A Dental Question?

I'm posting a question for my mom about her teeth. She's got a really complicated situation where a tooth was damaged and she had a root canal, then a retreatment on it by an endodontist. She's been to quite a few dentists and while some tell her that she needs a cap over the tooth, one told her that she doesn't. So, my question is, after retreatment, is it necessary for a cap to be placed over the tooth? Is there a great danger of the tooth becoming brittle and breaking? Oh, and another question: some time ago, my mom had one of her wisdom teeth crack and chip. In the past, she's had such situations taken care of with fillings. The dentist she just went to told her that a filling wasn't the solution; that she needed a cap over it. Is that true; does she need a cap, or can she have her tooth fixed simply with a filling? I appreciate any help. Thanks a lot.
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after a rct, the tooth becomes non vital, cut off its nutrients, so it becomes brittle & can fracture when some thing is bitten & the whole rct is wasted, it will have to go for an extraction. So to reinforce strenth to the tooth a metal or ceraminc crown is fitted.
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