İntroduction: Mechanical preparation is an important step of root canal therapy. Apical enlargement is recommended for effective disinfection.The aim of this study is to compare the shaping ability of PTG, PTN, RS and BR rotary file systems in curved canals up to the apical file size to 40Material and Method: Before root canal instrumentation, pre-instrumented CBCT images of 60 MB canals of mandıbular molar teeth were taken and canals curvature angles were calculated. The samples were randomly divided into four groups (n=15),and instrumented up to the apical size 40. Changes in canal curvatures were measured after each file used in post-instrumented images. Statistical analysis was performed with the significance level set at p=0.05.Results: As the apical tip size increased root canals were straightened significantly. In the apical size 25;RS and BR(25/04) were found to straighten the canal curvatures less than PTG whereas, PTG caused less straightening than PTN and BR(25/06). In the apical size 30; RS caused less straightening whereas PTN was the most. In the apical size 40; PTG and RS caused less straightening than PTN and BR(40/02), BR(40/04) caused the most straightening. Conclusions: While all of the treatments in this study straightened the root canals as the apical size increased, and PTG and RS showed promising outcomes, the results differed depending on the taper and tip size.