Identical Twins and “Oral Epigenetic Loading”

In this blog there are two submissions that address the nature of ankylosis of primary molars combined with hypodontia. Compare the panoramic x-rays of two sets of “identical twins” who exhibit disparate features in their oral anatomy. It seems difficult to grasp how two sets of twins with anatomical differences can be identified as “identical.” Our common sense tells us that identical means the same…and yet we observe enormous disparities between each set of twins.

See in this blog two submissions for comparison.

Primary Molar Ankylosis - A Review

A Review of Ankylosis in Monozygotic Twins

A review of each blog would indicate that the “identical” twins may not be identical in oral features considered to be heritable. Is it possible that one set of twins carries added features in the genome that are not identifiable using current genome sequencing techniques? If each twin were sequenced would the genome be identical? If so, then we must conclude that one of the sets of twins carries some additional “signals” that direct the formation of the periodontal ligament or the initiation of a permanent tooth follicle. If an identical twin has 10 to 16 discordant oral anatomical features, then we might surmise that they are different in some genetic fashion either heritable or non-heritable. Taken at face value, the variance between identical twins at the oral level creates the thought that there must be another factor that is operative. First thought might implicate epigenetics, a feature that has been explored at the cellular level of tooth formation. If the differences between two identical twins result in differing levels of oral development, including anodontia, ankylosis and a variety of other oral manifestations, can we then declare that they have a variety of oral epigenetic loading?