A tooth cavity changes appearance as it progresses, starting as a chalky white spot on the enamel and eventually becoming a visible brown or black hole. Most people searching for this want to know whether something they’ve noticed on a tooth is actually decay, so here’s what to look for at every stage.
The Earliest Stage: White Spots
Before a cavity becomes a hole, it starts as a flat, opaque white patch on the tooth surface. These white spot lesions form when acids from bacteria dissolve minerals out of the enamel, creating tiny pores that scatter light differently than healthy tooth structure. The spot looks dull and chalky compared to the natural gloss of surrounding enamel. You’re most likely to notice them near the gumline or around the edges of orthodontic brackets, where plaque tends to build up.
The important thing about white spots is that they’re reversible. At this stage, the enamel is partially demineralized but still intact. Fluoride treatments and improved brushing can help minerals redeposit back into the enamel, and studies show these lesions can improve or even fully reverse with proper care. If you catch decay at this point, you may never need a filling.
Brown and Dark Spots
When a white spot isn’t addressed, it gradually darkens. The porous enamel picks up pigments from food, drinks, and bacteria, turning light brown, then darker brown, and eventually black. At this point, you’re looking at active decay that has progressed beyond the earliest stage. The discoloration is typically concentrated in one spot, not spread evenly across the tooth surface.
This is also the stage where many people first wonder whether they’re looking at a stain or a cavity. A few differences help: stains tend to affect an entire tooth or multiple teeth evenly, while a cavity shows up as a single dark spot in one location. Stains also tend to come and go (fading after a cleaning, for example), while a cavity spot only gets darker over time. Spots that are black, brown, or gray and stay in one place are a strong sign of growing decay.
Visible Holes and Pits
As decay continues breaking down enamel, actual holes form. These can range from tiny pits you might feel with your tongue to larger craters you can see in a mirror. Once there’s a physical hole, the cavity has moved past the point of remineralization and needs professional treatment. Stains never cause holes in teeth, so a visible pit or depression is a definitive sign of a cavity.
On chewing surfaces, cavities often start in the natural grooves and fissures of molars, where they can be hard to spot visually. They may look like a dark line or small pit sitting in a groove. On smooth surfaces between teeth, you typically can’t see the cavity directly, but you might notice a dark shadow showing through the enamel from the inside, or your floss may shred repeatedly in the same spot.
Deep Decay With Exposed Inner Tooth
In advanced stages, the cavity eats through the enamel entirely and reaches the softer layer underneath called dentin. At this point, the hole is usually clearly visible, and you may see yellowish or brownish tissue inside it. Dentin decays faster than enamel, so cavities that reach this layer tend to widen quickly beneath the surface. Sometimes the enamel around the edges looks intact from the outside while the tooth is hollowed out underneath, creating a dark shadow visible through the remaining shell of enamel.
At the most severe stage, more than half the tooth surface can be destroyed, leaving a large, open cavity or just the root structure behind.
What Cavities Look Like on X-Rays
Many cavities, especially those forming between teeth, aren’t visible to the naked eye at all. On dental X-rays, cavities show up as dark spots against the lighter gray of healthy tooth structure. A shallow cavity appears as a faint shadow near the outer edge of the tooth. A deeper cavity casts a much darker shadow that extends further inward. The darker and larger the spot, the more advanced the decay. This is why dentists take periodic X-rays even when your teeth look fine from the outside.
How Cavities Look in Baby Teeth
Cavities in young children follow a distinctive pattern that’s worth knowing if you’re a parent. The decay, sometimes called “bottle mouth” or “nursing caries,” typically hits the four upper front teeth hardest while the lower front teeth stay healthy or nearly unaffected. This happens because the tongue shields the lower teeth during bottle or breastfeeding, while the upper teeth get prolonged contact with milk or formula.
The first sign is a white band of demineralization running along the gumline of the upper front teeth. Parents frequently miss this because it blends in with the white of the tooth. Left untreated, those white bands progress into brown or black rings that encircle each tooth near the gumline, sometimes described as a dark collar around the tooth’s neck. In severe cases, the visible crowns of the upper incisors can be completely destroyed, leaving only root stumps behind. Checking your toddler’s upper front teeth regularly, especially along the gumline, is the best way to catch this early.
Cavity vs. Stain: A Quick Comparison
- Location: Cavities appear as a single dark spot in one area. Stains tend to discolor a broader area or multiple teeth.
- Texture: A cavity may feel rough, sticky, or soft when you run your tongue over it. Stains feel smooth, the same as surrounding enamel.
- Persistence: A stain may lighten after a professional cleaning. A cavity only gets worse.
- Holes: Any visible pit or hole in a tooth is decay, not staining.
- Sensitivity: Cavities often cause pain or sensitivity to hot, cold, or sweet foods. Surface stains cause no sensation at all.
If you’re unsure whether a mark on your tooth is a stain or early decay, the safest move is a dental exam. Cavities between teeth and those hiding in the grooves of molars are nearly impossible to evaluate on your own, and catching them at the white spot stage can mean the difference between a remineralization treatment and a filling.