Near-infrared imaging of secondary caries lesions around composite restorations at wavelengths from 1300–1700-nm

Background and objectivesCurrent clinical methods for diagnosing secondary caries are unreliable for identifying the early stages of decay around restorative materials. The objective of this study was to access the integrity of restoration margins in natural teeth using near-infrared (NIR) reflectance and transillumination images at wavelengths between 1300 and 1700-nm and to determine the optimal NIR wavelengths for discriminating composite materials from dental hard tissues.Materials and methodsTwelve composite margins (n = 12) consisting of class I, II and V restorations were chosen from ten extracted teeth. The samples were imaged in vitro using NIR transillumination and reflectance, polarization sensitive optical coherence tomography (PS-OCT) and a high-magnification digital microscope. Samples were serially sectioned into 200-μm slices for histological analysis using polarized light microscopy (PLM) and transverse microradiography (TMR). Two independent examiners evaluated the presence of demineralization at the sample margin using visible detection with 10× magnification and NIR images presented digitally. Composite restorations were placed in sixteen sound teeth (n = 16) and imaged at multiple NIR wavelengths ranging from λ = 1300 to 1700-nm using NIR transillumination. The image contrast was calculated between the composite and sound tooth structure.ResultsIntensity changes in NIR images at wavelengths ranging from 1300 to 1700-nm correlate with increased mineral loss measured using TMR. NIR reflectance and transillumination at wavelengths coincident with increased water absorption yielded significantly higher (P < 0.001) contrast between sound enamel and adjacent demineralized enamel. In addition, NIR reflectance exhibited significantly higher (P < 0.01) contrast between sound enamel and adjacent composite restorations than visible reflectance.SignificanceThis study shows that NIR imaging is well suited for the rapid screening of secondary caries lesions.