Optical tomography and light irradiation to reduce bacterial loads in oral health application

Abstract

In my dissertation, a finite element-based method to solve the radiative transfer equation was proposed and verified by Monte Carlo simulations, which can be employed as an alternative forward model to the mainly used diffusion approximation approach. Second, experiments using mesoscopic fluorescence molecular tomography with linear dyes placed at different sites preliminarily proved the feasibility for accurate monitoring of pulp situations. Last, upconverting nanoparticles (UCNPs) mixed with dental fillings employed as theranostics agents are investigated to determine the distribution of fillings. Throughout the experiments, the relative volume error of reconstructions of UCNPs (mixed in the fillings) distribution is less than 10% compared with real distribution of UCNPs. The position error (centroid error) is around 1 mm. Moreover, the blue emission light of UCNPs was proven to be a bactericide by ex vivo experiments. Overall, this work preliminarily investigated the possibility to employ optical-based methods to detect pulp situations before root canal therapy, the fillings situation after surgery to ensure the success of root canal therapy, and kill residual bacteria in mouth.

Light based modalities can enable detection of physiologic functional parameters and can be used as therapies, especially in structures close to the surface, such as teeth. The integrity of teeth is dependent on the physiological function of its biological component: cells in the pulp cavity. Previous studies suggest that impairment of the biological component, as occurs in the presence of cavities (due to bacterial biofilms) or when the tooth structure has been compromised by other means (such as cracks), affects some measures of physiology (e.g. oxygenation). Because it may be possible to detect impairment of pulp function through changes in its oxygenation, and since currently used pulse oximetry based methods provide measures that are affected by other variables, we evaluate whether it is possible to provide 3-D measurements of pulp activity. When the tooth decay forms and surgery has to be performed to prevent further damage of teeth, it is necessary to determine whether the dental fillings provide good coverage of the surgical cavity. It is noted that teeth structures exhibit extremely high absorption and scattering coefficients relative to other tissues on which optical methods have conventionally been used (e.g. wounds, breast and brain). So it is important to determine whether optical methods are sensitive enough to enable imaging through teeth to obtain 3-D measurements of pulp or dental fillings.