Analyse synergistischer und antagonistischer Effekte endodontischer Spülprotokolle auf die Mikrohärte kanalwandnahen Wurzeldentins

Background and aims: If an endodontic treatment is necessary, the chemical disinfection via irrigation of the root canal system is of crucial importance, in addition to mechanical instrumentation. As there is currently no single irrigant that can combine all required and desired properties, the combination of irrigation solutions in the form of irrigation regimens is recommended. However, next to the desired effects, irrigation solutions and irrigation regimens can also have undesirable side effects, such as changing the physiochemical properties of the dentin. This study examines the influence exerted by different irrigation regimens on the micro hardness. Since the dentin shows regional differences in hardness, it will further be examined whether there are significant differences in the degree of the reduction in micro hardness between the apical, middle and coronal root canal section. Material and methods: Ten human, extracted, single-rooted teeth were prepared mechanically and irrigated solely with distilled water. The crowns were then separated, the roots cut in half lengthwise and embedded in acrylic resin blocks. The root halves were divided into 4 different groups of irrigation protocols in a randomized fashion: G1: 3 % NaOCl + 15 % EDTA + 3 % NaOCl; G2: 3 % NaOCl + 40 % citric acid + 3 % NaOCl; G3: 3 % NaOCl + 15 % EDTA + 2 % CHX; G4: 3 % NaOCl + 40 % citric acid + 2 % CHX. An irrigation time of 1 minute was selected for each irrigant, resulting in a total irrigation duration of 3 minutes per regimen. The Vicker’s micro hardness values were measured with a load of 1000 g and a dwell time of 10 s at a distance of 200 µm to the edge of the root canal lumen. Measurements were carried out before the start of the irrigation regimen to establish a baseline, and after the irrigation solution 1, 2 and 3. For statistical analysis, the collected data was evaluated via the Friedman test and Wilcoxon test. The level of significance was set at 5 %. Results: There were mainly nonsignificant changes in micro hardness and, albeit to a lesser extent, significant increases in micro hardness. The changes were observed irrespective of specific irrigation solution or regimen, indicating that the irrigation solutions and irrigation regimens in this study did not trigger any micro hardness reductions un-der the test conditions described. Although no statements could be made regarding region-dependent reductions in micro hardness, a tendency of micro hardness from central > coronal > apical could be determined, which was not only evident before the start of the irrigation treatment, but also in the course of the hardness measurements. Conclusion: The irrigation regimens used in this study were not critical in terms of their effect on dentin micro hardness. This is probably due to the limitation of the irrigation time to 1 min per irrigation solution and the mechanical instrumentation without the use of NaOCl. The duration time appears to constitute one of the crucial factors for micro hardness changes in dentin during irrigation. However, as long as no irrigation fluids are available to ensure unchanged micro hardness at similar or better effectiveness, the reduced micro hardness and thus the potentially increased risk of root fractures should be condoned in favor of a significantly higher probability of success for root canal treatment.