Assessment of the activity of root caries lesions using short wavelength infrared imaging - an in vitro pilot study.

OBJECTIVES: New kinetic approaches that exploit differential water absorption appear to be more effective for assessing lesion activity on root surfaces using short wavelength infrared (SWIR) imaging. The aim of this pilot study was to employ multispectral time-resolved SWIR imaging to assess the activity of root caries. METHODS: A SWIR imaging array and SWIR light sources at 1040 and 1470 nm were used to assess the activity of ten arrested and ten active root caries lesions on extracted teeth during forced air drying for 60 s. Cross-polarization optical coherence tomography (CP-OCT) was used to assess the presence of a highly mineralized transparent surface zone that was used to indicate lesion activity. Thermal imaging of matching lesion areas was also used for comparison. Multiple kinetic parameters were extracted from the time vs intensity SWIR dehydration curves and used to assess lesion activity. RESULTS: Kinetic parameters extracted from the SWIR dehydration curves showed large and significant differences between active and arrested lesion areas. The ratio of the means of the exponential decay constant for the time vs intensity 1040/1470 difference curves between active and arrested lesions was highest and it was similar to the ratio measured for the heat loss using thermal imaging. CONCLUSIONS: This study demonstrates that time-resolved SWIR reflectance imaging has great potential for the assessment of lesion activity on root surfaces in addition to other tooth surfaces. CLINICAL SIGNIFICANCE: Improved methods for the assessment of lesion activity are expected to reduce the number of unnecessary cavity preparations.