How can I detect cavity under veneer with opaque resin?

It is possible, but not probable that a cavity will form under the veneer, if the veneer was sealed on properly.  If in fact, this did happen to you, the first sign would likely be sensitivity in that tooth.  This would be investigated by your dentist with an exam and x-rays, which should uncover the hidden cavity.  My recommendation to you would be to not worry about this "what if" scenario, since it is not the most probable.   Good luck and I hope this helps. Follow me if you have more questions.Sarah Thompson, DMDSt. Louis, MO area (O'Fallon, IL)Real Self 100

The only way to get a cavity is to have bacteria affecting the teeth.  Unless decay was left behind underneath a veneer, there is no way to get a cavity underneath.  If you DO get decay, it will be at the edges of the veneer, and this is detectible both with xrays or with the eyes of the dentist or hygienist.Decay comes from Strep Mutans, a bacteria.  When S. Mutans digests food (fermentable carbohydrates) it emits acids.  These acids break down tooth structure.If there are no S. Mutans underneath the veneer, then there will be no decay.  New S. Mutans can only get underneath from the edges of veneers or crowns, and it will be seen before it ever got very far.