The enamel is the most highly mineralized tissue in the body. It’s made of over 98% minerals, which gives the opportunity for dental bonding. By applying an acid, it creates small pores on the surface by melting a part of its ingredients. This cannot be seen with a naked eye, it is only visible under a microscope. After the etching, the enamel has a significantly whiter color. The concentration of the acids varies depending on the type. The most commonly used one is the phosphoric acid in a range between 30% to 40%. When the dentists apply it, the acid affects the mineral content and creates a roughness on the surface, visible only via microscope. That way, the retention and adhesion with the dental materials are much stronger. The resin sealant gets into those small pores and there is a significantly larger contact surface compared to before. The acid also removes the smear layer. In the beginning dentists, we supposed to etch for around 60 seconds. Today with the advanced characteristics, that process is shortened to around 15 seconds. The self-etching agent is placed on a dry surface and the dentist waits for around 15 seconds. There are several types. Some have to be stimulated by light, while others don’t. There are systems that come in only one bottle and the ones that come in two bottles and are mixed together.