When black dots or lines appear on a child's teeth, cavities are usually the first thing that comes to mind. But there is more than one reason a tooth surface can look black.

One of them is black stain, which can be seen on both baby teeth and permanent teeth and is a type of extrinsic stain that forms on the outer surface of the teeth. It usually appears as a row of black dots or a thin line along the area where the gums meet the teeth.

A cavity is a disease that damages the tooth structure, whereas black stain is a dark deposit attached to the tooth surface. However, it is hard to tell the two apart by color alone.

Black stain usually looks like this:

Not all of these features appear in every case, and cavities or tartar can look similar. If you need to know for sure, it's best to have it checked at the dentist.

When substances produced during bacterial metabolism react with iron, dark deposits can build up on the tooth surface. Some studies have also found that certain microorganisms, including Actinomyces, are relatively more common in the dental plaque of people with black stain.

However, the cause has not yet been clearly pinned down to a single factor. Even with the same brushing habits, each person's oral microbiome and saliva composition differ, so the degree of staining can vary.

So having black stain does not mean your child has been neglecting their brushing.

Several studies have reported a tendency for children with black stain to have relatively fewer cavities.

Possible reasons that have been suggested include differences in the makeup of oral microorganisms and the minerals in saliva. However, current research alone is not enough to conclude that black stain itself prevents cavities.

Nor does it mean that black stain is a protective shield against cavities. Cavities can still develop even with black staining, so regular brushing and routine checkups are still necessary.

Black stain is firmly attached to the tooth surface, so it may not come off easily with everyday brushing.

Scraping it with sharp tools or repeatedly using highly abrasive products to force it off can irritate the teeth and gums. It's best to first have the dentist check whether the black area is a cavity or an external stain, and then, if needed, have it professionally cleaned and polished by a dentist.

Even after removal, the staining can come back depending on the oral environment. A recurrence does not mean the treatment went wrong. You can simply set an appropriate care schedule based on how much staining there is and how bothersome it is.

Black stain usually appears only on the tooth surface, but not every area that looks black is a stain.

If you also notice any of the following changes, it's a good idea to have the dentist check for cavities or other problems.