The next step is to define a direction of insertion. The idea is to direct an arrow in the direction of insertion to the model.
During this step, you can either adjust the arrow or the model (switchable) minimize the undercuts present on the model.

You set up the model on the screen that you can see as much as possible of the contour (1) and then take this view as the axis to remove the undercuts (2).

If the model shows undercuts, they must be removed  (3) to the extent that they are not a problem for further processing (arithmetic operations, milling).

After each change of the insertion direction, the remaining undercuts are visualized (colour 1).

Undercuts or undercuts sites cannot be milled or may lead to a product that cannot be implanted into the patient.