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Zirconia Abrasiveness: Is it or Isn’t it?

Full contour zirconia (FCZ) is very strong, very impervious, and, very misunderstood when it comes to abrasiveness and cementation. This article discusses the facts about abrasiveness.

The short answer about FCZ abrasiveness is, it depends. Research published by Hmaidouch, et al, International Journal of Oral Science (2014) 6, 241–246 shows that a rough zirconia surface is highly abrasive, a glazed rough surface is highly abrasive, but a highly polished zirconia surface is less abrasive than other ceramics. In fact, research by Tambra, et al, In vitro wear of human enamel opposing YTZP zirconia has shown highly polished zirconia can be less abrasive to enamel than Type IV gold.

Many dentists believe that veneering zirconia copings with feldspathic porcelain is kinder to opposing tooth structures. However, both the above authors have shown that not to be the case. Feldspathic porcelain is known to chip and etch in the mouth, making it the worst material with respect to opposing [enamel] wear. However, in the real world, the extent to which feldpathic porcelain degrades and abrades is more complicated. For example, in the presence of Coca Cola, three different feldspathic porcelains had three different results, increasing enamel wear from 12-74%, depending on the material type, The effect of clinical polishing protocols on ceramic surface texture and wear rate of opposing enamel: a laboratory study. In his, 2013, doctoral thesis, Zaninovich, explained that surface texture and roughness are more important than hardness when considering abrading enamel, and that in acid environments, both enamel and porcelain can degrade to more abrasive surfaces. However, the structure of the porcelain, occlusion quality, and occlusal habits, all contribute to determining the extent of degradation.

A shiny and smooth FCZ doesn’t mean a non abrasive surface will endure a short lived glaze. However, creating a highly polished surface is both time consuming and expensive. For those reasons, clinicians should check with their dental labs to learn if their FCZ needs further polishing.

The below chart, presented by Hmaidouch, illustrates the importance of knowing the differences when managing FCZ.

  Ground Polished
Group Ceramic Glazed Coarse Medium Fine Coarse Medium Fine
1 Y-TZP only glazed 4.3±1.9 12.6±4.4 5.5±2.1 3.8±1.0 3.4±0.8 2.9±0.6 2.4±0.5
2 Y-TZP/VM9 veneer 7.2±2.7 24.1±4.5 15.0±2.4 13.5±2.6 12.2±2.5 10.2±2.0 8.1±2.0

 

We can see that glazed, alone, is not nearly as smooth as finely polished. We can also see the difference between zirconia veneered with [only one] feldspathic porcelain and FCZ. Less clear is, the effect that different polishing methods and surfaces will have on surface texture.

From a different perspective, Stawarczyk, et al, measured the enamel loss of three types of surface-treated zirconia and a base alloy, using a chewing simulator. They reported, top of page, that the polished zirconia showed a lower wear rate on enamel antagonists, as well as, within the material itself.

The short answer to the question about FCZ abrasiveness is summarized by Miyazaki as: “A smooth surface of zirconia can be obtained with adequate polishing, because the microstructure of zirconia is fine and homogeneous. Highly polished zirconia shows the least wear of antagonist among various dental materials…Therefore, surface finishing and polishing procedure of zirconia full-contoured restorations was critical for obtaining clinical success.” Current status of zirconia restoration.