Nondestructive assessment of the severity of occlusal caries lesions with near-infrared imaging at 1310 nm

Abstract

The high transparency of dental enamel in the near-infrared (NIR) at 1310 nm can be exploited for imaging dental caries without the use of ionizing radiation. The objective of this study is to determine whether the lesion contrast derived from NIR imaging in both transmission and reflectance can be used to estimate lesion severity. Two NIR imaging detector technologies are investigated: a new Ge-enhanced complementary metal-oxide-semiconductor (CMOS)-based NIR imaging camera, and an InGaAs focal plane array (FPA). Natural occlusal caries lesions are imaged with both cameras at 1310 nm, and the image contrast between sound and carious regions is calculated. After NIR imaging, teeth are sectioned and examined using polarized light microscopy (PLM) and transverse microradiography (TMR) to determine lesion severity. Lesions are then classified into four categories according to lesion severity. Lesion contrast increases significantly with lesion severity for both cameras (p<0.05). The Ge-enhanced CMOS camera equipped with the larger array and smaller pixels yields higher contrast values compared with the smaller InGaAs FPA (p<0.01). Results demonstrate that NIR lesion contrast can be used to estimate lesion severity.

Figure 1

Different NIR imaging configurations used. (a) NIR 1310-nm source (S) focused with a cylindrical lens on the CEJ. (b) Two sources on each side of the tooth directed at the CEJ. (c) Reflectance imaging in which the NIR light is directed at the tooth occlusal surface. (Color online only.)

Figure 2

(a) Visible-light reflectance and (b) NIR transillumination images. The NIR image was captured with the Ge-enhanced CMOS camera using the setup of Fig. 1a. (c) A PLM image of a thin section cut along the yellow dotted lines in (a) and (b) shows the position and depth of the lesion that penetrates to the dentin-enamel junction and is classified as a D1 lesion. (Color online only.)

Figure 3

Images of one of the tooth samples with a D2 lesion. (a) Visible-light reflectance image, (b) radiograph, (c) and (d) PLM images of the sections cut along the yellow dotted lines in (a) NIR transillumination images captured with the (e) Ge-enhanced CMOS camera [setup of Fig. 1a] and (f) NIR InGaAs FPA [setup of Fig. 1b]. The lesion areas appear as darker areas in the NIR images. These are best resolved in (e). The lesion areas are the dark areas in the enamel in the PLM images (c) and (d). The lesion areas are harder to resolve in the dentin using PLM, and they actually appear lighter than the sound dentin. Therefore, TMR was used to confirm the lesion depth in dentin. (Color online only.)

Figure 4

Images of one of the tooth samples with an E2 lesion. (a) Visible-light reflectance image, (b) radiograph, (c) and (d) PLM images of the sections cut along the yellow dotted lines in (a). NIR transillumination images captured with the (e) Ge-enhanced CMOS camera [setup of Fig. 1a] and (f) NIR InGaAs FPA [setup of Fig. 1b]. (Color online only.)

Figure 5

Images of one of the tooth samples that had a D1 lesion with extensive hypomineralization. (a) Visible-light reflectance image, (b) radiograph, (c) and (d) PLM images of the sections cut along the yellow dotted lines in (a). NIR transillumination images captured with the (e) Ge-enhanced CMOS camera [setup of Fig. 1a] and (f) NIR InGaAs FPA [setup of Fig. 1b]. The yellow arrows in the PLM images indicate the position of hypomineralization. (Color online only.)