Anytime you have a root canal on any tooth, it causes that tooth to become very unstable because the dentist has to drill a tiny hole into the tooth to reach the chamber. A crown is always the best alternative. But because it was an anterior tooth, only one hole had to be drilled (I'm assuming it had one canal) therefore, it can be true that it may be able to be restored with a lingual composite (a white filling on the under side of the tooth). Talk to your dentist and ask about alternatives and your best option. If you have an honest and trustworthy doctor, chances are he'll let you know whats best for your wife.