Supernumerary Teeth: When an Extra Tooth Shows Up on an X-Ray, and What to Do About It

Most people have exactly 20 baby teeth and 32 adult teeth. A small percentage of people have more — an extra tooth, called a supernumerary tooth, that formed in addition to the normal set. Most parents only find out when a routine X-ray during a paediatric or orthodontic check-up shows a tooth sitting quietly in the jaw, unerupted, that nobody knew existed.

What Causes an Extra Tooth to Form

The exact cause is not always identifiable, but current understanding points to abnormal activity in the dental lamina — the tissue band responsible for tooth development — that leads to an extra tooth bud forming alongside the normal ones. Supernumerary teeth are also associated with certain genetic and developmental conditions, including cleft lip and palate and Gardner syndrome, though the majority of cases occur in people with no other underlying condition at all.

The Most Common Type: Mesiodens

The single most common supernumerary tooth is called a mesiodens — an extra tooth that forms between the two upper front teeth. It is usually small, cone-shaped, and can remain unerupted (staying below the gum) or occasionally erupt and become visible. Other, less common types are named by their location: a paramolar (near the molars) or distomolar (behind the last molar).

How It's Usually Discovered

• A routine dental or orthodontic X-ray taken for an unrelated reason
• Delayed eruption of a permanent tooth, prompting an X-ray to investigate why
• Crowding or displacement of neighbouring teeth
• Occasionally, visible eruption of the extra tooth itself

What Problems Can It Actually Cause

Not every supernumerary tooth causes a problem, but when it does, the issues usually fall into a few categories:

• Delayed or blocked eruption: An unerupted extra tooth can physically block a neighbouring permanent tooth from erupting normally, sometimes requiring the permanent tooth to be guided into place after the extra tooth is removed.
• Crowding or displacement: The extra tooth can push adjacent teeth out of alignment, contributing to crowding or rotation.
• Cyst formation: An unerupted supernumerary tooth left in place can occasionally be associated with the development of a cyst around it over time.
• Root resorption: Pressure from the extra tooth against a neighbouring root can, in some cases, cause resorption (gradual dissolving) of that root.

When It's Removed vs Left Alone

Treatment is not automatic just because an extra tooth is found. Dentists generally weigh removal against monitoring based on the tooth's position, whether it's interfering with eruption of a permanent tooth, and whether it shows any early signs of causing a cyst or resorption. A mesiodens blocking the eruption of the upper front teeth is commonly removed in childhood, often timed alongside orthodontic planning. An extra tooth positioned deep, causing no disruption, and stable on repeat X-rays may simply be monitored with periodic imaging rather than removed.

What the Removal Procedure Involves

When removal is recommended, it is typically a straightforward extraction under local anaesthesia, sometimes done by a paediatric dentist or oral surgeon depending on the tooth's depth and position. For a mesiodens blocking eruption, the neighbouring permanent tooth is monitored afterward and may need orthodontic guidance (such as a small appliance or space maintainer) to erupt into its correct position if it doesn't come in on its own within a reasonable time.