En‑face optical coherence tomography analysis of gold and silver nanoparticles in endodontic irrigating solutions: An in vitro study

Optical coherence tomography (OCT) is a non-invasive, non-radioactive optical diagnostic method based on low-coherence interferometry, which achieves images with different orientation. In dentistry, its major advantage is represented by the localization and characterization of the smallest defects in hard dental tissues, dental materials and of the smallest details in dental anatomy (supplementary canals, recesses, isthmuses, or intra-radicular connections). The aim of the present in vitro study was to evaluate using c-scan en-face optical coherence tomography, the optical opacity, and the distribution inside the root canal lumen of several extracted human teeth of silver and gold nanoparticles from special irrigating solutions used in endodontic treatment. Twelve root canals from 5 human teeth were instrumented using the ProTaper Universal system after initial negotiation with hand K-files ISO no. 10 and rotary nickel-titanium PathFile instruments. An initial c-scan OCT analysis was performed for each sample to confirm that the root canal lumen was empty from radiopaque materials (Group 1). Teeth were first irrigated with NanoCare Plus (Group 2) and then with NanoCare Gold (Group 3) and C-scans were repeated after each irrigation method. The OCT investigation started at the tooth apex, at a depth of 1 mm from its tip. Subsequently, 100 slices of 10 microns were obtained from each root canal. Images were captured and then analyzed with ImageJ software to calculate the level of grey inside the root canal lumen. The highest values of grey were obtained in the samples irrigated with NanoCare Gold after NanoCare Plus (Group 3). The present study proved that both nanoparticles inserted in root canal irrigants were evidenced through OCT imagistic analysis due to their optical opacity, which allowed their highlighting in an empty root canal lumen, after the endodontic treatment was performed and the root canal was cleaned and shaped using specific protocols.