Orthodontics

Treatment of Class II open bite in the mixed dentition with a removablefunctional appliance and headgearPeter Ngan* / Stephen Wilson"' "̂ / Michael Florman '̂ '̂ '•" I Stephen H, Y. Wei* * * *

Early diagno.ús of patients exhibiting open bites that are complicated by skeletal Class ¡Iand vertical growth problems can facilitale subsequent treatment. Eight patients withClass 11 skeletal open bite were treated with the high-pull activator appliance andcompared to reasonably matched controls to determine the effects of the appliance.The high-pull activator was found to reduce forward growth of the maxilla andincrease mandibular alveolar height, transforming the Class II molar relationship intoa Class ! molar relationship. The overjet atid open bite were decreased, and, inaddition, the appliance reduced the amount of forward and downward movement ofthe maxillary molars, providing vertical control of the maxilla during Class II ortho-pedic correction. These results demonstrated that open bite complicated by a Class 11vertical growth pattern can be treated during the mixed dentition with favorable resultsby a combination of a removable functional appliance and high-pull headgear,(Quintessence Int 1992,-23:323-333.)

Introduction

Anterior open bite is defined as the absence of con-tact between the maxillary and mandibular incisors atcentric relation,' In youuger children, il can be causedby one factor or a combination of factors, includingfinger- and lip-sucking habits: enlarged tonsils oradenoids that interfere with proper tongue position,creating mouth breathing, a constricted maxilla, and askeletal open bite growth pattern; mouth breathing as-sociated with allergies and inadequate nasal breathmg;abnormal tongue habits with tongue thrust and cheekbiting: macrogiossia: or abnormal tongue position.

Associate Professor, Department of Orthodontics, OhioStateUniversity, College of Dentistry, 305 West I2tli Avenue,Columbus, Ohio432tÜ,Assistant Professor. Department "i Pediatric Dentistry,Ohio State University,Dental Student, Ohio State University.Professor and Head, Department of Children's Dentistry andOrthodontics. University of Hong Kong, Prince Philip DentalHospital, 34 Hospital Road. Hong Kong,

A dental open bite is one that is limited to the an-terior region in an individual with good facial propor-tions," Current orthodontic treatment often consists offabrication of a habit appliance such as a tongue re-strainer, evaluation for airway insufficieucy, and place-ment of fixed orthodontic appliances if needed. How-ever, it is rare that a patient who requests orthodonticcare has an anterior open bite that is solely the resultof a habit. Dental changes are frequently complicatedby a Class II skeletal growth pattern with vertical and/or transverse complications.

The hallmarks of skeletal anterior open bite are in-creased anterior facial height, a steep mandibularplane, and excessive eruption of posterior teeth. Be-cause the mandible is rotated downward and hackwardin this circumstance, the patient is likely to have aClass II jaw relationship in addition to the verticalproblem.

One approach to the treatment of skeletal open biteis to control all subsequent growth so that the mandiblewill rotate in a counterelockwise direction, upwardand forward. Successful early treatment of these prob-lems in the mixed dentition ean prevent the worsening

Quintessence International Volume 23, Number 5/1992 323

Orthodontics

of the facial profile. The elimination of anterior openbite can also improve tongue function and lip seal.Recent research has shown that tongue thrust swallowis more often ati adaptation to the open bite than acause of it.̂ Myofunctional therapy for tongue thrust-ing in skeletal Class II open bite patients is. for thatreason, ineffectual and not recommended.

This paper discusses the use of high-pull headgearand functional appliances to maintain the verticalposition of the maxilla and inhibit eruption of themaxillary posterior teeth during the mixed dentitionperiod. Cephalometric analysis was used to evaluatethe skeletal and dental adaptations to this treatmentmodality. Because the general dentist is often the firstlo diagnose anterior open bite in the child piitient, theclinician's awareness of the differences between dentaland skeletal open bite and the proper timing for inter-cepting these malocclusions will facihtate subsequentorthodontic treatment.

Rationale for appliance selection

Effect of functional appliances

Functional appliances, such as activators, have beenused to treat Class II, division 1, patients who presentwith a retrognathic mandible. Functional appliancesreportedly alter a Class II relationship through trans-mission of muscular force to the dentition and alveolus,thereby positioning the mandible anterior to its maloc-clnded position. Additionally, they are often designedto alter the amount and direction of tooth eruption, in-fluencing the horizontal and vertical positions of theteeth. The use of simulated functional appliance therapyin animal models has been found to induce increasedcellular activity in the mandibular eondyle.''"' presum-ably leading to altered mandibular form and length.Harvold* and Harvold and Vargervick,' however,

. found no evidence of increased mandibular growth inpatients treated with activator therapy, but ratherreported, as a primary effect, a selective influence onthe occlusal development of the dentition. In anotherstudy, it was reported that vertical maxillary growthwas restrained during activator therapy by the hinderederuption of the maxillary posterior teeth.'"

Effect offiinctional appliances in combination with high-pull headgear

High-pull headgear has heen used with the aim ofprodueing intrusion and posterior displacement ofmaxillary molars with backward maxillary rotation.

producing a backward and upward displacement at themaxillary sutures." The orthopedic concept of using acombination of activator and headgear appliances wasintroduced hy Hasund.'- Pfeiffer and Grobety''' re-fined the combined orthopedic concept further to bettercope with the demands of differential diagnosis. Theychose the use of a eervicai headgear to extrude maxil-lary molars and to apply orthopedic traction to themaxilla and an activator to induce orthopedic man-dibular changes, restrain maxillary growth, and causeselective eruption of teeth. Levin'** reported theskeletal changes in 30 patients treated with activatorand cervical headgear. Patienis treated with this eom-bination of appliances were found to have their ClassII molar occlusion corrected to Class I and a simuhane-ous reduction of overbite and overjet. Teuscher'^'"'was the first to attach the facebow directly to the ac-tivator and, with applied occipital traction, achievedbetter vertical and rotational control during orthopedicClass II treatment.

The simultaneous use of both activator and high-pullheadgear appliances may result in a number of desirabletreatment effects greater than those induced by eachappliance separately. The effeetive changes are believedto be restraint of downward and forward maxillarygrowth, selective guidance of maxillary and mandibulardenloalveolar development, and some influence onmandibular growth and/or position.

The purpose of this study was to demonstrate theelinical and cephalometric findings of a sample ofeight patients with Class II skeletal open bite who weretreated with a high-pull activator (HPA) appliance.

Method and materials

Treated sample

The sample eonsisted of eight patients, two boys andsix girls, with Class II skeletal open bite malocclusionwho were treated with HPAs during the mixed dentitionperiod. All subjects were treated by one of the authorsat the Ohio State University, College of Dentistry.Before treatment, each patient had (1) a Class II, divi-sion 1, malocclusion with bilateral Class II molar re-lationship and excess overjet; (2) an anterior openbile, as measured by the overlapping of the maxillaryto mandibular incisai edges; and (3) a skeletal openbite pattern, measured cephalometrically and consi-dered to be a ratio of posterior facial height (sella-gonion) to anterior facial height (nasion-menton) ofless than 62%. The mean age of the subjects was 10

324 Quintessence internalional Volume 23, Number

Orthodontics

Fig 1 Activator prior to placement. Note the lingual exten-sions and the acrylio resin ledge covering the occtusalsurfaces of the molars and premolars. The Frankel iip shieldhas been incorporated in the appliance tor this particularpatient, who has mentalis hyperactivity.

Fig 2 (right) Activator together with the high-pullheadgear. Note the position of the torquing springs, whichare adjusted to touch the crowns ol the incisors as cioseiyas possible to the gingival margin on the maxillary incisors.

yeaTS 3 months before treatment. The average treatmenttime was 1 year 2 months.

Control sample

A control sample, consisting of eight untreated Class nchildren with a skeletal open bite pattern as describedin the treated sample, were obtained from the OhioState University Growth Study for use as a comparisongroup. These subjects were matched in age and sexwith the treated sample.

Objectives of treatment

The primary objectives of the treatment were to correctthe Class II molar occiusion to a Class I occlusion andproduce a concomitant reduction of the skeletal abnor-mality and open bite. Once these objectives were met,a second phase of treatment with fixed appliances wasundertaken as indicated.

Appliances and treatment procedures

Each appliance was constructed according to the man-ner described by Teuscher'* (Figs 1 and 2), Theappliance consisted of an activator with an attachedheadgear. Anchorage in the maxillary arch was securedby the upper part of the appliance, which covered theocclusal surfaces of all posterior teeth. It was not de-sirable to cover the entire palate across and forward upto the incisors; instead a transpalatal bar (1,2 mm in

diameter) was used, and the palate was kept free toprovide as much room as possible for the tongue. Tolink the activator to the inner arch of the facebow, a0.045-inch headgear tube was fastened in the acryhcresin between the maxiiiary and mandibular arches.The tube was placed sagittally between the primaryfirst and second molars or premolars. The magnitndeof the extraoral force was 400 g per side.

Because the activator headgear assembly transmitsforces to the acryhc resin covering the oeclusal andincisai portions of the teeth, with the result that theincisors tend to tip backward, a palatal root tippingforce was used if the maxillary incisors were already inan ideal position. Torquing springs were fabricatedwith 0.5- or 0,6-mm, resihent, stainiess steel wire, Tbelower part, with a horizontal leg on each side, wasembedded in acrylic resin. The vertical part was keptaway from the acrylic resin, and only the palatallycurved tip touched the crown immediately coronal tothe gingival margin.

The mandibular component of the appliance consistedof an incisai table for advancement of the mandibie.In patients with mentalis hyperactivity, the addition oflower labial pads as proposed by Frankel has provenhelpful in achieving reduction of adverse mentalisactivity. The iabial pads must be positioned deep inthe vestibular fold, parallel to the alveolar process,and should be teardrop shaped," The therapeutic po-

International Volume 23, Number 5/1992 325

Orthodontics

Fig 3 Cephalometrio landmarks, constructed lines, and dig-itized points used; (S) seiia; (N) nasion; (Co) condylion;(PNS) posterior nasal spine; (ANS) anterior nasal spine; (A)point A; (Go) gonlon; (B) point B; (SNP) selia-nasion perpen-dicular; iPgJ pogonion; fGn̂ gnathion; (Me) menton.

Fig 4 Determination of changesin (A¡ horizontal position oi maxil-lary molar and central incisor; (B)vertical position of maxillary molarand centrai incisor; (C) horizontaiposition of mandibuiar molar andcentral incisor; (D) vertical positionof mandibular moiar and centraiincisor

326 Quintessence International Volume 23, Number

Orthodontics

sitioning of the mandible was determined by the opera-tor with a wax registration bite, which served to orientthe casts for appliance construction. In most cases, themandible was advanced until the incisors were in anedge-to-edge position. The maximal advaneemcnt didnot exceed 5 mm.

Patients were instructed to wear the activator foronly 2 hours, during the daytime, for the first 3 days.Patients were to increase the number of hours of ac-tivator wear until they could wear the appliance 24hours a day and the headgear at night for 12 to 14hours. During this first phase of treatment, evalua-tions were made every 3 to 5 weeks until treatmentgoals of overcorrected dental and skeletal relationshipshad been met, an average of 1 year 2 months aftertreatment had begun.

Cephalometric analysis

Lateral eephalograms were taken before and at thecompletion of this phase of treatment. Ail eephalogramswere taken with the patients' teeth in occlusion andlips in a relaxed position to standardize soft tissueposture and morphology. Cephalometric landmarkswere identified and lines were constructed as shown inFigs 3 and 4, Cephalograms were digitized with aTexas Instruments digitizer, and all analyses wereperformed on an IBM PC with Ohceph OrthodonticSoftware (OH Inc).

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

ME =V 2d-/2n

where d is the difference between two registrations ofa pair, in millimeters, and n is the number of doubleregistrations. Before- and after-treatment cephalogramsfrom ten randomly chosen subjects were traced andsuperimposed with measurements recorded on two dif-ferent occasions. The combined ME did not exceed± 0.8 mm for any of the variables investigated.

Statistical analysis

Comparisons of starting forms and serial changes inthe eontrol and high-pull activator groups wereanalyzed using a two-sample f test. The a priori levelof statistical significance was set at .1.

Results

Equivalence of starting forms

Before serial changes observed in the treatmentgroups were compared with those in the controls forthe same age range, the starting forms of the twogroups were analyzed. There were no statistieally sig-nificant differences {P < .05) between the treated atideontrol groups in any maxillary or mandibular, hori-zontal or vertical measurements.

Cephalometric analysis of treatment effects

The changes in cephalometric values for the eighttreated patients and eight eontrol patients are shownin Table L For maxillary skeletal relationships, theannualized change in sella-nasion-point A in the treat-ment group was —1.90 ± 2.2 degrees, which was sig-nificantly different than the change in the controlsample (-1-0.23 ± 1.46 degrees). The relationship ofpoint A to sella-nasion perpendicular showed a similarsignificant change ( — 0.21 + 2,4 mm in the treatmentgroup, compared with +0.44 ± 1.52 mm in the controlsample).

For the maxillary dentition, the change in horizontalposition of the maxillary molar was determined bydropping a line perpendicular to sella-nasion to themesial contact point of the maxillary first molar (seeFig 4). The maxillary molars in the treatment groupmoved 0.64 ± 2.11 mm backward, while those in thecontrol group moved 0.90 ± 1.83 mm forward. Maxil-lary molars in the treatment group moved downwardonly 0.27 ± 2,61 mm: those in the control samplemoved 1.05 ± 1.31 mm. With reference to sella-nasion,the maxillary incisors were moved significantly fartherbackward (4.25 + 2.95 mm) than those in the control(0.50 + 2.31 mm). The vertical position of the maxillaryincisors remained relatively unehanged in both groups.

The positions of the mandibular molars sind incisorswere relatively unchanged with reference to sella-nasion.However, the mandibular incisors in the treatmentgroup were moved farther inferiorly (3.13 + 3.56 mm)than those in the control sample (0,12 ± 1,29 mm).

A greater increase in matidibular length was observedin the group treated with HPA (4.05 ± 2.74 mm) thanin the eontrol group (2.25 + 2.91 mm). However,there were no differences between the control andtreatment groups for the cephalometric measurementsof sella-nasion-pogonion and sella-nasion-point B.

The vertieal angular changes shown in Table 1 re-vealed a small but insignificant increase in skeletal an-terior facial parameters.

Quintessence irternationai Voiume 23, Number 5/1992 327

Orthodontics

Table I Change in measurements in control and HPA groups

SNA OSNP-pt A (mm)

Max molar horizont (mm)Max molar vert (mm)Max incisor horizont (mm)Max incisor vert (mm)

Mand molar horizont (mm)Mand molar vert (mm)Mand incisor horizont (mm)Mand incisor vert (mm)

Co-Gn (mm)SNB C)SNB-Pg(mm)SNP-pt B (mm)

Mand plane angle (°)Occlusal plane angle (")Palatal plane angle {")SN-ANS (mm)SN-Me(mm)

Control

Mean SD

Experimental

Mean

Maxillary skeletal

-0,230.44

1.461.52

-1.90-0.21

Maxiiiary dental

0.901.050.500.73

1.831.312.311.38

-0.640,27

-4,251.19

Mandibular dental

1,110.810,120.12

1,861.342.651.29

1,951,101,663,13

Man dibular skeletal

2,25-0.26

0,230.05

2.921.533.272.88

4,050,280,580,98

Vertical relationship

0.03-1.58-0.01

1.442.50

2.104.101.001.551.98

1,831,000,802,414,61

SD

2,202.40

2,112,612,950,82

1.701.701.853.56

2,740,992,331,59

2.112,671.820.852,65

t

1,760.64

1,560,753.58

-0.81

-0,94-0,38-1,35-2.24

-1,98-0,85-0,25-0,79

-1.70-1,47-1,11-1,55-1,81

Sig

*

*

NS

NSNSNS*

*

NSNSNS

NSNSNSNS*

NS = not significant* P<.\." F< ,05

Clinicül treatment eßects

Clitiically, a Class I molar occlusion was obtained ap-proximately 1 year after the start of treattnent. Simul-taneously, open bite was considerably reduced, result-ing in a concomitant improvement in lip balance. Thechnical results of two patients treated with HPA areused to illustrale the treatment effects of the appli-ance.

Case I

Figure 5 shows an 8-year-old girl who presented with aClass II, dtviston 1, malocclusion, protrusive incisors,and a retrognathic matidible. Clinically, the pafientexhtbited bilateral Class II molar oeclusion with 5 mmof excess overjet and anterior open btte (Figs 6 and 7)Cephalometric analysis showed a Class 0 j^w relation-ship with point A-nasion-point B angle of 10 degrees

328 Quintessence International Volume 23, Number 5/1992

Orthodontics

Fig 7 Lateral intraoral view of the same patient revealsCiass II melar and canine reiationships.

Fig 8 (right) Posttreatment view of the same patient.

Fig 6 Anterior intracrai view of fhe same patient revealsanterior open bite.

Fig 5 (left) An 8-year-old patient with a convex profile, anobtuse nasolabial angie, and a retrognathic mandible.

(norm of 2°) and a Wits appraisal of + 6.5 mm (normof 0 mm). The inclination of the maxillary incisors was105 degrees (norm of 98 to 108 degrees). The man-dibular plane angle of 29 degrees, y-axis of 60 degrees,and posterior-anterior facial height ratio of 61.5%,compared with the norms of 22 to 30 degrees, 59.4 de-grees, and 63% to 68%, respectively, suggested thatthe patient had a vertical skeletal growth pattern.

Figure 8 shows the same patient after 14 months ofHPA therapy. The posttreatment record revealed a

correction of the Class II molar occlusion into a Class Irelationship and a reduction in anterior open bite (Figs 9and 10). Cephalometric analysis of the posttrealmentradiograph revealed a point A-nasion-point B angleof 6 degrees, a Wits appraisal of -I- 3.0 mm, maxillaryincisor inclination of 100 degrees, a mandibular planeangle of 30.5 degrees, and a y-axis of 61.5 degrees.Superimposition of the pretreatment and posttreatmentcephalometric radiographs revealed the skeletal anddental effects of treatment: restraint in maxillary

Quintessence International Volume 23, Number 5/1992 329

Orthodontics

Fig 9 Posttreatment anterior intraoral view of the samepatient reveals a reduction in anterior open bite.

Fg 10 Posttreatment lateral irtraoral view of the samepatient reveals correction into a Class I moiar relationship.

Pretreatmeni1 0 - 1 5 - 8 8

Posrtreatment6 - S2 - 88

Fig 11 Pretreatment and posttreatment cephalometrictracings of the same patient reveai that the forward anddownward movement of the maxillary moiars and the lingualmovement of the maxillary incisors have been restrained.The palatal, occlusai, and mandibular piane angies remainrelativeiy unchanged.

growth and limited forward and downward movementof the maxillary molars (Fig 11). The mandible movedforward and downward with a i,5-degree opening ofthe growth axis. The palatal, occlusal, and mandibularplane angles were also slightly increased.

A second phase of comprehensive orthodontic treat-ment was undertaken for this patient to provide de-

tailed alignment as well as continued control of verti-cal growth of the maxilla and eruption of maxiilarymolars.

Case 2

Figures 12 and 13 show a 9-year-old boy who presentedwilh a Class II, division 1, malocclusion, an excessoverjet, and skeletal open bite. Clinically, the patientexhibited a bilateral Class II molar relationship and anoverjet of 5 mm. The cephalometric radiograph reveaieda point A-n as ion-point B angle of 6 degrees and Witsappraisal of 4- 4.5 mm. The maxillary incisal inclina-tion was 98 degrees. The mandibular plane angle was29 degrees and the y-axis was 62 degrees.

Figure 14 shows the same patient after 12 months ofHPA therapy. The Class II molar relationship was cor-rected to a Class I occlusion and overjet was reduced.Cephalometric analysis of posttreatment radiographrevealed a point A-nasion-point B angle of 4 degreesand Wits appraisal of -i- L5 mm. The maxillary incisalinclination was reduced to 90 degrees, and the man-dibular plane angle and y-axis did not change withtreatment, Cephalometric superimposition showed nomovement of the maxilla, but forward movement ofthe mandible {Fig 15). In addition, a forward anddownward movement of the maxillary molars was re-strained. No tipping of the palatal or occlusal planewas observed. The mandibular plane angle remainedrelatively unchanged.

Discussion

The results demonstrated that HPA had both skeletaland dental effects on the growing craniofacial complex.

330 Quintessence International Volume 23, Number 5/ig92

Orthodontics

Fig 13 Lateral intraoral view of the same patient reveals aClass il molar relationship and excess overjet.

Fig 12 (left) A 9-year-Qld patient with a long lower facialheight, an obuse nasoiabial angle, and a retrognathic man-dible.

Pretreatment6 - 1 - B7

Posttreatmeni6 - 1 4 -

Fig 14 Posttreatment lateral intraoral view cf the samepatient reveals the correction into a Class i molar relation-ship and the reduction in overjet.

Fig 15 Pretreatment and posttreatment cephalometriotracings of the same patient reveal that the forward anddownward movement of the maxiilaty moiars and the linguaimovement of the maxiiiary incisors have been restrained.The mandible has moved forward and downward, but therehas been relativeiy littie ohange in the mandibular planeangle.

Ouintessence International Volume 23, Number 5/1992 331

Orthodontics

Cephalometric measurements have shown that theeffect of treatment was not uniformly distributedthroughout the craniofacial region. The treatmentaffected some regions of the face more than others.

The HPA appliance can restrict maxillary skeletalgrowth. The decrease in forward movement of pointA was also related to the posterior tipping of themaxillary incisors, because point A is a maxillary den-toalveolar landmark intimately associated with themaxillary incisor. The lingual movement of maxillaryincisors by HPA was beneficial to patients who startedout with protrusive maxillary incisors and/or open bitecaused by forward positioning of the maxillary in-cisors.

One of the mechanisms of Class II correction, asproposed by Harvold and Vargervik,^ is the inhibitionof the downward and forward eruptive path of themaxillary posterior teeth, which allows the mandibularposterior teetli to erupt tnore vertieally. in this study,HPA reduced the amount of forward and downwardmovement of the maxillary molars. In addition, only asmall increase in vertical skeletal parameters (palatal,occlusal, and mandibular plane angles), was observed.Previous studies of patients treated with cervicalheadgear'"^ or in combination with an activator"reported a downward and backward displacement ofthe maxilla with posterior rotation, but this effect wasmuch less pronounced in patients in the present study.The high-pull appliance seemed to provide verticaland rotational eontrol of the maxilla during orthopedicClass II treatment. This aspect of the appliance wasparticularly helpful in preventing further bite openingin patients who started out with vertical growth patternand anterior open bite.

In the patient in ease 1. forward growth of the maxillawas inhibited, and there was a downward movementof the maxilla and the mandible, resulting in a 1.5-degree opening of the growth axis, despite the use ofhigh-pull headgear. However, in the second patient,no movement of the maxilla was observed, and therewas no ehange in any of the vertical parameters. Theseobservatiotis suggest that response to this treatmentmodality may vary in different individuals. Further-more, the treatment of skeletal open bite requireslong-term growth modification of the maxilla, so thatthe mandible will continue to rotate in a counterclock-wise direetion, forward and upward.

In this study, HPA inereased mandibular length duringtreatment as indicated by the measurement from lhecephalometric landmarks condyhon to gnathion. Theinfluence of activators on the growth of mandibular

length remains controversial, A significant increase inmandibular length by activators was not supported bystudies by Bjork,'̂ Harvold,^" or Jakobsson,'' whereasother investigators^^"^" have found a significant in-crease in growth of mandibular length by the use ofmonobloc type of appliance and other functionalappliances.''"''"' The contribution made to Class IIcorrections by increased mandibular growth has to beinterpreted with caution, because the landmark cou-dylion cannot be accurately determined on a lateralcephalogram, and the sample size in this study wasrelatively small.

Some investigators have reported that activatorspromote forward growth of the mandible.'^'^'^'"^^ Intbe present study, sella-nasion-point B and sella-nasion-pogonion did not change significantly after treatment,for Ihe group. However, forward movement of themandibie was demonstrated in case 2, and, in ease 1,forward movement of the mandible may have beenmasked by the rotation and vertical change of themandible.

Summary

The malocclusions of eight patients with Class IIskeletal open bite were eorrected by interceptive or-thodontic treatment with the high-pull aetivator. Theeffects of the HPA on Class II growth included reduc-tion of forward growth of the maxilla and an increasein mandibular alveolar height. This resulted in a trans-formation of the Class II molar relationship into aClass I molar relationship. The overjet and open bitewere decreased by the reduced forward growth of themaxilla in combination with lingual tipping of themaxillary incisors.

References

1. Worms FW, Mesiiin LH, Isaacson RJ; Opetl-bite./lin 7 Orthodt971;59:589-595.

2. Subtetny JD, Sakuda M: Open-bite: Diagnosis and treattnent.Am J Orihod 1964;50:337-358.

3. Proffit WR: Contemporary Orthodontics. St Louis, CV MosbyCompany, 1986, pp 47-49.

4. MeNamara JA Jr: Neuromuseular and sketetal adaptations toaitered funetion in tbe orofaciat region. Am 3 Orthod 1973;64:548-006.

5. MeNamara JA Jr. Carison DS: Quantitative analysis of tetti-poronaiidibular joint adaptations to protrusive function Am JOrthod t979;76:593-lill.

6. MtNamara JA Jr, Hinton RJ, Hoffman DL: Histologieanalysis of temporomandibular joint adaptations to protrusivefunction in young aduit rhesus montceys (Macaca mulatta) AmJ Orthod 1982 ;82:288-298.

332 Quintessence International Voiume 23, Number 5/1992

urtnodontios

7, TongE EA, Heath JK, Meikle MC: Anterior mandibular dis-placement and condylar growth. Am J Orthod 1982^82:277-2S7,

8, Harvold EP: The Activator in Imerceptive Orthodontics. StLouis, CV Mosby Co, 1974; p 236,

9, Harvold EP, Vargervick K: Morphogenetic response to ac-tivator treatment. Am J Orthod t971:60:478-490.

to, McNamarü JA. Bookstein FL, ShaughnessyTG: Skeletal anddetital changes following functional regulator therapy onClass II patients. Am J Orthod 19a5;88:9t-109,

It, Baumrind S. Korn EL, Isaacson RJ, et al: Quantitativeanalysis of the orthodontic and orthopedic effeets uf maxil-lary traction. Am J Orlhod t983;84:384-398,

12, Hasund A, The use of activator in a system employing fixedappliances, Eur Orthod Soc Rep Congr 1969; p 329,

13, Pfeiffer JP, Groberty D: A philosophy oí combined or-thopedic-orthodontie treatment./I Jij 7 O'-itoJ19S2;8t:tS5-20t,

14, Levin RL Activator headgear therapy. Am J Orthod 1985;87:91-109,

15, Teuscher UM: A growth-related concept for skeletal Class IItreatment. Am J Orthod l978;74;258-275,

16, Teuscher UM: Direction of force appiication for Class II, Di-vision 1, treatment with the activator-headgear combinatiiin,Studieweek. Nederlandse Vereiniging voor orthodontischeStudie, 1980;p 103,

17, McNamara JA Jr, Huge SA: The Frankel appliance (FR2);model preparation and appliance construction. Am J Orthod1981;80:478-482,

18, Wieslander L: The effect of tbrcc on craniofacial develop-ment. Am J Orthod 1974;65:i31-538,

19, Bjork A: The principle of the Andresen method of orthodontictreatment, a discussion based on cephalometric x-ray analysisof treated cases. Am J Orthod 1951;37:437-458,

20, Harvold E: The role function in the etiology and treatment ofmalocclusion. Am J Orthod 1968;54:883-898,

21, Jakobsson SO: Cephalometric evaluation of treatment effecton Class II, Division 1 malocclusinns. Am J Orthod 1967;33:446-455,

22, Harris E: A eephalometric analysis of matidibular growthrate. Am J Orlhod 1962:48:161-173,

23, Korhaus G: Present orthodontic thought in Germany, Am JOri/jod 1960:46:270-285,

24, Meach C: A cephalometric comparison of bony profilechanges in Class II division 1 patients treated with extraoralforce and functional ja«,' orthopedics. Am J Orthod 1966;52:353-369,

25, Jakobsson SO: Cephalometric evaluation of treatment effecton Class II, Division 1 malocclusions. Am J Orthod 1967;53:446-457,

26, Meach CL: Cephalometric comparison of bony profile inClass II. Division 1 patients treated with extraoral force andfunctional jaw orthopedics. Am J Orthod 1966;52:353-370,

27, Teuscher UM: Appraisal of growth and reaction to extraoralanchorage. Am J Orthod Demofac Orthop 1986:89:113-121,

28, Bass NM: Dcnto-facial orthopaedics in the correction of theClass II malocclusion, Br J Orlhod 1982;9:3-31, D

Quintessence International Volume 23, Number 5/t992

1st Greater InternationalBulgarian

Dental Congress2nd Annual Meetingof Bulgarian Dentists2nd Greater Bulgarian

Dental Exhibition

October 15-17, 1992,Plovdiv

COUPONI am Interested in the 1st Greater International BulgarianDental Congress, Please send further details to:

Strí

SatCily

Fir

Cc

si Name

kunliy

Telephon Ë

Mail coupon to:Quintessenz Verlags-GmbH - Ifenpiad 2-4 • D-tOOO Berlin 42Phone: -h30/74006-28 Telefax: +30/74t7805