We present here the first in vivo optical coherence tomography (OCT) images of human dental tissue. A novel dental optical coherence tomography system has been developed. This system incorporates the interferometer sample arm and transverse scanning optics into a handpiece that can be used intraorally to image human dental tissues. The average imaging depth of this system varied from 3 mm in hard tissues to 1.5 mm in soft tissues. We discuss the application of this imaging system for dentistry and illustrate the potential of our dental OCT system for diagnosis of periodontal disease, detection of caries, and evaluation of dental restorations.

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There is no diagnostic technology presently available utilizing non-ionizing radiation that can image the state of demineralization ofdental enamel in vivo for the detection, characterization and monitoring ofearly, incipient caries lesions. In this study, a Polarization Sensitive Optical Coherence Tomography (PS-OCT) system was evaluated for its potential for the non-invasive diagnosis of early carious lesions. We demonstrated clear discrimination in PS-OCT images between regions of normal and demineralized enamel in bovine enamel blocks containing well-characterized artificial lesions. Moreover, highresolution, cross-sectional images were acquired that clearly discriminate between the normal and carious regions of extracted human teeth. Regions that appeared to be demineralized in the PS-OCT images were verified using histological thin sections examined under polarized light. The PS-OCT system discriminates between normal and carious regions by measuring the state ofpolarization ofthe back-scattered 13 10 nm light, which is affected by the state of demineralization ofthe enamel. The demineralized regions of enamel have a large scattering coefficient, thus depolarizing the incident light. This initial study shows that PS-OCT has great potential for the detection, characterization, and monitoring of incipient caries lesions.

A pulsed photothermal technique to calculate internal temperatures from noncontact surface temperature measurements is presented. The inversion process is based on approximating the integral equation describing the thermal interaction with a matrix equation. The matrix equation is then solved using singular-value decomposition. The method was evaluated using computer simulations and experiments with tissue phantoms and skin. The algorithm predicted internal temperatures within 10% for homogeneous samples down to a depth of about 500 m. It did not predict internal temperatures accurately for inhomogeneous samples, but yielded fairly accurate estimates of the depths of subsurface absorbers and conserved energy. The uncertainty in the calculated depth of the absorber increased with depth. Currently this technique can probe depths to 500 m.

Optical coherence tomography is a new method for noninvasively imaging internal tooth and soft tissue microstructure. The intensity of backscattered light is measured as a function of depth in the tissue. Low coherence interferometry is used to selectively remove the component of backscattered signal that has undergone multiple scattering events, resulting in very high resolution images (< 15 microns). Lateral scanning of the probe beam across the biological tissue is then used to generate a 2-D intensity plot, similar to ultrasound images. This imaging method provides information that is currently unobtainable by any other means, making possible such diverse applications as diagnosis of periodontal disease, caries detection, and evaluation of restoration integrity. This chapter presents an overview of this exciting new imaging technique and its current application to dental diagnosis.