Cavity Stages Guide: Symptoms and Treatment by Stage, from Enamel and Dentin to the Pulp and Root Tip

A cavity starts in the outer enamel and deepens through the dentin, the pulp where nerves and blood vessels lie, and the bone around the root tip. Early on it barely hurts and is easy to overlook; once it starts to be sensitive it has probably reached the dentin, and once it throbs by itself it has probably reached the pulp. The deeper the stage, the more tooth is removed and the longer and costlier the treatment, so finding it at a checkup when there are no symptoms is the most advantageous.

Published 2026-11-08 · Updated 2026-11-08 · DentalStatics editorial team

Key facts

Purpose of fluoride application	Preventing cavities and stopping the progress of cavities that have already formed (source: Korea Disease Control and Prevention Agency (KDCA, 질병관리청) National Health Information Portal)
Symptoms that may need root canal treatment	Pain with cold or hot things, severe pain at rest, frequently recurring pus in the gums (source: Korea Disease Control and Prevention Agency (KDCA, 질병관리청) National Health Information Portal)
If pulp infection is left untreated	Inflammation spreads through the root tip to the surrounding bone, and extraction may be needed (source: Korea Disease Control and Prevention Agency (KDCA, 질병관리청) National Health Information Portal)
When a crown is needed	Cavities, excessive wear, fracture, and protecting a tooth after root canal treatment (source: Korea Disease Control and Prevention Agency (KDCA, 질병관리청) National Health Information Portal)
Dental caries testing for children	Decided to extend coverage of quantitative light-induced fluorescence testing to ages 15 and under and to once every 3 months (December 2024) (source: Ministry of Health and Welfare (보건복지부))

How many stages does a cavity have?

Dentists divide the progress of a cavity by how many layers of the tooth it has entered. Understanding it as four stages, namely the hard outermost enamel, the dentin beneath it, the pulp through which nerves and blood vessels pass, and the tissue around the root tip, makes it easy to link symptoms and treatment.

Even at the same stage, the time of discovery and the treatment method differ depending on whether the cavity is on the chewing surface or between the teeth or on the gum side. Cavities between teeth are hard to see with the eye and are often found on X-rays.

Stage 1, enamel: white spots or brown dots, almost no pain
Stage 2, dentin: sensitivity to cold and sweets, a hole where food gets trapped
Stage 3, pulp: spontaneous throbbing, pain worse at night
Stage 4, root tip: pain on biting, pus in the gums, facial swelling

What is done for an early cavity?

An early cavity limited to the enamel looks like a white cloudy surface or brown dots and usually does not hurt. If no hole has formed, it is not drilled right away but is sometimes monitored while its progress is stopped with fluoride application, brushing and diet control.

The fluoride application entry of the KDCA National Health Information Portal gives preventing cavities and stopping the progress of cavities that have already started as the purposes of applying fluoride. That is why fluoride is especially meaningful at the early cavity stage. In December 2024 the Ministry of Health and Welfare decided to widen the covered age for quantitative light-induced fluorescence caries testing for children to 15 and under and the interval to once every 3 months, making tests that find early cavities easier to receive.

What treatment is done once it reaches the dentin?

Dentin is softer than enamel and has many microscopic tubules connected to the nerve, so cavities spread quickly and sensitivity to cold or sweets appears. From this stage the decayed part must be ground away and filled with material.

If it is small, a direct restoration is done in which material such as resin is placed right in the mouth, and if the extent is wide and the remaining tooth walls are weak, an inlay or onlay made from an impression is used. If the cavity is deep and close to the nerve, a material that protects the nerve is sometimes placed first before filling.

What happens when it reaches the nerve and the root tip?

When a cavity touches the pulp, it often throbs even at rest and the pain gets worse at night. The National Health Information Portal explains that if pulp infection is left alone, inflammation spreads through the root tip to the surrounding bone and extraction may eventually be needed. At this stage root canal treatment removes the infected pulp, and the root canals are disinfected and filled.

Once the nerve has died, the pain may actually disappear, and then as pus builds up at the root tip, biting may hurt or a pus pocket may form in the gums. After root canal treatment, the weakened tooth is wrapped in a crown, and if the tooth has collapsed too far to be saved, an implant or bridge after extraction is considered.

How does the treatment burden change as the stage deepens?

At the enamel stage, fluoride and care alone can keep it under observation, but from the dentin stage a filling is needed, and once it reaches the pulp, root canal treatment and a crown are added, greatly increasing the number of visits and the duration. The National Health Information Portal guides that root canal treatment alone takes 3 to 4 or more visits at intervals averaging 3 to 7 days.

Cost also changes with the stage. Small fillings can often use covered materials, but inlays and crowns are uninsured and the burden grows. Getting a checkup at the stage when a cavity is only suspected removes less tooth and reduces cost and time.

Common myths and facts

Myth: If it does not hurt, the cavity is not severe.

Enamel cavities barely hurt, and a tooth whose nerve has already died can also be painless for a while. Pain alone makes it hard to judge how far it has progressed, so checkups and X-rays are needed.

Myth: If you see a black spot, it must always be ground and filled.

An early cavity without staining or a hole is sometimes monitored with fluoride and care. Whether to drill is judged by the dentist from the depth, extent and cavity risk.

Frequently asked questions

Can a cavity heal by itself?

Early changes in enamel before a hole forms can stop progressing or harden with fluoride and care. But a cavity that already has a hole does not fill itself in and needs treatment.

It is sensitive only to cold water. Do I need root canal treatment?

If it is briefly sensitive to cold and quickly goes away, it may be a dentin cavity or sensitive teeth, and it often ends with a filling. If pain lingers long after the cold is removed or hurts on its own, the condition of the nerve should be checked.

How fast do cavities progress?

The speed at which a cavity spreads differs by person and by part of the tooth. It progresses quickly with frequent sweets, dry mouth or difficulty brushing, so it is good to decide the checkup interval by consulting the dentist.

Are the stages the same for a child's baby-tooth cavity?

Baby teeth progress in the same order, but enamel and dentin are thin so a cavity can reach the nerve faster. Leaving a baby-tooth cavity untreated can cause pain and infection and also affect the permanent tooth coming in beneath it, so early treatment is recommended.

How is the cavity stage checked?

Visual examination, checking the surface with an instrument, and X-rays are looked at together. For children, a quantitative light-induced fluorescence test, which uses light to find early cavities, is sometimes done, and the Ministry of Health and Welfare decided to widen the covered age of this test to 15 and under.

References

Korean version →