Do milk teeth even matter if they fall out anyway?

A dentist has found a cavity in your child's milk tooth, and the first thought is the obvious one: it is going to fall out anyway.

This page covers which teeth go when, what a milk tooth does until then, what can happen to the adult tooth underneath, and when a cavity can safely be watched instead of filled.

Which milk teeth fall out, and when?

This is the part that settles most of the question on its own. The ages below come from the American Dental Association's chart for milk teeth.

Look at the teal rows: the first back teeth, the pointed teeth and the last back teeth. Twelve of your child's twenty milk teeth come in before the third birthday and stay until at least nine. The last back teeth stay until ten to twelve, and the back teeth are the ones your child chews with.

So when a dentist finds a cavity in a four-year-old's back tooth, the question is not whether a tooth that falls out is worth treating. It is whether a tooth your child will chew with for another five to eight years is worth treating. Asked that way, most parents answer it themselves.

Why are milk teeth important?

Three jobs, and chewing is only one of them.

• They hold the space for the adult teeth. The adult teeth that replace them need that room. If a milk tooth has to come out early, usually because decay went too far, the teeth on either side can drift into the space. For milk back teeth, a 2022 review of eight studies found the biggest drift happens in the first three months. Less room can leave the adult teeth crowded or crooked.
• They help with speech. Front teeth help shape some sounds. A 2020 review found that children who lost front milk teeth early were more likely to have unclear speech, although the reviewers rated that evidence as weak.
• They let your child eat without pain. The American Academy of Pediatric Dentistry (AAPD) lists nutritional deficiencies, missed school days and a poorer quality of daily life among the consequences of decay in young children.

Can a decayed milk tooth affect the adult tooth?

This is the part that changes minds, so it is worth being precise rather than dramatic.

The adult tooth is not waiting somewhere else. It forms in the jaw beneath the milk tooth, while your child is still using the milk tooth above it.

If decay in a milk tooth reaches the nerve inside it (the pulp) and turns into an infection, that infection sits close to the adult tooth still being built. Case reports describe adult teeth that came through with thin, pitted or misshapen enamel after the milk tooth above them was infected. Dentists call this Turner's tooth.

Enamel that forms badly protects less well. A 2015 review that pooled seven studies of children and teenagers found that those with enamel defects on their adult teeth, from any cause, had about twice the odds of decay.

The AAPD puts the wider link plainly: decay in young children brings a higher risk of new decay in both the milk teeth and the adult teeth.

To be clear about the scale, this is not what happens with every cavity. The case reports describe milk teeth where decay went on to infection. That is why the decision turns on how deep the decay is, not on how old the tooth is.

Dr. Sanchit Paul runs an initiative on exactly this point. It is called Temporary Teeth, Permanent Solutions, and its subtitle is the warning: don't fall for the vicious cycle.

Does every cavity in a milk tooth need filling?

Some cavities can also be stopped without a drill. The same American Dental Association guideline includes a liquid called silver diamine fluoride (SDF) among the treatments that can halt decay.

Outside those two situations, a real hole usually needs treating, and so does any tooth that hurts on its own. Treating does not always mean drilling. Depending on the tooth, it can be a filling, a cap or SDF, and the treatment page for cavities in children sets out how each one works.

You are entitled to ask, in the room, which of these you are looking at. A dentist who can point to the mark, show you where the line is, and tell you what happens if you wait is giving you a decision. A treatment plan that arrives without that conversation is not.

What if the tooth is nearly ready to fall out?

Then say so, and ask. If a tooth is genuinely close to coming out, the decay is shallow and your child is not in pain, watching it is often a reasonable choice. The honest version of this conversation includes the option of doing nothing yet, with a date to look again.

Two things change that answer: pain and depth. The AAPD treats pain that starts on its own, or swelling or a small boil on the gum beside a tooth, as signs that the nerve inside is badly inflamed or infected. A tooth like that needs treatment, whatever its age. Decay that has already reached close to the nerve is not one to wait on either.

Are milk teeth more prone to cavities?

Not in every way, but in one that matters. The hard outer layer (enamel) is thinner on milk back teeth than on adult ones. When 69 back teeth were measured under a microscope, the milk back teeth carried less enamel than the first adult back tooth. So a hole of the same depth has gone further through a milk tooth than it would through an adult one. That is why a dentist can be more concerned about a small hole in a three-year-old than its size suggests.

How often sugar reaches the teeth matters, not only how much. The AAPD lists night-time bottles of sweet drinks, all-day sipping from a cup of juice, and frequent sugary snacks or drinks between meals as things that raise the risk of decay.

None of this is a verdict on a parent. It is how decay works, and how often is something that can change at home, starting this week. The brushing, food and habits articles go into the detail.

When is it worth booking a visit?

You do not need to book an appointment because you read this page. These are the things worth acting on.

• Your child has not had a dental check yet. The AAPD recommends a first visit within six months of the first tooth coming through, and no later than the first birthday.
• You can see a chalky white line or patch near the gum on the upper front teeth. Lift your child's upper lip, for example while brushing, and look. A white patch along the gum line is one of the earliest signs of decay, at the stage when it can still be reversed. Not every white mark is decay, and a dentist can tell the difference. If you see one, a check in the next two to four weeks is sensible. This is the idea behind LIFT THE LIP, an initiative Dr. Sanchit Paul borrowed from SickKids Hospital, Toronto.
• A tooth hurts on its own, or the gum beside it is swollen. Book soon rather than waiting for the next routine check.
• A treatment plan does not feel right. Ask which kind of mark it is, how deep it goes and what happens if you wait. Wanting a second opinion is reasonable.

If none of these apply, the next routine check is the right time to ask about any mark you have noticed.