# Dental Applications of Optical Coherence Tomography (OCT) in Cardiology
## 3 Applications of OCT
### Erosive Tooth Wear  
Within the oral cavity, demineralization and remineralization of tooth surfaces (enamel, dentin) are in a state of equilibrium. Even without the participation of bacteria (caries) in a multifactorial process, a shift in the balance can occur towards demineralization, which is caused by different patient-related and nutritional factors, e.g., eating/drinking habits, oral hygiene, medication and saliva conditions. The destructive effect of acid-induced tissue loss of tooth surface and subsurface regions is known as dental erosion (erosive tooth wear) [50]. Clinical diagnosis indices for recording the erosive wear include morphological as well as quantitative criteria, particularly the Basic Erosive Wear Examination (BEWE) [51]. However, the validity of diagnostic criteria and grading/scoring are unsatisfactory or unclear. Thus, there is a need to develop practicable and preferably chairside diagnostic tools [51]. Different assessment  
Figure 12: Canine tooth in vivo. (**a**) A cervical composite restoration (C) shows a margin discoloration (white arrow); (**b,c**) In the 3D and 2D OCT images, a margin gap with ingress of material is detected (red arrows). At dentin (D), an extensive interfacial gap has formed (white arrows); (**d**) Using quantitative light-induced fluorescence the image showed red fluorescence (red arrow) at the cervical restoration margin indicating bacterial activity by porphyrin invasion into the gap. There are no signs of “secondary caries” at the restoration margin, but the stability of the situation requires observation over time (monitoring). methods have been applied for in vitro and in vivo studies to evaluate erosive tooth wear, e.g., profilometry, measuring microscopy techniques, TMR, SEM, atomic force microscopy, nano- and micro-hardness tests, and the iodide permeability test, as well as methods which chemically analyze minerals dissolved from dental hard tissue [52]. In this context, OCT has been described as a suitable tool for the investigation of early erosions of unaffected surfaces [52]. OCT allows the assessment of the mineralization degree of enamel or dentin and the visualization of very early demineralizations, and thus permits early erosive lesions to be characterized [52]. Until now, erosion could only be assessed clinically through long-term observations of the loss of hard tooth  
Figure 13: Extracted human incisor. (**a**) Starting situation. The SD-OCT shows a small bright band in the enamel surface (E), which could represent a lower mineralized zone (white asterisks). The yellow double-headed arrow indicates the surface area, which was covered by composite to prevent demineralization of the enamel; (**b**) After 5 min exposure of enamel to Coca Cola (37 \({}^{\circ}\)C) a broader bright area (red asterisks) can already clearly be distinguished, which represents a zone of erosion that also extended below the composite coating; (**c**) After 30 min of exposure, the demineralization has made further progress, which is indicated by the reduced contrast at the enamel-dentin junction (EDJ, red arrow) or its disappearance (white arrow); (**d**) After removal of the composite coating the tooth was stored in artificial saliva. Within 60 min, the bright demineralized area previously covered by composite (dotted double-headed arrow) completely disappeared indicating a process of repair (”remineralization”). In uncovered areas, the EDJ appears in a higher contrast compared to (**c**) and is more extended (green arrow). Particularly in the incisal area, the erosion is clearly reduced (**) compared to (**b,c**). tissue over months to years, well after the erosion has been initiated. With OCT, incipient erosion without loss of enamel height could be recognized and a therapeutic remineralization process could be monitored and assessed [8]. Figure 13 shows an initial enamel erosion before the thickness of hard tissue had changed, and its partial repair. The erosion was produced by the soft drink Coca Cola [53; 54].