Sarkhouh, Shaima Mansour; (2017) Investigating the ultrastructure of enamel white spot lesions (WSL) using Optical Coherence Tomography at different length scales. Doctoral thesis (D.Dent), UCL (University College London).

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Abstract

White spot lesion (WSL) is the clinical presentation of early caries, which is a demineralisation that occurs at subsurface level, with a well-mineralised surface layer enclosing the lesion. Early diagnosis and treatment of WSL is crucial to prevent further destruction of tooth structure. The aim of this research is to investigate the potential of optical coherence tomography (OCT) to be used as an adjunct diagnostic clinical tool to evaluate the severity of such lesions. This research also compared the OCT outputs with traditional histology, X-ray Microtomography (XMT), Synchrotron X-ray Diffraction (SXRD) and Scanning Electron microscope (SEM). All specimens were collected from patients undergoing dental treatment at Eastman Dental Hospital with informed consent following ethical approvall. Initially, Artificial WSLs were induced on sound enamel surfaces using a buffered methylcellulose gel system at pH 4.6 for 7 and 14 days. Type-matched native WSL and healthy control teeth were selected based on ICDAS for comparison. Imaging of samples was obtained using OCT of whole teeth and by polarised microscopy, SXRD, XMT and SEM of polished 250 μm thick sections. Polarised microscope, XMT and SEM confirmed the findings of the OCT results. Images showed that the more back scattered signals recorded, the deeper the destruction throughout enamel thickness. SXRD results showed changes in enamel texture, which was interpreted from measuring crystallite orientations and lattice parameter. SXRD result showed some correlation with OCT images, however more investigation is required to confirm the findings. In conclusion, the variations observed in the back-scattered light in OCT experiment were because of mineral density variation within enamel structure, as well as the changes in prismatic structure and may be related to crystallite texture and orientation. OCT has shown to be a reliable non-destructive technique, that can investigate the internal structure, by measuring the back-scattered light from materials such as enamel and dentine. In healthy samples, OCT B-scans showed a homogenous pattern of scattering intensity throughout enamel structure, indicating healthy structure, while in both natural and induced white spot lesions, a non homogenous scattering intensity was observed, indicating changes in enamel structure.

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