Aim: to compare fracture rates and morphologic results of three experimental rotary file systems with different flute designs. Materials and Methods: Plastic test blocks with artificial root canals were shaped to a size of ISO 30 using the three test files, one of them with a triangular shape (C1), one similar to C1 with an enhanced number of flutes (C2) and one with a square shape (C3). Flexmaster instruments have been added as a control group. These four experimental groups were processed by fifteen test persons, each of them prepared n=7 plastic blocks in every group. Fracture rate and morphologic alterations of the root canals were evaluated by one operator and statistically compared on a significance level of alpha=0.05. Results: There was no difference between the square-shaped file C3 and the triangular prototype C1 in view of fracture rate (p= 0,2289). C2 (increasing number of flutes and less dulled tip) showed a statistically significant higher fracture rate (log-rank test, p< 0.0001) compared to C3. The rectangular shape C3 showed also a significant higher fracture rate compared to the control group (p= 0.0039). With regard to morphologic alterations of the artificial root canal, there was no difference between the prototypes and the control group. Comparing different test persons, there was a highly significant effect (Kruskall-Wallis test, p< 0.001). Conclusion: The area of the inner core influenced the fracture resistance of the tested instruments. An increasing area of the inner core results in higher fracture resistance. The higher fracture rate of the prototype files compared to the control group depends possibly on the use of radial-lands. All instruments are highly technique sensitive regarding fracture and morphologic alteration, so the influence of the test person is not negligible and should be addressed with an extended training phase.