The best cements to use for zirconia crowns are RMGI (resin modified glass ionomer, GI (glass ionomer), or zinc phosphate. While you can use self adhesive resin cements or even resin cements, the material properties of zirconia don't work as synergistically with them, especially when compared to any of the bondable ceramics.
Recommended cements for zirconia crowns
The recommended cements for zirconia crowns are RMGI, GI, and zinc phosphate because they provide the most retention for the crown, which addresses a common issue of it falling off.
Why these cements provide better retention: They are more rigid and flex less than the self adhesive resin and resin cements. While their bond strengths are lower than their resin counterparts, they are more retentive for zirconia due to less flexing and thus decreased incidence of the caps popping off.
This was actually a tip that we picked up from one of Gordon Christensen's lectures.
It appears that since zirconia itself doesn't have much flex due to its high rigidity, it doesn't flex when the resin cements flex during functional occlusion. This asymmetry provides an opportunity for the tooth cap to pop off while chewing and eating.
Now, when you cement it with a more rigid cement like RMGI, GI, or Zinc phosphate, everything is more rigid and has less flex. In this case, having materials with similar properties is more advantageous.
Key takeaway: Zirconia works better with cements that are more rigid.
Zirconia crown cements that are less effective
In our opinion, the less ideal cements for zirconia crowns are the self-adhesive resin and resin cements because they end up being less retentive despite having higher bond strengths.
Examples of these cements:
Self-adhesive resin - RelyX unicem
Resin - Panavia v5 and RelyX ultimate
Once again the reason ZR crowns are more likely to pop off with these cements is because they flex while the crown does not. Having a cement that is more rigid and flexes less is better for mechanical retention of zirconia.
These cements are better used in combination with the bondable ceramics like lithium disilicate, feldspathic porcelain, and etc.
Alternative solution to zirconia retention issues
While it is good to pick the perfect cement for your zirconia crown, there are other ways to increase retention such as attempting to bond it or placing retentive grooves.
Bonding zirconia
There are plenty of primers available on the market which allege that use of it will increase bond strength to zirconia. Feel free to give these a try and let us know how it goes.
Personally, we've tried some of these methods but haven't really noticed a big difference in the outcomes. Then again, your experience may be different from ours.
Retention slots
We've had far better luck with placing retention slots into our preps such as one on the buccal and one on the lingual. These help to mechanically hold in the zirconia crown and prevent dislodgement.
To be frank our dentists in Long Island City have had the most success with using a combination of: retention slots, long bevels, RMGI cement, and a gold crown instead of zirconia.
Yes, when we have problems with ZR, we just switch to gold using the combination above and haven't had any issues thus far. Although due to the color of gold, it is only suitable for use on the 2nd molar.
If you're in need of a new crown because your zirconia crown keeps falling off, schedule an appointment with our dental office.
