Why Do I Get Cavities Even Though I Brush?

It is a genuinely fair complaint. You brush twice a day, you do not think of yourself as someone with a sweet tooth, and you still leave a check-up with news of a cavity. There are usually concrete reasons, and most of them are addressable.

A toothbrush cannot reach two of the five surfaces

Every tooth has five surfaces. Brushing cleans three of them well. The two where adjacent teeth touch are physically inaccessible to bristles, and those contact points are where a large share of cavities in otherwise diligent brushers begin.

That is the argument for cleaning between the teeth daily — floss, interdental brushes, or a water flosser, whichever you will actually use consistently. The technique that gets done beats the technique that is theoretically best.

How often you eat matters more than how much

Every time you eat or drink something with sugar or starch, bacteria produce acid and your enamel spends a period demineralising. Saliva then neutralises the acid and repairs the surface, but that takes time.

One dessert after dinner is a single acid episode your mouth recovers from. The same amount of sugar sipped across an afternoon keeps your teeth in that acidic state for hours, and the recovery never completes. This is why grazers and slow-sippers often get cavities despite consuming no more sugar than anyone else.

Other factors people do not connect

• Dry mouth, often from medication, which removes saliva's protective role — a common and under-recognised cause
• Deep grooves in molars that trap debris no brushing dislodges
• Receding gums exposing root surface, which decays more readily than enamel
• Old fillings with worn edges where new decay starts underneath
• Crowded teeth that are genuinely harder to clean thoroughly
• Acidic drinks — including sparkling water and citrus — which erode enamel without any sugar involved
• Brushing immediately after acidic drinks, when enamel is temporarily softened

What actually helps

• Clean between the teeth every day, without exception
• Group eating into meals rather than grazing
• Use fluoride toothpaste, and spit rather than rinsing afterward so it stays on the teeth
• Drink water between meals rather than sipping sweetened or acidic drinks
• Mention any dry mouth or new medications, because that changes your risk profile
• Ask whether sealants make sense for deeply grooved molars

If cavities keep appearing despite doing the right things, that is worth investigating rather than trying harder at the same routine — the cause is often something specific. Our general dentistry page covers preventive care, and our sensitive teeth guide may be relevant if discomfort is part of the picture.