Genetics and epigenetics of class II and class III malocclusions

Malocclusion is the major diagnosis in orthodontic field. According to Angle's classification, malocclusion is divided into Class I, Class II, and Class III malocclusion. All of these classifications have etiologic factors that establish every specific characteristic of malocclusion. Genetic, is one of the most important etiology in malocclusion since it can be inherited congenitally, for instance many variations in transcription and translation of multifarious genes occurred in masseter muscles, which is the main mastication muscle in human. MYH/MyH-C, MMPs and IGF genes are frequently used to determine the expression of genes in masseter muscle using RT-PCR or cRT-PCR. On the other hand, polymorphism of ACTN3, which can influence fibre type proportions and also muscle performance is found in muscle and skeletal type of Class II malocclusion. MATN1, HSPG2, ALPL, and EPB41 genes are found linked to lp36 related to Class III malocclusion. However, genetic factor does not usually stand alone. It can be influenced by environment which called epigenetic factors. Increasing acetylation activity will initiate a chromatin domain formation that consists of genes for MyH-C fast type gene expression. In contrast, increased of deacetylation activity resulting in closed chromatin confirmation on the chromatin area to limit the access into transcription complexes for MyHC type I gene expression in malocclusion cases. Recently, the most common way to study about heritability in malocclusion is using masseter muscles by analyzing their types of fibers related to every malocclusion's phenotype. In this review, writer will explain more about genetic study in masseter, histone modification, and also genetic and epigenetic factors of Class II and Class III malocclusions, which involve gene mutation and polymorphism for genetic factors and histone acetylation and deacetylation for epigenetic factors.