Taboo

No shoulder preparation and inclined shoulder preparation. Zirconia repair is not suitable for shoulder preparation without shoulder or shoulder preparation with inclined plane, otherwise it will form too thin edges and have the risk of fracture.

should

Gentle inclined shoulder or horizontal right angle shoulder with blunt axis neck angle. It should be prepared into the following forms: obvious inclined plane (90 °); The axis neck line angle of the shoulder is round and blunt; The cylindrical emery lathe needle with a circular tip is suitable for preparing the inclined plane, while the conical emery lathe needle with a circular edge is suitable for preparing the shaft neck line angle of the shoulder to be blunt.

Preparation amount of anterior teeth restoration

Edge width: 1.0mm, the shaft wall is round and blunt, like the lip surface (minimum radius: 0.4mm); Cutting edge width: from the perspective of aesthetics, the removal amount of cutting edge teeth is 2.0mm, and the minimum cutting edge width in the vestibular oral direction is 0.9mm, so as to ensure that the cutting device can accurately replicate the medial tissue surface of the basal crown; To form the palatal contour, it is recommended to use the palatal contour repair needle to form the lingual surface of maxillary anterior teeth and the palatal contour of canine (figure a).

Posterior tooth restoration preparation

Occlusal surface: after grinding out 1.5mm, the posterior teeth must reserve a minimum thickness of 1.0mm occlusal surface porcelain for decorative porcelain. The thickness of the basal crown is at least 0.4mm, so the occlusal surface should be ground away by 1.5mm. The degree of polymerization of axial surface is 6~8 °, and the connection between axial wall and occlusal surface should be round and blunt; To simplify the fluctuation of the occlusal surface, the diamond shaped emery needle can be used to cut and grind in a vertical direction with the long axis of the tooth, which is very suitable for the preparation of the occlusal surface; Determine the positioning path, and the taper of the corresponding axial surface of all abutments shall be at least 6 °, which is very important in the preparation of fixed bridge teeth, because in the process of digital scanning, the too steep slope will be regarded as vertical and cannot be accurately displayed in the software (Figure b).