Efficacy of three different irrigation systems on calcium hydroxide removal from round and oval canals: a scanning electron microscopy study

BACKGROUND: To evaluate by means of scanning electron microscopy the effectiveness of different irrigation systems in the removal of calcium hydroxide from round and oval canals. METHODS: 76 extracted single-rooted teeth were selected. Criteria for tooth selection included one single root canal; no visible root caries, fractures, or cracks; and a completely formed apex under light microscope examination (10x). Radiographs in bucco-lingual and mesio-distal direction were taken to cal- culate the ratio between canal diameters measured in the two projections. If ratio was less than or equal to 2.5, the canal was considered round, otherwise was considered oval. According to ratio and root length teeth were divided into 8 groups, with 2 control samples. After access cavity preparation, working length was determined 1 mm short of the length where the file extruded the apical foramen. To simulate clinical conditions the apex was sealed with glue. Glide path and canal instrumentation were performed with Path File size 13, 16, 19 and ProTaper Universal rotary system in a crown-down sequence to size 40 at the WL. A size 25 lentulo spiral was used to fill teeth with calci- um hydroxide. Radiographs were taken to confirm the complete filling of the canals. Samples were kept in an incubator at 37° C for a week. Canals were cleaned with Irrisafe, Endovac, Xp Endo Finisher and conventional endodontic needle irrigation. Teeth were split along their long axis in a bucco-lingual direc- tion into 2 halves. For scanning electron microscopic analysis, tooth halves were fixed on aluminum stubs, gold sputter coated and observed with a scanning electron microscope. Apical, middle, and coronal thirds were established by dividing the roots according to their length. The center of each third was examined at 500x magnification. Images were taken using backscattered mode and analyzed with a digital processing software (ImageJ v. 1.49, National Institutes of Health, NIH, USA) for a quantitative analysis. The efficacy of the irriga- tion system was evaluated calculating the amount of calcium hydroxide left inside the canal, expressed as percentage of the total area of the image. To compare the 8 groups, the results were statistically analyzed using the analysis of variance test (ANOVA) with Bonferroni test or T-test (P<0.05). RESULTS: No statistically significant differences were observed among different thirds for each group. Comparing canal shape for each instrument, significant differences were found only for Endovac, where coronal and middle thirds of oval canals were cleaner than round ones. Analyzing the whole canal, significant difference can be found between irrigation systems and conventional irrigation in the oval ones. In round canals Irrisafe and Xp Endo Finisher are more effective compared to conventional irrigation, but only Irrisafe is more effective compared to Endovac. No statistical- ly significant differences can be observed between Endovac and conventional irrigation. CONCLUSIONS: None of the investigated techniques removed the calcium hydroxide completely. However, the results demonstrate greater removal of calcium hydroxide if the irrigant solutions are activated, compared with conven- tional endodontic irrigation. Therefore, it is recommended to activate the irrigant solutions to enhance chemical debride- ment of the root canal system.