I was recently faced with a prosthetic challenge of preparing and impressing a tooth that is a terminal abutment for a removable partial denture (RPD) with both buccal and lingual clasps.
The laboratory fabricating the crown would always prefer to have the RPD for a few days but in this case I couldn't send it as it had most of his maxillary anterior teeth on it.
When faced with this situation, you have to make two impressions. One of the prepared tooth without the RPD, and a second with the prepared tooth and the RPD seated.
The scary part comes when removing the RPD from your impression without it distorting. There’s no way to really know if it’s accurate until you try to seat the RPD on your new crown in the mouth.
You can let the lab verify the accuracy by fabricating a GC Pattern or Duralay resin coping over your prepared tooth and then seat the RPD to it. It registers the position of the clasps and the rest seat.
While your assistant is mixing the resin, coat the prepared tooth and RPD clasps with Vaseline. Make a ball of it and then slightly flatten and seat on the prep. Then seat your RPD and start your clean up at the apical portion right away. You won't have much time but be sure not to pull any material away from the RPD or tooth once you see an initial set.
It's just as easy to trim it like a provisional once it has set (about three minutes). Your lab can then index the coping for the clasping and occlusal rest when they are finishing the wax-up or ceramics of the crown. You may have some minimal adjusting to do on the clasps when you seat the crown but you've insured the best adaptation that the lab can do.
Mary Anne Salcetti, DDS, PC, Spear Education Visiting Faculty. [ www.maryannesalcettidds.com ]