A baby tooth in adulthood: keep it, monitor it or replace it?

A baby tooth that is still in place at thirty or forty almost always surprises the person who discovers it, and it often prompts an immediate reflex: “it should come out and be replaced”. The scientific literature suggests more caution. In many cases that tooth, known technically as a retained primary (or deciduous) tooth, can keep working for years; in others it signals a problem that deserves to be clarified. The right decision does not depend on the patient’s age, but on what is, or is not, underneath that tooth.

Why does a baby tooth stay in the mouth into adulthood?

A baby tooth falls out when the permanent tooth developing beneath it resorbs its root. If the root is not resorbed, the primary tooth stays. There are two main reasons, and their consequences are very different.

The first is agenesis: the permanent tooth never formed. This is the most common situation when the tooth that persists is the lower second primary molar, because the lower second premolar is the permanent tooth most often missing through agenesis. With nothing pushing it out, the primary tooth remains in the arch.

The second is impaction: the permanent tooth exists but has remained trapped in the bone. This happens above all with canines. A study of orthodontic patients with an impacted lower canine found the persistence of the primary canine to be one of the findings most frequently associated with impaction (Guarnieri et al., 2024).

From the outside the two situations cannot be told apart. Only an X-ray can show whether there is an impacted permanent tooth or an empty space beneath the baby tooth, and it is the first step before any decision.

Does a baby tooth in an adult need to come out?

Not necessarily, and the available data are more reassuring than many people expect, with some limits that are worth stating at once.

The first limit concerns the type of tooth. Studies with long follow-up focus almost entirely on the lower second primary molar when the premolar is missing. For primary incisors and canines the literature is far thinner, and data on molars cannot be transferred to them without caution.

The second limit concerns sample size. A study from the University of Iowa followed twenty adults with twenty-eight lower second primary molars without a permanent successor, with a mean age of thirty-six at the first visit and a mean observation period of more than twelve years. At the end, twenty-four of the twenty-eight teeth were still functioning; the other four were lost to caries or periodontal disease, at a mean age of around fifty-one, and the mean shortening of the roots was negligible. The authors note that the time before those four teeth were lost approaches the lifespan of some prosthetic restorations, and conclude that keeping a healthy primary molar is a viable treatment option (Sletten et al., 2003). A second, Swedish study followed ninety-nine people from the age of twelve into adulthood: during the observation period only seven of the ninety-nine primary molars were lost, through extensive root resorption, infraocclusion or caries, and the authors consider long-term survival in more than ninety per cent of cases a reasonable expectation (Bjerklin et al., 2008).

These figures do not say that every baby tooth will last for ever. They say that, if the tooth is healthy and stable, preventive extraction is not a rule, and that monitoring is a legitimate clinical choice, not a surrender.

What needs to be monitored over time?

Anyone who decides to keep a baby tooth into adulthood is, in effect, choosing to keep it under observation. Periodic check-ups focus on a few precise points: the length of the root, which can resorb slowly; the stability of the tooth; its position relative to the neighbouring teeth, because a baby tooth can gradually sit “lower” than the biting surface, a phenomenon called infraocclusion; the presence of caries and the condition of the surrounding gum and bone.

There is one practical detail whose value is out of all proportion to its simplicity. X-rays taken in previous years, even for other reasons, make it possible to assess how the tooth and its root have changed over time. A current image shows what the tooth is like today; comparison with earlier ones shows how quickly it is changing, and it is that rate of change that guides the decision.

When is it best to replace it?

Replacement becomes appropriate when the tooth loses stability, when the root is significantly resorbed, when infraocclusion compromises chewing or the balance of the neighbouring teeth, when caries or periodontal disease can no longer be managed, or, in the front of the mouth, when the appearance of the baby tooth, smaller and differently coloured, is no longer acceptable to the patient.

The best moment to decide is not when the tooth falls out on its own. When a baby tooth is lost without planning, the bone that supported it tends to shrink, especially in width, and the next solution becomes more complex. Planning the replacement while the tooth is still in the mouth allows the options to be weighed calmly: an implant, a minimally invasive resin-bonded bridge in selected cases, or, where the bite allows it, orthodontic closure of the space. The differences between these routes are described in the articles on the missing second premolar, on missing lateral incisors and on implants in agenesis sites.

For anyone who has only now discovered that a baby tooth hides an agenesis, the article on what changes when agenesis is discovered in adulthood and the complete clinical guide to tooth agenesis set out the condition as a whole.

Frequently asked questions

Is it normal to have a baby tooth at thirty?

It is not rare. It happens above all when the corresponding permanent tooth never formed, a condition called agenesis, or when it has remained impacted in the bone. An X-ray clarifies which of the two situations is present.

Can a baby tooth last a lifetime?

In some cases it lasts for decades. Long-term studies of lower primary molars show that most remain in function for many years in adults, but no one can guarantee it for an individual tooth: that is why periodic check-ups are needed.

If the baby tooth is loose, can an implant be placed straight away?

It depends on the bone available, the position of the tooth and the condition of the surrounding tissues. In an adult the constraint of growth has largely been overcome, but assessing bone width and the space between the neighbouring teeth remains essential before choosing the solution.

What should I bring to the appointment?

A recent panoramic X-ray, if available, and above all X-rays from previous years, even if they were taken for other reasons: comparison over time is the most useful information for the decision.

First appointment. If you have a baby tooth in adulthood and would like to understand whether to keep it, how to monitor it or when to replace it, the practice offers a structured first appointment with an analysis of causes and a written report on the options.