Preparation of all ceramic teeth
Preparation of porcelain crowns and teeth
Before preparation, the lips and tongue surface of the prepared teeth shall be covered with silicone rubber - Preparation reference. The scope of silicone rubber reference shall at least include the prepared teeth and one adjacent tooth on both sides
Cut the silicone rubber along the cutting edge of the teeth to prepare the lip reference, divide the lip side part into the tangential half and the gingival half, discard the tangential half, only keep the lip and gingival part as the reference, and check the consistency with the tooth surface in the reset entrance. If the porcelain crown will obviously change the original lip shape, the silicone rubber reference can be prepared on the diagnostic wax model with the expected tooth shape
According to the sagittal line of the prepared teeth, the hardened silicone rubber impression is cut into two parts from the lip end to the tongue end of the gingiva. This reference can better indicate the comprehensive preparation along the midline of the preparation, including the cutting edge and tongue surface, but it can not indicate the preparation near and far middle lip surface. The surgeon can decide which reference to use according to his own needs. If time is sufficient, two kinds of silicone rubber reference can be prepared
Preparation of deep groove with flat cone carborundum
It has been many years since the preparation of porcelain crowns. When cutting the molar with a known diameter of the lathe needle, the depth of the grinding can be obtained by comparing with the adjacent uncut enamel. Make the flat tapered needle parallel to the gingival segment of the lip.
Use the needle body to cut into the center of the lip in the near and far middle direction, and make the needle parallel to the gingival segment of the lip. The trocar needle must be cut into the human teeth in full diameter or even deeper. Although the marginal finish line will eventually be flush with or slightly below the gingival margin, the tip of the needle should remain slightly above the gingival margin. Repeat the above process twice, and prepare the same trench in the center between the midsagittal trench and the two adjacent line angles
Then make the needle parallel to the tangent section of the lip
Prepare 2 or more longitudinal grooves in the tangential section of the lip, and the groove depth shall not reach the full diameter of the needle. The longitudinal sulcus gradually disappeared at the level near the middle of the labial surface, where the curvature of the tooth surface was also the largest
Cut end preparation: use flat cone emery lathe needle
At least 2 grooves with a depth of 2.0 mm were prepared on the cutting edge. When cutting, the direction of the needle should be the same as that of the lip and tongue when the cutting edge is not cut
The preparation depth of cutting edge described in the literature ranges from 10 mm, 15 mm to 20 mm. In order to get enough aesthetic effect, it is better to cut off 20 mm marginal tissue to reach the depth of the groove. Too much grinding of the cutting edge will lead to too much stress on the lip surface, which will lead to the half moon shaped porcelain crack mentioned before. The prepared section should be parallel to the original cutting edge, and more importantly, perpendicular to the direction of chewing force. This is about 45. The bevel of the cutting tongue of can cause excessive stress at the shoulder
Preparation of the tangential part of the lip: use the flat cone emery lathe needle
The preparation of lip surface should be divided into two planes. In this way, the preparation of lip cutting angle can be carried out as far as possible in the direction of the tongue to achieve a satisfactory aesthetic effect, and at the same time, it will not hurt the pulp or make the lip axis wall excessively inclined. All the residual tooth tissues between the deep grooves of the lip section were removed by the flat cone emery lathe needle.
Preparation of the gingival part of the labial surface: use the flat head conical carborundum needle
Continue to prepare the lip of gingival part with the same needle. At first, the complete line of the shoulder edge was roughly prepared, and the polymerization angle between the axial surface of the lip and the longitudinal wall of the tongue was formed as small as possible. The thickness of the teeth on the lip should be about 1.0mm
Extend the lip preparation to the adjacent surface and prepare the shoulder. At this time, the shoulder can be extended to the tongue surface, but the sequence should be carried out after the preparation of lingual protrusion is completed, which can make the distinction between the vertical lingual wall preparation surface and concave lingual protrusion preparation surface more obvious
Prepare to use small wheel emery lathe needle on tongue surface
In order to fully prepare the tongue protrusion, a spherical carborundum lathe needle with a diameter greater than 1.4 mm of the shaft handle is used to grind several fixed depth pits on the tongue surface, so that the lathe needle can penetrate into the tooth until the shaft handle contacts with the glaze surface, so that the pit depth is 0.7 mm. Generally, three such depth references should be prepared. The thickness of o.5-1.0mm should be removed from the surface of the tongue
The convex area of the tongue surface is prepared to be concave with a small wheel shaped turning needle. Because most teeth need to prepare as much space as possible in the middle of the tongue, concave grinding can make this part get the most possible preparation. At the same time, the curved surface formed by tongue protrusion preparation can be divided into two parts: horizontal section and vertical section, so that the retention force and resistance of the preparation are strengthened. In addition, the concave preparation of the tongue surface can reduce the stress, while the inclined preparation can produce greater tensile stress. In the preparation of canine teeth, the thin lingual crest should be prepared; the protuberance of the kidney and tongue should be divided into two concave surfaces to increase the anti rotation force of the prosthesis
Preparation of tongue axis surface: use flat cone emery lathe needle
Prepare the vertical tongue shaft wall with the flat tapered carborundum lathe needle used for preparing other shaft surfaces. 1.0 mm thick tooth should be removed here. In preparation, the polymerization angle between the lingual wall and the gingival segment of the labial surface should be kept as small as possible, because the excessive preparation cone will lead to insufficient resistance, increase of stress and even fracture of the porcelain crown
Carefully connect each axis surface with the adjacent axis surface (in the figure, the tongue axis surface and the far middle adjacent axis surface). If the axial connections are not smooth, the ceramic crowns will become thin and easy to crack in these transition areas. The square preparation with edges and corners may be very stable, but the blunt preparation will make the prosthesis have high strength
No. 171 tungsten steel lathe needle is used for shaft surface finishing
Use 171 cone-shaped non die split drill to level all axial surfaces. Although it is not easy to scratch the tooth surface by using the lengthened and thickened special lathe needle, if it is used properly, the No
Polish the shaft surface, and pay attention to remove the residual corner of the line corner. Pay special attention not to form the undercut near the gingival shoulder
Use the conical crack to drill any obvious corner on the blunt preparation surface, and the residual sharp line angle can cause the porcelain crack
Shoulder top finish: use 957 needle
Finishing shoulder
Shoulders with blunt internal corners are different from those shown in figure 15-28. The acute angle of the shoulder can not be copied on the porcelain prosthesis, so it has poor supporting effect on the prosthesis. On the other hand, shoulder less crowns often lead to poor edge fit and excessive shape. The absence of the adjacent shoulder will increase the tension on the proximal and distal surfaces of the porcelain crowns.
The width of the shoulder is generally considered to be 1.0 mm. Although it is recommended that the shoulder width be between 0.5mm and 1.0mm, the shoulder preparation narrower than 1.0mm is only suitable for the restoration of over small teeth. In order to protect the pulp, such teeth can only bear the minimum preparation.
First, use flat head emery lathe needle for shoulder preparation, and then use end blade emery lathe needle with beveled edge, as introduced by gldstein. On the one hand, it can reduce the soft tissue damage, on the other hand, it can prepare the "up and down undulation" shape along the shoulder in the gingival cutting direction from the lip surface to the adjacent surface and then to the tongue surface, without scratching the shoulder. The shoulder table can also be further refined with tungsten steel turning needle with slightly inclined edge, and the cutting teeth can be prevented from digging in the high part of shoulder table.
The edge finish line of porcelain crowns is usually in the form of a smooth shoulder. The shoulder should be perpendicular to the direction of masticatory force or the long axis of the teeth, and the angle between the shoulder and the external surface of the teeth should be approximately at right angles. Although the preparation line is sometimes in the form of concave shoulder, the angle between the preparation line and the tooth surface is obtuse, and the increase of this angle can lead to the corresponding increase of stress
In order to ensure that the prepared shoulder is smooth and consistent, the surface of the shoulder is leveled with enamel chisel. At the same time, its width is detected. Do not make sharp internal angle at the junction of shoulder and tooth shaft wall. Only on the basis of smooth shoulder preparation, can we make porcelain crowns with good edge suitability
During the preparation, the horizontal lip of silicone rubber was placed on the tooth surface, and the preparation degree of the lip gingival cutting was tested
The overall condition of tooth preparation can be checked by reference to the midsagittal plane. It can be seen that the quality of tooth preparation in all parts is basically the same
Maxillary central incisors prepared with porcelain crowns
A lingual view of the same preparation. Note that there is no sharp line angle on the tongue and section
The structural characteristics and function of the preparation of anterior teeth with porcelain crowns
Preparation of cast porcelain crown and teeth
The buccal and lingual surfaces of posterior teeth were covered with silicone rubber. Take out the polymerized silicone rubber block, cut vertically along the midline of the preparation teeth near, far and middle adjacent to the tooth tip, then cut horizontally on the buccal and lingual surfaces of the teeth and intersect with the vertical section. The buccal lingual composite reference can be made by removing the free silicone segment. This silicone rubber reference can accurately indicate the preparation degree of buccal and lingual surfaces of teeth
Making of midsagittal reference. In addition, take the silicone rubber ball to cover the prepared teeth. Take out the mouth after hardening. Cut the silicone rubber block along the vertical midline of a single tooth or the midline of the near midpoint of the molar, that is, to make the midsagittal reference. It can be used alone or in combination with buccal lingual composite reference to check tooth preparation
The completed midsagittal plane refers to the near view pattern. To facilitate observation, adjacent teeth have been removed. It shows that the silicone rubber block closely matches the midline of the prepared front teeth
Preparation of (occlusal) surface: use a large round head cone-shaped carborundum lathe needle
To prepare a deep groove on the occlusal surface with a large cone-shaped carborundum lathe needle. The setting position should include each trigonal ridge and the main developmental sulcus in the proximal and distal sides of the trigonal ridge
Use a 1.5mm or 2.0mm wide enamel chisel to detect the depth of the deep groove. Finally, the occlusal surface should be reduced by 1.5-2.0 mm
The residual (occlusal) surface of the deep groove was removed by using a large conical emery lathe needle. We should pay attention to the preparation according to the geometric slope shape of the occlusal surface, so as to ensure that the porcelain prosthesis can obtain enough support thickness, and the prepared teeth can maintain a certain height at the same time
Preparation of functional sharp bevel: use the large round head tapered carborundum lathe needle
In order to prepare the functional sharp bevel, the deep groove is first prepared with a large round head carborundum lathe needle. The deep groove is set on the buccal slope of the buccal tip
Prepare the functional cusp to ensure that the thickness of the ceramic restoration on the buccal cusp and buccal inclined plane is the same as that on the lingual inclined plane. The functional cusp of maxillary teeth should be prepared on the cusp of the tongue. The direction of the functional cusp should be approximately parallel to the cusp of the opposite teeth
The degree of preparation of occlusal surface can also be judged by gripping a 1.5mm-thick flexible clearance Guide: in the case of patients gripping teeth, if the indicator strip can be pulled out from buccal side, it indicates that the space of preparation of occlusal surface has reached 1.5mm, if not, it indicates that further preparation is needed. Observation of the patient's wax bite record can help identify areas that require additional grinding
Preparation of buccal and lingual axial surfaces: use the large round head conical carborundum lathe needle
In order to ensure adequate preparation, a deep groove is prepared on the cheek and tongue surface. In order to ensure that the thickness of the porcelain crown at the edge of the gingival margin is 1.0 mm, the axial preparation of the middle part of the crown must be 1.5 mm or less than 1.5 mm. The preparation of the functional cusp and the furcation of the cast ceramic crown can remove more tooth tissues than most other preparations. The functional cusp can also divide the buccal preparation area into two planes
Remove the residual tooth tissue in the deep groove. Axial preparation should be extended to buccal abduction space as far as possible, and the adjacent teeth should not be injured at the same time. Preparation time