Want to Improve Your Access? Follow the Law of Color Change in Endodontics

When it comes to root canals, there’s one area in particular where I see dentists get stuck, and it’s probably not what you’d expect. Ladies and gentlemen, I’m talking about endodontic access!

People always think instrumentation and obturation are the endo problem children, but in reality, these areas are easy to master. I can teach you a consistent, repeatable instrumentation workflow that makes obturations a breeze… but what I can’t teach you is how to prepare for every single kind of tooth anatomy you’ll encounter—and tooth anatomy is the key to your endodontic access.

Perhaps someday there will be a Google Maps for endo that can tell you exactly how to navigate any tooth. Unfortunately, those aren’t the times we live in. For now, you’ll need to know how to adapt to each unique tooth—and each unique patient—to be able to master your access.

The good news is there’s a quick tip to help you overcome this endodontic hurdle, improve your endodontic confidence, and reduce your chair time, and it’s called the Law of Color Change! Let me share with you what this rule is, where I first learned it, and how it can transform your endodontic access.

The Law of Color Change in Endodontics

The Law of Color Change comes from a classic and highly valuable article by Krasner and Rankow discussing the difficulties in locating the number and position of orifices on pulp-chamber floors. In the article, they propose a number of laws—including the Law of Color Change—to help dentists determine the position of the pulp-chamber and the exact location and number of root canals in any individual tooth.

The article is chock full of great information, so if you haven’t read it yet, I highly encourage you to check it out. But for our purposes here, we can summarize their proposal like this: The color of the pulp chamber is always darker than the surrounding walls. 

Why is this information useful? Because simply having an awareness of endodontic Law of Color Change will help you navigate tooth anatomy more successfully and prevent things like perforations during your access preparation. That’s HUGE, my friends!

My First Encounter With the Law of Color Change in Endodontics

Like you, I didn’t learn about the Law of Color Change in dental school. In fact, it wasn’t until I was a few weeks into my endodontic residency that I first encountered it, and it completely transformed both my approach to endo and my self-confidence.

I remember it like it was yesterday. We were working on extracted teeth (as one does before working on patients), and I was trying to access a premolar. After finding all the canals—or so I had thought—I excitedly walked over to my attending to show him my work. To my dismay, he grabbed the tooth from my hand, took one look at it, and within a millisecond told me I hadn’t unroofed the chamber.

I hadn’t what? “Unroofed”? What the hell does that even mean?!?

My heart sank. There I’d been, so proud of the work I’d done, and now I felt like a total endodontic failure. It’s a moment I’ll never forget. When I asked what he meant, he told me that I had only found the pulp horns, and that I needed to adjust my access so that I was fully dropped into the chamber. How? By following the endodontic Law of Color Change!

My attending explained to me that the roof of the chamber is yellow, and the floor of the chamber is gray. When you see gray, that’s your sign that you’ve accessed the chamber and it’s time to STOP! Because if you pass that point, you’ll be into the furcation—a place you definitely don’t want to be.

That day, I had a choice: either feel like a failure, or let that hard endo lesson land wholeheartedly. I chose the latter, and I’m so glad I did, because I only had to make a mistake once before I truly embodied the lesson and have let it safeguard me in every access that I’ve done since.

Passing On the Lesson Through E-School LIVE

One of my motivations in dedicating my career to helping dentists improve their endo is the opportunity to pass on what I’ve learned to a new generation—just like my mentors did for me! So when a similar situation came up last year during E-School LIVE (my 4-day, hands-on, live-patient endo CE course) that mirrored my own experience years earlier, I jumped at the chance to pay it forward.

To set the scene, one of my students was doing a few molar accesses on extracted teeth—just as I had been on that fateful day during my endodontic residency. In an eerily similar fashion, she walked up to me—proud and confident in work—so I could assess her molar access.

I took one look at the tooth and was instantly transported back to my own endodontic failure. The student had found the canals, but she had only found the pulp horns and the pulp roof. Do you see how the color of what she thought was the “pulpal floor” is yellow? She hadn’t unroofed the chamber!

And that meant it was time to teach her a valuable lesson she would never forget.

Just as my attending had done for me way back when, I explained my student’s error and taught her about the Law of Color Change in endodontics. Remember: The roof of the pulp chamber is yellow, and the floor of the pulp chamber is gray.

The only thing left now was to fix her access!

Connecting the Dots—Literally and Figuratively!

Once my student was aware of the Law of Color Change, it was easy as pie to fix the issue. All she had to do was connect the dots! I personally like to use a tapered diamond (my go-to is from Kerr Dental). It’s something you already have for your own crown preps and is likely already in your bur block.

After I explained what to do, the student went back to work on the tooth. A little while later, she came back to me with this:

Do you see the difference now? Do you see how the floor of the chamber is gray? When you see gray, that means there’s no need to go any further apically. If you can’t find a canal, you probably need to search more laterally—unless it’s an MB2! I swear, when you experience this once, you will never unsee it. It will change your awareness and your endodontic access confidence f-o-r-e-v-e-r.

Let’s look at them side by side so that you can really appreciate the Law of Color Change in endodontics:

That’s what I’m talking about!

So what can we learn here? No matter how good we are—even as specialists—we cannot change what Mother Nature has in store for us. You never know what tooth anatomy is going to land under your loupes, so your access will always have the potential to be the most challenging part of the procedure.

But when you keep the Law of Color Change at the top of your mind every time you access a tooth, it will not only make your access a lot less stressful (and much more safe), it will also reduce your chair time, boost your endo confidence, and transform your approach to endo.

Master Your Instrumentation With My Very Own Workflow

As I mentioned earlier, instrumentation may seem like one of the most difficult parts of endo, but when you have a repeatable workflow, it can make obturation a breeze. That’s why I’ve made a downloadable version of my very own Instrumentation Workflow. Follow it step by step or adapt it in a way that makes sense to you, and watch your instrumentation troubles melt away!

– Sonia