In January of 2013 my dentist removed and old filling and did an onlay on #3 (second last upper molar) to close a gap between two molars. (Never should have let him do it-\-the gap returned 6 mos. later!) In Jan 2014 the tooth acted up and I got a root canal on the tooth in mid-Feb; it was infected. Now, 5 weeks later, I'm on my 3rd antibiotic and I think the sinus infection I got following the RC is finally clearing up.\n\nBefore the RC, my dentist told me he could just put a filling in after the RC, but the endo recommended a crown. I got a second opinion from another dentist who also recommends a crown. When I discussed it with my dentist, he said the porcelain is super-hard and it can be difficult prepping the tooth for a crown, but he could do it.\n\nBecause my dentist did not offer a discount after his bad advice/screw-up, I've made an appt to have the crown done by the second dentist. But I'm worried that the crown prep will require some of tooth #2 & #4 to be drilled away, and then I could need RCs+crowns on THOSE teeth, too. Or the prep work on #3 might cause part of the tooth to break, and then I'd need it extracted anyhow. Or that the prep work on #3 would cause micro-cracks and I'd need it extracted within the next few yrs.\n\nAt night I do clench my teeth, and I've been using Plackers "Grind No More" on my lower teeth. I like that they are not bulky. My jaw is never sore and no TMJ, no problem with gum recession, so I think I'm a mild-mod clencher.\n\nShould I just have it extracted now, or do you think the porcelain onlay could be drilled away without needing to traumatize #3 and the adjacent teeth to make room for the crown? \n\nAnd what if the sinus infection symptoms are worse when I finish the antibiotic tomorrow? How long can I go before the RCd tooth gets re-infected without a crown?