Correlation between Optical Coherence Tomography and Synchrotron X-ray diffraction for the diagnosis of enamel defects

Objectives: Currently, dental enamel defects (e.g. Molar Incisor Hypomineralisation, MIH) are diagnosed clinically by inspection (and radiographs), which have limitations: visual examination is subjective; being dependent on the dentist, lighting, and dryness of the tooth. Radiographs have poor spatial resolution, expose the patient to ionizing radiation and under-represent superimposed buccal and lingual features. We propose Optical Coherence Tomography (OCT) as a new diagnostic tool for assessing the prognosis of MIH, which we are currently developing for clinical use. Since enamel is a hierarchically ordered material with organisation at the crystallographic, nano- and micro-scale, a crucial aspect of the successful translation of OCT into clinical use, is the precise and reliable interpretation of how the OCT image data, reports the underlying enamel crystallography, nano- and micro- structures.
Methods: In this study, we characterise the crystallographic texture, crystal lattice parameters, and particle sizes in healthy and affected enamel specimens by X-ray Micro-tomography (XMT) and Synchrotron X-ray Diffraction (SXRD) before relating these parameters to the OCT profiles in the same regions of the same specimens.
Results: We demonstrated how OCT using en-face imaging mode can be used as a simple and convenient diagnostic technology, to evaluate the extent of the MIH lesion 3-dimensionally, including subsurface lesions. In a recent experiment on XMaS (ESRF Grenoble), we found correlative evidence between OCT image contrast (localised photons scattering) and crystallite organization (azimuthal angles extracted from sequential diffraction patterns) in enamel affected by MIH.
Conclusions: The use of OCT for the clinical diagnostics of enamel defects is promising and may pave the way for this approach to be adopted to advance the diagnostics of more common dental conditions, such as tooth decay or erosion.