Near-infrared Imaging of Natural Secondary Caries

Objectives: Near-IR reflectance and transillumination, and optical coherence tomography are promising new methods for imaging secondary caries. Dental enamel is transparent at wavelengths around 1300-nm. Moreover, dental composite and demineralized tissues are visible with increased contrast while there is reduced interference from stains. The objective of this study was to determine whether near-IR transillumination (λ=1300-nm) and near-IR cross-polarized reflectance (λ=1500-1700-nm) images can be used to yield high contrast images of demineralization surrounding restorations.
Methods: Composite margins (n=12) were imaged in vitro using near-IR transillumination and reflectance, polarization-sensitive optical coherence tomography (PS-OCT) and 3D digital microscopy. Restored premolars (n=12) were imaged in vivo using near-IR reflectance and transillumination and then extracted and collected for histology. Samples were serially sectioned into 200–μm slices and imaged with polarized light microscopy (PLM) and transverse microradiography (TMR). Line profiles from near-IR images were overlaid with TMR line profiles for comparison of near-IR contrast values and tissue mineral percentage of in vitro samples. Two independent examiners evaluated the presence of demineralization at the sample margin using visible detection and near-IR images presented digitally for in vitro samples.
Results: Near-IR image line profiles demonstrate high contrast signals relative to enamel and composite along restoration margins and are consistent with TMR percent mineral profiles from the same cross sections. Near-IR reflectance images resulted in the highest kappa value, κ=0.68, near-IR transillumination, κ=0.65, NIR modality aggregate, κ=0.66 and visible inspection, κ=0.50.
Conclusions: The results demonstrate the utility of near-IR light for detecting recurrent decay and suggest that near-IR images could be a reliable screening tool used in conjunction with PS-OCT for the detection and diagnosis of secondary caries.