Assessment of the activity of secondary caries lesions with short-wavelength infrared, thermal, and optical coherence tomographic imaging.

Significance: Leakage in the interfaces between restorative materials and tooth structure allows for fluid and bacterial acid infiltration, causing restoration failure due to secondary caries. Dentists spend more time replacing composite restorations than placing new ones. Previous in vitro and in vivo studies on enamel and root surfaces using shortwave-infrared (SWIR) and thermal imaging during dehydration with forced air have been promising for assessing lesion activity. Aim: We hypothesized that SWIR reflectance and thermal imaging methods can be used to monitor the activity of secondary caries lesions around composite restorations. The objective of this study was to employ these methods to measure the rate of fluid loss from lesions during dehydration with forced air to assess lesion activity. Approach: Sixty-three extracted human teeth with total of 109 suspected secondary lesions were examined using SWIR and thermal imaging during dehydration. The thickness of the highly mineralized transparent surface layer (TSL) at lesion interfaces indicative of lesion activity was measured by optical coherence tomography (OCT). Micro-computed tomography (MicroCT) was used to further confirm lesion severity and structure. OCT and MicroCT measurements of lesion structure, depth, and severity were correlated with fluid loss rates measured with SWIR reflectance and thermal imaging. Results: TSL thickness measured with OCT correlated with both SWIR reflectance and thermal measurements of rates of fluid loss ( p < 0.05 ). Increasing TSL thickness led to decreased permeability of lesions, potentially indicating full lesion arrest at TSL ≥ 70 µ m . SWIR performed better than thermal imaging for secondary lesion activity assessment, although both methods performed best on smooth surface lesions. Conclusions: Nondestructive SWIR reflectance and OCT imaging methods are promising for clinically monitoring the activity of secondary caries lesions.

Assessing lesion activity of secondary lesions on extracted teeth by thermal dehydration measurement and optical coherence tomography.

Secondary caries occurs when leakage in the interfaces between restorative materials and tooth structure allow fluid and bacterial acid infiltration. Thermal imaging coupled with dehydration can be used to measure this increase in fluid permeability for secondary lesions in teeth. Thermal imaging exploits the temperature change due to water evaporation during dehydration to measure the rate of water diffusion from porous lesion areas. Previous in vitro and in vivo thermal imaging studies on enamel and root surfaces have been promising for assessing natural lesion activity. In this study, the rates of dehydration for secondary lesions on extracted teeth were measured. The secondary lesions were also assessed by optical coherence tomography (OCT) and correlated with dehydration rates to determine lesion activity. Future studies with µCT will be used to further confirm lesion severity and structure.