During a root canal, your dentist or endodontist places several different materials inside your tooth at different stages of the procedure. The main filling material is gutta-percha, a rubbery substance derived from tropical trees, but it’s far from the only thing that goes in. From the rinses used to clean out infection to the final seal that protects the tooth, each material has a specific job.
Irrigation Solutions That Clean the Canal
Before anything permanent goes in, the infected pulp tissue (the nerve and blood supply) is removed and the hollow canals are flushed with liquid disinfectants. The most common is sodium hypochlorite, essentially a medical-grade bleach solution used at concentrations between 0.5% and 6%. It dissolves dead tissue and kills bacteria deep inside the canal walls.
Sodium hypochlorite can’t do it all on its own, though. When the dentist drills and shapes the canal, a thin layer of debris called the smear layer builds up along the inner walls. This layer contains minerals and bacteria that bleach alone won’t remove. To clear it, the canal is rinsed with a chelating solution called EDTA, which dissolves the mineral component and leaves the canal walls clean enough for the filling material to bond tightly.
Medication Between Appointments
If your root canal is done over two visits, the dentist will pack a medicated paste inside the tooth to keep bacteria from regrowing between appointments. The most widely used is calcium hydroxide paste. It creates a highly alkaline environment inside the canal that kills remaining bacteria, neutralizes toxins produced by the infection, and even encourages the surrounding bone to begin healing. This paste typically stays in the tooth for one to two weeks before the final filling is placed.
In some cases involving younger patients or teeth with open, still-developing roots, a mix of three antibiotics (ciprofloxacin, metronidazole, and minocycline) is used instead. This triple antibiotic paste is mixed at equal parts to a very low concentration and packed into the canal to sterilize it thoroughly as part of a regenerative approach that tries to encourage new tissue growth rather than simply filling the space.
Gutta-Percha: The Main Filling
Once the canal is clean and shaped, it needs to be sealed permanently. The standard material for this is gutta-percha, which comes in small, tapered, cone-shaped points that match the shape of the prepared canal. Despite its name suggesting a single substance, commercial gutta-percha points are mostly zinc oxide (59 to 75%), with only about 19 to 22% actual gutta-percha polymer. The rest is a mix of waxes, coloring agents, antioxidants, and metal salts that make the filling visible on X-rays.
The dentist coats the gutta-percha cones with a thin layer of sealer cement before sliding them into the canal. This sealer fills the microscopic gaps between the gutta-percha and the canal walls, creating an airtight seal that prevents bacteria from re-entering. Several cones are often packed together, with the dentist compressing them using heated instruments so they conform tightly to every curve and irregularity in the canal. The result is a dense, rubber-like plug that extends from the tip of the root to the opening of the tooth.
Repair Materials for Special Situations
When a root has a crack, a perforation, or an open tip that hasn’t fully formed, your dentist may use a cement called mineral trioxide aggregate (MTA). It’s a fine powder made primarily of calcium and silicate compounds, with bismuth oxide added so it shows up on X-rays. Mixed with water, it forms a paste that sets in about three to four hours and creates an exceptionally tight seal.
What makes MTA valuable is its biological compatibility. When placed against living tissue, it encourages the body to deposit new cementum (the thin minerite layer that naturally covers tooth roots) right over the material. This makes it ideal for sealing perforations where the root wall has been breached, for capping an exposed nerve to keep it alive, and for closing the open tip of an immature root so it can then be filled normally.
Temporary Fillings That Seal the Opening
Between appointments, and sometimes briefly after the final fill, a temporary material is placed in the access hole on top of the tooth. Two materials dominate here. Cavit is a premixed paste containing zinc oxide, calcium sulfate, and a polymer blend that expands slightly as it sets, pressing against the cavity walls for a snug seal. IRM is a zinc oxide-eugenol cement reinforced with polymer for extra strength. Both are designed to block bacteria from leaking back into the freshly cleaned canal during the healing window.
These temporary fillings aren’t meant to last. They’re replaced within a few weeks by a permanent restoration, typically a crown or a composite filling that rebuilds the tooth’s chewing surface.
Posts and Cores for Badly Damaged Teeth
If the tooth has lost a significant amount of its structure to decay or fracture, a post may be cemented down into one of the filled canals to anchor a rebuilt core on top. Traditionally, these posts were cast from metal alloys as a single piece with the core attached. The downside is that metal posts can show through a ceramic crown, giving the tooth a grayish tint.
Newer options include prefabricated glass fiber or carbon fiber posts, which are tooth-colored and more flexible. Their flexibility is actually an advantage: a rigid metal post concentrates stress at one point and can crack the root, while a fiber post flexes more like natural tooth structure, distributing force more evenly. After the post is cemented in place, the dentist builds a core around it using composite resin, creating a solid foundation for the final crown.
What It All Adds Up To
A root canal tooth, by the time it’s finished, contains a surprisingly layered stack of materials. Residual traces of the disinfecting rinses. A dense core of gutta-percha and sealer filling the canals from root tip to crown. Possibly a fiber post anchored in one canal. A composite or amalgam core rebuilding the missing tooth structure. And a crown on top tying it all together. Each layer serves a single purpose: keeping bacteria out and giving the tooth enough structural support to function for years.