High Translucent (HT)
High Translucent (HT) zirconia can be used for anterior and posterior restorations, full contour and frameworks. It’s made with Japanese raw materials, has very high flexural strength and while made to be highly translucent, it was primarily developed/optimized to have the highest fracture toughness value on the dental market today.
Normal zirconia quoted from the University of Iowa study has a fracture toughness value between 4 and 5 (MPa m1/2), but the Kerox HT is between 15-16 – really off the chart!
Zirconia manufacturers often refer to Megapascals (MPa) when referring to the strength of their dental ceramic products, however strength can actually be measured in two different ways. MPa is a one time measurement of flexural or bending strength, which is basically how much force the material can take when pressing down from above until it breaks. The other measurement of strength which is often neglected and can be considered an even more important discussion point, is fracture toughness. It measures how many times the material can take that force and shows how the finished tooth reacts to repeated pressure and mechanical impact in the mouth. Since we don’t only chew once with our mouths, but many times a day for years and years, a quality zirconia should have a high fracture toughness value.
The constant chewing and drinking hot and cold liquids can cause zirconia to shrink and expand, further causing mechanical stress. If there’s enough of these repeated stresses, the material can develop micro cracks and possible chipping – fracture toughness measures how many of these actions the material can withstand before this occurs and how far the micro crack will penetrate into the material. The HT has a greater ability to withstand these micro cracks. If there is a crack, it stops and will not travel across the zirconia and break in the mouth, due to its self-healing properties. This is a great advantage for the dentist and a major benefit to the patient.