Non-destructive clinical assessment of occlusal caries lesions using near-IR imaging methods

Abstract

Objective: Enamel is highly transparent in the near-IR (NIR) at wavelengths near 1,300 nm, and stains are not visible. The purpose of this study was to use NIR transillumination and optical coherence tomography (OCT) to estimate the severity of caries lesions on occlusal surfaces both in vivo and on extracted teeth.

Methods: Extracted molars with suspected occlusal lesions were examined with OCT and polarization sensitive OCT (PS-OCT), and subsequently sectioned and examined with polarized light microscopy (PLM) and transverse microradiography (TMR). Teeth in test subjects with occlusal caries lesions that were not cavitated or visible on radiographs were examined using NIR transillumination at 1,310 nm using a custom built probe attached to an indium gallium arsenide (InGaAs) camera and a linear OCT scanner. After imaging, cavities were prepared using dye staining to guide caries removal and physical impressions of the cavities were taken.

Results: The lesion severity determined from OCT and PS-OCT scans in vitro correlated with the depth determined using PLM and TMR. Occlusal caries lesions appeared in NIR images with high contrast in vivo. OCT scans showed that most of the lesions penetrated to dentin and spread laterally below the sound enamel.

Conclusion: This study demonstrates that both NIR transillumination and OCT are promising new methods for the clinical diagnosis of occlusal caries.

Figure 1

An extracted tooth with occlusal lesions mounted on the acrylic base is shown with a laser etched 2×2 mm square area for analysis before and after serial sections were cut for histological examination with PLM and TMR.

Figure 2

The PS-OCT system showing the relative positions of the sample holder with the tooth, scanning stages and probe. The incident beam was aligned with one corner of the brass holder so that the scan position could be matched to the position of serial sectioning for histology.

Figure 3

Photograph of the NIR clinical imaging system with InGaAs imager with probe in use. Inset in upper right shows a diagram of the occlusal probe, which directs light via two teflon diffusers near the tooth roots and the light diffuses up through the crown.

Figure 4

Photograph of the clinical PS-OCT system in action. The handheld linear scanner is also shown without the outer Delrin sterilizable sheath.

Figure 5

Image series of PS-OCT b-scans (⊥-axis) (left), PLM (center), and TMR (right) for four different teeth, A-D. The lesion is demarcated by the black boxes in the OCT and PLM images. OCT images are shown in a red-white-blue false color scale in dB with high reflectivity in red.

Figure 6

Lesion depths measured using OCT, PLM and TMR for 20 teeth. Correlation plots are also shown for (OCT & PLM, solid line) r=0.63 (Pearson), P < 0.01 and (OCT & TMR – dotted line) r = 0.75, P < 0.001.

Figure 7

Photographs and NIR images of two of the occlusal lesions imaged in vivo.

Figure 8

Four OCT b-scans of occlusal lesions showing the higher reflectivity at the DEJ peripheral to each fissure shown by the upward pointing arrows. Downward pointing arrows demarcate the center of the fissure and lesion.