Q. When a post cannot be removed with ultrasonics, is there any other backup techniques that can be employed?
A. Certain posts resist removal even after ultrasonic efforts using the “10 Minute Rule”. Clinicians need a fall-back position to liberate these posts from the canal. The Post Removal System (PRS) (SybronEndo) is the next line of offense and provides an extraordinary opportunity to remove a post or other intracanal obstructions. In this removal method a trephine is used to machine down the most coronal aspect of the post 2-3 mm. Then a correspondingly sized tap is screwed in a counterclockwise direction to securely engage the post head. Once the tap is firmly seated and engaged on the post, the extracting pliers are used to safely and progressively elevate the post out of the canal. More information on the PRS system is posted to the Inventions
page of this site. In addition, I also refer you to my Ruddle on Retreatment
DVD "Removal of Posts and Broken Instruments" to exactly explain this precise clinical technique.