the vertical dimension of the face when the teeth or occlusion rims are in contact in centric occlusion; decrease in occlusal vertical dimension may result from modification of tooth form by attrition or grinding, drifting of teeth, or, in edentulous patients, by resorption of residual ridges; increase may result from modifications of tooth form, tooth position, height of occlusion rims, rebasing or relining, or occlusal splints.