The early identification of proximal carious lesions is still one of the most challenging issues in modern cariology and odontology, whereas several visual, optical, and radiographic techniques have been developed and improved in recent years.^1,2 Providing depth-resolved, high-resolution images of biological samples, optical coherence tomography (OCT) is a promising tool for detecting caries noninvasively, since first investigations of dental hard tissue in vitro and in vivo were performed by OCT,^3,4 and imaging in the near-infrared range proved convenient scattering and absorption properties.⁵ So far, OCT has shown the potential to provide effective and reproducible diagnoses for clinical applications,⁶ and algorithms that enable early caries segmentation from conventional OCT images have been presented.⁷ Additionally to the structural imaging based on backscattering intensities, miscellaneous modalities and extensions for OCT have been developed, which provide tissue-dependent contrast. This includes polarization sensitive imaging and the consequent measurement of depth-resolved birefringence, which until now has been applied in many biomedical as well as nonmedical fields.^8,9 In terms of hard dental tissue and caries detection, first polarization sensitive OCT (PS-OCT) measurements confirmed the birefringent properties of enamel and dentin,^4,10 and it was determined that demineralization, accompanying carious infections, results in depolarization of light.¹¹ Since then, several studies have shown the potential of PS-OCT to observe the internal structure and the remineralization of lesions, as well as an early detection of variously located caries.¹² 13. ^{– 14} Thereby, the occurring depolarization effect for linearly polarized incident light is usually evaluated by an intensity measurement of the perpendicular polarization state.¹⁵

The middle ear consists of the tympanic membrane and the ossicles, and ensures the transduction of sound from the auditory canal to the inner ear. Thus, diseases of the middle ear are often accompanied by hearing loss, especially in case of Eustachian tube dysfunction, acute or chronic otitis media, or otosclerosis. In the clinical routine, the diagnosis of pathological alterations in the middle ear is carried out using otoscopy or ear microscopy, audiometry, and tympanometry in order to assess morphological and functional changes of the middle ear.

To date, there is still a lack of reliable imaging modalities to improve the quality of consultation, diagnostic and medical examinations of the oral mucosa in dentistry. Even though, optical technologies have become an important element for the detection and treatment of different diseases of soft tissue, for the case of oral screenings the evidence of the benefit in comparison to conventional histopathology is mostly still pending. One promising optical technology for oral diagnostics is optical coherence tomography (OCT). To prove the potential of OCT, even the amount of freely accessible OCT data is not sufficient to describe the variance of healthy human oral soft tissue in vivo. In order to remedy this deficiency, the present study provides in vivo OCT cross sections of the human oral mucosa of the anterior and posterior oral cavity as well as the oropharynx of 47 adult volunteers. A collection of representative OCT cross sections forms the basis for a randomized blinded image analysis by means of seven criteria to assess the main features of the superficial layers of the human oral mucosa and to determine its correlation to regional features known from hematoxylin and eosin (HE) stained histology.

The common way to diagnose hard and soft tissue irregularities in the oral cavity is initially the visual inspection by an experienced dentist followed by further medical examinations, such as radiological imaging and/or histopathological investigation. For the diagnosis of oral hard and soft tissues, the detection of early transformations is mostly hampered by poor visual access, low specificity of the diagnosis techniques, and/or limited feasibility of frequent screenings. Therefore, optical noninvasive diagnosis of oral tissue is promising to improve the accuracy of oral screening. Considering this demand, a rigid handheld endoscopic scanner was developed for optical coherence tomography (OCT). The novelty is the usage of a commercially near-infrared endoscope with fitting optics in combination with an established spectral-domain OCT system of our workgroup. By reaching a high spatial resolution, in vivo images of anterior and especially posterior dental and mucosal tissues were obtained from the oral cavity of two volunteers. The convincing image quality of the endoscopic OCT device is particularly obvious for the imaging of different regions of the human soft palate with highly scattering fibrous layer and capillary network within the lamina propria.

Various biological tissues change the polarization of light, for which reason tissue polarization properties can be important for the diagnosis of pathological alterations in tendons, bones, cartilages, teeth, and skin. Biological media are often birefringent caused by asymmetrically oriented structures, e.g., collagen fibers and dentinal microtubules, as well as molecular and mineralized compositions in biological tissue. Since polarization imaging is innovative and promising for medical diagnosis of pathologies, technical solutions for clinical in vivo applications are in demand. Because optical coherence tomography (OCT) is a prospective noninvasive imaging technique for three-dimensional high-resolution imaging of subsurface tissue morphology¹ 2. 3. ^{– 4} with the possibility of functional imaging by polarization-sensitive OCT (PS OCT), it is attractive for depth-resolved tissue-specific contrast imaging with high speed and sensitivity in vivo. Although conventional intensity-based OCT provides a high spatial resolution in the micrometer range, tissue micro- and nanostructures cannot be resolved optically. By detecting the polarization change of the reflected light with PS OCT, properties of polarization changing microstructures can provide information of early pathological alterations before morphological tissue remodeling occurs in larger scale detectable with intensity-based OCT.^5,6

This study presents a highly miniaturized, handheld probe developed for rapid assessment of soft tissue using optical coherencetomography (OCT). OCT is a non-invasive optical technology capable of visualizing the sub-surface structural changes that occur in soft tissue disease such as oral lichen planus. However, usage of OCT in the oral cavity has been limited, as the requirements for high-quality optical scanning have often resulted in probes that are heavy, unwieldy and clinically impractical. In this paper, we present a novel probe that combines an all-fiber optical design with a light-weight magnetic scanning mechanism to provide easy access to the oral cavity. The resulting probe is approximately the size of a pen (10 mm × 140 mm) and weighs only 10 grams. To demonstrate the feasibility and high image quality achieved with the probe, imaging was performed on the buccal mucosa and alveolar mucosa during routine clinical assessment of six patients diagnosed with oral lichen planus. Results show the loss of normal tissue structure within the lesion, and contrast this with the clear delineation of tissue layers in adjacent inconspicuous regions. The results also demonstrate the ability of the probe to acquire a three-dimensional data volume by manually sweeping across the surface of the mucosa. The findings of this study show the feasibility of using a small, lightweight probe to identify pathological features in oral soft tissue.