Root canal therapy is meant to remove infected tissue from inside a tooth and seal it. But in real life, an infection can still develop, or linger around, underneath a root canal treated tooth, sometimes months or even years later. In biological dentistry, we pay close attention to hidden infection patterns, how they impact the surrounding bone and gums, and what long-term solutions (including a zirconia implant) may be appropriate when a tooth can’t be predictably stabilized.

Why a Root Canal Infection Can Still Happen

Teeth are not simple hollow tubes—they contain complex anatomy that can hide bacteria. Here are the most common reasons that the infection can form underneath a root canal:

Hidden anatomy that’s difficult to fully disinfect

Teeth contain:

• Accessory canals (tiny branches off the main canal)
• Isthmuses (thin corridors connecting canals)
• Dentinal tubules (microscopic channels throughout the tooth)

Even with careful treatment, these areas can be difficult to fully clean and bacteria may continue to trigger inflammation at the root tip or trigger inflammation while harvesting inside the canals, leading to persistent or recurring infection.

Microleakage: bacteria re-enter through a compromised seal

A root canal depends on a strong seal:

• Inside the tooth (canal filling)
• On top of the tooth (filling/crown)

If the crown margin opens, a filling wears down, or decay forms under a restoration, bacteria can seep back in (microleakage) and cause reinfection over time.

Missed canals or incomplete canal cleaning

Some teeth (especially molars) may have additional canals that can be difficult to locate. If a canal is missed or not cleaned thoroughly to the full length, bacteria can remain and continue to infect the area around the root.

New decay under an existing crown or filling

A root canal treated tooth can still get cavities, around crown edges, where plaque can accumulate. Once decay creates a pathway, bacteria can travel down into the tooth and contaminate the canal space again.

Cracks or fractures create a hidden pathway for bacteria

Root-canaled teeth can become more brittle, especially if they’ve lost significant tooth structure. A vertical fracture can allow bacteria to infiltrate areas that are impossible to seal.

Symptoms of Infection Under a Root Canal

Some people feel nothing at first, which is why routine monitoring matters. Others notice symptoms such as:

• Pain or pressure when biting
• Persistent tenderness near the tooth
• Swelling or a “pimple” on the gum (draining sinus tract)
• Bad taste or occasional drainage
• Sensitivity in the surrounding gums or jaw
• For upper molars: sinus pressure-like symptoms

How Biological Dentistry Evaluates Root Canal Infection

A biological dentistry approach typically emphasizes thorough diagnostics and a treatment plan that aligns with whole-body health.

Evaluation may include:

• Clinical exam (mobility, bite test, percussion)
• Gum measurements to check for isolated deep pockets
• 2D X-rays to look for bone changes near the root tip
• CBCT / 3D imaging when indicated (helpful for hidden infections, missed canals, or fractures)

Treatment Options for Root Canal Infection

The right option depends on the cause of infection and whether the tooth is structurally stable.

Extraction and replacement

If there is a vertical fracture, persistent reinfection, or severe decay, extraction may be the most predictable option. Replacement may include a bridge, partial denture, or implant.

FAQ: Root Canal Infection and Zirconia Implants

Can a root canal tooth be infected without pain?

Yes. Some infections are low-grade and asymptomatic at first, showing up only on imaging or during routine evaluation.

What’s the difference between a “failed root canal” and a reinfected root canal?

A “failed” root canal may mean the infection never fully resolved due to missed anatomy or persistent bacteria. A “reinfected” root canal often suggests bacteria re-entered later due to microleakage, new decay, or a compromised crown.

Will antibiotics fix a root canal infection?

Antibiotics may temporarily reduce symptoms, but they usually don’t eliminate the source inside a tooth. Definitive care typically requires addressing the cause.

When is a zirconia implant a good option?

A zirconia implant may be considered when a tooth has poor prognosis. Candidacy depends on bone, bite, and overall health factors.

What to Take Away

A root canal infection can form underneath a treated tooth due to hidden anatomy, microleakage, missed canals, decay, or fractures. A thorough evaluation can clarify what’s happening and guide next steps. For patients exploring whole-body approaches through biological dentistry, a zirconia implant may be a long-term option when extraction is the most predictable path.

Learn more here:

• Internal link #1: https://www.seattledentalcare.com/services/biological-natural-holistic-dentistry/
• Internal link #2: https://www.seattledentalcare.com/services/ceramic-implant/