Visualisation of Calculus by Optical Coherence Tomography

Methods:  10 extracted human front teeth and premolars, partially covered with calculus, were embedded in epoxy resin omitting the root surface. A ‘region of interest’ (ROI) was marked by small notches coronally and apically of the calculus and was imaged by spectral domain coherence tomography (3D image stacks; SD OCT, Telesto SP5, center wavelength 1325 nm, scan field 11 mm x 2 mm; Thorlabs, Germany) and by light microscopy (LM, Stemi 2000C, 1x; Zeiss Microscopy, Germany). To evaluate the impact of different fluids on calculus visualisation by OCT, root surfaces were covered by a layer of physiological saline solution (NaCl) and human blood, respectively, and displayed by OCT. Subsequently, the tooth was complete covered with epoxy resin and teeth were sectioned for histological evaluation. Within the ROI the lengths of root surface and calculus were measured by LM (AxioVision, Zeiss MicroImaging) and OCT (ImageJA) and the ratio [%] was calculated. Additionally, at three sites of each ROI the agreement of location and extent of the calculus was evaluated. The data were statistically analysed by t-test, Cohen's kappa coefficient (κ) and Pearson’s correlation.

Results:  More calculus was measured by OCT compared to LM in the groups dry root surface (p = 0.023) and NaCl (p = 0.035). Regarding to location and extend of the calculus, the agreement between LM and OCT was strong (Κ_i= 0.783). Measurements with both methods were strongly correlated (r_i > 0.906; p_i < 0.001)

Conclusions:  Calculus on the root surface could be visualised by SD OCT. Differences between methods have to be verified by an enhanced spatial resolution of light microscopy to exclude false positive interpretation of OCT signals.

Support: Provision of OCT by Thorlabs, Germany