When providing a full coverage restoration (crowns/ cap), there are many things to consider. One of the choices is to decide the type of material for the crown, which brings me to the topic of discussion today: Zirconia. Zirconia can be used as porcelain fused to Zirconia (more aesthetically pleasing) or full Zirconia (stronger and less likely to fracture).
For those of us that are more analytically inclined and love the technical/factual details:
- Zirconia is the dioxide form of the metallic element Zirconium, a member of the titanium family.
- Zirconia comes in a puck, pre-sintered form.
- Using a CAD system (3 shapes or exo-cad) we can now virtually design crowns and bridges. Then, using CAM system (there are many different kinds of milling units), we can mill a puck into the shapes of crowns and/or bridges at 125% size. Once it is sintered in a furnace, Zirconia shrinks to the exact 100% size.
- Zirconia crowns can be made monolithic (uniform colour) by cutting back and layering to improve the aesthetic quality, as nature is never monolithic.
Like any new material, there were pains in the beginning. In the early 2000’s , there were debonding and chipping issues close to 8%. In my opinion, that was an unacceptably high number. However, with better control of heating and cooling cycles and an improved layering ceramic system, chipping and debonding issues have been reduced to almost the same percentage as that of other materials such as PFM (the most common posterior crown material still in use today).
1) Opacity – The high opacity of Zirconia can be useful to hide poor tooth color such as darkened root (from RCT), metal post, or tetracycline staining.
2) Colour- Even though Zirconia is metal based, it has a white base color. This delivers a better aesthetic outcome around tissue areas compared to PFM (porcelain fused to metal).
3) Strength- Zirconia has a 800-1200 MPA (2-3 times stronger than EMAX). If using Zirconia for bridges, I would only recommended it for smaller spans until more data comes forward. If a crown is being made for posterior teeth, Zirconia can be made in full contour for decent aesthetic quality and maximum strength.
4) Unlike other white/tooth coloured materials, Zirconia can be cemented. This can be an advantage, as cementing is likely to be a less sensitive procedure than bonding and has a more predictable clean up.
1) Opacity – High opacity can also be a disadvantage. It can be useful in some cases, such as the ones mentioned above, but to mimic the details of a natural smile, such as multi-layered transparency, Zirconia alone has its limitations. Light hitting Zirconia simply does not react the same as light passing through natural tooth structure.
2) Zirconia can be cemented only. Zirconia crowns are not bondable. Etching can be applied to increase about 20% of the cementing surface for better mechanical retention, but zirconia cannot be chemically bonded.
3) Zirconia is not recommended for veneers, maryland bridges, or very thin restorations.
4) If someone has significant metal allergies, they should consider testing prior to the use of such a material.
5) If layering Zirconia, more tooth reduction is required. Therefore, a more aggressive preparation of the tooth is required to achieve the desired aesthetic results.
Like any material used in treatment, it is best to make that personal choice with the council and advise of your dentist and dental team.
– Braeside Dental Centre