Dr. Rich Mounce discusses strategies for negotiating canals and achieving apical patency
Achieving and maintaining apical patency are at the heart of all cleaning and shaping strategies, as optimal microbial disinfection and three-dimensional obturation are only possible when patency has been obtained. A lack of patency predisposes the procedure to clinical failure due to microbes and tissue left in the canal, in addition to a myriad of potential clinical iatrogenic misadventures. This column was written to discuss principle-driven clinically effective strategies for negotiating canals and achieving apical patency.
Among other goals of canal preparation, it is desirable to keep the canal at its original position and to keep the apical foramen at its original position and size. Achieving these goals requires effective and safe use of stainless steel hand files (SSHF) to gain apical patency. Effective canal negotiation and achievement of apical patency are the precursor to glide path preparation. An excellent glide path makes nickel titanium (NT) canal preparation safer. Without an adequate glide path, clinicians must “horse” (force) their NT instruments to gain length rather than allowing the NT file to flow down the canal. Such force is antithetical to safe and effective canal shaping with NT files.
Tactile control of SSHF requires straight-line access, removal of the cervical dentinal triangle, and shaping the coronal third with orifice openers prior to apical negotiation.
In my hands, after the preceding steps, a new SSHF is used for every insertion into the canal, for any purpose, every time. Said differently, after sterilization, SSHF is used for one single insertion, into one canal, and then discarded, and a new SSHF is subsequently inserted. Using a new SSHF for every insertion saves time and money as tactile control and efficiency are improved along with reduced iatrogenic misadventure.
While a description of every type of hand file used for canal negotiation is beyond the scope of this column, suffice it to say that I use a No. 6 Mani K file as the first hand file into every canal, regardless of the canal diameter. Assuming that the No. 6 provides apical patency, I can quickly move to a No. 8 SSHF (regardless of the type of hand file required). If a No. 8 or No. 10 SSHF is inserted first (in lieu of a No. 6 K file), and these will not advance easily, and/or the canal is not negotiable, the clinician will never know if a No. 6 might have negotiated the canal and/or if the No. 8 or No. 10 SSHF blocked the canal. For curved and calcified canals, I use Mani D Finders, as they are much stiffer than K files or triangular (more flexible) SSHF.
Insertion is passive, yet intentional. Attention must be paid to the resistance to advancement of the file. If the clinician feels as though he/she is pushing the file into a sponge, generally, there is more negotiable canal to be explored. If the file hits a hard wall and bounces off, either the canal is blocked (and/or possibly transported), or the canal makes an acute curvature away from the main canal.
Attenuating the direction and pressure of insertion is essential as too much pressure can cause the creation of a false pathway that ultimately leads to perforation. Too little pressure can leave the clinician without enough power to break through a blockage in an otherwise negotiable canal.
All canals are curved to one degree or another; all SSHF used to negotiate canals should also be curved to one degree or another as well. Customizing SSHF curvature is an art, and, in general terms, the more acute the canal curvature, the more acute the curve that must be put on the SSHF. Canals can be curved with cotton pliers or Endo-Bender® pliers (SybronEndo), or both, depending on the particular canal requirements.
Many curved and calcified canals will require multiple insertions to gain length. Once apical patency is obtained, canals can be efficiently and safely enlarged using a reciprocating handpiece like the NSK ER-10.
This column has discussed several nuances of using stainless steel hand files to negotiate curved and calcified canals. Emphasis has been placed on choosing the right-sized file for the task, pre-curving, and carefully interpreting the tactile feedback the canal is providing. I welcome your feedback.