**5. Conclusions**

In conclusion, the common aim of the discussed studies was to investigate and improve the capabilities of OCT in monitoring the pathophysiological process of early enamel caries and remineralization. Researchers have proposed multiple quantitative indicators for the assessment of early enamel caries and have studied correlations with the results of multiple histological detection techniques. By far the most widely used quantitative indicators include lesion depth, integrated reflectivity and attenuation coefficients. The differences in quantitative results are mainly attributed to the use of different systems, different methods and different sample preparation. Among them, there is a high linear correlation between depths of enamel lesions determined by OCT and DM, as well as between integrated reflectivity calculated by OCT and mineral loss determined by DM. However, the assessment methods using these three quantitative indicators still have certain limitations and lack objectivity and accuracy. It is a remarkable fact that the scattering coefficient of tooth enamel is very sensitive to changes in mineral content and increases significantly with increasing mineral loss at the initial stages of the enamel caries process. Therefore, the early detection of enamel lesions using the scattering coefficient based on OCT is a potential research direction. Meanwhile, most studies on quantitative assessment of enamel caries have been performed in vitro due to the limitations of the probe, and in vivo studies are mainly focused on the buccal and incisal/occlusal surfaces of premolars and anterior teeth. With the development of intraoral probes [4,86], the problem of device availability is being solved slowly. However, a very important issue is the lack of consensus on the method, and OCT has not been applied for the clinical diagnosis of early caries. Although OCT has made great progress as a noninvasive imaging method for quantitatively assessing early enamel caries, efforts to standardize rigorous methodology in future research are crucial for detection, diagnosis, and treatment guidance of early enamel lesions using OCT.

**Author Contributions:** Conceptualization, all authors; methodology, B.S., J.N., X.Z.; formal analysis, B.S., J.N.; investigation, B.S., J.N.; resources, all authors; data curation, B.S., J.N.; writing—original draft preparation, B.S., J.N.; writing—review and editing, all authors; visualization, B.S., J.N.; supervision, X.Z., X.D.; project administration, B.S., J.N.; funding acquisition, B.S., J.N. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Natural Science Foundation of Tianjin (grant number 19JCYBJC16200) and the Science and Technology Program of Tianjin (grant number 20YDTPJC01530).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** All the abovementioned data can be found in the references.

**Conflicts of Interest:** The authors declare no conflict of interest.

## **References**


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