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Effects of a fixed magnetic appliance on the dentofacial complex
Effects of a$xed magnetic appliance on the dentofa/ciaZ complex Varun Kalra, BDS, MDS, D. Orth., MS,* Charles J. Burstone, DDS, MS,** and Ravindra Nanda, BDS, MDS, PhD*** Farmington,
Corm.
The purpose of the study was to design and evaluate the effects of a fixed magnetic appliance that hinged the mandible open and exerted an intrusive force on the teeth. Ten patients between the ages of 8 years and 10 years 6 months, with Class II, Division 1 malocclusion associated with mandibular retrusion and increased lower facial height, were treated with this appliance. The length of treatment was 4 months, after which the appliance was removed and the patients were followed up for 4 months. Ten children with similar age, sex, and dentofacial characteristics acted as controls and did not receive any appliance therapy. Changes in morphology of the dentofacial complex were evaluated by use of lateral cephalograms and study models. In addition temporomandibular joint and muscle functions were assessed. During treatment mandibular length increased 3.2 mm, angle of facial convexity decreased 2.8”, the upper and lower teeth intruded an average of 1.5 mm each, and the mandibular plane angle decreased 1.3”. In the follow-up period, some rebound eruption was noted; however, all other changes were stable. (AM J ORTHOD DENTOFAC ORTHOP 1989;95:467-78.)
I
t has been estimated that two thirds of the patients treated by orthodontists in the United States have mandibular retrusion characteristics.’ Some of these patients also have an increased lower facial height and large interlabial gap. In such patients treatment with conventional orthodontic appliances may lead to Class I occlusion. However, this often does not provide a satisfactory result in terms of stability and facial esthetics. At present the only definitive method of improving dentofacial harmony in these patients is by means of surgical superior repositioning of the maxilla. This procedure increases the interocclusal space and allows upward and forward autorotation of the mandible, thereby decreasing lower facial height and facial convexity. Often concomitant with superior repositioning of the maxilla, the mandible also is surgically advanced to further reduce mandibular retrusion. Recently Dellinger’ reported on the use of a magnetic appliance to treat patients with skeletal open bite. This appliance resulted in intrusion of posterior teeth and an upward and forward autorotation of the mandible. There were two hypotheses for this study. (1) If all erupted teeth in the upper and lower arches could be From the University 3f Connecticut School of Dental Medicine. Supported in part by NIH Grant DE-03953-12. *.ksistant Professor. Department of Orthodontics. **Professor and Chairman. Departmenr of Orthodontics. ***Professor. Department of Orthcdomics.
LINGUAL WIRE
Fig.
1. Schematic
drawing
of appliance.
intruded with an appliance, the mandible would autorotate upward and forward into the interocclusal space created. (2) If this appliance could displace the condyle downward and forward, away from the posterior part of the glenoid fossa, stimulation of condylar growth might occur. Both these effects, an increase in length of the mandible and an upward and forward autorotation of the mandible, would be beneficial in treating Class II malocclusions associated with increased lower facial height and a retrusive mandible. The objectives of this study therefore were to (1) design an appliance that hinges the mandible open and exerts an intrusive force 467
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Nanda
Orthop. June 1989
Fig. 2. Occlusal view of appliance. Table I. Force produced by the appliance Distance between and lower splints
upper (mm)
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 6.0
Repelling force fgm) 3500 2640 2040 1630 1315 1080 890 730 600 480 330
on the teeth and (2) evaluate the effects of this appliance on the morphology and function of the dentofacial complex. MATERIALS AND METHODS The subject pool in the study consisted of 20 boys and girls who were between the ages of 8 years and 10 years 6 months and who had Class II, Division 1 malocclusion associated with mandibular retrusion. The angle of facial convexity, lower facial height, and interlabial gap were greater than normal. The permanent first molars and incisors had erupted; the overjet ranged from 6 to 10 mm and the overbite varied from 0 to 3 mm. The 10 subjects in the treatment group and the 10 subjects in the control group were closely matched with regard to age, sex, and dentofacial characteristics. The active treatment time was 4 months, after which
appliances were removed and the patients observed for an additional 4 months. Subjects in the control group were studied for 8 months. Appliance design The working bite was taken with the mandible in centric relation and opened 7 to 8 mm in the permanent first molar region. The appliance consisted of upper and lower acrylic splints that were bonded on the occlusal halves of the permanent first molars, deciduous molars or premolars, and canines (Figs. 1 through 3). Samarium cobalt magnets measuring 20 X 8 x 2 mm were encased in a stainless steel case 0.007-inch thick and embedded into the upper and lower acrylic splints in a repelling mode. In addition a 0.028-inch wire was embedded in the acrylic. This wire rested on the lingual surfaces of the four permanent incisors and was individually bonded to them; thereby intrusive forces were transmitted to the entire arch. The size and shape of the magnets were designed in collaboration with Recoma Inc.* The steel cases were fabricated in cooperation with the Bioengineering Department, University of Connecticut Health Center. The forces produced by the appliance are listed in Table I. Cephalometric
analysis
Changes in craniofacial morphology caused by growth and treatment were determined from a set of lateral cephalometric head films. A set consisted of two cephalograms, one taken with the mandible in centric relation and the other with the mouth wide open to *Recoma Inc., Fairfield, N.J.
Vo/ume 9s Numhrr 6
Fig.
3. Buccal
facilitate visualization of the condyles. For each patient in the treatment group, the first set of head films was taken before treatment, the second set of films after 4 months active treatment, and the third set 4 months posttreatment. In the control group, an initial set and a final set of cephalograms were taken 8 months apart. Changes between the two sets of films in the control group were divided by two to obtain changes throughout a 4-month period. Subsequent cephalograms were superimposed on the anterior cranial base of the previous cephalogram as described by Baumrind, Miller, and Molthen. Vertical and horizontal positional changes of certain landmarks were measured in relation to two Cartesian coordinate systems. In the first system, the originally constructed Frankfort horizontal (FH) plane (constructed by subtracting 7” from the sella-nasion line) served as the X axis and a line perpendicular to it through sella served as the Y axis. In the second system, the original natural occlusal plane formed the X axis and a line perpendicular to it through sella formed the Y axis. The two coordinate systems were transferred from the first tracing to the next. In addition certain other linear and angular measurements were assessed (Figs. 4 through 6). Separate maxillary and mandibular tracings were superimposed3 to determine changes in the position of the teeth within the maxilla and the mandible. Changes in the position of the teeth were measured in relation to the original occlusal plane (X axis) and a line perpendicular to it through sella (Y axis). The length of the mandible, condylionprognathion (Co-Pgn), was measured from the open mouth cephalogram.
view
of appliance.
N FH
co*J cos COP
Fig. 4. Cephalometric landmarks and linear measurements used in the study. (1) N-ANS, Upper anterior facial height measured perpendicular to Frankfort horizontal (FH) plane. (2) ANSMe, Lower anterior facial height measured perpendicular to FH plane. (3) A-El to occlusal plane. (4) Condylion-pogonion (CoPg), Length of mandible parallel to FH plane. (5) Co-Go, Posterior facial height measured perpendicular to FH plane.
Assessment of temporomandibular muscle function
joint and
An assessment of the function of the masticatory system was conducted to ascertain the status of any signs and symptoms of dysfunction that were present or that might develop. The assessment was based on a
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Fig. 5. Mandibular length, condylion-prognathion measured from wide open mouth cephalogram.
Orthop. June 1989
(Co-Pgn),
clinical dysfunction examination and on anamnestic dysfunction as described by Helkimo.4 For the treatment group, assessments were made at the following time intervals: before treatment, 3 days after insertion of appliance, 3 months after insertion of appliance, on removal of appliance, and 4 months posttreatment. For the control group, assessments were made at the start of the examination period and 8 months later. Results of the cephalometric and study model analyses were statistically analyzed. To assess the significance of differences between the treatment and control groups, mean and standard deviation were calculated and Student’s t tests were performed. The null hypothesis was rejected at the 0.05% level of confidence. The size of the combined error in locating, superimposing, and measuring the changes in different landmarks was calculated with the following. formula: SE measurement =
Dentofac.
J
Zd2 2n
The combined standard error did not exceed 0.6 mm in the horizontal and vertical dimensions. RESULTS
The effects of the magnetic appliance during treatment and during the follow-up period are given in Tables II and III. Mandible
During treatment the length of the mandible, condylion-prognathion (Co-Pgn) , increased 3.2 mm as compared with 0.8 mm in the control group (p < 0.001). In the follow-up period, no difference was seen in growth rates of the treatment and control groups (Fig. 7).
Fig. 6. Angular measurements used in the study. (6) 1 to-FH plane. (7) Y axis. (8) N-A-Pg, Angle of facial convexity. (9) 1 to mandibular plane. (10) FH-MP, Mandibular plane angle.
In the treatment group, the mandible autorotated upward and forward as judged by the mandibular plane angle and Y axis. The mandibular plane angle decreased 1.3” and 0.3”; the Y axis decreased 1.1” and 0.3” in the treatment and follow-up periods, respectively. These changes were small but statistically significant. Overall facial form
Downward and forward displacement of2 the maxilla, as represented by anterior nasal spine and point A, did not show any significant differences between the treated and control groups. There was a significant decrease in the angle of facial convexity (p < 0.001) (Fig. 8) and improvement in the relationship of A-B to occlusal plane (p < 0.001) (Fig. 9). Even though the mandible autorotated upward and forward, increased mandibular growth was responsible for an increase in anterior (ANS-Me) and posterior (CoGo) facial heights (p < 0.001). Fig. 10 shows the change in overall facial form in the treatment group as compared with the control group. Dentition
During treatment the upper and lower incisors intruded approximately 1.3 mm each and the molars 1.6 mm each. During this period, in the control group, these teeth erupted 0.3 and 0.4 mm, respectively (Fig. 11). In the follow-up period, the posterior teeth reerupted until they achieved occlusal contact with their antagonists (Fig. 12). However, overall the lower incisor
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Table II. Comparison of changes between treatment and control groups during treatment period Treatment p-oup (N = IO) Measurements Mandible Length Co-Pgn (mm) Co-Pg parallel to FH (mm) Displacement in relation to FH Pg horizontal (mm) Pg vertical (mm) Rotation MP-FH (“) Y axis (“) Maxilla Displacement in relation to FH Point A horizontal (mm) Point A vertical (mm) ANS horizontal (mm) ANS ven:ical (mm) Facial height ANS-Me perpendicular to FH (mm) Co-Go perpendicular to FH (mm) Facial convex,@ N-A.-Pg (“) A-B perpendicular to OP (mm) Dentitinn Overjet (mm) Overbite (mm) Molar relation (mm)* Upper incisor to FH (“) Lower incisor to MP (“) Changes in tooth position within the maxilla and mandible (measured from maxillary and mandibular superimposition tracings)** Vertical displacement Upper molar (mm) Lower molar (mm) Upper incisor (mm) Lower incisor (mm) Horizontal displacement Upper molar (mm) Lower mlolar (mm) Upper incisor (mm) Lower incisor (mm)
Control group (N = IO) Mean difference
Mean
SD
Mean
SD
+3.2 +2.1
0.5 0.6
+0.8 1-0.5
0.2 0.2
2.4 1.6
< 0.001 < 0.001
+2.6 + 1.9
0.9 I.1
+0.5 +0.5
0.2 0.3
2.1 1.4
< 0.001 < 0.01
- 1.3 - 1.1
0.8 0.5
0 0
0.2 0.1
1.3 1.1
< 0.001 < 0.001
+0.5 +0.3 +0.5 +0.2
0.2 0.2 0.3 0.2
+0.4 +0.2 +0.4 +0.2
0.3 0.2 0.2 0.3
0.1 0.1 0.1 0
NS NS NS NS
+ 1.8 +2.6
1.1
+0.4 +0.6
0.2 0.2
1.4 2.0
i 0.01
0.9
-2.8 +2.3
0.9 0.9
-0.1 +0.1
0.1 0.1
2.7 2.2
< 0.001 < 0.001
-2.1 -3.8 +2.0 +0.2 -0.1
0.7 0.9 0.8 0.6 0.7
-0.1 +0.1 -0.1 +0.2 +0.1
0.2 0.2 0.1 0.5 0.6
2.0 3.9 2.1 0 0.2
< 0.001 < 0.001 < 0.001 NS NS
+ +
0.3 0.3 0.4 0.2
+0.2 -0.3 +0.4 -0.3
0.1 0.2 0.3 0.1
1.8 1.9 1.8 1.5
< < < <
0.4 0.2 0.4 0.5
+0.1 0 +0.1 0
0.2 0.3 0.1 0.3
0 0.2 0.1 0
1.6 1.6 1.4 1.2
+0.1 +0.2 0 0
p value
< 0.001
0.001 0.001 0.001 0.001 NS NS NS NS
+ Denotes downward or forward displacement of landmark. - Denotes upward or backward displacement of landmark. * + Denotes imprc’vement of molar relationship toward Class I. **The maxilla was superimposed on the hard palate and the anterior maxillary structures with main consideration being given to the region between point A ar,d the anterior nasal spine with the images of the superior surfaces of the hard palate aligned. The mandible was superimposed on the inner tables of the symphysis and the line of distal extension of the mandible.
(p < O.OOl), upper incisor (p < O.Ol), and upper molar (p < 0.05) showed less eruption in the treated group than in the control group as seen in Table IV and Fig. 13. In the treatment period, the overjet was reduced 2.1
mm and the molar relationship improved 2.0 mm toward Class I occlusion as a result of increased forward displacement of the mandible in relation to the maxilla; this remained unchanged during the follow-up period. Magnets used in the repelling mode produce lateral
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Tabie III. Comparison of changes between treatment and control groups during follow-up period Treatment group (N = 10) Measurements
Length Co-Pgn (mm) Co-Pg parallel to FH (mm) Displacement in relation to FH Pg horizontal (mm) Pg vertical (mm) Rotation MP-FH (“) Y axis (“) Maxilla Displacement in relation to FH Point A horizontal (mm) Point A vertical (mm) ANS horizontal (mm) ANS vertical (mm) Facial height ANS-Me perpendicular to FH (mm) Co-Go perpendicular to FH (mm) Facial convexity N-A-Pg (“) A-B perpendicular to OP (mm) Dentition Overjet (mm) Overbite (mm) Molar relation (mm)* Upper incisor to FH (“) Lower incisor to MP (“) Changes in tooth position within the maxilla and mandible (measured from maxillary and mandibular superimposition tracings)** Vertical displacement Upper molar (mm) Lower molar (mm) Upper incisor (mm) Lower incisor (mm) Horizontal displacement Upper molar (mm) Lower molar (mm) Upper incisor (mm) Lower incisor (mm)
Control group (N = 10) Mean difference
Mean
SD
Mean
SD
+0.7 +os
0.2 0.3
i-O.8 +0.5
0.2 0.2
0.1 0
NS NS
+0.6 +0.4
0.2 0.2
+0.5 +0.5
0.2 0.3
0.1 0.1
NS NS
-0.4 -0.3
0.2 0.2
0 0
0.2 0.1
0.4 0.3
< 0.05 < 0.05
+0.3 +0.4 +0.4 +0.2
0.2 0.4 0.2 0.3
+0.4 +0.2 +0.4 +0.2
0.3 0.2 0.2 0.3
0.1 0.2 0 0
NS NS NS NS
+0.2 +0.5
0.2 0.2
to.4 +0.6
0.2 0.2
0.2 0.1
NS NS
-0.3 +0.3
0.2 0.2
-0.1 +0.1
0.1 0.1
0.2 0.2
< 0.05 < 0.05
0 +2.8 +0.1 +0.4 -0.4
0.3 0.4 0.2 0.6 0.5
-0.1 +0.1 -0.1 +0.2 to.1
0.2 0.2 0.1 0.5 0.6
0.1 2.1 0.2 0.2 0.5
NS < 0.001 NS NS NS
+ 1.8 -2.1 +1.4 - 1.4
0.4 0.5 0.5 0.3
+0.2 -0.3 +0.4 -0.3
0.1 0.2 0.3 0.1
1.6 1.8 1.0 1.1
< < < <
+0.1 +0.2 +0.2 -0.1
0.4 0.3 0.2 0.4
+0.1 0 +0.1 0
0.2 0.3 0.1 0.3
0 0.2 0.1 0.1
p value
0.001 0.001 O.ctOl 0.001 NS NS NS NS
+ Denotes downward or forward displacement of landmark. - Denotes upward or backward displacement of landmark. * + Denotes improvement of molar relationship to Class I. **The maxilla was superimposed on the hard palate and the anterior maxillary structures with main consideration given to the region point A and the anterior nasal spine with the images of the superior surface of the hard palate aligned. The mandible was superimposed inner tables of the symphysis and the line of distal extension of the mandible.
forces as they are moved toward each other. stilted in buccolingual tipping of the teeth in terior segments. It was found that in centric seven patients had a molar crossbite on one
This rethe pos-, relation, side and
between on the
an increased buccal overjet on the other side. However, during the follow-up period, the teeth uprighted to their original inclinations, thereby correcting the crossbite on one side and the increased buccal overjet on
EfJects of‘,fixed magnetic appliance
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Co-Pgn H Treatment Group q Control Group
(MM) 0
1’
Treatment
Period
Follow-up
Perlod
Fig. 7. Change in mandibular length (Co-Pgn).
the other side. The intermolar width remained unchanged. Function None of the patients in the treatment or control groups complained of difficulty in opening the mouth maximally, of stiffness of jaws, locking, luxation or pain on movement of the mandible, pain in the region of the temporomandibular joint, or pain of the masticatory musculature during any stage of the study. Similarly clinical examination of the muscles of mastication and temporomandibular joint function showed that patients in the treatment group did not experience any discomfort, pain, or temporomandibular joint dysfunction at any stage of treatment. The appliance was accepted extremely well by the children and, apart from initial awkwardness, none complained of discomfort nor difficulty in speech and eating. Patients used a fluoride rinse daily and maintained good oral hygiene; as a result neither caries nor decalcification was noted during treatment. DISCUSSION The two most important findings in the study were that the length of the mandible increased significantly in the treated group and the entire upper and lower arches intruded during treatment. In 4 months of treatment, the length of the mandible in the treated group increased 3.2 mm as compared with 0.8 mm in the control group. The specially constructed magnetic appliance held the mouth open 7 to
8 mm in the first molar region when the upper and lower splints were in contact, and 10 to 11 mm open when the mandible was in the acquired “rest” position. This caused the condylar heads to rotate and translate forward, away from the posterior aspect of the glenoid fossa. A number of researchers5-‘7have shown increased condylar growth in animal studies with appliances that caused protraction or hyperpropulsion of the condyles. Reports on the use of functional appliances, either a form of activator or the Frankel FR, present contradictory results. Some studies’*-*’ show increase in mandibular growth; others22-28find that mandibular growth is not increased with the use of either type of appliance. Conflicting results with the use of removable functional appliances could be attributed to the fact that they are dependent on patient cooperation and clinical expertise and at best are worn only part of the day. It is possible that in growing persons there is stimulation of condylar growth when the condyles are protracted by the functional appliance, but this ceases when the appliance is removed from the mouth. All anima15-” and human studies29-33that use fixed splint-like devices to hold the mandible forward 24 hours a day show an increase in mandibular growth. It could be that the determining factor is the amount of time the appliance is worn each day. Moss and Salentijn34 claim that growth at the condyle appears to take place as a secondary phenomenon to fill the space left by the mandible as it is displaced forward by the tissues around it. Enlow” also reports condylar growth to be of a compensatory nature rather than a primary process.
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N-A-Pg q Treatment b9 Control
-4'
Treatment
Period
Follow-up
Group Group
Period
Fig. 8. Change in the angle of facial convexity (N-A-Pg).
A-B (OP) S Treatment Group RI Control Group
MN
0
-1'
Treatment
Period
Follow-up
Period
Fig. 9. Change in the relationship of A-B to occlusal plane.
Petrovi? and McNamara, Connelly, and McBride12 attributed increased condylar growth to increased activity in the lateral pterygoid muscles. Later studies’3-‘7 indicated that the effect of the lateral pterygoid muscles may be mediated to the condyles via the stretch of the posterior portion of the capsule, the meniscotemporal ligament as the condyles come forward. Whetten and JohnstonJ6 have shown that severing the lateral pterygoid msucle did not affect growth of the condyle on the affected side. Recently McNamara and Carlson” noted that the adaptive changes in the temporomandib-
ular region may be caused by alteration in the biomechanical or biophysical environment of the joint that may be produced by muscular or nonmuscular forces. With the magnetic appliance in the mouth, the condyles moved down the articular slope about 10 mm away from the posterior aspect of the glenoid fossa. This could cause articular tissue strain with increased condylar growth as a fill-in process. However, the present state of knowledge precludes a definite answer to the mechanism of increased condylar growth. After removal of the appliances, the rate of growth
V&me 95 Number 6
Ejfects
’ _ ,’ ,’ :‘Y. ‘I.*‘ “II:,,,’!’ =._ I -._* q ‘a. --.* *.*..* -*. ‘v
,’uIi ,-I’ ,I’ ,’ /R,,;,;; :: ,/ . : : a’ a......,
Fig. 10. Composite tracing of lateral cephalograms showing the mean differences in dentofacial form between the treatment and control groups. Differences between the two groups are interpreted as changes caused by treatment. -, Pretreatment; - - -, 4 months posttreatment. The lateral cephalogram was superimposed on the anatomic structures of the floor of the anterior cranial fossa with primary consideration given to the region between the anterior clinoid process and crista galli.
of the mandible was found to be similar to that in the control group. Petrovic3’ and McNamara3’ have reported a decrea.sed amount of growth for a period following removal of “hyper-propulsion” appliances in animals. However, human studies29-33with the Herbst appliance have shown normal mandibular growth after removal of the appliance. The results of this study concur with those of the latter. It was decided to use magnets to provide the intrusive force on the teeth since any other form of mechanical device would either interfere with function or not provide such an efficient system. The size and shape of the magnets were dictated by space available in the mouth, patient comfort, and the force that they could generate. Samarium cobalt magnets were chosen since they have an excellent ratio of magnetic force to size.3g4’ In addition they are far superior in resisting loss of magnetic energy with time and are safe to use in the mouth.394’ However, samarium cobalt is susceptible to corrosion in the oral environment39; therefore
of’jked
magnetic
appliance
on dentofacial
comple?r
475
Fig. 11. Composite of maxillary and mandibular superimposition tracings showing the mean differences in the position of the teeth between the treatment and control groups during the treatment period. Differences between the two groups are interpreted as changes caused by treatment. -, Pretreatment; - - -, posttreatment. The maxilla was superimposed on the hard palate and the anterior maxillary structures with main consideration given to the region between point A and the anterior nasal spine with the images of the superior surfaces of the hard palate aligned. The mandible was superimposed on the inner tables of the symphysis and the line of distal extension of the mandible.
the magnets were encased in a stainless steel case and embedded in the acrylic splints so that they were not exposed to the oral environment. With the appliance in the mouth, the subject tended to maintain an interocclusal space of about 3.0 mm between the upper and lower splints. At this distance the magnets produce a repelling force of 1080 gm, thereby subjecting each tooth in the arch to an intrusive force of approximately 90 gm. Burstone recommends an intrusive force of 20 gm for incisors. Dellingep3 showed that a force of 100 gm was adequate to intrude premolars in dogs. However, an optimum force value has not been established for intrusion of posterior teeth or large segments of teeth. Since some of the teeth covered by the appliance had large root surfaces, a force in the range of 90 gm per tooth was considered adequate, though perhaps excessive, for intrusion. More research is needed in this area to determine an optimum intrusive force. In a repelling mode, when the magnets are moved toward each other, lateral forces are generated. In most patients this caused the mandible to deviate about 2 mm to one side in the acquired “rest” position. This shearing force generally caused both upper buccal segments to be tipped to the right side of the patient and both lower buccal segments to be tipped to the left side. This re-
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and Nanda
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June 1989
Fig. 12. Composite of maxillary and mandibular superimposition tracings showing the mean difference in the position of the teeth between the treatment and control groups during the follow-up period. Differences between the two groups are interpreted as the amount of relapse. -, Posttreatment; - - -, 4 months posttreatment. The maxilla was superimposed on the hard palate and the anterior maxillary structures with main consideration given to the region between point A and the anterior nasal spine with the images of the superior surfaces of the hard palate aligned. The mandible was superimposed on the inner tables of the symphysis and the line of distal extension of the mandible.
Fig. 13. Composite of maxillary and mandibular superimposition tracings showing the mean differences in the position of the teeth between the treatment and control groups during treatment plus follow-up. Differences between the two groups are interpreted as overall additional change in the treated group. -, Pretreatment; - - -, 4 months posttreatment. The maxilla was superimposed on the hard palate and the anterior maxillary structures with main consideration given to the region between point A and the anterior nasal spine with the images of the superior surfaces of the hard palate aligned. The mandible was superimposed on the inner tables of the symphysis and the line of distal extension of the mandible.
IV. Comparison of changes in tooth position between treatment and control groups during treatment plus follow-up (measured from maxillary and mandibular superimposition tracings)*
Table
Treatment group (N = IO) Measurements Dent&ion Vertical Upper Lower Upper Lower Horizontal Upper Lower Upper Lower + Denotes - Denotes *The maxilla point A and inner tables
displacement molar (mm) molar (mm) incisor (mm) incisor (mm) displacement molar (mm) molar (mm) incisor (mm) incisor (mm)
Control group (N = 10) Mean difference
Mean
SD
Mean
SD
p value
+0.2 -0.5 0 -0.2
0.2 0.3 0.3 0.4
+0.4 -0.6 +o.s -0.6
0.2 0.2 0.2 0.2
0.2 0.1 0.8 0.4
+0.2 +0.4 +0.2 -0.1
0.3 0.3 0.5 0.3
+0.2 0 +0.2 0
0.3 0.2 0.5 0.3
0 0.4 0 0.1
NS NS NS NS
downward or forward displacement of tooth. upward or backward displacement of tooth. was superimposed on the hard palate and the anterior maxillary structures with main consideration given to the region the anterior nasal spine with the images of the superior surface of the hard palate aligned. The mandible was superimposed of the symphysis and the line of distal extension of the mandible.
sulted in a crossbite on the left side and an increased buccal overjet on the right side. The crossbite was dental in nature and tipping of the teeth in the buccal segments was very apparent on removal of appliances.
between on the
During the follow-up period, the tipped teeth reverted to their original inclinations and the crossbites were self-correcting. Since both the buccal segments in the upper arch tipped to the same side and both the buccal
Volume 95 Number 6
segments in the lower tipped to the other side, there were no significant changes in the upper and lower intermolar arch widths. In an effort to minimize or prevent the occurrence of crossbites, it is proposed that the amount of repelling force produced by the magnets be reduced, thereby also reducing the lateral forces generated. If buccal crossbites still occurred, they would be mild in nattire and self-correcting once the appliance was removed. Treatment with the magnetic appliance is followed by a phase of fixed appliance treatment to correct dental relationships; therefore correction of any buccolingual tipping, were it to remain, could readily be achieved at this stage. On removal of appliances, it was noticed that since the teeth had intruded, occlusion occurred only on the gum pads covering the unerupted second molars, leaving the posterior teeth about 4.0 mm out of occlusion. In retrospect examination of pretreatment study models and x-ray films showed that even though the upper and lower second molars were not close to eruption, the clearance between the soft tissues of the upper and lower pads averaged only about 1.0 mm. When the appliances were removed, upward and forward a&orotation of the mandible was limited by the gap between these pads. Autorotation of the mandible occurs when the freeway space is increased after surgical superior repositioning of the maxilla.“A7 In such instances the mandible acquires a new rest position, which appears stab1e.4s-47[t could therefore be assumed that if the gum pads had not caused obstruction, the mandible would have autorotated further and acquired a new, potentially stable rest position. Dellinge? reported on cases in which intrusion of posterior teeth had been achieved with the use of an Active Magnetic Vertical Corrector. He found that both intrusion of teeth and the ensuing autorotation of the mandible were stable 3 years later. In this study the teeth were prevented from achieving occlusal contact, resulting in reeruption until full occlusion of the posterior teeth was obtained. Nevertheless, throughout the entire treatment and follow-up period, the teeth in the treated group underwent statistically significant intrusion as compared with the control group. The limited autorotation of the mandible that was achieved was stable. In fact during the follow-up period, the mandible autorotated further. The appliance may have caused mild inflammation of the soft tissues distal to the first molars; once the appliances were removed, the inflammation gradually subsided and this allowed the mlandible to close a littler further. Since the slight intrusion and autorotation achieved were both stable, it can be hypothesized that if the gum pads had not prevented further autorotation, the enhanced auto-
.Effects of @fixedmagnetic appliance
on dentqfizcial complex
477
rotation achieved would also have remained stable and the teeth would not have reerupted to the extent they did. In the future it is proposed that removal of the tissue overlying the upper and/or lower second molars about a week before removal of appliances would be beneficial. This would allow autorotation of the mandible as determined by the amount of intrusion. CONCLUSIONS
A fixed magnetic appliance was designed that hinged the mandible open and exerted an intrusive force on the teeth. Treatment with this appliance resulted in: 1. An increase in length of the mandible 2. Intrusion of teeth 3. Upward and forward autorotation of the mandible 4. Reduction of A-B to occlusal plane 5. Improvement in the angle of facial convexity 6. Creation of temporary buccal crossbite caused by the shearing force of repelling magnets During follow-up there was some rebound eruption of teeth; however, all other changes were stable. This appliance presents a promising mode of improving facial harmony in patients with Class II, Division 1 malocclusion associated with mandibular retrusion, increased lower facial height, and increased interlabial gap. In addition reduction in overjet and improvement in molar relationship toward Class I occlusion make the second stage of conventional orthodontic treatment less demanding. Further research and development of the appliance are advocated. REFERENCES I. Graber TM. Orthodontics:
principles and practice. 3rd ed. Philadelphia: WB Saunders Company, 1972:205. 2. Dellinger EL. A clinical assessment of the Active Vertical Corrector-a nonsurgical alternative for skeletal open bite treatment. AM J ORTHOD 1986;89:428-36. 3. Baumrind S, Miller D, Molthen R. The reliability of head film measurements. 3. Tracing superimposition. AM J ORTHOD 1976; 70:617-44. 4. Helkimo M. Studies
5.
6.
7.
8.
on function and dysfunction of the masticatory system. II. Index for anamnestic and clinical dysfunction and occlusal state. Sven Tandlak Tidskr 1974:67: 101-Z 1. Petrovic A, Stutzmann J, Oudet C. Control processes in the postnatal growth of the mandibular condylar cartilage. In: McNamara JA Jr, ed. Determinants of mandibular form and growth. Ann Arbor, 1975. Center for Human Growth and Development. University of Michigan. Stockli PW, Willert HG. Tissue reactions in the temporomandibular joints resulting from anterior displacement of the mandible in the monkey. AM J ORTHOD 1971:60:142-55. Baume LJ, Derichsweiler H. Is the condylar growth center responsive to orthodontic therapy? An experimental study in Macaca mulatta. Oral Surg Oral Med Oral Path01 1961;14: 1371. Petrovic A, Stutzmann JJ, Gasson N. The final length of the mandible: Is it genetically predetermined’? In: Carlson DS, ed.
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Burstone, and Nanda
Craniofacial biology. Monograph 10, Craniofacial Growth Series. Ann. Arbor: 1981. Center for Human Growth and Development, University of Michigan. 9. McNamara JA Jr, Hinton RJ, Hoffman DL. Histologic analysis of temporomandibular joint adaptations to protrusive function in young adult rhesus monkeys (Macaca mulatta). AM J ORTHOD 1982;82:288-98. 10. Charlier JP, Petrovic A, Herrmann-Stutzmann J. Effects of mandibular hyperpropulsion on the prechondroblastic zone of young rat condyle. AM J ORTHOD1969;55:71-4. 11. Graber TM, Rakosi T, Petrovic AG. Dentofacial orthopedics with functional appliances. St. Louis: The CV Mosby Company, 1985.. 12. McNamara JA Jr, Connelly T, McBride MC. Histological studies of temporomandibular joint adaptations. In: McNamara JA Jr, ed. Determinants of mandibular form and growth. Ann Arbor: 1975. Center for Human Growth and Development, University of Michigan. 13. Petrovic AG, Stutzmann JJ. Further investigation into the functioning of the peripheral “comparator” of the servosystem (respective positions of the upper and lower dental arches) in the control of the condyle cartilage growth rate and of the lengthening of the jaw. In: McNamara JA Jr, ed. The biology of occlusal development. Ann Arbor: 1977. Center for Human Gmwth and Development, University of Michigan. 14. Petrovic A, Stutzmann J. Tierexperimentelle Untersuchungen uber das Gasichtsschadelwachstum and seine Beeinflunssung: eine biologische Erklarung der songenannte Wachstumsrotation des Unterkiefers. Fortscbr Kieferorthop 1979;40: 1. 15. McNamara JA Jr, Carlson DS. Quantitative analysis of temporomandibular joint adaptations to protrusive function. AM J ORTHOD1979;76:593-611. 16. Petrovic A. An experimental and cybernetic approach to the mechanism of action of functional appliances on the mandibular growth. In: McNamara JA Jr, ed. Malocclusion and the periodontium. Monograph 15, Craniofacial Growth Series. Ann Arbor: 1984. Center for Human Growth and Development, University of Michigan. 17. Petrovic AG, Stutzmann JJ, Lavergne J. Effects of functional appliances on the mandibular condylar cartilages. In: Graber TM, ed. Physiologic principles of functional appliances. St. Louis: The CV Mosby Company, 1985. 18. McNamara JA Jr, Bookstein FL, Shaughnessy TG. Skeletal and dental changes following function regulator therapy on Class II patients. AM J ORTHOD1985;88:91-110. 19. Marschner JF, Harris JE. Mandibular growth and Class II treatment. Angle Orthod 1966;36:89-93. 20. Friinkel R, Reiss W. Zur Problematik der Unterkiefermachentwicklung bei Distalbissfallen. Forts&r Kieferorthop 1970; 31:345-55. 21. Righellis EG. Treatment effects of Fr&kel activator and extraoral traction appliances. Angle Orthod 198353: 107-21. 22. Bjijrk A. ,The principle of the Andresen method of orthodontic treatment, a discussion based on cephalometric x-ray analysis of treated cases. AM J ORTHOD1951;37:437-58. 23. Jakobsson SO. Cephalometric evaluation of the treatment effect on Class II, Division 1 malocclusions. AM J ORTHOD1967; 53446-7. 24. Harvold EP, Vargervik K. Morphogenic response to activator treatment. AM J ORTHOD1971;60:478-90. 25. Ahlgren J. Late results of activator-treatment: a cephalometric study. Br J Orthod 1976;3:181-7.
Orthop. June 1989
26. Schulhof RJ, Engel GA. Results of Class II functional appliance treatment. J Clin Orthod 1982;16:587-99. 27. Creekmore TD, Radney ,LJ. Fr%nkel appliance therapy: orthopedic or orthodontic? AM J ORTHOD1983;83:89-108. 28. Robertson NRE. An examination of treatment changes in children treated with the function regulator of Frlnkel. AM J ORTHOD 1983;83:229-310. 29. Pancherz H. Treatment of Class I malocclusions by jumping the bite with the Herbst appliance: a cephalometric investigation. AM J ORTHOD1979;76:423-41. 30. Pancherz H. The effect of continuous bite jumping on the dentofacial complex: a follow-up study after Herbst appliance treatment of Class II malocclusions. Eur J Orthod 1981;3:49-60. 31. Pancherz H. The mechanism of Class II correction in Herbst appliance treatment. A cephalometric investigation. AM J ORTHOD1982;82:104-13. 32. Wieslander L. Intensive treatment of severe Class II malocclusions with a headgear-Herbst appliance in the early mixed dentition. AM J ORTHOD1984;86:1-13. 33. Kalra V, Be&man M, Sachdeva R, Nanda R. Effects of anterior repositioning of the mandible on the dentofacial complex. J Dent Res 1985;64:344. 34. Moss ML, Salentijn L. The capsular matrix. AM J ORTHOD 1969;56:474-90. 35. Enlow DM. Handbook of facial growth. Philadelphia: WB Saunders Company, 1982:122-3. 36. Whetten LL, Johnston LE Jr. The control of condylar growth: an experimental evaluation of the role of the lateral pterygoid muscle. AM J ORTHOD1985;88:181-90. 37. Petrovic A. Control of postnatal growth of secondary cartilages of the mandible by mechanisms regulating occlusion: cybernetic model. Trans Eur Orthod Sot 197469-75. 38. McNamara JA Jr. Functional adaptations in the temporomandibular joint. Dent Clin North Am 1975;19:457-71. 39. Tsutsui H, Konouchi Y, Sasaki H, Shiota M, Ushita T: Studies on the SmCo magnet as a dental material. J Dent Res 1977;58:1597-1606. 40. Blechman AM. Magnetic force system in orthodontics. AM J ORTHOD1985;87:201-10. 41. Blechman AM, Smiley M. Magnetic forces in orthodontics. AM J ORTHOD1978;74:435-43. 42. Burstone CJ. Deep overbite correction by intrusion. AM J ORTHOD1977;72:1-22. 43. Dellinger EL. A histologic and cephalometric investigation of premolar intrusion in the Macaca speciosa monkey. AM J ORTHOD 1967;53:325-54. 44. Bell WH, Creekmom TD, Alexander RG. Surgical correction of the long face syndrome. AM J ORTHOD1977;71:40-67. 45. Schendell SA, Eisenfeld J, Bell WH, Epker BN. Superior repositioning of the maxilla: stability and soft-tissue osseous relations. AM J ORTHOD1976;70:663-74. 46. Fish LC, Wolford LM, Epker BN. Surgical-orthodonic correction of vertical maxillary excess. AM J ORTHOD1978;73:241-57. 47. Wessberg GA, Washburn MC, LaBanc JP, Epker BN. Effect of surgical superior repositioning of the maxilla in mandibular resting posture. AM J ORTHOD1982;81:465-72. Reprint
requests
to:
Dr. Varun Kalra Department of Orthodontics University of Connecticut Health Center School of Dental Medicine Farmington, CT 06032
Corm.
The purpose of the study was to design and evaluate the effects of a fixed magnetic appliance that hinged the mandible open and exerted an intrusive force on the teeth. Ten patients between the ages of 8 years and 10 years 6 months, with Class II, Division 1 malocclusion associated with mandibular retrusion and increased lower facial height, were treated with this appliance. The length of treatment was 4 months, after which the appliance was removed and the patients were followed up for 4 months. Ten children with similar age, sex, and dentofacial characteristics acted as controls and did not receive any appliance therapy. Changes in morphology of the dentofacial complex were evaluated by use of lateral cephalograms and study models. In addition temporomandibular joint and muscle functions were assessed. During treatment mandibular length increased 3.2 mm, angle of facial convexity decreased 2.8”, the upper and lower teeth intruded an average of 1.5 mm each, and the mandibular plane angle decreased 1.3”. In the follow-up period, some rebound eruption was noted; however, all other changes were stable. (AM J ORTHOD DENTOFAC ORTHOP 1989;95:467-78.)
I
t has been estimated that two thirds of the patients treated by orthodontists in the United States have mandibular retrusion characteristics.’ Some of these patients also have an increased lower facial height and large interlabial gap. In such patients treatment with conventional orthodontic appliances may lead to Class I occlusion. However, this often does not provide a satisfactory result in terms of stability and facial esthetics. At present the only definitive method of improving dentofacial harmony in these patients is by means of surgical superior repositioning of the maxilla. This procedure increases the interocclusal space and allows upward and forward autorotation of the mandible, thereby decreasing lower facial height and facial convexity. Often concomitant with superior repositioning of the maxilla, the mandible also is surgically advanced to further reduce mandibular retrusion. Recently Dellinger’ reported on the use of a magnetic appliance to treat patients with skeletal open bite. This appliance resulted in intrusion of posterior teeth and an upward and forward autorotation of the mandible. There were two hypotheses for this study. (1) If all erupted teeth in the upper and lower arches could be From the University 3f Connecticut School of Dental Medicine. Supported in part by NIH Grant DE-03953-12. *.ksistant Professor. Department of Orthodontics. **Professor and Chairman. Departmenr of Orthodontics. ***Professor. Department of Orthcdomics.
LINGUAL WIRE
Fig.
1. Schematic
drawing
of appliance.
intruded with an appliance, the mandible would autorotate upward and forward into the interocclusal space created. (2) If this appliance could displace the condyle downward and forward, away from the posterior part of the glenoid fossa, stimulation of condylar growth might occur. Both these effects, an increase in length of the mandible and an upward and forward autorotation of the mandible, would be beneficial in treating Class II malocclusions associated with increased lower facial height and a retrusive mandible. The objectives of this study therefore were to (1) design an appliance that hinges the mandible open and exerts an intrusive force 467
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Am. J. Orrhod. Denrofuc.
Nanda
Orthop. June 1989
Fig. 2. Occlusal view of appliance. Table I. Force produced by the appliance Distance between and lower splints
upper (mm)
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 6.0
Repelling force fgm) 3500 2640 2040 1630 1315 1080 890 730 600 480 330
on the teeth and (2) evaluate the effects of this appliance on the morphology and function of the dentofacial complex. MATERIALS AND METHODS The subject pool in the study consisted of 20 boys and girls who were between the ages of 8 years and 10 years 6 months and who had Class II, Division 1 malocclusion associated with mandibular retrusion. The angle of facial convexity, lower facial height, and interlabial gap were greater than normal. The permanent first molars and incisors had erupted; the overjet ranged from 6 to 10 mm and the overbite varied from 0 to 3 mm. The 10 subjects in the treatment group and the 10 subjects in the control group were closely matched with regard to age, sex, and dentofacial characteristics. The active treatment time was 4 months, after which
appliances were removed and the patients observed for an additional 4 months. Subjects in the control group were studied for 8 months. Appliance design The working bite was taken with the mandible in centric relation and opened 7 to 8 mm in the permanent first molar region. The appliance consisted of upper and lower acrylic splints that were bonded on the occlusal halves of the permanent first molars, deciduous molars or premolars, and canines (Figs. 1 through 3). Samarium cobalt magnets measuring 20 X 8 x 2 mm were encased in a stainless steel case 0.007-inch thick and embedded into the upper and lower acrylic splints in a repelling mode. In addition a 0.028-inch wire was embedded in the acrylic. This wire rested on the lingual surfaces of the four permanent incisors and was individually bonded to them; thereby intrusive forces were transmitted to the entire arch. The size and shape of the magnets were designed in collaboration with Recoma Inc.* The steel cases were fabricated in cooperation with the Bioengineering Department, University of Connecticut Health Center. The forces produced by the appliance are listed in Table I. Cephalometric
analysis
Changes in craniofacial morphology caused by growth and treatment were determined from a set of lateral cephalometric head films. A set consisted of two cephalograms, one taken with the mandible in centric relation and the other with the mouth wide open to *Recoma Inc., Fairfield, N.J.
Vo/ume 9s Numhrr 6
Fig.
3. Buccal
facilitate visualization of the condyles. For each patient in the treatment group, the first set of head films was taken before treatment, the second set of films after 4 months active treatment, and the third set 4 months posttreatment. In the control group, an initial set and a final set of cephalograms were taken 8 months apart. Changes between the two sets of films in the control group were divided by two to obtain changes throughout a 4-month period. Subsequent cephalograms were superimposed on the anterior cranial base of the previous cephalogram as described by Baumrind, Miller, and Molthen. Vertical and horizontal positional changes of certain landmarks were measured in relation to two Cartesian coordinate systems. In the first system, the originally constructed Frankfort horizontal (FH) plane (constructed by subtracting 7” from the sella-nasion line) served as the X axis and a line perpendicular to it through sella served as the Y axis. In the second system, the original natural occlusal plane formed the X axis and a line perpendicular to it through sella formed the Y axis. The two coordinate systems were transferred from the first tracing to the next. In addition certain other linear and angular measurements were assessed (Figs. 4 through 6). Separate maxillary and mandibular tracings were superimposed3 to determine changes in the position of the teeth within the maxilla and the mandible. Changes in the position of the teeth were measured in relation to the original occlusal plane (X axis) and a line perpendicular to it through sella (Y axis). The length of the mandible, condylionprognathion (Co-Pgn), was measured from the open mouth cephalogram.
view
of appliance.
N FH
co*J cos COP
Fig. 4. Cephalometric landmarks and linear measurements used in the study. (1) N-ANS, Upper anterior facial height measured perpendicular to Frankfort horizontal (FH) plane. (2) ANSMe, Lower anterior facial height measured perpendicular to FH plane. (3) A-El to occlusal plane. (4) Condylion-pogonion (CoPg), Length of mandible parallel to FH plane. (5) Co-Go, Posterior facial height measured perpendicular to FH plane.
Assessment of temporomandibular muscle function
joint and
An assessment of the function of the masticatory system was conducted to ascertain the status of any signs and symptoms of dysfunction that were present or that might develop. The assessment was based on a
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Fig. 5. Mandibular length, condylion-prognathion measured from wide open mouth cephalogram.
Orthop. June 1989
(Co-Pgn),
clinical dysfunction examination and on anamnestic dysfunction as described by Helkimo.4 For the treatment group, assessments were made at the following time intervals: before treatment, 3 days after insertion of appliance, 3 months after insertion of appliance, on removal of appliance, and 4 months posttreatment. For the control group, assessments were made at the start of the examination period and 8 months later. Results of the cephalometric and study model analyses were statistically analyzed. To assess the significance of differences between the treatment and control groups, mean and standard deviation were calculated and Student’s t tests were performed. The null hypothesis was rejected at the 0.05% level of confidence. The size of the combined error in locating, superimposing, and measuring the changes in different landmarks was calculated with the following. formula: SE measurement =
Dentofac.
J
Zd2 2n
The combined standard error did not exceed 0.6 mm in the horizontal and vertical dimensions. RESULTS
The effects of the magnetic appliance during treatment and during the follow-up period are given in Tables II and III. Mandible
During treatment the length of the mandible, condylion-prognathion (Co-Pgn) , increased 3.2 mm as compared with 0.8 mm in the control group (p < 0.001). In the follow-up period, no difference was seen in growth rates of the treatment and control groups (Fig. 7).
Fig. 6. Angular measurements used in the study. (6) 1 to-FH plane. (7) Y axis. (8) N-A-Pg, Angle of facial convexity. (9) 1 to mandibular plane. (10) FH-MP, Mandibular plane angle.
In the treatment group, the mandible autorotated upward and forward as judged by the mandibular plane angle and Y axis. The mandibular plane angle decreased 1.3” and 0.3”; the Y axis decreased 1.1” and 0.3” in the treatment and follow-up periods, respectively. These changes were small but statistically significant. Overall facial form
Downward and forward displacement of2 the maxilla, as represented by anterior nasal spine and point A, did not show any significant differences between the treated and control groups. There was a significant decrease in the angle of facial convexity (p < 0.001) (Fig. 8) and improvement in the relationship of A-B to occlusal plane (p < 0.001) (Fig. 9). Even though the mandible autorotated upward and forward, increased mandibular growth was responsible for an increase in anterior (ANS-Me) and posterior (CoGo) facial heights (p < 0.001). Fig. 10 shows the change in overall facial form in the treatment group as compared with the control group. Dentition
During treatment the upper and lower incisors intruded approximately 1.3 mm each and the molars 1.6 mm each. During this period, in the control group, these teeth erupted 0.3 and 0.4 mm, respectively (Fig. 11). In the follow-up period, the posterior teeth reerupted until they achieved occlusal contact with their antagonists (Fig. 12). However, overall the lower incisor
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ESfects of fired magnetic appliance
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471
Table II. Comparison of changes between treatment and control groups during treatment period Treatment p-oup (N = IO) Measurements Mandible Length Co-Pgn (mm) Co-Pg parallel to FH (mm) Displacement in relation to FH Pg horizontal (mm) Pg vertical (mm) Rotation MP-FH (“) Y axis (“) Maxilla Displacement in relation to FH Point A horizontal (mm) Point A vertical (mm) ANS horizontal (mm) ANS ven:ical (mm) Facial height ANS-Me perpendicular to FH (mm) Co-Go perpendicular to FH (mm) Facial convex,@ N-A.-Pg (“) A-B perpendicular to OP (mm) Dentitinn Overjet (mm) Overbite (mm) Molar relation (mm)* Upper incisor to FH (“) Lower incisor to MP (“) Changes in tooth position within the maxilla and mandible (measured from maxillary and mandibular superimposition tracings)** Vertical displacement Upper molar (mm) Lower molar (mm) Upper incisor (mm) Lower incisor (mm) Horizontal displacement Upper molar (mm) Lower mlolar (mm) Upper incisor (mm) Lower incisor (mm)
Control group (N = IO) Mean difference
Mean
SD
Mean
SD
+3.2 +2.1
0.5 0.6
+0.8 1-0.5
0.2 0.2
2.4 1.6
< 0.001 < 0.001
+2.6 + 1.9
0.9 I.1
+0.5 +0.5
0.2 0.3
2.1 1.4
< 0.001 < 0.01
- 1.3 - 1.1
0.8 0.5
0 0
0.2 0.1
1.3 1.1
< 0.001 < 0.001
+0.5 +0.3 +0.5 +0.2
0.2 0.2 0.3 0.2
+0.4 +0.2 +0.4 +0.2
0.3 0.2 0.2 0.3
0.1 0.1 0.1 0
NS NS NS NS
+ 1.8 +2.6
1.1
+0.4 +0.6
0.2 0.2
1.4 2.0
i 0.01
0.9
-2.8 +2.3
0.9 0.9
-0.1 +0.1
0.1 0.1
2.7 2.2
< 0.001 < 0.001
-2.1 -3.8 +2.0 +0.2 -0.1
0.7 0.9 0.8 0.6 0.7
-0.1 +0.1 -0.1 +0.2 +0.1
0.2 0.2 0.1 0.5 0.6
2.0 3.9 2.1 0 0.2
< 0.001 < 0.001 < 0.001 NS NS
+ +
0.3 0.3 0.4 0.2
+0.2 -0.3 +0.4 -0.3
0.1 0.2 0.3 0.1
1.8 1.9 1.8 1.5
< < < <
0.4 0.2 0.4 0.5
+0.1 0 +0.1 0
0.2 0.3 0.1 0.3
0 0.2 0.1 0
1.6 1.6 1.4 1.2
+0.1 +0.2 0 0
p value
< 0.001
0.001 0.001 0.001 0.001 NS NS NS NS
+ Denotes downward or forward displacement of landmark. - Denotes upward or backward displacement of landmark. * + Denotes imprc’vement of molar relationship toward Class I. **The maxilla was superimposed on the hard palate and the anterior maxillary structures with main consideration being given to the region between point A ar,d the anterior nasal spine with the images of the superior surfaces of the hard palate aligned. The mandible was superimposed on the inner tables of the symphysis and the line of distal extension of the mandible.
(p < O.OOl), upper incisor (p < O.Ol), and upper molar (p < 0.05) showed less eruption in the treated group than in the control group as seen in Table IV and Fig. 13. In the treatment period, the overjet was reduced 2.1
mm and the molar relationship improved 2.0 mm toward Class I occlusion as a result of increased forward displacement of the mandible in relation to the maxilla; this remained unchanged during the follow-up period. Magnets used in the repelling mode produce lateral
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Dentofac.
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Tabie III. Comparison of changes between treatment and control groups during follow-up period Treatment group (N = 10) Measurements
Length Co-Pgn (mm) Co-Pg parallel to FH (mm) Displacement in relation to FH Pg horizontal (mm) Pg vertical (mm) Rotation MP-FH (“) Y axis (“) Maxilla Displacement in relation to FH Point A horizontal (mm) Point A vertical (mm) ANS horizontal (mm) ANS vertical (mm) Facial height ANS-Me perpendicular to FH (mm) Co-Go perpendicular to FH (mm) Facial convexity N-A-Pg (“) A-B perpendicular to OP (mm) Dentition Overjet (mm) Overbite (mm) Molar relation (mm)* Upper incisor to FH (“) Lower incisor to MP (“) Changes in tooth position within the maxilla and mandible (measured from maxillary and mandibular superimposition tracings)** Vertical displacement Upper molar (mm) Lower molar (mm) Upper incisor (mm) Lower incisor (mm) Horizontal displacement Upper molar (mm) Lower molar (mm) Upper incisor (mm) Lower incisor (mm)
Control group (N = 10) Mean difference
Mean
SD
Mean
SD
+0.7 +os
0.2 0.3
i-O.8 +0.5
0.2 0.2
0.1 0
NS NS
+0.6 +0.4
0.2 0.2
+0.5 +0.5
0.2 0.3
0.1 0.1
NS NS
-0.4 -0.3
0.2 0.2
0 0
0.2 0.1
0.4 0.3
< 0.05 < 0.05
+0.3 +0.4 +0.4 +0.2
0.2 0.4 0.2 0.3
+0.4 +0.2 +0.4 +0.2
0.3 0.2 0.2 0.3
0.1 0.2 0 0
NS NS NS NS
+0.2 +0.5
0.2 0.2
to.4 +0.6
0.2 0.2
0.2 0.1
NS NS
-0.3 +0.3
0.2 0.2
-0.1 +0.1
0.1 0.1
0.2 0.2
< 0.05 < 0.05
0 +2.8 +0.1 +0.4 -0.4
0.3 0.4 0.2 0.6 0.5
-0.1 +0.1 -0.1 +0.2 to.1
0.2 0.2 0.1 0.5 0.6
0.1 2.1 0.2 0.2 0.5
NS < 0.001 NS NS NS
+ 1.8 -2.1 +1.4 - 1.4
0.4 0.5 0.5 0.3
+0.2 -0.3 +0.4 -0.3
0.1 0.2 0.3 0.1
1.6 1.8 1.0 1.1
< < < <
+0.1 +0.2 +0.2 -0.1
0.4 0.3 0.2 0.4
+0.1 0 +0.1 0
0.2 0.3 0.1 0.3
0 0.2 0.1 0.1
p value
0.001 0.001 O.ctOl 0.001 NS NS NS NS
+ Denotes downward or forward displacement of landmark. - Denotes upward or backward displacement of landmark. * + Denotes improvement of molar relationship to Class I. **The maxilla was superimposed on the hard palate and the anterior maxillary structures with main consideration given to the region point A and the anterior nasal spine with the images of the superior surface of the hard palate aligned. The mandible was superimposed inner tables of the symphysis and the line of distal extension of the mandible.
forces as they are moved toward each other. stilted in buccolingual tipping of the teeth in terior segments. It was found that in centric seven patients had a molar crossbite on one
This rethe pos-, relation, side and
between on the
an increased buccal overjet on the other side. However, during the follow-up period, the teeth uprighted to their original inclinations, thereby correcting the crossbite on one side and the increased buccal overjet on
EfJects of‘,fixed magnetic appliance
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Co-Pgn H Treatment Group q Control Group
(MM) 0
1’
Treatment
Period
Follow-up
Perlod
Fig. 7. Change in mandibular length (Co-Pgn).
the other side. The intermolar width remained unchanged. Function None of the patients in the treatment or control groups complained of difficulty in opening the mouth maximally, of stiffness of jaws, locking, luxation or pain on movement of the mandible, pain in the region of the temporomandibular joint, or pain of the masticatory musculature during any stage of the study. Similarly clinical examination of the muscles of mastication and temporomandibular joint function showed that patients in the treatment group did not experience any discomfort, pain, or temporomandibular joint dysfunction at any stage of treatment. The appliance was accepted extremely well by the children and, apart from initial awkwardness, none complained of discomfort nor difficulty in speech and eating. Patients used a fluoride rinse daily and maintained good oral hygiene; as a result neither caries nor decalcification was noted during treatment. DISCUSSION The two most important findings in the study were that the length of the mandible increased significantly in the treated group and the entire upper and lower arches intruded during treatment. In 4 months of treatment, the length of the mandible in the treated group increased 3.2 mm as compared with 0.8 mm in the control group. The specially constructed magnetic appliance held the mouth open 7 to
8 mm in the first molar region when the upper and lower splints were in contact, and 10 to 11 mm open when the mandible was in the acquired “rest” position. This caused the condylar heads to rotate and translate forward, away from the posterior aspect of the glenoid fossa. A number of researchers5-‘7have shown increased condylar growth in animal studies with appliances that caused protraction or hyperpropulsion of the condyles. Reports on the use of functional appliances, either a form of activator or the Frankel FR, present contradictory results. Some studies’*-*’ show increase in mandibular growth; others22-28find that mandibular growth is not increased with the use of either type of appliance. Conflicting results with the use of removable functional appliances could be attributed to the fact that they are dependent on patient cooperation and clinical expertise and at best are worn only part of the day. It is possible that in growing persons there is stimulation of condylar growth when the condyles are protracted by the functional appliance, but this ceases when the appliance is removed from the mouth. All anima15-” and human studies29-33that use fixed splint-like devices to hold the mandible forward 24 hours a day show an increase in mandibular growth. It could be that the determining factor is the amount of time the appliance is worn each day. Moss and Salentijn34 claim that growth at the condyle appears to take place as a secondary phenomenon to fill the space left by the mandible as it is displaced forward by the tissues around it. Enlow” also reports condylar growth to be of a compensatory nature rather than a primary process.
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N-A-Pg q Treatment b9 Control
-4'
Treatment
Period
Follow-up
Group Group
Period
Fig. 8. Change in the angle of facial convexity (N-A-Pg).
A-B (OP) S Treatment Group RI Control Group
MN
0
-1'
Treatment
Period
Follow-up
Period
Fig. 9. Change in the relationship of A-B to occlusal plane.
Petrovi? and McNamara, Connelly, and McBride12 attributed increased condylar growth to increased activity in the lateral pterygoid muscles. Later studies’3-‘7 indicated that the effect of the lateral pterygoid muscles may be mediated to the condyles via the stretch of the posterior portion of the capsule, the meniscotemporal ligament as the condyles come forward. Whetten and JohnstonJ6 have shown that severing the lateral pterygoid msucle did not affect growth of the condyle on the affected side. Recently McNamara and Carlson” noted that the adaptive changes in the temporomandib-
ular region may be caused by alteration in the biomechanical or biophysical environment of the joint that may be produced by muscular or nonmuscular forces. With the magnetic appliance in the mouth, the condyles moved down the articular slope about 10 mm away from the posterior aspect of the glenoid fossa. This could cause articular tissue strain with increased condylar growth as a fill-in process. However, the present state of knowledge precludes a definite answer to the mechanism of increased condylar growth. After removal of the appliances, the rate of growth
V&me 95 Number 6
Ejfects
’ _ ,’ ,’ :‘Y. ‘I.*‘ “II:,,,’!’ =._ I -._* q ‘a. --.* *.*..* -*. ‘v
,’uIi ,-I’ ,I’ ,’ /R,,;,;; :: ,/ . : : a’ a......,
Fig. 10. Composite tracing of lateral cephalograms showing the mean differences in dentofacial form between the treatment and control groups. Differences between the two groups are interpreted as changes caused by treatment. -, Pretreatment; - - -, 4 months posttreatment. The lateral cephalogram was superimposed on the anatomic structures of the floor of the anterior cranial fossa with primary consideration given to the region between the anterior clinoid process and crista galli.
of the mandible was found to be similar to that in the control group. Petrovic3’ and McNamara3’ have reported a decrea.sed amount of growth for a period following removal of “hyper-propulsion” appliances in animals. However, human studies29-33with the Herbst appliance have shown normal mandibular growth after removal of the appliance. The results of this study concur with those of the latter. It was decided to use magnets to provide the intrusive force on the teeth since any other form of mechanical device would either interfere with function or not provide such an efficient system. The size and shape of the magnets were dictated by space available in the mouth, patient comfort, and the force that they could generate. Samarium cobalt magnets were chosen since they have an excellent ratio of magnetic force to size.3g4’ In addition they are far superior in resisting loss of magnetic energy with time and are safe to use in the mouth.394’ However, samarium cobalt is susceptible to corrosion in the oral environment39; therefore
of’jked
magnetic
appliance
on dentofacial
comple?r
475
Fig. 11. Composite of maxillary and mandibular superimposition tracings showing the mean differences in the position of the teeth between the treatment and control groups during the treatment period. Differences between the two groups are interpreted as changes caused by treatment. -, Pretreatment; - - -, posttreatment. The maxilla was superimposed on the hard palate and the anterior maxillary structures with main consideration given to the region between point A and the anterior nasal spine with the images of the superior surfaces of the hard palate aligned. The mandible was superimposed on the inner tables of the symphysis and the line of distal extension of the mandible.
the magnets were encased in a stainless steel case and embedded in the acrylic splints so that they were not exposed to the oral environment. With the appliance in the mouth, the subject tended to maintain an interocclusal space of about 3.0 mm between the upper and lower splints. At this distance the magnets produce a repelling force of 1080 gm, thereby subjecting each tooth in the arch to an intrusive force of approximately 90 gm. Burstone recommends an intrusive force of 20 gm for incisors. Dellingep3 showed that a force of 100 gm was adequate to intrude premolars in dogs. However, an optimum force value has not been established for intrusion of posterior teeth or large segments of teeth. Since some of the teeth covered by the appliance had large root surfaces, a force in the range of 90 gm per tooth was considered adequate, though perhaps excessive, for intrusion. More research is needed in this area to determine an optimum intrusive force. In a repelling mode, when the magnets are moved toward each other, lateral forces are generated. In most patients this caused the mandible to deviate about 2 mm to one side in the acquired “rest” position. This shearing force generally caused both upper buccal segments to be tipped to the right side of the patient and both lower buccal segments to be tipped to the left side. This re-
476
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and Nanda
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Fig. 12. Composite of maxillary and mandibular superimposition tracings showing the mean difference in the position of the teeth between the treatment and control groups during the follow-up period. Differences between the two groups are interpreted as the amount of relapse. -, Posttreatment; - - -, 4 months posttreatment. The maxilla was superimposed on the hard palate and the anterior maxillary structures with main consideration given to the region between point A and the anterior nasal spine with the images of the superior surfaces of the hard palate aligned. The mandible was superimposed on the inner tables of the symphysis and the line of distal extension of the mandible.
Fig. 13. Composite of maxillary and mandibular superimposition tracings showing the mean differences in the position of the teeth between the treatment and control groups during treatment plus follow-up. Differences between the two groups are interpreted as overall additional change in the treated group. -, Pretreatment; - - -, 4 months posttreatment. The maxilla was superimposed on the hard palate and the anterior maxillary structures with main consideration given to the region between point A and the anterior nasal spine with the images of the superior surfaces of the hard palate aligned. The mandible was superimposed on the inner tables of the symphysis and the line of distal extension of the mandible.
IV. Comparison of changes in tooth position between treatment and control groups during treatment plus follow-up (measured from maxillary and mandibular superimposition tracings)*
Table
Treatment group (N = IO) Measurements Dent&ion Vertical Upper Lower Upper Lower Horizontal Upper Lower Upper Lower + Denotes - Denotes *The maxilla point A and inner tables
displacement molar (mm) molar (mm) incisor (mm) incisor (mm) displacement molar (mm) molar (mm) incisor (mm) incisor (mm)
Control group (N = 10) Mean difference
Mean
SD
Mean
SD
p value
+0.2 -0.5 0 -0.2
0.2 0.3 0.3 0.4
+0.4 -0.6 +o.s -0.6
0.2 0.2 0.2 0.2
0.2 0.1 0.8 0.4
+0.2 +0.4 +0.2 -0.1
0.3 0.3 0.5 0.3
+0.2 0 +0.2 0
0.3 0.2 0.5 0.3
0 0.4 0 0.1
NS NS NS NS
downward or forward displacement of tooth. upward or backward displacement of tooth. was superimposed on the hard palate and the anterior maxillary structures with main consideration given to the region the anterior nasal spine with the images of the superior surface of the hard palate aligned. The mandible was superimposed of the symphysis and the line of distal extension of the mandible.
sulted in a crossbite on the left side and an increased buccal overjet on the right side. The crossbite was dental in nature and tipping of the teeth in the buccal segments was very apparent on removal of appliances.
between on the
During the follow-up period, the tipped teeth reverted to their original inclinations and the crossbites were self-correcting. Since both the buccal segments in the upper arch tipped to the same side and both the buccal
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segments in the lower tipped to the other side, there were no significant changes in the upper and lower intermolar arch widths. In an effort to minimize or prevent the occurrence of crossbites, it is proposed that the amount of repelling force produced by the magnets be reduced, thereby also reducing the lateral forces generated. If buccal crossbites still occurred, they would be mild in nattire and self-correcting once the appliance was removed. Treatment with the magnetic appliance is followed by a phase of fixed appliance treatment to correct dental relationships; therefore correction of any buccolingual tipping, were it to remain, could readily be achieved at this stage. On removal of appliances, it was noticed that since the teeth had intruded, occlusion occurred only on the gum pads covering the unerupted second molars, leaving the posterior teeth about 4.0 mm out of occlusion. In retrospect examination of pretreatment study models and x-ray films showed that even though the upper and lower second molars were not close to eruption, the clearance between the soft tissues of the upper and lower pads averaged only about 1.0 mm. When the appliances were removed, upward and forward a&orotation of the mandible was limited by the gap between these pads. Autorotation of the mandible occurs when the freeway space is increased after surgical superior repositioning of the maxilla.“A7 In such instances the mandible acquires a new rest position, which appears stab1e.4s-47[t could therefore be assumed that if the gum pads had not caused obstruction, the mandible would have autorotated further and acquired a new, potentially stable rest position. Dellinge? reported on cases in which intrusion of posterior teeth had been achieved with the use of an Active Magnetic Vertical Corrector. He found that both intrusion of teeth and the ensuing autorotation of the mandible were stable 3 years later. In this study the teeth were prevented from achieving occlusal contact, resulting in reeruption until full occlusion of the posterior teeth was obtained. Nevertheless, throughout the entire treatment and follow-up period, the teeth in the treated group underwent statistically significant intrusion as compared with the control group. The limited autorotation of the mandible that was achieved was stable. In fact during the follow-up period, the mandible autorotated further. The appliance may have caused mild inflammation of the soft tissues distal to the first molars; once the appliances were removed, the inflammation gradually subsided and this allowed the mlandible to close a littler further. Since the slight intrusion and autorotation achieved were both stable, it can be hypothesized that if the gum pads had not prevented further autorotation, the enhanced auto-
.Effects of @fixedmagnetic appliance
on dentqfizcial complex
477
rotation achieved would also have remained stable and the teeth would not have reerupted to the extent they did. In the future it is proposed that removal of the tissue overlying the upper and/or lower second molars about a week before removal of appliances would be beneficial. This would allow autorotation of the mandible as determined by the amount of intrusion. CONCLUSIONS
A fixed magnetic appliance was designed that hinged the mandible open and exerted an intrusive force on the teeth. Treatment with this appliance resulted in: 1. An increase in length of the mandible 2. Intrusion of teeth 3. Upward and forward autorotation of the mandible 4. Reduction of A-B to occlusal plane 5. Improvement in the angle of facial convexity 6. Creation of temporary buccal crossbite caused by the shearing force of repelling magnets During follow-up there was some rebound eruption of teeth; however, all other changes were stable. This appliance presents a promising mode of improving facial harmony in patients with Class II, Division 1 malocclusion associated with mandibular retrusion, increased lower facial height, and increased interlabial gap. In addition reduction in overjet and improvement in molar relationship toward Class I occlusion make the second stage of conventional orthodontic treatment less demanding. Further research and development of the appliance are advocated. REFERENCES I. Graber TM. Orthodontics:
principles and practice. 3rd ed. Philadelphia: WB Saunders Company, 1972:205. 2. Dellinger EL. A clinical assessment of the Active Vertical Corrector-a nonsurgical alternative for skeletal open bite treatment. AM J ORTHOD 1986;89:428-36. 3. Baumrind S, Miller D, Molthen R. The reliability of head film measurements. 3. Tracing superimposition. AM J ORTHOD 1976; 70:617-44. 4. Helkimo M. Studies
5.
6.
7.
8.
on function and dysfunction of the masticatory system. II. Index for anamnestic and clinical dysfunction and occlusal state. Sven Tandlak Tidskr 1974:67: 101-Z 1. Petrovic A, Stutzmann J, Oudet C. Control processes in the postnatal growth of the mandibular condylar cartilage. In: McNamara JA Jr, ed. Determinants of mandibular form and growth. Ann Arbor, 1975. Center for Human Growth and Development. University of Michigan. Stockli PW, Willert HG. Tissue reactions in the temporomandibular joints resulting from anterior displacement of the mandible in the monkey. AM J ORTHOD 1971:60:142-55. Baume LJ, Derichsweiler H. Is the condylar growth center responsive to orthodontic therapy? An experimental study in Macaca mulatta. Oral Surg Oral Med Oral Path01 1961;14: 1371. Petrovic A, Stutzmann JJ, Gasson N. The final length of the mandible: Is it genetically predetermined’? In: Carlson DS, ed.
478
Kalra,
Am. J. Orthod. Dentofac.
Burstone, and Nanda
Craniofacial biology. Monograph 10, Craniofacial Growth Series. Ann. Arbor: 1981. Center for Human Growth and Development, University of Michigan. 9. McNamara JA Jr, Hinton RJ, Hoffman DL. Histologic analysis of temporomandibular joint adaptations to protrusive function in young adult rhesus monkeys (Macaca mulatta). AM J ORTHOD 1982;82:288-98. 10. Charlier JP, Petrovic A, Herrmann-Stutzmann J. Effects of mandibular hyperpropulsion on the prechondroblastic zone of young rat condyle. AM J ORTHOD1969;55:71-4. 11. Graber TM, Rakosi T, Petrovic AG. Dentofacial orthopedics with functional appliances. St. Louis: The CV Mosby Company, 1985.. 12. McNamara JA Jr, Connelly T, McBride MC. Histological studies of temporomandibular joint adaptations. In: McNamara JA Jr, ed. Determinants of mandibular form and growth. Ann Arbor: 1975. Center for Human Growth and Development, University of Michigan. 13. Petrovic AG, Stutzmann JJ. Further investigation into the functioning of the peripheral “comparator” of the servosystem (respective positions of the upper and lower dental arches) in the control of the condyle cartilage growth rate and of the lengthening of the jaw. In: McNamara JA Jr, ed. The biology of occlusal development. Ann Arbor: 1977. Center for Human Gmwth and Development, University of Michigan. 14. Petrovic A, Stutzmann J. Tierexperimentelle Untersuchungen uber das Gasichtsschadelwachstum and seine Beeinflunssung: eine biologische Erklarung der songenannte Wachstumsrotation des Unterkiefers. Fortscbr Kieferorthop 1979;40: 1. 15. McNamara JA Jr, Carlson DS. Quantitative analysis of temporomandibular joint adaptations to protrusive function. AM J ORTHOD1979;76:593-611. 16. Petrovic A. An experimental and cybernetic approach to the mechanism of action of functional appliances on the mandibular growth. In: McNamara JA Jr, ed. Malocclusion and the periodontium. Monograph 15, Craniofacial Growth Series. Ann Arbor: 1984. Center for Human Growth and Development, University of Michigan. 17. Petrovic AG, Stutzmann JJ, Lavergne J. Effects of functional appliances on the mandibular condylar cartilages. In: Graber TM, ed. Physiologic principles of functional appliances. St. Louis: The CV Mosby Company, 1985. 18. McNamara JA Jr, Bookstein FL, Shaughnessy TG. Skeletal and dental changes following function regulator therapy on Class II patients. AM J ORTHOD1985;88:91-110. 19. Marschner JF, Harris JE. Mandibular growth and Class II treatment. Angle Orthod 1966;36:89-93. 20. Friinkel R, Reiss W. Zur Problematik der Unterkiefermachentwicklung bei Distalbissfallen. Forts&r Kieferorthop 1970; 31:345-55. 21. Righellis EG. Treatment effects of Fr&kel activator and extraoral traction appliances. Angle Orthod 198353: 107-21. 22. Bjijrk A. ,The principle of the Andresen method of orthodontic treatment, a discussion based on cephalometric x-ray analysis of treated cases. AM J ORTHOD1951;37:437-58. 23. Jakobsson SO. Cephalometric evaluation of the treatment effect on Class II, Division 1 malocclusions. AM J ORTHOD1967; 53446-7. 24. Harvold EP, Vargervik K. Morphogenic response to activator treatment. AM J ORTHOD1971;60:478-90. 25. Ahlgren J. Late results of activator-treatment: a cephalometric study. Br J Orthod 1976;3:181-7.
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26. Schulhof RJ, Engel GA. Results of Class II functional appliance treatment. J Clin Orthod 1982;16:587-99. 27. Creekmore TD, Radney ,LJ. Fr%nkel appliance therapy: orthopedic or orthodontic? AM J ORTHOD1983;83:89-108. 28. Robertson NRE. An examination of treatment changes in children treated with the function regulator of Frlnkel. AM J ORTHOD 1983;83:229-310. 29. Pancherz H. Treatment of Class I malocclusions by jumping the bite with the Herbst appliance: a cephalometric investigation. AM J ORTHOD1979;76:423-41. 30. Pancherz H. The effect of continuous bite jumping on the dentofacial complex: a follow-up study after Herbst appliance treatment of Class II malocclusions. Eur J Orthod 1981;3:49-60. 31. Pancherz H. The mechanism of Class II correction in Herbst appliance treatment. A cephalometric investigation. AM J ORTHOD1982;82:104-13. 32. Wieslander L. Intensive treatment of severe Class II malocclusions with a headgear-Herbst appliance in the early mixed dentition. AM J ORTHOD1984;86:1-13. 33. Kalra V, Be&man M, Sachdeva R, Nanda R. Effects of anterior repositioning of the mandible on the dentofacial complex. J Dent Res 1985;64:344. 34. Moss ML, Salentijn L. The capsular matrix. AM J ORTHOD 1969;56:474-90. 35. Enlow DM. Handbook of facial growth. Philadelphia: WB Saunders Company, 1982:122-3. 36. Whetten LL, Johnston LE Jr. The control of condylar growth: an experimental evaluation of the role of the lateral pterygoid muscle. AM J ORTHOD1985;88:181-90. 37. Petrovic A. Control of postnatal growth of secondary cartilages of the mandible by mechanisms regulating occlusion: cybernetic model. Trans Eur Orthod Sot 197469-75. 38. McNamara JA Jr. Functional adaptations in the temporomandibular joint. Dent Clin North Am 1975;19:457-71. 39. Tsutsui H, Konouchi Y, Sasaki H, Shiota M, Ushita T: Studies on the SmCo magnet as a dental material. J Dent Res 1977;58:1597-1606. 40. Blechman AM. Magnetic force system in orthodontics. AM J ORTHOD1985;87:201-10. 41. Blechman AM, Smiley M. Magnetic forces in orthodontics. AM J ORTHOD1978;74:435-43. 42. Burstone CJ. Deep overbite correction by intrusion. AM J ORTHOD1977;72:1-22. 43. Dellinger EL. A histologic and cephalometric investigation of premolar intrusion in the Macaca speciosa monkey. AM J ORTHOD 1967;53:325-54. 44. Bell WH, Creekmom TD, Alexander RG. Surgical correction of the long face syndrome. AM J ORTHOD1977;71:40-67. 45. Schendell SA, Eisenfeld J, Bell WH, Epker BN. Superior repositioning of the maxilla: stability and soft-tissue osseous relations. AM J ORTHOD1976;70:663-74. 46. Fish LC, Wolford LM, Epker BN. Surgical-orthodonic correction of vertical maxillary excess. AM J ORTHOD1978;73:241-57. 47. Wessberg GA, Washburn MC, LaBanc JP, Epker BN. Effect of surgical superior repositioning of the maxilla in mandibular resting posture. AM J ORTHOD1982;81:465-72. Reprint
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Dr. Varun Kalra Department of Orthodontics University of Connecticut Health Center School of Dental Medicine Farmington, CT 06032