Note for interpreting the message above: SE = Segment Editor
There are many ways to create “smoother” cuts:
You can create straight cut edges if you select circle or rectangle mode in Scissors effect.
You can apply local smoothing (e.g., opening with kernel size of 3mm).
You can create a cutout shape using Baffle Planner module (in SlicerHeart extension) and then use that shape to cut out from the model using Combine models module (in Sandbox extension).
You can use Dynamic Modeler module’s “ROI Cut” tool to cut straight edges with a resizable, rotatable, rectangular ROI
Do you have any specific concern (anticipating issues with sterilization, difficulty 3D printing…) or just aesthetics? Is there any requirement that you would like to fulfill?