I am trying to extrude the surface of a lower jaw. The surface from the outside, the inside and the top. they are selected as one object from the stl file of a mandible. when extruded in the z axis, one side is extruded (eg the outer) while the opposing side is extruded to the inside of the mandible. Is there a way to extrude relative to the original object so I end up with extrusion from both sides similar to each other.