Dental Zirconia Applications
VOLUME VI
A comparison of layered and solid zirconia restorations Clinical grade zirconia has been used throughout the dental industry for over a decade, but the interest level has accelerated recently due to its versatility as well as the ever increasing cost of noble alloys, especially gold. Yttria tetragonal zirconia polycrystal (Y-TZP) material, a zirconia oxide, is the standard form of zirconia that is currently utilized. Y-TZP is a monophasic material formed by sintering crystals directly together without interference. This allows the material to keep its inherent properties and stabilizes the overall structure. All zirconia materials are not innately equal, as there may be differences in the overall flexural strength and cosmetic capabilities. When prescribing zirconia restorations, a solid understanding of the specific benefits and potential drawbacks is vital. Zirconia restorations are available in two distinct versions: 100% monolithic or a zirconia coping with a porcelain overlay. >>>
Dental Zirconia Applications Layered Zirconia Restorations Layered zirconia restorations combine both the highest esthetics and the strength and flexibility you need for all posterior and anterior cases. The zirconia substructure typically has a flexural strength of 1200 MPa, comparing favorably to traditional porcelain fused to metal crowns. Additional, extensive laboratory testing has shown the fracture toughness and flexural strength of zirconia are significantly higher than that of alumina or any other allceramic materials. With layered zirconia there is no metal to show through and no unsightly black lines at the gingival margins. Layered zirconia crowns and bridges are cemented conventionally with resin ionomers cement and demonstrate outstanding biocompatibility in the mouth. They can easily be adjusted chair-side with a green stone or a diamond bur.
Solid Zirconia Restorations If you need a crown that requires minimal clearance or a crown to stand up to a severe bruxer, then a solid zirconia restoration is a viable alternative for posterior crowns and bridges. Designed and milled using CAD/CAM technology, solid zirconia restorations are sintered for over six hours at 1,500 °C. Solid zirconia does not have the same level of esthetics as the layered version, but what is lacks in esthetics, it makes up in sheer strength. Fabricated out of 100% monolithic medicalgrade zirconia, it is virtually unbreakable. Even patients with the most severe form of bruxism will not have fracturing issues. A solid zirconia restoration should be properly glazed and highly polished to avoid grinding and wear down on opposing teeth. This smooth surface will also lead to a reduction in plaque accumulation inside the patient’s mouth.
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LAB-300203 Š 2011 DDS Lab. All rights reserved.
VOLUME VI
Layered Zirconia ----
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Solid Zirconia
Yes
Anterior
No
Yes
Posterior
Yes
Crowns Bridges spanning up to 48 mm Inlay or wing-type bridges with up to a two-pontic span
Indications
1200 MPa (substrate only)
Strength
1200 MPa (full restoration)
Yes
Porcelain
No
No
For Bruxism
Yes
Anterior full-coverage crowns require a chamfer with 1.5 mm facial reduction, 1.5 mm lingual contact clearance, 1.5 mm incisal reduction 1.25 mm reduction at the gingival margin with rounded internal line angles; or a shoulder with 1.0 mm lingual reduction, 2.0 mm incisal reduction, 1.5 mm labial reduction, 1.0 mm 360° rounded shoulder.
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Posterior full-coverage crowns require a chamfer margin with 2.0 mm occlusal reduction, 1.5 mm buccal and lingual reduction with rounded internal line angles.
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Resin-reinforced glass ionomer cement (RelyX Luting Cement, 3M ESPE; GC Fuji Plus, GC America)
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Resin cements for short or over-tapered preparations (RelyX Unicem, 3M ESPE; Panavia F2.0, Kuraray)
Adjustment of the internal aspect of the zirconia is not recommended. If the porcelain overlay requires an adjustment, use a fine diamond at low-speed with water and air to deter porcelain fracture. Use a porcelain specific polishing system or pink rubber wheel and diamond polishing paste to polish the porcelain.
Preparation
Cementation
Technical Tip
Need an expert’s advice? We’re available for a consultation on your cases. Call us at 877-337-7800. LAB-300203 © 2011 DDS Lab. All rights reserved.
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Crowns Bridges spanning up to 35 mm Implants
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Shoulder preparation not needed
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Feather edge is satisfactory
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Conservative preparation similar to full-cast gold, so any preparation with at least 0.5 mm of occlusal space is acceptable
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Minimum occlusal reduction of 0.5 mm, however 1.0 mm is ideal.
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Resin-reinforced glass ionomer cement (RelyX Luting Cement, 3M ESPE; GC Fuji Plus, GC America)
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Resin cements for short or over-tapered preparations (RelyX Unicem, 3M ESPE; Panavia F2.0, Kuraray)
Always use a high speed hand piece with a diamond bur and copious amounts of water to cool the restoration, as any overheating could cause micro-fractures.
Billy Schrader, CDT Quality Control Manager Billy Schrader is DDS Lab’s Quality Control Manager and has over 19 years of dental lab experience. He is an expert in crown and bridge as well as ceramics.