Caries affects hard tooth tissues - enamel and dentin. When bacteria cross their boundaries, they infect the nerve of the tooth and cause pulpitis. For very deep caries, when the dentin is thinned to ten or hundreds of millimeters, the likelihood of death is very high. Biological treatment is a method in which teeth with caries that reach the nerve are kept alive. An important condition for such treatment is the isolation with cofferdam - this allows in sterile medium, without further infection by saliva, the communication with the nerve to be covered with special bio-tolerable cement and the tooth to be restored with photopolymer. The procedure can also be performed by a doctor who does not use cofferdam, but the likelihood of success is greatly reduced.