Root canal treatment saves a tooth whose soft inner tissue has become inflamed or infected. Follow one lower molar through eight stages of care, from diagnosis to healing. Hover, tap, or tab to any structure in the illustration to learn what it is.
Educational illustration, not medical advice.
The procedure
Eight stages
Step 1 of 8 · DiagnosisSchematic, not to scale. Hover or tap to identify.
STEP 01
Diagnosis
A root canal is considered when the pulp, the soft tissue at the center of the tooth, is irreversibly inflamed or has died and become infected, often from deep decay, a crack, or injury. Signs can include lingering sensitivity to hot or cold, pain when biting, or swelling, though some infected teeth cause no pain at all. Dental X-rays help show what is happening around the root tip.
In the illustration: decay reaching toward the pulp, inflamed pulp tissue, and a darker area of bone at the root tip.
Clinician detail
Diagnosis combines history with clinical testing (cold and electric pulp tests, percussion, palpation, periodontal probing) and periapical radiographs; CBCT may be used selectively. A common working diagnosis is symptomatic irreversible pulpitis or pulp necrosis, with or without apical periodontitis.
Apical periodontitis can appear as a periapical radiolucency, but a lesion may not be visible on a 2D radiograph until bone loss is advanced.
STEP 02
Anesthesia & isolation
Local anesthetic numbs the tooth and the area around it. A rubber dam, a thin sheet held by a small clamp, then isolates the tooth so it is the only one exposed. This keeps saliva and its bacteria out of the canals and protects the patient from small instruments and disinfecting solutions.
In the illustration: the dam sheet draped at the neck of the tooth and the clamp jaws gripping just above the gumline.
Clinician detail
The American Association of Endodontists considers dental dam isolation the standard of care for nonsurgical root canal treatment. It maintains an aseptic field, prevents aspiration or ingestion of files, and contains irrigants such as sodium hypochlorite.
Teeth with extensive breakdown may need a pre-endodontic build-up so the dam clamp can seat and a seal can be maintained between visits.
STEP 03
Access opening
Working through the chewing surface, the dentist removes the decay and makes a small opening into the pulp chamber. The opening is shaped so instruments can travel in a straight line toward each canal.
In the illustration: a funnel-shaped opening through enamel and dentin that meets the roof of the pulp chamber.
Clinician detail
Access design follows chamber anatomy: complete removal of caries and the chamber roof, including pulp horns, followed by locating every canal orifice. Magnification and illumination (loupes or an operating microscope) help.
This section shows one canal per root, but a lower first molar typically has at least three canals, commonly two in the mesial root. A missed canal is a recognized cause of persistent infection.
STEP 04
Pulp removal & working length
The inflamed or infected tissue is removed from the chamber and canals with fine instruments. The dentist then measures each canal's working length: how far instruments should travel, ending just short of the root tip. Getting this length right lets the whole canal be cleaned without pushing material past the end of the root.
In the illustration: the emptied canal space, a small file reaching near the apex, and the rubber stop marking the measured length.
Clinician detail
Working length is measured from a stable coronal reference point, often a cusp tip, to a point at or near the apical constriction. It is commonly determined with an electronic apex locator and confirmed radiographically; a silicone stop on the file marks the reference.
Small, precurved hand files are used to negotiate the canal and establish a glide path before rotary shaping.
STEP 05
Cleaning & shaping
Files of gradually increasing size shape each canal into a smooth taper, wider near the top and narrow at the tip. Between files, the canal is flushed with a disinfecting solution that dissolves remaining tissue and carries debris out. Shaping matters largely because it lets that solution reach the whole canal.
In the illustration: the file handle changes color as sizes increase, the canal widens, and irrigant carries debris up and out.
Clinician detail
Sodium hypochlorite is the most widely used irrigant for its tissue-dissolving and antimicrobial action; EDTA is often used to remove the smear layer. Irrigant is delivered with a side-vented needle placed loosely in the canal to reduce the risk of extrusion past the apex.
Shaping is typically done with nickel-titanium rotary or reciprocating files. ISO file sizes are color-coded, for example 15 white, 20 yellow, 25 red, 30 blue, 35 green. In multi-visit cases, calcium hydroxide may be placed between appointments.
STEP 06
Obturation
Once the canals are clean and dry, they are filled and sealed, most commonly with gutta-percha, a rubber-like material, together with a sealer cement. The seal helps keep bacteria from re-entering the root.
In the illustration: orange gutta-percha filling each tapered canal, outlined by a thin layer of sealer.
Clinician detail
Common techniques include cold lateral compaction, warm vertical compaction, and single-cone obturation with a hydraulic (bioceramic) or resin-based sealer. A master cone is fitted to working length and checked radiographically.
The goal is a dense, three-dimensional fill to working length without gross overextension.
STEP 07
Restoration
The tooth then needs a lasting restoration. Back teeth usually receive a core build-up and a crown, which helps protect the remaining tooth from fracture and keeps the seal intact. A well-sealed final restoration is an important part of long-term success.
In the illustration: core material rebuilding the inside of the tooth, covered by a full-coverage crown.
Clinician detail
Coronal leakage can recontaminate an obturated canal, so the definitive restoration should be placed promptly. Cuspal coverage (crown or onlay) is generally recommended for root canal treated posterior teeth.
A post is used only when needed to retain the core; it does not strengthen the root.
STEP 08
Healing
With the source of infection removed, the body can repair the bone around the root tip. On follow-up X-rays, a dark area at the root tip often becomes smaller over months as bone fills back in. Your dentist will check the tooth at recall visits.
In the illustration: the periapical lesion shrinking as the surrounding bone heals.
Clinician detail
Healing is assessed clinically and radiographically at recall. Guidelines generally recommend review for at least a year, with longer monitoring when healing is incomplete; larger lesions can take more time to resolve.
A persistent or enlarging lesion, or ongoing symptoms, prompts evaluation for nonsurgical retreatment or endodontic surgery.
Infection control
Instrument reprocessing
A root canal works by removing bacteria, so everything that enters the tooth has to be clean. Reusable instruments move through the same loop between every patient, alongside gloves, masks, eye protection, and surface disinfection.
Cleaning
Used instruments are cleaned of debris, usually in an ultrasonic cleaner or instrument washer, by staff wearing heavy-duty utility gloves. Sterilization cannot be relied on if debris remains.
Packaging
Dry instruments are wrapped or sealed in pouches, often with an internal chemical indicator, so they stay sterile after the cycle.
Autoclave
Pressurized steam sterilizes the packs. Each cycle's time, temperature, and pressure are checked.
Indicator check
Chemical indicators change color to show exposure to the process. Biological indicators (spore tests) verify that the sterilizer actually works, and the CDC recommends running them at least weekly.
Storage
Packs stay sealed in a clean, dry area and are opened chairside at the time of use. A wet or torn pack is reprocessed.
Items labeled single-use, including many rotary files and irrigation needles, are discarded rather than reprocessed.
Myths & facts
Well-established points only
Myth
Root canals are extremely painful.
Fact
With modern local anesthesia, many patients find the procedure feels similar to getting a filling. Some tenderness for a few days afterward is common and usually manageable.
Myth
A root canal removes the tooth's roots.
Fact
The roots stay in place. Only the soft tissue inside the canals is removed, and the space is cleaned and sealed.
Myth
If it doesn't hurt, it doesn't need treatment.
Fact
A tooth whose pulp has died can be painless while infection persists at the root tip. That is one reason regular exams and X-rays matter.
Myth
Root canal treatment causes illness elsewhere in the body.
Fact
This idea traces to early 20th-century "focal infection" research that later studies could not reproduce. There is no valid scientific evidence linking root canal treated teeth to disease elsewhere in the body.
Myth
Pulling the tooth is always the simpler choice.
Fact
Keeping a natural tooth is generally preferred when it can be restored. A missing tooth often needs a replacement, such as an implant or bridge. The right option depends on the tooth and is worth discussing with your dentist.
Myth
Once treated, the tooth needs no more care.
Fact
The tooth still needs a well-sealed restoration and can still develop decay or gum disease, so brushing, flossing, and checkups still matter.