Supernumerary teeth are teeth in addition to the normal complement of 20 primary and 32 permanent teeth. The majority of these supernumerary teeth are conical shaped, assume an inverted orientation and remain un-erupted. Therefore, radiographic examination is considered critical for the identification of supernumerary teeth. A meta-analysis to determine the variations in the prevalence figures based on the diagnostic tools employed revealed that a clinical examination plus selected radiograph(s) are essential for determining the prevalence of supernumerary teeth; the vast disparities in the quoted prevalence of supernumerary teeth make their value questionable. Therefore, the reliability of panoramic radiographs and the influence of the level of dental training of the 18 examiners for identifying supernumerary teeth were evaluated, which demonstrated that panoramic radiographs are unreliable as a diagnostic tool, and that a high level of dental training is essential for the identification of supernumerary teeth. Based on the sensitivity figures for panoramic radiographs the prevalence of supernumerary teeth was re-analyzed and this demonstrated that the prevalence figures are higher than reported in the literature, ranging from 2.4% to 6%, or even higher; thus, indicating the need for new diagnostic tools for the identification of supernumerary teeth. Proposed hypotheses and recent molecular research, using animal models to gain new insights into the development of supernumerary teeth, have been unable to identify the etiology of supernumerary teeth. Based on the existing published reports and an additional 10 familial cases, the only definitive factors is that supernumerary teeth have a genetic component to their etiology. To identify the genetic risk factors responsible for the formation of supernumerary teeth large scale genetic epidemiological studies, with efficient and convenient methods for obtaining sufficient genomic DNA from study participants, are essential. Evaluation of the storage stability of saliva at room temperature, over an 18-month period, did not adversely influence the DNA yield and purity, or the genotyping efficacy; which clearly demonstrates that saliva is a possible alternative to blood as a source of human DNA. Supernumerary teeth are commonly associated with cleidocranial dysplasia (CCD), a genetic disorder affecting the skeletal system. Novel identical compound heterozygous mutations were identified in the RUNX2 gene of a southern Chinese family with CCD, which has been the first report of compound heterozygous mutations in CCD patients. Several mouse mutant genes have reported an association with supernumerary teeth; most of these genes have human orthologs. A case-control association study was performed to determine the role of human orthologs of the mouse mutant genes associated with supernumerary teeth in 457 southern Chinese children. DNA samples were obtained and 140 single nucleotide polymorphisms (SNPs) from 19 genes were genotyped. The findings revealed that polymorphisms on SNPs rs17619858 and rs12699798, in the sclerostin-domain containing-1 (SOSTDC1) gene on chromosome 7, were associated with the development of supernumerary teeth in the anterior region of the maxilla. This dogma of genetic risk assessment for early diagnosis facilitates the implementation of the proposal of Genetic Risk Assessment for Personalized Health and Individual Care (GRAPHIC) concept in dentistry. / published_or_final_version / Paediatric Dentistry / Doctoral / Doctor of Philosophy

published_or_final_version / Paediatric Dentistry / Master / Master of Dental Surgery