The principles of abutment preparation for zirconia restorations are the same as for known all-ceramic restorations. Therefore, zirconia restorations are not suitable for preparation without an abutment or for preparation with a beveled abutment. Both methods create too thin margins with a risk of fracture. It is preferable to have a rounded, gently beveled shoulder or a horizontal, right-angle shoulder with a rounded axis-neckline angle. The shoulders should be prepared in the following forms: 1. Clearly beveled (90 degrees) 2. Rounded axial-neckline angles with rounded tips for cylindrical diamond needles are suitable for beveling, while tapered diamond needles with rounded edges are suitable for preparing shoulders with rounded uranium-neckline angles. Basic principles: The preparation of anterior restorations is based on the basic preparation principles as described previously. The circumferential margin should be prepared with a width of 1.0 mm, while the axial wall must be rounded and blunt, just like the labial surface (minimum radius: 0.4 mm) Width of the cutting edge: From an aesthetic point of view, the cutting edge should be removed to 2.0 mm, and the minimum width of the cutting edge in the vestibular-oral direction should be 0.9 mm, in order to ensure that the cutting device can precisely reproduce the medial tissue surface of the basal crown. Forming the palatal profile: It is recommended to use the palatal profile trimming turning pin shown to form the palatal profile of the lingual and cuspid surfaces of the maxillary anterior teeth. Posterior restorations The occlusal surface is abraded by 1.5 mm. For trimmed trichomes in the posterior region a minimum thickness of 1.0 mm of the occlusal porcelain layer must be reserved for the veneer porcelain. The thickness of the basal crown is at least 0.4 mm, so the occlusal surface should be abraded by 1.5 mm. the relative axial surface convergence angle should be 6-8°, and the connection between the axial wall and the occlusal surface should be rounded. Simplification of the degree of undulation of the occlusal surface The degree of undulation of the occlusal surface should be simplified. An open angle of 120-140° on the occlusal surface will ensure a precise replication of the inner crown surface during the cutting process and thus a perfect fit. The use of a long diamond-shaped diamond turning pin with a perpendicular cut to the long axis of the tooth is well suited for preparing the occlusal surface. Determining the orientation of the insertion When determining the orientation of the insertion, it is important that all bridge abutments have a taper of at least 6° in the corresponding axial plane, especially for fixed bridges. Too steep a bevel during the scan will be considered vertical and will not be accurately displayed in the software.