

Max incisorvert (mm)

Incisor angle* (")

Co-Gn C)SNB C)SN-Pg(=)Ar-Go-Gn H

79.33.0

48.6

18.9

11.1

25.4

104.7

106,880.080,1

130.1

2,81,9

4.5

2.3

4.6

2.5

8.7

4.82.21,92.4

77,64.4

Maxillary dental50,3

18.7

78.9

23.6

104.1

Man dib ular skele tal110.078.179.5

131.9

SN-ANS C)ANS-Me C)Co-Go nMandibular plane

angle"* (°)Occlusal plane

anglet (°)Palatal plane

angle^ (°)SN-Me C)

NS = not significant.

• Maxillary centralincisor/SN.' Go-Ma/SN,• Occlusal plane/SN.^ ANS-PNS/SN.

49.461.648.737.4

21.6

9.2

107.8

2.93.93.92.8

6.0

2.5

6.2

Maxilloma nd¡bular reía tiotiship-0.7 1.5 -1.3

Vertica I relation ship50.360.949.435.0

18.9

9,3

108,1

3.73.3

4.3

1.8

4.2

4.0

9.9

4.03.23.54,4

3.1

2.76.33.96.1

5.0

3.2

5.7

1.10 NS-1.08 NS

0.84

0,19

0.84

1,17

0.14

1.501,400.511.09

0.54

0.710.270.431.05

1,11

0.13

0.13

NS

NS

NS

NS

NS

NSNSNSNS

NS

NSNSNSNS

NS

NS

NS

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Table 2 Change in measurements after 6 months of treatment

Control Experimental

SNA C)N as ion perp

toptA(mm)

Max molarhorizont (mm)

Max molarvert (mm)

Max incisorhorizont (nun)

Max incisorvert (mm)

Incisor angle^ {°)

Co-GnC)SNB (")SN-PgOAr-Go-Gn (")

Mean

-0.760.46

-0.68

0,98

-0.06

0.80

0.92

1,97-0.26-0.23-0.14

SD

0,730,66

1,77

1.13

2,04

2,58

2,25

Mean

Maxilla ryuke letal0.81

-0,51

Maxillary dental0,56

1.31

1.7S

1.25

0.27

Mandibular skeletal1.430,750,671,59

2.65-0.86-0.70-0,16

SD

0.881,00

0,97

1,32

1.65

2,24

3,31

1,200,880.901,03

t

-4,182.57

-1,91

-0,58

-2.16

-0,40

0,48

-1,131,581.270,04

Sif

*

NS

NS

NS

NS

NSNSNSNS

Maxillom andi bular rela tion ship-0.58 0,67 1,64

Ve rtica I rela tionship

0.84 -6.26

SN-ANS (-)ANS-Me (°)Co-Go {")Mandibtilar plane

angle Í (°)Occlusal plane

angle* (°)Palatal plane

angle* (°)SN-Me C)

NS = not significant.

• P<.a5. •• P<.01,^ Maxillary central incisor/SN,• Go-Me/SN,^ Occlusal plare/SN.• ANS-PNS/St^,

0.970.771.61

- 0 , H

-0.93

0.90

1,62

0,751,341.241.14

2.66

1,04

0,84

1,422.741.971.16

-0.60

-0,02

3,35

1,041.890,921,38

1,71

1,35

2,10

-1.07 NS-2.59 *-0,73 NS-2,17 *

-0.32 NS

1,64 NS

-2,30 *

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Fig 7 Pretreatment cephalometric radiograph of the samepatient reveals a Class IN malocciusion caused by maxiliarydeficiency and mandibular prognaihism.

Fig 6 (left) An 8-year-old patient with a straight profile anda slightly prognathic mandible.

in the treated sample were found to move forward by0,56 mm while in the control group they moved back-ward by 0.68 mm. Maxillary incisors were found tomove forward 1.78 mm in the experimental group, butbackward in the control group (by 0.06 mm; P < .05).No changes in incisai inclination were observed.

For mandibular skeletal relationships, no statisti-cally .significant changes were observed either in thelength of the mandible (Co-Gn) or the position ofpoint B or pogonion when the treated group was com-pared with the control group. However, the maxill-omandibular relationship (ANB) was significantly dif-ferent from that of the control group (P < .01). Inaddition, vertical changes, as measured by anteriornasal spine-menton, mandibular plane, and sella-nasion-menton, were all found to be significantly dif-ferent between the treatment and control groups. Theocclusal and palatal plane angles, as measured fromSN, were found to increase as compared to controlgroup, but the increase was not statistically significant.

Clinical effects

Clinically, in most cases, a Class f molar occlusion wasobtained within 6 months of the start of treatment. Theclinical results of one patient treated with protractionheadgear and palatal expansion appliance are used toillustrate the treatment effects of the appliance.

Case analysis

Figures 6 and 7 show an 8-year-old patient who pre-sented with a Class III malocciusion with a combina-tion of deficient maxilla and prognathic mandible.Clinically, the patient exhibited a bilateral Class Ilfmolar occlusion, anterior crossbite involving all fourincisors, and bilateral posterior crossbite (Figs 8 and9). On closure, the patient presented with a l-mmanterior shift and a l-mm lateral shift to the right,Cephalometric analysis showed a Class III maxil-lomandibular relationship with a point A-nasion-pointB angle of —2 degrees (norm of +2 degrees) and Witsanalysis of —4 mm (norm of 0 mm). Both sella-na-sion-point A (77 degrees compared to a norm of 80 de-grees) and nasion perpendicular to point A (-4 mmcompared to a norm oiO to —1 mm) showed that themaxilla was retrusive. The inclination ofthe maxillaryincisors was normal (114 degrees to Frankfurt horizon-tal; the norm is 114.4 degrees). The mandibular in-cisors were slightly proclined (99 degrees to mandibularplane; the norm is 90 degrees).

Figures 10 and 11 show the same patient after palatalexpansion followed by 6 months of protraction head-gear therapy. The posttreatment record revealed a cor-rection of Class III molar occlusion to a Class I re-lationship with concomitant corrections of anteriorand posterior crossbites (Figs 12 and 13). Superimposi-tion of the pretreatment and po.st treat ment cephalo-

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Fig 8 Anterior view of the same patient's pretreatmentstudy cast reveals anterior crossbite involving all four of theincisors and bilateral posterior crossbite.

Fig 9 Laterai view of the same patient's pretreatmentstudy cast reveáis Class III molar and canine relationships.

Fig 11 Pcsttreatment cephalometric radiograph of thesame patient reveáis a Ciass I skeletal relationship.

Fig 10 ¡tett) Posttreatment profiie of the patient.

HP

Fig 12 Posttreatment anterior intraoral view of the samepatient reveals the correction of anterior and posteriorcrossbites.

Fig 13 Posftreatment lateral intraoral view of the samepatient reveals the correction to Ciass I molar and caninerelationships.

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Pretreatment2-90

Fig 14 Superimposition of the pretreatment and posttreat-ment cephalometric radiographs reveals an increase in for-ward and downward movement of the maxilla and back-ward and downward rotation of the mandible.

metric radiographs showed a forward and downwardmovement of the maxilla with downward and backwardrotation of the mandihle (Fig 14).

Discussion

These results demonstrate that significant changes inthe craniofacial complex can be expected from maxil-lary expansion followed by protraction headgear treat-ment for as little as 6 months. Midfacial orthopedicexpansion has been shown to be beneficial in the treat-ment of certain Class HI malocclusions. Haas^-''̂ '̂"has demonstrated that rapid palatal expansion can pro-duce a slight forward movement of point A and aslight downward and forward movement of the maxiila.In addition, the maxilla articulates with nine otherbones of the craniofacial complex; frontal, nasal, lacri-mal, ethmoid, palatine, vomer, zygoma, inferior nasalconcha, opposite maxilla, and, occasionally, sphenoid.Palatal expansion will "disarticulate" the maxilla artdinitiate ceUular response in the sutures, allowing amore positive reaction to protraction forces. Anotheradvantage of maxillary expansion is the correction ofthe posterior crossbite that often accompanies a ClassIII malocclusion because of deficient transverse maxil-lary growth and the abnormal anteroposterior relation-ship of maxilla to mandible. Lastly, a palatal expan-

sion appliance splints the maxillary dentition duringprotraction and helps transmit force from the teeth tothe maxilla, thus limiting unwanted tooth movement,

Cephalometric analysis of the data revealed that theeffects of treatment vary among different parts of thecraniofacial complex. The treatment enhanced for-ward and downward movement of the maxilla, asnoted by movement of point A and anterior nasalspine. This direction of movement is desirable forClass III correction and is a result of applying protrac-tion forces from a more anterior part of the maxillarydentition. Posteriorly directed forces have been shownto cause the deleterious effect of upward and forwardrotation of the nasal floor in maxillary protraction.''The importance of force direction has been demonstrat-ed hy Nanda'*-'" in the craniofacial structure ofMacaca mulatta monkeys.

The treatment also induced a forward movement ofthe maxillary molars and incisors with little change inthe incisai angle. However, the effect of the applianceon forward tipping of the incisors may be masked bythe downward and forward rotation of the maxilla, asdemonstrated by the increase in palatal and occlusalplane with reference to the cranial base (SN).

In the mandible, no significant change was observedin the length of the mandible (Co-Gn), indicating that6 months of treatment had no inhibitory growth effecton the mandible, Pogonion and point B were movedbackward. However, these changes were not signifi-cant when compared to control group. Hence, redirec-tion of mandibular growth cannot be substantiated bythese data. Similar results have been reported byothers with maxillary protracting appliance alone.'"'There were also no significant changes in the gonialangle, which has been reported by others using chin-cap therapy.'''"-" Analysis of vertical changes showedan increase in mandibular plane angle, anterior facialheight, and occlusai and palatal plane angles, whichindicates a downward and backward rotation of themandible as a result of the movement of the maxilla.

Summary

This was a prospective study on the effect of maxillaryexpansion followed by protraction headgear therapyon growing patients with Class III malocclusions. Thistreatment modality was indicated for Class TTI patientswho deniotistrated primarily maxillary deficiency asdetermined in a comprehensive diagnostic evaluation.

The findings of this study indicated that significantskeletal changes can be expected with as little as 6

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months of treatment with the appliances. The correc-tion of Class III malocclusion was primarily due to for-ward and downward movement of the maxilla withdownward and backward rotation of the mandible.

Data from this study should be interpreted cautiouslyhecause (I) the cephalometric radiographs were takenin centric occlusion and the amount or direction ofmandibular functional shift on closure will influencethe data: (2) the sample size in this study was relativelysmall, and only the largest of trends were shown to besignificant. Future sttidies should include a larger sam-ple of patients as well as long-term followup to revealthe stability of this treatment modahty with furthergrowth.

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