When an individual has a tooth that is severely decayed or fractured, they may not have enough tooth structure remaining to securely hold a crown in place. A core build up will save the tooth by restoring missing surface area and tooth mass. During preparation, the dentist uses a mild etching solution that prepares the surface of the tooth for core build up. This etching solution creates lines to form in the tooth enamel. These lines give the bonding material a surface to more tightly attach to so it will seat more permanently into the tooth surface. After the etching process is complete, the dentist applies the composite material to the tooth creating the build-up. Once this material hardens, the dentist will shape the tooth so it can be fitted with a crown.