# Potential Imaging Capability of Optical Coherence Tomography as Dental Optical Probe: A Mini-Review
## 3 Application of OCT for Subgingival Area Visualization  
### Periodontal Tissues Condition  
Table 2 summarizes the different studies that attempted to visualize and measure the morphometry of periodontal tissue using OCT. OCT has been successfully employed to generate images of periodontal hard and soft tissues at the subgingival area with microscopic detail [16; 17; 18; 19; 20; 21; 22]. A comparison of reported visualization of periodontal structures at the subgingival area from the reviewed literatures was shown in Figure 1. All of the  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Imaging Modality** & **Resolution (\(\mu\)m)** & **Penetration Depth** & **Source of Image** \\ \hline OCT & \(\sim\)20 [3] & 1–3 mm & Near-infrared light \\ Medical Ultrasound & 500–1500 [2] & 10–20 cm & Ultrasound \\ Micro CT & \(\sim\)50 [4] & Entire tissues & X-ray \\ CBCT & 80–600 [5] & Entire tissues & X-ray \\ Medical CT & 100–1000 [2] & Entire tissues & X-ray \\ MRI & 100–1000 [2] & Entire tissues & Magnetic field \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparison of optical coherence tomography (OCT) and other imaging modalities.  
studies demonstrated that OCT is able to visualize enamel, dentin, dentino-enamel junction, free gingival margin, and epithelial and connective tissue of gingiva [16; 17; 18; 19; 20; 21; 22]. Visualization of attached gingiva [16; 18; 19; 20; 22], alveolar bone [16; 19; 20; 22], and calculus deposition were also reported [16; 17; 19; 22]. [PERSON] et al. compared ex vivo OCT images of beagle dogs' periodontal structure with micro-CT and histologic appearance. The overall shape of the tooth and surrounding soft tissues of images procured using OCT were similar to those of the histological appearance. In this study, OCT could not reveal the internal architecture of tooth and bone, which were clearly depicted in micro-CT images due to a much higher penetration range [17]. However, there are other reports demonstrating that it can successfully distinguish microstructural aspect of periodontal soft tissues in animal and human subjects. These studies documented that important periodontal parameters such as biological width [20], gingival thickness [16; 22], gingival sulcus [16; 17; 19; 20; 21], and periodontal pocket can be measured using OCT [18; 23]. It has also been reported that biofilm [22], plaque [16] and calculus deposition can be detected using this imaging technique [16; 17; 22; 24].  
Since OCT has emerged as a promising approach toward determining periodontal microstructures (as reported through a number of studies), [PERSON] et al. conducted a pilot study to investigate the potential of OCT as a tool to evaluate the treatment of periodontal diseases. In this study, periodontal conditions of 14 human subjects with periodontal disease were evaluated using OCT on days 0, 30, 60, and 90 following treatment. The results provided evidence that OCT was able to depict changes in gingival thickness, deposition of biofilm and calculus upon treatment, and change in depth of probing comparable to manual and automatic probing [22]. Due to aforementioned important findings, the implementation of OCT in clinical use may be expected as an alternative diagnostic tool  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**No**} & \multirow{2}{*}{**Authors**} & \multirow{2}{*}{**Subjects**} & \multicolumn{8}{c}{**Subgingival Visualization**} & \multirow{2}{*}{**Main Findings**} \\ \cline{3-14}  & & & **En** & & & & & & & & & & & & & OCT can visualize periodontal structures. Longer wavelength shows a deeper tissue penetration  
of conventional and automatic probe, the so-called \"optical probe\". Nevertheless, further controlled clinical trials are needed to provide stronger evidence.