# Dental Applications of Optical Coherence Tomography (OCT) in Cardiology
## 3 Applications of OCT  
### Caries Diagnosis  
Today the big challenge in caries diagnosis is the detection of very early stages of demineralization, especially in enamel [12; 39]. Effective caries management presupposes that these early lesions (represented by porous areas very different in extension) can be reliably recorded. On smooth tooth surfaces, beginning demineralizations can be detected visually as white spot lesions on dried enamel surfaces (ICDAS II Code 1, Figure 1) [3; 40], which are a common complication during treatment with fixed orthodontic appliances [41]. At this stage, the subsurface enamel porosity can be stopped or reversed using appropriate non- or minimally invasive therapies and biofilm control [8]. White spot lesions appear whitish as the incident light is backscattered off porous regions to a considerable extent [29; 39]. OCT makes use of the same phenomenon. In contrast to the clinical detection solely at the surface, OCT can image structures up to a depth of 2.5 mm and might therefore be a useful supplement to the visual-tactile assessment of tooth surfaces (ICDAS II) and radiography. More reliable differentiation between the really early lesion signs (ICDAS II Codes 0-2) might become possible, irrespective of existing color changes or surface moisture (Figures 1 and 2). Unlike other diagnostic methods, cross-sectional OCT images can present the axial and lateral extension of different demineralized zones (Figure 5). In vitro studies showed an adequate to strong agreement, when SS- or SD-OCT were compared to histology [29; 42; 43], confocal microscopy, X-ray microtomography, or transverse microradiography and a diagnostic superiority compared to bitewing radiography [44] (Figures 1, 2 and 5-11 and 14). Figure 5: (**a**) Extracted human molar. A curious lesion (ICDAS-II Code 2) without cavitation, but with involvement of dentin (D); (**b**–**d**) Using different positions or angles, SS-OCT cross-sectional images reveal bright areas (signals) indicating the extension of the lesion (white arrows) and to detect further tissue destructions like enamel cracks ((**e**), red arrows, *), which are primarily invisible in light microscopy. EDI: enamel–dentin junction. Image contrast and the spatial separation of the lesion body versus sound enamel can be further enhanced using polarization-sensitive OCT [45]. Additionally, variation of the imaging beam angle by using different positions of the OCT probe can improve the detectability of non-cavitated occlusal carious lesions (Figure 8). The sensitivity of the method can be increased among others by increasing the integration time (A-scan rate) or using coupling media [46] to minimize surface reflections, which can also contribute to enhance the image contrast (Figure 9). Figure 6: Extracted human premolar with a carious lesion (L) of ICDAS II Code 1. (**a**) ROI; (**b**) The demineralization within the ROI (white arrow) is equally imaged by dark-field light microscopy (DFLM); (**c**) spinning-disc confocal microscopy (SDCM); (**d**) X-ray microtomography (\(\mu\)CT); as well as (**e**) SD-OCT. E: enamel, D: dentin, EDJ: enamel-dentin-junction. Figure 7: (**a**) Extracted human molar with occlusal caries (ICDAS II Code 2); (**b**) In the histological section through ROI, lesions (white arrows) and enamel cracks (yellow arrows) appear; (**c**) In the conventional digital radiograph no defects or lesions are visible; (**d**) Bright signals in the OCT image of the ROI demonstrate caries lesions (white arrows) and enamel cracking (yellow arrow). E: enamel; D: dentin. The International Caries Detection and Assessment System in combination with radiography is insensitive to early caries detection. This has been confirmed by a number of the authors' own OCT evaluations of apparently sound enamel surfaces (ICDAS II Code 0), particularly in cross-sectional OCT images where early stages of decay can often be detected without any clinical findings (Figures 10 and 11). Figure 8: Extracted human molar with occlusal carious lesions without cavitation (L, arrow).