Why zirconia?

inciseTM ceramic restorations are produced by a revolutionary dental system that focuses on accuracy at every stage of the process. The choice of zirconia as a framework material (machined in the hard state) is vital for a crown or bridge that not only looks great, but also fits perfectly.  

inciseTM copings are made from densely sintered medical grade Y-TZP zirconia.  This provides excellent properties in terms of strength and thermal conductivity, plus a translucency that allows for more natural-looking restorations.

Benefits of zirconia

• Biocompatible
• Strong
• Insulating
• Great aesthetics

Great aesthetics

All-cermaic restorations provide a natural translucent appearance, whilst their biocompatibility ensures no more unsightly dark lines around the margin.

Gold crowns	Metal-based bonded crowns	All-ceramic crowns*

What is zirconia?

Zircon, the main source of zirconia, is a mineral present in the earth's crust.  It contains the metallic element zirconium combined with silicon and oxygen.

Renishaw's inciseTM frameworks are made from Y-TZP (yttria-stabilised tetragonal zirconia polycrystal), the strongest and toughest of the forms.  Y-TZP possesses a toughening mechanism that is key to its high performance as a dental material.  This "transformation toughening" is unique to zirconia and its effect is most marked in TZP material.

Properties of zirconia

Property	Value	Test
Density	6.05 gcm-3	ASTM-C20
Crystal size	1 µm	Thin section
Water absorption	0%	ASTM-373
Flexural strength (MOR, 20 °C)	1240 MPa	ASTM-C1161
Elastic modulus (20 °C)	210 GPa	ASTM-F417
Hardness	81	Rockwell 45N
Fracture toughness K(lc)	13 MPa m1/2	Notched beam
Coefficient of thermal expansion (25 °C - 100 °C)	10.3 x 10-6 / °C	ASTM-C372

 

Comparison with other dental materials

Although not as hard as densely sintered alumina, zirconia has much greater flexural strength, making it suited for posterior crowns and multi-unit bridges.  By comparison, castable ceramics are very weak.

Zirconia's ultra-low thermal conductivity also gives greater patient comfort.

Hard state machining

Renishaw's inciseTM frameworks are made from Y-TZP zirconia that has been machined in the hard state.  Renishaw has made this choice as it provides the optimal marginal adaptation.

According to an evaluation published in the CRA Newsletter (Vol 29, Issue 9, Sept 2005), "margins milled from hard state zirconia were consistently superior to green state milled zirconia."

A further benefit is the superior machined finish that can be achieved:
	inciseTM zirconia machined in the hard state.		Zirconia machined in the soft state prior to sintering.