Root Canal Failure Signs: How to Tell if It Failed (Symptoms, Causes, and Solutions)

Practice Perspective (Biocrede Endodontics)

Root canal therapy is designed to save a tooth by removing infected or inflamed pulp, cleaning and disinfecting the canal system, and sealing the tooth to prevent reinfection. Most teeth heal well and can function for many years. However, a previously treated tooth can sometimes become painful or infected again—weeks, months, or even years later.

This guide explains the most common root canal failure signs, what a failed root canal can feel like, why failures occur, and what to do next. If you are searching for terms like failed root canal symptoms, root canal infection years later, how to know if root canal failed, or tooth hurts years after root canal, you are in the right place.

Start here: For the complete overview, see Pain After Root Canal: Causes, Timeline, and What to Do (Start Here).

Quick Answer: How to Tell if a Root Canal Failed

A failed root canal typically means the tooth did not heal as expected or became reinfected. Common signs include:

• Persistent or returning pain (especially pain that does not trend better)
• Swelling of the gum, cheek, or face
• Drainage, bad taste, pus, or odor
• A pimple-like bump on the gum (sinus tract / abscess)
• Sharp pain when biting or tapping on the tooth
• New symptoms months or years later (for example: root canal tooth hurts years later)

If you have swelling, fever, drainage, or trouble swallowing/breathing, treat this as urgent and contact a dental professional or seek emergency care.

Most Common Failed Root Canal Symptoms

1) Persistent Pain or Pain That Returns

Some soreness is common after treatment, but pain that persists, worsens, or returns after improvement can be a warning sign. Patients often search: failed root canal symptoms, what does a failed root canal feel like, how to tell if root canal failed, or old root canal pain.

2) Swelling and Tenderness

Swelling in the gum or face, or tenderness when chewing or touching the area, can indicate inflammation or infection. This may appear as signs of infection after root canal.

3) Signs of Infection: Drainage, Bad Taste/Odor, Pus

Drainage or a persistent bad taste can suggest infection. People also describe “pus,” “pressure,” or a foul smell, including searches like symptoms of root canal infection or infection in tooth with root canal.

4) Gum Abscess or “Pimple” Near the Tooth

A visible bump or pimple-like lesion on the gum can be a strong sign of a draining infection. This may show up as root canal infection years later or symptoms of failed root canal years later.

5) Temperature Sensitivity or “It Still Feels Alive”

A properly treated tooth should not have classic “pulp cold sensitivity,” but patients sometimes report temperature sensitivity due to: nearby teeth, a crack, leakage under a restoration, or bite trauma. This deserves evaluation—especially if it is worsening.

Normal Healing vs Concerning Signs

Often normal (and improving):

• Mild tenderness to bite for a few days
• Soreness that steadily improves
• Minor sensitivity around the gum tissue early on

Concerning (needs evaluation):

• Pain that is not improving after 7–14 days, or returns after initial improvement
• Sharp pain when biting, or pain on release (crack screening)
• Swelling, fever, drainage, bad taste, or a gum “pimple”
• New symptoms months or years later (e.g., why is my root canal tooth hurting after years)
• If the main issue is pain when chewing or biting, read Pain When Biting After Root Canal.

Why a Root Canal Tooth Can Hurt Years Later

It can be alarming to develop pain long after treatment. Common reasons include:

• Reinfection through leakage (a crown/filling margin breaks down over time)
• New decay under or around a restoration
• Crack or fracture (sometimes under a crown)
• Missed anatomy (complex canals that were difficult to clean initially)
• Bite overload / clenching causing ligament inflammation that mimics tooth pain

This is why people search root canal pain after years, toothache years after root canal, root canal failure years later, or can a root canal get infected years later.

Why Do Root Canals Fail?

Root canal outcomes depend on anatomy, infection severity, and restoration quality. The most common reasons include:

• Incomplete cleaning / persistent bacteria (especially in curved, narrow, or hidden canals)
• Missed canals (complex root anatomy)
• Compromised coronal seal (leaky filling or crown allows saliva/bacteria back in)
• Cracks and fractures that develop before or after treatment
• Delayed final restoration (waiting too long for the crown increases risk)

Root Canal Filling Fell Out / Crown Delay: What to Do

If your root canal filling fell out before crown placement—or you suspect leakage—do not ignore it. A lost or broken temporary seal can allow bacteria to re-enter the canal system.

• Do not chew on that tooth.
• Contact your dentist/endodontist promptly to re-seal the access and assess the tooth.
• If you are searching how to know if root canal filling fell out, common clues include a new hole, rough edge, food packing, sudden sensitivity, or a “hollow” feeling.

Partial or Unfinished Root Canal (Incomplete Treatment)

A partial root canal, unfinished root canal, or incomplete root canal leaves the tooth vulnerable. If a tooth was opened but not fully cleaned and sealed, bacteria can persist and symptoms may escalate.

If you are mid-treatment (for example, a temporary was placed and you missed the next appointment), schedule completion as soon as possible. Long delays increase the risk of reinfection, flare-ups, or fracture.

Is the Tooth Dead After a Root Canal?

Patients commonly ask: root canal dead tooth, if you have a root canal is the tooth dead, or does a dead tooth need a root canal.

A root canal treats or removes the inflamed/infected pulp tissue (the “nerve” tissue). After treatment, the tooth no longer has living pulp, but the tooth structure remains functional—supported by the surrounding ligament and bone. This is why a crown or definitive restoration is often recommended: it protects the tooth from fracture and leakage.

“Toxic Root Canal Symptoms” and “Death by Root Canal”

You may see alarming searches online such as toxic root canal symptoms or death by root canal. These claims are frequently circulated online and can be frightening.

In modern dentistry, root canal therapy is a widely accepted, evidence-based procedure used to eliminate infection from within a tooth and reduce the risk of spreading infection. If you feel systemically unwell (fever, facial swelling, trouble swallowing/breathing, severe worsening pain), the concern is not “toxicity” from the root canal—rather, it may reflect an infection or medical issue that requires prompt evaluation.

• If you want a symptom timeline and what to do first, start with Pain After Root Canal: Causes, Timeline, and What to Do (Start Here).
• If you’re considering whether the tooth can be saved again, see Root Canal Redo: Can a Root Canal Be Redone?.

If you have concerns about systemic symptoms, seek in-person care so your clinician can assess both dental and non-dental causes appropriately.

What Happens When a Root Canal Fails?

When a root canal fails, it usually means infection or inflammation persists around the root tip or the tooth becomes reinfected through leakage. Some patients have obvious symptoms; others are identified during an exam and imaging.

The key point: a tooth infection generally does not “heal itself.” Timely diagnosis improves the chance of saving the tooth and prevents complications.

Treatment Options: Retreatment, Apicoectomy, or Extraction/Implant

Option 1: Endodontic Retreatment

Retreatment is often the first-line solution when a tooth is restorable. It involves reopening the tooth, removing the old filling material, disinfecting the canals again, identifying missed anatomy when possible, and resealing the tooth.  If you’re considering whether the tooth can be saved again, see Root Canal Redo: Can a Root Canal Be Redone?.

Option 2: Apicoectomy (Endodontic Microsurgery)

An apicoectomy may be recommended when retreatment is not feasible or when persistent apical disease remains. The endodontist accesses the root tip through the gum, removes inflamed tissue, and seals the end of the root.

Option 3: Extraction and Replacement (Implant/Bridge)

If the tooth has a vertical root fracture, severe structural damage, or cannot be predictably restored, extraction may be recommended. Replacement options commonly include a dental implant or bridge. Some people search: root canal failure leads to tooth implant.

How to Reduce the Risk of Root Canal Failure

• Restore the tooth promptly (avoid delaying the crown when indicated)
• Protect against fracture (especially for back teeth)
• Maintain excellent oral hygiene and routine check-ups
• Address clenching/grinding (nightguard may be appropriate)
• Follow post-op guidance and call early if symptoms worsen

Is the Dentist Responsible for a Failed Root Canal?

Patients sometimes ask: should dentist pay for failed root canal or who is responsible for a failed root canal.

In most cases, failure is related to biology/anatomy, restoration breakdown, fracture risk, or reinfection—not a single simple cause. Responsibility (including any financial remedy) depends on details such as:

• Whether the original diagnosis and procedure were appropriate
• Whether the tooth had unusually complex anatomy or cracks
• Whether the final restoration (crown/filling) was placed on time and maintained a good seal
• Whether new decay or trauma occurred later

If you are concerned, start with a calm, documentation-based conversation with your dental office and consider an endodontic evaluation for a clear diagnosis. (This is general information, not legal advice.)

Frequently Asked Questions

Can a root canal fail?

Yes. Although most root canals are successful, a tooth can become reinfected or fail to heal properly due to complex anatomy, cracks, or a compromised seal.

How often does a root canal fail? What percent of root canals fail?

Failure rates vary by tooth type, anatomy, and restoration quality. Rather than focusing on a single number, focus on getting an accurate diagnosis and a plan to preserve the tooth when possible.

Can an old root canal get infected?

Yes. A previously treated tooth can become reinfected if bacteria re-enter through leakage, new decay, or cracks. This is a common reason for root canal infection years later.

My root canal tooth hurts years later—what should I do?

Schedule an evaluation. Common causes include leakage under a crown, new decay, a crack, bite trauma, or persistent apical inflammation. Early evaluation improves outcomes.

Conclusion: Root Canal Failure Signs and the Safest Next Step

If you are worried about root canal failure, the most reliable approach is to focus on objective warning signs and the symptom trend. Common failed root canal symptoms include persistent pain, sharp pain when biting, swelling, drainage/bad taste, and a gum pimple or abscess near the treated tooth. Many patients experience new symptoms months or years later—searching phrases like root canal tooth hurts years later, toothache years after root canal, root canal infection years later, or how to know if root canal failed. These scenarios are not reasons to panic, but they are strong reasons to get evaluated promptly.

The “why” often comes down to a short list of causes: complex anatomy that was difficult to fully disinfect, a canal that was missed, a cracked tooth, or (very commonly) a compromised seal from a leaking filling or crown—especially if the crown was delayed or the temporary broke down. If you suspect your root canal filling fell out, if the tooth feels suddenly different, or if you have signs of infection after root canal, protect the tooth by avoiding chewing and arranging a dental or endodontic assessment.

The good news is that many failed root canals are treatable. Depending on diagnosis, solutions may include endodontic retreatment, apicoectomy, or—when the tooth is not restorable—extraction with an implant or bridge. The highest-value decision you can make is to get a precise diagnosis early, before infection progresses or the tooth fractures. If you have swelling, fever, drainage, rapidly worsening pain, or difficulty swallowing/breathing, seek urgent care.  If you’re unsure what “normal side effects” look like, compare with Understanding Root Canal Treatment Side Effects.

Medical disclaimer: This page is for general education and does not replace an in-person dental evaluation or individualized medical advice.