3M ESPE Answers Your Zirconia Questions
3M ESPE Answers Your Zirconia Questions
1. What is zirconia?
Zirconia (Zr O2) is a ceramic oxide. It can be formed from a chemical reaction between zirconium metal (Zr) and oxygen (O2). The dioxide is now referred to as zirconia or more correctly by chemists as zirconium dioxide. The main crystal phases of this oxide ceramic are mono-clinic, tetragonal and cubic.
2. Is there a difference between zirconias?
Yes, there are differences between zirconia-based dental restorations. Not only are there differences in the dental grade zirconia based powders, but the performance is also influenced by the processing methods of different manufacturers and techniques applied by dental laboratories. These differences can have a major affect on clinical outcomes, such as marginal fit, translucency, strength and long-term stability.
3. Is there a difference between zirconia and zirconium?
Please see answer to question 1.
4. Does zirconia degrade when exposed in the oral fluids?
Any restoration material may experience a slight degradation in chemical performance over time. This is dependent on chewing forces of the patient and oral fluid exposure. In the case of zirconia-based restorations, a veneering layer of porcelain helps protect the zirconia material. However, the rate of degradation between different zirconia materials can differ based on chemical formulation and manufacturing processes. 3M has conducted a number of studies where 3M™ ESPE™ Lava™ Zirconia has been artificially aged under cyclic forces in a moisture environment. Dr G Fleming (University Birmingham, UK) did not find any significant decrease in the strength of Lava zirconia.
5. Does the bond strength of veneering porcelain to a zirconia substrate degrade with exposure to oral fluids?
Please see answer to question 4.
6. At what temperature during firing does zirconia begin degrading?
Performance characteristics vary greatly by the manufacturer of zirconia. Zirconia of some manufacturers may not degrade at all.
7. Is there any degradation of the zirconia substructure after repeated firing cycles?
There is no degradation of the zirconia structure after firing cycles of veneering as these temperatures are typically much lower than the zirconia sintering temperatures.
8. Zirconia substructures have high flexure strength, 900-1200 MPa, what is the flexure strength of the zirconia/porcelain system?
A typical overlay porcelain system will have a flex strength of 80-110 MPa. The flexure strength of the zirconia/porcelain system is highly dependent on the technique used by the lab technician.
9. What is the shear bond strength of the overlay ceramic to the zirconia substructure?
This is proprietary information.
10. Are there any standardized testing protocols for testing zirconia and its systems? If so, what are those protocols?
Yes. Please refer to ISO 6872, DIN-EN 843.
11. Some clinical studies have shown that there is a weakness in the overlay materials that causes fractures at the marginal ridge areas. How much strength do you really need with zirconia if the overlay materials have less strength that can result in fractures?
Porcelain veneers have been used successfully for a very long time. If applied correctly with a good load bearing design and care is taken to follow the company guidelines for application, veneers of glass (glass ceramics) with varying flex strengths will perform well. By following manufacturer’s guidelines, technicians should be reassured that overlay materials will perform as expected.
12. What is the best substructure design to provide sufficient support for the proximal overlay ceramics?
This depends on the size and shape of the coping. In general, it is strongly suggested that technicians use software tools that allow expansion of the coping for maximum porcelain support. 3M has 100+ years of manufacturing excellence and more than 25 years of zirconia research and processing. We offer world-class software and training, and with our precision CAD/CAM system labs can design restorations to meet the specific needs of any region of the mouth.
13. Have there been any studies completed regarding substructure designs? If so, what are the findings?
Yes, studies we’re aware of found that porcelain is more likely to chip if there is too much unsupported porcelain.
14. What is the chemistry of the current YTZP Zirconia used in dentistry?
Not all YTZP zirconia´s have the same chemical composition. This is dependent on the zirconia powder supplier. In addition to the quality of the powder, the particle size distribution, and additives such as binders to aid particle flow in pressing, we need to consider the powder chemistry. Aside from zirconia, the powder usually contains other oxides to stabilize the zirconia through the sintering and cool-down process. At a very basic level, the stabilizer is added to ensure that after the final sintering step, the zirconia is in the desired tetragonal crystalline state.
15. Are all zirconia blocks the same? If not, how can I differentiate a high-quality block from a low-
quality block?
No, not all zirconia blocks (or blanks) are the same. Unfortunately many of the differences, though clinically significant, cannot be seen by the naked eye. Ultimately, differences in the zirconia powder, green block pressing and the pre-sintering process will affect the final strength and long-term stability of the materials, marginal fit and translucency of the restoration. 3M has 100+ years of manufacturing excellence and more than 25 years of zirconia research and processing.
16. What type of porcelain or glass is used for the overlay materials?
Most commonly used glass/porcelains are feldspathic-based materials.
17. Do the new feldspathic veneering porcelains for zirconia offer a different (better/worse) bond
strength to zirconia substructures?
This depends on what it is being compared to.
18. Is there a standard material specification for YTZP used in dentistry?
No, there are several suppliers of zirconia that add one or more of various amounts of other oxides, such as yttrium oxide, cerium oxide and alumina. The actual chemical content of the YTZP powder is dependent on the supplier.
19. Are there any testing protocols that a laboratory can use to determine that his substructure has been processed to provide maximum strength and durability? If so, what are those protocols?
This is not possible in a dental lab. Currently there aren’t any testing protocols that a laboratory can use. In addition to chemical composition, it’s important that the lab uses a manufacturer that has clinical studies and quality control of the manufacturing process and thorough testing to substantiate material reliability.
20. What is the strength difference between pressed-to-zirconia versus traditional stacked or layered porcelain-to-zirconia?
If instructions are properly followed, strength differences should be minimal. However, there is more potential for variability in a traditional stacked or layered process.
21. Please provide any empirical and non-biased bond strength data of buildable and pressable ceramics to zirconia.
3M does not offer a pressable solution, so we do not have any comparison data.
22. Please provide any non biased data on the strength of zirconia copings/crowns cemented on NBS dies.
Unsure as to what NBS dies means.
23. Does the wiggle room of a milled restoration compromise the retention factor of a crown?
If the crown restoration is prepared with an accurate margin of fit, there is very little movement of the crown over the tooth. Once a self-adhesive cement like Rely X Unicem is used, we do not expect any movement (wriggle room) of the restoration. This is why it is important that restorations are made using a high quality CAD/CAM system supported with reproducible material processing.
24. There are rumblings from Europe that some are experiencing failures of zirconia implant abutments at the interface with the fixture. This only pertains to connections that are zirconia and not the titanium basket design. What could account for this and have there been any studies?
3M is currently launching a zirconia implant abutment so long term clinical data does not yet exist.
25. Why use zirconia – is this clinician driven or manufacturer driven?
There are a number of reasons why zirconia is used, one reason is driven by the clinicians desire to provide an improved product for the patient. For example, zirconia is used mainly to provide a huge improvement on the esthetic quality of the final restoration. Clinicians have been asking for restorations that offer better esthetics with a similar strength and fit as that provided by PFM. In addition, zirconia provides a high comfort level for the patient due to the lower temperature conductivity of the ceramic compared to metal frames (less tooth sensitivity).
Because 3M ESPE has 25 years of experience with zirconia, we are well-positioned to meet those needs for clinicians. Lava zirconia has been clinically proven to give clinicians all of the attributes they look for in a quality restoration – strength, fit and esthetics.
26. How strong is strong enough when it comes to zirconia?
It depends on the region in the mouth where the restoration is placed, chewing forces, as well as clinician and patient preference. Ultimately the zirconia substructure and porcelain need to work together to provide the ideal strength.
In general, a highly dense sintered zirconia with strong mechanical properties (flex strength and fracture toughness) allows the designer to provide a final zirconia restoration with thinner wall thicknesses. For the practitioner, this means less removal of tooth hard tissue.
27. What are the long-term, five-year clinical results of using zirconia in the anterior or posterior?
http://iadr.confex.com/iadr/pef06/techprogram/abstract_85451.htm
Reference: IADR Abstract 2006: Clinical long-term behavior of Zirconia-based bridges (LAVA): Five years results. F.P. NOTHDURFT1, P.R. ROUNTREE2, and P.R. POSPIECH1, 1Saarland University, Homburg/Saar, Germany, 2Private Practice, Munich, Germany
The purpose of this prospective study was to observe the clinical performance of zirconia posterior bridges for the replacement of molars. Since October 2000 a total of 31 bridges were placed and recalled in March 2006 after an observation time of five years. CONCLUSION: After five years of clinical service one can conclude a high performance of zirconia based posterior bridges.
28. Where do the fractures occur of the bonded zirconia restorations compared to the PFM restoration?
Zirconia restorations are typically cemented using self-adhesive cement like Rely X Unicem. The cement is bonded to zirconia through its unique chemistry. The low number of fractures that are seen are typically within the layered glass structure where the glass veneer has suffered cohesive failure, which is commonly the case with PFM as well. By following manufacturer’s guidelines, technicians should be reassured that both porcelain and cements will perform as expected.
29. What is the research on connector size/strength for multiple unit zirconia fixed restorations?
You can determine the thickness of the framework wall to fit your needs. The minimum wall thickness is 0.5 mm for bridges and posterior crowns and 0.3 mm for anterior crowns. The minimum connector cross section highly depends on the bridge position and the amount of pontics. For special indication, please contact your laboratory or milling center. 
Minimum Connector Cross Section:
3-unit bridges 7 mm2 9 mm2 
4-unit bridges 7 mm2 9/12/9 mm2 
Wall thickness Connector 
Maryland bridges 0.5 mm 7 mm2 
In-/ Onlay bridges 0.5 mm 9 mm2
30. Do the milled or sintered zirconia abutments fit the implant the best?
Please clarify.
31. How dimensionally accurate is zirconia when used as an abutment for an implant?
It depends on the scanning system, design of the abutment, milling system and the material’s properties which control shrinkage uniformity.
32. What is the research demonstrating that zirconium can transmit light?
There are many different clinical studies. Please reference: Translucency of different zirconia materials, Prof. R. Scotti, Prof. P. Baldissara, Dr. A. Llukacej, Dr. L. F. Valandro and Prof. M. A. Bottino, Academy of Dental Materials Conference, 2006. [Abstract 103].
Translucency Comparison of CAD/CAM Materials, R. ALKHUNAIZI, R. POBER, and R. GIORDANO, Boston University, MA, USA, Objective: To compare the translucency of eight core and five full-contour CAD/CAM materials using reflectance contrast ratio as a method of measurement. IADR 2008 #3154
33. How does bonding affect a zirconia restoration?
It should have no effect at all.
34. What type of bonding material should be used?
For Lava, RelyX™ Unicem Self-Adhesive Universal Resin Cement is the preferred bonding material.
35. How does blasting or grinding affect the zirconia?
Mild sand blasting of the interior restoration can help with cementation and provide a slightly stronger interaction between the zirconia and underlying tooth structure. 3M´s IFU explains this in detail. If larger particles are used (greater than 50 microns), this can have a detrimental effect on performance, for example, can cause crystallite grain phase-change from stabilized tetragonal to monoclinic.
36. Some research has shown that the cements being used for zirconia are not doing the job well. Can you elaborate?
3M ESPE has done rigorous testing on which cement performs best with Lava zirconia. Internal testing shows that RelyX Unicem performs the best.
Reference: Piwowarczyk A, Lauer H-C, Sorensen JA: In vitro shear bond strength of cementing agent to fixed prosthodontic restorative materials. J Prosthet Dent 92:265-273, 2004
C.-P. ERNST, E. ASKOY, E. STENDER, and B. WILLERSHAUSEN, Johannes Gutenberg University Mainz, Germany; In vitro retentive strength of Lava Zirconia crowns, 2006 AADR #1875 / 2006 IADR PEF #0248
37. What blasting or grinding procedures are recommended?
For Lava: SEE IFU - 2,0 bar pressure and 50 µm Aluoxyd. See the Cementation of Maryland-bridges.
38. Because of the bonding problems with cement, can composite be used?
Yes, but not because of bonding problems. This is more of a personal preference by the clinician.
39. What makes one brand of zirconia superior to another?
Final quality of the finished restoration. This includes fit and esthetics, supported by considerable in-vitro and in-vivo studies (eg. Lava). Please see answer to question 12.
40. What is an acceptable fracture rate in zirconia restorations?
Please see answer to question 41.
41. What is the average life of a zirconia restoration?
At this time, that is yet to be determined. Lava restorations have been commercially available since 2003 with little to no zirconia failures. In addition, internal lab tests show low degradation due to chewing.
42. What is the cheapest block of zirconia you’ve heard of and would you recommend its use?
For differences stated above, we would not recommend zirconia from an untrusted supplier regardless of price.
43. What is the science behind zirconia?
Please clarify exactly what you are looking for (i.e. chemical make-up,...).
44. Is anyone tracking the data about zirconia remakes?
3M ESPE has a rigorous quality control process where we capture lab and dentist remakes, however this is confidential data. In general, zirconia has performed very well as a restoration.
45. What is the strength difference between more translucent and less translucent zirconia blocks?
This is highly dependent upon the manufacturer. 3M ESPE has optimized zirconia processing to achieve high strength and high translucency.
46. How many unsupported elements (pontics) can you put side by side in a bridge using zirconia?
It depends on the manufacturer and their specifics instructions for use.
47. What are the limits of radioactivity in zirconium oxide and how can I measure that?
Described ISO 6872.
48. Are there required strength limits to different indications?
Yes. Strength needs differ by indication because of differing forces applied to the restoration.
49. Do different ZrO2 have different CTE's?
Yes, depending on the chemistry and concentration of other oxides the CTE’s for zirconia can vary somewhat over the range 9-10. The porcelains applied to zirconia should have a CTE slightly less than the zirconia coping to provide the best mechanical conditions for the layered glass. The glass veneer CTE will also depend on the manufacturer.
50. How strong is my restoration when my substructure has 1,200 Mpa and the surface ceramic has 110Mpa?
See answer to question 8.
51. Does infiltration of color, prior to the sintering process, influence the strength of the zirconia? If it does not why isn’t everybody doing it?
It greatly depends on the shading and coloring technology. 3M ESPE has intellectual property covering our unique substructure shading system. Research by S.Farsi, R.Giordano and P.Pober (Boston University, US – published at AADR 2006 (1874)) showed clearly that the 3M ESPE method for frame shading does not reduce the strength of zirconia. We know that other producers add coloring pigments to the zirconia powder prior to processing, but we are unable to comment on the influence to zirconia strength.
52. How can I increase the bond strength between ZrO2 and the cover ceramic?
By following the manufacturer’s instructions for use, and ensuring the zirconia’s compatibility with the overlay porcelain, the bond strength should perform consistently and is dependent on the design used by the lab technician.
53. What's a closed zirconia milling system and what is the benefit of an open system?
Yes there are closed zirconia milling system’s and open system’s and each has their own benefits and draw-backs. This is why 3M ESPE has chosen to operate under a selectively open system. The benefits of a selectively open system include flexibility, productivity, consistency and familiarity.
54. Does a cheaper zirconia block necessarily mean that it is not the same quality as a higher priced block?
When weighing the quality of a material, be sure you’re evaluation is based on a comprehensive list of criteria such as marginal fit, strength, esthetics and long-term stability, as well as the company behind the product.
55. With porcelain to metal, ceramic bonds to the oxide layer on the metal. What does the zirconia veneering ceramic bond to? Is it as strong as the bond of porcelain to metal?
56. Since I can not test the materials in my laboratory, how do I determine if the block has uniform micron and submicron particle size and minimal porosity to ensure strength? What is the standard for the micron and submicron particle size? Also what would the “proper chemical composition” be in order to maintain long-term stability?‚Ä®Because there aren’t any current testing protocols for a dental lab, these material properties cannot easily be measured. However, if a lab was interested it could measure block density to determine porosity. Unfortunately there is no simple answer related to the proper chemical composition. Powder manufacturers have their own oxide ingredients that they use to enhance the presence of a tetragonal crystalline structure. In general, good long term stability is related to the oxide stabilizer (in some cases yttria) that is distributed within the grain structure and not at the grain boundaries.‚Ä®‚Ä®
57. Since the experts had a range of answers regarding the acceptable fracture rate for zirconia restorations, (a) where would a laboratory find this information from a block manufacturer, and (b) what is the median within the range of answers?
For acceptable fracture rates for zirconia restorations we strongly recommend that various clinical trials be reviewed that compare different materials and their proven survival rates. Typically, materials with high flex strength and toughness (eg. zirconia) provide an important safety range between forces encountered in the mouth and the higher forces that zirconia can withstand. The median range is difficult to define because not all zirconias are the same. 


58. What is the average lifespan of a zirconia restorations? Our experts said that there hasn’t been enough clinical trails to determine – when should we expect to know?‚Ä®3M ESPE has a six year trial running with Lava zirconia and no reported failures as of yet.
‚Ä®‚Ä®59. What would be considered “sufficient support for the overlay porcelain and the marginal ridge area”?
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60. How do you avoid the fracturers that are caused by “internal stress caused by the heating and cooling of the zirconia and porcelain”?‚Ä®3M ESPE avoids these type of fractures by matching the CTE of the porcelain to that of the underlying zirconia core. ‚Ä®‚Ä®
61. Since the experts answered that there is no standard material specification for YTZP is there a minimum or maximum amount for the necessary components (i.e. before the fillers)?
Because each power manufacturer has their own standard material specifications, it is difficult to provide a minimum or maximum amount. 


62. How/where can a laboratory obtain the manufacturer’s durability information‚Ä®3M ESPE has several independent technical papers concerning Lava data that have been published. These are available online at HYPERLINK "http://www.3MESPE.com/Lava" www.3MESPE.com/Lava. In addition, 3M has information regarding some of the in-vitro and in-vivo tests it has conducted on the website as well.‚Ä®‚Ä®
63. Where can a laboratory obtain the CTE information on the blocks?
3M ESPE has this information listed for both Lava Zirconia and Lava Ceram and is available through their product data sheets.
