Activator headgear therapy

Activator headgear therapy

America,n Journal of ORTHODONTICS Founded in 1915 Volume 81, Number 2 Copyright February, 1985 0 198.5 by The C. V. Mosby Company ORIGINAL ARTI...

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America,n Journal of ORTHODONTICS Founded

in 1915

Volume 81, Number 2 Copyright

February,

1985

0 198.5 by The C. V. Mosby Company

ORIGINAL

ARTICLES

Activator headgear therapy R. I. Levin, B.D.S., M.D. [email protected], The Netherlands A method of treatment is described using an activator and cervical headgear simultaneously to correct malocclusions of the Class II, Division 1 type. The case reports of ten treated patients are used to demonstrate the effects of the application of this technique. Changes in the dentition and facial skeleton were analyzed and the significance of the different responses to the application of the same appliances assessed. The hypothesis proposing that a simultaneous application of both appliances may result in a number of desirable effects greater than that induced by each individual applianoe is examined. The hypothetical basis for the application of this technique is partially substantiated by the clinical observations. Within a period of about 1 year, correction of the Class II molar occlusion to a Class I molar occlusion is obtained, with a simultaneous reduction of overbite and overjet. Skeletal changes were found to be variable and related to facial type and the rate of facial growth. Srachyfacial and mesofacial types responded most favorably to treatment. The most favorable effects were observed when there was a large quantitative mandibular growth and brachyfacial or mesofacial growth pattern. In dolichofacial types with a slow mandibular growth rate, mandibular rotation was found to be clockwise; cervical traction appears contraindicated, and a combination of activator with occipital medium to high pull is considered more appropriate.

Key words: Activator, cervical headgear, ClassII, occlusal development, mandibular rotation

H

amessing the growth of the mandible to facilitate treatment of a Class II, Division 1 malocclusion may be considered the most desirable aim but also the most difficult objective for a successful treatment result. In most techniques, however, with the exception of those involving functional appliances, only an indirect control of the mandible is attempted by limiting vertical maxillary and dentoalveolar growth in order to allow for a forward mandibular rotation. It is evident that treatment procedures that are enhanced by the inherent mandibular growth process will result in a more effective reduction of the Class II malocclusion. Likewise, procedures that induce mandibular growth or facilitate forward mandibular rotation will aid in reduction of the malocclusion. Conversely, a backward mandibular rotation as a result of growth or treatment will compound the severity of the malocclusion. The purpose of this article is to describe a method

of treatment that involves a simultaneous combination of an activator and cervical headgear. Some of the dental and skeletal changes occurring during treatment were investigated in order to gain a deeper insight into the nature of the response to treatment. RATIONALE

FOR APPLIANCE

SELECTION

Experimental simulation of activator therapy has been found to induce increased cellular activity in the mandibular condyle . I-4 Harvold ,5.6 however, found no evidence of increased mandibular growth in patients treated with activator therapy, and he convincingly described the selective influence of the activator on occlusal development. Although vertical maxillary growth was found to be restrained during activator therapy,‘, ’ a clinical study using implants indicated that the maxilla rotated backward during treatment.’ The differences in treatment effects may be due to the construction of the 91

Fig. 1. A, Working models in occlusion. B, The construction bite registers the vertical and displacement of approximately 10 mm with an open edge-to-edge bite and a molar occlusion to Class III. The construction bite should not impinge on the gingival or retromolar areas and end distally in the region of the first mandibular molars. The vertical displacement is directly to the depth of the overbite. A deep overbite will have a larger vertical displacement.

appliance and a maximum forward positioning of the mandible to elicit maximum muscular restraining forces on the vertical development of the maxilla. Cervical headgear forces have been found to result in extrusion and posterior displacement of maxillary molars with backward maxillary rotation,’ producing a backward and downward displacement at the maxillary sutures. It is claimed to be the most effective type of headgear for initiating an orthopedic displacement of the maxilla.” Pfeiffer and Grobety’ have previously described combination activator-cervical headgear therapy. They preferred to use cervical headgear, where necessary, for two reasons: (1) to extrude maxillary molars, and (2) to apply orthopedic traction to the maxilla and an activator to induce orthopedic mandibular changes, restrain maxillary growth, and cause selective eruption of teeth. Irrespective of the diversity of facts and opinions

sagittal tending should related

regarding the application of cervical headgear or activator, clinical experience has shown that both appliances can be effectively used. Hypothetically, a simultaneous application of both appliances may result in a number of desirable treatment effects greater than those induced by each appliance separately. These changes are believed to be a restraining of maxillary growth, selective guidance of maxillary and mandibular dentoalveolar development, and some influence on mandibular growth or position. INDICATIONS

FOR TREATMENT

Treatment with combined headgear-activator appliances is indicated for adolescent patients with malocclusions of the Class II, Division 1 type. Dental development may be in the mixed- or permanent-dentition stage, preferably with well-formed dental arches although an abnormal arch shape or dental crowding is

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Fig. 1 (Cont’d). C, Waxed-up working models. The mandibular occlusal plane and areas palatal and lingual to the lower incisors are waxed up. D, Waxed-up activator with clasp distal to first molar and labial bow.

not necessarily a contraindication. Maxillary prognathism, mandibular retrognathism, and decreased or increased facial height are treated differently by varying the design and application of the appliances. OBJECTIVES OF TREATMENT

The objectives vary according to the nature of the malocclusion. In all cases the primary objective is correction of the Class II molar occlusion to a Class I occlusion and a concomitant reduction of the skeletal abnormality and of the other aspects of the dental malocclusion. Once these objectives have been met, a second phase of treatment with fixed or remova.ble appliances may be necessary. APPLIANCES AND TREATMENT PROCEDIJRES

A cervical headgear with a long outer bow is used. The inner bow is inserted into buccal tubes attached to

the maxillary first molars and the outer bow is adjusted to about 5” below the inner bow. This produces a predominantly distal force through the center of resistance of the molar teeth and a lesser vertical extrusive force component. ” During treatment, once a Class I molar occlusion has been established, the outer bow is raised above the inner bow if uprighting of the molars is indicated. The inner bow is expanded about 5 mm and activated to produce a distobuccal maxillary molar rotation. The neck strap produces a force of approximately 400 grams, measured unilaterally. The activator used is based on the design and application described by Harvold.’ It is modified for use with a cervical headgear applied to the maxillary first molars. Patients are instructed to wear the appliances simultaneously for 14 continuous hours a day. Patients are seen about once every 6 weeks, at which time the necessary adjustments are made.

Fig. 1 (Cont’d). E, Activator prior to placement. Note the lingual extensions and the acrylic ledge covering the occlusal surfaces of the molars and premolars. F and G. The activator. Upper incisors are free; lower incisors are well embedded within the acrylic as seen from the labial aspect. For acceptance by the patient, it is essential that the appliance fit without causing discomfort.

Activator construction

The design and construction of the activator are illustrated in Fig. 1. In construction of the appliance, two important factors for controlling vertical maxillary growth are taken into account: first, the muscular forces elicited by application of the activator and, second, the method of trimming or relieving specific areas of the appliance. Impressions for working models are taken with deep lingual impressions of the mandible. Deep lingual extensions on the activator are necessary to maintain mandibular position and prevent loss of the appliance during sleep. For construction of the activator, a wax construction bite which positions the mandible downward and forward beyond the rest position is taken. It is used to orient the models for appliance construction. The dimensions of the construction bite depend on the individual patient. It is of the utmost importance in eliciting the muscular forces needed to restrain maxillary

growth. According to Harvold,’ the rest position, tonicity of the lip musculature, and size of the overjet should be taken into account in obtaining the construction bite. A larger bite opening will stimulate lip musculature and allow space for retraction and remodeling of the alveolar process palatal to the maxillary incisors. The greater the forward positioning, the larger will be the muscular forces to restrain maxillary growth and to tip the maxillary incisors lingually. Pfeiffer and Grobety,’ suggest that, to restrain maxillary growth, the sagittal activation should be 2 or 3 mm short of maximum forward positioning and vertical activation at least 3 or 4 mm beyond the freeway space. This position is considered to cause sufficient isometric contraction of the mandibular retractors to restrain maxillary growth. In deep-bite cases there should be sufficient bite opening for at least a 3 mm acrylic layer between the incisor teeth. The above guidelines were used in ob-

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Fig. 2. Patient P. A. Lateral cephalometric tracings. a, Pretreatment cephalometric tracing. b, Posttreatment cephalometric tracing. c, Changes in position of the teeth in the mandible. d, Changes in position of the teeth in the maxilla. e, Superimposition illustrating maxillary changes. f, Superimposition illustrating change in position of chin.

Table I. Ricketts’ summary analysis-Mean

initial values and changes occurring with treatment (Tl-T2)

and the RMIS clinical mean

“ariable

Facial depth Facial axis Mandibular plane Lower facial height Mandibular arc Facial convexity Interincisal angle Mandibular incisor inclination Mandibular incisor to AP line Upper first molar to PTV

/----

84.7 85.8 26.0 45.8 24.5 6.7 130.8 14.4 -2.0 13.9

3.16 2.91 4.91 3.26 4.22 3.07 7.64 6.59 2.83 2.92

0.3 - 1.3 1.3 3.6 -0.7 - 1.3 6.2 7.4 3.2 -2.1

2.26 1.83 1.88 2.27 3.43 1.49 5.92 6.19 1.32 1.57

81 90 25 47 28 3 130 22 I 16

88 90 25 47 28 2 130 22 1 16

The cephalometric points and measurements have been cescribed previously.” Mean age sample Tl, 11.7 years; T2, 13 years. Tl, start of treatment; T2, end of treatment; Tl-T2, treatment change. Measurements are in degrees except facial convexity, mandibular incisor to AP, and upper first molar to PTV, which arc in millimeters,

95

96 Levin

Fig. 2A to D. Patient

P. A.

Table II. Individual values and changes occurring during treatment Patient I. K. Variable Facial depth Facial axis Mandibular plane Lower facial height Mandibular arc Facial convexity Interincisial angle Mandibular incisor inclination Mandibular incisor to AP line Upper first molar to PTV

Tl

P. A. TI-T2

Tl

87 88

1 I

88 89

23 44 28 I 121 19 1 14

0 1 5

20 41 29 8 130 13 -4 18

Tl, Start of treatment; T2, end of treatment; Tl-T2, Measurements are in degrees except facial convexity,

-2 I I 4 -1

A. J. T&T2 2 I -I 1 -4 -3 6 22 2 -1

change during treatment. mandibular incisor to AP, and upper

I. G.

TI

TI-T2

87 86

-I

28 45 20 2 142 8 -5 12

first molar

TI 1

85 89

0 2

1 3

21 42 26 1 142 12 -2 11

2 3 6

-1 0 0 9 3 -3

to PTV,

Tl-T2

which

are in millimeters.

-1 I 8 4 .- 2

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Fig. 2E to H. Patient P. A.

Patient B. H.

A. L.

c. c.

Tl

Tl -T2

TI

Tl-T2

TI

83 89 28 43 24 5 125 25 2 11

-1 -2

90 86 19 41 27 8 121 17 2 19

-5 -4

82 84 32 48 16 10 128 10 -4 13

0 2 -3 0 -2 4 2 -3

4 3 -3 1 14 1 1 -5

J. v.

N. V. TI-T2 1 -3 7 -2 -3 8 9 5 -4

Tl

Tl-T2

Tl

81 81 29 48 29 9 137 6 -5 11

-1 -3

83 82 27 50 22 9 132 10 -4 16

4 7 -3 0 9 10 5 -5

K. V. Tl-T2 2 -1 3 6 -1 -3 14 4 3 -2

Tl 81 84 33 50 24 8 130 24 -1 14

Tl-72 3 1 -1 3 -1 -2 11 0 3 -1

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a KV 12.8

d

e

Fig. 3a to f. Patient K. V. (For explanation of tracings in this and subsequent illustrations, see legend to-Fig. 2.)

taining the construction bite in the cases examined in this investigation. Trimming of the activator is largely eliminated in practice by construction of the appliance so that areas where vertical eruption of teeth or remodeling of the alveolar process is to be inhibited are in contact with the acrylic. Areas where eruption or remodeling is required are freed from the acrylic (Fig. 1). The occlusal surfaces of the maxillary molars and premolars are embedded in acrylic, which also covers the hard palate. The areas palatal to the maxillary incisors and canines are freed. The incisal edges of the maxillary and mandibular teeth are covered with acrylic, while the lingual aspects of the mandibular incisors and their adjoining alveolar process are freed. Labial tipping of mandibular incisors is limited by partially covering the labial surfaces with acrylic. Lingual extensions are as deep as possible without impinging on gingiva or mucosal tissues. The labial bow is in contact with the maxillary incisors and free from the canines to allow for buccal expansion.

MATERIALS AND METHODS OF ANALYSIS A sample of thirty consecutive cases treated in my practice was collected. From these cases, ten were selected to illustrate the considerable variability of the effects of treatment seen in different patients and to gain insight into the nature of the responses to treatment. All cases were of the Class II, Division 1 dental type. They were all skeletal Class II and varied from brachyfacial to dolichofacial types of growth pattern. Cephalometric analysis was performed on lateral cephalometric radiographs taken at the start and end of activator headgear therapy. The analysis was performed by Rocky Mountain Information Services. Of the measurements made, the most relevant to the present discussion are listed in Tables I and II. The measurements have previously been defined and discussed.” The individual measurements (to the left) and the clinical norm (to the right) are shown on the individual cephalometric tracings. In Figs. 2 to 11, a shows tracings at the start of

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AL9-8

Fig. 4. Patient A. L.

treatment and at the end of activator-headgear treatment (b). The tracings were also superimposed according to the methods described by Ricketts and his coauthors. ‘* The superimpositions of individual patients are denoted c, d, e, andf. The mandible was superimposed on the corpus axis of the mandible and registered at the anterior border of the mandibular symphysis (c). The hard palate was superimposed and registered at the anterior nasal spine (d). Basion-nasion lines were superimposed and registered at nasion (e). This superimposition illustrates maxillary growth and rotation. Basion-nasion lines were superimposed and registered on the most posterior-superior point of the pterygomaxillary fissure (f). The superimposition illustrates the change in position of the chin and facial axis and represents mandibular growth and rotation. Tracings c and d illustrate dental changes, and e andfshow orthopedic changes or facial growth. In addition to the cephalometric data, three cases are also illustrated with dental casts and cephalometric radiographs (Figs. 2, 5, and 11).

TREATMENT

RESULTS

The means and standard deviations of the cephalometric measurements are listed in Table I. The individual values and changes occurring during treatment are listed in Table II. The individual cephalometric data have also been listed on the individual tracings. The following general observations were made: A Class I molar occlusion is usually obtained within a period of about 1 year after the start of treatment. Simultaneously, overbite and overjet are considerably reduced, with a concomitant improvement in lip balance. Reduction of dental crowding is often evident. Skeletal changes vary. Individual facial growth pattern and the rate of facial growth occurring during treatment are associated with considerable individual variability in the skeletal changes observed during treatment. The most notable variation is the effect of treatment on facial rotation. In some patients a clockwise facial rotation occurred, resulting in a lengthening of the anterior facial height. In other cases no discernible clockwise rotation was observed. Clockwise rotation was observed to be

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,Pf ‘i

Fig. 5a to f. Patient N. V.

Fig. 5A to D. Patient N. V.

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Fig. 5E to H. Patient N. V.

related to the rate of facial growth and to the growth pattern of the face. In those cases in which the growth rate had been slow, irrespective of facial type, a tendency for clockwise rotation was observed. Clxkwise rotation was also more prevalent in cases with a dolichofacial type of pattern. The most favorable effect of treatment occurred in cases in which there was a large quantitative mandibular growth and a favorable growth pattern. In these patients an increase in mandibular prognathism occurred and facial rotation was only slightly clockwise or counterclockwise. CASE REPORTS PATIENT

closing rotation. Maxillary changes were slight, maxillary clockwise rotation is evident. PATIENT

although

P. A.

This male patient had a severe skeletal Class II malocclusion with a mild brachyfacial growth pattern. The skeletal Class II relationship was due to a combination of maxillary prognathism and mandibular retrognathism. The brachyfacial growth pattern was unaltered by treatment, although the skeletal Class II pattern was less severe after treatment. The salient features are the considerable mandibular growth, the vertical stability of the mandible, and the reduction of maxillary prognathism. The vertical position of the incisors appears stable. Vertical and distal movement of the molars was noted.

I. K.

This female patient was diagnosed as having a severe skeletal Class II malocclusion with a mild brachyfacial growth pattern. Cephalometric analysis revealed a prognathi; maxilla and a retrognathic mandible. A severe overbite and overjet were present. The brachyfacial growth pattern persisted during treatment. The most pertinent feature of the changes that occurred during treatment is that of mandibular growth. Vertical and mesial mandibular molar movement occurred. Vertical incisor position was stable. Considerable mandibular growth occurred and there was some counterclockwise or

PATIENT

K. V.

This female patient had a mild dolichofacial pattern and a severe skeletal Class II malocclusion. The skeletal Class II malocclusion was due to a retrognathic mandible and a vertical mandibular growth tendency. Overjet was increased and overbite was normal, although, as a result of the vertical growth tendency, a tendency for a skeletal open bite to develop was anticipated. The major changes appear to be a result of mandibular growth. Despite the diagnosis of vertical growth, a slight counterclockwise (closing) rotation of the mandible

102

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Levin

a IK 12.L

d

Flg. 6. Patient I. K.

occurred. A small distal maxillary displacementoccurred and rotation was not discernible. Dental movement was slight, with the exception of the mandibular first molar.

the mandibular molar erupted more than the incisor. The deep overbite was reduced. PATIENT B. H.

PATIENT A. J.

This male patient presented with a mild dolichofacial growth pattern. A ClassII malocclusion with severeoverbite and ovetjet was noted; this was causedby proclined maxillary incisors and a retracted mandibular dentition. The vertical position of the mandible was relatively stable during treatment, despite a more obvious maxillary rotation. Mandibular growth appearsto have been considerable.Mandibular growth in combination with some distal maxillary molar movement appearsto have resulted in a reduction of the Class II malocclusion. Noteworthy is the observation that, despite the dolichofacial type and vertical molar movement, the dolichofacial pattern was scarcely influenced adversely during treatment. PATIENT I. G.

This female patient had mesofacial growth pattern with a ClassII malocclusion. The dominant feature was the severe dentoskeletaldeep bite. During treatment, facial rotation was slightly clockwise. Some mandibular growth occurred, and

This female patient had a mesofacial growth pattern and a Class II malocclusion. The most conspicuouschange was that of clockwise facial rotation. There was little evidenceof a dental repositioning, the changes appeared to be predominantly orthopedic in nature, and little facial growth appeared to have occurred. PATIENT A. L.

This female patient had a mild brachyfacialgrowth pattern and a severeClass II skeletal malocclusion due to maxillary prognathism. The dominant effect of treatment appears to have been orthopedic, with a resulting clockwise facial rotation. Lengthening of the anterior facial height resulted in a mesofacial type. The maxillary molar was moved distally, and vertical movement of both maxillary and mandibular molars occurred. Incisors were vertically stable. PATIENT C. C.

This female patient had a dolichofacial growth pattern with a severeClass II skeletal and dental pattern. Cephalo-

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a AJ 12 3

C

d

142,130

Fig. 7. Patient A. J.

metric analysisshowed a severeskeletal ClassII malocclusion due to a retrognathic mandible. Considerable orthopedic and dental changesoccurred in the maxilla. Clockwise (opening) mandibular rotation occurred, and mandibular dental changes were slight. The severe skeletal pattern persisted, although facial convexity was considerably reduced as a result of a reduction in maxillary prognathism. PATIENT N. V.

This female patient had a mesofacial growth pattern with a severeskeletal Class II malocclusion due to a retrognathic mandible. During treatment a clockwise facial rotation occurred. Distal repositioning of the maxillary teeth ;andmaxillary rotation are the most prominent features of the changes during treatment. Mandibular growth appears to have been slight and clockwise rotation is evident. PATIENT J. V.

This male patient had a dolichofacial growth pattern with a severeskeletal Class II malocclusion due to a retrognathic mandible. Reduction of the skeletal Class II malocclusion is evident, facial rotation was limited, and little vertical maxillary or mandibular molar eruption occurred. Vertical position

of the incisors also appears to have been stable. The most salient feature is the overall vertical stability. The casesof Patients P. A., N. V. and J. V. are further illustrated in Figs. 2, 5, and 11. They represent changesin a brachyfacial type of facial pattern undergoing rapid facial growth (Patient P. A.), a mesofacial type with limited facial growth during the treatment period (Patient N. V.), and a dolichofacial pattern with rapid facial growth during the treatment period (Patient J. V.). DISCUSSION The combination of activator and headgear appliances can be used effectively in the treatment of selected cases. With this method, Class II, Division 1 malocclusions can be reduced significantly within a relatively short time span. Reduction of the dentoskeletal abnormality may be followed, when indicated, by a further period of fixed or removable appliance treatment. Although the effect of the activator on the growth of the mandible is beyond the limits of the data presented in this investigation, it is not to be inferred that mandibular growth does not adapt in response to the

104

Loin

a IG 13.2

C

Fig. 8. Patient

effects of the activator. However, it is evident that a favorable growth pattern and a large quantitative mandibular growth seem to be prerequisites for an improvement in mandibular prognathism. The combined effects of the appliances have been shown to influence dentoalveolar development, restrain sagittal maxillary growth, and induce facial rotation. The dentoalveolar changes appear to be similar to those changes described by Harvold.5 6 BjSrk and Skieller’3 have shown, in untreated cases, that a compensatory occlusal development occurs in response to anterior jaw rotation. Mandibular molar eruption and mesial migration take place, molar eruption is greater than incisor eruption, and the occlusal plane opens backward. In normal occlusal development the mandibular rotation and rotation of the occlusal plane take place around the lower incisor edge. In abnormal occlusal development, rotation of the mandible occurs around a center in the premolar area. Extrapolation of Bjork’s findings to the changes found in activator headgear cases would appear to provide an insight into the

d

I. G.

function of the activator. It appears that when the activator is worn, in addition to the obvious mandibular protrusion, it stabilizes the vertical position of the mandibular incisors so that the growth rotation of the mandible and rotation of the occlusal plane take place around the lower incisor edge, as in normal occlusal development. This appears to facilitate correction of the molar occlusion and a leveling of the curve of Spee. The curve of Spee is leveled by greater eruption of the molars and premolars relative to the mandibular incisors. In the maxillary dental arch the path of eruption of the molar, which normally is directed mesially, is guided distally. Palatal movement of the incisors occurs, and the prominence of the anterior aspect of the maxilla is reduced. In some cases a downward and backward rotation of the maxilla is evident. The vertical position of the maxillary incisors within the alveolus remains relatively stable. The lower incisor edge is generally repositioned forward by about 3 mm relative to the AP line. The maxillary and mandibular dentoalveolar changes, occurring during a period of facial

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d

Fig. 9. Patient B. H.

growth in which mandibular growth is greater than that of the maxilla, result in a reduction of the Class II dental malocclusion. The combination of the changes results in an occlusal realignment. In those cases in which facial growth was quiescent or slight or in which a dolichofacial type existed, downward and backward maxillary and mandibular rotation was observed (with the exception of Patients J. V., K. V., and A. J.). This occurrence results in a lengthening of the anterior facial height. This finding has been previously described and attributed to the ven:ical effects of the appliance exceeding vertical condylar growth.‘, 9 The case of Patient J. V. is interesting in that, despite the obvious dolichofacial type, adverse facial rotation was not observed. In Patient P. A., despite a backward rotation and increase in height of the maxilla, the mandible rotated slightly counterclockwise or closed. A period of rapid mandibular growth may account for the lack of rotational effect on the mandible in these cases, in contrast to the cases of Patient C. C. and N. V. In Patients B. H. and A. L., little mandibular growth was observed and appliance application ap-

peared to result in a predominantly orthopedic effect, expressed as a downward and backward facial rotation. Thus, although a reduction in facial convexity occurs, it may be accompanied by a lengthening of the anterior facial height. Characteristically, the Class II skeletal abnormality persists in a reduced form, and a tendency toward a more dolichofacial pattern may be noted. The hypothetical basis for the simultaneous application of activator and cervical headgear appears to be partially substantiated by the clinical observations. The combined effect of the appliances appears to be enhanced when their action on dentoalveolar development is considered. This aspect of the hypothesis appears to be corroborated. However, this is not so in relation to the effect of the appliances on skeletal development. Selective guidance of tooth eruption effected by the activator is enhanced by the distal translatory forces of the headgear moving molars distally. This aspect seems to be important as it results in a more efficient handling of the maxillary molars in order to rapidly establish a Class I molar occlusion. The vertical forces elicited by the activator appear to be insufficient to produce the

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Loin

a cc 10 0

z

\ .

84./d

P: c

d

Fig. 10. Patient C. C.

most desirable vertical control of maxillary development and hence limit adverse mandibular rotation. Possibly the vertical extrusive effects of the headgear override the inhibiting effect of the activator or the effects of the activator cause a clockwise (opening) rotation. The hypothesis that proposes greater vertical control of maxillary development when using the activator, although unsubstantiated in the present study, should not be disregarded. Rather it should be re-examined in the light of a recent study by Luder,14 who found that the height of the construction bite is significant in determining the effect of the activator on facial rotation. Greater height results in greater control of facial rotation. In Luder’s investigation, as well as in the present study, the height of the construction bite was related to the depth of the overbite. Further study on the effects of the activator constructed with a construction bite, where height is unrelated to the depth of the overbite, is necessary. CONCLUSIONS

It may be concluded that activator cervical headgear therapy results in a simulation of normal mandibular occlusal development and a redirection of maxillary

dentoalveolar development. Clockwise rotation of the maxilla or mandible may occur, and an occlusal realignment occurs within the framework of the rotating jaws. In a period of reduced facial growth there was a tendency for an orthopedic effect to predominate, resulting in a clockwise facial rotation and hence a tendency toward a more dolichofacial type. Mesofacial and brachyfacial types appear to respond most favorably to treatment. Nevertheless, recognition of the difficulties generally encountered in the treatment of dolichofacial types, especially in view of the apparent ease with which the patients described here were treated, indicates that there may be some merit in considering activator cervical headgear therapy for dolichofacial types undergoing rapid facial growth. However, these cases should be handled very cautiously, with particular attention to factors influencing the control of the vertical dimension. Factors of importance in controlling the vertical dimension are the construction bite, trimming of the activator, and the cervical headgear, which could be favorably substituted by an occipital low- or medium-pull headgear. In cases of the dolichofacial type and a slow growth rate, cervical traction appears contraindicated and a combination of ac-

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Fig. lla to f. Patient J. V.

Fig. 11A to D. Patient J. V.

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Fig. 11E to H. Patient J. V.

tivator with occipital medium- to high-pull headgear is more appropriate. Indirectly, the vertical control of facial growth may be improved by the following clinical procedures: Coordination of treatment with the circumpubertal growth period to ensure that the treatment is timed to occur in a period of the most rapid facial growth. A clinical method of growth prediction to estimate the period of maximum growth rate using standard height measurements has been suggested.” Finally, clinical monitoring of the rate of bite opening and changing facial appearance indicate the possibility of an adverse treatment effect. In dolichofacial types a rapid bite opening with a tendency for an open bite to develop indicates that an adverse facial rotation is occurring. Further study is indicated to evaluate the effects of the appliances on facial rotation when an activator for which the height of the construction bite is unrelated to the depth of the overbite is used. Additional study, relating timing of treatment to facial rotation and the

influence of extraoral traction in combination with the activator on facial rotation, is necessary. REFERENCES 1. McNamara JA Jr: Neuromuscular and skeletal adaptations to altered function in the orofacial region. AM .I ORTHOD 64: 578606, 1973. 2. McNamara JA Jr, Carlson DS: Quantitative analysis of temporomandibular joint adaptations to protrusive function. AM J ORTHOD 76: 593-611, 1979. 3. McNamara JA Jr, Hinton FU, Hoffman DL: Histologic analysis of temporomandibular joint adaptations to protrusive function in young adult rhesus monkeys (Mucaca mulurra). AM J ORTHOII

82: 288-298, 1982. 4. Tonge EA, Heath JK, Meikle

MC: Anterior mandibular displacement and condylar growth. AM J ORTHOD 82: 277-287. 1982. 5. Harvold EP: The activator in interceptive orthodontics, St. Louis, 1974, The C.V. Mosby Company. 6. Harvold EP, Vargervick K: Morphogenetic response to activator treatment. AM J ORTHOD 60: 478-490, 1971. 7. Pfeiffer JP, Grobety D: A philosophy of combined orthopedicorthodontic treatment. AM J ORTHOD 81: 185-201, 1982.

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8. Williams S, Melsen B: The interplay between sagittal and vertical 1982. growth factors. AM .I ORTHOD 81: 327-332, 9. Melsen B: Effects of cervical anchorage during and after treatment: an implant study. AM J ORTHOD 73: 526-539, 1’978. 10. Kragt Cl: Initial dentofacial orthopedic reactions: a ho.ographic study. Medical Dissertation, University of Groningen, 1981. 11. Jacobson A: A key to the understanding of extraoral forces. AM J ORTHOD 75: 361-386, 1979. 12. Ricketts RM, Bench RW, Gugino CF, Hilgers JJ, Schulhof RJ: Bioprogressive therapy, Book I, Denver, 1979, Rocky Mountain/ Orthodontics. 13. Bjork A, Skieller V: Facial development and tooth eruption. AM J ORTHOD 62: 339-383, 1972.

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14. Luder HU: Skeletal profile changes related to two patterns of activator effects. AM .I ORTHOD 81: 390-396, 1982. 15. Sullivan PC: Prediction of the pubertal growth spurt by measurement of standing height. Eur J Orthod 5: 181-197, 1983.

Reprint requests to: Dr. R. I. Levin Koningsplein 10 2611 XD Delft, The Netherlands