Hi again,
As I think I understand what you said...you have a temporary filling in a tooth that is going to receive an onlay...correct? Is that temporary filling being used as the temporary between visits for the onlay or is it a temporary filling placed in your tooth and it still has to be prepared for the onlay?
It seems like a nit picking question but it's not. Most dentists would refer to the temporary in the tooth prepared for the onlay as a temporary ONLAY rather than temporary filling. This type of temporary is fabricated to fit the intricate shape of the onlay preparation. We would refer to a temporary filling if something was plugged into your tooth but you still had to return for the onlay preparation and the insertion of the temporary onlay.
So you're probably wondering, "Why is it so darned important to know whether the tooth is prepared for the onlay?" Here's why...onlays involve partial coverage of the tooth cusps and as such have margins or finish lines that are exposed in the mouth. These margins are fragile until the onlay is completed. The onlay preparation is also shaped so that the final restoration can be inserted into the tooth...the vertical wall of the preparation are very slightly divergent allowing the onlay to be inserted.
A filling, is prepared with convergent vertical walls. Once placed into the tooth, it will not slip out unless it is broken.
A TEMPORARY FILLING will not protect the margins/finish lines very well. A TEMPORARY ONLAY offers more protection. It is usually made of plastic, carved to shape OUTSIDE the mouth and is cemented into the preparation. A temporary filling is made of a fairly soft material that is pushed into a hole, allowed to harden and carved to shape in the mouth.
There are occasions where a filling material can be used in the onlay preparation but it affords little protection against breakage of the margins.
Diving with an uncompleted onlay with a filling material inside risks chipping the margins/finish lines. If that occurs, the preparation has to be repaired or re-prepared, a new impression is needed along with a new temporary. The pressure of the regulator bite tabs on the chewing surface of you molar could predispose ruining the preparation.
If you are indeed wearing a temporary onlay rather than a temporary filling, there is another risk...aspiration of the temporary onlay if it becomes loose during your dive. Since the walls are divergent, it could become loosened and then slip out. If this happens on a dive and your are taking a breath, the onlay will end up in the lungs.
Strangely, if you simply have a temporary FILLING placed into the tooth and are still waiting to prepare it for the onlay, that filling has a better chance of not coming loose. Because it is a soft material though care must be taken not to break it.
Neither a temporary filling nor a temporary onlay is an absolute contraindication to diving but you must be careful and be prepared in case it comes out.
Regards,
Laurence Stein, DDS