If you attended my lecture at the Pacific Dental Conference last month, I mentioned “The Laws” that allow us to safely and predictably locate canals without being worried about mishaps (i.e. perforations, over-enlarged access cavities, etc.). One of the scenarios that we have to always be prepared for is accessing through a crown that is placed on a rotated tooth. One of the key elements discussed was the use of a probe to gain a better appreciation of the root outline at the CEJ level. The “Law of Concentricity” then allows us to start our access cavity preparation in the right direction.
The case below shows a rotated tooth #1-4 under a PFM crown. Preparing a typical access cavity in the Buccal-Lingual direction would definitely result in mishaps. Understanding the orientation of the tooth prior to the start of root canal treatment can result in achieving a safe and a conservative access prep. Note that even the rubber dam clamp wings are not good guides for the orientation of the chamber floor and for locating canals.