INTRODUCTION

Treatment of Class III malocclusion in growing patients has been one of the most challenging orthodontic procedures in daily orthodontic practice. Numerous treatment protocols have been reported for correction of Class III malocclusion. In growing patients, interceptive approaches include removable functional appliances,^1–3 chin cup,^4,5 protraction headgear/facemask,^6,7 and skeletal anchorage systems.⁸ The use of reverse functional appliances, including the Frankel III (FR-III) or reverse twin-block appliance, in cases involving Class III malocclusion have been reported in the literature; Loh and Kerr² reported the successful correction of a developing Class III malocclusion with the FR-III appliance.

In orthodontic practice, patient cooperation during treatment has become more of a concern in the past few decades, and several studies have addressed this as one of the key factors for success of any orthodontic treatment.^9–11 Unlike removable functional devices, fixed functional appliances do not require patient compliance, and they can be used concurrently with brackets. The Forsus fatigue-resistant device (FRD) was introduced by William Vogt¹² as a semi-rigid fixed functional device for correction of Class II malocclusion. Elsheikh et al.¹³ presented a method of Class III treatment on a typodont using the Forsus FRD. They found that Forsus FRD could effectively correct mild Class III malocclusion in the typodont by moving the upper dentition forward. However, there is little in the literature regarding the use of fixed functional appliances as a treatment modality for correction of Class III malocclusion in growing patients.

Titanium miniplates have been recently used as a method of skeletal anchorage together with various orthopedic devices to apply orthopedic forces directly to the maxilla. Consequently, the undesirable dentoalveolar effects of the orthopedic device can be avoided. However, the use of miniplates necessitates two surgical procedures for insertion and removal of the miniplates. On the other hand, the introduction of temporary anchorage devices (TADs) has made it possible to achieve absolute anchorage control in daily clinical orthodontic practice when used in conjunction with fixed functional appliances.¹⁴ TADs can be easily placed clinically in one appointment by the orthodontist with no need for complicated surgical procedures to facilitate safe and precise implant placement or to connect it to the teeth. Eissa et al.¹⁵ recently reported the use of a miniscrew-anchored Forsus in correction of Class II malocclusion. However, there is no evidence in the literature supporting the clinical effectiveness of miniscrew-anchored fixed functional appliances for the treatment of Class III malocclusion.

The purpose of this controlled clinical trial was to evaluate the skeletal, dental, and soft tissue effects of a novel treatment protocol for Class III malocclusion using an inverted Forsus FRD appliance indirectly anchored with miniscrews in consecutively treated patients compared with growth changes in a matched control group of untreated Class III subjects.

MATERIALS AND METHODS

The protocol of this study was approved by the Research Ethics Committee of the Faculty of Dentistry, Tanta University, Egypt. After a detailed and informative explanation of the treatment procedures to all participants, written informed consent and assent forms were obtained from the parents and children. Sample size calculation was based on a significance level of .05 and a power of 80% to detect a clinically meaningful difference of 1.5 mm for maxillary forward growth. Power analysis showed that 14 patients were required. To compensate for possible dropouts, two more patients were included in the treatment group. Thus, the treated group consisted of 16 consecutively enrolled patients (nine girls and seven boys; age 12.45 ± 0.87 years) who were treated with miniscrew-anchored inverted Forsus FRD. The control group consisted of 16 untreated patients (eight girls and eight boys; age 11.95 ± 1.04 years).

The patients were included according to the following criteria: skeletal Class III malocclusion (−4° < ANB < 0°), maxillary deficiency (SNA <78°) with or without mandibular prognathism, Angle Class III molar relationship with or without anterior crossbite, normal vertical growth pattern (SN/MP angle 28°–36°), minimal or no crowding in the maxillary and mandibular arches (0–5 mm), no extracted or missing permanent teeth (third molars excluded), immediately before and during the circumpubertal phases of skeletal development (cervical vertebrae maturation index [CVMI] 2 and 3), and no medical history or systemic disease that could affect normal growth of the body and/or the jaws. The CVMI was used for patient selection: CVMI stages 2 and 3 were defined by lateral cephalometric radiographs.¹⁶

A matched control group of 16 untreated subjects with Class III malocclusion was obtained from the Department of Orthodontics, Tanta University, Egypt, to account for the possible effects of growth in the treatment group. The control group matched the treated group in malocclusion, stages of skeletal maturation at each time point, gender, and mean observation duration.

A nonextraction approach was planned for all patients in the treated group. Mini Diamond Twin brackets (Ormco Corporation, Orange, Calif), with a 0.022-inch slot and low-torque maxillary incisors and high-torque mandibular incisors, were bonded to both arches. All patients received hygiene instructions before placement of the orthodontic appliances. Alignment and leveling were done until stainless steel arch wires of 0.019 × 0.025 inches were passively engaged in both arches. Both arch wires were cinched back, and teeth were ligated in a figure 8 pattern. Anchorage was reinforced by using a lingual arch in the mandibular arch to minimize buccal tipping of the mandibular molars due to buccally applied forces from the Forsus appliance on these molars. Although the lingual arch can restrict expansion of the arch and lateral movement of the molars, it was expected to minimally affect distalization of these molars.

Before insertion of the miniscrews, a small amount of local anesthesia was applied. The end of a periodontal probe was used to mark the insertion site on the soft tissue between the roots of the maxillary canine and premolar at the level of the mucogingival junction. Miniscrews (1.6 × 10 mm; MCT Tech, South Korea) were inserted bilaterally between the maxillary canine and first premolar root areas at the level of mucogingival junction. Maxillary canines were bonded with Damon 3MX brackets (Ormco Corporation, Orange, Calif), which have a vertical slot (0.018 × 0.018 inches). A segment of 0.016 × 0.016-inch stainless steel wire was inserted between the vertical slot of the maxillary canine bracket and the hole in the miniscrew neck to establish indirect anchorage (Figure 1).

View Figure

• Download as Powerpoint
• Download Figure

The Forsus FRD size was selected following the manufacturer's instructions using the Forsus ruler to measure the distance between the distal end of the mandibular headgear tube to the distal end of the maxillary canine bracket. The appliance was inserted in an inverted fashion: the mandibular end of the FRD was inserted into the headgear tube of the mandibular first molar by means of EZ2 module clips. The pushrod was inserted onto the maxillary arch wire distal to the canine brackets and crimped around the arch wire. While having the patient keep his or her mouth open, the spring was compressed until the push rod was inserted (Figure 2).

View Figure

• Download as Powerpoint
• Download Figure

Patients were observed every 3–4 weeks. During follow-up visits, if the spring module was compressed more than 2.5 mm above the stop on the push rod, reactivation was performed by cinching a crimp onto the push rod to provide an additional 1.5 mm of activation. The Forsus FRD and miniscrews were removed when normal overjet and overbite had been achieved with Class I canine and molar relationships. The mean time to achieve this was 6.4 ± 1.46 months (Figures 3–5). The fixed appliances were then left in place using light Class III elastics to stabilize the results and avoid relapse. To finalize the occlusion, light intermaxillary box elastics were used, and the mandibular arch wire was replaced with a lighter, more flexible wire.

View Figure

• Download as Powerpoint
• Download Figure

View Figure

• Download as Powerpoint
• Download Figure

View Figure

• Download as Powerpoint
• Download Figure

Cephalometric Analysis

Skeletal, dental, and soft tissue changes were evaluated from the lateral cephalograms taken with the same cephalostat by the same technician just before insertion (T1) and immediately after (T2) removal of the Forsus FRD. In the control group, cephalometric radiographs were taken at the beginning and at the end of the observation period. Using Dolphin Imaging Software version 11.9, tracings were made and all measurements were recorded to compare the treatment outcomes. The cephalometric planes and landmarks, as well as skeletal, dental, and soft tissue measurements, are illustrated in Figure 6.

View Figure

• Download as Powerpoint
• Download Figure

RESULTS

There were no statistically significant differences between the control and treated patients in the skeletal, dental, and soft tissue cephalometric measurements at T1 (Table 1). Skeletal, dental, and soft tissue changes between T2 and T1 in the treatment and control groups are shown in Table 2. Comparison of the mean cephalometric skeletal, dental, and soft tissue changes between the treatment and control groups are shown in Table 2.

Table 1 Descriptive Statistics of All Parameters at T1 and Significance Values of the Differences Between Groups^a

View Fullscreen

Table 2 Changes in Skeletal, Dental, and Soft Tissue Measurements in Both Groups^a

View Fullscreen

There was a significant increase in maxillary forward projection in the treated subjects (SNA°: 1.73 ± 0.53 mm; P < .05). There was no significant effect of the treatment on mandibular projection (P > .05). The anteroposterior intermaxillary skeletal variables including ANB° and Wits appraisal demonstrated significant improvement in the FRD group (1.8 ± 0.59 and 3.3 ± 0.75 mm, respectively).

No significant changes were detected in vertical skeletal measurements including the mandibular plane (MP-SN and FMA) and lower anterior facial height. However, there was a significant counterclockwise rotation of the occlusal plane in the treatment group from before to after treatment (Sn-Occ°: −1.36 ± 0.96; P < .05).

The maxillary incisors showed significant proclination (U1-NA°: 0.5 ± 0.25; P < .05) and intrusion (HRL-U1: 0.91 ± 0.65; P < .05), whereas significant retroclination was observed in the mandibular incisors (L1-NB°: 1.65 ± 0.83; P < .05). Significant mesial movement of the maxillary molars was observed (VRL-U6: 0.77 ± 0.66 mm; P < .05). The mandibular molars exhibited significant distalization (VRL-L6: −0.82 ± 0.73 mm) and intrusion (HRL-L6: 1.11 ± 0.69 mm). The overjet improved significantly (4.6 ± 1.91 mm; P < .05) in the treated group.

Soft tissue measurements demonstrated a significant retrusion of the lower lip in relation to the E-plane (1.56 ± 0.76 mm). However, the upper lip showed significant protrusion 0.95 ± 0.74 mm). The nasolabial angle in the treated group exhibited significant reduction (3.68 ± 1.33 mm).

DISCUSSION

This was the first study that investigated the effects of Class III treatment using an inverted Forsus FRD with miniscrew anchorage. Mini Diamond Twin Brackets were used in this study because they offer versatility in torque prescription. For the maxillary incisors, low-torque brackets (+7°) were used to minimize labial tipping of the maxillary incisors caused by the anterior force of the FRD appliance. To the contrary, high-torque mandibular incisors brackets (−1°) were used to minimize lingual tipping of the mandibular incisors due to the backward force of the FRD appliance. Miniscrews were originally designed to withstand regular orthodontic forces; thus, indirect anchorage was performed in this study to avoid applying a direct orthopedic load on the miniscrews with a subsequent increase in their failure risk.¹⁴ The dimensions of the miniscrews used in the present study were 1.6 mm in diameter and 10 mm in length to optimize mechanical retention of the mini-implants and to eliminate any risks of root proximity or contact that might contribute to failure during treatment. The miniscrews were inserted at the level of the mucogingival junction. This site was clinically accessible for insertion of the mini-implants without the need to incise the mucosa or reflect a mucoperiosteal flap. In addition, it provided adequate cortical bone thickness to ensure better primary stability and long-term success of the mini-implant.

The use of skeletal anchorage in the maxilla for orthopedic Class III correction has been reported in the literature⁸ using miniplates as a means of skeletal anchorage. This requires two surgeries: one for insertion and one for removal of the miniplates. The use of miniscrews along with the fixed functional appliances in this study might have favorably affected compliance of the patients.

The maxilla moved forward significantly in the treated group (1.73 mm) when compared with the control group. This can be attributed to the mesially directed force acting on the maxillary arch. However, this effect on maxilla was limited to the alveolar bone and did not extend to the level of the mid-face. This is in contrast to the findings of De Clerck et al.,⁸ who studied the treatment effects of bone-anchored maxillary protraction with miniplates in the maxilla and mandible using Class III elastics. In their study, they reported significant advancement of the whole maxillary bone. This difference could be attributed to the direction of the protraction force in their study, which was close to the center of resistance of the maxilla.

Anteroposterior mandibular changes were nonsignificant. Although the vertical dimensional changes of the mandible were negligible, there was a significant counterclockwise rotation of the occlusal plane. This rotation could be explained by the vertical force component of the device, which tends to intrude the maxillary incisors and mandibular molars.¹³ Carriere¹⁷ concluded that counterclockwise rotation of the occlusal plane could alter the anteroposterior relationship between the maxilla and the mandible.

The vertical and horizontal force components of the device resulted in intrusion (0.9 mm) and proclination (0.39°) of the maxillary incisors. Although the effects on maxillary incisors were statistically significant, their clinical significance could be considered negligible, particularly in the anteroposterior direction. On the other hand, the distally directed force of the Forsus transmitted through the heavy arch wire to the mandibular incisors could result in significant retroclination (1.69°). Direct forces on the mandibular first molars resulted in intrusion and distalization of the mandibular posterior segment. To the contrary, significant mesial movement and extrusion of the maxillary molars were observed.

Patients in the treatment group showed a statistically significant reduction in overjet. This was related to combined treatment effects of the forward maxillary growth together with mesial movement of maxillary teeth and distalization of mandibular teeth as well as retroclination of the mandibular incisors.

Significant retrusion of the lower lip was observed in the treated group, as evidenced by changes in the lower lip to E plane relationship. Significant upper lip protrusion in the treated group could be attributed to forward maxillary growth together with mesial movement of maxillary teeth, which could be the main reason for the significant reduction in the nasolabial angle.

The intermaxillary relationships in the treatment group were greatly improved due to maxillary advancement. However, this treatment protocol showed a nonsignificant increase in growth of the mandible, which may preclude its use in cases of Class III malocclusion due to mandibular prognathism. Although there was a significant counterclockwise rotation of the occlusal plane, nonsignificant vertical skeletal changes were detected in the treatment group. Thus, the inverted Forsus FRD may not be an appropriate treatment choice for cases with Class III malocclusion with a significantly increased vertical facial dimension.

The limitation of this study was the lack of evaluation of treatment effects on the temporomandibular joint, which would have necessitated three-dimensional imaging. Another limitation was the lack of long-term follow-up. A long-term, comprehensive randomized controlled trial with cone-beam computed tomography is needed to study the treatment effects of the inverted Forsus with and without miniscrew anchorage.

CONCLUSIONS

• The use of miniscrew-anchored inverted FRD could effectively increase maxillary forward growth and result in counterclockwise rotation of the occlusal plane.

• Clinically non significant proclination of the maxillary dentition was observed.

• Distalization of the mandibular dentition together with intrusion of mandibular molars and maxillary incisors were inevitable treatment results.

• Significant esthetic improvement of the facial profile, mainly due to lower lip retrusion and upper lip protrusion, could be achieved.