Nonsurgical Class III Correction in Adolescence Using Modified Fixed Reverse Twin-Block Therapy and Fixed Appliances – A Case Series

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INTRODUCTION
In spite of lower prevalence rates as compared to class I and class II malocclusions [1] , class III malocclusions usually present with therapeutic challenges due to the complex interplay between environmental and innate factors involved in the genesis of these malocclusions.Though frequently overlooked, skeletal class III malocclusions with anterior crossbites and mandibular overclosure often present with a myriad of complex problems, including anterior functional shifts due to incisal interferences. [2]Since late mandibular growth tends to exacerbate the class III discrepancy [1] , successful treatment of class III anomalies poses a greater difficulty with the passage of time. [3]n adolescent and adult patients, although camouflage of the skeletal class III condition (through dentoalveolar compensations) by employing temporary skeletal anchorage devices (TSADs) for mandibular total arch distalization, extractions, or class III elastics can improve overall occlusion, the profile may worsen due to increasingly visible chin projection, thereby negatively impacting smile aesthetics. [4]Moreover, nonsurgical treatment options for adolescent or adult class III patients are usually limited when patients decline camouflage treatment with TSADs. [3]Few investigators have reported the successful use of reverse functional appliances such as monobloc and fixed reverse twin-block (RTB) in conjunction with fixed appliances in adult class III patients. [2,5,6]his article chronicles the treatment of two patients with skeletal class III malocclusion during late adolescence and early adulthood.The patients were treated using a renovated and modified fixed RTB appliance as a functional treatment modality in conjunction with comprehensive fixed mechanotherapy.The stability of clinically acceptable aesthetic and functional outcomes is also discussed.
The modified fixed RTB consists of a banded maxillary and mandibular component cemented to the permanent maxillary and mandibular molars, respectively, using glass ionomer type-I luting cement.The maxillary component consists of bite blocks anchored on a modified palatal arch soldered onto the molar bands.The mandibular component comprises a modified lingual arch onto which the lower occlusal planes are anchored.The entire wire framework is fabricated with 0.040-inch stainless steel wire.In accordance with the recommendations of Clark [7] , bite blocks are inclined at 40-70° to the occlusal plane in a reverse configuration achieved by placing the upper block (covering the upper premolars) anteriorly and enabling the lower block (covering the lower molars) to occlude behind it.

Diagnosis and etiology
A 17-year-old girl presented with complaints of prominent lower front teeth and compromised mastication and phonation.Her familial, medical, and dental histories were non-contributory.Extraoral examination revealed an apparently bilaterally symmetrical face, concave facial profile with midface deficiency, relatively strong chin projection, retrusive upper lip, prominent lower lip, and a shallow mentolabial sulcus (Fig. 1).TMJ exhibited normal functional activity with no clicking or popping.The patient's mandible could be postured to achieve an edge-to-edge incisal relationship in the retruded contact position (RCP) with no pain or discomfort in the TMJ (Fig. 1).
Intraorally, she displayed Angle's class III subdivision left malocclusion, with three incisors in the anterior crossbite.A reverse overjet of 4 mm and a reverse overbite of 8 mm were also found.The upper arch form was square with mild anterior crowding, whereas moderate crowding was observed in the ovoid-shaped lower arch (Fig. 1).The tongue was normal in size and function.
Based on the clinical and cephalometric examinations, the patient was diagnosed as having a class III malocclusion with moderate anteroposterior jaw disharmony, anterior crossbite with mandibular overclosure.

Treatment objectives
The treatment goals were to (1) improve the skeletal jaw relationship, (2) correct the anterior crossbite, (3) achieve esthetically favorable and functionally effective overjet and overbite, (4) establish canine guided functional occlusion with anterior guidance, and (5) improve frontal and profile esthetics.

Treatment plan and alternatives
A traditional camouflage treatment approach involving mandibular premolar extractions and class III elastics was considered a tentative treatment plan.However, in view of the inadvertent effects of camouflage treatment involving the extraction of mandibular premolars and the use of class III elastics on the inclination of the occlusal plane, the interincisal relationship, the TMJ, and soft tissue profile esthetics [4] , mandibular premolar extractions were not considered a viable treatment option for our patient.Another possible treatment option of miniscrew-assisted enmasse distalization of the mandibular arch was contemplated and discussed, but the patient and her parents intensely rejected or did not agree with the use of TSADs.Since the patient's mandible could be postured backwards to achieve an edge-to-edge incisal relationship in the retruded contact position (RCP) with no pain or discomfort in the TMJ, a conservative, noninvasive, two-stage treatment approach commensurate with the patient's wish/desire was adopted.A functional approach involving the use of modified fixed RTB was contemplated as a stage 1 procedure, followed by fixed orthodontic mechanotherapy during phase 2 to achieve well-intercuspated buccal occlusion.However, because of the possibility of worsening of the intermaxillary sagittal relationship during late mandibular growth, the patient was also informed about the possibility of requiring orthognathic surgery in the future.

Following acceptance of the functional treatment protocol by the patient and her family, a modified fixed RTB appliance was delivered. The appliance was constructed at the position of maximum possible retrusion of the mandible with an interincisal clearance of 2 mm and a posterior vertical clear-
ance of 5 mm (Fig. 3).Subsequent visits were scheduled at 4-week intervals to assess treatment progress.In the fourth month, 0.022-inch slot low-torque brackets were bonded on the maxillary central and lateral incisors, and initial alignment was initiated using 0.014-inch nickel-titanium wire (Figs.4a-4c).After six months, when a positive incisor overjet had been achieved, the fixed RTB appliance was removed (Figs 4d-4f), and the remaining teeth were then bonded to initiate the second phase of treatment.Alignment and leveling of the arches were performed with superelastic continuous 0.016-inch and 0.017×0.025-inchnickel-titanium archwires (Figs 4g-4i).Simultaneously, uprighting of the left maxillary canine was accomplished using a sectional box loop fabricated from 0.017×0.025-inchTMA wire.0.017×0.025-inchtitanium molybdenum and 0.014-inch stainless steel were used during finishing and detailing (Figs 5a-5e).After 18 months, the appliances were removed.For retention, circumferential removable retainers were delivered to both arches.

Treatment results
Following treatment, overjet and overbite improved, and well-interdigitated class I occlusion was achieved (Fig. 6).The posttreatment panoramic radiograph indicated wellaligned roots without any root resorption (Fig. 7a).The maxillary and mandibular incisors were flared labially, and the molars were retracted and extruded vertically (Figs 7b, 7c).Vertically, the maxillary incisors were slightly intruded, and the mandibular incisors were slightly extruded (Table 1).Although the lower facial height remained elongated, the patient and her parents were satisfied with the facial profile and occlusion that were achieved without orthognathic surgery (Fig. 7c).The patient demonstrated well-maintained, stable occlusion and facial esthetics throughout the follow-up period of 36 months (Fig. 8).

CASE 2 Diagnosis and etiology
A 20-year-old male with euryprosopic facial features presented with anterior crossbites, a concave profile, and anteri-or mandibular displacement with a prominent chin.His past medical, dental, and familial histories were unremarkable.Intraoral examination showed a class I molar relationship on the right side and a 1/2 cusp class III molar relationship on the left side.Overjet was −3.5 mm, and overbite was 6 mm.crepancy was observed in the anterior segment of the upper arch.The mandibular dental midline was 3 mm to the left of the facial midline.The patient demonstrated mandibular overclosure and an anterior functional shift, making the class III problem appear worse than it was (Fig. 9).No TMJ signs or symptoms were evident.

The treatment objectives were to: (I) correct the skeletal class III relationship by rotating the vertical segment clockwise to improve the ANB angle; (II) achieve coordination of upper and lower dental arches; (III) establish normal overjet, overbite, and functional occlusion; and (IV) improve facial appearance and profile by increasing the vertical dimension of the occlusion.
To accomplish these objectives, a two-phase treatment plan involving modified fixed reverse twin block therapy during phase 1 accompanied by comprehensive fixed mechanotherapy during phase 2 was formulated.

Treatment progress
Phase 1 of treatment commenced with the placement of a modified fixed RTB appliance (Figs 11a-11c).Following the removal of the RTB appliance after six months, the skeletofacial esthetics improved considerably, and an open bite developed in the posterior segments (Figs 11d-11f).In the second phase, 0.022-inch slot MBT brackets were bonded to both arches.In the initial phases, an open-coil spring was inserted/used on a 0.018-inch SS wire ligated piggyback over a 0.014-inch nickel-titanium wire to create space for two maxillary central incisors (Figs 12a-12c).Thereafter, the progressive arch wire sequence used in sliding mechanics was 0.016×0.022-inchnickel-titanium, 0.019×0.025-inchstainless steel, and finally, 0.021×0.025-inchtitanium molybdenum and 0.014-inch stainless steel during finishing stages (Figs 12d-12i).
Post-debonding, Hawley-type retainers were delivered in the maxillary and mandibular arches.The maxillary right central and lateral incisors were reshaped/restored with composite resin to increase their mesiodistal size to improve anterior fit and optimize smile esthetics.

Treatment results
After 17 months of treatment, an adequate overjet, overbite, and well-interdigitated canine-guided class I buccal occlusion was established with a corrected midline (Fig. 13).The panoramic radiograph revealed acceptable root parallelism with no significant apical root resorption (Fig. 14a).A slight opening of the mandibular plane angle (SN-MP, 20°) was noted because of the downward and backward rotation of the mandible.Both the maxillary and mandibular incisors were proclined.The maxillary molars were protracted and slightly

DISCUSSION
The present case series chronicles the individualized orthodontic management of two patients who presented with a class III malocclusion, anterior crossbites, and evident functional shifts with an acceptable facial profile in centric relation.The etiology of the class III malocclusion in the reported patients appeared to be a combination of skeletal, dental, and functional factors.The patients were successfully treated nonsurgically over two phases of treatment that included the use of modified fixed RTB and fixed appliances.The main mechanisms included the active clockwise rotation of the mandible, the labial inclination of the  maxillary incisors, and the mild labial inclination of the mandibular incisors.It has been observed that many class III patients presenting either late for treatment in adolescence or adulthood usually reject or are not willing to accept surgical orthodontic therapy, and persist in their pursuit of conservative orthodontic treatment, which often presents a therapeutic challenge. [3]However, the presence of favorable orthognathic profile and class I relation in buccal segments in cen- tric relation, along with premature contact of the incisors resulting in a functional shift of the mandible, make such patients suitable candidates for conservative/camouflage treatment [8] , which was selected for our patients.
[11][12] However, the literature reporting the effectiveness of the RTB appliance in achieving better relationships between the maxilla and the mandible in late adolescence and adults is relatively limited.
It is worth noting that the mechanics of a functional treatment for the correction of a class III malocclusion using a novel modified fixed RTB appliance was applied to our patients.In contrast to the modification proposed by Liu et al. [5] , wherein bite blocks were located in the premolar region of the upper and lower appliances, for our fixed RTB appliance, the upper bite block was set to cover the upper premolars and occlude posteriorly, with the lower block covering the lower molars.Also, the occlusal pads were not trimmed to prevent eruption of the molars and inadvertent hinge opening of the mandibular plane angle during treatment.Tongue exercises involving the practice of a tongue posture to contact the palatal surface were prescribed to all patients.After removal of the modified fixed RTB appliance, signifi-cant skeletal anteroposterior correction was observed with a normal incisor relationship and an open bite in the posterior region, and fixed mechanotherapy was commenced immediately without any time lag for functional retention.More significant immediate dental changes observed following phase 1 of RTB therapy included mild lingual inclination of both the maxillary and mandibular incisors.
Clark [7] demonstrated that in the RTB appliance, reverse 45°-70° angulation of intersecting inclined occlusal planes harnesses occlusal forces to exert a class III traction effect on the jaws, resulting in maxillary advancement, while using the lower arch as an anchorage and transiently restricting forward mandibular development.It has also been reported that when the bite is maximally retruded, distalizing force exerted on the mandibular condyles is not detrimental because the bite is hinged open with the condyles down and forward in the fossae; and the inclined planes are directed downwards and backwards on the mandibular teeth.According to Seehra et al. [10] , the RTB appliance's primary effects are dentoalveolar, as evidenced by upper incisor proclination and lower incisor retroclination, with minimal favorable skeletal effects.All these combine to contribute to the correction of the anterior cross bites and achieving a class I molar relationship.It is interesting to note that these dentoalveolar changes can be utilized even past a patient's peak pubertal growth period to obtain changes that aid in correcting a class III malocclusion.Modified fixed RTB helped control and stabilize the growth of the overclosed mandible, resulting in an improvement of the maxillomandibular relationship by inducing mild clockwise rotation of the mandibular base within the functional boundary and overall improving the unesthetic facial concavity.Following the completion of fixed treatment, an anterior functional guide was obtained for the eccentric movements of the mandible.
Establishment of the individualized treatment plan envisaging the concept of goal-oriented therapy should be based on efficacy, ease of application by the clinician, and acceptance by the patient.Based on the Wits appraisal of −13 mm (i.e., greater than 12 mm) in Case 1, the severity of class III was labeled as 'red' category, and in Case 2 as 'yellow' category in accordance with the Wits appraisal of −8 mm. [13]Even so, with the implementation of a sequenced non-surgical alternative treatment plan in all three patients, the desired treatment objectives were attained, which justified the adopted treatment procedure decisions.
For our modified fixed RTB, promising results have been obtained with the use of the appliance at the late permanent dentition stages, when patients have growth potentials of 5% to 65% according to vertebral evaluations.Unlike removable functional appliances, treatment protocols using modified fixed RTB do not rely on the patient's compliance, and by virtue of the unlocking of posterior interdigitation, brackets can be used concurrently with the RTB appliance.Other advantages include ease of adaptation to normal functions of speech and mastication, ease of fabrication with minimal armamentarium (no specialized inventory required), cost-effectiveness, and minimalistic design allowing for correction of interarch relationships.
With correction of the skeletal problems during late adolescence by tooth movement alone, the major concern is the impending possibility of adaptive difficulties due to a change in condylar position within the fossa, thus resulting in discomfort or pain in some patients.However, with the accomplishment of nonsurgical treatment by the use of fixed RTB therapy accompanied by simple fixed orthodontic treatment, satisfactory occlusion was established while respecting the anatomic limits of the alveolar housing.No signs or symptoms of temporomandibular dysfunction were noted during treatment or in the follow-up period, and the entire treatment process was well tolerated by all patients.
Class III malocclusions not amenable to functional correction and patients exhibiting allergy/delayed hypersensitivity to methyl methacrylate resins are contraindications to the use of modified fixed RTB therapy.
From both functional and esthetic standpoints, orthodontic treatment involving the use of modified fixed RTB and fixed appliances was satisfactory based on the final outcome.However, high-quality, long-term studies are warranted to support the benefits of a combination of modified fixed RTB therapy and fixed mechanotherapy to improve skeletal and dental relationships in patients with class III malocclusion.

CONCLUSION
In aptly selected cases, a synergistic combination of modified fixed RTB therapy accompanied by comprehensive fixed mechanotherapy can be a viable treatment alternative for the correction of mild to moderate skeletal class III malocclusion associated with functional anterior shift and mandibular overclosure.Based on the principle of patient-centered outcome and in accordance with clinical practice guidelines, this minimally invasive treatment protocol brought about significant improvement in esthetics and occlusion with long-term stability, addressed the patients' chief concerns, and improved their self-esteem.

Figure 1 .
Figure 1.Pretreatment extraoral and intraoral photographs showing class III malocclusion with anterior crossbites and the ability to achieve an edge-to-edge incisor relationship during posterior mandibular positioning.

Figure 3 .
Figure 3. Treatment progress photographs with a modified fixed RTB in situ.

Figure 4 .
Figure 4. Stage photographs: (a-c) Incisor alignment in progress in conjunction with modified fixed RTB; (d-f) Improvement in the overjet and appearance of a bilateral posterior open bite after the RTB appliance had been removed; (g-i) Alignment and leveling of upper and lower arches in progress and sectional box loop being used for uprighting of upper left canine.

Figure 5 .
Figure 5. (a, b) Uprighting of upper left canine in progress; (c-e) Finishing and detailing of arches in progress.

Figure 8 .
Figure 8. Three-year follow-up photographs demonstrating stability of achieved results.

Figure 9 .
Figure 9. Pretreatment extraoral and intraoral photographs indicating reverse overjet, mandibular overclosure, and functional shift of the mandible

Figure 11 .
Figure 11.Treatment progress photographs showing: (a-c) Placement of a fixed RTB appliance; (d-f) Improvement in the sagittal relationship and presence of a posterior open bite following completion of functional phase.

Figure 12 .
Figure 12. (a-c) Space gaining in upper anterior segment in conjunction with leveling and alignment of both arches; (d-f) Progression of alignment, leveling and settling of the posterior open bite; (g-i) improvement of torque in anterior segment and detailed buccal occlusion during final stages.

Figure 13 .
Figure 13.Posttreatment extraoral and intraoral photographs showing improved facial appearance and restored occlusal symmetry with well-interdigitated class I buccal occlusion.

Figure 15 .
Figure 15.Three-year follow-up extraoral and intraoral photographs depicting well-maintained stable results.

Table 1 .
Lateral cephalometric analysis of Case 1 Folia Medica I 2024 I Vol.66 I No. 4