Optical coherence tomography (OCT) has been developed during the last 10 years as a new noninvasive imaging tool and has been applied to diagnose different ocular and skin diseases. This technique has been modified for cross–sectional imaging of dental structures. In this first preliminary study the technique was applied to obtain tomographic images of extracted sound and decayed human teeth in order to evaluate its possible diagnostic potential for dental applications. Classical OCT images based on reflectivity measurements and phase retardation images using polarization–sensitive OCT were recorded. It was demonstrated that polarization–sensitive OCT can provide additional information which is probably related to the mineralization status and/or the scattering properties of the dental material. One of the attractive features of OCT is that it uses near–infrared light instead of ionizing radiation. Furthermore, high transversal and depth resolution on the order of 10 μm can be obtained. Present limitations, e.g. the limited penetration depth, and possible solutions are discussed.

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Partial coherence interferometry (PCI) and optical coherence tomography (OCT) are noninvasive and noncontact techniques for high precision biometry and for obtaining cross-sectional images of biologic structures. OCT was initially introduced to depict the transparent tissue of the eye. It is based on interferometry employing the partial coherence properties of a light source with high spatial coherence but short coherence length to image structures with a resolution of the order of a few microns.Recently this technique has been modified for cross sectional imaging of dental and periodontal tissues. In vitro and in vivo OCT images have been recorded, which distinguish enamel, cemento and dentin structures and provide detailed structural information on clinical abnormalities (e.g. caries lesions).In contrast to conventional OCT, where the magnitude of backscattered light as a function of depth is imaged, polarization sensitive OCT uses backscattered light to image the magnitude of the birefringence in the sample as a function of depth. First polarization sensitive OCT recordings show, that changes in the mineralization status of enamel or dentin caused by caries or non-caries lesions can result in changes of the polarization state of the light backscattered by dental material. Therefore polarization sensitive OCT might provide a new diagnostic imaging modality in clinical and research dentistry.

Optical coherence tomography (OCT) is a new imaging modality capable of recording cross-sectional images of transparent and semi-transparent structures with a resolution on the order of 10 jim. Classical OCT images the distribution of backscattering and -reflecting sites within the sample. However, as is known from microscopy, many objects yield only a poor image contrast if imaged on a pure intensity basis. These objects may, however, change other properties ofthe light which can be used for improving the image contrast. This forms the basics of advanced optical contrast enhancement techniques. We report on recent results we obtained with two of these techniques: polarization sensitive (PS) OCT and differential phase contrast (DPC) OCT.