Are root canals necessary before crowns?

Root canals are not required just because teeth need crowns.  Root canals are required when the nerve of the tooth becomes irreversibly damaged or dies.  There are instances when root canals may be done in order to utilize the root of the tooth to give strength to a restoration/crown if there is insufficient tooth structure remaining.  Also, if the teeth are misaligned and there is not enough space to prepare the teeth without encroaching on the nerve, root canals may be done to assist in getting the best final outcome of the crowns.Without pictures and x-rays it would be impossible to tell you if the treatment done was indicated.  

I am sorry to hear this.  This is very unfortunate.  Root canals are required when the nerve of the tooth becomes irreversibly damaged or dies.  Root canals are not necessarily required only because the tooth needs a crown.If your bite is very collapsed, and you are having crowns placed, and preparing the tooth will be too close to the nerve, sometimes root canals will be done due to over preparation of the tooth (which in some cases it's the only way to create space).  I am not sure this was your case, especially because your dentist did not take any X-rays.  Additionally, having 6 root canals completed in 2 hours is not of ideal.  In the future, it's always best to get a second opinion.