Zirconia Dental Restorations
Standard of care used to be porcelain fused to metal and full gold crowns for dental restorations. Today with the development and application of metal-free restorations that are durable and bio-compatible, Zirconia can be an ideal solution for a variety of clinical applications and are natural looking blending with a person’s own teeth.
Zirconia is a crystalline dioxide of zirconium that is the strongest ceramic for the dental market today. It is widely used for the fabrication of crown copings, bridge frame works and custom implant abutments.
Zirconia offers some significant physical properties that are advantageous for some dental restorations. Zirconia products on the market today boast a flexural strength from 850MPa to 1,465MPa compared to porcelain ceramics with typical ranges of 71MPa to 419MPa – strength advantage becomes clear. Zirconia has an excellent resistance to thermal shock which means it will remain very stable in the mouth and face fewer stress factors from expansion and contraction. Zirconia can be stained and glazed to a prescribed tooth shade, giving the finished product a more tooth like appearance. Finally Zirconia is considerably less expensive than traditional, precious metal restorations.
Indications for use of full contour Zirconia is for posterior crowns, crowns over implants and crowns with limited occlusal clearance. It is also indicated for full arch bridges up to 14 units. Other candidates would include patients who do not desire cast gold or metal occlusal PRM restorations. Zirconia has a good opacity and may be advantageous when trying to block out underlying discolored teeth or restorative materials. Zirconia is considered a desirable substitute substructure for a bi-layered crown due to its high-strength properties and more tooth-like appearance.
When using Zirconia for crowns some specific features will need to be address to ensure a dependable product. General guidelines for tooth preparation for a zirconia crown include at least 1.2mm of axial reduction, 1.5mm of clearance in the central fossa and 2 mm of clearance over functional cusps.
As Zirconia is a good thermal insulator the crown must be cooled slowly or risk creating residual stress within the restoration that could lead to surface porcelain failures.
Next, Zirconia restorations are designed using a state-of-the art technical computer aided design/computer aided milling (CAD/CAM) systems to designed, fabricate and place all-ceramic inlays, onlays, crowns and veneers. Current CAD systems have the design capability to ensure a uniform thickness of the veneering porcelain that can give the crowns a higher fracture strength. New design shapes of Zirconia copings are being investigated to maximize the strength of the bi-layered restoration. Ceramic restorations produced by this method have demonstrated excellent fit, strength and longevity.