Expert: Gary Backlund, DMD, MSD - 11/19/2008

Question
QUESTION: I have two questions.

1)  How would you do a root canal on a tooth with a porcelain onlay on it?  What happens to the onlay after the root canal--does a new one get put on top?  

2)  My situation is that I had a porcelain onlay placed on a back molar one month ago because I had a leaking amalgam filling and the tooth had some hairline fractures in it.  

Everything was fine after the onlay was put on until two weeks ago, when I bit something hard (like a seed) on that tooth.  Since then, I have had pain upon chewing hard things on that tooth (like hard cheese).  I have no pain when chewing soft things and no pain otherwise.  I am worried that I need a root canal now--that maybe I worsened the cracks in the tooth under the onlay when I bit the seed.  Does this sound like a situation where a root canal would be necessary?  I have an appt. with my dentist but it's in a week so I'm worrying in the meantime.

ANSWER: Hi Kate,

I'm sorry to hear you're going through all this! From what you describe, it sounds like you have made the cracked tooth worse bitting on the seed. The usual treatment for a cracked tooth is to put on a full crown to splint the crack so it can't get larger. Without being able to exam you, I can't tell if your onlay does the trick, but since the problem started after you had it done, I would doubt it will be much help as a splint. If splinting the tooth fixes the bitting sensitivity and you aren't having any other symptoms with the tooth, it would probably not be necessary to do a root canal as long as the tooth is still alive. You can check that yourself by touching the tooth along the gum with a sliver of ice....if you feel cold the tooth is still alive. What we usually suggest is to put on the temporary crown for 2-3 months....if everything settles down and feels fine, go ahead with the final crown. If the tooth starts to hurt, then do the root canal.

I hope this helps.

Gary Backlund DMD, MSD

---------- FOLLOW-UP ----------

QUESTION: Thank you for your response.  I am wondering: how does the dentist put on a full crown when there is already a porcelain onlay in place?  Do they remove the porcelain onlay first, or do the full crown on top of the porcelain onlay?  

My porcelain onlay covers one cusp of the tooth, and pretty much takes up the whole biting surface of the tooth.

Answer
Hi Kate,

Actually, it could be done either way. Without being able to see your situation, I really can't tell you. Whatever will give the most internal bonding to help keep the tooth from cracking any farther is the way to go. I'm sure your dentist will talk to you about that when you see him/her.

Good luck!

Gary Backlund DMD, MSD