What Do They Put in a Root Canal? Materials Used

A root canal involves a surprising variety of materials, and most of them never stay in the tooth permanently. During the procedure, your dentist or endodontist flushes the hollowed-out canal with disinfecting solutions, may pack it temporarily with a medicated paste, and then fills it with a rubber-like core material sealed in place by a thin cement. The final restoration on top adds yet more layers. Each material has a specific job, and the choices your clinician makes among the options available can affect how well the tooth holds up over time.

Cleaning Solutions That Go in First

Before anything permanent enters the canal, the space needs to be thoroughly disinfected and cleared of dead tissue. The workhorse solution is sodium hypochlorite, essentially a medical-grade bleach diluted to concentrations typically between about 1% and 5%. It works by breaking down the fats in bacterial cell membranes, disrupting cellular metabolism, and dissolving organic tissue left behind after the nerve is removed.¹ Among commonly tested irrigants, higher concentrations of sodium hypochlorite dissolve pulp tissue most effectively.²

Sodium hypochlorite is excellent at killing bacteria and dissolving soft tissue, but it cannot remove the thin layer of debris and mineral deposits that drilling creates on the canal walls, called the smear layer. To tackle that, clinicians follow up with a chelating rinse. EDTA at a 17% concentration has long been the standard for this step, though laboratory studies show that alternatives like maleic acid and etidronic acid can outperform EDTA at clearing the smear layer from the hardest-to-reach apical third near the root tip.³ One study found that an etidronate-based protocol removed smear layer roughly four times more effectively than EDTA alone.⁴

Some practitioners also use chlorhexidine, a broad-spectrum antimicrobial familiar from surgical hand scrubs, as a supplementary rinse. It does not dissolve tissue the way sodium hypochlorite does, but it has the advantage of binding to dentin surfaces and continuing to release antimicrobial activity for a while after application.

Ultrasonic Agitation

How the irrigant is delivered matters almost as much as which irrigant is chosen. Simply squirting liquid into a canal with a syringe leaves pockets of debris, especially in curved or irregularly shaped canals. Passive ultrasonic irrigation uses a small vibrating tip inserted into the canal to agitate the solution. This creates acoustic streaming and micro-cavitation that push the irrigant into side canals and dentinal tubules that a syringe alone cannot reach. Studies consistently show that ultrasonic activation significantly improves debris removal and enhances the antimicrobial effect of both sodium hypochlorite and chlorhexidine.⁵ ⁶ When chlorhexidine is paired with ultrasonic agitation, it can penetrate deep into the tiny tubules of dentin, reaching depths far greater than syringe delivery alone.⁷

Medication Between Appointments

If the infection is severe or the procedure is split across two visits, the clinician may place a temporary medicated paste inside the canal. The most common choice is calcium hydroxide, a strongly alkaline paste that creates a hostile environment for bacteria. Its high pH (around 12.5) is directly toxic to most oral pathogens. Calcium hydroxide is mixed into a paste and packed loosely into the canal, then covered with a temporary filling material until the next visit.

The evidence on how much additional disinfection this step provides is mixed. A randomized clinical trial found that leaving calcium hydroxide in the canal for seven days did not prevent bacterial counts from rising back to the level seen immediately after the initial cleaning and shaping, though counts did not climb higher than that baseline either.⁸ In other words, calcium hydroxide holds the line rather than dramatically improving disinfection. Many endodontists still use it in cases of persistent infection, apical abscesses, or when the tooth needs time to settle before final filling.

Temporary Fillings That Seal the Access

Between appointments, the hole drilled into the crown of the tooth needs to be sealed so saliva and bacteria cannot re-contaminate the canal. Several temporary filling materials are used for this purpose. Cavit, a moisture-activated zinc oxide material, is one of the most popular. IRM (Intermediate Restorative Material), a reinforced zinc oxide eugenol cement, is another common option. In laboratory testing, a layer of Cavit or the light-cured material Dyract held off bacterial leakage for about two weeks, while IRM began leaking slightly earlier, around ten days.⁹ For most patients, these materials hold up well enough over the one to three weeks between visits, but delays in returning for the permanent filling increase the risk of recontamination.

Gutta-Percha, the Core Filling Material

Once the canal is clean, shaped, and dry, it needs to be filled with something that seals the space and prevents bacteria from returning. The material that has dominated this step for well over a century is gutta-percha. Despite its name suggesting a single substance, commercial gutta-percha points contain only about 20% actual gutta-percha polymer. The bulk of each point, roughly 66%, is zinc oxide filler, with about 11% heavy metal sulfates added to make the material show up on X-rays, and around 3% waxes or resins that act as plasticizers.¹⁰

The result is a semi-rigid, slightly rubbery cone that can be compressed and warmed to conform to the shape of the canal. Clinicians either use a cold lateral compaction technique, wedging multiple cones side by side and pressing them against the walls, or a warm vertical technique where heated gutta-percha is softened and pushed down to fill irregularities. Neither technique alone achieves a perfectly hermetic seal, which is why a thin layer of sealer cement is always used alongside gutta-percha.

One practical advantage of gutta-percha is that it can be dissolved and removed if retreatment becomes necessary. Solvents like xylene and orange oil effectively soften the material, with xylene being the most efficient option in laboratory comparisons.¹¹ This removability is actually considered a feature: if the tooth develops a new infection years later, the filling can be taken out and the canals re-treated rather than extracting the tooth.

Root Canal Sealers

Gutta-percha does not bond to the walls of the canal on its own. It needs a sealer, a thin cement that fills the microscopic gaps between the gutta-percha and the dentin. Sealers come in several chemical families, and the choice among them is one of the more consequential decisions in the procedure.

Zinc Oxide Eugenol Sealers

These are the oldest and most traditional type. They combine zinc oxide powder with eugenol, an oil derived from cloves that gives dental offices their distinctive smell. Zinc oxide eugenol sealers have natural antimicrobial properties, which made them popular for decades. Their downsides include slow setting time, noticeable shrinkage as they harden, and relatively poor solubility resistance once set.¹² In leakage comparisons, zinc oxide eugenol sealers consistently rank below newer alternatives.¹³

Resin-Based Sealers

Epoxy resin sealers like AH Plus and its predecessor AH 26 have become the benchmark against which other sealers are measured. They set slowly, which gives clinicians working time, and they exhibit excellent dimensional stability, meaning they neither shrink nor swell much after curing. In head-to-head comparisons, AH Plus typically shows less apical leakage than both zinc oxide eugenol and MTA-based sealers.¹³ In a bacterial leakage study, the epoxy resin AH 26 kept bacteria out for an average of over 13 days, far outlasting the zinc oxide eugenol sealer’s roughly 6 days.¹² However, resin sealers can be difficult to remove during retreatment, and solvents like xylene or newer products such as GuttaClear are often needed to dissolve them from the dentinal tubules.¹⁴

Bioceramic Sealers

The newest generation of sealers is based on calcium silicate chemistry, commonly called bioceramics. Products like EndoSequence BC Sealer and MTA Fillapex use moisture from the surrounding dentin to set, which means they actually benefit from the slightly damp environment inside a tooth. Bioceramic sealers demonstrate bioactivity, meaning they can promote mineralization and interact positively with the body’s own repair processes.¹⁵ They also tend to show lower toxicity to surrounding tissues compared to older sealer types.¹⁶ The tradeoff is that once set, bioceramic sealers are extremely hard and difficult to remove if retreatment is needed.

MTA for Repairs and Special Situations

Mineral trioxide aggregate, or MTA, deserves separate mention because it plays a unique role. Derived from Portland cement, MTA is not used to fill entire canals the way gutta-percha is. Instead, it is placed in specific locations where the tooth structure has a defect or where the root tip is not fully formed. When a root has a perforation, meaning an accidental or pathological hole in the wall, MTA is packed into that spot to create a biocompatible plug. When exposed to the body’s fluids, MTA forms hydroxyapatite, the same mineral that makes up natural tooth and bone structure, which helps it integrate with surrounding tissues.¹⁷

MTA is also used as an intra-orifice barrier, a plug placed at the opening of the canal just below the crown restoration. This provides a secondary seal against bacteria leaking down from the mouth. Laboratory testing shows MTA produces less coronal leakage than glass ionomer or flowable composite when used in this role.¹⁸ In young patients whose root tips have not finished developing, MTA is placed at the apex to create an artificial barrier against which gutta-percha can then be packed, a procedure called apexification.

What Goes on Top of the Filling

Everything described so far happens inside the root canal itself. But the long-term success of the tooth depends just as much on what goes on top. After the canal is filled, the access hole through the crown must be sealed with a permanent restoration. This typically involves a core build-up material, often a bonded composite resin, placed over the canal filling to rebuild the internal structure of the tooth. Laboratory studies confirm that well-bonded restorative materials produce minimal to zero dye penetration when sealing the access cavity.¹⁹

If the tooth has lost a lot of its original structure, a post may be inserted into one of the filled canals to help anchor the core and the crown on top. Posts come in two broad categories: metal (typically stainless steel, titanium, or cast gold alloy) and fiber (usually glass-fiber reinforced composite). A systematic review and meta-analysis found that fiber posts showed significantly higher medium-term survival rates than metal posts when used to restore heavily damaged teeth with no more than two remaining coronal walls.²⁰ The likely reason is that fiber posts flex in a way that is closer to natural dentin, distributing stress more evenly and reducing the chance of catastrophic root fracture. A metal post is stiffer, and when it fails, it tends to crack the root itself rather than debond, making the tooth unsalvageable.

Biocompatibility and Tissue Reactions

All of these materials sit in intimate contact with living tissue at the root tip and through the dentinal tubules. A systematic review of both laboratory and animal studies found that root canal sealers in general produce mild to severe toxic effects on cells, with the degree of toxicity depending on factors like how long the material has been setting, its concentration, and the type of tissue exposure.¹⁶ That sounds alarming in isolation, but context matters: freshly mixed sealers are more toxic than fully set ones, and the amount of material that contacts living tissue at the root tip is extremely small. Newer formulations, particularly bioactive and bioceramic sealers, consistently show better cell viability and lower inflammatory responses compared to conventional sealers.²¹

True allergic reactions to root canal materials are rare but documented. Components like eugenol (from zinc oxide eugenol sealers), formaldehyde (released by some older sealers), latex (from natural rubber gutta-percha), and various resins have all appeared in case reports of allergic responses.²² If you have known allergies to latex or specific chemicals, mention it before treatment so your endodontist can choose alternatives. Synthetic gutta-percha formulations and non-eugenol sealers exist for exactly this situation.

Why Materials Show Up on X-rays

After your root canal, the dentist takes a final X-ray showing the filling as a bright white shape inside the tooth. This visibility is not accidental. Radiopacity, the ability to block X-rays and appear white on the image, is deliberately engineered into every material that stays in the canal. In gutta-percha, the heavy metal sulfates (about 11% of the point’s composition) serve this role. In sealers, compounds like bismuth oxide, barium sulfate, zirconium dioxide, or calcium tungstate are added as radiopacifiers. Researchers have been experimenting with alternatives because bismuth oxide, while effective, can cause tooth discoloration and may interfere with the biological properties of calcium silicate cements.

Discoloration from filling materials is a genuine cosmetic concern, particularly in front teeth. A review of the literature concluded that essentially all endodontic sealers can cause tooth discoloration if left in the pulp chamber. Epoxy resin sealers containing bismuth oxide can trigger a chemical reaction that produces dark compounds, and any residual silver-containing materials corrode to grey or black tones.²³ Careful cleaning of the pulp chamber walls after obturation, before placing the final restoration, minimizes this problem. Some clinicians deliberately choose bioceramic sealers or calcium-silicate cements with zirconium oxide radiopacifiers in anterior teeth to reduce the risk of staining.

Nanoparticles and the Next Generation

The materials used in root canals today are effective, but researchers are actively working on improvements. Much of the current innovation revolves around nanoparticles. Silver nanoparticles are being incorporated into sealers and irrigating solutions for their potent antimicrobial properties. Chitosan nanoparticles can serve as drug-delivery vehicles inside the canal. Hydroxyapatite nanoparticles are being added to sealers to promote remineralization. Bioactive glass nanoparticles, graphene, titanium dioxide, and several other nanomaterials have all shown promising results in laboratory studies when incorporated into sealers, obturating materials, irrigants, and intracanal medicaments.²⁴

The general trajectory is toward materials that do more than passively fill space. Ideal future materials would actively kill residual bacteria, encourage the body to form a mineralized seal at the root tip, resist degradation over decades, and cause zero tissue irritation. Bioceramics already move in this direction, and nanotechnology is pushing the concept further. Clinical adoption lags behind laboratory results, as it always does, but the gap between “inert space-filler” and “biologically active healing material” is steadily narrowing.

What Happens if the First Treatment Fails

About 5% to 15% of root canal treatments eventually need retreatment, depending on the complexity of the case. When that happens, every material placed during the first procedure must come back out. This is where the choice of original materials has lingering consequences. Gutta-percha is relatively easy to soften and remove with rotary instruments and solvents. Resin-based sealers like AH Plus are harder to clear because they bond tenaciously to dentin. Retreatment studies show that solvents like xylene and GuttaClear outperform others at dissolving AH Plus from the dentinal tubules, with GuttaClear being particularly effective in the apical third where access is most difficult.¹⁴ Bioceramic sealers, once fully set, are the most difficult of all to remove and sometimes require additional ultrasonic instrumentation.

After the old material is cleared, the canal is re-cleaned, re-shaped, and filled again with fresh materials, often using the same categories described above. The retreatment itself uses the same irrigants, the same sealer options, and the same gutta-percha. What changes is that the clinician is now working inside a canal that has already been enlarged once, with thinner remaining walls and potentially more complex anatomy to navigate.