INTRODUCTION

The most commonly reported treatment protocols for Class III malocclusions have included Frankel III appliances,1 face mask therapy,23 orthopedic chincups, and magnetic appliances. The Fr-III appliance was recommended by Frankel for patients with skeletal maxillary retrusion. Face mask therapy produces protrusive forces to the maxilla and maxillary dentition. It has been stated that circummaxillary sutures are affected by this therapy.23 The protraction forces on the maxilla by face mask therapy can be supported by orthopedic expansion because expansion is believed to facilitate the orthopedic effect of the mask. It has been reported that maxillary expansion produces a slight forward movement of the maxilla.4

The orthopedic chincup is also used in the treatment of Class III malocclusion. This therapy is useful in patients who have a protrusive mandible rather than a small and retrusive maxilla. It has been pointed that the primary effect of chincup therapy is a reduction in mandibular growth.5

Pseudo Class III is defined as the functional forward displacement of the mandible as a result of retroclined maxillary incisors.6 Early treatment of Class III individuals, especially pseudo Class III individuals, has been suggested in several studies. The optimum treatment timing and the treatment modalities influence the effects of the therapies. Various appliances such as removable plates, fixed or removable inclined planes, functional appliances, fixed appliances, and chincups have been designed for early treatment of pseudo Class III subjects.7

Medical and dental applications are favorable fields for the use of magnets. Magnetic forces offer some advantages in orthodontics by their biologic effects, but there is some controversy about the effects on periodontal tissues. The clinical application of magnetic forces has been presented in several studies.8–11 Darendeliler et al9 developed a magnetic activator device for Class II division 1 malocclusions and stated the advantages of the less-bulky design of the appliance. Successful use of a magnetic appliance in skeletal Class III subjects has been achieved. Because of their high costs and the debate about the effects on human tissues, magnets have not yet been routinely used.12

There are only a few studies concerning functional Class III subjects. The aim of this study was to determine the craniofacial and dentoalveolar changes of a magnetic device in functional Class III malocclusions.

MATERIALS AND METHODS

A group of 10 children with pseudo Class III malocclusion (six boys, four girls), mean skeletal age of nine years six months ± 1.02, mean chronological age nine years seven months ± 1.04, were observed for one year without any orthodontic treatment. Mean skeletal age at the second observation was 10 years five months ± 1.02 and mean chronological age 10 years seven months ± 1.04. Serial lateral cephalograms and hand-wrist films were obtained both before and after the observation period and also just after the treatment period. The intraoral and extraoral photographs are shown in Figures 1a,b and 2a,b.

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The patients were treated with a magnetic device consisting of upper and lower removable appliances carrying magnets in both segments. Heated wax with five mm of vertical activation was prepared for a bite and the patient's mandible was manipulated to the most posterior position. Each appliance had Adams clasps on the first molars, a labial bow, and three neodymium (Nd2Fe17B) magnets. Two of the magnets were placed in the molar region and one in the anterior region (Figure 3a).

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The upper-arch magnets were placed three mm distal to the lower-arch magnets (Figure 3b). This way, the upper and lower magnets try to locate at the same level by attractive forces, and a backward force toward the mandible was maintained. Magnets were placed to produce an attracting force of 300 g on each side, producing a total magnetic force of 900 g. The magnets had 2.5 mm height and nine mm radius (Figure 3c). The subjects were instructed to wear the two appliances approximately 18 hours per day and were seen every four weeks.

After obtaining the desired amount of overjet and correction of the anterior crossbite, a full set of records was obtained. The overall treatment period ranged from 5.5 to 12 months. The dentofacial changes were evaluated by linear and angular parameters on the lateral cephalometric films and the landmarks were digitized.

Evaluations were made by the RMO JOE Jiffy 5.0 orthodontic program (Rocky Mountain, Denver, Colo). Statistical evaluation was performed using a t-test.

RESULTS

Descriptive statistics for the cephalometric variables before and after the observation and also posttreatment periods are shown in Table 1. Table 2 shows the results of the statistical comparisons during the observation period. The statistical comparisons of the treatment period are represented in Table 3. The statistical comparisons of changes determined in the observation and treatment periods are shown in Table 4.

TABLE 1.  Descriptive Statistics for all Variables^a

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TABLE 2.  Statistical Comparison on the Differences Between Preobservation and Postobservation

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TABLE 3.  Statistical Comparison on the Differences Between Pretreatment and Posttreatment Periods

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TABLE 4.  Statistical Comparison on the Differences Between Observation and Treatment Periods

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DISCUSSION

The early treatment need of nonskeletal and skeletal orthodontic anomalies is intended to prevent the development of major anomalies. There is a general consensus in the literature that early therapy is indicated in cases of both anterior and lateral crossbites, Class III malocclusion, mandibular retrognathism, and open bite.13 Kidner et al14 stated that Class III twin-blocks have been used successfully for early treatment of Class III malocclusion with proclination of the upper incisors, retroclination of lower incisors, reduction in the SNB angle, and increases in the maxillary/mandibular plane angles.

Treatments with reverse headgear have been investigated several times.1516 Skeletal Class III anomalies due to maxillary retrusion cases have also been treated by Frankel III appliances with no effect on maxillary development. In addition, chincup therapy has been shown to produce a change in the mandible associated with a downward and backward rotation.5

In this study, a decrease occurred in the ANB angle during the observation period. Therefore, the increase in ANB angle might depend on the decrease in SNB angle. The increase in the lower facial height and palatomandibular plane angle by treatment contributes to the backward rotation of the mandible. Baccetti et al17 found that after the treatment with the removable mandibular retractor appliance, the palatomandibular plane angle increased. Darendeliler et al9 found a significant increase in the ANB angle, and Vardimon et al11 presented the same results using a functional orthopedic magnetic appliance.

The SNB angle showed significant decrease during the treatment period, and the difference between the control and treatment periods was significant. The Facial axis increased during the control period and decreased during treatment. The y-axis also increased during treatment.

Class III treatment has been shown to demonstrate a backward and downward direction of mandibular growth in studies. Our findings in facial axis, y-axis, and mandibular plane angle are due to the posterior mandibular displacement.

Studies concerning the effects of Frankel III appliance resulted in a decrease in the SNB angle and an increase in the y-axis, mandibular plane angle, and lower anterior facial height, indicating the posterior rotation of the mandible by the treatment.18–23

It has been stated that chincup treatment induces a backward rotation of the mandible and that the vertical control is extremely important for such subjects and no increase in lower anterior facial height occurred.24 In the subjects of this study, a significant increase in lower facial height and total anterior facial height occurred relative to the control period. These are in accordance with such studies.202225–28

In this study, the overjet increased and the overbite decreased during treatment. The protrusion of the upper incisors and retrusion of the lower incisors were assessed, and the magnetic appliance showed improvement of any anterior crossbite. The magnetic force may produce an extrusive force on the incisors and, therefore, the mandibular incisor extrusion was decreased by the treatment. The acrylic portion of the appliance overcomes the extrusive force.

The increase in the distance of upper first molar to ANS-PNS plane demonstrated the effective forces of the two magnets placed posteriorly. This is in accordance with the results obtained in face mask therapies. A study with a larger sample size may add strength to such studies.

CONCLUSIONS

In the current study, a two-piece magnetic device was used for correction of functional Class III malocclusions. The Class III subjects were observed for one year as the control group and then treated with the magnetic appliance. The primary effects of the therapy were the backward and downward rotation in the mandible, protrusion of the upper incisors, and retrusion of the lower incisors. Lower anterior facial height was affected during treatment. No significant effect on maxilla was determined.