# Dental Applications of Optical Coherence Tomography (OCT) in Cardiology
## 3 Applications of OCT
### Caries Therapy
#### 3.3.3 Composite Restorations  
Today, the adhesive bonding of composite materials to enamel and dentin is the predominant restoration technique. The concept is based on both a durable micro retentive and a chemical bond between composite, adhesive and tooth to obtain restorations, which are free of interfacial adhesive defects. As composites shrink during polymerization, the adhesive technique is the crucial prerequisite for minimally invasive treatment. Conversely, this means that the adhesive failure of the bond can be considered as a parameter to assess the quality of restorations [60] (Figure 16).  
The morphological correlate for this is the formation of interfacial gaps, or so-called adhesive defects. For the evaluation of composite restorations, clinical trials are still the gold standard, with clinical success assessed by functional, biological, and esthetic criteria [15; 61]. Clinically interfacial adhesive defects can only be detected at restoration margins. According to FDI (Federation Dentaire Internationale) [15], marginal gaps of score 2 (50 \(\upmu\)m width) are to be removed by polishing. Gaps of score 3 (50-150 \(\upmu\)m), cannot be removed by polishing but are to be monitored. Restorations with  
Figure 16: A clinical situation. It is unclear and difficult to determine visually whether the discolored margin of the composite restoration results from an interfacial margin gap.  
Figure 15: Extracted human molars trimmed and cross-sectioned longitudinally through pulp chamber (PC). Imaging of the pulp borders by (**a**,**c**) light microscopy, and (**b**,**d**) SD-OCT, the pulp horns and pulp chamber roof (P) can be clearly visualized in the OCT images. EDJ: enamel-dentin junction.  
marginal gaps of score 4 (width \(>\) 250 \(\upmu\)m) must be repaired or replaced if these are loose (score 5). However, statements on the clinical performance of a restoration system are possible after the passage of at least three years [61; 62; 63]. Furthermore, clinical studies have additional disadvantages, for instance, personnel and financial expenses are relatively high and the filling systems are often no longer on the market at the conclusion of clinical trials after 3-5 years. Consequently, early experimental evaluation of adhesive systems and composites is desirable and a prerequisite for further developing restoration systems. It is also desirable to formulate clear statements regarding the quality of the adhesive bond and the long-term prognosis of restorations immediately after restoration placement, or at early follow-up. On this matter, OCT could provide relevant information. The method enables high-resolution real-time images to be made of composite restorations in 2D and 3D in vitro, ex vivo and in vivo, up to an imaging depth of 2.5 mm. The homogeneity of different restoration materials can be checked, as well as interfacial adhesive defects. Especially the clinically relevant integrity of enamel- and dentin-restoration margins can be reliably evaluated, including (at least partially) the situation beneath the gingiva, as well as the seal quality at these locations (Figure 17). The validity and reproducibility of the method has been demonstrated [64; 65].