Why is fluoride varnish necessary when it is already in our toothpaste?

Fluoride in toothpaste is an important preventive measure against cavities when used to brush teeth at least twice a day. To be maximally effective, the excess toothpaste should be expectorated (spit) after brushing, but there should be no additional swishing of water in the mouth or drinking fluid. The remaining toothpaste should remain in contact with the teeth, especially overnight. Fluoride varnish provides an additional preventive benefit for children because it stays in contact with the teeth longer than toothpaste and is more concentrated. It helps to remineralize the teeth when early childhood caries is starting and prevents enlargement of caries already present until the child can be seen by a dentist.