Class II Correction with an Intermaxillary Fixed Noncompliance Device: Twin Force Bite Corrector

Class II Correction with an Intermaxillary Fixed Noncompliance Device: Twin Force Bite CorrectorSupervisor prof : Maher fouda

By : ameen mohammed

Class II malocclusion is one of the most common problems presenting to orthodontists. Skeletally, a prognathic maxilla, a retrognathic mandible, or a combination of the two is a possible etiology for this malocclusionStudies in the literature 912 report that Class II malocclusion is more commonly associated with mandibular retrognathism than with maxillary prognathism

Stahl et al. reported that features of a skeletal Class II occlusion develop early in the deciduous dentition and do not tend to self-correct with age, implying that some sort of intervention is necessary to achieve correction. Depending on the patients growth status, treatment options commonly include use of functional appliances or fixed functional appliances (FFAs) to enhance mandibular growth, headgear to restrict maxillary growth, camouflage by extraction of upper and/or lower premolars, or surgical correction of the underlying skeletal discrepancy in patients in whom facial growth has been completed.

The term functional appliance refers to a group of appliances that posture the mandible forward in an attempt to stimulate mandibular growth.Typically a functional appliance is advocated for a minimum of 12 hours per day for 6 to 9 months to observe dentoskeletal changes. Thus patient compliance is critical to the success of removable functional appliances. In general, the factors associated with patient compliance are age, nature of the treatment delivered, and psychosocial characteristics of the individual patient.

The compliance with treatment is better in adults than in children and that younger children are more compliant with treatment than are adolescents. The most growth modulation procedures are undertaken in the adolescent phase, proficient patient compliance may be difficult to obtain in certain patients. Removable appliances such as headgear and functional appliances are usually rejected by patients due to discomfort, pain, restriction, and constraints on physical activity and movement

To eliminate patient compliance for Class II correction, the use of nonpatient-compliance-based FFAs was first propagated by Emil Herbst in 1905 with the Herbst appliance. The appliance never really gained popularity until Pancherz revived it in the 1970s. Since then there have been numerous modifications of the rigid Herbst appliance and various other FFAs have also been reported in the literature.

Herbst appliance.

These FFAs may be broadly classified as rigid, flexible, and semirigid fixed functional appliances. The major difference between functional appliances and FFAs is that the mandible is forcefully postured in an anterior position with FFAs with the help of inter-arch anchorage using the maxillary denture base as the anchor unit.

Using the concept of equilibrium, it can be understood that when a rigid FFA is placed in the mouth, the appliance is in static equilibrium. This essentially means that when there is a mesial or forward directed force on the lower arch, there exists an equal and opposite distal or backward directed force on the upper arch. This effect has been proved by cephalometric studies as the headgear effect of FFAs.

Apart from the skeletal effects on the denture bases, effects on the dentition such as retroclination of maxillary incisors, proclination of mandibular incisors, distalization of upper molars and mesialization of lower molars, and clockwise rotation of the occlusal plane 38 have also been observed with FFAs.

Cephalometric analysis can be performed to evaluate the cranial base, the relationship of the maxilla to the cranial base, the mandibles size and position relative to the cranial base, the relationship between the maxilla and the mandible, the vertical dimension, maxillary and mandibular dentition, and soft tissue. Table 13-1 provides an example of such analysis

DIAGNOSIS AND TREATMENT PLANNING

A relatively easy, quick, and reliable way to assess the outcome with a functional appliance or FFA is a visualized treatment objective (VTO). The patient is asked to posture the mandible forward, obtaining anterior incisal contact with the posterior teeth in a Class I or super Class I relationship. If the profile of the patient improves, it indicates that the patient may be a good candidate for functional jaw orthopedics

A Profile view of Class II patient before treatment. B, Visualized treatment objective (VTO). Patient is asked to posture the mandible forward to estimate improvement in the soft tissue profile. Note the improvement in the soft tissue profile of the patient.

If on posturing the mandible forward the profile does not show improvement, the patient may not be an ideal candidate for a functional appliance and other methods for Class II could be considered or a prefunctional orthodontic phase may be required

A, Profile view of Class II patient before treatment. B, Visualized treatment objective (VTO) of the patient. Note that the soft tissue profile of the patient is not improved, indicating that the patient may not be an ideal case for functional appliances.

As a general rule, a functional appliance (FFA) is most ideally indicated in growing Class II patients who are essentially mandibular deficient, with an average to flat mandibular plane angle and upright lower anterior teeth over the mandibular basal bone with minimal to moderate crowding.

TWIN FORCE BITE CORRECTOR APPLIANCEThe Twin Force bite corrector (TFBC) appliance is a hybrid fixed pushtype, semirigid FFA clamped to archwires in both the upper and the lower arches bilaterally. Each unit is made up of two 15-mm telescopic parallel cylinders. Within the cylinder is a nickel-titanium (Ni-Ti) coil spring that is activated when the patient occludes.

TWIN FORCE BITE CORRECTOR APPLIANCEA plunger is incorporated at the end of each cylinder on both ends. At the end of each plunger, hex nuts are present to attach the appliance to the archwires mesial to the upper molars and distal to the lower canine . At full compression a force of approximately 210 g is delivered on each side by compression of the coil spring. This force is synergistic to the indirectly applied force by the muscles of mastication due to the forced anterior repositioning of the mandible

Twin Force Bite Corrector Class II Corrector

Twin Force Bite Corrector Class II Corrector

A unique feature of the TFBC appliance is that since the point of force application is closer to the C RES of the maxillary dentition, compared to other traditional FFAs where the point of force application in the maxillary arch is distal to the upper molar , a lesser clockwise moment is generated with the appliance on the maxillary arch. Also, since the appliance is clamped to the archwire, the intrusive component of the spring force is probably redistributed along the entire denture base. In addition, since the force is applied buccal to the C RES of the maxillary molar, estimated to be at the center of the trifurcation of the maxillary molar, a buccal expansive force is experienced

Treatment ProtocolPre-treatment records for a patient are obtained (Fig. 13-6) and after the initial leveling and alignment phase, the arch wires are progressively increased to 0.019 0.025-inch stainless steel in the upper arch and 0.021 0.025-inch stainless steel in the lower arch (Fig. 13-7, AC). Both archwires are cinched to consolidate the arches into a single unit to avoid any spaces developing or flaring of the incisors

Pre-treatment records of Class II patient treated with the Twin Force bite corrector (TFBC) appliance. AC, Facial views. DH, Intraoral views.

Additionally, to minimize lower incisor flaring, MBT bracket prescription with 6-degree torque lower anterior brackets is advised. A 0.032-inch 0.032-inch transpalatal arch is placed to counteract the buccal forces exerted by the TFBC appliance. The standard TFBC version is attached by the hex nuts to the archwires mesial to the maxillary molars and distal to the lower canines, posturing the mandible forward in an anterior edge-to-edge relationship

After 3 to 4 months of appliance placement, the patient usually has an overcorrected Class I molar and canine relationship. This helps to overcompensate for any relapse that may occur after appliance removal (Fig. 13-7, GI).

Appropriate finishing and detailing is performed and the patient is subsequently debonded (Fig. 13-8). The retention protocol involves a fixed lingual retainer for the lower arch and a removable wrap-around retainer for the upper arch.( Post-treatment )

Effects of the TFBC Appliance (Skeletal) During the 3-month period of using the TFBC appliance In an unpublished study a comparison was done between 20 subjects with TFBC appliance and an untreated Class II sample, A point in the maxilla moved 0.5-mm posteriorly under the distal force of the appliance and 1.7-mm inferiorly by the clockwise moment acting on the upper arch (compared to 0.1-mm anterior and 0.4-mm inferior movement in the control sample .The absolute length of the maxilla was similar in both groupsThe palatal plane rotated clockwise 0.5 degree in the TFBC sample compared to 0.1 degree in the control sample. The mandibular length (Ar-Pog) increased significantly2.1-mm in the TFBC sample compared to 0.7-mm in the control sample which could be attributed to a combination of growth and forward posturing which could be attributed to a combination of growth and forward posturing

Effects of the TFBC Appliance (Dentally) The upper incisors showed distal crown tipping of 7.0 degrees in the TFBC sample compared to 0.1 degree mesial tipping in the control sample. The upper molar distalized 0.7-mm and intruded 1.1-mm in the TFBC group; in the control group the upper molar mesialized 0.3-mm and extruded 0.2-mm. The lower incisors flared 7.3 degrees and mesialized 2.6-mm in the TFBC group compared to no movement in the control group.The lower molar mesialized 1.8-mm in the TFBC group whereas in the control group the molar mesialized only 0.2-mm.Therefore the Class II correction was due to a combination of skeletal and dental effects.

Treatment Timing with the TFBC ApplianceThe earlier studies with functional appliances treated patients early for Class II correction, more recent evidence suggests that the optimum treatment timing for removable functional appliances appears to be during or slightly after the onset of the pubertal peak in growth velocity . The a study conducted on patients that were divided into two groups: prepubertal and postpubertal, based on skeletal maturity at the beginning of treatment They concluded that the post pubertal phase is the preferred phase for Class II intervention with the TFBC appliance.

Case report 1Patient ProfileThe patient was a 12-year-old prepubertal male who presented with a chief complaint of deep bite. He was diagnosed with a Class II malocclusion due to a retrognathic mandible with full cusp Class II molars bilaterally, 100% deep bite, and 6-mm of overjet

Treatment ProgressAfter initial leveling and alignment, stiff upper (0.019- inch 0.025-inch and lower 0.021-inch 0.025-inch) stainless steel archwires were placed with the TFBC appliance inserted with 5-mm of activation. Three months later the patient was in a super Class I relationship and the appliance was removed. Class II elastics were used to maintain the corrections and finishing and detailing were done. The patient was debonded with improvement of the soft tissue profile and good posterior occlusion

Retention ReviewThe patient was evaluated 6 years in retention and showed stable Class I molar and canine relationship bilaterally (Fig. 13-26). Overall and regional superimpositions (Fig. 13-27) showed that, in the treatment phase, the upper molar was held in place with mesialization of the lower molar. In the retention phase, both the upper and the lower molars were very stable with negligible changes. The flaring of the lower anterior teeth caused by the TFBC appliance was found to be stable in the retention evaluation.

A, Pre-treatment lateral cephalogram. B, Post-treatment lateral cephalogram. C, Lateral cephalogram in retention. D, Overall and regional cephalometric superimpositions. Black is pre-treatment, red is post-treatment, and green is retention.

CASE REPORT 2Patient ProfileThe patient was an 11-year-old prepubertal male in late mixed dentition who presented with a chief complaint of crooked teeth. The patient was diagnosed with a Class II malocclusion due to a retrognathic mandible with end on molars bilaterally and minimal crowding in both the upper and the lower arches. The patient had 5-mm of overjet and 50% deep bite

Treatment ProgressAfter initial leveling and alignment, the deciduous upper left second molar was extracted and the second premolar was exposed and evaluated to be small and rotated. Subsequently, stiff upper and lower archwires were placed with the TFBC appliance for 3 months to achieve the overcorrected super Class I molar and canine relationship. The patient was debonded in good Class I molar and canine relationship.

Retention Review

The patient was evaluated after 6 years and stable class I molar and canine relationship was observed . However, mild relapse of the midline diastema was noted. Overall and regional superimpositions showed that, in the treatment phase, both the upper and the lower molars mesialized. In the retention phase, there was no change in the position of the upper and lower molars. There was significant flaring of the lower anteriors, which was stable in the retention phase.

A, Pre-treatment lateral cephalogram. B, Post-treatment lateral cephalogram. C, Lateral cephalogram in retention. D, Overall and regional cephalometric superimpositions. Black is pre-treatment, red is post-treatment, and green is retention.

CASE REPORT 3Patient ProfileThe patient was an 11-year-old female who presented with a chief complaint of crowding . She was diagnosed with a Class II, Division I malocclusion due to a prognathic maxilla and a retrognathic mandible with Class II molars and canines on both sides and an overjet of 7-mm, overbite of 70% with crossbite of the molars bilaterally, and a convex soft tissue profile

Treatment Progress

The patient presented with a severe Class II skeletal relationship with an ANB angle of 12 degrees . However, since the patient was still growing, growth modulation was attempted. There was moderate crowding in the upper arch and minimal crowding in the lower arch.

Treatment began with banding of the maxillary molars and rapid maxillary expansion (RME) in the upper arch to create space for the crowding. Subsequently, the patients upper and lower arches were set up for TFBC appliance placement. The patient was debonded after 24 months of active treatment with a Class I molar and canine relationship bilaterally

Retention ReviewThe patient was evaluated after 7 years and showed a harmonic soft tissue profile with maintenance of stable buccal occlusion bilaterally Overall and regional superimpositions showed mesial movement of both the upper and the lower molars in the treatment phase and no changes in the retention phase. Flaring of the lower anteriors was observed to be stable in the retention phase.

A, Pre-treatment lateral cephalogram. B, Post-treatment lateral cephalogram. C, Lateral cephalogram in retention. D, Overall and regional cephalometric superimpositions. Black is pre-treatment, red is post-treatment, and green is retention.

conclusionClass II correction with the semirigid TFBC appliance appears to be predominantly a combination of dentoalveolar and mild skeletal changes. Long-term retention evaluation of Class II correction achieved with the TFBC appliance showed the correction to be stable. Dental effects of the appliance, such as occlusal plane rotation, distalization, and intrusion of the maxillary molars, appear to be transient effects that do not contribute to overall Class II correction; however, mesial movement and extrusion of the lower molar with use of the appliance appear to be stable effects in the long-term. Treatment efficiency based on overall treatment time suggests that the postpubertal phase is the preferred phase for Class II correction with the TFBC appliance.