Fluorosis: the white mark mistaken for an early carious lesion

A white mark on enamel gives rise to two possible diagnoses with opposite consequences, which is why the distinction must be made before deciding anything.

Fluorosis arises from excessive fluoride intake during enamel formation, which takes place in the years before the tooth erupts.

This defines a precise time window. For the permanent incisors the critical period falls in the first years of life, and after eruption fluoride intake can no longer produce it.

It follows that a mark appearing on an already erupted tooth is not fluorosis, however much fluoride toothpaste the patient uses. It is a piece of information that settles the diagnosis in one step.

The distinction from an early carious lesion rests on three elements. Fluorosis is symmetrical and affects matching teeth on both sides, because it depends on a shared developmental period.

An early carious lesion, by contrast, is isolated and sits where plaque stagnates: necks, proximal surfaces, fissures. Its position follows hygiene rather than development.

The second element is the surface. Mild fluorosis has smooth, glossy enamel, whereas an early carious lesion is dull and rough to the probe, with a chalky appearance.

The third is behaviour on drying. A carious mark becomes more obvious when the surface is dried, because the porosity loses water; fluorosis changes little.

There are also enamel opacities unrelated to fluoride, from trauma or infection of the deciduous teeth, and these are typically isolated and asymmetrical, often on a single tooth.

In practical terms the distinction matters because an early carious lesion calls for remineralisation and plaque control, while mild fluorosis requires no treatment other than aesthetic.

In talking to parents it is worth being precise. Mild fluorosis, the form most often seen, is a variation in appearance and not a functional defect: the enamel is not weaker.

Fluoride advice in children comes from this balance, and the useful recommendation concerns the amount of toothpaste and supervision of brushing in small children, who tend to swallow it.

In summary: fluorosis forms before eruption and not after, it is symmetrical where caries is isolated, it has a smooth surface where caries is rough, caries becomes more marked on drying, and the mild form does not impair function.