Multimodal Optical Detection of Early Childhood Caries

Thesis (Ph.D.)--University of Washington, 2013As prevalence of dental caries in children rises worldwide, there is an increasing need for a safe, easy to use and cost-effective technique to detect and identify childhood caries at an early stage where remineralization of the tooth is possible and damage may be reversed. It would be beneficial to have a noninvasive multimodal optical device for diagnosing early stage caries in vivo. In this research, the author develops and proposes an optical device which utilizes multiple modalities to screen for, and diagnose early stage dental caries. A clinical prototype device is developed and tested in a clinical setting to verify its suitability for in vivo use. To develop a screening technique that can be used to alert the clinician to an area of suspected caries, an ultrathin scanning fiber endoscope (SFE) was used. Enhanced image resolution of tooth surfaces was obtained using a short-wavelength 405 nm illumination laser using the SFE. In addition, enamel with demineralization of varying depths were also imaged with 405 nm, 444 nm, 532 nm, and 635 nm illumination lasers. Contrast between sound and demineralized enamel was quantitatively computed for each imaging modality. For shallow demineralization, the image contrast with respect to sound enamel was greatest for the 405 nm reflected image. Furthermore, images obtained with a shallow penetration depth illumination laser (405 nm) provided the greatest detail of surface enamel topography since the reflected light does not contain contributions from light reflected from greater depths within the enamel tissue. Multilayered Monte Carlo simulations were also performed to confirm the experimental results. To quantitatively determine health of the tooth enamel, the author developed a simple and robust autofluorescence (AF) technique that uses the dental AF spectra from 405 nm and 532 nm laser excitation and computes a ratio of the integrated areas of the spectra. The 405/532 nm AF ratio was obtained from healthy as well as unhealthy enamel regions of teeth. A clear distinction between the ratios for healthy enamel and unhealthy enamel was seen. The author has developed a multimodal optical clinical prototype by combining the high contrast and high surface resolution SFE imaging modality with the quantitative AF modality. The device can be used to quickly image and screen for any signs of demineralized enamel by obtaining high-resolution and high-contrast surface images using a 405-nm laser as the illumination source, as well as obtaining autofluorescence and bacterial fluorescence images. When a suspicious region of demineralization is located, the device also performs dual laser fluorescence spectroscopy using 405-nm and 532-nm laser excitation. An autofluorescence ratio of the two excitation lasers is computed and used to quantitatively diagnose enamel health. The device was tested on in vivo patients as well as extracted teeth with clinically diagnosed carious lesions. The device was able to provide detailed images which highlighted the lesions identified by the clinicians. The autofluorescence spectroscopic ratios obtained from the extracted teeth successfully discriminated between sound and demineralized enamel