Hemimandibular hyperplasia: Description, Causes and Risk Factors:
Hemimandibular hyperplasia is an uncommon maxillofacial deformity. Patients with this affliction present clinically with varying degrees of asymmetry characterized by an increase in ramus height, a rotated facial appearance with kinking at the mandibular symphysis, and prominence of the lower border of the mandible. In the advanced form, maxillary and mandibular alveolar bone overgrowth result in a compensatory canting of the occlusal plane and a significant functional malocclusion requiring bimaxillary surgical correction.
The true causes of hemimandibular hyperplasia is unknown, but the following are the contributory factors:
Tumors and cysts.
- Condylar resorption.
- Condylar fractures.
- Mandibular displacement.
Unilateral hemimandibular hyperplasia is characterized by a three-dimensional enlargement of one side of the mandible, i.e., the enlargement of the condyle, the condylar neck, and the ascending the horizontal rami. The anomaly terminates exactly at the symphysis of the mandible. That is why we call this anomaly, which affects one half of the mandible, "hemimandibular hyperplasia."
The prevalence is very less ranging from 3-4%.
Clinically, the following details are discernible, in pronounced cases the striking increase in height on the affected side and the medial shift of its mandible and the lateral and upward push of the contralateral mandible give the face a rotated appearance. The unilateral asymmetric increase
in height of the face, even when not well-marked, gives rise to a sloping rima oris. The mouth can be opened without restriction and the sloping rima oris and the facial asymmetry still remain discernible
, even if they are less marked. The corner of the lip commissure on the affected side is displaced inferiorly only and not laterally also. This is clear contradiction to hemimandibular hypoplasia, in which the corner of the lip commissure is more lateral and higher than on the normal side.
The diagnosis of hemimandibular hyperplasia is quite difficult because of the morphological complexity of the deformity. Careful history, clinical exam, and radiographic examination will usually reveal the true nature of the disease.
Radiographically, a panoramic tomogram will show that the ascending ramus is elongated vertically with enlargement of the condyle. There is also an elongation and thickening of the condylar neck. The angle of the mandible is rounded, whilst the lower border is bowed downwards to a lower level compared tothe opposite side. There is an increase in the height of the mandibular body, which appears to increase the distance between the molar roots and the mandibular canal. The unaffected side appears to have a normal height. This growth defect is clearly demarcated by the symphysis.
Other radiographic views, including the transcranial and transpharyngeal views of the temporomandibular joint, can also be taken to investigate Pathology.
Laser scanning: Optical surface scanning has been used to monitor three-dimensional facial growth.This is a non-invasive technique and the associated software allows the digitization and comparison of images over time. Over 60,000 points are recorded in 10 seconds producing an accuracy of 0.5 mm.Hence, it is possible to examine facial asymmetry quantitatively. Laser scanning has also been used in plastic surgery to study facial asymmetry.
Computed tomography (CT): CT scanners use X-rays to produce sectional images but the radiographic film is substituted with sensitive gas or crystal detectors. These convert the X-ray beams passed from the patient into digital data. It provides excellent imaging of the hard and soft tissues with more manipulation of the tomographic sections. However, they are both expensive and tend to require high radiation dosage. They can be used for the investigation of pathology, including tumors and temporomandibular joint imaging. Sectional images and 3D reconstructions can also be used to study developmental deformities.
Stereophotogrammetry: Stereophotogrammetry is a method of acquiring three dimensional images using multiple photographs of the same object taken at different angles. In orthodontics, this can be used to quantify facial morphology and detect changes in growth and development of the face. It can be used to monitor facial asymmetry as it is both non-invasive and reproducible.
Treatment is primarily surgical with or without orthodontics, and depends on the degree of severity and status of condylar growth. Different surgical options have been proposed for treating this anomaly, such as high condylectomy, orthognathic surgery, or a combination of both. When performed properly, this protocol stops mandibular growth and provides highly predictable and stable outcomes with great jaw function.
Fixed appliance approaches include the use of the quadhelix, rapid maxillary expansion and auxiliary expansion arches used in conjunction with routine bonded appliance.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.