Thinking About the Canal in Halves
Before I explain my rotary workflow, I want to share a simple way to conceptualize the canal. I like to think of it in two halves: the top half and the bottom half.
Top half: This can usually be opened with larger files (e.g., 25/.04). Doing so allows irrigants to reach the apical portion more effectively.
Bottom half: This is where you need to be more cautious. Rushing in with larger files can easily lead to ledging or even file separation, turning a straightforward case into a complicated one.
Using Pre-Op X-Rays for Guidance
You might be wondering: “How do I know where the top half ends and the bottom half begins?” That’s where pre-op radiographs come in.
Use the ruler function on your X-ray software to measure from the top of the crown to about the midpoint of the root. While angulation makes it less than perfect, it gives you a reasonable estimate.
Another approach is measuring from the crown to 0.5 mm short of the radiographic apex to approximate total working length.
Challenges with Vital Cases
In vital cases with significant bleeding, establishing the exact working length early on can be tricky. An apex locator may even indicate you’re “past the apex” when, in reality, it’s just being confused by pulp tissue.
In these situations, a pre-op X-ray estimate can save you time and reduce the number of working length X-rays you need. Sometimes, simply opening the top half of the canal with a 25/.04 file allows the pulp tissue to come out, making it easier to stop bleeding and obtain a more reliable measurement with the apex locator.
Why File-Shot X-Rays Still Matter
I always recommend taking a working length (file shot) radiograph—even if you have an apex locator. Here’s why:
Accuracy: Apex locators are not foolproof.
Curvature assessment: The file shot helps visualize canal curvature, which can guide your judgment about case complexity before proceeding further.
My General Workflow
Regardless of which non-heat-treated file system you prefer, the principles above form the foundation of my workflow. By treating the canal in halves, relying on pre-op X-rays, and confirming with file shots, you minimize complications and maximize efficiency.
My First File of Choice: 25/.04
The very first file I place in the canal is a 25/.04. Why? Because opening the top half of the canal with rotary reduces the amount of hand filing needed later. More importantly, when I do need to use hand files—such as in ledges, curved canals, or broken file cases—I can rely on much better tactile feedback. Hand files allow me to “feel” the canal and safely instrument in complex situations.
If the 25/.04 reaches working length (WL), the rest of the procedure becomes much easier. At that point, I know I can safely open the canal to larger sizes. Realistically, if a 25/.04 can get to WL, then in the vast majority of cases, larger rotary files will follow without difficulty.
In the video below, it was a tricky canal in the bottom half of the canal. So I started with top half with 25/.04 and then hand filed to size 10,15 to the working length. Then the bottom half of the canal is prepped to 02 taper. Then, you “blend” the taper to .04 with rotary file for master cone to have a perfect fit and open up the canal enough for adequate cleaning and irrigation.
Adjusting Based on Case Complexity
Of course, every case is different, and the sequence may change depending on complexity. Still, this approach works for me in roughly 90% of primary root canal treatments—whether in anteriors, premolars, or most molars.
I still rely on hand filing quite a bit, especially in more challenging cases. I’ll cover that in greater detail in a future article.
