Description, Causes and Risk Factors:
Mandibular prognathism is a common clinical problem all over the world. However, its prevalence varies relative to populations: the highest incidence has been observed in Asian populations (approximately 15%) and the lowest in Caucasian populations (1%). The unique concave profile of mandibular prognathism not only seriously affects the masticatory function but also extremely endangers psychology to patients. Today, this type of disharmony remains difficult for dentists because of varied etiologies and limited understanding of the mandibular growth.
It is well known that environmental and genetic components have both contributed to the etiology of mandibular prognathism. Various environmental etiologies, e.g. imbalances in the endocrine system and hormones, enlarged tonsils have been reported to be involved in the forming of mandibular prognathism. However, there is great interest in the genetic component of the etiology and numerous studies suggest that genetic components play an important role in its etiology. But the inheritance pattern of mandibular prognathism is heterogeneous, findings have been reported suggesting autosomal-recessive inheritance, autosomal-dominant inheritance, dominant inheritance with incomplete penetrance or a polygenic model of transmission.
Recent progress in molecular genetics has enabled the genetic determinant to be approached directly. Genetic linkage maps using various types of polymorphic markers are essential tools in many genetic studies. Short tandem repeat (STR) become popular genetic markers because of their polymorphism and hereditary. Yamaguchi and Frazier-Bowers performed genome-wide linkage analysis with STR respectively and found out some mandibular prognathism susceptibility loci - 1p36, 6q25, 19p13.2 and 1p22.1, 3q26.2, 11q22, and 12q23.
Recently Cruz RM examined data on 55 extended families with at least one affected member with mandibular prognathism and performed a complex segregation analysis to access the inheritance pattern. It turned out that the majority of the pedigrees suggested autosomal dominant inheritance.
Anxiety and concerns about jaw alignment.
There is difficulty talking, biting, or chewing related to the abnormal jaw alignment.
Diagnostic tests may include:
Imprints of the bite (a plaster mold is made of the teeth).
Orthognathic surgery in conjunction with orthodontic treatment is required for the correction of adult mandibular prognathism. The two most commonly applied surgical procedures to correct mandibular prognathism are sagittal split ramus osteotomy (SSRO) and intraoral vertical ramus osteotomy (IVRO). Both procedures are suitable for patients in whom a desirable occlusal relationship can be obtained with a setback of the mandible, and each has its own advantages and disadvantages. In bilateral SSRO, the intentional ostectomy of the posterior part of the distal segment can offer long-term positioned stability. This may be attributable to reduction of tension in the pterygomasseteric sling that applies force in the posterior mandible.
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.
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