The damage starts within minutes of eating, but a cavity that needs a filling usually takes months to years. For most adults an enamel cavity develops over roughly six months to several years. It moves much faster in high-risk situations, which is why one person can go a decade without a cavity while another develops several between two checkups.

Bacteria in plaque turn sugars and starches into acid, and that acid begins pulling minerals out of the enamel within a few minutes. Saliva then reverses the process over the following half hour or so, washing the acid away and putting minerals back. A cavity forms when that balance tips the wrong way often enough for long enough. It is a tug of war repeated many times a day, not a single event.

Yes, and that is exactly why the interval is six months rather than a year. In an adult with low risk it is uncommon. In a child, in someone wearing braces, in anyone with a dry mouth, or in anyone sipping sweet drinks through the day, it is entirely possible. Six months is short enough that most new decay is still small when we find it.

How often you eat matters more than how much. Frequent snacking or sipping keeps the mouth acidic all day and never gives saliva a chance to repair. A dry mouth removes the defense entirely, and many common medications cause it. Braces and other appliances create places a brush cannot reach. Children’s teeth have thinner enamel, and exposed root surfaces in older adults are softer than enamel. Existing fillings and crowns add margins where decay can start.

Only at the earliest stage. A white spot lesion, where minerals have been drawn out of the enamel but the surface has not broken, can remineralize with fluoride, better cleaning at that spot, and less frequent sugar. Once the surface breaks and bacteria are inside the tooth, no amount of brushing, toothpaste or diet change closes the hole. From that point it needs a filling, and finding it early is the only way to keep it small.

Faster than in adults. Baby teeth have thinner, softer enamel, so decay reaches the nerve in less time and with less warning. Snacking patterns and drinks tend to work against them as well. That combination is why children’s checkups are not optional and why sealants on the biting surfaces of the back teeth are worth asking about as soon as those teeth come in.

Almost never at the stage where it is easy to treat. Enamel has no nerve supply, so early decay is silent. Pain usually arrives once decay has reached the dentin underneath or the nerve itself, by which point the repair is often larger than a simple filling. This is the whole reason we take X-rays on a schedule rather than waiting for a complaint.

With a visual and tactile exam plus digital X-rays, which show the surfaces between teeth and the area under existing fillings that nobody can see by looking. We also compare this year’s images against your previous ones, because the useful question is not whether a shadow exists but whether it is new or has been stable for years.