Video: The SLOB Rule Explained

Today’s lesson is going to be about the SLOB rule. What’s the SLOB rule, you ask? The SLOB rule is a little trick you can use with your x-rays to help you more easily identify which canal is which when dealing with a tooth that has two canals superimposed on each other. It’s one of my favorite endo tips, because it makes something that seems complex so much simpler.

The SLOB rule is much easier to understand with a visual aid, so I’ve created a handy dandy video to show you exactly when and how to use the rule, with a transcript below for backup. It’s a really clear demonstration that I think you’ll find enlightening, so be sure to watch—even if you prefer to read!

Let’s dive in.

Endo Tip: The SLOB Rule Explained

A lot of times when doing a root canal, you have two canals that are superimposed on each other—specifically the buccal and the lingual canals in a tooth like a lower molar—and you don’t know which canal is which, because you’re looking at a two-dimensional image of a three-dimensional object. 

When you have two canals that are right on top of each other, inside one root, it’s really easy to get confused on which canal is which! To illustrate, put your hands up and make a peace sign, and then turn it to the side and look at it. You can see that it looks like there’s just one canal there, but really, there’s two! So… how do you identify when you’re doing root canal therapy which canal is which? The SLOB rule was created to help you understand that.

A Real-Life Example

Let me explain how the SLOB rule works with this real-life example from when I was working on a maxillary premolar. This first x-ray shows that one of my gutta-percha points was right on the money and the other one was a little bit long.

Now, I need to know without taking too many radiographs which canal needs to be adjusted, but it’s really difficult to figure that out from this periapical radiograph. Fortunately, if you do the SLOB rule right, you’re going to see that this process is really efficient, and it will make your root canals that much easier. Plus, you can train your team how to do it, and you can radiate your patient a whole lot less.

So, when I take an x-ray, I want to take one that’s straight on, like in this image here (above). Then, I want to make an adjustment to the x-ray tube head, like in this other image (below), so I can split these canals.

See how you can clearly identify that there’s two different roots in this tooth? Now I need to know which canal needs to be adjusted, and I make that decision based on how I actually move the x-ray tube head.

Let’s go back to our peace sign, where we see our two canals that are superimposed on each other, so I can explain the SLOB rule with a visual. Let’s pretend that my head is the x-ray tube head, and we’re going to say the finger that’s closer to my face is the buccal canal, and the finger that’s further away is the lingual canal. When I move my head to the right (we’re going to call that mesial, and the left will be distal), you’re going to see which of those canals—buccal or lingual—moves with your tube head. 

So, if I move my head to the right, or that x-ray tube is moving to the mesial, then one of these canals is now to the mesial, which is this one, my lingual. If we remember what SLOB means—”Same Lingual Opposite Buccal”—that means the lingual canal follows the same path as the direction of your x-ray tube head, and since my head moved mesial, the more mesial canal on the x-ray is going to be my lingual, and the opposite one will be my buccal.

The SLOB Rule In Action

So, to further explain the SLOB rule, now I’m going to have my assistant Michelle show you exactly what we mean by that with the actual x-ray tube head, and I’m going to play the patient.

Pretend the x-ray sensor is in my mouth, and we’re doing a lower-molar x-ray. She places a sensor in there, and then she’s going to take one x-ray—you want that x-ray to be straight on. Then you want to press the button, and you don’t want the patient or the sensor to move. You will come right back to the patient and move that x-ray tube head either mesial or distal, and your x-ray is going to adjust based on that x-ray tube head movement. 

I want you to see exactly how much she moves the tubehead, because the amount of movement that she does has an impact on how much of that split of the roots you’re going to get in your x-ray. It’s not an itty bitty movement—it’s quite drastic! But you always want to make sure that you’re still capturing that sensor in your x-ray. And remember: You don’t want to adjust the sensor, you want to make sure the sensor stays in the same place so you know you’re making an adjustment in that angulation.

So, if your tube head comes mesial, the canal that shows more mesial now on the x-ray is going to be your lingual canal. Then, if you adjust it distal, the canal that shows more distal is going to be your lingual canal again. So, “Same Lingual Opposite Buccal”—that’s the SLOB rule explained. It’s as simple as that!

Implementing the SLOB Rule in Your Practice

Now that you’ve got the hang of it, make sure you train your team on this and show them this video so they really understand what you’re talking about. Oh, and one other tip! When you’re saving your x-ray, label it as “mesial conefit” or “distal conefit”. That way, if you have to re-reference your x-ray later on, you know exactly what direction your tube head moved, so you know which canal is which.

That’s it for explaining the SLOB rule. I hope you’ve found it easy, and that now it’s simplified for you so you can implement it as early as tomorrow!

Frequently Asked Questions

1. What is the SLOB rule?

The SLOB rule is an endo acronym to help you more easily identify which canal is which on an x-ray when there are two canals superimposed on each other. SLOB stands for “Same Lingual Opposite Buccal,” and remembering that acronym will aid you in knowing which canal needs to be adjusted without taking too many radiographs.

2. How does the SLOB rule work?

Here’s a visual to help you understand: Hold a peace sign up in front of you, and then turn it on its side so that it looks like there’s just one finger—like two canals superimposed on each other on an x-ray. Imagine that your head is the x-ray tube head, the finger closest to you is the buccal canal, and the finger furthest from you is the lingual canal.

Now, tilt your head to the right (mesial). Which finger—or which canal—moves with your head? The lingual. So, the lingual canal moves mesially (the same direction as your head), and the buccal canal moves distally (the opposite direction of your head). What about when you tilt your head to the left (distal)? Which canal moves with your head? The lingual. So in that case, the distal finger (finger that is now on the left) is your lingual canal, and the mesial (or finger on the right, or opposite the movement of your head) is your buccal canal. Remember: Same–Lingual, Opposite–Buccal. The SLOB rule explained!

3. Are there any sticky points I might run into when implementing the SLOB rule?

One thing to keep in mind is that when you move the tube head to adjust the x-ray, it’s not a small movement. You actually have to move quite a bit to have the split in the canals show up on the image, while still making sure you’re capturing the sensor in the same place.

– Sonia