The Case of an Overfilled Canal: Proper Endodontic Diagnosis Is Key To Giving Teeth A Chance

Every unnecessary extraction I’ve ever seen—and I’ve seen a lot—started with an inaccurate endodontic diagnosis. 

Diagnosis is the foundation of everything. It determines what tooth you treat, how you treat it, who you refer to, and what you tell your patient.

Get it wrong and the chance to save your patient’s tooth is at risk. Get it right and you give the tooth its best possible chance.

This is my complete endodontic diagnosis process—the cold tests, the CBCT, the patient history, all of it—along with tooth stories that show exactly what happens when the diagnosis is done right.

It breaks my heart when I see my own tooth story reflected in my patients. There’s nothing more frustrating than facing an unnecessary extraction due to an improper endodontic diagnosis. Diagnosis sounds simple, but it can really stump a lot of dentists. Today, I want to talk about a tooth story that highlights just how important it is.

Tooth Story: A Case Of An Improper Endodontic Diagnosis

This patient came to me after another endodontist had diagnosed her with Symptomatic Apical Periodontitis and told her the tooth was unsaveable and extraction was the only option.

Many patients would have accepted their doctor’s endodontic diagnosis and treatment plan and said, “Okay, extract my tooth,” but not her! She didn’t accept losing her tooth as her fate and instead sought out another opinion…mine. She was a patient after my own heart!

Did She Really Have To Have Her Tooth Extracted?

Through my evaluation, I learned she had a root canal several years prior and was now experiencing pain when she bit down.

When I looked at her imaging, I could see the root canal filling was overextended by about 5mm. That overextension sat very close to the inferior alveolar nerve.

If surgery had been the treatment of choice, there was real risk of paresthesia. But surgery wasn’t first on my list. I wanted to try opening up the tooth, removing gutta-percha, and retreating the tooth.

Why? Because first of all, extracting teeth is NEVER my first choice. I’m here to SAVE teeth, not remove them! But I also had a feeling that the overextended gutta-percha was not the source of the patient’s pain and infection. 

(We’ll talk about my complete endodontic diagnosis shortly!)

Before moving forward with my plan of action, however, I first had to talk to the patient about all of the possibilities and risks. With complete transparency, I told her that while I had removed overextended gutta-percha before, there was no guarantee that I could do it in her case.

With all the information in front of her, she made an informed decision and asked me to try. I always say: I never know what I can do until I try.

Getting to the Bottom of It. Literally.

We got to work. I started by cleaning out as much gutta-percha as I could and got to working length.

Then I took a 50 Hedstrom file to the apex, engaged it slightly, and gave it a yank.

That little ”tail” came right out.

The dance party that happened in that operatory was incredible. My patient, my assistant, and I were all so happy. No one wants to have a tooth extracted and we’d just done the one thing she’d been hoping for.

Our success was great, but what made sure we could save the tooth was making a proper endodontic diagnosis. 

Remember when I said that I suspected the patient’s pain was NOT due to the overextended gutta-percha? 

Well, it turns out my suspicion was correct. 

When I accessed the tooth and removed the gutta-percha, I found that it was entirely BLACK inside. I promise that isn’t an exaggeration! (Thank you to my hand-dandy endo tool, calcium hydroxide, for taking care of that!)

You can only imagine the amount of bacteria needed to cause that level of infection inside not just the one canal, but ALL the canals inside the tooth. This conclusion is only strengthened when you refer back to the pre-operative CBCT. 

The canal with the overextension wasn’t the only one with a lesion. The other canal had one too. That means it was a disinfection issue, not an overextension issue, causing the failure.

That’s why surgery had never been the right answer. Surgery would have removed the overextended material, but it would have done nothing to address the bacterial infection destroying the tooth from the inside. Only a proper retreat that would treat and disinfect the entire length of each canal could save the tooth.  

Getting that confirmation was vindicating for both me and the patient, because it told us that we had made the right choice—together. I love my intuitive patients!

Retreating The Tooth After A Proper Endodontic Diagnosis

With a proper endodontic diagnosis and gutta-percha removed, we were able to move forward.  By the time she came back to obturate the tooth, she was pain free.

One year later, she was doing well. She had no pain, and the area had healed!

Two years after treatment, the tooth was still going strong.

This is a great example of why we must understand the true etiology of root canal failure and not make assumptions. 

When I understood it was the bacteria causing the symptoms and not the extra-long gutta-percha, I was able to approach the case appropriately. 

And I truly believe that even if we hadn’t been able to remove the overextension, but had nevertheless completed a thorough disinfection, the tooth still would have healed.

Extraction Is Not Always the Answer, But A Proper Endodontic Diagnosis Is

Here’s how I approach my diagnosis every single time—whether it’s a new patient, an emergency, or a second opinion case.

1. Patient History and Chief Complaint

Start before you touch a single instrument. Ask your patient everything. 

Where is the pain? When did it start? What makes it better or worse? Has this tooth been treated before? Do they have a history of trauma?

The patient’s story gives you clues about where to look. It narrows the field before you ever take an image or pick up endo ice. Don’t skip it.

2. Cold Testing Is Non-Negotiable

I get this question constantly: how do I improve my endodontic diagnosis? 

My answer is always the same. Do a cold test. Every. Single. Time.

You cannot rely on a radiograph alone to guide your diagnosis. This is the most common error I see and it leads directly to a misdiagnosis.

A tooth can present with a radiographic lucency and still be vital. 

A tooth can look fine on a radiograph and be completely necrotic. 

The radiograph does not tell you what the pulp is doing. The cold test does.

Do a cold test. Every patient. Every time. No exceptions.

How to Cold Test Correctly

Two things kill the accuracy of a cold test: using a cotton swab, and not saturating adequately. A cotton swab cannot hold temperature long enough to give you a reliable result. If you’re consistently finding more “necrotic teeth” than seem warranted, this is probably why.

Instead: use a cotton pellet on college pliers, saturated generously with endo ice. Make sure you test the suspected tooth AND adjacent teeth AND a control tooth. 

Document the response to each one: lingering, immediate, none.

Be sure to prep your patient by telling them the test will be briefly uncomfortable and explain why you’re doing it. 

A patient who understands what’s happening tolerates it better and gives you more accurate feedback.

3. Percussion and Bite Testing

Tenderness to percussion tells you about periapical inflammation. 

Tenderness to biting tells you about the periodontal ligament. 

Test gently, test systematically, and always compare to adjacent teeth. A tooth that’s dramatically more sensitive to percussion than its neighbors is giving you important diagnostic information.

If you want a step-by-step resource for pulpal and periapical diagnosis that you can apply to every patient who walks through your door— start with my free Pulpal & Periapical Diagnosis Checklist.

4. Probing

Probe every tooth in the area you’re investigating. Isolated, narrow, deep probing next to a tooth can signal a vertical root fracture or crack extending into the root, or perhaps that they have periodontal issue. The pattern matters.

5. Radiographic Interpretation — 2D First, Then CBCT

Start with a good periapical radiograph. Look carefully. Not just at the apex but along the entire root surface, at the furcation, at the bone pattern, at any existing restorations and their depth. 

Then ask yourself: does this image explain the symptoms?

If yes, you may have enough. If there’s ambiguity, that’s when the CBCT earns its place.

6. Cone Beam

The CBCT changes the root canal diagnosis game. 

A CBCT can help us dentists diagnose a problem early on and even spot disease before it starts to present as serious symptoms. Which means we can start treatment right away without waiting for things to get nasty, and it can also confirm our diagnosis. 

So yes, I’m a huge advocate for cone beam technology because it can help us get the whole story!

I use my cone beam as part of the diagnostic process because it helps me get a handle on the anatomic features of a tooth and understand more completely what’s going on underneath the surface. A cone beam catches things that 2D imaging simply cannot show you.

CBCT is particularly valuable for:

• Identifying missed canals. The axial and coronal views are invaluable here. A missed DL canal that looks adequately treated on a periapical can show clearly undertreated on a CBCT.
• Distinguishing lateral canals from cracks. These can look identical on a 2D film. On CBCT, a lateral canal shows as a line extending from the canal with an associated lateral lesion in the adjacent bone. A crack has a different pattern entirely.
• Sizing periapical lesions accurately. A lesion that looks modest on a periapical can be surprisingly large on sagittal CBCT views—changing the prognosis and treatment plan.
• Assessing proximity to critical anatomy. Inferior alveolar nerve, sinus floor, adjacent roots. Before you treat a mandibular molar with a large lesion or an overextended fill near the IAN, you need the CBCT.
• Patient education. CBCT images are powerful communication tools. When a patient can see the lesion on a screen in front of them, the conversation about treatment becomes much more concrete.

Root Canal Diagnosis Isn’t Complete Without A Conversation

Here’s something I believe deeply: the diagnosis doesn’t end when you arrive at a clinical conclusion. 

It ends when your patient understands what’s happening in their mouth and has been given the information they need to make a real decision about their care.

It’s very important that you, as a dentist, take the time to make sure your patient has the same understanding of your endodontic diagnosis—or what’s causing their pain—as you do. 

Talk to your patient transparently about the possible outcomes of treatment so they can evaluate the situation realistically. 

This allows them to make an informed decision about their own health and builds the kind of trust that keeps patients coming back.

That means laying out every option, including the ones you don’t recommend, and explaining why. 

And that means telling patients what you don’t know, not just what you do.

Use your CBCT images as education tools. 

When a patient can see the lesion on a screen, the conversation about treatment shifts completely. 

You’re no longer telling them what to do. You’re showing them what’s there and walking through the options together. 

That’s how you build trust and get to the right outcome.

The Bottom Line

Proper endodontic diagnosis is not a box to check before treatment. It’s the foundation that makes good treatment possible in the first place.

Cold test every tooth. Use your CBCT when the 2D picture doesn’t fully explain the symptoms. Talk to your patient like a partner, not a bystander. 

And never recommend extraction without first asking yourself: have I done everything I can to understand what’s actually happening here?

For extra motivation, you can also ask yourself: would I want to have my tooth extracted? That question keeps you honest, and keeps you seeing your patient with compassion, which is at the heart of good dentistry.

The teeth you save with a thorough diagnosis? 

Those are the ones your patients remember. 

Those are the ones that build your reputation. 

And those are the ones that make this work worth doing.

So take your time, follow the clues, and place the blame for the pain where it actually belongs. There’s always a root cause…pun intended.

Endodontic Diagnosis FAQs

What is endodontic diagnosis?

Endodontic diagnosis is the process of identifying the source and nature of a patient’s dental pain or pathology using a combination of clinical tests, patient history, and imaging. 

Why is the cold test so important for root canal diagnosis?

The cold test is the most direct way to assess pulp vitality and pulp status is the foundation of endodontic diagnosis. 

A radiograph cannot tell you whether a pulp is vital, reversibly inflamed, or necrotic. The cold test can. Without it, you’re guessing. 

That guesswork can lead to treating the wrong tooth, undertreating, overtreating, or making extraction recommendations that aren’t warranted.

When should I use CBCT for endodontic diagnosis?

Use your cone beam when:

• 2D imaging doesn’t fully explain the clinical findings
• you suspect a missed canal in a retreatment case
• you need to assess proximity to critical anatomy 
• a crack vs. lateral canal distinction matters for the treatment plan
• when the lesion size appears larger than periapical films suggest

What’s the difference between pulpal and periapical diagnosis?

Think of it this way: pulpal diagnosis tells you what’s going on inside the tooth: is the pulp vital, inflamed, or dead? 

Periapical diagnosis tells you what’s happening in the bone around the root tip:  is there infection, inflammation, or an abscess forming? 

You need both before you treat. Together they give you the full picture..

How do I know if a tooth needs a root canal vs. extraction?

That determination requires a complete endodontic diagnosis—not just a radiograph. 

Key factors include: whether the tooth is restorable, the extent of any crack or fracture, probing depths, bone levels, and the patient’s own goals for their care. 

In most cases, I recommend exhausting every treatment option before recommending extraction. Extraction is never my first choice.

Want To Learn Faster, More Reliable Endodontic Diagnosis?

Diagnosis is Module 1 of E-School for a reason. Without mastering it, you risk your patient’s tooth.

If you want to build the kind of diagnostic confidence that holds up under pressure so you can make the best decisions for your patients, enroll in E-School and get instant access to the diagnostic module.

– Dr. Sonia Chopra

P.S. For more case studies and helpful tidbits, connect with me on Facebook, Instagram, or LinkedIn.