Correction of Class II Malocclusion in a Late Adolescent Patient with Forsus (FRD) Appliance

Fixed functional appliances are non-compliance dependent devices, which can assist the correction of Class II malocclusion. The mechanics of the fixed functional appliances may vary depending on the type of device used. We report the observed biomechanical effects of using the Forsus Fatigue Resistant Device (FRD) fixed functional appliance. The patient was a 14-year-old female presented with a Class II division I malocclusion on a Class II skeletal base. The malocclusion was complicated by a 10mm overjet and increased traumatic overbite. She was treated with the Forsus FRD appliance worn for 5 months after the alignment with fixed appliances (0.022” X0.028” MBT prescriptions) and finished on a non-extraction base. Dento-alveolar changes were the main contribution to the correction of the malocclusion and simultaneously improved the patient’s profile in the end of treatment. In conclusion, Forsus FRD appliance can be suggested to effectively correct Class II malocclusion.


INTRODUCTION
Class II malocclusion is a type of malocclusion, which contributes a major reason for the patient to seek for orthodontic treatment. Class II division 1 malocclusion can be attributed either by maxillary prognathism on a normal mandibular base or mandibular retrusion on a normal maxillary base or a combination of both maxillary prognathism and mandibular retrusion. The options of the treatment depend on the age of the patient, compliance and the severity of the skeletal involvement. The most common cause is contributed by mandibular retrognathism, which is one third of the population [1]. There are several treatment options to treat Class II malocclusion, which includes camouflage orthodontic treatment, orthognathic surgery in adult patient and functional jaw orthopaedic with mandibular advancement in a growing patient [2]. Functional jaw orthopedics with mandibular advancement can be categorised into fixed functional appliances and removable functional appliances. The main advantages for using fixed functional appliances are it requires minimal patient compliance compared to removable functional appliances and it can be used concurrently with fixed appliances. The Herbst appliance, mandibular anterior repositioning appliance (MARA), Jasper Jumper and Eureka Spring are fixed functional appliances, which can be used to manage non-compliant patients with Class II malocclusion [3].
Forsus TM , is a semi-rigid fixed functional appliance for Class II correction that incorporates a stainless steel coil spring on each side of the jaws attached to the upper molar headgear tube and a rigid stainless steel lower archwire distal to either the lower canine or lower first premolar brackets. It was developed using a unique coaxial spring design that has been claimed to be able to maintain consistent force delivery during treatment, thus called as a Fatigue-Resistant Device (FRD) [4]. The bilateral springs are compressed during activation of the appliance, which transmit consistent forces to the upper molars and the lower arches during the spring force unloading.
According to Franchi et al. [5], the Forsus TM FRD is effective in correcting Class II malocclusion with a combination of skeletal (mainly maxillary) and dentoalveolar (mainly mandibular) modifications. However, according to Aras et al. [6], this device did not appear to cause significant increases in mandibular dimensions in subjects in late puberty. The effects of the mandible were mainly at the dento-alveolar level with a large amount of mesial movement of the lower incisors and first molars [5]. In addition, in the late adolescents, there were no significant changes observed in mandibular dimensions and the dental changes were found to be practically the same in adolescents at the peak of puberty and in late puberty [6].
Past studies have discussed the effect of this appliance on skeletal and dento-alveolar changes that is relevant to sagittal correction Class II malocclusion [5,6]. However, the biomechanical effects in other key directions of this appliance have not been described in the literature. This paper reports the correction of Class II malocclusion in a late adolescent patient using the Forsus TM fatigue resistant device (Forsus TM ; 3M Unitek TM , Monrovia, CA, USA) and discusses the biomechanical effects of this appliance in the sagittal, vertical and transverse directions to highlight the key areas for future case selection.

CASE PRESENTATION
A 14-year-old, Indian, female, presented with a chief complaint of protruding upper front teeth. She was in a good health and had no significant medical history.
Clinical examination revealed that she had a Class II Division 1 malocclusion on a moderate Class II skeletal base with an average lower facial height ratio. There was no obvious facial asymmetry. The lips were incompetent, showing 7mm of upper incisors at rest and 2 mm maxillary gingival display on smiling with a normal upper lip length. The nasolabial angle was obtuse and the labiomento fold was deep ( Figure 1).

Figure 1. Pre-treatment facial and intraoral photographs
Intraorally, revealed full permanent dentition with 2mm crowding in the upper and well aligned the lower arches. Both the maxilla and mandibular arch shapes were U-shaped. The upper and lower incisors were proclined. On occlusion, the incisor relationship was in a Class II division 1 relationship with an overjet of 10mm. The overbite was increased by 60% and complete to the palate. The curve of Spee measured from the occlusal plane between the distal cusp of the lower second molar to the lower central incisal edge was 2mm. The buccal segment on the right side was in ¾ unit class II and left side was in ¼ unit Class II molar relationships. The canine relationships on the right side were full unit Class II and ½ unit Class II on the left side. The upper centerline was coincident with facial midline and lower centre line was 1mm to the right from facial midline.
The pre-treatment panoramic radiograph ( Figure 2) showed that the bone level was normal and all teeth were present in the upper and lower arches. All third molars were in the developing stage. Radiopaque restorations were noted on 17 and 37. The lateral cephalometric radiograph ( Figure 3) showed that the patient presented with Class II skeletal base with an average maxilla mandibular planes angle, upper and lower incisors were proclined. The lower lip appeared protrusive from the E-plane by 2.5mm. The cervical vertebral maturation was estimated at cervical stage 5, where the peak in mandibular growth was predicted to have ended at least 1 year before this stage [7].

Treatment Objectives
Our treatment for this patient focused on seven objectives: (1) Secure the optimum oral hygiene before starting the orthodontic treatment; (2) To improve Class II skeletal pattern; (3) Eliminate the dental crowding, level and align the teeth; (4) To achieve a Class I canines and molars relationships bilaterally; (5) Correct overbite and overjet; (6) Achieve a mutually protective functional occlusion and (7) Retention.

Treatment alternatives
The main problem for this patient was Class II skeletal pattern with increased overjet and overbite. Based on these problems, four options were proposed to the patient's mother.
1. The first option involved a growth modification to take advantage of any remaining residual growth potential despite her age and cervical vertebral maturation stage, in the first phase of treatment. This includes wearing twin block functional appliance for a year and followed by a second phase of treatment comprising upper and lower fixed appliances. This will prolong the treatment and requires great compliance from the patient. The mother doubted her daughter's ability to be compliant to wear the twin block at all times.
2.The second option involved growth modification with fixed functional appliance (Forsus TM Fatigue Resistant Device, 3M Unitek TM ). This required alignment of the upper and lower teeth followed by the insertion of Forsus TM when reaching 0.019 X 0.025-in stainless steel archwires.
3.The third option involved orthodontic camouflage. This option requires extraction of 14, 24 and 35 with anchorage reinforcement with headgear or mini implant in the upper arch. Extraction of the teeth in the upper arch facilitates the reduction of the overjet but it may worsen the nasolabial angle due to the retraction of upper lip. The patient also refused to have headgear as a part of the treatment. 4.The fourth option involved orthognathic surgery to advance the mandible and improve the facial profile. After the discussion with her father regarding the treatment options, the father did not want her to undergo orthognathic surgery.
After discussing the treatment options with the patient and parents, they agreed with the second option. Written consent was obtained from the parents and the tentative treatment plan included the following:   [5]. Lateral cephalometric radiograph at this stage showed no significant anterior-posterior skeletal changes but dental compensations by retroclination of the upper incisors and proclination of the lower incisors was observed.
The patient was seen after three months to monitor for relapse prior to phase 2 skeletal and dental assessments. It was felt that any extractions would be unfavourable to her facial profile. In particular, the nasolabial angle may appear obtuse if the upper lip support was brought back with further retraction of the upper anterior segment during space closure. Thus, it was decided to proceed with non-extraction approach. At this phase, all the second molars were bonded. Upper and lower 0.012-in nickel titanium archwire were placed and treatment progressed until 0.019x0.025-in stainless steel archwires. Continuous elastic closed powerchains were placed in the upper and lower arches in order to close minor spaces. Finishing and detailing were done in 2 months and brackets were removed in October 2016. The patient was instructed to wear the retainers for 24 hours within 6 months and to continue wearing the retainers at night indefinitely as suggested by Shawesh, 2010 [8]. aesthetics. The severe overjet and deep overbite were corrected without extractions. At the end of treatment, Class I molars and canines relationships were achieved. The overjet and overbite were also normalized. The post treatment lateral cephalometric radiograph analysis and superimpositions showed there was significant improvement of the facial profile from the general superimposition ( Figure 6). The maxillary incisor proclination was improved with a slight retroclination (U1 to MxP, 117 o ), and the mandibular incisor proclination was slightly increased (IMPA, 101 o ) to camouflage the skeletal Class II discrepancy. The facial convexity improved with the slight retrusion of the upper lip and increased protrusion of the lower lip.

DISCUSSION
Fixed Functional appliances seem to be effective in improving Class II malocclusion in the short term, although their effects seem to be mainly dentoalveolar rather than skeletal [9]. Fixed functional appliance such as PowerScope and Forsus TM FRD are effective in correcting Class II malocclusion [10]. However, Forsus TM FRD has significantly found to have greater in sagittal skeletal effects [10]. The Forsus TM FRD is a fixed functional appliance, which can bring about mandibular growth and favourable changes in dental and soft tissues while correcting the Class II relationship in patients at or just before the peak phase of pubertal growth. For patients near the end of the pubertal growth period, Forsus TM was deemed to be able to only induce dental compensations [11]. However, in this report, this 14year-old girl patient who was expected have passed the pubertal growth spurt for at least a year at the first visit as assessed based on the cervical vertebral maturation method [7], showed improved facial profile on top of the dental compensations observed post-treatment. This paper will provide a deduction of the biomechanical effects of this appliance, which has not been previously explained in the literature.
The mandible is postured forward during first installation of the Forsus TM and further activation of 1.5mm using one split crimp. This incremental activation is better when compared to single stage advancement based on studies of Hagg and Rabie [12,13]. The neuromascular tendency to relax the muscles compresses the springs placed between the upper first molars and stainless steel archwire in the lower arch. In turn, Forsus TM create orthodontic forces by the pushing mechanics during force unloading of the compressed springs to result in changes of the dentition in transverse, vertical and sagittal direction [14].
In the sagittal direction, the compression forces created horizontal forces toward the upper first molars and distalised the upper first molars ( Figure  7(A)). On the other hand, the moment created in the upper arch and caused the retroclination of the upper incisors. The retroclination of the upper incisors were favourable in this case in order to reduce the overjet and protrusion of the upper lip. In the lower arch (Figure 7(B)), the compression forces created the horizontal forces in the lower arch and mesialised the lower molars. In addition, the moment also created in the lower arch and caused the proclination of the lower incisors. The proclination of the lower incisors also contributed to the reduction of the overjet. Slight proclination of the lower incisors can be favourable for Class II correction but over proclination of the lower incisors may compromise the stability [15].
As Forsus TM requires great anchorage demand in the lower arch to avoid unfavourable effects, clinicians are advised to use mandibular rectangular archwires of full archwire to bracket slot size, the addition of a negative torque also to the archwire in the lower incisor region, tight ligation, rigid tiebacks of the arches, cinchbacks of the wires and negative torque (-6 o ) bracket of the lower incisors [5]. In this case, such anchorage enhancement technique was incorporated but the lower incisors still proclined. On hindsight, the proclination could have been reduced with incorporation of mini-implant in the lower arch [16].
However, in this case the proclination was within the acceptable limits of 7 degrees [17]. In a vertical direction (Figure 7(C)), the compression forces created vertical forces towards the upper first molars. The direction of force caused the intrusion of the upper molars and the moment created caused extrusion of the upper incisors. Thus the upper occlusal plane rotated in a clockwise direction. In this case, the extrusion of the upper incisors was acceptable and did not compromise the smile aesthetics. Clinician needs to be cautious to treat the Class II division I with a gummy smile using Forsus TM because the extrusion of the upper incisors may worsen the gummy smile. Such Class II division 1 malocclusion with a gummy smile need to be treated with fixed functional appliances, which has a compression force near or towards the estimated center of resistance of the maxilla in order to reduce the clockwise rotation of the maxilla [14]. In the lower arch, the vertical force minimally intruded the lower incisors and simultaneously caused extrusion of the lower molars. The moment created also changed the lower occlusal plane in a clockwise direction.  Correction of Class II division I malocclusion required large amount of space of about 14mm in order to reduce the overjet, which is commonly managed with extractions of the upper premolars. In this case, the pre-treatment nasolabial angle did not favour extraction to reduce the overjet as the retracted incisors would displace posteriorly, reducing the lip support and resulting a more obtuse nasolabial angle. By using the Forsus TM , space creation was observed through expansion, distalisation and distobuccal rotation of the upper molars as a biomechanical consequence from the use of this appliance. The overjet correction was facilitated by proclination of lower incisors and retroclination of the upper incisors. The facial profile was improved as the lip changes followed the supporting incisors. Overall, a forward and downward displacement of the mandible was observed. This was mainly contributed by a combination of dento-alveolar change and skeletal growth. During Forsus TM treatment as the moment of the forces caused rotation of the occlusal plane, the upper incisors extruded with intrusion of the upper molars. This displaces the mandible downwards as the lower incisors contacts the more extruded upper incisors. Relapse of the Forsus TM treatment caused the occlusal plane to rotate back minimally in an anticlockwise direction. The mandible follows and displaces in anterior direction as the lower incisors occlude on the more intruded positioned upper incisors. The mandible did not displace back posteriorly because some skeletal growth had occurred as observed on the mandibular superimpositions.
Other changes to the airway were also observed in this case. Mandibular retrognathia has been associated with a decreased oral airway volume, which may be due to posterior positioning of the tongue or a posterior position of the hyoid bone has been associated with reduced oropharyngeal airway volume [18,19]. Previous study shows that functional appliance therapy in growing patient increases oropharyngeal airway volume, airway dimensions, and anteroposterior hyoid bone position [20]. Meanwhile, functional appliances also used for adults with obstructive sleep apnoea to prevent upper airway collapse during sleeping [21]. In this case, there was enlargement of the airway, which compared in between the pre-treatment and posttreatment lateral cephalometric radiographs ( Figure  4). Therefore, Forsus TM FRD may be suggested for obstructive sleep apnoea treatment.
The FRD protocol has led to successful correction of Class II malocclusion in 87.5% of the patients. The protocol had a greater skeletal effect on the maxillary structures by restraining the sagittal advancement of the maxilla. The effects on the mandible were mainly at the dentoalveolar level, with a large amount of mesial movement of the lower incisors and first molars [5].

CONCLUSION
Class II division I adolescent patient with 10mm overjet was successfully treated using Forsus TM FRD. The correction of the overjet and overbite was mainly through dentoalveolar compensation and minimal mandibular growth, which simultaneously improved the patient's profile at the end of treatment