SEM evaluation of thermoplastic endodontic materials alterations after disinfection: a new experimental model

This study assessed a new experimental model to analyze the effects of sodium hypochlorite solution 2.5% for 10 min and chlorhexidine 2% for 15 s on cones surface alterations. Twenty five gutta-percha and 25 thermoplastic synthetic polymer-based cones had their last 1 mm from the tapered end examined by scanning electron microscopy (SEM) before and after being exposed to the disinfectant solutions. To allow the surfaces to be compared, the samples were not metalized, a voltage of 1 kV was used and the images were captured within standardized angles. The samples were immersed on the test solutions. The comparison of the alterations of the cones was performed using the software program Adobe Photoshop CS. A measurement was taken of the standard deviations of the pixel intensity in this area, higher standard deviations represent more irregular areas. Differences in standard deviation before and after disinfection for each cone were compared between groups by means of analysis of variance supplemented by the Tukey test. Gutta-percha cones showed higher standard deviations than Resilon cones (P < 0.001). In the gutta-percha cones, sodium hypochlorite generated more irregular areas than chlorhexidine and the control group (P < 0.001). The present study has demonstrated the feasibility of using a modified SEM method. This opens opportunities to the use of new and precise tools for evaluating a sample in different moments.