A computer based method and system for defining and representing a shape and geometry of an occlusal access cavity to the tooth roots prior to endodontic treatment, include the step or elements for: loading onto the computer information of the geometry of a tooth obtained via one or more imaging techniques, creation of a 3D computer model of the tooth, including its internal architecture, visualization of the computer model, visualization of the location(s) of the entrance(s) to root canal(s) relative to the tooths occlusal surface, and based on the locations of the root canal orifices a shape of the access cavity is calculated.
