Epigenetic influences may explain dental differences in monozygotic twin pairs

The document attached has been archived with permission from the Australian Dental Association (8th Jan 2008). An external link to the publisher’s copy is included.Background: Comparisons between monozygotic (MZ) co-twins have tended to focus on the similarities between their dentitions rather than differences. The aim of this study was to determine the prevalence of discordant expression for simple hypodontia and supernumerary teeth in MZ twin pairs and to explain how phenotypic differences might occur despite their similar genotypes. Methods: Records of 278 pairs of MZ twins, including dental casts and radiographs, were examined and the prevalences of discordant expression for missing upper lateral incisors (ULI) or second premolars (PM2), and of mesiodentes, were determined. Zygosities were confirmed by comparisons of blood markers and DNA. Results: There was evidence of at least one missing ULI or PM2 in 24 of the 278 MZ pairs (8.6 per cent), with 21 of these 24 pairs (87.5 per cent) showing discordant expression. Nine of the 278 MZ pairs (3.2 per cent) displayed evidence of mesiodentes, with eight of these nine pairs (88.9 per cent) being discordant. Conclusion: Our findings show that differences in the expression of missing or extra teeth occur often between MZ co-twins whose genetic make-up predisposes them to simple hypodontia or mesiodentes. We postulate that minor variations in epigenetic events during odontogenesis may account for these distinct differences.GC Townsend, L Richards, T Hughes, S Pinkerton and W Schwerd

Ectopic maxillary third molar in Early Pleistocene Homo antecessor from Atapuerca‐Gran Dolina site (Burgos, Spain)

Objectives Here we describe the case of an ectopic maxillary third molar (M3), preventing the eruption of the M2, in the individual H3 of the hominin hypodigm of level TD6.2 of the Early Pleistocene site of Gran Dolina (Sierra de Atapuerca, Spain). Materials and Methods The fossil remains from the TD6.2 level of the Gran Dolina site (about 170 specimens) are assigned to Homo antecessor. Different geochronological methods place these hominins in the oxygen isotopic stage 21, between 0.8 and 0.85 million years ago (Ma). The immature individual H3 is represented by an almost complete midface (ATD6‐69), preserving various teeth in situ. We used high‐resolution microtomograhy (mCT) to investigate the abnormal position of the left M3, virtually reconstruct M2, and M3 as well as assessing the development stage of these. Finally, we compare this case with extinct and extant populations. Results Based on the identified signs, we suggest that individual H3 suffered from a unilateral impaction of the M2 as a result of the ectopic position of the developing M3. Discussion We conclude that the most likely etiology for the ectopic position of the M3 is the lack of space in the maxilla. We discuss possible contributing factors, such as morphometric aspects of the maxilla and the early mineralization of the M3, to support the M2 impaction. Finally, due to the early age at death of this individual we did not identify any secondary lesion associated with the M2 impaction