Validation of Optical Coherence Tomography against Micro–computed Tomography for Evaluation of Remaining Coronal Dentin Thickness

• We used optical coherence tomography (OCT) and micro–computed tomographic (micro-CT) imaging to scan teeth after deep dentin caries removal.
• The remaining dentin thickness (RDT) at pulpal horns was measured and compared.
• A strong correlation was found in measurements between OCT and micro-CT imaging.
• It was possible to clearly visualize pulp horns with RDT up to 1.5 mm in thickness.
• A refractive index value of 1.54 is valid to convert optical readings of RDT by OCT.

IntroductionOptical coherence tomography (OCT) is a noninvasive modality to obtain in-depth images of biological structures. A dental OCT system has become available for chairside application. This in vitro study hypothesized that swept-source OCT can be used to measure the remaining dentin thickness (RDT) at the roof of the dental pulp chamber during excavation of deep caries.MethodsHuman molar teeth with deep occlusal caries were investigated. After obtaining 2-dimensional and 3-dimensional OCT scans using a swept-source OCT system at a 1330-nm center wavelength, RDT was evaluated by image analysis software. Microfocus x-ray computed tomographic (micro-CT) images were obtained from the same cross sections to confirm OCT findings. The smallest RDT values at the visible pulp horn were measured on OCT and micro-CT imaging and compared using the Pearson correlation. Pulpal horns and pulp chamber roof observation under OCT and micro-CT imaging resulted in comparable images that allowed the measurement of coronal dentin thickness.ResultsRDT measured by OCT showed optical values range between 140 and 2300 μm, which corresponded to the range of 92–1524 μm on micro-CT imaging. A strong correlation was found between the 2 techniques (r = 0.96, P < .001).ConclusionsFurther analysis indicated linear regression with a slope of 1.54 and no intercept, closely matching the bulk refractive index of dentin. OCT enables visualization of anatomic structures during deep caries excavation. Exposure of the vital dental pulp because of the removal of very thin remaining coronal dentin can be avoided with this novel noninvasive technique.