The surface to be bonded is cleansed and dried.  It is then etched with a mild acidic solution to roughen the surface.  This creates a network of very tiny pores (micropores).  

 A liquid plastic bonding material is brushed over the etched surface where it flows into the micropores, creating a mechanical and chemical bond when set.  The bonding material is hardened by brief exposure to a special curing light or a chemical process.

They are hardened with a curing light and the composite is then carefully contoured and finely polished.