Mohamed Ibrahim, NB; (2013) A Study of the Genetics and Physical Properties of Dentine Defects. Doctoral thesis , UCL (University College London).

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Abstract

Dentinogenesis Imperfecta (DI) and Dentine Dysplasia (DD) are rare inherited condition affecting the dentine. Previous studies have reported the histological presentation of teeth with dentine defects but the differences between clinical appearances and physical properties, and how do they link to the underlying gene defects, is limited. In addition, the differences between primary and permanent teeth are poorly understood. Aim and Objective: The aim of this study was to investigate if there is an association between the underlying gene defect (genotype) and the physical properties and appearance (phenotype) of teeth with dentine defects. The objectives were to assess the colour, radiographic feature and dentine hardness of the teeth with dentine defects, to discover any other unidentified genes that might involve in causing inherited dentine diseases, and to relate them to the phenotype recorded clinically. Materials and Method: The discolouration and radiographic features of teeth from 16 patients (6 DI type I, 5DI type II, 4 OI and 1 DD type I respectively) were recorded. 20 control primary teeth and five DI teeth (four DI type I, one DI type II) were sectioned transversely using a diamond wheel saw. The dentine hardness measurement was done using Wallace Hardness Machine and recorded as Vickers Hardness Number (VHN). Dentine microstructure was examined using scanning electron microscope (SEM). Saliva samples were obtained from 14 patients for genomic analysis. Results: All DI type II and DI type I patients had marked discolouration of their teeth. DD and OI patients had normal teeth colour. The mean value of dentine hardness of control teeth was VHN=57.11±62. The VHN for DI teeth were significantly low compared to control teeth. The mean value for DI teeth was 30.61±8.24 VHN. Histologically, both DI type I and DI type II teeth showed reduced number of dentine tubules. DI type II had irregular dentine surface, while DI type I dentine showed a tear-like appearance on an empty dentine surface. Genetic analysis did not show any known mutations on COL1A1 and no novel genetic mutations has been observed. Conclusion: Collagen plays a role in maintenance of healthy dentine. Therefore, defects on COL1A1 and COL1A2 lead to abnormality of collagen thus the occurrence of OI and DI type I. Mutation in DSPP caused disruption in dentine mineralisation which also present as dentine defects in DI type II. Both DSPP and COL1A1/COL1A2 caused dentine abnormalities which present as teeth discolouration, abnormal appearance and reduced dentine hardness.

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