Effect of protraction headgear on Class III malocclusion

Orthodonties
Effect of protraction headgear on Class III malocclusion Peter Ngan* /Stephen H. Y Wei** /Urban Hagg*** /Cynthia K. Y Yiu**** / Daniel Merwin ' '* ^ / Brian Stickel ^
Ten patients with skeletal Class HI malocclusion in the early mixed dentition who were treated with maxillary expansion appliance and protraction headgear were compared with reasonably matched controls. Significant orthopedic effects were found after as little as 6 months of treatment. Cephalornetric analysis revealed that the correction of Class III malocclusion was primarily a result of forward and downward movement of the maxilla and backward rolaUon of the mandible. The clinical result of one patient treated with this appliance is used to demonstrate the importance of force magnitudes and directions, as well as the design of the appliance, to the success of the treatment. (Ouintessence lnt 1992:23:197-207.)
Introduction
Approximately 5% of the white population exhibits skeletal Class III malocclusion, "^ characterized by either mandibular protrusion, maxillary retrusion, or a comhination of the two.^"" The incidenee has heen re- ported to be significantly higher in the Japanese,'" Scandinavian,'"* and Chinese'"* populations.
The treatment of Class III malocclusion dates to the 1800s. Whereas '"psendo-Class III" malocclusion with forward mandibular displacement can sometimes be corrected using removable or fixed appliances, most Class III malocclusions with underlying skeletal dis- crepancies require orthopedic intervention. Early treatment with chincap therapy has been shown by many investigators to be effective ¡n treating develop- ing Class III malocclusions,'^""
* Associate Professor, Department of Orthodünlics. Ohio Stale University, College ot Dentislry, 305 West 12th Avenue. Columbtis, Ohio 43210,
*•• Professor and Head, Department of Children's Dentistry and Orthodontics, Faculty of Dentistry, university of Hong Kong, Prince Philip Dental Hospital, 34 Hospital Road, Hong Kong.
'•' Reader, Department of Children's Dentistry and Orthodon- tics, Faculty of Dentistry, University of Hong Kong.
•*•' Clinical Dental Surgeon. Department of Children's Dentis- try and Orthodonties. Faculty o( Dentistry. University of Hong Kong.
** Dental Studenl, Ohio State University.
However, many practitioners continue to avoid this treatment modality. It is believed that developing man- dibular prognathism cannot be altered. The commonly recotnmended treatment for these patients at the end of the growth period is orthognathic surgery. More- over, clinicians are not always familiar with the avail- able orthopedic devices. Some of these appliances for Class III corrections can be uncomfotiahle, and the treatment time is usually quite long. Consequently, the cooperation from these patients is poor.
In .lapan. where the incidence of Class III malocclu- sions is significantly higher, extraoral forces such as chincap therapy are often used in an attempt to cor- rect the developing skeletal Class III malocclusion. Researchers performing animal and clinical studies of chincap treatment""^' have reported and confirmed numerous statistically significant changes in the cranio- facial complex, including a decrease in gonial and sella-nasion-point B angles, a decrease in mandibu- lar plane angle, and redirection in the downward verti- cal growth of the midface. However, a recent study by Sugawara et al- has shown that Class III patients treated early with ehineap therapy alone have latent catch-up of mandibular displacement in a forward and downward direction. The authors suggested that chin- cap therapy does not necessarily guarantee positive correction of skeletal profile after complete growth. In addition, this modality of treatment may not be suit- able for Class III malocclusion that is characterized by maxillary retrusion. '' ^
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Orthodontics
Protraction headgear has been used to provide direct- ed, forward growth of the maxilla at an early age. This is particularly useful in treating patients with underde- velopment of the maxilla and/or overdevelopment of the mandible. The orthopedic force is used to protract the maxilla, while the chincap, or mental anchorage, serves to redirect mandibular growth. The use of this appliance was described more than 100 years ago,^'' with other descriptions appearing early in this century, Tlie individual most responsible for reviving interest in this technique is Delaire,"' Mote recently. Petit"'' mod- ified the basic concepts of Delaire by increasing the atuount of force generated by the appliance, thus de- creasing the overall treatment time. Several inves- tigators have demonstrated the dramatic skeletal changes that can be obtained in animals with continu- ous protraction forces to the maxilla,"'*"'"' In these studies, not only was point A affected through forward movement of the incisors, but the entire maxilla was displaced anteriorly, with significant effects as far pos- teriorly as the zygomaticotemporal suture.
Recently, McNamara" reported on two patients (aged 8 and 9) who received early orthopedic interven- tion for Class III malocclusions using protraction headgear in combination with a rapid palatal expan- sion appliance. Two other patients (aged 7 and 9) were treated by Turley,"" who used the same approach, ex- cept that the protraction headgear was individualized, or custom-made, for each patient to increase patient comfort and compliance. Palatal expansion "disarticu- lates" the maxilla and initiates cellular response in the sutures, allowing a more positive reaction to protrac- tion forces, ^
However, the sample size in each of those two studies was small and without comparison to a control group of patients; thus there seems to be a need to qnantify the changes in response to protraction head- gear and palatal expansion appliances. The objective of this prospective study was to investigate the dimen- sional changes that occur in specific areas of the craniofacial complex in response to this treatment modality.
Method and materials
Treated sample
The sample consisted of ten patients who had a skeletal Class III malocclusion and a retrusive maxilla as described in the section on diagnosis and treatment planning. All patients were treated with protraction headgear and palatal expatision appliances by one of
the authors at Ohio State University, College of Den- tistry, All patients had tio history of any other cranio- facial anomalies and had not undergone prior orth- odontic treatment. There were three boys and seven girls, ranging in age from 7 years 2 months to 10 years 8 months (mean age of 8.06 years).
Control sample
A control sample, consisting of ten untreated Class III children obtained from Ohio State University and Uni- versity of Hong Kong Growth Studies, was used as a comparison group. These subjects were matched by age and sex to the treated sample.
Diagnosis and treatment planning
For diagnosis of Class III malocclusion in young pa- tients, cephalometric values can only provide the rela- tive contributions of skeletal and dental components to a malocclusion. Further, cephalometric values are often unrehable in a young child, and neither jaw may be identified as the obvious contributor to a Class HI condition. Sue et al''' found that the determination of structural cause varied with different cephalometric analyses. In addition, all mandibular cephalometric measurements must take into account the amount and the direction of any retruded contact position-inter- cuspal position (RCP-ICP) mandibular shift on clo- sure.
Because of the variability of cephalometric analyses, other factors such as the overall facial profile, chin position, maxillary position, and mandibular reposi- tioning were considered (Fig 1), Patients with (1) a straight or concave profile: (2) a protruded mandible and retruded maxilla according to the method ofTur- ley"*"; and (3) a cephalometric analysis indicating a Class III skeletal pattern were included in the study.
Facial pattern considerations
Studies have shown that the direction of protraction forces can influence the repositioning of the maxillary complex,^' A horizontal protraction force can cause a counterclockwise rotation of the maxilla, resulting in an open bite. On the other hand, a downward force can produce almost translatory repositioning of the complex and its surrounding structure. These effects have been demonstrated both in animal models"""* and humans,^'' Therefore, in treatment planning for a Class III patient with skeletal open bite or deep bite, the direction of protraction force shouid he taken into account.
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Orthodontics
Figs la to 1c Facial profile evaluation.
Fig la Profile is concave, suggesting maxillary retrusion. Fig 1b Blocking out lips focuses on chin to assess man- dibular prognathism.
Fig 1c Blocking out the chin and mandible focuses on the midface. Maxillary deficiency is indicated by straight verti- cal shadow from infraorbital margin, through alar base of nose, to corner of mouth.
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Fig 2 Hyrax tapid palatal expansion appliance with bands fitted on the maxillary pnmat second molars and permanent first molars. An 0,045-inch wire is soldered bilaterally to the buccal aspects of the molar bands and extended anteriorly to the canine area for engagement to mtraoral elastics.
Fig 3 Face mask with adjustable anterior wire and hooks to accommodate a downward and forward pull to the maxilla with mtraoral elastics.
Objectives of treatment
The primary objective of the treatment was to correct the Class III molar occlusion to a Class I occlusion, correct atiy crossbites, if present, and improve the skeletal profile of the patient. Once these objectives were met, a second phase of treatment with fixed appliances was to be undertaken if indicated.
Appliances and treatment procedures
The Hyrax rapid palatal expansion appliance was con- structed by using bands on the posterior teeth. Bands were fitted on the maxillary primary second molars and permanent first molars (Fig 2), These bands were joined by a heavy wire (0.045-inch) to the palatal plate, which had a jack screw in the midline. The appliance was activated twice daily (0,25 mm per ttirn) hy the patient for 1 week. In patients with a con- stricted maxilla, activation of the expansion screw was applied for 2 weeks. An 0,ü45-inch wire was soldered bilaterally to the buccal aspects of the molar hands, and extended anteriorly to the canine area. In addi- tion, a lingual wire could be soldered to the premolar band and extended TO the cingulum of the maxillary incisors to increase anchorage control if needed.
The face mask was a one-piece construction with ad- justable anterior wire and hooks to accomodate a downward and forward pull of the maxilla with elastics (Fig 3), To avoid an opening of the bite as the maxilla was rotated, the protraction elastics were attached near the maxillary canines with a downward and for- ward pull of 45 degrees to the occiusal plane. Attach- ment of elastics from the soldered buccal wire to the hooks on the face mask ran across the lip to the other side to avoid irritation around the commissure of the hps.
Orthopedic effects require greater forces than do orthodontic movements, Maxiiiary sutural protraction generally requires 600 to 800 g per side, depending on the patient. Elastics that delivered between 14 and 18 oz of force (as measured by a gauge) were used, Pa- tietits were instructed to wear the headgear 12 to 16 hours a day to obtain maximal skeletal effect, but min- imal tooth movement,
Cephalometric analysis
Lateral cephalograms taken before and at the comple- tion of this phase of treatment were used. All cephalc- grams were taken with the teeth in occlusion (centric occlusion) and the hps in a relaxed position to standard- ize soft tissue posture and morphology. The amount of RCP-ICP mandibular shift on closure were noted, A lateral cephalogram was taken with the patient's jaw wide open, to help in locating the position of condyl- ion, to obtain an accurate measurement of condylar length (Co-Gn) as reference, Cephalogram landmark identifications and constructed lines were established as shown in Figs 4 and 5, Cephalograms were digitized nsing a Texas Itistrumcnt digitizer, and all analyses
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Orthodontics
Rg 4 Cephalometric landmarks, constructed lines, atid di- gitized points used: (S) sella; (N) nasion; {Co) condyiion; (Ar) articulare; {PNS] posterior nasal spine; {ANS) anterior nasal spine; {A) point A; (Go) gonion; (B) point B; (SHP) seiia- nasion perpendicular; {Pg) pogonion; {Grt) gnathion; {Me) menton.
Fig 5 Deiermjnation of changes in {A) horizontal position of maxillary molar and centrai inoisor; {B) vertioai position of maxillary molar and central incisor; {C) horizontai posi- tion of mandibular molar and central incisor; {D) verticai position of mandibuiar moiar and central incisor.
were performed on an IBM PC using Oliceph Orthodontic Software (OLI Inc).
The size of the combined method error (ME) in locating, superimposing, and measuring the changes in the different landmarks was calculated by the formula
ME = Kd-/2n where d is the difference (mm) between two registra- tions of a pair and n is the number of double registra- tions. Before- and after-treatment cephalograms from ten randomly chosen subjects were traced and super- imposed with measurements recorded on two different occasions. The combined ME did not exceed 0.6 mm for any variable investigated.
Statistical analysis
Comparisons of starting forms in the control and treated groups as well as the serial changes observed between these two groups were analyzed using a two- sample t test. The a priori level of statistical signifi- cance was set at .05.
Equivalence of starting forms
Before serial changes observed iti the treatment group
were compared with those in the controls for the same age range, the starting forms of the two groups were compared. There were no statistically significant differ- ences in any maxillary mandibuiar, horizontal, or ver- tical measurements between the treated and control groups (Table I). However, since the sample sizes were small, with large variances, some differences be- tween the two starting groups may not have been statistically supported.
Results
Cephalometric effects
The 6-month cephalometric changes in both the con- trol group and the experimental group treated with protraction headgear and palatal expansion appliances are shown in Table 2, For maxillary skeletal relation- ships, the treatment induced a forward movement of point A by 0.81 mm, while the control group exhibited backward movement (hy 0.76 mm; P < .01). Similar results were found when point A was meai,ured with reference to nasion perpendicular.
For maxillary dentai relationships, maxillary molars
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Control Experimental
ANBO
to pt A (mm)
Max molar horizont (mm)
Max molar vert (mm)
Max incisor horizont (mm)
Max incisor vert (mm)
79.3 3.0
131.9
angle"* (°) Occlusal plane
anglet (°) Palatal plane
angle^ (°) SN-Me C)
NS = not significant.
49.4 61.6 48.7 37.4
18.9
9,3
108,1
Orthodontics
Table 2 Change in measurements after 6 months of treatment
Control Experimental
toptA(mm)
2.65 -0.86 -0.70 -0,16
Ve rtica I rela tionship
0.84 -6.26
angle Í (°) Occlusal plane
• P<.a5. •• P<.01, ^ Maxillary central incisor/SN, • Go-Me/SN, ^ Occlusal plare/SN. • ANS-PNS/St^,
0.97 0.77 1.61
-0.32 NS
1,64 NS
Orthodontios
Fig 7 Pretreatment cephalometric radiograph of the same patient reveals a Class IN malocciusion caused by maxiliary deficiency and mandibular prognaihism.
Fig 6 (left) An 8-year-old patient with a straight profile and a slightly prognathic mandible.
in the treated sample were found to move forward by 0,56 mm while in the control group they moved back- ward by 0.68 mm. Maxillary incisors were found to move forward 1.78 mm in the experimental group, but backward in the control group (by 0.06 mm; P < .05). No changes in incisai inclination were observed.
For mandibular skeletal relationships, no statisti- cally .significant changes were observed either in the length of the mandible (Co-Gn) or the position of point B or pogonion when the treated group was com- pared with the control group. However, the maxill- omandibular relationship (ANB) was significantly dif- ferent from that of the control group (P < .01). In addition, vertical changes, as measured by anterior nasal spine-menton, mandibular plane, and sella- nasion-menton, were all found to be significantly dif- ferent between the treatment and control groups. The occlusal and palatal plane angles, as measured from SN, were found to increase as compared to control group, but the increase was not statistically significant.
Clinical effects
Clinically, in most cases, a Class f molar occlusion was obtained within 6 months of the start of treatment. The clinical results of one patient treated with protraction headgear and palatal expansion appliance are used to illustrate the treatment effects of the appliance.
Case analysis
Figures 6 and 7 show an 8-year-old patient who pre- sented with a Class III malocciusion with a combina- tion of deficient maxilla and prognathic mandible. Clinically, the patient exhibited a bilateral Class Ilf molar occlusion, anterior crossbite involving all four incisors, and bilateral posterior crossbite (Figs 8 and 9). On closure, the patient presented with a l-mm anterior shift and a l-mm lateral shift to the right, Cephalometric analysis showed a Class III maxil- lomandibular relationship with a point A-nasion-point B angle of —2 degrees (norm of +2 degrees) and Wits analysis of —4 mm (norm of 0 mm). Both sella-na- sion-point A (77 degrees compared to a norm of 80 de- grees) and nasion perpendicular to point A (-4 mm compared to a norm oiO to —1 mm) showed that the maxilla was retrusive. The inclination ofthe maxillary incisors was normal (114 degrees to Frankfurt horizon- tal; the norm is 114.4 degrees). The mandibular in- cisors were slightly proclined (99 degrees to mandibular plane; the norm is 90 degrees).
Figures 10 and 11 show the same patient after palatal expansion followed by 6 months of protraction head- gear therapy. The posttreatment record revealed a cor- rection of Class III molar occlusion to a Class I re- lationship with concomitant corrections of anterior and posterior crossbites (Figs 12 and 13). Superimposi- tion of the pretreatment and po.st treat ment cephalo-
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Fig 8 Anterior view of the same patient's pretreatment study cast reveals anterior crossbite involving all four of the incisors and bilateral posterior crossbite.
Fig 9 Laterai view of the same patient's pretreatment study cast reveáis Class III molar and canine relationships.
Fig 11 Pcsttreatment cephalometric radiograph of the same patient reveáis a Ciass I skeletal relationship.
Fig 10 ¡tett) Posttreatment profiie of the patient.
HP
Fig 12 Posttreatment anterior intraoral view of the same patient reveals the correction of anterior and posterior crossbites.
Fig 13 Posftreatment lateral intraoral view of the same patient reveals the correction to Ciass I molar and canine relationships.
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Pretreatment 2-90
Fig 14 Superimposition of the pretreatment and posttreat- ment cephalometric radiographs reveals an increase in for- ward and downward movement of the maxilla and back- ward and downward rotation of the mandible.
metric radiographs showed a forward and downward movement of the maxilla with downward and backward rotation of the mandihle (Fig 14).
Discussion
These results demonstrate that significant changes in the craniofacial complex can be expected from maxil- lary expansion followed by protraction headgear treat- ment for as little as 6 months. Midfacial orthopedic expansion has been shown to be beneficial in the treat- ment of certain Class HI malocclusions. Haas^-'' '" has demonstrated that rapid palatal expansion can pro- duce a slight forward movement of point A and a slight downward and forward movement of the maxiila. In addition, the maxilla articulates with nine other bones of the craniofacial complex; frontal, nasal, lacri- mal, ethmoid, palatine, vomer, zygoma, inferior nasal concha, opposite maxilla, and, occasionally, sphenoid. Palatal expansion will "disarticulate" the maxilla artd initiate ceUular response in the sutures, allowing a more positive reaction to protraction forces. Another advantage of maxillary expansion is the correction of the posterior crossbite that often accompanies a Class III malocclusion because of deficient transverse maxil- lary growth and the abnormal anteroposterior relation- ship of maxilla to mandible. Lastly, a palatal expan-
sion appliance splints the maxillary dentition during protraction and helps transmit force from the teeth to the maxilla, thus limiting unwanted tooth movement,
Cephalometric analysis of the data revealed that the effects of treatment vary among different parts of the…