How long should a zirconia crown last?
If you have full-zirconia crowns, they are the strongest non-metal crowns available in dentistry today, not necessarily the prettiest though. I should say they are the hardest crown material available, though not unbreakable. Some dental labs even guaranty them (for years to even for life) against breakage. The dentist who did them may not redo them for free (they are 8–9 years old already) because of his chair time and overhead costs, but he/she may pass the lab discount on to you.
Crowns can last a lifetime, but they only average 5–10 years. I’ve seen 30 years, and I’ve also seen 1 year. It depends on very many factors, some of which happen at home that the dentists don’t know anything about.
If it’s 100% Zirconia, they are almost impossible to break. If its porcelain fused to Zirconia, the porcelain can break if it’s not thick enough. Your original dentist would probably warranty the work, but I wouldn’t worry about all of them breaking. The molars are where you do 90% of your chewing. Replacing 4 crowns in 9 years isn’t unheard of. If you have solid oral hygiene, and stay away from candy, soda, etc, with minimal dry mouth, I would venture to say they will last forever, unless you are eating nails and bolts, where the porcelain chips off or breaks. If the porcelain breaks but the zirconia core (substructure) is intact, you can still use them as normal as long as the tooth is completely covered. Good luck!
Zirconia is a strong material & all crowns are supposed to last a life time, subject to good eating habits i.e. normal aerated drinks, eating less non-vegetarian food (Western food by definition is non-vegetarian). Think your gums are failing leading to crown failures. This material has an abrasive quality which can cause friction against the root of the tooth as well as other teeth
As you are also suffering from other dental disorders, suggest you turn vegetarian. Though one might have artificial material in place of natural tooth, yet, one has to treat them with same caution as applicable to natural teeth.
The crowns may be porcelain fused to zirconia and not monolithic zirconia. If that is the case then it is possible that the porcelain is breaking due to a defect in the bond between the components. There were problems with this technology early on. Porcelain is essentially glass and is prone to chipping as well.
On the other hand, it does seem a little strange that this is just beginning to show up after 7 years. I would look at the bite which also could have changed after several years.
To me, I would say that your bite probably needs some attention, and you might very well be doing some intense grinding or clenching, even during the day. I would recommend finding a dentist with proper device for a precise digital view of what your bite looks like. Often with multiple porcelain restorations, the bite can be off, just a bit, but enough to trigger that bruxing I speak of.
You need to find out if these are all Zirconia or Zirconia-Porcelain.
Failure of all zirconium crowns is rare. In bridges, failure is usually at the connection point between the units of the bridge.
Zirconium-Porcelain crowns will indeed chip under certain loads.
You wear a night guard so I’m assuming you brux or grins your teeth.