Contrast-enhanced micro-CT to assess dental pulp tissue debridement canals of extracted teeth: a series of cascading experiments towards method validation.

AIM To validate a new method for the evaluation of pulp tissue debridement in the root canals of extracted teeth using an impregnation protocol involving potassium triiodide, a radiocontrast solution known as Lugol's, combined with micro-computed tomographic (micro-CT) imaging. METHODOLOGY The impact of NaOCl on the radiopacity of Lugol's solution was assessed using a series of 1:1 dilutions of Lugol in distilled water and 5.25% NaOCl, which were then pipetted into transparent dishes and radiographed. To verify the influence of Lugol on the oxidizing ability of NaOCl, a dissolution test was performed using fresh bovine meat. Ten slices did not undergo any tissue processing, whilst twenty slices were fixed in formaldehyde for 24 h. After that, 10 of them were immersed in Lugol for another 24 h. Then, all specimens were placed in NaOCl and the time required for a complete pulp tissue dissolution was recorded. For the last experiments (histological validation and micro-CT assessment), 8 extracted mandibular premolars with vital pulps were immersed in buffered formalin, scanned in a micro-CT device, accessed, immersed in Lugol for 7 days and scanned again. Then, the root canals of 5 teeth were prepared, scanned, and the volume of remaining pulp tissue identified and quantified, whilst 3 teeth were histologically processed. The same specimens were subjected to histological assessment and the images of the histologic sections were registered with the corresponding micro-CT images to qualitatively verify whether the pulp tissue in the histological sections matched its counterpart in the Lugol-impregnated tissues identified in the micro-CT slices. RESULTS There was no discernible effect on radiopacity when NaOCl was mixed with Lugol. Tissue processing did not affect the time required for the complete dissolution of fresh bovine meat. Histological evaluation revealed a correlation between micro-CT and histological images confirming the identification of Lugol-impregnated pulp tissue in micro-CT images. CONCLUSIONS The radiocontrast Lugol's solution was unaffected by NaOCl and did not interfere with its pulp tissue dissolution capability. The pulp tissue impregnation protocol using Lugol allowed the visualization of pulp tissue on micro-CT images and the identification of remaining pulp tissues during the evaluation of chemical-mechanical canal procedures.