Clinical monitoring of smooth surface enamel lesions using CP-OCT during nonsurgical intervention

Abstract

Introduction: Studies have shown that cross-polarization optical coherence tomography (CP-OCT) can be used to image the internal structure of carious lesions in vivo. The objective of this study was to show that CP-OCT can be used to monitor changes in the internal structure of early active carious lesions on smooth surfaces during non-surgical intervention with fluoride.

Methods: Lesions on the smooth surfaces of teeth were imaged using CP-OCT on 17 test subjects. Lesion structural changes were monitored during fluoride varnish application at 6-week intervals for 30 weeks. The lesion depth (L_d ), integrated reflectivity (ΔR), and surface zone thickness (S_z ) were monitored.

Results: A distinct transparent surface zone that may be indicative of lesion arrestment was visible in CP-OCT images on 62/63 lesions before application of fluoride varnish. The lesion depth and internal structure were resolved for all the lesions. The overall change in the mean values for L_d , ΔR, and S_z for all the lesions was minimal and was not significant during the study (P > 0.05). Only 5/63 lesions manifested a significant increase in S_z during intervention.

Conclusion: Even though it appears that most of the lesions manifested little change with fluoride varnish application in the 30 weeks of the study, CP-OCT was able to measure the depth and internal structure of all the lesions including the thickness of the important transparent surface zone located at the surface of the lesions, indicating that CP-OCT is ideally suited for monitoring lesion severity in vivo. Lasers Surg. Med. 48:915-923, 2016. © 2016 Wiley Periodicals, Inc.

Keywords: cross polarization optical coherence tomography; dental caries; tooth demineralization.

Fig. 1

CP-OCT system from Santec used for the clinical study. (A) Scan is acquired in test subject, (B) scanning handpiece, (C) scanner with delrin sleeve and cellophane covering for infection control, and (D) delrin sleeve.

Fig. 2

A surface rendering of a typical 3D image acquired showing the position of the enamel (E) and the gingiva (G) with the areas of high reflectivity shown in yellow. High reflectivity areas on the enamel indicate the position of the lesion (L).

Fig. 3

Two dimensional projection images of ΔR, L_d, and S_z, calculated for one of the lesions at a single time point. The lesion is located in the area of the yellow rectangular box. The half moon shaped region of high reflectivity below the yellow box is the gingiva.

Fig. 4

Processed CP-OCT b-scans of a cervical enamel lesion taken at week 0 (A) and again at week 30 (B). The lesion is clearly visible and it has a well-defined surface zone (S_z) that is visible. The dentinal enamel junction (DEJ) and the gingival (G) are visible in the image and the position of the scans are indicated on the photograph of the tooth. A-scans extracted at the position of the dashed line from each image are shown on the right with the tooth surface oriented on the right. The weakly scattering surface zone is located at the position of the arrow. The sharp spike to the right of the arrow is reflection from the tooth surface and the lesion body is the large broad peak to the left of the arrow. There was little change in the lesion structure after 30-weeks.

Fig. 5

Processed CP-OCT b-scans of a cervical enamel lesion taken at week 0 and again after 30 weeks. A-scans extracted at the position of the dashed line from each image are also shown. The lesion (L) is clearly visible and it has a well defined surface zone that is visible. After 30 weeks a double layer is visible in the lesion at the positions of the two arrows.

Fig. 6

Processed CP-OCT b-scans of a tooth with two lesions acquired at week 0 and week 30. A-scans extracted at the position of the dashed line from each image are also shown. The surface zone thickness increased by 30% after 30-weeks. Note a well defined surface zone is also present on the cavitated lesion on the right as well as after 30-weeks.

Fig. 7

Plots of S_z, L_d, and ΔR for one of the five lesions for which the surface zone thickness manifested a significant (P < 0.05) increase over time (solid square) along with a lesion that manifested no significant increase (P < 0.05) (open triangles). There was no significant change in L_d and ΔR over time for either lesion.