Trimodal detection of early childhood caries using laser light scanning and fluorescence spectroscopy: clinical prototype

Abstract

There is currently a need for a safe and effective way to detect and diagnose early stages of childhood caries. A multimodal optical clinical prototype for diagnosing caries demineralization in vivo has been developed. The device can be used to quickly image and screen for any signs of demineralized enamel by obtaining high-resolution and high-contrast surface images using a 405-nm laser as the illumination source, as well as obtaining autofluorescence and bacterial fluorescence images. When a suspicious region of demineralization is located, the device also performs dual laser fluorescence spectroscopy using 405- and 532-nm laser excitation. An autofluorescence ratio of the two excitation lasers is computed and used to quantitatively diagnose enamel health. The device was tested on five patients in vivo as well as on 28 extracted teeth with clinically diagnosed carious lesions. The device was able to provide detailed images that highlighted the lesions identified by the clinicians. The autofluorescence spectroscopic ratios obtained from the extracted teeth successfully quantitatively discriminated between sound and demineralized enamel.

Fig. 1

The multimodal caries detection clinical prototype device. The scanning fiber endoscope imaging module in the photo is beneath the laptop computer. Live video images are sent in real time to a display monitor (not shown). The spectrometer module, which also houses the two lasers, is packaged into a mobile case. The spectrometer case is open in the photo but may be closed during clinical examinations.

Fig. 2

Schematic diagram of the dual laser spectroscopy module. A flexible fiber illuminated the teeth with either 405- or 532-nm laser. Switching between the lasers was controlled by an MEMS switch. The collected fluorescence was directed through an in-line filter to remove the excitation laser wavelengths before entering the spectrometer. The spectra were saved on a computer and analyzed.

Fig. 3

The operational flow of the device. The system begins in imaging mode, which captures reflectance, AF, and bacterial fluorescence images. When the clinicians notice a suspicious area, they will center the image over the area and push a software icon button to temporarily disable the imaging mode and begin collecting spectroscopic data. Approximately 1 s later, numerical spectroscopic results are displayed and the system resumes imaging.

Fig. 4

Use of the prototype device in vivo. The small size and flexibility of the fiber-optic-based probe is ideally suited for use in children. Note the display of the video image in the background. The image displayed on the screen is of the patient’s tongue.

Fig. 5

Protocol for obtaining dual laser fluorescence from a tooth. The blue oval indicates a suspicious region to be measured. AF spectra are obtained at intervals of $\sim 2\mathrm{mm}$ along the dashed line, which spans through both sound enamel and the suspected carious lesion. The baseline reading is taken to be in a sound enamel region furthest away from the lesion and the lesion measurement is taken to be the centermost reading within the lesion area.

Fig. 6

Images obtained from the multimodal clinical device. (a) a 405-nm reflectance image with high resolution and contrast of the enamel surface. (b) The AF image of the same tooth obtained concurrently with the reflectance image. The arrows indicate a region with early caries.

Fig. 7

A mixed-mode SFE image of a lower incisor viewed from the buccal facing near the gum line. The image consists of reflectance (grayscale) data with bacterial fluorescence overlaid.

Fig. 8

Typical AF emission spectra recorded from sound (a) and demineralized (b) enamel. The valley on the 405-nm emission curve at 532 nm is a result of the in-line 532-nm rejection filter. In (b), there is increased contribution from the bacterial fluorescence, which manifests as a hump-like feature centered around 635 nm in the 405-nm excited AF. The 532-nm emission curve is shifted further out toward red compared to the 405-nm emission curve. Since the bacterial fluorescence is centered around 635 nm, the superposition of the 532-nm curve with the bacterial fluorescence curve leads to stronger fluorescence from the 532-nm emission curve compared to the 405-nm emission curve from $\sim 600$ to 650 nm.

Fig. 9

(a) 405/532-nm AF ratios obtained from both healthy and demineralized regions for each specimen. In all cases, healthy enamel exhibited higher AF ratio than demineralized ratios. However, significant interspecimen variations are seen. When changed to RPC in AF ratio compared to a baseline AF ratio for each tooth (b), the delineation between healthy and demineralized enamel becomes more distinct.

Fig. 10

Polarized light microscopy used to measure depth of natural carious lesions. Shown here is an interproximal lesion, which appears dark in the image. The depth of the lesion is 220 μm.

Fig. 11

Comparison plot of PLM-measured lesion depth in blue (axis on right) and the corresponding RPC in AF ratio in red (axis on left).

Fig. 12

Top left: 405-nm reflectance images of an upper-left premolar of a 4-year-old patient with an occlusal lesion. The white spot lesion (B) is evident by the increased reflectance leading to a brighter appearance compared to the surrounding enamel (A). A more severe portion of the lesion (C) is evidenced by the dark spot near the center of the lesion. Top right: AF spectra from a sound region on the tooth (a). Bottom left: AF spectra from the white spot lesion (b). An RPC value of 41% is observed between sound (a) and white spot (b) enamel. Bottom right: AF spectra from the brown spot (c). An RPC value of 70% is observed between sound (a) and lesion (c). Presence of bacterial red fluorescence as evidenced by the spectral feature near 635 nm in both bottom spectra.