Fluoride is the single-most important ingredient in toothpaste. It greatly helps oral health by strengthening the tooth enamel, making it more resistant to tooth decay. It also reduces the amount of acid that the bacteria on your teeth produce.
When you rinse your teeth with water immediately after brushing, the fluoride in the tooth paste does not spend much time in contact with the teeth. Therefore, it is important to let it work after you have already brushed your teeth.
It is best not to rinse immediately after brushing or to do so with a very small amount of water.
This is a fairly common advice among dentists. Of course, it is not highly recommended to follow this practice for children who are still to lose their baby teeth. For adults, however, it is an excellent tip. Using a mouthwash with fluoride also prevents the appearance of cavities, although it is not necessary to use it instead of water.