Did you know: a cavity is a “thing”, and tooth decay is a “process”?

Author: Dr Alexandra Jones, Co-Founder and Board Chair

Surely “cavities” and “tooth decay” are the same? Mmmmm well, turns out understanding the differences can save a lot of confusion, worry, and “how did this happen?” moments.

Here’s a simple way to think about it: a cavity is a thing you can see or feel, whereas tooth decay is a biological process that can be quietly happening in the background.

The process comes first

Tooth decay is often a relatively slow, chemical process driven, first by acids produced by bacteria. Over time, those acids draw minerals out of the tooth, weakening it from the outside in. With time and progress, the bacteria (apologies if this sounds a bit much) start to feed upon the actual tooth structure.

Who knew things so tiny could get together and be so destructive to strong tooth structure?

There tends to be an ebb and flow to the process. The rate of progress of the decay can speed up, slow down and even stop in some cases.

Sometimes that process stays unnoticed for a long while.

What causes the thing?

It's a good question. Often the process results in the tooth becoming weaker; it loses its structural integrity, which means losing its ability to be strong and withstand the force from the bite.  

That’s when a tooth can “suddenly” break – a thing becomes obvious!

Why cavities and active decay don’t always line up

Most cavities are caused by tooth decay, but the presence of a cavity doesn’t reliably tell you how much decay is present or if that decay is active.

Some teeth have extensive decay with no obviously visible cavity (that’s another blog post!).

Some teeth develop a cavity from relatively small amounts of decay, because of tooth shape or heavy bite forces or another pre-existing issue.

Sometimes teeth lose structure not from decay, but rather due to different processes, like wear and tear, erosion, or mechanical stress.

So, while a cavity tells us something is going on, it doesn’t automatically mean “this is the worst tooth in the mouth”. And it definitely doesn't mean “my teeth are the worst in the world”.

The stealthy part (and why this can feel unsettling)

Decay can be quiet. Very quiet.

People are often genuinely shocked when a dentist identifies significant decay in a tooth that felt completely normal. No pain, no warning, and no obvious “hole”.

From the patient’s perspective, it can feel like the tooth was “fine until the dentist touched it”!

From a dentist’s perspective, assessing decay (especially when it’s active and hidden beneath the surface) can be genuinely challenging. This is one of the reasons x-rays and other tests are sometimes needed, even when everything looks okay on the surface.

None of this means anyone has done anything wrong. It simply reflects how stealthy the process can be.

When a cavity can be a useful thing

Here’s a counterintuitive idea: sometimes a cavity is a helpful signal.

When a decayed tooth breaks open in a way that doesn’t trap plaque and allows saliva and a toothbrush to reach the surface, the decay process can actually slow, stop, or even begin to reverse!

Saliva is really remarkable stuff. Any tooth surface exposed to healthy saliva has the potential to remineralise and harden. Over time, the surface may darken and become more resistant, a sign that healing is happening.

This process is seen all over the world, particularly in places where people have limited access to dental treatment. Even advanced decay can sometimes stop if the environment in the mouth shifts back toward health.

This is why some people experience that strange phenomenon where a tooth breaks, panic sets in… and then, somehow, things stabilise.

It’s not a strategy to rely on, but it does explain why things don’t always keep getting worse.

Shape matters (a lot)

For a cavity to become self-healing, its shape matters.

If part of the decayed area remains hidden, or if the cavity traps plaque, saliva can’t do its job. Likewise, if someone avoids brushing the area out of fear, and pain (totally understandable), the tooth misses out on fluoride and mechanical cleaning, and the decay process can continue.

This understanding forms the basis of a real, evidence-based approach used in children.

If a young child can’t tolerate a more technical dental procedure, a dentist can sometimes gently reshape a decayed baby tooth so it becomes self-cleansing.

If the mouth environment is healthy, that tooth can stabilise and be lost naturally when the adult tooth is ready.

That can mean avoiding fillings altogether, and avoiding a lot of stress for little people.

Sometimes a similar approach is taken for permanent teeth that aren’t replaced in adults. Teeth do best when they share load evenly. A defect, even a carefully shaped one, can sometimes reduce a tooth’s long-term durability.

That said, there are always exceptions. Some people live happily for many years with adjusted teeth and no major issues. It depends on how tooth-friendly the mouth environment is overall.

It's all about understanding how to manage the process

A cavity is a thing that doesn’t automatically mean disaster.

And the absence of a cavity doesn’t mean everything is fine.

Understanding tooth decay as a process, not just a hole, helps explain why dental care can sometimes feel counterintuitive. It also helps reduce fear and surprise.

Daily habits and lifelong preventive support can help us to understand and manage the process, which can save piles of worry.