Written by Dr. Tanya Prasad | Medically Reviewed by Dr. Shaista Salam BDS
Class III malocclusion, commonly referred to as an "underbite," is a type of dental misalignment characterised by the lower front teeth protruding beyond the upper front teeth when the jaw is closed. This condition can have various causes, including genetic factors, abnormal jaw growth, or a combination of both. Class III malocclusion may be associated with maxillary growth deficiency (and/or maxillary retrognathia), mandibular growth excess (and/or mandibular prognathism), or a combination of both along with vertical and transverse malformations. (1)
A recent systematic review reported a global prevalence of Angle Class III malocclusion within the interval of 0%–26.7% for different populations. Prevalence rates of 15.80%, 15.69%, and 16.59% were revealed for Southeast Asian countries, Chinese, and Malaysian groups, respectively. (1)
Individuals with Class III malocclusion may experience challenges in chewing, speaking, and maintaining proper oral hygiene due to the misalignment of their teeth and jaws. Along with that, Class III patients experience problems with their esthetic appearance due to a concave profile and vertical functional pattern that limits the function to vertical movements. (2)
Orthodontists employ various treatment modalities, such as fixed braces, removable orthodontic appliances, and occasionally surgical intervention, to correct Class III malocclusion. The goal is to achieve proper alignment of the teeth and jaws to improve both function and aesthetics. In some cases, early orthodontic treatment during childhood or adolescence can help guide the growth of the jaws and prevent more severe Class III malocclusion from developing.
The development of Class III malocclusion results from a myriad of factors, primarily rooted in genetic heredity. Extensive research has shown that hereditary influences play a significant role in the manifestation of Class III malocclusion. Familial inheritance patterns, such as the well-documented "Habsburg Jaw" in European royalty, underscore the genetic underpinnings of mandibular prognathism. However, it is crucial to recognize that genetics alone do not tell the entire story. Environmental factors also contribute significantly to this condition (3).
Wrong postural habits of the mandible can pathologically alter the positioning of the mandibular condyle, leading to a forward spatial shift of the mandible. Additional factors include atypical swallowing patterns, nasal airway obstructions, mouth breathing, functional mandibular shifts due to respiratory needs, hormonal imbalances (e.g., gigantism or pituitary adenomas), trauma, premature loss of primary teeth, congenital defects like cleft lip or cleft palate, and muscle dysfunction, alone or in combination with other environmental factors. The precise interaction between these genetic and environmental elements remains a topic of ongoing research and debate (4).
Class III malocclusion presents a distinct set of clinical features that orthodontists must keenly observe for accurate diagnosis. Among the primary clinical indicators are anterior crossbites, where the lower front teeth protrude beyond the upper front teeth, resulting in an underbite appearance. Patients often experience difficulties in chewing and speaking due to the misalignment of their teeth and jaws. In addition to functional challenges, Class III malocclusion can have a significant impact on facial aesthetics, affecting a patient's self-esteem and overall quality of life. (5)
Class III malocclusion can be manifested in various forms, with differing degrees of severity. It can be categorised into three primary types:
This type primarily involves skeletal discrepancies between the upper and lower jaws, characterised by either a deficient maxilla, protruded mandible, or both. Genetic factors often play a predominant role in skeletal Class III malocclusion.
In this form, the discrepancy between the upper and lower teeth is primarily dental, with relatively normal jaw alignment. Dental Class III malocclusion may result from factors such as tooth size discrepancies or dental arch crowding.
This type is characterised by a discrepancy in the way the upper and lower jaws function during biting and chewing, while falling into a skeletal Class I malocclusion category. It may result from muscular imbalances or incorrect functional habits.
When treating a patient with Class III Malocclusion, the orthodontic treatment plan would largely vary according to whether it’s a true skeletal or a functional/pseudo class III malocclusion. To differentiate between the two, proper clinical diagnosis is essential as both cases exhibit an anterior crossbite. This can be done by guiding the patient into centric relation. If incisors have an edge-to-edge relationship with a posterior open bite, and a forward mandibular shift must occur for posterior teeth to occlude in centric occlusion, then this indicates the presence of a pseudo-class III. Radiographic analysis, a necessary adjunct to clinical diagnosis, of such a case would show a skeletal class I relationship with normal sizes of the maxilla and mandible.
Class III malocclusions may be corrected through a combined surgical-orthodontic approach or by orthodontic camouflage, depending on various factors. Orthodontic camouflage could be done using fixed appliances or clear aligners.
Correcting Class III malocclusion with clear aligners is a complex and intricate process that relies on a thorough understanding of the biomechanics involved. In this informative piece, we will explore the key aspects of the biomechanics of aligner therapy in Class III malocclusion correction, focusing on the use of attachments and the necessary movements to achieve successful outcomes.
Attachments are small, precisely positioned raised areas bonded to the teeth that serve as anchor points for aligners. They play a pivotal role in the treatment of Class III malocclusion by facilitating the desired tooth movements. To address this specific malocclusion, attachments are strategically placed on the teeth to apply force in a controlled manner, enabling targeted tooth repositioning (6).
Successful correction of Class III malocclusion using clear aligners necessitates a range of specific tooth movements, each meticulously planned to achieve the desired occlusal outcome. The following movements are commonly employed (7):
1. Mandibular anterior retraction: To address the protrusion of lower front teeth in Class III malocclusion, anterior retraction is often required. This movement involves retracting the lower anterior teeth while ensuring optimal alignment with the upper anterior teeth.
2. Mandibular incisor retroclination: Pseudo Class III is characterised by proclination of mandibular incisors as a compensatory mechanism by dentoalveolar components. Hence correction of axial inclination of mandibular incisors is often required by retroclining them accordingly (10).
3. Maxillary incisor proclination: In Class III malocclusion patients, the maxillary incisors are often proclined to achieve a Class I anterior relationship via orthodontic camouflage.
4. Midline Correction: Misalignment of the midline can be a characteristic feature of Class III malocclusion with a functional shift. Aligners can be designed to address this by guiding the midline into proper alignment.
Now let's take a look at a Class III case treated using the Eon Aligner system by Dr. Samer Sunna.
A 32 year old male patient came with the chief complaint of a reverse overjet or an underbite. The patient seeked orthodontic consultation for a protrusive mandible and an unesthetic smile. The clinical examination revealed a mild concave facial profile and lower lip protrusion. The patient had an unremarkable medical history with no significant dental history.
Clinical findings did not reveal any signs or symptoms of temporomandibular joint dysfunction. The maxillary midline was coincident to the facial midline with a lower midline shift towards left by 2 mm. From the frontal view, the patient's face was symmetrical. Intra oral examination revealed a bilateral class III molar and canine relationship with a reverse overjet of 2mm.
Subsequently, the patient’s lateral cephalogram reported an increased lower third facial height along with the presence of a vertical growth pattern. The OPG of the patient displayed an asymptomatic temporomandibular joint and absence of upper third molars.
The treatment objectives for this patient were:
Orthognathic surgery following orthodontic decompensation of the dental arches along with fixed mechanotherapy was suggested to the patient to address the underlying Class III skeletal discrepancy. The patient declined this treatment.
An alternative treatment plan was suggested to the patient that entailed correction of dental malocclusion and camouflage of skeletal discrepancy with a non-extraction treatment plan along with expansion and retraction of the lower arch using clear aligners
Attachments were planned and placed on both upper and lower lateral incisors, canines, premolars and molars at the preliminary stage of treatment. The patient was put on a weekly wear cycle.
The first stage of treatment showed promising results with correction of arch forms and expansion of the upper and lower arch in the transverse dimension. Proclination of upper anteriors with intrusion of lower anteriors was carried out along with mesialization of upper molars to achieve a stable Class I molar relation.
This was followed by retraction of lower anteriors in the subsequent phase of the treatment. Initially, 17 aligner trays were used in the upper arch and 20 trays for the lower arch. Later, 17 refinement aligners for the maxillary arch and 7 for the mandibular arch were used. The entire treatment was successfully carried out in 10 months without the need for interproximal reduction.
The patient's chief complaint of reverse overjet was effectively addressed and treated at the end of the treatment. A Class I molar and canine relationship was established bilaterally that provided for a stable and functional occlusion. The patient's facial profile showed great improvement along with the correction of anterior dental relationship resulting in a positive overjet and overbite with coincident midlines. Permanent lingual retainers that extended from canine to canine were bonded on the maxillary and mandibular arches.
The above reported case demonstrates how clear aligners can be used to successfully and effectively treat complex cases such as a class III malocclusion. The use of clear aligners enabled the patient to achieve an aesthetic smile while ensuring optimal comfort.
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