Frequently Asked Questions
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PFM-Porcelain fused to metal is a high noble, semi-precious, and non-precious. Porcelain receives its greatest strength from compression, and it is strongest when the porcelain is 1.0 -1.5 in thickness...and decreases as the porcelain gets thicker.
Metal can be reduced to 3/10 mm which leaves more room for the opaque, body and incisal porcelain. Semi-precious has a wider application range, and is commonly used for single and large span bridges
Non-precious metal can be reduced 2/10 mm and has great opaque to metal bond, which makes it great for singles, and bridges. The disadvantages of non-precious metal is the dark oxide color, which can be hard to hide at the margin without prepping for a porcelain margin. Additionally, a few patients were found to be allergic to non-precious metals which make up the porcelain metal. Also, traditional non-precious (that contains nickel) metal should be used over titanium abutments as some studies say this metal combination can cause a galvanic reaction in the oral cavity, in which the patient can constantly taste metal...similar to biting on aluminum foil. As of 2016, we are now able to use a non-precious porcelain metal over titanium abutments that does not contain nickel...so problem solved.
EMAX- PRESSED AS ONE SOLID PIECE - (Monolithic). This is Lithium Desilicate, which is a glass ceramic composed of 1/2 dozen materials and yields a very high edge strength, which allows the lab tech or the doctor to finish the margins thinner without chipping. Emax is highly esthetic material that works very well on veneers and inlays/onlays, along with anterior crowns. some doctors are using Emax press for thickness on the occlusal, including the central groove. ( Dr. Frank Spear recommends 1.5 mm thickness on the occlusal, including the central groove and 1/3 of the occlusal axial walls, and then 1.0 1.0 mm at the margin for his Emax crown.) Emax press (monolithic) is indicated for the single units on anterior, pre-molars and some first molars (depending on prep reduction, make-up of the opposing, if bruxism is present, etc.) except the 2cd molar, and bridge with 1 pontic back to the 2cd premolar.
Emax crowns can be bonded or cemented. Emax pressed (monolithic) works very well if the shade is a basic shade from the vita shade guide....A-1 to D-3. If the desired shade is more complex or needs more than one shade, or if the prep is severely discolored, or if additional porcelain might be needed to a pontic (bridge) after continued healing in the extraction site, then an Emax/ZCAD crown (bridge) will provide better results
This product is made from a Zirconia core, or as a bridge framework, with Emax Porcelain fired onto it. It is also a very commonly used product for the above reasons, including bridge fabrication. This Zirconia core and/or framework (sub-structure) is the main reason this product can be used for long span bridges in the anterior and/or posterior.
Zirconia Crowns with a facial or buccal cutback are called a Zirconia cutback crown. If the lingual or occlusal clearance is limited, or the strength is needed for connectors and/or a demanding shade needs to be met, then this a very good application as the substructure is Zirconia and the facial or buccal is porcelain.
We offer the bruxzir and the Imair products. Both are Zirconia. the full contour Bruxzir has a mega pascal strength of 800 and the Imari full contour has a mega strength of 1450. These 2 products are used primarily for the molars and pre-molars. They are very good alternative for full crowns vs. full gold or full contour semi-precious metal crowns. because of their strength, they are also ideal for bruxzir. Full Zirconia was originally introduced as a stronger alternative to the PFM crown and PFM metal occlusion crown, with minor shading sacrifices. however, Zirconia continues to improve on its shade matching and is no longer just considered for its strength. In addition, the Zirconia Anterior Crown is milled from a more translucent zirconia puck, giving a more translucent incisal while staying as a monolithic product. If the prep is stained, or is the shade is complex (multiple colors) shade, then the zirconia anterior is not recommended.
A term used to measure the intensity of pressure (force per unit area) in multiple areas, including crowns, enamel bond strength, detin bond strength, flexural strength of metals and ceramics, etc.
Mega pascal strengths are:
- PFM - 90-160
- Emax ZCAD - 360
- Emax Full press - 400
- Bruxzir Anterior - 650
- Bruxzir Full - 800
- Imari Anterior - 1100
- Imair Full - 1450
The major reasons for remakes or crown fractures that we found were not enough occlusal tooth reduction, incorrect triple tray impressions, laboratory not designing the sub-structures correctly...in that porcelain was left unsupported, especially around the marginal ridge areas, laboratory not trimming the margins on the dies correctly.