Class II Correction

800Angle Orthodontist, Vol 74, No 6, 2004

Original Article

The Mechanism of Class II Correction in Surgical OrthodonticTreatment of Adult Class II, Division 1 Malocclusions

Hans Pancherz, DDS, Odont Dra; Sabine Ruf, DDS, Dr Med Dentb; Christina Erbe DDSc;Ken Hansen, DDS, Odont Drd

Abstract: The purpose of this investigation was to assess the dentoskeletal effects and facial profilechanges as well as the mechanism of Class II correction in adult Class II subjects treated by surgicalmandibular advancement in combination with orthodontics. The subject material comprised 46 adults witha Class II, division 1 malocclusion treated by nonextraction with a mandibular sagittal split osteotomy aswell as with pre- and postsurgical multibracket appliances. Lateral head films from before treatment andafter treatment were analyzed. The results revealed the following statistically significant (P , .001) treat-ment changes: (1) the mandibular prognathism enhanced; (2) the sagittal interjaw base relationship im-proved; (3) the mandibular plane angle increased; (4) the lower anterior facial height increased; (5) thelower posterior facial height decreased; (6) the facial profile straightened; (7) the overjet and Class II molarrelationship were corrected. Overjet reduction was accomplished by 63% skeletal and 37% dental changes.The Class II molar correction was accomplished by 81% skeletal 19% dental changes. In conclusion, itcan be said that mandibular sagittal split osteotomy in combination with pre- and postsurgical orthodonticsis an effective and consistent method for the correction of Class II, division 1 malocclusions and for thestraightening of the facial profile. A negative effect of treatment counteracting Class II correction is anincrease in the mandibular plane angle. (Angle Orthod 2004;74:800809.)

Key Words: Sagittal mandibular split osteotomy; Orthodontics; Treatment effects; Facial profile

INTRODUCTION

In the literature, a large number of surgical mandibularadvancement procedures have been described for the ther-apy of skeletal Class II malocclusions with mandibular de-ficiency.1 However, the current standard method is the ret-romolar mandibular sagittal split osteotomy introducedoriginally by Schloessmann in 1922.2 The most frequentlyused modifications of this method are those of Obwegeser3and Dal Pont4 and of Hunsuck5 and Epker.6

Many studies have been performed evaluating the ske-letofacial changes occurring during surgicalorthodontic

a Professor and Head, Department of Orthodontics, University ofGiessen, Giessen, Germany.

b Professor and Head, Department of Orthodontics, University ofBerne, Berne, Switzerland.

c Assistant Professor, Department of Orthodontics, University ofGiessen, Giessen, Germany.

d Associate Professor, Department of Orthodontics, University ofGothenburg, Gothenburg, Sweden.

Corresponding author: Hans Pancherz, DDS, Odont Dr, Depart-ment of Orthodontics, University of Giessen, Schlangenzahl 14, Gies-sen, D-35392, Germany(e-mail: [email protected]).Accepted: November 2003. Submitted: October 2003.q 2004 by The EH Angle Education and Research Foundation, Inc.

treatment of Class II malocclusions.712 However, no studyhas ever addressed the relative contribution of the skeletaland dental components involved in the changes of the sag-ittal occlusion.

Therefore, the purpose of this investigation was to ana-lyze the effects of a sagittal split osteotomy in combinationwith pre- and postsurgical orthodontics on the facial hardand soft tissue structures in adult Class II, division 1 mal-occlusions.

METHODS AND MATERIALSThe subject material in this study comprised 46 (38 fe-

males and eight males) adult Class II, division 1 malocclu-sions treated surgically; exclusively by a mandibular ret-romolar sagittal split osteotomy. For the tooth alignmentpre- and postsurgery fixed (multibracket) appliances wereused for different periods of time. The mean pretreatmentage of the subjects was 26 years (SD 8.1 years). The youn-gest subject (a female) was 16 years old (skeletal maturitystage R-J according to Hagg and Taranger,13 indicating thatgrowth was completed). Total treatment time (surgery pluspre- and postsurgical orthodontics) for the 46 subjectsamounted to an average of 1.7 years (SD 0.7 years).

Twenty-three of the 46 subjects were treated at the Or-thognathic Surgery Department in Malmo, Sweden, using

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801SURGICAL CLASS II TREATMENT

Angle Orthodontist, Vol 74, No 6, 2004

FIGURE 1. Reference points and lines used in the standard ceph-alometric analysis.

FIGURE 2. SO-Analysis. The OL/OLp reference grid and the mea-suring landmarks are shown.

the Hunsuck5 and Epker6 sagittal split osteotomy. The other23 subjects were treated at the Orthognathic Surgery Clinicin Minden, Germany, with the Obwegeser3 and Dal Pont4procedure.

Lateral head films in habitual (centric) occlusion frombefore treatment and after all treatments (which means fromafter postsurgical orthodontics) were analyzed. All registra-tions were performed twice, and the mean value of the du-plicate registrations was used in the final evaluation. Nocorrection was made for linear enlargement (approximately8% in the median plane for both the Swedish and Germanhead films).

Standard cephalometrics

Changes of sagittal and vertical jaw base relationship,overbite, facial height, facial profile convexity, and lip po-sition were assessed using standard variables. The cepha-lometric landmarks used are shown in Figure 1.

SO-Analysis

The SO-Analysis of Pancherz14 was used for the assess-ment of sagittal occlusal changes (Figure 2).

Individual changes

For the assessment of the clinical significance of indi-vidual changes only those exceeding 60.5 mm, 60.58 or60.5 Index values were considered.

Statistical methodsFor the different variables, the arithmetic mean (Mean)

and standard deviation were calculated. Students t-test forpaired samples was used to assess the significance of treat-ment changes. The statistical significance was determinedon the confidence levels of 0.1%, 1%, and 5%. A confi-dence level larger than 5% was considered not significant(NS).

RESULTSNo differences in pre- and posttreatment cephalometric

records existed when comparing the 23 subjects treated inSweden and the 23 subjects treated in Germany. Therefore,the two subject samples were pooled in the presentation ofthe results. Furthermore, no sex differentiation was madebecause only eight of the 46 subjects (17%) were males.

Standard cephalometricsThe standard cephalometrics in 46 adult subjects are

shown in Table 1.Sagittal jaw relation. The surgical mandibular advance-

ment resulted in a significant (P , .001) increase in theangles SNB (mean 2.128) and SNPg (mean 1.608). Therewas a significant (P , .001) reduction in the angles ANB(mean 2.418), ANPg (mean 1.898), and in the Wits (mean4.11 mm). Considering clinical significant individualchanges, there was an increase of the SNPg angle in 78%(36 of 46) and a reduction of the ANPg angle in 89% (41of 46) of the subjects (Figures 3 and 4, respectively).

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802 PANCHERZ, RUF, ERBE, HANSEN


TABLE 1. Standard Cephalometrics in 46 Adult Subjects Treated by Orthognathic Surgery (Mandibular Sagittal Split) in Combination withPre- and Postsurgical Orthodontics

Variable

SurgeryBefore

Mean SDAfter

Mean SD

Treatment changesAfter 2 before

Mean SD tSagittal jaw relation

SNA (8)SNB (8)SNPg (8)ANB (8)ANPg (8)Wits (mm)

81.4175.3777.086.044.334.72

4.013.393.752.753.463.01

81.1277.4978.683.622.440.61

3.893.413.802.733.193.36

20.292.121.60

22.4121.8924.11

1.131.311.311.291.331.90

21.72 NSa10.98***8.25***

212.71***29.59***

214.64***Vertical jaw relation

ML/NSL (8)NL/NSL (8)ML/NL (8)

30.088.77

21.31

7.822.917.34

33.418.39

25.02

7.863.577.78

3.3320.38

3.71

2.481.732.63

9.12***21.47 NS

9.54***Incisor relation

Overbite (mm) 4.23 2.84 2.16 0.94 22.06 2.56 25.43***Facial height

Spa-Gn 3 100/N-Gn (index)Spp-Go9 3 100/S-Go9 (index)

54.8446.89

2.344.89

56.1144.88

2.585.64

1.2722.01

0.922.51

9.36***25.43***

Profile convexityNAPg (8)NS/Sn/PgS (8)NS/No/PgS (8)

170.87158.12121.35

7.336.714.22

175.32163.57124.55

6.796.714.50

4.455.453.20

2.803.372.67

10.78***10.97***8.12***

Lip positionULE-line (mm)bLLE-line (mm)b

22.5521.67

2.843.27

25.0522.79

2.873.38

22.4921.12

1.742.33

29.73***23.26*

a NS indicates P . .05 (not signifigant).b UL indicates upper lip; LL indicates lower lip.* P , .05*** P , .001

FIGURE 3. SNPg angle (sagittal mandibular position). Individual treatment changes in 46 adult subjects treated by orthognathic surgery(mandibular sagittal split) in combination with pre- and postsurgical orthodontics.

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FIGURE 4. ANPg angle (sagittal interjaw base relationship). Individual treatment changes in 46 adult subjects treated by orthognathic surgery(mandibular sagittal split) in combination with pre- and postsurgical orthodontics.

FIGURE 5. ML/NSL angle (mandibular plane angle). Individual treatment changes in 46 adult subjects treated by orthognathic surgery (man-dibular sagittal split) in combination with pre- and postsurgical orthodontics.

Vertical jaw relation. The mandibular plane angle (ML/NSL) and interjaw base angle (ML/NL) were increased sig-nificantly (P , .001) by an average of 3.338 and 3.718,respectively. With respect to clinical significant individualchanges, the ML/NSL was increased in 89% (41 of 46) ofthe subjects (Figure 5).

Facial height. The lower anterior facial height was, onaverage, increased by an Index value of 1.27 (P , .001),whereas the lower posterior facial height was reduced byan Index value of 2.01 (P , .001). Considering clinicalsignificant individual changes, lower anterior facial heightwas increased in 80% (37 of 46) and lower posterior facialheight was reduced in 72% (37 of 46) of the subjects (Fig-ures 6 and 7, respectively).

Profile convexity. The convexity of the hard and soft tis-sue facial profiles were significantly (P , .001) reduced.The average reduction in the hard tissue profile convexity

(NAPg) was 4.458, in the soft tissue profile excluding thenose (NS/SN/PgS) 5.458, and in the soft tissue profile in-cluding the nose (Ns/No/PgS) 3.208. With respect to clinicalsignificant individual changes, the straightening of the hardtissue profile occurred in 91% (42 of 46), the soft tissueprofile excluding the nose in 98% (45 of 46), and of thesoft tissue profile including the nose in 76% (35 of 46) ofthe subjects (Figures 810, respectively).

Lip position. The upper (UL) and lower (LL) lips becamesignificantly more retrusive in relation to the Esthetic (E)line of Ricketts.15 Average changes were: for UL, 2.49 mm(P , .001) and for LL, 1.12 mm (P , .05).

SO-Analysis

The results of SO-Analysis are shown in Figures 11 and12 and Table 2.

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FIGURE 6. Spa-Gn 3 100/N-Gn (lower anterior facial height index). Individual treatment changes in 46 adult subjects treated by orthognathicsurgery (mandibular sagittal split) in combination with pre- and postsurgical orthodontics.

FIGURE 7. Spp-Go9 3 100/S-Go9 (lower posterior facial height index). Individual treatment changes in 46 adult subjects treated by orthognathicsurgery (mandibular sagittal split) in combination with pre- and postsurgical orthodontics.

Mechanism of overjet correction. The overjet was, onaverage, reduced by 6.31 mm. This was accomplished by63% skeletal and 37% dental changes. When consideringclinical significant individual changes, overjet reductionwas achieved in 98% (45 of 46) of the subjects (Figure 13).

Mechanism of class II molar correction. The sagittal mo-lar relation was, on average, improved by 5 mm. This wasaccomplished by 81% skeletal and 19% dental changes.With respect to clinical significant individual changes, themolar relation was improved in 96% (44 of 46) of the sub-jects (Figure 14).

A clinically significant individual mandibular base (Pg/OLp) advancement was seen in 89% (41 of 46) of the sub-jects (Figure 15).

DISCUSSIONIn the literature, there is general agreement that one of

the main reasons for adult Class II subjects seeking treat-ment are dental and facial esthetics.1618 The more dissat-isfied the patients are with their facial appearance, the morelikely they will choose a surgical instead of an orthodonticapproach.19,20

No difference in the outcome of treatment was foundwhen comparing the Swedish sample in which the Hun-suck5 and Epker6 method was used with the German sampletreated by the surgical procedure according to Obwegeser3and Dal Pont.4 This was somewhat surprising because thetwo surgical approaches differed in terms of the preserva-tion (Hunsuck and Epker procedure) and the nonpreserva-

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FIGURE 8. NAPg angle (hard tissue profile convexity). Individual treatment changes in 46 adult subjects treated by orthognathic surgery(mandibular sagittal split) in combination with pre- and postsurgical orthodontics.

FIGURE 9. NS/Sn/PgS angle (soft tissue profile convexity excluding the nose). Individual treatment changes in 46 adult subjects treated byorthognathic surgery (mandibular sagittal split) in combination with pre- and postsurgical orthodontics.

tion (Obwegeser or Dal Pont) of the chewing muscle at-tachments at the proximal mandibular bone fragments. Itwould, namely, have been expected that the more the ele-vator muscles are detached during surgery, the more theremodeling of the gonial area and the shortening of ramusheight will occur.

In accordance with earlier studies in adult orthodonticand orthognathic subjects,7,9,10,21,22 there was an overrepre-sentation of females. This might be associated with the ob-servation that women are more interested in their facialappearance than men.23

An interesting finding in the present subjects was theincrease in anterior facial height and the decrease in pos-terior facial height. These changes were also reflected inthe increase of the mandibular plane angle (ML/NSL), anobservation which has been described earlier.7 As the man-

dibular plane angle and the anterior as well as the posteriorfacial heights were, on average, normal pretreatment,24 theobserved changes counteract the mandible coming forward,which is one of the goals in surgical Class II treatment.Furthermore, an increase in the mandibular plane anglewould be disadvantageous in especially those Class II sub-jects with an increased anterior facial height pretreatment.

The increase in the anterior facial height was most likelydue to the bite rising effect in conjunction with the surgicalmandibular advancement procedure. The reduction of theposterior facial height could be explained by the bone re-modeling processes at Gonion taking place after mandibularsurgery. Possible causes discussed are an inadequate over-lap between the two bony fragments,25,26 the postsurgicaladaptive processes of the soft tissues, tendons, and musclesthat have been directly or indirectly affected by the surgical

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FIGURE 10. NS/No/PgS angle (soft tissue profile convexity including the nose). Individual treatment changes in 46 adult subjects treated byorthognathic surgery (mandibular sagittal split) in combination with pre- and postsurgical orthodontics.

FIGURE 11. Mechanism of overjet correction in 46 adult subjectstreated by orthognathic surgery (mandibular sagittal split) in combi-nation with pre- and postsurgical orthodontics.

FIGURE 12. Mechanism of Class II molar correction in 46 adult sub-jects treated by orthognathic surgery (mandibular sagittal split) incombination with pre- and postsurgical orthodontics.

procedure and the jaw displacement.8,11,27,28 Finally, the pos-sibility of a condylar resorption can not be excluded as acause for the lower posterior facial height reduction. Sucha resorption has been reported to occur rather frequently inorthognathic surgery subjects8,22 and especially in thosewith a pretreatment derangement of the TMJ.29

In the present Class II subjects, the surgical advancementof the mandible and thereby also of the chin resulted in astraightening of the hard and soft tissue profiles, which isone of the main treatment objectives in Class II subjectswith a convex facial profile. However, by a mandibular ad-vancement, the distances of the UL and LL to the E-linewill increase.30 Such a retrusion of the lips in relation to

the E-line may result in a disadvantageous older appearenceof the face.

In the therapy of the present Class II subjects, surgicalorthodontic treatment was most successful. When consid-ering individual cases, overjet was reduced in 98% and sag-ittal molar relationship was improved in 96% of the sub-jects. Furthermore, both standard cephalometrics and theSO-Analysis demonstrated that the Class II correction wasaccomplished mainly by skeletal changes. Mandibular ad-vancement contributed 63% to overjet correction and 81%to Class II molar correction. All dental changes seen werecertainly a result of both the multibracket appliance treat-ment and the postsurgical dental compensation of the skel-etal relapse.31

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TABLE 2. The Mechanism of Class II Correction (SO-analysis) in 46 Adult Class II, Division 1 Subjects Treated by Orthognathic Surgery(Mandibular Sagittal Split) in Combination with Pre- and Postsurgical Orthodontics

Variable (mm)

SurgeryBefore

Mean SDAfter

Mean SD

Treatment changesAfter 2 before

Mean SD tOverjet Is/OLpIi/OLpMolar relationa Ms/OLpMi/OLpMaxillary base A/OLpMandibular base Pg/OLp

9.6911.77a78.8977.67

2.681.974.805.54

3.3823.23a78.8981.72

1.133.004.805.97

26.3125.00

04.05

2.463.1302.49

217.40***210.84***

0 NSb11.03***

Maxillary incisor Is/OLpMandibular incisor Ii/OLpMaxillary molar Ms/OLpMandibular molar Mi/OLp

88.3678.6656.3754.60

5.115.415.515.95

86.9983.6157.0660.29

5.595.815.716.65

Maxillary incisor Is/OLp(D)A/OLp(D)Mandibular incisor Ii/OLp(D)Pg/OLp(D)Maxillary molar Ms/OLp(D)A/OLp(D)Mandibular molar Mi/OLp(D)Pg/OLp(D)

21.360.900.691.64

2.212.361.992.02

4.17***2.56**2.35*5.51***

a Plus (1) implies Class II molar relation; minus (2) implies Class I molar relation.b NS, P . .05.* P , .05.** P , .01.*** P , .001.

FIGURE 13. Overjet. Individual treatment changes in 46 adult subjects treated by orthognathic surgery (mandibular sagittal split) in combinationwith pre- and postsurgical orthodontics.

In adult skeletal Class II treatment, two alternatives tosurgery are possible, either camouflage orthodontics withthe extractions of maxillary teeth9,32 or dentofacial ortho-pedics using the Herbst appliance.3338 However, in cam-ouflage orthodontics, only the main symptom of the ClassII malocclusion (the large overjet) is dealt with whereas thebasic mandibular and facial esthetic problems remain. Onthe other hand, in adult Herbst treatment, the mandibularand esthetic problems are attacked and also solved, al-though to a lesser extent as compared with mandibular sur-gery (S. Ruf and H. Pancherz; in preparation). When choos-ing between the different treatment options of surgery,Herbst, or camouflage, one should not forget the costs and

risks11,12,3941 involved, which are clearly larger with the sur-gical approach.

CONCLUSIONS

Mandibular sagittal split osteotomy in combination withpre- and postsurgical orthodontics is an efficient approachin the therapy of adult Class II, division 1 malocclusions.Sagittal occlusal malrelationships are corrected and thehard- and soft tissue profiles straightened in a consistentway. A negative effect of treatment counteracting Class IIcorrection is an increase in the mandibular plane angle.Such an angular increase would also be a disadvantage,

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FIGURE 14. Molar relation. Individual treatment changes in 46 adult subjects treated by orthognathic surgery (mandibular sagittal split) incombination with pre- and postsurgical orthodontics.

FIGURE 15. Pg/OLp (sagittal mandibular position). Individual treatment changes in 46 adult subjects treated by orthognathic surgery (mandib-ular sagittal split) in combination with pre- and postsurgical orthodontics.

especially in those Class II subjects with a pretreatmentincreased anterior facial height.

ACKNOWLEDGMENTSThe authors want to express appreciation to Dr. Hansen (Sweden)

and Dr. Witschel (Germany) for making available the head film sam-ples from the two countries.

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Class II Correction