Insight 27 — Low Temperature Degradation in Zirconia; a Slow but Real Change
Clinical explanation
Low Temperature Degradation (LTD) refers to a change that occurs in the presence of oral moisture and at normal body temperature. In this process, the crystalline structure of zirconia changes at the surface of the material and may, over time, lead to surface microcracks.
This phenomenon is usually neither sudden nor severe, but under certain conditions it can become important in the long term.
First note — the surface matters
LTD starts from the surface. If, after delivery of the crown, an occlusal adjustment is performed but the final polishing is not precise, the rough surface can become prone to hydrothermal changes.
So after every occlusal adjustment, the final polishing must be taken seriously.
Second note — the type of zirconia matters
Older-generation zirconia (3Y) has higher strength but is more sensitive to LTD.
The newer, more translucent zirconia (4Y and 5Y) is more resistant to LTD, but has lower flexural strength.
The choice of material must be made based on the site of use and the level of force.
Third note — moisture is the main factor
This change occurs because of the presence of water, not necessarily acid or decay.
In very thin crowns or in patients with bruxism, it becomes more important.
Clinical summary
LTD usually does not cause an immediate problem, but in thin designs, poor polishing, or high forces it can come to matter over time.
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