In an earlier submission to this blog entitled, “The Agenesis of the Primary Molar Periodontal Ligament”, we discussed the timing and matters related to the early formation of the primary molar periodontal ligament. In this submission our interest is focused upon the timing of the histologic formation of that particular oral anatomic structure. We observe that the Mandibular Second Primary Molar begins initial calcification at 18 intrauterine weeks. The crown is complete at 10 months and at that time the Periodontal Ligament (PDL) begins formation. The root is complete by 3 years of age providing us with a 2 year and 2 month time frame for PDL formation.
Contained within an article published online in Stem Cells Dev the lineage commitment of mesenchymal stem cells positioned around the developing tooth bud is regulated by epigenetic mechanisms, such as histone modifications. In this paper two odontogenic neural crest derived intermediate progenitor populations were compared…the dental pulp (DP) and the dental follicle (DF). The two undifferentiated cellular elements were taken from extracted permanent bicuspids and cultured prior to the use of histochemical analysis to determine the role played by epigenetic regulatory mechanisms. This paper reveals that the differentiation of mesenchymal pluripotent cells into the cellular elements that ultimately form the PDL and surrounding anatomic structure of the developing primary molar may be ultimately regulated by epigenetic mechanisms.
If the pluripotency of the mesenchymal cells fails in the maturation of cellular elements that form the basic anatomy of the primary molar periodontal ligament (the PDL) we must surmise that the etiology of primary molar ankylosis is an early event in the histologic differentiation of the cellular elements. A likely explanation is that the differentiation of the pluripotent cells of the mesenchymal tissues that surround the developing primary molar fail to mature due to factors that are not closely related to chromosomal abnormalities.
The earlier posting “Agenesis of Primary Molar Periodontal Ligament” notes three non-conforming oral traits between identical twins. In this submission the variation in oral anatomy palls in relation to the overall amount of pathology that appears in each patient that is identical in form. We might posit that the genome sequence is identical in each twin, but that the non-concordant pattern has its etiology in epigenetics. The vote seems to be out as to whether epigenetic traits are inheritable, however the future may well reveal some ability for transmissibility. Many investigators have suggested that Primary Molar Ankylosis displays a pattern of family inheritance, however that connection will benefit from additional research into the familial aspects of this pediatric oral pathology. 1
- 2013 Mar 15. Epigenetic marks define the lineage and differentiation potential of two distinct neural crest-derived intermediate odontogenic progenitor populations.
Gopinathan G1, Kolokythas A, Luan X, Diekwisch TG.
Published online 2013 February 4. doi: 10.1089/scd.2012.0711