Twelve adolescent patients with Class II, Division 1 malocclusions were selected for the study. Each patient wore the headgear for a 6-month period, an average of 12 hours a day. A group of untreated adolescent patients with Class II, Division 1 malocclusions who were in a similar age range, as well as skeletal and dental characteristics were chosen as controls. Lateral cephalometric films were taken before and after the 6-month treatment period, and before and after the observation period in the control group of patients. Our data indicate that by directing the force of the headgear approximately through the center of resistance of the maxillary molars, it is possible to accomplish simultaneously a substantial distal movement of the molars (2.6 ± 0.6 mm), as well as significant intrusion (0.54 ± 0,54 mm). In addition, our results demonstrate that the applied force of 500 gm was sufficient to initiate maxillary orthopedic changes in the treated patients. These changes include relative restriction of horizontal and vertical maxillary growth, as well as distal movement (mean: 0.8 mm) of the maxillary anterior border in the treatment group relative to an untreated control group. Such orthopedic changes have been previously described only in association with much higher force levels.
The use of headgear therapy is very common in the treatment of Class II, Division 1 malocclusions. Extraoral maxillary traction appliances are used to improve the dental relationship between the maxilla and the mandible, as well as the skeletal relationship between the two jaws.
The most widely used appliances for extraoral anchorage are the cervical face how and high-pull headgeSr. Cervical pull extraoral appliances are commonly used because of the case of their fabrication and better acceptability by the patient as compared with the other types of headgear. Cervical appliances, however, have several adverse side effects that are especially undesirable in a majority of Class II, Division I maloeclusions. With a cervical appliance, the line of action of the force often passes below the center of resistance of the maxillary first molar, producing a moment that moves the crown distally and the roots inesially. Cervical face bow therapy also causes significant extrusion of the molars that might result in an increased lower facial height. Furthermore, one would question the stability of the correction achieved since significant tipping of the molars does occur.
With the high-pull headgear, it is possible to generate the force in the direction which is consistent with the treatment objectives of Class II, Division 1 malocclusion. Forces produced by the high-pull headgear, like those produced by the cervical appliance, include a distally directed component. However, the high-pull headgear produces, in addition, an intrusive component instead of an extrusive one. Furthermore, with the high- pull headgear, it is possible to change the direction of force in relation to the center of resistance of the dental units to which the force is being applied, to achieve better control of the resulting tooth movement.
Several clinical investigations have demonstrated that with the high-pull headgear it is possible to achieve significant distal movement of the dentition and to modify vertical changes in the maxillary molar position. These effects may be due in part to orthopedic changes. There are still considerable variabilities, however, in the magnitude of force which is described as necessary to produce these orthopedic changes. Various animal studies have shown significant dental and skeletal changes in response to extraoral forces.’3’ However, these studies failed to describe the force system applied on teeth and bones. The purpose of the present study is to investigate the dental arid skeletal changes produced by a high-pull headgear with a well-defined force system designed to translate the maxillary molars to correct Class II relationship by using relatively a lower magnitude of forces.
MATERIALS AND METHODS
Patient selection
Twenty-four white adolescent patients were included in the current study. Their molar occlusions were between 3.0 to 7.0 mm Class II at the onset of treatment. Their skeletal ages determined from hand-wrist films ranged from 9.5 to 12.5 years. All the patients had at least a 2.0 mm interlabial gap and increased lower facial height. Twelve patients received headgear therapy for 6 months, and the remaining patients served as controls.
Appliance design
An lnterlandi type high-pull headgear (Orthoband Co. Inc., Barnhart, Mo.) was used for all of the patients, and the outer bows were attached to the head straps of the headgear with ½ inch latex elastics. The direction of the applied force was modified by changing the point of attachment of the elastics. The level of buccal trifurcation of the maxillary first molars was clinically and radiographically determined, and the headgear force was directed through that point as an approximation of the center of resistance of these teeth. The inner bow was made parallel to the occlusal plane, and the length of the outer bow was reduced so that it did not extend distal to the maxillary first molar. A force of 500 gm was used for each side, as measured by a force gauge. Thus the appliance generated a force including intrusive, as well as distally directed components. The headgear bow position and the line of force are shown in Fig. 1.
An 0.032 X 0.032 stainless steel transpalatal arch (Ormco Corp., Glendora, Calif.) was fabricated and tied to welded lingual brackets. This arch was made to fit these brackets passively, and its main function was to maintain symmetry and arch widths and prevent molar rotation.”
To examine the possibility that the elastics might lose some of their force after the 12-hour required wear, individual elastics were stretched on a spring tester to generate 500 gm of force. The distance was then held constant, and the force measured periodically. Mean force decay over a 15-hour period was relatively small and probably clinically insignificant. Every effort was made to keep the activation and the direction of the force of the elastic constant throughout the treatment. Patients were asked to change elastics at least once a day. In the current study elastics were used to deliver the headgear force. However, the danger of using elastics without safety devices has been well documented, and we recommend the use of quick release or comparable safety mechanisms, which are currently used in our clinics.
Patient cooperation
The patients were asked to wear the headgear a minimum of 12 hours a day and to keep a daily diary of their headgear wear. During visits, which were scheduled at 3- to 4-week intervals, compliance was assessed in the following ways:
1. The headgear daily record sheet was checked, 411d its accuracy was confirmed with the parents.
2. The mobility of the maxillary first molars as assessed.
3. The ease of insertion of the headgear bow was observed.
4. The headgear was examined for physical signs that would indicate it had been worn regularly.
5. During the intraoral examination performed at each orthodontic appointment, any significant changes, such as interdental spacing or reduction in the overjet or improvements in the buccal occlusion, was recorded.
Analysis of the cephalometric data
Lateral cephalometric films were taken at the onset of treatmen and after a 6-month period of headgear therapy. Radiographs were taken with the patients in centric occlusal relation and with the lips at rest. Tracings of lateral cephalometric hcadfilms were analyzed with the computer-aided analysis developed at the University of Connecticut, School of Dental Medicine, Departnieni of Orthodontics. In this technique, 53 cephalometnc landmarks are identified, digitized, and the measurements are made relative to a constructed line at 70 relative to the S-N line (constructed Frankfort horizontal). Lateral tracings were superimposed by using the sellanasion line and the anterior cranial base. Horizontal and vertical changes in the position of the ANS line, the A point, and the PNS line were measured parallel and perpendicular to the constructed Frankfort horizontal (FH) plane. Maxillary supcrimpositions, on the basis of the zygomatic process, the orbital rims, and the ptei-ygomaxillary fissure, were used to examine maxillary dental changes. The dental and the skeletal cIanges are summarized in Tables I and TI. Mean and standard deviations were calculated for the changes that took place in the 6-month period for both the treatment and the control group, and Student’s t test was performed.
RESULTS -
All 12 patients selected for treatment with the high- pull headgear completed the 6-month course of treatment without any discomfort or complications. The headgear was worn by all the patients an average of 12 hours a day. Figs. 2 to 10 show dental and skeletal changes in two patients representative of the treatment group. The most significant changes were noted in the maxillary molars. After the 6-month period, the maxillary molars in the treatment group were distally displaced (mean 2.56 mm, Table I). In contrast, the maxillary molars in the control group were mesially displaced (mean 0.23 mm). At the end of the 6-month headgear wear, the maxillary molars in the treatment group were intruded an average of 0.54 mm. No vertical eruption of the maxillary molars was noted in any of the treatment patients. The maxillary molars in the control group erupted on the average by 0.23 mm. Thus the maxillary molars in the treatment group were displaced in accordance with the distal and intrusive direction of the applied headgear force. The changes in tooth position during the treatment period were clinically and statistically significant (p < 0.01). The distal molar movement in the treatment group significantly contributed to the correction of the Class II molar relationship. Overall, the displacement of the maxillary molars was in the form of translation-like tooth movement. In fact, the roots of these molars were displaced slightly farther distally than the crowns (Table I).
Significant skeletal changes were observed in the maxilla. Anteroposterior growth of the maxilla during the 6-month treatment period, as measured by changes at ANS and PNS, in reference to constructed FH plane, was reduced in the treatment group relative to the control group by approximately 0.5 mm (p <0.01). Horizontally, the maxilla in the treatment group moved posteriorly by an average of 0.33 mm, as measured by the position of A point, in controls, A point moved forward in all 12 control patients (mean 0.5 mm). The headgear not only restricted or redirected the anteroposterior growth of the maxilla, but also exerted an orthopedic effect by moving the maxilla distally.
A significant difference was observed also in the downward growth of the maxilla between the control and the treatment groups. In the treatment group, both the ANS and the PNS grew downward less than half the amount of downward growth that was observed in the controls, (p < 0.01 and p <0.05, respectively, Table II).
There were no clinical or statistical differences in measurements of the nasal floor, mandibular plane, skeletal convexity, soft tissue convexity, and other soft tissue measurements between the treatment and the control groups (Table II).
DISCUSSION
Armstrong and Badell suggest continuous headgear wear (24 hours per day) to achieve optimal orthodontic results. The results of the present study indicate that intermittent headgear wear, on a daily basis, can also create clinically significant correction of Class II molar relation in a relatively short period of 6 months.
Armstrong, Watson, Badel), and Graber used force in excess of 400 gm and sometimes up to two or three times that amount, particularly if rapid orthopedics was desired. The results of the present study show that the forward growth of A point was significantly decreased by using about 500 gm of force. This finding also shows that orthopedic maxillary changes are possible even if the whole maxillary dentition is not fully bonded. The only wire in place was passive palatal arch, which was tied to the two molar bands. The normal forward growth of the ANS seen in the controls was significantly reduced in the treatment group. Baum- rind et al.20 attribute the backward movement of A point to normal remodeling at the anterior maxillary surface. The present study shows a 0.5 mm of reduction in horizontal growth of the maxilla in the treatment group versus the control group.
Weislander, using only 300 to 400 gm of force, reported that the A point and the ANS moved distally 2.0 mm in almost a 3-year period. Watson showed that A point and ANS could move distally as much as 4.0 mm in less than 1 year using 600 to 1000 gm of force on each side. Baumrind et al., in their comparison of different types of headgear, observed that in neither of the treatment groups, which were studied, did the body of the mandible grow as much as it did in the control group. The present study also demonstrates that there was a non-significant tendency for reduced mandibular growth in the treatment group compared with the control group.
The force of our appliance was directed approximately at a 20 degree angle relative to the occiusal plane. Therefore the resultant intrusive force of the headgear on the maxillary molars can be estimated as 500 x sin 20°. Intrusive remodeling of the ANS downwards, as described by Baumrind et al. and as seen in the control group of the present study, was significantly decreased in the treatment group and the same tendency was noted at the PNS. Since the normal downward movements of the ANS and the PNS were reduced practically the same amount, no changes in the nasal floor angulalion were noted. Watson in his study of the high-pull headgear found an average change in palatal plane angulation of only 1.04° per year, which very similar to the report by Baumrind et al. of 1.1 degree change in palatal plane angulation in untreated patients.
The intrusive component of the headgear that was used in the present study was sufficient to produce 0.54 mm of intrusion of the maxillary molars as determined from separate maxillary superimpositions, whereas the maxillary molars in the control group of patients erupted 0.42 mm. This intrusion, however, did not produce a statistically significant reduction in the lower facial height. The lower first molars did not show a compensatory eruption in response to the maxillary molar intrusion, and the level of the functional occiusal plane was maintained throughout the 6-month period.
Although the skeletal and facial angles of convexity were both reduced, these reductions were not statistically significant. It is likely that if the patients had continued to wear the headgear for an additional year or even longer, these skeletal changes would have become more pronounced. Watson has shown molar intrusion of as much as 4.0 mm with higher force levels and headgear treatment over a longer time period.
The single most important clinical change observed in the current study was the distal displacement of the maxillary molars by 2.56 mm and a subsequent change in the direction of occlusal molar relationship from Class II to Class I. BadelI’8 achieved a 2.3 mm Class 11 occlusal correction with a combination headgear worn full time for an average of 4 months. Weislander achieved almost 3.0mm of dental movement with force levels, comparable to those used in our study, over a 2- to 3-year period. Watson2 also found an average of 3.0 mm of distal maxillary molar movement over a period of 5 to 16 months. In the present study, similar dental results were achieved with much lighter forces in a relatively short period of 6 months.
It is particularly important to now that the molar movement was in the form of translation. This is confirmed by the fact that not only the molar crowns but also the roots moved distally. In fact, the roots moved almost 2.5° further back than the crowns, when the normal mesial tipping of the maxillary molars is taken into account (Table I). This finding is consistent with the results of Dermaut et al. who illustrated that the center of resistance of the molars lies somewhat below the trifurcation area. Since the force in the present study was directly applied through the level of the trifurcation, therefore a small moment was generated to move the roots distally. This slight change in the axial inclination of the molars suggests that our line of force application was slightly above the center of resistance to the maxillary molars. The use of palatal arch as demonstrated in the present study also facilitated symmetric movement of the right and left molars.
The following conclusions are based on significant trends and findings in the present study:
1. By directing the force of the headgear approximately through the center of resistance of the maxillary molars with the high-pull headgear, it is possible to translate the molars in the direction of the applied force. One can therefore accomplish both instrusion and distal movement of the molars at the same time.
2. An average of 500 gm of force is sufficient to translate the molars distally, and at the same time initiate maxillary changes that are normally associated with higher force levels.
3. If the headgear is used for a short period of 6 months and the pattern is cooperative, one can expect a significant dental improvement in the Class II molar relationship.
REFERENCES
1. Bowden DEJ. Theoretical considerations of headgear therapy: a literature review. Br i Orthod 1978;5:145•52.
2. Baumrind S. Korn EL. Molthcn R. West EE. Changes in mandibular dimensions associated with the use of force 10 retract the maxilla. AM i ORThOD l981;79:17.30.
3. Baumrind S, Moithen R, Korn EL. Mandibular plane changes during maxillary retraction. AM J ORmoD 1978.74:32.
4. Baumrind S. Korn EL, Moithen R. West EE. Changes in facial dimensions associated with use of forces to retract the maxilla.
AM J ORThOD 1983;84:384-98.
5. Poulton DR. The influence of cxtraoral traction. AM J ORThOD
1967:53:8-18.
6. Schudy FE. Vertical growth versus antcroposterior growth as related to function and treatment. Angle Orthod 1964;34:75-93.
7. Silverstein A. Changes in the bony facial profile coincident with treatment of Class 11, division I malocclusion. Angle Orthod
1954;24:2 14.37.
8. Weislander L. The effect of force on the craniotacial development. AM I ORmon l974;65:531-8.
9. Burstone Cl. The biomechanics of tooth movement. In: Draus BS. Riedel RA, eds. Vistas in orthodontics. Philadelphia: Lea & Febiger, 1962:197-213.
10. Armstrong MM. Controlling the magnitude, direction, and duration of extraoral force. AM I ORmoD 1971:59:217-43.
11. Brown P. A cephalometric evaluation of highpull molar headgear and facebow neck strap therapy. AM J ORTHOD 1978:74:621-32.
12. Watson WG. A computenzed appraisal of the highpull facebow. AM J ORmon l972;62:561-79.
13. Droschl H. The effect of heavy orthopedic force on the maxilla in the growing Saimiri sciureus (squirrel monkey). AM J ORTHOD 1973;63:449-57.
14. Elder JR. Tbenge RH. Cephalometric and histologic changes produced by extraoral highpull traction to the maxilla in Macoca, nulatt. Art J ORTHOD 1974;66:599-617.
15. John JP. Change in form and size in the mandible in the orthopedically treated Macaca iris (an eApclimcrltal study). Tram. Eur Orihod Soc 1968,44:161-73.
16. Sproule WR. Dentofacial changes produced by extraoral cervical traction to the maxifla of Macaca mulana: a histologic and serial cephalometric study, 1968; [Thesis]. Seattle: University of Washington.
I7. Burstone Ci. Precision lingual arches. J Clin Orthod l989;23: 101-10.
18. Badell MC. An evaluation of extraoral combined highpull cervical traction to the maxilla. AM I ORTHOD 1976;69:431-46.
19. Graber TM. Extra oral force—facts and fallacies. AM I ORTHOD l955;41 :490-505.
20. Baumnnd S. Korn EL, Ben-Bassat Y, West EE. Quantitation of maxillary remodeling. I. A description of osseous changes relative to superimposition on metallic implants. AM J ORmon
DENTOPAC ORTHOP l987;92:29-41.
21. Baumrind S. Moithen R. West EE. Miller DM. Distal displacement of maxilla and the upper first molar. AM I ORmoD
1979;75:630-40.
22. Dermaut LR, Kleutghen JPJ, DeClerck HIH. Experimental determination of the center of resistance of the upper first molar in a maccrated, dry human skull submitted to horizontal headgear traction. AM I ORTHOD DENTOFAC ORTItOP 1986:90:29-36.
Reprint requests to:
Dr. Ravindra Nenda
University of Connecticut Health Center
School of Dental Medicine
Department of Orthodontics
263 Fannington Ave.
Farmingon, CT 06030
|
Featured Dentist Articles
