What’s the reason of the wax shrinkage upon fabrication of the bridge/ crown
Pontics are classified according to their surface toward the ridge of the missing tooth,..........
A-Both statment are true
b- both are false
c-1st is true ,2nd is false
d-1st false , 2nd true
-----------------------------
The Brånemark dental implant has undergone a gradual development with regard to both the body of the implant itself and the parts that connect it to the prosthesis1-4. The first pieces designed for full arch restorations included small gold screws, which meant the dentist could remove the restoration. However, these pieces had a limited adaptability for the restoration of single teeth.
Unless the placement of the implant was ideal, attempts to achieve esthetic restorations often required the placement of a saddle. Due to repeated loosening of the gold screws with forces exceeding the screw retention potential, the implant required more maintenance from the dentist. Several models of screws and abutments, such as the UCLA5.6 abutment and the DIA7.8 anatomical abutment, have been launched with varying degrees of success. These components could indeed be stabilized mechanically during the tensioning of the screws and pillars to avoid damaging the bone interface as suggested by Brånemark.
NobelPharma (now Nobel Biocare, Gothenburg, Sweden) launched the CeraOne pillar in 1990 for single implant restorations incorporating the capacity of the external counter-torque and improving the design of the gold screw9,10. With this development, the priority has gone from retention by means of a screw to cementing. Despite the persistence of major defects, this was a welcome improvement. More experienced clinicians often preferred to use a pillar made to measure to maintain cemented restoration11-13. A considerable expansion of the emergence profile of restoration was often required to ensure the creation and maintenance of adequate soft tissue contours around the restoration.
In 1990, NobelPharma designed the Procera system using Computer Assisted Design and Manufacturing (CAD / CAM) technology 14-16. The implant abutments created with this system were launched in 1998. These abutments were designed to allow the use of an internal counter-torque to protect the bone interface while the abutment is tight. The restorative dentist could now modify the external face as required. The modified model of the screw makes it easier to insert the screw head. The counter-torque has been improved to suit different implant sizes and lengths of abutments. Thanks to these characteristics, traditional bridge and crown techniques can be used for the manufacture of the restoration and this restoration is recoverable when a suitable cement is used on a preparation with adequate undercut.
This article reviews the techniques currently available to create a custom Procera pillar and outlines the relevant applications of this type of pillar. Particular attention is paid to the complications associated with the use of this technique.
Technical:
1- A fingerprint is taken to record the position of the implant in three dimensions. Non-repositionable transfers are used to create a master model requiring the use of an imprint technique with windowed individual trays.
2- The analog is repositioned on the transfer, and a soft tissue model is created and articulated.
3- A lab technician then proceeds in one of two ways.
CAD / CAM Process Procera:
A screw with a graduated rod to determine the height of the abutment is placed in the replica of the implant on the master model to allow the technician to visually align the image of the computer with the master model. The software allows you to change the viewing angle, height, width and depth of the abutment. The marginal margin of the gingiva can be modified according to the height, the width and the angle of emergence. The software includes a limiting device preventing the operator from designing an inadequate pillar. Represented on the screen in the form of a wire mesh, the completed pillar model is electronically transmitted to the production house where the pillar is milled into a solid titanium block. The implant is delivered to the technician within four days. The laboratory stores the wire mesh model of each of the implant abutments in a data file so that it can be used again and used as a starting point for future cases.
Although it is faster to design the abutment than to shape it with wax (as described below), this technique has several disadvantages:
- It is impossible to retransmit exactly from the master model to the computer the position of the implant, and a last milling of the titanium abutment, either in the laboratory or at the dentist, is usually necessary.
- The Procera pillars of CAD / CAM should be designed with four cross-sectional areas (mesial, distal, buccal and lingual) to give them the shape of a circle or a modified square. Since some natural teeth have triangular roots in cross-section (eg, the upper central incisors), it is possible that the Procera abutment needs to be further modified.
- As the shape of the abutment can not be checked by the technician or the dentist before its manufacture, rework is sometimes necessary.
- When a pillar for the construction of multiple units is misaligned, all pillars must be modified to ensure the insertion of the bridge.
The CAD / CAM software can only be used to design abutments for Nobel Biocare regular platform (PR) implants (3.75 mm in diameter). The wax modeling kit, which can also be used for PR implants, should be used for narrow and wide platform implants.
Rotation of single crowns is prevented, especially when the abutment is cylindrical, creating an upward and downward movement along the soft tissue contours on the gingival margin. An oral or labial alignment groove must be incorporated into the abutment to facilitate the proper positioning of the restoration and create a groove for excess cement to flow.
Custom-made and waxed pillar with Procera scanning technique:
A machined base cylinder is screwed to the analog of the implant and wax is applied to shape the abutment with all its contours. The shape and position of the wax-coated and reduced pillar are checked as is the amount of space available for restoration. The gingival line usually follows the soft tissue contours, from the oral or lingual point to the proximal point, as it would do on the preparation of a conventional crown. The resulting model is removed from the master model and positioned in the Procera scanner to digitize the wax-coated abutment, resulting in a wire mesh model that is revised on the screen and then, as with CAD / CAM technology, emailed to the production house.
4- Often, the pillar must be modified before the construction of the temporary restoration. The pillar and the provisional restoration are delivered to the dentist or dentist restorer. The abutment is inserted at its proper location on the implant verified visually or radiographically. While the abutment screw is tightened, a counter-torque is used to prevent the application of excessive forces to the bone interface. The access port for the screw is filled with a small cotton swab, which is placed on the head of the screw, and the rest of the chamber is filled with a soft cured composite resin like the Clip 97 ( VOCO, Cuxhaven, Germany).
5- The final contours must be examined carefully to ensure that the temporary restoration is fully seated. Occlusion is evaluated and adjusted as needed to prevent initial contact and to eliminate lateral and propulsion contacts. The temporary restoration is then cemented with temporary cement such as Temp-Bond (Kerr Manufacturing Company, Romulus, MI).
6- After sufficient soft tissue maturation, the temporary restoration is removed and a retractor wire is placed to obtain a final impression using standard bridge and crown impression techniques. In some cases, when there is excessive removal of soft tissue, a modification of the finish line of the metal abutment may be desirable. Jemt reported soft tissue hypertrophy up to two years after implant placement. Care must be taken to avoid placing the implant too much under the marginal margin of the gum, which may greatly complicate the removal of the cement.
7- The final restoration is inserted, adjusted and positioned carefully with a temporary or permanent cement. Annual reassessments are recommended to maintain optimal loading of the implant.
Discussion:
The Procera technique for creating custom implant abutments offers significant improvements over previous implant-based restoration methods. In all machining techniques, tolerance margins are set between the various parts in order to ensure complete support of the abutment on the head of the implant and to provide a good adaptation to the counter-torque device. A slight rotation or slight movement of the pillar is usually noticed during tightening. As Binon and McHugh explain, this is the movement of the hexagonal interfaces during preloading of the screw. Because of this movement, the final restoration must be constructed from a new final footprint of the completed pier, especially when multiple pillars are used.
Sometimes, the emergence profile of the abutment can give outlines that encroach on the proximal bone and prevent complete abutment support. The position of the abutment must be carefully examined by radiography before the screw is tightened. It is suggested, it is suggested, a horizontal space of at least 2 mm between the pillars or between a pillar and the adjacent tooth to be able to keep the tissues healthy enough. In the absence of this space after the installation of the final abutment, the clinician must modify it in the cabinet and adjust the provisional restoration.
The location of the finishing lines should be discussed in detail with the dental technician. For a surgical impression technique, the finishing lines should be approximate, since the gingival tissues are repelled by the implant. In the buccal position, position lines 1 mm below the gingival crest of adjacent teeth are usually sufficient. Lingual margins may be equigingival to adjacent teeth. The locations of the interdental margins should be corrugated according to the crown below the mesial and distal planes to be approximately 0.75 to 1.00 mm below the gingiva.
As much time as possible should be allowed for the maturation of the gum (at least six weeks to three months or more) before taking a definitive impression of the abutment. However, the gingival finishing line and soft tissue may need to be modified.
conclusions:
The Procera Abutment is the advanced implant abutment for restorations supported by single or multiple Brånemark implants. The traditional cementing procedure minimizes the stress applied to multi-piece restorations and, if desired, lateral attachment screws can be used to enhance retention.
Problems with parts inventory, incorrect pillar selection, poor tissue contours and angulation can be avoided or greatly reduced. And problems with dissimilar metals and interfaces between machined and cast parts are eliminated.
The implants can be placed in their ideal positions, the change in the coronal angulation of the restoration being obtained by means of the pillar made to measure.
The application of this technology requires experience with pre-machined implant parts to maintain high standards of excellence in restorations.
The operator must be experienced in taking direct impressions of the implant itself and not only the subgingival abutment.
It is possible that there are complications when the cement is not removed completely.
With the development of the tailor-made abutment, implant dentistry has returned to its starting point, and the complex multitude of parts has been greatly reduced. Because the process of restoring dental implants is now closer to the one used to restore natural teeth, we can expect more use of dental implants to replace missing teeth in the future.
