Figure 8. The interaction between facet shape and occlusal path. The attrition facet is outlined by thick line on the '3D shape', and shown as a thick line when viewed side-on in the remainder of the figures. Three basic facet shapes are illustrated – planar, concave and convex. The four allowable combinations of occluding facets are illustrated. The movement of the lower with respect to the upper is shown at the bottom, with successive positions of the lower shown in a darker shade. All combinations other than the planar-planar combination give a curved occlusal path (dashed line). The convex-convex combination gives the highest relief between the blades.