Safe-ended hand files: What, when, how, why

Dr. Rich Mounce discusses the benefits of safe-ended files

Despite the widespread adoption of powered (rotary and reciprocating) nickel-titanium instruments, stainless steel hand files (SSHFs) are an indispensible part of the endodontic armamentarium. While more time consuming and prone to iatrogenic misadventure, globally, SSHFs are still the predominant means to shape canals due primarily to their economy. This article was written to describe the specific attributes provided clinically by the use of safe-ended hand files and to feature Mani safe-ended K and H files (SEC-O K and SEC-O H files, respectively). While there are other marketplace options, the author uses Mani hand files confidently, hence the products referenced are Mani.

SSHFs vary by manufacturing process (ground versus twisted), design, and functional use characteristics. SSHFs vary considerably within the instrument class by design and physical characteristics. These variations include material of manufacture (nickel-titanium or stainless steel), pitch, cross section, taper, tip configuration, length, and handle design, among many characteristics.

K files are the universal standard for canal negotiation, shaping, and recapitulation of root canal systems. They are generally used with a quarter turn “watch-winding” motion and vertical pull. Despite their function, K files possess limitations, primarily their lack of stiffness in negotiation of curved and calcified canals, and tip design.

SSHFs are square in cross section up to a size 40. Above a size 40, their cross section is triangular. The difference is not academic. Up to a size 40, the square cross section provides greater rigidity to enhance canal negotiation. (The cross section becomes triangular above a size 40 to provide greater flexibility to offset what otherwise would be a very stiff hand file with limited clinical functionality.) Despite these cross-sectional differences, clinically, above approximately size 20, due to their stiffness, using K to prepare canals invites risk of canal transportation, especially in the apical third. In essence, K files are not stiff enough in the small sizes (6-20) and too stiff in the larger sizes (above 20).

Alternatively, to shape canals rather than to negotiate them, K Flex^® type files (Mani Flexile Files) are triangular in cross section in all sizes (15-40). The triangular cross section provides a more flexible hand file option where needed (relative to K files) in the smaller sizes (15-40).

Modifying the tip configuration of a K or H file provides similar changes in functionality and clinical usefulness. Mani SEC-O K and H files are distinguished from standard K files due to a “safe-ended” tip. Standard K files have an “active” (cutting) tip. Specifically, the tip of a standard K file is quite sharp due to the acute transition from the tip to the fluting. An active tip results in an increased possibility of ledging and canal transportation. Due to the active cutting tip, as the file is moving around a curvature, it tends to become engaged preferentially against the outer canal wall as it rounds the curve leading to possible transportation.

Alternatively, a safe-ended file has a rounded transition at the junction of the tip and the fluting. As a result, the file tip is less likely to “dig into” the canal wall and initiate canal transportation. While using a safe-ended tip is not a guarantee to avoid transportation, it provides a relative protection without decreasing the functionality of the K or H file. In essence, the clinician is able to perform all of the same clinical actions and yet minimize the risk of transportation present using a cutting tip. As a result, one option for the clinician is to use SEC-O K (and H files) exclusively to minimize the risk of canal transportation and simplify ones armamentarium at a minimal cost increase per file. Safe-ended K files are especially valuable in avoiding transportation when using a reciprocating handpiece (NSK ER-10, MounceEndo) to power K files in the creation of the glide path (Figures 1-3).

H files
H files, with either a cutting tip (Mani H files) or safe-ended hand files (Mani SEC-O H) are both used to grasp canal obstructions (often gutta percha but possibly separated files and/or carriers) and deliver them coronally through application of an upward force. Clinically, to deliver this upward force, the clinician must first bypass the obstruction with a K file (or its equivalent — possibly a “stiff” Mani D Finder). Once bypassed, the H file is inserted beyond the obstruction, and the aforementioned upward force is delivered using the engaged flutes of the H file. Notably, once the obstruction is bypassed, and the H file inserted beyond the obstruction, the H file is often tightly bound along its entire length.  The possibilities for apical canal transportation with an active cutting tip are very real in this environment if using an H file. Use of a Mani SEC-O H file provides a relative measure of safety against apical transportation in such circumstances.

This article has addressed the indications for safe-ended hand K and H files in the form of Mani SEC-O K and Mani SEC-O H files. Emphasis has been placed on the benefits of eliminating the cutting feature of an “active” hand file tip and using a “safe-ended” tip, resulting in less canal transportation in the apical third. Reduced canal transportation is correlated with cleaner canals, less postoperative pain, and enhanced clinical outcomes. I welcome your feedback.