Vergleich zweier maschineller Nickel-Titan-Revisionssysteme hinsichtlich der Revisionseffizienz von Wurzelkanalfüllungen in ovalen Wurzelkanälen mit und ohne Einsatz des Lösungsmittels Eukalyptol

Aim and Background Due to the fact until now there do exist adequate alternatives to replace a tooth if necessary with similar aesthetic and functional aspects, research and treatment efforts are focused on the improvement of conservative treatment. Thus, root canal treatment and endodontic retreatment of non-vital teeth are become more and more important. The aim of endodontic retreatment is the preservation or restitution of periapical health of endodontically treated teeth. This procedure includes a removal of the existing root canal filling, a proper chemomechanical treatment with filing and rinsing of the soot canal system followed by a sufficient reobturation and functional coronal restoration (DGZMK-Stellungnahme). The present study aimed to assess and to compare the retreatment efficiency of the two endodontic retreatment systems D-RaCe und Mtwo-retreatment files. Further, the effect of the use of a solvent (eucalyptol) and a sonic or reciprocating activation of EndoActivator or EndoExpress respectively to improve the retreatment efficiency was investigated. Methods 60 extracted human teeth with straight root canals and oval canal cross section were used. Canal length was standardized by decoronation of the teeth resulting in a root length of 10 mm. Root canals were instrumented to .04/#40 using Mtwo instruments. Further, it was ensured that the instrumented root canals showed distinct oval canal cross sections. Root canals were obturated with gutta-percha points and AH Plus using the lateral compaction technique. Teeth were stored for two months in thymol 0,1% and were randomly assigned to one of the four experimental groups (n=15). Retreatment was performed with D-RaCe- and Mtwo retreatment system with and without the use of eucalyptol as solvent. Canals were reinstrumented to the initial file size of .04/#40 and retreatment time was recorded. After longitudinal splitting the specimen were photographed under a microscope (10 x magnification) and digital images were stored for further investi-gation. Teeth were reassembled and underwent a second retreatment step using activation. Root canals of the teeth in the solvent groups were filled with eucalyptol and the solvent activated using the EndoActivator. Root canals of the teeth in the non-solvent groups were filled with sodium chloride 0.9% and activation performed using an ISO 30 K file and the EndoExpress handpiece. The specimen were again separated and photographed. The microphotographs were investigated for residual obturation material and statistical analysis was computed with SPSS 20.0 software using non-parametric tests. Results The investigation revealed significant more residual obturation material after both retreatment steps when oval canals were retreated with D-RaCe and RaCe instruments in combination with eucalyptol than in the other groups. After the first retreatment step the least percentage of residual obturation material was observed in the Mtwo group without solvent used. In contrast, the most efficient retreatment after the second retreatment step was observed in the D-RaCe group without solvent. Regarding the instrumentation time and total retreatment time no significant differences were detected. Conclusion The present study showed that no retreatment system and no activation allowed a complete retreatment of the root canal. However, the study indicated that both instrument systems allowed a sufficient retreatment of root canal fillings in oval root canals. In contrast to the anticipation the use of eucalyptol in combination with both retreatment instrument systems did not show any advantage but had an adverse effect. Nevertheless, the use of an activated K file was found to be a promising alternative to increased instrumentation of the root canal. Both described activation techniques were found to raise the retreatment efficiency without additional weakening of the root dentine by increased instrumentation with potential risk of root perforations.