Here is their secret:
Place 1 tablespoon of coarse salt in half a glass of water, which was boiled and then cooled. Whisk aggressive for one minute using a spoon. You will see that foam has been formed. You should remove it.
You may feel some kind of discomfort at the start because of the cold, hot and sour-sweet impact on your teeth, which is a result of thinner enamel.
You may have the same sensation from the toothpaste you are buying in the market. However, you will need to hold on because the salty paste will eliminate the pathogenic bacteria from your mouth, and will also firm the enamel of your teeth, or cement some holes and bumps formed on your teeth.