SEM Analysis of Smear Layer Removal in Root Canals

Objectives: In this study we evaluated, using scanning electron microscopy (SEM), the capacity of solution-saturated ozone (O3) to facilitate removal of the smear layer (SL) from root canal walls by selected irrigant media. Methods: 80 human pre-molar teeth were distributed randomly into 8 groups of 10 (G1-G8) which were irrigated with the following media: G1, 0.50% (w/v) sodium hypochlorite (Na+OCl-); G2, 0.50% (w/v) Na+OCl- and O3; G3, distilled-water; G4, distilled-water and O3; G5, saline; G6, saline and O3; G7, Sterilox anolyte (SA); G8, SA and O3. Teeth were split and prepared for examination by SEM. Results: Specimens irrigated with ozonated OCl- (G2) contained less SL with more open dentinal tubules than those treated with OCl- alone (G1). Although most of the SL was not removed from the G3 treatment specimens, in G4 (with added O3) 50% of cases showed only a moderate SL with some opening of dentinal tubules in the apical one-third. Similarly, G6 exhibited a greater level of SL removal than G5 (especially in the middle- and apical-thirds). Moreover, ozonated SA (G8) was a more effective SL removal solution than untreated SA (G7). Statistical analysis of SEM-determined SL scores (Kruskal-Wallis and Mann-Whitney U tests) revealed a significant difference in cleanliness of the SL between groups 5 and 1, 2, 4, 7 and 8 in the coronal-third, whilst there was a significant difference between groups 5 and 1, 2, 4, 6, 7 and 8 in the middle- and apical-thirds of the root canal. There were no significant differences between groups 5 and 3 in the coronal-, middle- and apical-thirds. Conclusions: Ozonation of OCl- and SA irrigant solutions gave rise to improvements in their ability to remove the root canal SL. Furthermore, ozonation of water and saline generated a SL removal potential in these media (they were ineffective when untreated).