Mohd Noor, M; (2014) Phenotypic properties of enamel in Molarincisor Hypomineralisation (MIH) and Amelogenesis imperfecta (AI) teeth. Doctoral thesis , UCL (University College London).

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Abstract

Background: Enamel is an external layer of the crown, and its production can be affected by genetic, systemic or environmental causes, leading to the formation of developmental defect of Enamel (DDE). Molar incisor Hypomineralisation (MIH) can be defined as a qualitative defect of systematic origin of the enamel, involving one or more first permanent molar, which is frequently associated with affected incisors. Amelogenesis Imperfecta (AI) is genetic condition, affecting the structure and clinical appearance of the enamel of all or nearly all the teeth in a more or less equal manner, and which may be associated with morphologic or biological changes elsewhere in the body. Knowledge about the chemical and mechanical properties of both conditions is beneficial to predict the severity and to provide appropriate treatment for individual patients. Aim and Objectives: The aim of this study is to characterise the phenotypic properties of MIH and AI teeth in primary and permanent teeth. The objectives were to assess: tooth colour, radiographic features, hardness (on and off the anomaly), chemical variation and the ultrastructure of affected enamel vs. normal enamel. Material and Methodology: Ethical approval was obtained. Twelve control, 12 MIH and 7 AI teeth were collected. The phenotype (DDE Index) for each sample was recorded. Prior to characterisation, the teeth were debrided and stored in 0.1% thymol at 4°C. Colour was examined using a spectrophotometer (SpectroShadeTM Micro) to quantify the variation in colour as defined by ÄE. Wallace indentation (H.M Wallace, Croydon, England) was also performed to assess the hardness value, denoted by Vickers Hardness Number (VHN). Raman microspectroscopy (HR 800, Jobin Yvon, Horiba, Japan) was used to study the chemical variation for each sample. Finally, the samples were sectioned at specific affected sites to image the ultrastructure of the enamel layer using a scanning electron microscopy (FEI XL30 FEGSEM (FEI UK, UK). Results: All MIH and AI teeth showed various degrees of discolouration, with ÄE ranging from 2.47 for white/cream to 22.2 for yellow/brown defects. The range of enamel hardness of control teeth was 226.2 - 360.3 VHN. Meanwhile, enamel hardness for MIH and AI teeth was significantly reduced (P = 0.004) ranging from 13.1 - 142.6 VHN. Chemically, both MIH and AI teeth showed a significant increase in carbonate to phosphate ratio when studied under Raman spectroscopy (P = 0.000). Histologically, the affected hypomineralised enamel appeared more porous, disorganised, with loss of enamel rod structure and presence of structureless layer compared the normal enamel. Conclusion: Teeth diagnosed with MIH and AI showed marked discolouration and lower hardness values compared with normal enamel. Yellow/brown opacities had lower hardness values than white/cream opacities. These conditions also caused changes in the chemical properties and histological structure of the enamel.

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