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]
In 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]
This 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.
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 centric 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.
Regarding the functional therapeutic choices for skeletal class III correction, favorable treatment outcomes with the use of removable RTB appliances in mixed dentition and early permanent dentition have been well-documented.[9-12] 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, significant 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.