Remaining Dentine Thickness to Pulp Assessed With Optical Coherence Tomography

Objectives: The aim of this in vitro study was to explore the ability of OCT to identify pulpal horns through different depths of sound and carious dentine in extracted teeth.
Methods: Thirty-eight sound and carious extracted human molars were sectioned in the coronal plane and occlusally ground; leaving 2-0.5mm remaining dentine thickness (RDT) to the pulp-horns, then occlusally scanned using swept-source OCT. The points at which the pulp horns initial shadow and visually evident appearance on the B-scan was recorded; along with the first pulp horn peak on the A-scan (plotted profile of the B-scan). Data were extracted from these B-scans, between the dentine surface and pulp horn. The difference between detection depth when using the A or B-scan was statistically assessed using the Wilcoxon signed-ranks test. The maximum RDT through which a pulp horn could be detected in non-carious, soft-carious and hard-carious dentine along with their scattering gradients was assessed and statistically analysed using the Kolmogorov–Smirnov and Mann-Whitney U-test.

Results: The B-scan pulp horn shadow was initially noted followed by an A-scan peak and finally clear visualisation on the B-scan. Non-carious and hard-caries samples showed a statistically greater RDT pulp horn detection depth compared to the soft-caries sample (p<0.0001). Non-carious and hard-caries samples showed a statistically significant difference in scattering gradient, compared to the soft-caries sample (p<0.05 first gradient/p<0.0001 second gradient).
Conclusions: OCT can be used to detect pulp horns and measure the RDT. The A-scans pulp horn peak usually occurs before a pulp horn is visually identified on the B-scan. More than 85% of pulp horns can be detected through 1000-1750mm of RDT in sound or remineralize dentine, however soft-caries significantly reduces this depth. Dentins optical density can be determined from A-scan’s, which varied significantly between soft-carious and non-carious or remineralize dentine. OCT’s clinical use could reduce un-necessary pulpal exposures.