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Laboratory Considerations for the Procera?Ü System

Laboratory Considerations for the Procera?Ü System

 In Recovering Self-Esteem with Ceramic Restorations on Anterior Teeth we discuss a case where the Procera‚ System was used. Here is an in-depth look at how the ProceraÆ System worked in that case. You can read the full article in the February 2007 issue of the Journal of Dental Technology.

In this case a 34-year-old patient has an esthetically compromised smile in terms of form, position, color change of the upper central incisors and a reverse smile line. After fully repairing the gingival tissue, the temporary prostheses were removed for the final preparation of the ProceraÆ all-ceramic crowns (Nobel Biocare). After manufacturing the stone die (type IV), in the laboratory or the dental office, the procedures for the Procera“ system are started.

1.       CAD system (scanner): Reading of the original die is made by a mechanical scanner. The scanner tip (sapphire or ruby tip, depending on scanner type) touches two contact points of the die ñ one approximately 1mm below the lower edge of the preparation, and the other at the apex of the preparation. The scanner arm rotates 360∞ and, after each full turn, the tip rises 200 mm and the scanner arm rotates another 360∫.

2.       Data processing: The information from the scanner is converted into 3D points, which faithfully reproduce the tooth preparation outline on a computer screen (Figure 1) using a specific application from the Procera‚ system which runs on the Windows operating system. With this software, the edges of the preparation, the thickness of the coping and the emergence profile can be determined. The thickness of the inner space for the bonding agent is preset at 50mm, and is therefore unchangeable. After all the details required for the coping manufacturing are determined (Figure 2), the information is sent via Internet to the production center for substructure manufacturing.

3.       Die duplication: At the substructure production centers, located in Sweden or in the United States, two dies are produced by a machining system (CAM), using the information obtained from the original die. A working die is made 15 percent to 20 percent larger than the original die. Pure aluminum oxide (99.5 percent) is compacted over this die, under a pressure of two tons, to produce the ceramic substructure (coping). The working die is produced in a larger size to compensate for the contraction during the sinterization process of compacted aluminum oxide (Al2O3). The second die is produced in the same size as the original die and its purpose is to verify final adaptation of the coping.

4.       Sinterization of the aluminum oxide: On the working die, aluminum oxide is compacted in larger quantities than those determined for manufacturing the coping. A pre-sinterization is carried out and, using a computerized mechanical machining system (CAM), the compacted powder is machined to reach its predetermined dimensions. Once the machining is completed, the coping is placed in a special sinterization oven for one hour at temperatures from 1550∞C to 1650∞C.

5.       Analysis of the coping: Together with the copy of the original size die, the coping is examined under a microscope for color, microfractures and adaptation integrity analysis. Once the examination is concluded, the coping is sent to the dental laboratory.

6.       Coping adjustment: The coping can be produced with a thickness of .4mm or .6mm. The .4mm thickness coping can be produced in white or translucent colors. The .6mm thickness coping can only be produced in the color considered traditional, which ranges between A2 and A3 on the VITA color guide.

7.       Ceramic covering: Only specific alumina ceramic is compatible with the aluminum oxide (Al2O3) coping of the Procera‚ system. The selection of the ceramic for the Al2O3 coping is based on the coefficient of thermal expansion (CTE), which must be close to the aluminum oxide CTE = 7.3X10ñ6 ∞C. The melting temperature is not a problem, since the Al2O3 melting temperature is close to 2050∞C and its sinterization occurs near 1600∞C. Dental ceramics are sinterized at much lower temperatures, from 600∞C to 1100∞C.

Currently, there are five ceramics available that can be used with the Procera‚ system:

1.     AllCeram, at 910∫C (Ducera).

2.     Cerabien, at 960∫C (Noritake).

3.     VM7, at 910∫C (Vita).

4.     AV, at 910∞C (Creation).

5.     Nobel Rondo Alumina, at 910∞C (Nobel Biocare).

There are four image capture systems. Three of them are: Scanner PROCERAÆ Model 40, Model 50 and Piccolo. Each are equipped with scanners with two-dimensional reading technology and a two-coordinate display (X and Y). Acquiring an optimal marginal adaptation greatly depends on the machining of the die. The non-adaptation rate is lower than 40 micrometers. The abutment emergence profile can be read with an inclination of up to 26∫. With these systems, it is possible to produce laminate veneers, individual copings, customized abutments and fixed bridges of up to 3 units (welded).

The fourth system, PROCERAÆ Forte, is the most advanced. It is a 3D scanner system, displaying three coordinates (X, Y and Z). It is the most sensitive to preparation, since it is possible to select among three ruby tips available and it enables the development of a greater number of units (of up to 60mm in length). The non-adaptation rate is lower than 20 micrometers. The abutment emergence profile can be read with an inclination of up to 45∫. One of the differentials during scanning is that for preparations with a higher degree of difficulty speed is changed, as well as even digitization direction. It enables scanning the bite record of the antagonist. The flexural strength of alumina coping is 680 MPa and zirconia coping is 1100 MPa.

With this system, it is possible to produce laminate veneers, individual copings, customized abutments, alumina fixed bridges of up to four units without welding (monoblock), zirconia fixed bridge of up to nine units (60 X 60 X 25 block), PIB (Procera Implant Bridge) made of titanium (total arch) and zirconia (up to eight units).

 

Read more about this case in the February 2007 issue of the Journal of Dental Technology.

Author Information
Jansen Ozaki, Dr. Waldyr Romo Jr., Dr. Eduardo Kian and Siro Kiatake