Should my dentist be responsible financially for fees incurred at another office caused by a file being left behind?

It is an accepted fact that files become seperated during root canal therapy and is not considered negligence as long as your dentist informed you of the broken file.  Typically files break in tight curved canals.What your dentist actually does is his choice.  I rarely see broken files (has been several years) but I normally refer immediately to endodontist and do not charge for my root canal therapy.  That is my preference because I want to make sure my patient receives the best possible treatment.

File breakage is an occurance that is part of the risk of all root canal procedures. In fact you  may have signed a consent form that stated that this is a possibility. Most of the time these separated tops don't cause a problem and the source of your infection may not actually be the file tip but untreated root material.  In most cases the dentist would not be liable , but I would call him and talk to him about your concerns.  

Separation of file tips, while not common nor the desired outcome, unfortunately can happen.  If a file were to separate in a canal our offices standard operating procedure is the immediate informing of the patient to what occurred, the referral to an endodontist (root canal specialist) and there would be no charge for the work I had done.  Typically the sooner you are seen by the endodontist the better chance for a good prognosis. Ideally the endodontist is able to retreicpve the separated file and complete the root canal like normal, however this is is not always possible.  If the they can work around the file and complete the root canal the prognosis is very good, if they cannot then depending on where in the root the file is logged a surgical option may be required.  I would not expect the dentist to cover the cost of a crown as that procedure was most likely required anyway.  As far as the cost for the endodontist fees that would be something you would have to ask your dentist about.  

File breakage is an occurance that is part of the risk of all root canal procedures. You may recall signing a consent form that stated that this is a possibility.  Most of the time these separated tops don't cause a problem and the source of your infection may not actually be the file tip, but a deep seated nidus of infection that never healed.so the long answer is no, he's usually not liable, but talk to him in a non judgemental way and ask if his liability carrier might not help you out.