Visualization of the pulp chamber roof and residual dentin thickness by spectral-domain optical coherence tomography in vitro

The aim of this study was to evaluate the ability of spectral-domain optical coherence tomography (SD-OCT) to display the roof of the pulp chamber and to estimate the residual dentin thickness (RDT) of the pulp complex. The roots of 20 extracted human molars were embedded in epoxy resin, and crowns were longitudinally sectioned in the mesial-distal direction, exposing the pulp chamber. The coronal part of the crown was removed up to an RDT to the pulp chamber roof of 2mm. Samples were imaged by SD-OCT from coronal view and by light microscopy (LM) in the sagittal plane. Using a microtome, dentin was subsequently removed in four levels from the occlusal aspect in steps of 250 m. At each level, RDT was documented and measured by both methods. The data were compared (Spearman's rho correlation coefficient, Wilcoxon signed-rank test). Using OCT, the roof of the pulp chamber was first displayed at a maximum RDT of 1.94 mm. The minimal RDT that could be imaged by OCT was 0.06 mm. Values from both methods were strongly correlated (r, 0.83-0.95; p(i) <= 0.05) and differed significantly for large RDTs (dentin levels 1, 2; p(i) < 0.05) but not for small RDTs (levels 3, 4; p(i) >= 0.226). The roof of the dental pulp chamber could be already visualized by SD-OCT with a RDT of 1.94mm. Therefore, the method could be a useful diagnostic tool during the preparation of deep dentin cavities and might help to preserve the integrity of the pulp chamber.