For some reason the canal is closed off(calcified) it can be the way the tooth protects itself from an irritant. The crown can be adjusted in the mouth so long as it is repolished.
the bit can be adjusted with the crown on... it's easy to do-- however, i would be inclined to have it redone (i'm assuming the root canal was done through the brand new crown) since it is significantly weakened. the access hole plus more bite adjusting weakens it. I always cement crowns on temporarily at first with temporary cement so they can be removed if a root canal is needed. i permanaently cement them after the root canal or after a month or so if the tooth is doing well. In my opinion (again, just my opinion) you should have it redone and not have to pay for it.
a calcified canal means that the canal at some point in the past began closing up on its own-- usually due to the nerve dying (for whatever reason-- a big filling, trauma, a crack etc). these canals are hader to "clean out becasue they are very very narrow and require much more instrumentation----- if it was done well the fact that it was calcified has no bearing on the success of the procedure). In the upper first molar, there is a 4th canal 50% of the time, and it is always the most narrow and most difficult to instrument. hope this helps.
just re-read your post. it seems the crown was removed for your root canal procedure. in that case, if a bite adjustment is needed it can be done either way-- in the mouth or out. moe often than not, large adjustments are done out of the mouth (perhaps even by the lab) and small adjustments in the mouth. howeve, if you've been weaing it for a month, it should need very little adjusting. if alot of adjusting is needed, it weakens the crown and thins out the porcelain (which makes it very prone to fracture)--- i would question why the lab did not get it right (or at least very close) and ask to have it remade if this is the case.
Thanks for your comments Mike. The root canal was *not* performed through the crown as my dentist never permanently cemented it on because I was having problems with it. He only did a temp cement on it thankfully.