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Dentistry/questionable margin for new gold crown

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Question
Hello Dr. Dalin.

I'm feeling uncomfortable about the preparation (done by my dentist today) of the margin for a new high noble metal crown on #18, to replace an 18-yr old high noble metal onlay ). I would appreciate your opinion.
 
I was fairly convinced with the first part of the preparation he did, which included: remove gold onlay, drill out soft carious tooth structure at lingual-mesial corner of tooth, seal the resulting newly drilled cavity with composite material, contour the new margin, and cover the crown of the tooth temporarily with composite material.

Now, here's my concern. Beforehand, we had also discussed a 4-year old small-to-medium-sized single-surface "round-shaped" amalgam filling located on the distal surface of #18 starting at about 2-mm below the old tooth-onlay margin and ending just above the gum line. I thought that the dentist was going to remove that amalgam as part of the preparation; and I was pleased thinking that finally I'd be rid of the last amalgam in my mouth.

However, instead the dentist dropped the new margin down to meet the edge of the amalgam restoration, persisting in his explanation that the amalgam restoration had been done well, that it would be better to leave it in, and that the new margin comprising both natural tooth and amalgam would be fine for the new high noble metal crown. Then he took an impression, which goes to the lab tomorrow.

I'm left wondering about any risk to the long term integrity of the new margin, and also wondering whether there could be an undesirable/harmful interaction in my mouth between the new metal crown and the amalgam material.

I'm torn on whether to try to reject the course that my dentist has chartered by insisting on his removing the amalgam and making a new impression before proceeding with the lab work for the new crown.

Thank you for your consideration.

Answer
this is a tough question to answer without seeing the tooth in person. sometimes we want to remove all of the amalgam in a tooth but if we did just that there might not be enough tooth to support and retain the new crown. i always want to end a crown on sound tooth...i never want to end it on an old restoration. i feel more secure in having this solid foundation at the margins. i am assuming the dentist ended the preparation just below where the amalgam ended. so as you can see there are good reasons to shape preparations depending on clinical conditions. now there is the other issue of what the patient desires. i always try to honor my patients wishes. if there is a reason to not do that (such as removing the amalgam would jeopardize the success of the crown), i would sit down and show the patient exactly why this is the case and get their acceptance. one option could be removing the amalgam and replacing it with composite resin and then finishing the preparation just below it. you might want to present this as an option. good luck...i hope this helps

jeff dalin, dds

Dentistry

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Jeff Dalin DDS

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general dentistry questions with topics ranging from cosmetic dentistry to dentistry for children

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Fellowships in American College of Dentists, the Academy of General Dentistry, and the International College of Dentists.

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