Evaluation of the Treatment Effects of the Functional Regulator of Fränkel in the Correction of Angle Class II Malocclusions

Abstract

One of the greatest challenges an orthodontist faces is the correction of Angle Class II malocclusions. Several different treatment options are available to correct saggital jaw discrepancies that often exist in these individuals. Traditionally, headgear has been used to restrain forward maxillary growth, or to distalize the maxilla. However, there is evidence that suggests that the majority of Class II skeletal relationships are due to a retrusive mandible, rather than a protrusive maxilla. Functional appliances are designed to alter the soft tissue environment of the oral facial capsule creating an environment that allows for optimal growth and development of the teeth, bones, and soft tissue. The functional regulator of Frankel (FR) is a functional appliance that is thought to act through modification of muscle and soft tissue patterns. The design of the FR has a lingual hyperpropulser subjacent to the lingual alveolar mucosa that causes a more forward posture of the mandible. It is thought by some investigators that this forward posture results in enhanced mandibular growth at the condyle which enables correction of Class II skeletal relationships. There is conflicting data regarding the efficacy of the FR at enhancing mandibular growth. Several studies show that the primary mechanisms of Class II molar correction with the FR are restrained maxillary growth, and an increase in the occlusal plane angle. Other investigations have shown enhanced mandibular growth (measured from condylion to gnathion) to be the primary mechanism of Class II correction with the FR. Due to the conflicting data that exists regarding the FR, the current study was conducted to further elucidate the treatment effects of this appliance. Fifty cases that met the inclusion criteria of the study were randomly selected from the patient files of a private practitioner experienced with the clinical management of the FR. In order to determine the treatment effects of the FR, cephalometric analysis, as well as composite and regional superimpositions were completed. The mean change from pre- to posttreatment of the experimental group was compared to the published data of untreated Class II individuals from the University of Michigan Growth Study using a two sample t-test. The radiographs were also scanned and digitized using the Dolphin™ imaging software to determine whether the manual tracing technique was similar to the digital tracing technique by using an ANOVA with fixed effects for method, time point, method by time point interaction, and a random effect for patient. The null hypotheses for this investigation were:

There are no statistically significant differences (p<0.05) in the cephalometric measurements between the experimental FR group and an untreated Class II control group. In particular, there are no significant differences (P<0.05) in mean mandibular length change (Condylion-Gnathion) from pre-treatment to post-treatment between the FR treated group and controls.

There is no statistically significant difference (p<0.05) between the cephalometric measurements obtained from manually traced and measured cephalograms, and those obtained utilizing the Dolphin™ imaging system.

The results of this study showed a statistically significant difference (p<0.02) in all cephalometric parameters indicative of enhanced mandibular growth in the FR group. Additionally, the intermaxillary relationship was found to be significantly improved in the FR treated group (p<0.01) relative to controls. These findings are similar to those reported by other investigators who have found that the FR is capable of improving the sagittal jaw relationship of Class II individuals, and that a large portion of this correction is due to enhanced mandibular growth. The present study also found statistically significant differences between the experimental group and controls for several other cephalometric categories. The appliance had a statistically significant (p<0.05) restraining influence on the forward growth of the maxilla which has been previously described as the "headgear effect". The effect the FR has on the dentition was also assessed. The present investigation found that the FR causes significant (p<0.01) flaring of the lower incisors (2.0° from pre- to posttreatment), as well as a significant (p<0.0001) reduction in the axial inclination of the upper incisors (-3.2° from pre- to post-treatment). Further, it was found through regional superimpositions that the FR resulted in significant (p<0.05) posterior movement of the upper incisors (-0.4mm from pre- to post-treatment), as well as forward movement of the lower incisors (0.8mm from pre- to post-treatment). It was found that the appliance had no statistically significant (p<0.05) effect on the sagittal movement of the upper or lower molars. The FR treated group also showed statistically significant changes in vertical cephalometric measurements. The FR group had a significantly (p<0.05) increased posterior face height (2 .5mm from pre- to post-treatment), mandibular plane angle (0.4° from pre-to post-treatment), and occlusal plane angle (0.7° from pre- to post-treatment) relative to the control group. With the exception of increased posterior face height, the increases in the other vertical cephalometric measurements are thought to be deleterious side-effects of FR therapy that may impact Class II correction, and facial esthetics. The results of the comparison of the two measurement techniques showed that in general the measurements between the two methods were similar. Only one cephalometric measurement (Co-Gn) showed a significant difference (p<0.0001) between the two methods at both time points. The intraclass correlation coefficients were found to be greater than 0.80 for all cephalometric measurements made with the exception of the occlusal plane angle (OP), and upper incisor to the SN line (1/-SN). The present study further demonstrates the ability of functional appliances to increase mandibular length. The present investigation is one of the few studies that have conducted pre- to post-treatment superimpositions to determine the treatment effects of the functional regulator of Frankel. To the author's knowledge this investigation is the first to make a comparison between manually traced and measured cephalometric measurements and those made with Dolphin™ imaging. Although several measurements were found to be statistically different between the two measurement techniques, these differences are generally less than 1 mm or 1 degree. Therefore, the difference between the two measurement techniques is not likely to be clinically significant.