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Zirconia-toughened Alumina VS Alumina-toughened Zirconia

Because zirconia generally remains partially stabilized in the tetragonal phase, and alumina presents a moderate toughness, there is a trend in the development of alumina-zirconia (zirconia-toughened alumina [ZTA]) and zirconia-alumina (alumina-toughened zirconia [ATZ]) composites with structure at either the micro or nano scale, as proposed for arthroplasty applications.

Alumina toughened Zirconia
In 1976, Claussen first described that the addition of unsta-bilized zirconia to alumina increased the fracture toughness of alumina due to interaction between the crack front and the second phase combined with interactions between the crack front and pre-existing microcracks formed during the tetragonal to monoclinic transformation of zirconia.
Zirconia Toughened Alumina

The percentage of zirconia or alumina in the composite can be tailored and may be altered according to de-mand or manufacturers’ manipulation. Advantages of these composite materials when compared to Y-TZP are resistance to low-temperature degradation, higher strength, and fracture toughness, and more than twice Y-TZP’s cyclic fatigue strength.

A recent material development that, so far, has not been made available to the profession is that of graded alumina and graded zirconia. They are a variation of the polycrystalline restorative materials in which glass is infiltrated into the surface of either alumina or zirconia substrates. This infiltration creates a more damage-tolerant and esthetic sys-tem for improved clinical performance.

A graded structure consists of a material composition (low stiffness glass to high stiffness core) that gradually changes across an interface (eg, between core and veneer and/or the core intaglio surface). Zirconia was infiltrated with a silicate glass with a matched coefficient of thermal expan-sion.

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