Root canal therapy can save many natural teeth, but sometimes the tooth itself is not strong enough to support chewing on it for years to come. The guideline used to assess this is called ferrule, and means we need 360 degrees of healthy tooth structure of 1.5-2.0mm height to predictably retain a crown and prevent fracture. If there are small areas that don’t meet this requirement saving the tooth is still possible but may be less predictable. If there is no ferrule then it may not be in your best interest to save the tooth. A review article was published in the Journal of Endodontics in Jan. 2012 that covers the information in more detail.