Ondine:
I posted this yesterday, but I don't think I did it right. So, if this is a repeat, please disregard!
I have several crowns. I had to get six new front ones a few years ago. I had concerns about losing one to the ocean so discussed options with my dentist who, while not a diver, was concerned and worked with me for a solution. I suggested a plastic tray like those used for whitening teeth. My dentist agreed to make this for me though he was't convinced I'd lose a crown. Well, I lost a frontal crown at the airport shortly before flight time. I used toothpaste to hold the drown temporarily but I knew that certainly wouldn't work underwater. Thankfully, I had the plastic tray and it worked just fine till I was able to have a Canadian dentist on Grand Cayman bond the crown in place for me. Since I have beaucoup crowns, I always wear the plastic trays. The pressure has never been the issue. Crowns simply aren't always bonded permanently.
Aquafinna
Hey Aquafinna,
I have to admit that you had me confused for a moment...Here was a thread that I didn't remember and I didn't have any recent PM's from Ladydiver...then I checked the date. There is no rule on the Board that says you have to ask your question by adding it to a really old thread. Just post a new one.
It seems you really lucked out...the plastic tray "saved you". If I were a betting dentist, I would have said that you WOULD need a plastic tray to help maintain your caps would have been a snowball's chance in H*LL. Now I would have to eat my words.
There are all kinds of cements used inside crowns. Most of the older cements work by simply filling the space between the crown and the tooth. The space is typically about 50 microns. Putting something hard between the crown and prepared tooth kind of wedges the restoration in place. There is no adhesive quality to that cement.
Now-a-days, modern cements not only fill the space but can actually bond to both the crown material and the tooth structure. While these can create a much stronger union, they are also more technique sensitive. Any little bit of blood, saliva or moisture may render the bond ineffective and lead to a future cementation failure.
You called you front restorations crowns but in layman's terms a crown could be anything from a porcelain jacket to a porcelain laminate veneer. The type of cement used would be different for some of the different possibilities.
A veneer would come off very easily if there was a poor bond in the cementation. These are typically "bonded" onto the front surface of the tooth.
A porcelain jacket or porcelain fused to metal crown surrounds the tooth and is less likely to be "bonded" on to the tooth. If the cement loosens under one of these, the restoration can be still rather difficult to remove because the cement may still wedge it on.
Some of the newer all ceramic crowns have a precision machined zirconia core (kind of like the porcelain on a spark plug) and are covered by more traditional porcelain. For any of you out there that has a knife with a ceramic blade, this is the type of stuff the blade is made of. It is very hard, very strong and very smooth.
These are exceedingly strong but the zirconia's smooth texture really cannot be etched or sandblasted to increase the surface area for cementation. The result is that sometimes, these can slip off...leaving the underlying prepared tooth completely covered with a layer of the hardened cement.
No matter what your crowns were made of, it is my opinion, that if a cementation fails quickly, i.e., immediately to a year, the most likely culprit is technique. This not to say your dentist didn't know what he was doing. Instead, he could have looked away for just a second during cementation, just as, perhaps, you fought back the urge to swallow, and the little squirt gun under your tongue sprayed a drop of saliva onto the back of the tooth to be cemented. As soon as he put the crown with cement onto the tooth, the saliva spread entirely around the prepared tooth, under the cement and prevented a good union to the tooth.
This kind of thing happens to the best of us. All we can do it try to minimize the posibility.
Here is an interesting article about dental cements and diving. It indicates that with repeated cycles to depth, a degradation of cement strength may occur. The formatting for the data tables does not "cut and paste" properly. I think you get the gist of the article though.
Glad everything worked out OK on GC.
OOPS! The article makes this answer too long. I'm gonna post it in the next reply.
Regards,
Laurence Stein, DDS
