# Dental Applications of Optical Coherence Tomography (OCT) in Cardiology
## 3 Applications of OCT
### Caries Diagnosis
(**a**) \(\mu\)CT image of a ROI as reference; (**b**) Bright signals show extended lesion areas (arrows); (**c**) The varying of the OCT probe angle provides increased OCT signals and additional information about dentin involvement. Figure 10: Extracted human canine. There is no conformance of visual assessment with OCT. Visual inspection of the dry smooth surface does not reveal signs of an early-stage carious lesion (L). In contrast, the 3D SD-OCT cross-sectional image of the ROI showed a distinct bright area (L) within the first quarter of enamel (E) with a shadow underneath. The lesion can be confirmed using light microscopy (LM). The A-scan of the position marked in the OCT-image shows the depth profile of the demineralized zone in the enamel surface (A-Scan average 5, additional signal median averaging 6). * grey scale between demineralized and healthy region. Figure 9: Extracted human molar with occlusal carious lesions without cavitation (L). (**a**) \(\mu\)CT image of ROI. After application of glycerin gel signal-to-noise ratio in the SD-OCT cross-sectional image (**c**) can be improved towards the image (**b**) (without glycerine, white arrows) leading to an adequate conformance of \(\mu\)CT with OCT.  
Another highly relevant scenario in need of diagnostic information is the field of restoration assessment. In Figure 12, a clinical case of a discolored restoration margin gap is shown. However, it could be seen that discoloration at margins of composite restorations is not an indicator for deeper interfacial gap formations. OCT allows the identification of weak spots in the composite restorations and the differentiation of the findings associated with discolorations. If a curious lesion is detected, the treatment depends on its longitudinal stability. If progression is identified, treatment will be related to the extent of the lesion and speed of progression (activity). Today, there is no single method that can be considered the gold standard for imaging the morphology of the hard tooth tissue while simultaneously assessing the longitudinal activity of a curious lesion. Quantitative light-induced fluorescence (QLF) is known as an imaging technique with the option to visualize present bacterial activity in various lesions [11; 47]. The method is based on autofluorescence of tooth hard tissues and quantifies the autofluorescence difference between sound and carious (pathogenic) enamel. This difference results from the decrease of autofluorescence with increasing porosity of progressing subsurface enamel lesions [48]. With the QLF-D Biluminator(tm) 2 (Inspektor Research Systems by, Amsterdam, The Netherlands), a tool becomes available that  
Figure 11: Extracted human premolar with early proximal demineralizations. There is a partial match of the visual and OCT assessment. (**a**) Hardly visible on wet enamel, the early demineralization (1) could also be seen on the dry surface (**b**); (**c**–**f**) SD-OCT reveals a clinically invisible demineralization in the outer enamel zone (**’**); (**c**,**d**) The OCT images reveal a bright signal in position 1 (L, shadow); (**e**) The OCT of the wet surface shows an early demineralization in position 2 of image (**b**); (**f**) After air drying, an additional signal arises in position 3. Visually both lesions are invisible (**a**,**b**). With the knowledge of the OCT images, at points 2 and 3, slight opacities could also be anticipated on the images (**a**,**b**). The A-scans (average 5) of the marked positions 1 and 2 in the OCT-images demonstrate the depth profiles of the demineralized zones of the enamel surface. \({}^{\Delta}\) grey scales between demineralized and healthy region. makes it possible to additionally image and quantify the red fluorescence of oral bacteria induced by various porphyrin species as products of anaerobic bacterial metabolism. Thus, detection of low porphyrin concentrations would be an indicator of early stage caries formation [49].