extrusion of the face of a 3D model 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.
Press Alt+E then select Extrude along normals.