What Happens If You Leave a Cavity Untreated?

A lot of patients know they have a cavity. They felt the twinge when drinking something cold, or their dentist mentioned it at the last visit. Then life gets busy, the discomfort fades, and the appointment gets pushed. Here is what happens in the meantime.

What a Cavity Actually Is

A cavity is damage to your tooth's hard outer surface, caused by bacteria that feed on sugar and produce acid. That acid slowly erodes the enamel, creating a small hole or pit. At this early stage, there is often no pain and no obvious sign. But the damage is happening whether you feel it or not.

Left alone, a cavity does not stabilise. It always progresses.

Stage 1: Enamel Decay

At this first stage, the acid has only penetrated the enamel, the outer layer of your tooth. You may notice slight sensitivity to sweet foods or cold drinks, or nothing at all. This is the easiest and least expensive stage to treat: a straightforward filling done in one appointment.

If you come in at Stage 1, you leave with a filling. If you wait, you leave with something more involved.

Stage 2: Decay Into the Dentin

Underneath the enamel is dentin, a softer and more porous layer that sits much closer to the tooth's nerve. Once decay reaches the dentin, sensitivity increases noticeably. Hot and cold foods become uncomfortable. Biting can cause a sharp twinge.

A filling is still typically possible at this stage, but the cavity is larger and the procedure more involved. Depending on the depth and location of the decay, your dentist may recommend a larger composite filling or, if significant tooth structure has been lost, a dental crown.

Stage 3: Reaching the Pulp

The pulp is the innermost part of the tooth, where the nerve and blood vessels live. When decay reaches the pulp, you know about it. This is where the classic toothache comes from: persistent, throbbing, often worse at night or when lying down.

At this point, a filling is no longer an option. You need a root canal: the nerve is removed, the canals are cleaned and sealed, and the tooth is typically capped with a crown. Root canals have an undeserved reputation for being painful. The procedure relieves the pain; the pain you are living with beforehand is worse.

In Ontario, root canal treatment is covered in part by most private dental insurance plans. Cost varies by tooth: front teeth are simpler than molars. Expect $800 to $1,500 before insurance, with a crown adding $1,000 to $2,000 on top.

Stage 4: Abscess and Tooth Loss

If the infection spreads beyond the pulp into the surrounding tissue and jawbone, an abscess forms. This is a dental emergency. Symptoms include throbbing pain, swelling in the jaw or face, fever, and a persistent bad taste from pus drainage. An abscess is not a problem to manage at home.

At this stage, extraction is sometimes the only viable option. Once the tooth is lost, you face the decision of how to replace it. That means implants, bridges, or dentures, all of which cost significantly more and take far more time than the filling you could have had months earlier. Our post on dental implants vs. dentures walks through those options in detail.

What Treatment Costs at Each Stage

Stage	Condition	Treatment	Approx. Ontario Cost (before insurance)
1	Enamel decay	Composite filling	$150 to $300
2	Dentin decay	Large filling or crown	$300 to $2,000
3	Pulp infection	Root canal plus crown	$1,800 to $3,500
4	Abscess or tooth loss	Extraction plus replacement	$3,000 to $8,000 or more

Costs are estimates based on the Ontario Dental Association fee guide and vary by practice and complexity. Most private dental plans cover 50 to 80 percent of basic restorative care.

Why Dental Anxiety Makes This Worse

Patients who avoid the dentist because of fear tend to arrive at Stage 3 or 4, when treatment is more complex, more expensive, and genuinely more uncomfortable than it would have been earlier. If anxiety is part of why that appointment keeps getting postponed, our post on managing dental anxiety has practical strategies for making dental visits feel manageable.

Frequently Asked Questions

How long does it take a cavity to go from small to serious?

It varies. Enamel decay can take months or even a year or two to progress in a healthy adult. Once decay reaches the dentin, it moves faster because dentin is softer. Some cavities stay small for years; others progress quickly, especially with a high-sugar diet or dry mouth. There is no safe window to wait.

Can a cavity heal on its own?

Very early enamel lesions can be remineralised with fluoride, improved oral hygiene, and diet changes before they break through the enamel surface. Once the surface is actually broken, remineralisation cannot close the hole. It needs to be treated by a dentist.

Does getting a cavity filled hurt?

No. The area is numbed with local anaesthetic before any drilling begins. Most patients feel pressure and vibration but not pain. If you are anxious about needles or the procedure itself, tell your dentist when you book. There are options for making it more comfortable.

Will my dental insurance cover a filling in Ontario?

Most private dental plans through employers cover fillings at 70 to 80 percent of the Ontario Dental Association fee guide amount. The Canadian Dental Care Plan (CDCP) also covers basic restorative care, including fillings, for eligible Canadians. Ask at the front desk and we can help clarify your coverage before treatment begins.

If you have been putting off a filling, this week is a good time to act. The sooner a cavity is treated, the simpler the procedure and the lower the cost. Book an appointment with Lornview Dental.