Zirconia Crowns and Bridges

Zirconia is rapidly becoming the material of choice for dental crowns. It is a remarkably robust material able to withstand the wear and tear of every day use. Zirconia is 100% biocompatible and because the body does not reject zirconia, this material is the preferred modern material for medical applications. Unlike amalgams and metal alloys used in the dentistry in the past, the body accepts zirconia as a natural material, so you don't have to worry about allergies or adverse reactions Zirconia also has a translucency that is very similar to a natural tooth, in the past, most crowns and bridges have been Porcelain-Fused-to-Metal (PFM). These restorations, built on a dark metal alloy base, tend to look opaque and monochromatic, with a darker grayness at the gum line. All ceramic dental restorations made with Zirconia match the appearance and translucency of natural teeth, this means that Zirconia will produce the best aesthetic effect, which is particular important for all anterior restorations. Due to the strength of Zirconia, we can now make crowns and bridgework without needed to add metal and so these new crowns are virtually impossible to distinguish from 'real teeth' - except of course we can control their size, shape and colour and thereby provide a perfect, yet natural looking smile.

What makes our Zirconia the best

All our Zirconia crowns and bridges are made using the latest in CAM/CAM technology to give you the best in strength and asthetics. Some problems that occurred with early zirconia crowns was fractures of the porcelain, this was caused by insufficient support of the overlay porcelain in the marginal ridge area. Porcelain is much stronger in compression that in is in tension and may shear if the marginal ridge area isn't built out with sufficient zirconia. All our frameworks are designed by our skilled technicians using the latest software in such a way as to provide support for porcelain at the marginal ridge, so there is no more than 2mm of unsupported porcelain, you won't see as many fractures and these crowns can offer a very strong and asthetic restoration that will last for many years. Zirconia is now becoming one of the most popular restoration materials.

What are the long-term clinical results of using zirconia in the anterior or posterior?

Prof. Trevor Burke (University of Birmingham Dental School, UK) and Castle Ceramics Dental Laboratory (Tamworth UK) have Five-Year evaluation of zirconia – based bridges in general practice: - click here to download a PDF.

What is zirconia?

Zirconia is another name for zirconium dioxide (ZrO2), an oxide of the metal zirconium.

Does zirconia ceramic degrade in strength intraorally in 5-10 years?

Yes, all-ceramic materials degrade in strength over time - some more than others. Zirconia ceramic has an initial flexural strength of over 1200 MPa, so even if it degrades 5-10% or more, it is still significantly stronger than other ceramics.

Does it take longer to remove a zirconia crown with a bur compared to a PFM crown?

Fine diamond burs can cut thru a zirconia crown just as fast as a PFM crown.

Does shading or coloring zirconia ceramic reduce the strength as compared to the uncolored zircona?

Weakening of coloured zirconia ceramic copings has not been observed.

Is the fit of crowns and bridges based on zirconia copings as good as that of PFM crowns and bridges?

Yes, the marginal fit of crowns and bridges fabricated from zirconia copings can be as good or better than PFM crowns and bridges.

Is the fit of a zirconia coping important since the zirconia ceramic is so strong?

The thicker the cement the weaker the all-ceramic restoration. Cements are not as rigid as zirconia ceramic, so a thicker cement layer will cause more flexural deformation of a ceramic core, increasing the potential for fracture.

Does silane treatment improve the bond strength of a resin cement to a zirconia coping?

No, but the use of Rocatec/Cojet (3M ESPE) does. Silica particles are embedded into the surface of zirconia and then silanated. This treatment can increase the bond strength of a resin cement to a zirconia coping.

Is it ok to grind on a zirconia coping without water spray?

Water spray is necessary when grinding on a zirconia ceramic coping. The white light or hot spot you see between a diamond and a zirconia ceramic has been measured at 1500 ºC. If the temperature of zirconia ceramic rises above 1000 ºC, a phase change can occur that will induce cracking and surface defects, lowering the strength of the coping.

Is preparation design of a zirconia coping important since the zirconia ceramic is so strong?

Preparation design of the zirconia coping is very important. The thickness of unsupported porcelain should not exceed 2 mm. The zirconia coping should be as thick as needed to avoid unsupported porcelain.

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?

The fractures are most likely caused by insufficient support of the overlay porcelain in the marginal ridge area. Porcelain is much stronger in compression that in is in tension and shear. If the marginal ridge area isn’t built out with sufficient zirconia, it will leave the porcelain in that area unsupported and vulnerable to tensile and shear forces. If the framework is designed in such a way as to provide support for porcelain at the marginal ridge, you won’t see as many fractures. Another cause of fracture is internal stress caused by the heating and cooling of the zirconia and porcelain during firing. It is important you find a lab that knows how to work with zirconia - the handling and firing cycles are completely different compared to P.F.M.

What is the best substructure design to provide sufficient support for the proximal overlay ceramics?

The overlay porcelain should not be thicker than 1.5 to 2 mm depending on the location and should be adequately supported by the zirconia coping. See Fig. 1 ,2 and 3 above for an example how we do this.

What type of porcelain is used for the overlay materials for zirconia copings?

There are a number of zirconia-optimized porcelain systems available. At Castle Ceramics we use Vita VM9 layering porcelain and Emax Pressable Fluorapatite Porcelain onto zirconia.

Do the new feldspathic veneering porcelains for zirconia offer a different (better/worse) bond strength to zirconia substructures?

The Vita VM9 veneering porcelains Castle Ceramics use for zirconia are formulated to match the coefficient of thermal expansion of the zirconia and to bond to the zirconia coping. Vita VM9 has a coefficient of thermal expansion (CTE) of about 10 which is ideal for fusing onto Zirconia.

Are there any testing protocols that a dental laboratory can use to determine that his substructure has been processed to provide maximum strength and durability? If so, what are those protocols?

Flexural properties of sintered zirconia specimens can be measured but this test is destructive in nature. It is crucial that the dental laboratory work with a reputable milling center. We use Bristol Crown Milling Centre.

What is the difference in strength between pressed-porcelain-to-zirconia versus traditional stacked or layered porcelain-to-zirconia?

Both techniques should produce adequate strength if the heating and cooling temperatures encountered during processing do not create adverse thermal gradients that cause residual stresses.

Does the wiggle room of a milled restoration compromise the retention of a crown?

The better the fit, the better the retention. Highly retentive zirconia-based crowns can be cemented, whereas poorly fitting crowns should be bonded to tooth structure. Use a self-adhesive resin cement ( Rely x Unicem by 3M Espe ) or bonded resin cement ( Vitique by D.M.G. ) for cases with poor retention.

Why use zirconia – is this clinician driven or manufacturer driven?

The use of zirconia copings is driven by improved aesthetics, biocompatibility, and durability as compared to PFM.

How strong is strong enough when it comes to zirconia?

It is important that zirconia-based restorations be stronger initially than PFM due to a small amount of potential deterioration of properties intraorally over time. A zirconia with a flexural strength of 800 MPa should be adequate.

Where do the fractures of the bonded zirconia restorations compared to the PFM restoration occur?

Failures of zirconia-based restorations typically involve chipping or delaminating of the overlaid porcelain. These failures can be minimized by proper design of the zirconia coping to properly support the overlaid or pressed ceramic.

What is the connector size for multiple-unit zirconia fixed restorations?

A cross section of 9 mm2 is recommended.

How does bonding affect a zirconia restoration?

Bonding of zirconia-based restorations can improve retention when additional strength is needed. Use self-adhesive resin cements ( Rely Unicem by 3M ESPE )or dual cure resin cements ( Variolink by Ivoclar, Nexus by Kerrs, Vitique by D.M.G, Panavia by Kuraray ).

How does blasting or grinding affect the zirconia?

Sand blasting improves the bond strength of resin cements to the intaglio surface of zirconia-based restorations as does grinding. However, excessive grinding can cause a crystalline transformation of zirconia that can compromise its strength. Water spray during grinding is recommended.

With porcelain-fused-to-metal systems, ceramic bonds to the oxide layer on the metal. What does the zirconia veneering ceramic bond to?

Usually the overlaid porcelain bonds to a compatible porcelain wash material that is applied to the zirconia first.

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Zirconia Crowns and Bridges

What makes our Zirconia the best

What are the long-term clinical results of using zirconia in the anterior or posterior?

Prof. Trevor Burke (University of Birmingham Dental School, UK) and Castle Ceramics Dental Laboratory (Tamworth UK) have Five-Year evaluation of zirconia – based bridges in general practice: - click here to download a PDF.

What is zirconia?

Zirconia is another name for zirconium dioxide (ZrO2), an oxide of the metal zirconium.

Does zirconia ceramic degrade in strength intraorally in 5-10 years?

Yes, all-ceramic materials degrade in strength over time - some more than others. Zirconia ceramic has an initial flexural strength of over 1200 MPa, so even if it degrades 5-10% or more, it is still significantly stronger than other ceramics.

Does it take longer to remove a zirconia crown with a bur compared to a PFM crown?

Fine diamond burs can cut thru a zirconia crown just as fast as a PFM crown.

Does shading or coloring zirconia ceramic reduce the strength as compared to the uncolored zircona?

Weakening of coloured zirconia ceramic copings has not been observed.

Is the fit of crowns and bridges based on zirconia copings as good as that of PFM crowns and bridges?

Yes, the marginal fit of crowns and bridges fabricated from zirconia copings can be as good or better than PFM crowns and bridges.

Is the fit of a zirconia coping important since the zirconia ceramic is so strong?

The thicker the cement the weaker the all-ceramic restoration. Cements are not as rigid as zirconia ceramic, so a thicker cement layer will cause more flexural deformation of a ceramic core, increasing the potential for fracture.

Does silane treatment improve the bond strength of a resin cement to a zirconia coping?

No, but the use of Rocatec/Cojet (3M ESPE) does. Silica particles are embedded into the surface of zirconia and then silanated. This treatment can increase the bond strength of a resin cement to a zirconia coping.

Is it ok to grind on a zirconia coping without water spray?

Is preparation design of a zirconia coping important since the zirconia ceramic is so strong?

Preparation design of the zirconia coping is very important. The thickness of unsupported porcelain should not exceed 2 mm. The zirconia coping should be as thick as needed to avoid unsupported porcelain.

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?

What is the best substructure design to provide sufficient support for the proximal overlay ceramics?

The overlay porcelain should not be thicker than 1.5 to 2 mm depending on the location and should be adequately supported by the zirconia coping. See Fig. 1 ,2 and 3 above for an example how we do this.

What type of porcelain is used for the overlay materials for zirconia copings?

There are a number of zirconia-optimized porcelain systems available. At Castle Ceramics we use Vita VM9 layering porcelain and Emax Pressable Fluorapatite Porcelain onto zirconia.

Do the new feldspathic veneering porcelains for zirconia offer a different (better/worse) bond strength to zirconia substructures?

The Vita VM9 veneering porcelains Castle Ceramics use for zirconia are formulated to match the coefficient of thermal expansion of the zirconia and to bond to the zirconia coping. Vita VM9 has a coefficient of thermal expansion (CTE) of about 10 which is ideal for fusing onto Zirconia.

Are there any testing protocols that a dental laboratory can use to determine that his substructure has been processed to provide maximum strength and durability? If so, what are those protocols?

Flexural properties of sintered zirconia specimens can be measured but this test is destructive in nature. It is crucial that the dental laboratory work with a reputable milling center. We use Bristol Crown Milling Centre.

What is the difference in strength between pressed-porcelain-to-zirconia versus traditional stacked or layered porcelain-to-zirconia?

Both techniques should produce adequate strength if the heating and cooling temperatures encountered during processing do not create adverse thermal gradients that cause residual stresses.

Does the wiggle room of a milled restoration compromise the retention of a crown?

Why use zirconia – is this clinician driven or manufacturer driven?

The use of zirconia copings is driven by improved aesthetics, biocompatibility, and durability as compared to PFM.

How strong is strong enough when it comes to zirconia?

It is important that zirconia-based restorations be stronger initially than PFM due to a small amount of potential deterioration of properties intraorally over time. A zirconia with a flexural strength of 800 MPa should be adequate.

Where do the fractures of the bonded zirconia restorations compared to the PFM restoration occur?

Failures of zirconia-based restorations typically involve chipping or delaminating of the overlaid porcelain. These failures can be minimized by proper design of the zirconia coping to properly support the overlaid or pressed ceramic.

What is the connector size for multiple-unit zirconia fixed restorations?

A cross section of 9 mm2 is recommended.

How does bonding affect a zirconia restoration?

Bonding of zirconia-based restorations can improve retention when additional strength is needed. Use self-adhesive resin cements ( Rely Unicem by 3M ESPE )or dual cure resin cements ( Variolink by Ivoclar, Nexus by Kerrs, Vitique by D.M.G, Panavia by Kuraray ).

How does blasting or grinding affect the zirconia?

Sand blasting improves the bond strength of resin cements to the intaglio surface of zirconia-based restorations as does grinding. However, excessive grinding can cause a crystalline transformation of zirconia that can compromise its strength. Water spray during grinding is recommended.

With porcelain-fused-to-metal systems, ceramic bonds to the oxide layer on the metal. What does the zirconia veneering ceramic bond to?

Usually the overlaid porcelain bonds to a compatible porcelain wash material that is applied to the zirconia first.

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