INTRODUCTION

Class III skeletal malocclusions were generally viewed as a problem of the mandible. Until the 1970s, Class III and mandibular prognathism were virtually synonymous.1 However, a developing Class III malocclusion can include maxillary skeletal retrusion, mandibular skeletal protrusion, or a combination of both.2 In the skeletal Class III malocclusions, the selected treatment plan should directly reflect not only the type of Class III malocclusion but also the timing of the treatment.3 The chin-cup can be used to treat excessive mandibular growth4 and maxillary protraction can be used in treating retruded maxillae by accelerating maxillary growth5–7 in growing patients.

For growing patients with skeletal Class III malocclusion characterized by maxillary retrognathism, orthopedic appliances such as reverse headgear and face mask are recommended in moderate to severe cases. Treatment options for young adult and adult patients, however, include orthodontic camouflage treatment in mild to moderate cases and orthognathic surgery in moderate to severe cases. Surgical treatment is more effective to eliminate skeletal problems due to maxillary retrusion. However, this treatment modality had higher risks and greater costs. Therefore, if face mask treatment in young adults proved to be effective and maxillary skeletal changes could be accomplished, the disadvantages of the treatments of orthodontic camouflage and orthognathic surgery might be overcome.

Clinical studies indicate a limited ability to achieve a permanent reduction in the amount of mandibular growth.8–11 Conversely, it is well established that sutural growth can be stimulated.61213 For these reasons, and because relative mandibular prognathism is more often due to maxillary deficiency than mandibular excess,14–17 maxillary protraction may be the treatment of choice for the majority of the cases with Class III malocclusion.18 The principle of maxillary protraction is to apply tensile force on the circum-maxillary sutures and thereby stimulate bone apposition in the suture areas.19

One of the most important factors to consider in treating skeletal Class III patients with orthopedic force is the optimal treatment timing.2021 Early intervention facilitates growth modification, but there may be difficulty in retaining treatment effects through the growth period, necessitating long-term treatment and patient cooperation.2223 A review of the literature reveals that greater skeletal changes with the use of the maxillary protraction appliance are possible in young patients.19–22 It has been found that in the postpubertal period there was a decrease in skeletal effect, whereas the dentoalveolar effect was increased with protraction therapy.3 However, some researchers reported that comparison of the treatment effect according to age showed no significant difference.192425 Therefore, the purpose of this study was to determine the skeletal, dental, and soft-tissue effects of face mask therapy and examine the effect of age on treatment response.

MATERIALS AND METHODS

The material consisted of the lateral cephalograms and hand-wrist films of 28 female subjects with skeletal Class III malocclusions caused by maxillary deficiency, which were treated with a face mask at the Department of Orthodontics, Atatürk University and Faculty of Dentistry. The initial cephalometric radiographs (T1) were obtained before face mask treatment, the second (T2) after achieving a positive overjet and/or Class I occlusion.

The patients were divided into two developmental groups according to Fishman's26 system of hand-wrist skeletal maturation assessment. Group 1 (adolescents), which represented the accelerating growth velocity (SMI 1–3) consisted of 15 female patients. Group 2 (young adults), which represented the completing adolescent growth spurt (SMI 10, 11) consisted of 13 female patients. The mean ages of the adolescent and young adult patients were 11.8 ± 0.80 years and 14.02 ± 0.63 years, respectively.

The inclusion criteria were zero or negative overjet, Class III molar relationship, ANB angle of 0° or less, and Wits appraisal of −1 mm or less. Exclusion criteria were any craniofacial anomaly, severe posterior crossbite, any previous orthodontic treatment, and severe skeletal open bite.

Protraction Device

Petit27 type face mask (GAC Int Inc, 355 Knickbocker Avenue, Bohemia, NY) was used for 16 hours a day with 300 g to 500 g of force per side. All face mask treatment was stopped once the anterior crossbite was corrected satisfactorily. Fixed orthodontic treatment with and without extraction was initiated after face mask treatment.

All cephalometric radiographs were taken with the same cephalometer and the same specifications. Ten linear and nine angular measurements were used to investigate the dentofacial changes (Figures 1 and 2). All linear and angular measurements were recorded exactly as measured without correction for magnification. Cephalometric assessments were made by using a Quick Ceph analysis program (Quick Ceph Systems, San Diego, Calif) on a Macintosh PC.

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RESULTS

The value of the coefficient of reliability was above 0.90 (range 0.90–0.98) for all measurements. The mean chronological age was 11.8 ± 0.8 years, and the mean treatment period was 6.89 ± 1.53 months for the adolescent group. However, the mean chronological age was 14.02 ± 0.63 years, and the mean treatment duration was 8.0 ± 1.65 months for the young adult group (Table 1).

Table 1.  Maturational Stage, Chronological Age, and Treatment Period of Each Group

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Descriptive statistics including means and standard deviations of pretreatment and posttreatment measurements and the results of the paired t-test are presented for adolescents and young adults in Tables 2 and 3, respectively. The results of the Student's t-test are given in Table 4.

Table 2.  Mean and Standard Deviation of Pretreatment and Posttreatment Measurements and the Results of the Paired t-Test in the Ado lescent Group

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Table 3.  Mean and Standard Deviation of Pretreatment and Posttreatment Measurements and the Results of the Paired t-Test in the Young Adult Group

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Table 4.  The Results of Student's t-Test

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The changes in the adolescent group were statistically significant except for the gonial angle and LL-E line. In this group, the measurements of SNB, mand incisor-MP, and PP-SN exhibited significant decrease, whereas the other measurements showed significant increase. The changes in the young adult group were statistically significant except Co-Gn, gonial angle, and LL-E line. In this group, the measurements of SNB, mand incisor-MP, and PP-SN exhibited significant decrease, whereas the other measurements showed significant increase. The differences between adolescent and young adult groups were statistically significant in the measurements of the A-N perp, SNA, Co-A, Co-Gn, Go-Me, ANB, PP-SN, LAFH, TAFH, and TPFH. The other measurements showed no significant differences between groups.

DISCUSSION

In recent years face mask therapy has become a common technique used to correct the developing Class III malocclusion because of the increasing acceptance of the significant influence of maxillary deficiency in Class III structural etiology.3

One of the most important factors in considering facial mask treatment is the optimization of treatment timing. Because time, duration, and intensity of maxillofacial growth differ among individuals, the physiologic age has considerable influences on diagnosis, treatment planning, and ultimately the outcome of the treatment.3

The results of this study showed that treatment with face mask induces significant skeletal and dentoalveolar changes in both age groups. However, these changes in the adolescent group are more pronounced than in the young adult group. Our results revealed a significant amount of maxillary forward movement represented by the increase in the SNA angle, A-N perp, and Co-A distances in both groups. These findings indicate that a significant maxillary response occurred in this group of patients. Other investigators have reported similar findings.2329–34 In addition, the experimental studies61213 constantly demonstrate pronounced forward movement of the maxilla due to heavy and continuous protraction forces.

Takada et al23 and Kapust et al34 observed significant rotation of the palatal plane with maxillary protraction treatment, in agreement with our findings. This rotation may be affected by many factors, including side of the force application, direction of elastic traction, and the facial pattern of the patient. All patients in this study were treated with elastic traction attached in the area of the canine, with the direction of pull predominantly downward (30° to 40°) from the horizontal.

There was a significant correction in maxillary-mandibular relationship and soft-tissue profile in both groups. This correction was a result of a significant increase in ANB angle and Wits appraisal and a significant decrease in SNB angle. Clinical studies focusing on maxillary protraction describe not only forward and downward maxillary movement, but a clockwise rotation of the mandible.23182434–36 Mandibular rotation may be due to a combination of vertical maxillary movement and retraction force on the chin. This rotation is a major contributing factor in establishing an anterior overjet improvement.

A force exerted by the chin cup has been speculated to help in redirecting the mandibular downward and backward growth.37 The downward and forward movement of the maxilla and the downward and backward rotation of the mandible improves the maxillomandibular skeletal relationship and the convexity of the profile but results in an increase in lower anterior facial height. In the present study, therefore, there was a significant increase in lower and total anterior facial heights in both groups.

Various soft-tissue changes combined to improve the Class III profile. The upper lip showed significant forward movement in both groups. However, the lower lip showed no significant changes. This movement of the upper lip, coupled with downward and backward movement of the soft-tissue chin, contributed to the profile becoming more convex. The observed soft-tissue effects appeared to result from the induced skeletal changes. This is consistent with the observation by Ngan et al32 that significant correlations were found between changes of the sagittal relationships of skeletal and soft-tissue profiles in both jaws.

The maxillary incisors were significantly proclined during treatment in both groups. It is possible that the upper incisor proclination was due to mesial dental movement. However, the mandibular incisors were significantly retroclined, despite the fact that no appliances were attached to these teeth. This effect may be due to soft-tissue pressure from the chin-cup component of the face mask. Similarly, Kapust et al34 reported, in addition to skeletal changes in the maxilla and mandible, that orthodontic effects included forward and downward movement of the maxillary dentition and a decrease in the inclination of the lower incisors.

In recent years, investigators have examined the effect of age on maxillary protraction therapy. Although mild and moderate skeletal Class III malocclusion characterized by maxillary retrognathism can be treated during late pubertal growth using a face mask to minimize total treatment time, many orthodontists prefer to treat the anomaly early because they believe the skeletal improvement will be greater if treatment is initiated early. Takada et al23 examined the effects of maxillary protraction therapy in three age groups. Although statistical comparisons among the age groups were not reported, they concluded that a greater orthopedic effect was observed when therapy was initiated before or during the pubertal growth spurt. Similarly, Kapust et al34 examined the effects of maxillary protraction and expansion therapy in three age groups. They reported minimal significant differences among age groups when comparing angular and linear measurements alone. However, they concluded that when analyzing the algebraic sum of treatment effects, significantly greater differences were observed in apical base change in the younger age groups. Baccetti et al38 showed significant advancement of the maxilla in the early treatment group and reported that there was no significant improvement in maxillary advancement in the late treatment group.

Kim et al37 evaluated the influence of age on the protraction face mask therapy. For this purpose, the selected studies were divided into two groups: younger (4 to 10 years) and older (10 to 15 years). They reported that the comparison revealed a trend that all mean values of the younger group were greater than those of the older group, implying greater treatment effects in the younger group. On the other hand, Baik24 studied maxillary protraction and expansion treatment in Korean subjects divided into three groups. Baik24 concluded that changes produced from face mask/expansion therapy in younger children were not significantly different from changes in older children. Similarly, Yüksel et al25 concluded that there were no significant differences in skeletal and dental changes between the age groups due to face mask therapy. The results of the present study show that there were some statistically significant differences between adolescent and young adult groups in treatment response. These differences concentrated on maxillary and mandibular skeletal variables and vertical facial dimensions; especially the significantly greater amount of forward movement of the maxilla in the adolescent group than in the young adult group. Results of this study also demonstrated that treatment changes in the younger group were larger than those in the older group.

Although these results suggest that early treatment may be most effective, protraction face mask therapy can provide useful results for young adult patients with good cooperation. Therefore, it can be said that protraction face mask therapy may be considered an alternative to orthognathic surgery and camouflage treatment in young adult patients with mild and moderate skeletal Class III malocclusion characterized by maxillary retrognathism. Although the results of the present study suggest that protraction face mask therapy in adolescent patients may be most effective, this treatment modality can provide useful results for young adult patients.

CONCLUSIONS

• Correction of a skeletal Class III malocclusion characterized by maxillary retrognathism with face mask therapy appears to result from a combination of skeletal and dental changes.

• In both age groups, skeletal change was primarily a result of anterior and vertical movement of the maxilla. Mandibular position was directed backward and downward with a significant increase in lower face height.

• Dental changes also contributed to the correction, and soft tissues changed in a more convex profile.