# Dental Applications of Optical Coherence Tomography (OCT) in Cardiology
## 3 Applications of OCT
### Quality Control Using OCT  
Thanks to the fast processing of highly resolved images and its non-invasive and harmless approach, OCT has great potential for time-resolved visualization of fast processes [9]. This is also the case in the fields of learning and teaching, and consequently in quality or process control and in monitoring therapy outcomes. The technique allows many opportunities for self-checking. Individual work steps during restoration placement can be demonstrated, better understood and single procedural errors and resulting failures can be clearly seen. This results in great potential in supporting the development of dental materials, and to teach and learn therapeutic procedures (Figures 18 and 19). Figure 17: **(a)** Screenshot of the clinical image of a cervical composite restoration (C) on a premolar; **(b)** The cross-sectional OCT image reveals a homogeneous filling showing an extended bond failure at the dentin and enamel (bright signal lines, white arrows). At enamel margin (E), no gap appears, whereas the gingival margin (G) shows a gap which is extended along the composite-dentin interface. In multiple equidistantly distributed cross-sectional images, the length of the interfacial adhesive failures can be measured for dentin (D) and enamel (E). From these, the “percentage gap” of this restoration can be derived separately for enamel and dentin. EDJ: enamel-dentin junction. As OCT is non-invasive, it inevitably follows that it offers the possibility of monitoring the bond failure at the same composite restorations in the same cross-sectional images at any time. In long-term clinical studies conducted by the authors, composite restorations will be imaged parallel to clinical assessment using SD-OCT (vestibular areas, Class V, Figure 4c). In a B-scan by measurement the lengths of adhesive failure and interface the proportion (%) of the interfacial adhesive failure can  
Figure 19: OCT quality control in vivo. **(a)** A cervical composite (C) restoration at a premolar 34 immediately after filling the cavity. The gingiva (G) is slightly retracted. In contrast to Figure 18 the composite has been homogeneously dispersed; **(a)** Using visual-tactile assessment the restoration margins appear smooth; **(b)** However, in the OCT image at dentin (D, ROI) a margin gap in combination with a composite overhang indicates a critical area (bright line, red arrow). In knowledge of the OCT image, the overhang could easily be removed. An adhesive layer (A) could only be partially detected. Figure 18: OCT quality control in vivo. 3D OCT imaging of a cervical composite (C) restoration at a premolar after filling the cavity in small increments **(a–d)**. Images **(b–d)** show the image stack using a sequence of three OCT B-scans in y-direction (ROI shown in **a**). The bright lines at the tooth-composite interface demonstrate a margin gap at dentin (D) and extended interfacial bond failures (white arrows). Additionally, communicating bubbles are clearly evident (yellow arrows) and reach the restoration surface, forming an entrance for material to penetrate into the restoration (**a–d, red arrows). be calculated separately for enamel, dentin or cement. In 25 equidistantly distributed B-scans of an image stack the mean values of a restoration result with regard to enamel, dentin or cement. From these the values per group can be calculated over the entire period of study. The results of the clinical studies will reveal whether OCT can be an early, cost-effective, and time-saving tool for evaluating the performance of adhesives or composite restoration systems in vivo. In vitro and ex vivo, an exceptional methodological advantage is that identical cross-sectional images will be assessed and compared before and after artificial aging. This results in pairs of measured values. In this case the variance between specimens can be excluded and just the variance within the specimens remains. Compared with unpaired values, at identical ratings of statistical power the number of specimens can be reduced.