Near-Infrared Imaging for Detecting Caries and Structural Deformities in Teeth

Abstract

2-D radiographs, while commonly used for evaluating sub-surface hard structures of teeth, have low sensitivity for early caries lesions, particularly those on tooth occlusal surfaces. Radiographs are also frequently refused by patients over safety concerns. Translucency of teeth in the near-infrared (NIR) range offers a non-ionizing and safe approach to detect dental caries. We report the construction of an NIR (850 nm) LED imaging system, comprised of an NIR source and an intraoral camera for rapid dental evaluations. The NIR system was used to image teeth of ten consenting human subjects and successfully detected secondary, amalgam-occluded and early caries lesions without supplementary image processing. The camera-wand system was also capable of revealing demineralized areas, deep and superficial cracks, and other clinical features of teeth usually visualized by X-rays. The NIR system's clinical utility, simplistic design, low cost, and user friendliness make it an effective dental caries screening technology in conjunction or in place of radiographs.

Keywords: Demineralization; dental caries; near-infrared imaging; transillumination.

FIGURE 1.

Common NIR imaging modes. (a) Reflectance imaging has light directed at the tooth, with reflected rays collected by a camera positioned in a desired orientation; a beamsplitter is commonly employed to redirect the illuminated surface for imaging. (b) Transillumination imaging focuses on capturing the source light after it has transited the tooth. Emitters of low coherence, such as SLDs and LEDs, are usually placed adjacent to the tooth to maximize the input of light; lasers can be placed further away. Transillumination most commonly has the tooth positioned between the source and camera, although this orientation is not mandatory. If the camera is angled to view the occlusal surface and is orthogonal to light source, the tooth is undergoing occlusal transillumination imaging (c).

FIGURE 2.

Archetypical examples of dental features in various NIR modes. Images are of tooth 9 in a 56-year-old female; views in (a)-(c) are taken from the lingual side with the distal direction leftwards. (a) White light image. (b) The NIR system’s transillumination image exhibits areas of reduced luminescence indicative of demineralization or caries. Caries are darker and more pronounced than demineralization. Select areas of interest are highlighted; two proximal restorations (blue) displaying leakage and secondary caries (red). A large area of demineralization (yellow) denotes a region where the incisal edge of tooth 24 on the mandible has caused enamel attrition. A large horizontal fracture (cyan) runs between the two restorations. (c) Periapical radiograph section with both proximal restorations visible and darkening from corresponding secondary caries. (d) In the DEXIS CariVu occlusal view, teeth lacking a larger occlusal surface, such as this incisor, are more difficult to image.

FIGURE 3.

Multiple images of an amalgam filling under different imaging modes. The presence of the metal amalgam inhibits assessment. The red “X” denotes the same amalgam edge in all images. (a) The DEXIS CariVu’s occlusal imaging shows some demineralization. (b) White light examination reveals no immediate problems. (c) Amalgam appears opaque in the two-dimensional radiograph and blocks evaluation of superimposed tooth material. Secondary caries has started in the lower amalgam margin, as circled in red. (d) Scanning of the amalgam margin with the NIR system shows secondary caries along the bottom of the amalgam circled in red, as seen in the radiograph in (c). Midway down the side of the filling, circled in blue, was another secondary caries spot undetected by the other imaging methods. No indication of this caries is present in the white light image in (b). (a) was taken in vivo, and (b)-(d) were taken after extraction.