The Stages of Tooth Decay

Written & Reviewed by Dr David Chen

Tooth decay progresses through sequential stages of decay. All cavities start the same way and when left untreated they will progress through each stage with increasing severity. That means it will not indiscriminately start off at a random stage nor will it ever skip one. They all progress sequentially without fail.

Human tooth diagram - KDS4444
Credit: KDS4444

Understanding which stage of the cavity that you’re in can provide you with a wealth of information.

  • The severity of your condition.
  • The urgency of requiring treatment.
  • The type of treatment that is needed.

Essentially it helps you make an informed decision as to what you should do with your decayed tooth.

Stage 1 – Demineralization

The first stage of tooth decay is demineralization which is essentially the very beginning of a cavity. It all starts at the outermost layer of the the tooth, the enamel layer because that is the only layer the bacteria are in contact with.

In this stage the tooth begins to weaken because as the name of the condition implies, it is demineralizing (losing minerals). Essentially the plaque full of bacteria that are covering the enamel surface are producing acids. These acids melt away the minerals from the teeth but you can also think of it as pulling the minerals out.

demineralization remineralization of teeth
Credit: Sangi Co

When the dentition loses its tooth minerals, calcium and phosphate, we refer to it as demineralization or otherwise known as the first stage of a cavity.

During this stage, there are imperceivable changes on the x-rays. Clinically however, you may notice chalky white spots on the enamel. Although if you try to scrape it the surface will feel intact and that is why studies refer to it as a subsurface lesion.


Since it is the start of tooth decay no treatment from your dentist is required because these can be reversed. Demineralized teeth can be remineralized, where minerals are added back into the tooth.

How to remineralize teeth:

  1. Baking soda mouth rinse immediately after your meal for 2 minutes.
  2. Wait 30 minutes for your mouth to naturally buffer.
    • Chew xylitol gum while you wait.
    • Drink water while waiting.
  3. Floss your teeth.
  4. Brush your teeth with a remineralizing toothpaste for at least 2 minutes.
  5. Repeat steps #1-4 every time after you eat.

Teeth in this condition won’t progress to the next stage immediately but if you don’t take care of them, they eventually will. You do have some time to try to reverse it but you don’t have an infinite amount of time.

Stage 2 – Enamel Decay

The second stage of a cavity is enamel decay, which comes directly after demineralization. It happens if you fail to remineralize the teeth and the lesion progresses. Usually it is because you haven’t kept up with your oral hygiene or you didn’t stop eating sweets.

What happens at this stage is the demineralized part of your enamel weakens enough that the tooth structure collapses. The collapse of the structure is essentially a hole in your tooth, hence the name cavity.

x-ray of enamel decay in between molar tooth

This is also the first progression of a cavity which becomes visible on a dental x-ray. What it looks like on the xray is a small little black line in the outer white shell (enamel).

In the mouth you may or may not be able to clinically see a cavitation or hole. The color is often a light brown or black. If you probe it with an explorer it will feel soft and sticky.


Depending on how far in the decay has progressed in the enamel, the treatment will differ.

  • Very shallow enamel decay you may still be able to remineralize it. You may follow the remineralization protocol above.
  • Moderate-severe enamel decay you will need a cavity filling.

If your dentist determines that it needs a filling in the tooth, it means that it has become irreversible. In other words, it can no longer remineralize so waiting to see if it improves will never happen.

What to expect for the dental filling:

  1. Local anesthesia.
  2. Drill out the decay.
  3. Fill the tooth back in with a composite resin.
  4. Polish and you’re done!

Stage 3 – Dentin Decay

The third stage of a cavity is dentin decay which is when the lesion has progressed beyond the enamel and into dentin. The decay is no longer at the outer layer of your tooth and has now moved into the middle layer.

Your tooth may not have been feeling any symptoms or sensitivity but now that all changes with dentin decay. Certain people may start feeling sweet sensitivity such as when you eat candy, chocolate, or even ice cream. That is your body’s way of letting you know that something is wrong and you need to address it.

Large cavity on premolar x-ray

Cavities in the dentin are very distinct on x-rays. They typically show up as a medium sized black circle in the tooth. In the x-ray above, the upper premolar has decay in the dentin.

Inside the mouth they will often look brown to black in color. It will feel very soft if you probe it with an explorer. Reason is because the tooth structured is completely decayed, almost similar to how termite infested wood feels soft.

This is also the stage where parts of the decayed tooth structure may sporadically “fall out.”


Cavities that are big enough to have progressed into the dentin are definitively non-reversible. Don’t even waste your time trying to remineralize this stage of a cavity because it will be futile.

The only treatment option for these would be either a filling or possibly a dental crown.

  • Dental filling. This is sufficient for decay that is small to medium in size.
  • Dental crown. If the cavity is big enough to compass about 50% of the tooth or more, you’ll most likely need a crown on it. A regular filling wouldn’t offer enough structural protection for that much missing tooth structure.

Due to the fact that it is irreversible and it can only grow, we do not recommend postponing treatment at this stage. You should try to address it as promptly as possible because if it gets bigger, treatment only gets more complex and expensive.

A filling costs less than a crown and if you could’ve treated it at that point you should. However if you leave it untreated, it will definitely progress to needing a crown and that costs multiples more than a filling.

Stage 4 – Pulp Decay

The third stage of tooth decay is a cavity that has reached the pulp. Essentially the decay has worked its way through all three layers of your tooth, enamel, dentin, and pulp.

The pulp is located in the middle of the tooth and is filled with nerve endings. Enamel decay is usually asymptomatic while dentin decay may be sweet sensitive. Pulp decay on the other hand can elicit an unbearable toothache that will keep you up at night. It is all because that is where all of the nerves of your tooth is located so it is extremely sensitive to stimuli.

periapical x-ray of a large cavity into the pulp

The x-ray above shows decay that has reached the nerve of the tooth. You can see a very large black circle that has reached the middle of the tooth, which lets you know it is serious.

What it looks like in the mouth is often a big hole or large cavity. It will be dark brown or black in color. The texture will be very soft if you try to probe it with an explorer. You may also find food and plaque stuck inside the hole since it is so large.

Last but not least, you should expect the tooth to be highly symptomatic. Most likely you’ll be experiencing a lot of pain. Usually if you have spontaneous pain that is not trigger by stimuli, it is a tell tale sign of the decay having reached the pulp.


This tooth decay stage cannot be treated by remineralization, cavity fillings, nor dental crowns. The only treatment option for it is a root canal, which is when your dentist removes the nerve from the tooth. The tooth remains in the mouth but the nerve gets extirpated.

What to expect for root canal treatment:

  1. Apply local anesthesia.
  2. Drill out the cavity.
  3. Extract the nerve from the tooth.
  4. Disinfect the entire canal.
  5. Place a root canal filling.
  6. Return back to your general dentist to get a crown.

The reason why a root canal is needed because that is treatment for the tooth nerve. Fillings and crowns don’t treat the nerve, they only treat decay that is in the enamel and dentin. A root canal is nerve treatment, that is the only way to deaden the pulp.

Stage 5 – Tooth Abscess

The fifth and final stage of a cavity is a tooth abscess. If you’ve reached this stage, you must’ve been extremely unlucky or you’ve been avoiding the dentist! In order for a dental abscess to form, the decay has to progress through every stage of decay. That means the cavity travel through the enamel, dentin, pulp, and then down the root of the tooth to form an abscess.

Front tooth after root canal x-ray

The x-ray above shows what a tooth abscess looks like, a big black circle around the tip of the root. That is essentially how you distinguish an abscess from pulp decay. The black circle has traveled from the middle of the tooth and down to the tip of the root.

Typically what these abscesses look like in the mouth is a lot of swelling around the tooth. Most commonly, you’ll see a pimple on the gums next to the infected tooth. That pimple is the abscess trying to eat through the bone. If the pimple pops you’ll see white fluid come out called pus.


Depending on the severity of the tooth abscess, you’ll either need a root canal or tooth extraction.

  • Root canal. If the infection is severe but the prognosis of the tooth is still good, you can save it by removing the nerve. Afterwards you can protect the tooth with a crown.
  • Tooth extraction. If the infection is too severe for your dentist to save it, you may need the entire tooth removed. If that is the case, the only way to restore the missing tooth would be to get a dental implant.

If you’re able to save the tooth with a root canal, we highly recommend so because it typically costs less and takes less time than an implant. The implant may be twice as expensive and takes about a year to complete. The root canal can be done within 4-6 weeks total.


Cavities don’t magically appear where ever they want on the tooth. They must follow the tooth decay stages and progress through each one sequentially. They all start off at the outermost layer, the enamel and work their way into the dentin, pulp, and then down the root.

As the decay progresses through each stage, the treatment gets more complex and also more expensive. It would behoove you to treat them at the earliest stage that you can find them so that you can save yourself as much money as possible. No one wants to be spending all of their time and money at the dentist!


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