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Type: Thesis
Title: The nature and extent of sexual dimorphism in dental and dermatoglyphic traits of twins
Author: Taduran, Richard Jonathan Ordóñez
Issue Date: 2018
School/Discipline: Adelaide Dental School
Abstract: Human teeth and fingerprints have similar embryological origins from epithelial-mesenchymal interactions. The general aim of this study was to determine the nature and extent of sexual dimorphism in the teeth and fingerprints of Australian twins. The specific aims of this research were to 1. investigate the influences of genetic, epigenetic and environmental factors on observed variation in selected dental and dermatoglyphic features; 2. identify which dental and dermatoglyphic traits display sexual dimorphism and whether this is consistent with the Twin Testosterone Transfer Hypothesis; and 3. identify any evidence of associations and covariance between the studied dental and dermatoglyphic phenotypes. These aims were investigated by measuring crown dimensions, mesiodistal (MD) and buccolingual (BL), of primary and permanent teeth; scoring the Carabelli trait (CT) on primary and permanent upper molars; counting friction ridges (RC) and white lines (WLC) of dermatoglyphs; and classifying fingerprint patterns (FP). Dental and dermatoglyphic development stages were assessed against intrauterine testosterone levels. Phenotypic variation was examined within the context of general somatic development and the properties of a Complex Adaptive System by exploring the possible effects of the Y chromosome and testosterone in utero and the role of epigenetic factors. Results showed sexual dimorphism in both the primary and permanent dentitions, with the permanent teeth showing greater differences. Some sexual dimorphism was observed in the fingerprints. The correlations between teeth and fingerprints were found to be statistically significant but low in magnitude. Strong genetic influence in sexual dimorphism was suggested through MD and BL measurements of MZ twins; this was the only zygosity group where all tooth types were observed as sexually different. The additional role of environmental factors was suggested for the sexual dimorphism of WLC in DZSS twins. Epigenetic influence in sexual dimorphism has been observed in DZOS females, with MD and BL measurements and CT scores being larger than MZ and DZSS females. DZOS females were also observed to have more loop or whorl than arch fingerprints compared to MZ and DZSS females. The differences in tooth size and shape and fingerprint pattern provide further support on the Twin Testosterone Transfer (TTT) hypothesis. While teeth and fingerprints had low correlations in both sexes, it was observed that fingerprint patterns were associated with measurements of MD and BL in both primary and permanent teeth. In conclusion, sexual dimorphism in teeth and fingerprints was confirmed by the larger tooth size and higher Carabelli scores in males, and in DZOS females; and the different WLC in DZSS and fingerprint patterns in DZOS. While teeth and fingerprints have low correlations in both sexes, it was observed that fingerprint patterns are associated with measurements of MD and BL in both primary and permanent teeth. Moreover, the findings provide further evidence that the development of teeth and the development of fingerprints are outcomes of Complex Adaptive Systems.
Advisor: Brook, Alan Henry
Ranjitkar, Sarbin
Hughes, Toby
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, Adelaide Dental School, 2018
Keywords: Sexual dimorphism
complex adaptive system
human development
Provenance: This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at:
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