WHY FRACTURE TOUGHNESS IS SO IMPORTANT IN ZIRCONIA AND OTHER CERAMICS

You have most probably come across the term “facture toughness” in your work. But what exactly does it mean? Fracture toughness is a key property of dental materials which is often underestimated by dental professionals. If you expect the materials you use – for example zirconium oxide – to produce long-lasting results, you should always keep this property in mind.

What is fracture toughness?

Fracture toughness – or crack resistance – is a measure that describes the ability of a material with a crack in it to resist further fracture. This measure, therefore, indicates the amount of force that needs to be applied to cause crack extension in, for example, a lithium disilicate glass-ceramic or zirconium oxide. In other words:

• The higher the value, the lower will be the probability of the crack spreading in a material.
• A high value, therefore, is an indicator of superior clinical long-term performance – and consequently a longer lasting material.

That is why fracture toughness is a clinically significant value. It is expressed as MPa· m1/2.

A comparison of fracture toughness

• Titanium alloys and steel show very high values in terms of their fracture toughness. They reach values of more than 50 MPa· m1/2. In comparison, concrete with which houses and bridges are built has a fracture toughness of only 0.2-1.4 MPa· m1/2. This means that the material is quite brittle. Therefore, it is generally reinforced with steel.
• Zirconium oxide is the dental ceramic that shows the greatest fracture toughness. Nevertheless, enormous differences are found within this group of materials. For example, IPS e.max ZirCAD Prime has a fracture toughness of 5 MPa · m1/2* in the dentin area, while other zirconium oxide materials show values in the region of only 2 MPa · m1/2.

Interestingly enough, opaque zirconium oxide exhibits higher fracture toughness values than translucent zirconium oxide. Nonetheless, IPS e.max ZirCAD MT and MT Multi demonstrate relatively high fracture toughness. The less translucent IPS e.max ZirCAD LT and the opaque IPS e.max ZirCAD MO exhibit even higher fracture toughness values.

IPS e.max ZirCAD Prime combines high-strength and high-translucency zirconia raw materials in a single material. Areas requiring high strength (e.g. mandibular region and bridge pontics) are provided with high-strength material. Areas needing a high degree of translucency are reproduced in the more translucent component of IPS e.max ZirCAD Prime, fulfilling the criteria of both being strong and delivering the desired esthetic outcome

Important: Don’t compare apples with oranges!

Please note: As is the case with the related topic of flexural strength, comparisons of the fracture toughness of materials are only meaningful if the same measuring method is used to test all the specimens. When different measuring methods are used to evaluate various specimens, the results will not be comparable.