INTRODUCTION

Class II malocclusions are frequently observed in orthodontic practice. Droschl1 found the frequency of Class II malocclusions to be 37% among the children between 6 and 15 years of age. Mc Namara2 reported mandibular retrusion as the most common characteristic of Class II malocclusion. Removable or fixed functional appliances3–9 should be used to advance the mandible.

Herbst was the first fixed functional appliance, introduced by Emil Herbst in 1905. However, it was not used until Pancherz10 reintroduced it in the late 1970s. The studies of Pancherz,510–12 Wieslander,13 and Mc Namara et al14 have reported both skeletal and dentoalveolar changes with the Herbst appliance. The disadvantages of this appliance were the rigidity of the mechanism and the requirement of complex laboratory stages.14–16

In 1987, Jasper17 developed a new and more flexible fixed functional appliance, the Jasper Jumper (JJ). It has been observed in studies17–22 that the module applies posterior forces to the maxillary dentition and reciprocal anterior forces to the mandibular dentition. Although the force module was rather large and sometimes caused wounds on the cheek, it was usually well tolerated by patients. The disadvantage of the appliance was the risk of breakage.19 The soft gray synthetics, in which the open-coil spring was embedded, usually became deformed after about 3 months, and the appliance had to be changed to obtain continuous forward force on mandible.20

The Forsus Nitinol Flat Spring (FNFS) is another fixed functional appliance, developed by Bill Vogt in 2001.23 It comprises spring bars (nickel-titanium) coated with a transparent plastic to prevent the cheek from bulging.

In the dental literature, the effects of FNFS appliance have not been compared with any other fixed appliance. The purpose of this study was to compare the dental and skeletal changes obtained by FNFS and JJ appliances.

MATERIALS AND METHODS

Clinical application of FNFS and JJ

The FNFS (3M Unitek, St Paul, Minn) is produced in four different lengths, 28, 31, 34, and 37 mm. The JJ (American Orthodontics, Sheboygan, Wis) (Figure 1A,B) is produced in seven different lengths, 26, 28, 30, 32, 34, 36, and 38 mm. Size of the appliances was determined by adding 12 mm to the distance between the mesial edge of the headgear tube and the distal edge of the mandibular canine bracket when the patient was in centric occlusion: 4 mm for activation, 4 mm for the length of headgear tube, and 4 mm for the distal extension of the ball pin.

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Appliances were attached to headgear tubes of maxillary first molars through ball pins and to the mandibular archwire by an auxiliary arch. The distal end of the auxiliary arch was attached to the second tube of the first molar band and cinched back. The mesial end was hooked over the mandibular archwire between the canine and the first premolar brackets.

Patients were observed at 3-week intervals, and the appliances were activated as needed. Average treatment period of FNFS and JJ appliances were 5.28 ± 1.18 months and 5.23 ± 1.2 months, respectively. After Class I molar relationship was obtained, the appliances were removed, and treatments were carried out with Class II elastics for retention of the treatment results. Lateral cephalograms and study models were taken before attachment and just after removal of FNFS or JJ.

Cephalometric analysis

Cephalograms were traced by one investigator with verification of anatomic outlines and landmarks by the other three. The suspicious structures and landmarks were retraced to the mutual satisfaction of the investigators. A single average tracing was made in instances of bilateral structures.

The analysis of anteroposterior linear changes was carried out using the method of Pancherz.10–12 A coordinate system consisting of the occlusal line (OL), and a perpendicular to this line through the point sella (OLP) was drawn on the cephalogram taken after the leveling phase. These reference lines were transferred to the final cephalogram by superimposing on the cranial base. The cephalometric points, planes, and parameters are shown in Figures 2 through 4.

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Study model analysis

Study model analysis was carried out to determine the expansion effects of the appliances. Intermolar and intercanine widths were measured to quantify the changes in the anterior and posterior arch width of maxilla and mandible (Figure 4).

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RESULTS

Cephalometric findings

A Class I molar relationship was achieved, and the overjet was decreased with both the fixed functional appliances. Cephalometric findings of the treatment groups and the control group are shown in Table 1.

TABLE 1.  Descriptive Statistics of Cephalometric and Study Model Measurements at T2 and T3 for All Groups

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Skeletal parameters revealed similar alterations in both the treatment groups. ANB was decreased because of the retrusion of maxilla and protrusion of the mandible (SNA decreased and SNB, Pog-OLP, and Co-Gn increased). Although the maxilla was retarded, effective maxillary length (Co-A) increased because of the changes in the condyle, which also increased the posterior face height (S-Go). Significant posterior rotation of the mandible (increase in the y-axis) elongated the anterior facial height because of the lower anterior face (increase in N-Me and ANS-Me) (Table 2).

TABLE 2. Comparison of the Between Group Differences for Cephalometric and Study Model Measurements at T2–T3^a

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Dental alterations denoted that upper incisors were retruded, extruded, and distally tipped (U1I-OLP, U1IA/SN decreased, and U1I-SN increased), whereas the lower incisors were protruded, intruded, and labially tipped (L1I-OLP, L1IA/MP increased, and L1I-MP decreased). Upper molar teeth were distalized and intruded (decreased U6M-OLP and U6O-SN). Contrarily, lower molars were moved to the mesial and extruded (L6M-OLP and L6O-MP increased). Dental changes included not only decreased overjet and overbite but also posterior rotation of the occlusal plane (SN/ Occ increased). Improvement in the profile was attained with both the appliances because of the protrusion of lower lip and soft tissue pogonion (increase in LI-OLP and StPog-OLP) (Table 2).

When the cephalometric findings of the treatment groups were compared, decrease in ANB and increase in S-Go was found statistically significant.

DISCUSSION

Removable or fixed functional appliances should be used in the treatment of Class II malocclusion if the etiology is retrognathia of the mandible. In 2001, Vogt introduced a fixed functional appliance, “Forsus Nitinol Flat Spring,” and this study was aimed at comparing the effects of the FNFS and JJ appliances.

Decrease at the SNA angle was found statistically significant, showing the appliances were effective in restraining the forward growth of the maxilla. However, the distance between point A and OPL did not change. It is a known fact that point A is influenced by the dentition. When the upper incisors are retruded, labial tipping of the roots can shift the point A anteriorly. In our opinion, although maxilla was retruded, backward displacement of point A was masked because of the dental alterations. An increase in the Co-A distance was significant, and it was probably because of the adaptive growth in the condyle. Growth of the condyle also increased the posterior face height.

Regarding the maxilla, our results were conflicting with the studies of some authors.20212324 However, in some studies of the Herbst appliance121525 and the JJ,1926 it has been reported that maxillary growth was inhibited, similar to our results. Sari et al8 used the JJ combined with highpull headgear and reported maxillary retrusion.

Forward displacement of the mandible was found in both the treatment groups. The appliances applied a forward and downward force to the mandible and caused a slight posterior rotation. This increase also elongated the lower anterior face height.

Heinig and Göz,23 Stucki and Ingervall,20 Weiland and Bantleon,21 and Weiland et al24 have reported increases in the mandibular length. Similar effects on the mandible were detected also in the studies with Herbst appliance.51214 On the other hand, Cope et al19 and Covell et al26 concluded that the JJ had no orthopedic effect on the mandible.

Dentoalveolar changes were also similar in both groups. The maxillary first molars were significantly intruded and distalized because the vector of force was below and behind the “center of resistance” of the maxillary dentition. This highpull headgear effect also influenced the incisors through the archwire, and maxillary centrals were extruded and retruded with significant palatal tipping. However, palatal tipping of the upper centrals was not significant in the JJ group compared with the control. It was believed to be because of the close posttreatment mean values of the JJ and control groups.

The mandibular incisors were significantly protruded and intruded with labial tipping. Both FNFS and JJ appliances applied downward and forward forces to the mandibular dentition, and because of this effect, the mandibular molars were extruded and showed mesial movement. Intrusion of the upper molars also allowed for eruption of the mandibular molars. As a result of these changes, significant posterior rotation was observed in the occlusal plane. The overjet and overbite were decreased significantly in both the groups, mainly because of the dentoalveolar changes and to a lesser extent to the increase in mandibular length. These dentoalveolar findings are similar with nearly all the previous studies10–1218–24 carried out with fixed functional appliances.

It was determined that the profile improvement in both the groups was because of the changes observed in the lower lip and soft tissue pogonion that were influenced from the forward displacement of the mandible and protrusion of the mandibular incisors. This finding was similar with those of Weiland et al24 and Pancherz10–12 but was contrary to the results of Cash27 who observed a significant change in the sagittal position of the upper lip.

In the comparison of treatment groups, no significant difference was found between any cephalometric measurements except the ANB and S-Go, emphasizing that the skeletal, dental, and soft tissue effects were nearly the same. This was probably related to the similar strength of the appliances. The Herbst,51214 MARS,28 and MARA7 are also fixed functional appliances that work with same biomechanical principles, but they are more rigid than the FNFS and JJ. Rigidity restricts the lateral movements of the mandible, but at the same time, it provides stimulation of mandibular growth by causing more forward positioning of the mandible.

It has been reported that the force applied by fixed functional appliances has three vectors, ie, the sagittal, intrusive, and buccal.172223 Study model analysis showed that the anterior and posterior width of the upper and lower dental arches were expanded. The appliances created not only sagittal and intrusive forces, but also buccal forces, which were the causes of the posterior maxillary width expansion. This influenced the anterior part of the maxillary arch through the archwire. The mandibular arch was also expanded as a result of interdigitation with the upper jaw. This effect has also been reported by various authors.23 In our study, buccal root torque was not adequate to eliminate the expansion of the upper jaw.

CONCLUSIONS

• The FNFS and JJ stimulated the mandibular growth and inhibited the maxillary growth.

• Both the appliances cause significant incisor and molar movements, and these dentoalveolar changes are more effective than the skeletal changes in attaining Class I molar relationship.

• The FNFS and JJ change the inclination of the occlusal plane and also expanded the dental arches during the treatment. If this expansion effect is needed to be controlled, more precautions, such as inserting a transpalatal arch, should be considered.

• The skeletal, dental, and soft tissue effects of the appliances are nearly the same. Being the last generation of fixed functional appliance, the FNFS does not have an advantage over JJ.

• Treatment period with the fixed functional appliances was not an uncomfortable experience, and the patients got used to these appliances in a few days. During the treatment period, two of the JJ and one of the FNFS appliances were broken, and they were renewed.