Chin Cup Treatment Outcomes in Skeletal Class III Dolicho- Versus Nondolichofacial Patients

The advantages of early treatment in children with Class III malocclusion are not only induction of normal skeletal growth but also reduction of the psychological pressure of being nicknamed “a moon face.” A combination of exclusively maxillary protraction and rapid palatal expansion (RPE) is the most popular and effective orthopedic approach to early treatment of skeletal Class III abnormalities.1–10 

Use of the chin cup appliance is still one of the most effective approaches for treating growing Class III patients.11–14 There are two different characteristic skeletal morphological Class III patterns that are known by a variety of names, ie, dolichofacial vs brachyfacial,15 divergent vs convergent,16 skeletal open bite vs skeletal deep bite,17 and hyperdivergent vs hypodivergent.18 The dolichofacial category describes the long-face syndrome associated with a large anterior facial height, a small posterior facial height, a large (obtuse) angle of the mandible, and large mandibular and occlusal plane angles.

Without excellent patient compliance, achieving effects from the orthopedic treatment of dolichofacial skeletal Class III abnormalities can be much more difficult than achieving effects in mesiobrachial facial subjects.19 There has been no study to examine the differences in treatment outcome of chin cup therapy between dolichofacial and nondolichofacial Class III patients. This cephalometric study statistically determines the differences in treatment outcome of the two different facial patterns and sex differences in Class III chin cup subjects using long-term retention records.

All the 33 male and 32 female chin cup subjects selected for this study had a full record with dental casts, photographs, and radiographs at pretreatment, posttreatment, and retention and also showed excellent treatment results in occlusion and profile. A combination of occipital and high-pull orthopedic forces was applied in dolichofacial subjects and a single occipital force was applied in nondolichofacial subjects (Figure 1A,B).

The force, either occipital or high pull, was adjusted to 250–300 g and applied to the center of the chin as reported previously for dolichofacial male and female samples undergoing chin cup therapy.14 All patients were instructed to wear the chin cup 14 hours per day for the first two years. For the subsequent three years, the force was reduced to 200 g and was applied only during sleep. Patient compliance was excellent under the careful observation of the codental staffs.

The skeletal Class III male subjects consisted of 17 nondolichofacial and 16 dolichofacial Japanese patients. Four bicuspid extractions were performed on six of the nondolichofacial and eight of the dolichofacial patients. RPE without maxillary protraction was performed on the patients with posterior crossbite whenever necessary. Six of the nondolichofacial and five of the dolichofacial subjects underwent RPE.

The skeletal Class III female subjects consisted of 16 nondolicho- and 16 dolichofacial Japanese patients. Four bicuspid extractions were performed on six of the nondolichofacial and seven of the dolichofacial patients. RPE was performed on six of the nondolichofacial and nine of the dolichofacial subjects. Characteristics of nondolicho- and dolichofacial male and female subjects are given in Table 1.

All patients of both sexes showed an anterior crossbite. Patients were classified as either nondolicho- or dolichofacial type based on the two criteria16,20 of mandibular plane angle (MP-SN) or the angle of the mandible (gonial angle), as shown in Table 1. The nondolicho-and dolichofacial groups were divided based on a mean MP-FH of 39° (31° MP-FH, Japanese norm21) or gonial angle of 132° (130.5° male, Japanese norm21) or 130° (128.6° female norm21,22). The angle of the mandible or the gonial angle represents the characteristic morphology of vertical excessive growth pattern not only in Class III22 but also in Class II patients.23– 25 Patients with an open bite were excluded.

All subject data were collected from the pretreatment (T0), posttreatment (T1), and retention (T2) records. At T1, all patients completed the second-phase treatment with a 0.018-inch slot standard or preadjusted edgewise brackets. At T1, most of the patients also stopped wearing the chin cup appliance. The patients who agreed to continue the chin cup for a longer period were allowed to do so, and the maximum period of chin cup use in a dolichofacial patient was 125 months. At T1, the maxillary and mandibular removal retainers were placed, and the wear time was gradually reduced.

At T2, chin cup and removal retainers were stopped. Retention records were taken at the age of 16 years or more from all male and female subjects.

Three sets of lateral head films were available. One set was obtained before treatment (T0), one at posttreatment (T1), and one at retention (T2). Landmarks and skeletal measurements of cephalometric analysis are presented in Figure 2A,B,C. Differences (mean and SD) in the skeletal measurements between the nondolicho- and dolichofacial types in both male (Table 2) and female (Table 3) groups were statistically analyzed.

The length of S-N in nondolichofacial subjects increased more significantly (P < .05) than that in the dolichofacial subjects at the T1 − T0 difference (Table 2). At T0, NSGn and Ar-Go showed significant differences (P < .05) between the two groups. From T0 to T2 phases, MP/SN and ArGoMe cephalometric measurements maintained the initial significant differences between the groups.

As in the male samples, the length of S-N in the nondolichofacial subjects increased more significantly (P < .01) than that in the dolichofacial subjects at the T1 − T0 difference (Table 3). At T0, the SNA angle was significantly (P < .01) smaller in the dolichofacial subjects than in nondolichofacial subjects. Ar-A and Ar-Go at T0 showed no significant differences between the groups but showed significant differences at the T1 (P < .05 or .01) and T2 (P < .01). From T0 to T2 phases, MP/SN, NSGn, and ArGoMe of the female samples maintained the initial significant differences between both groups, the same as those in the male groups.

Because the maxillary dentitions in the Chinese are sufficiently wide, RPE is not commonly indicated in the treatment of Chinese Class III malocclusions.26 This ethnic morphological difference in the maxillary arch may explain the smaller incidence of RPE application in Mongoloid Class III subjects than in Caucasian Class III subjects. In the present Class III subjects, less than half the subjects underwent RPE to correct bilateral posterior crossbites.

In the case of a mild, true mandibular prognathism, correction of an anterior crossbite and acceptable posterior occlusion could be obtained in a year or a little longer after the chin cup was applied and correction was followed by removal of the chin cup.22,27 

Studies by Uner et al27 and Sugawara et al28 are cited as reporting negative chin cap data.29 Uner et al27 found that the initial −2.18° of ANB in the skeletal Class III group improved to 0.09° at the end of chin cap use and to −0.04° in the four years after chin cap removal. They concluded that the abnormality tended to return to the original position during the four-year period after chin cap removal. Deguchi and Kitsugi22 found a similar change of ANB angle in prepubertal (the initial ANB was 1.0°, 1.2° at posttreatment, and unchanged at retention) and pubertal (the initial ANB was −1.3°, 0.5° at posttreatment, and unchanged at retention) groups of identical skeletal Class III cases associated with a similar treatment approach in chin cup use. Sugawara et al28 reported that chin cap therapy did not necessarily guarantee a positive reaction of skeletal profile during the retention period. However, the groups that started the chin cap use at seven and nine years showed satisfactory clinical improvement with a little more advanced maxilla and more retrusive mandible in comparison with untreated Class III subjects as shown by skeletal profile diagrams.

Relapse is a physiological rebound common to all orthodontic and orthopedic treatments. The problem is the degree of skeletal relapse after removal of the chin cap appliance, recognizing the fact that the ANB angle decreases on aging not only in untreated Class III patients but also in skeletal Class I patients. Severe dolichofacial skeletal Class III abnormalities that may also be related to abnormal oral function and a tongue of a larger size and lower position show more tendency toward dentoskeletal relapse. Tahmina et al30 reported that the unstable group showed a larger gonial angle initially, but when compared with those of the stable group the upward–forward rotation of the mandible increased over time. These results indicate that the opening of the gonial angle and the anterior displacement of the mandible are main factors of skeletal relapse in severe skeletal Class III malocclusion.

Ferro et al31 reported that only six of 52 patients treated with splints, Class III elastics, and the chin cup had clinical relapses, and they concluded that a low Wits appraisal, small ANB angle, and large SNB angle were the best predictors of relapse. Their results showed no backward rotation of the mandible at the end of treatment or forward mandibular rotation after treatment. In this study, dolichofacial subjects were treated by a combination of occipital and high-pull chin cup force to get more efficient vertical force control. There is no description of the chin cup force vector for dolichofacial Class III subjects in the Class III treatment objectives of Tahmina et al30 and Yoshida et al32.

The results in this study showed a significant decrease of the gonial angle at the end of treatment. The results also show that the gonial angle continued to decrease the same amount at the retention stage and was associated with a slight anterior displacement of the mandible in both male and female subjects.

In a previous study of treated Class III subjects, there was significant backward rotation of the mandible at the end of the treatment and a nicely maintained position of the mandible associated with an acceptable posterior occlusion at the retention phase, in contrast with untreated Class III subjects.13 If patient compliance was excellent, moderate or severe dolichofacial skeletal Class III abnormalities were nicely treated after a two-year chin cup treatment and stabilized more during the subsequent three-year use of only night-time wear.13 

The percentage of relapse (T2 − T1 differences) for ANB angle and Wits appraisal in our short- and long-term data was 10% to 30%. Yoshida et al32 studied long-term changes in Class III female patients treated by maxillary protraction and chin cap therapy for an average of 15 months. They concluded that the maxilla and mandible maintained their improved positions during the posttreatment period but showed some amount of relapse. Hägg et al33 reported on the follow-up of reverse headgear treatment in Class III malocclusion with retrusive maxilla. The results showed the increased lower facial height and mandibular plane angle in the relapse group, and the mandible in the relapse group grew twice as much as that in the stable group. The degree of relapse could have been different in each, particularly because of patient compliance.

Fortunately, if a patient is satisfied with the results obtained after two years of the chin cup wear, the patient is willing to wear the chin cup for the subsequent three years of night-time wear.13 In clinics, many chin cup patients with nonextraction discontinued visits after the first phase of chin cup treatment and may have been satisfied with the results obtained during first-phase chin cup treatment.

Treatment objectives in Class III malocclusion are to obtain an acceptable occlusion and normal skeletal pattern (skeletal Class I). Although all subjects showed significant improvement of dolicho- or nondolichofacial skeletal Class III malocclusion, the treatment outcome in the two groups maintained the original characteristics of skeletal morphology at retention (Figure 3).

Severe dolichofacial Class III abnormalities are generally diagnosed as surgical cases. However, this study indicated that not only horizontal but also vertical improvement of skeletal Class III abnormalities were obtained with excellent patient compliance.

In the near future, by understanding the etiology and racial problems of Class III malocclusion, candidate gene identification of the complexes of Class III components could be a very interesting approach to early orthopedic Class III treatment aimed at preventing Class III abnormalities.34 

• The treatment period and wear time of the chin cup appliance in nondolichofacial (mostly mesiofacial pattern) patients can be shorter than those of dolichofacial patients.

• All subjects showed significant improvement of dolicho-or nondolichofacial skeletal Class III malocclusion.

• The treatment outcome in the two groups maintained the original characteristics of skeletal morphology at retention.

• Not only horizontal but also vertical improvements of skeletal Class III abnormalities were obtained with excellent patient compliance.

We express our gratitude to Dr Takao Kuroda, private practice, Tokushima City, Shikoku Island, Japan, for providing excellent and valuable chin cup records.