A cavity in the tooth is called tooth decay or dental caries in medicine, the surface of the tooth is corroded by bacteria without timely treatment causing the lesion area to expand, this kind of progressive dental caries will cause necrosis of the nerve if it is not treated. The best method is to fill the tooth, timely filling can be beautiful your teeth, experts introduce whether it is tooth decay, defect, trauma and so on caused by tooth tissue loss need to fill the tooth, in order to restore its appearance and function. The substance used for repair is called filling material. When the lesion has spread to the pulp and even caused periapical disease, the pulp should be treated first and then the filling dentist. The filling includes two main steps, namely, cavity preparation and filling: (1) cavity preparation: the cavity consists of cavity wall, cavity edge and cavity angle. (1) Remove the diseased tissue, otherwise it will cause secondary caries (2) Establish a good retention and resistance shape, so as to avoid the fracture and loss of the filling 2, filling, isolate the saliva, disinfect the cavity, deploy the filling material to fill the cavity, and sculpt the shape immediately, pay attention to remove the part that exceeds the high occlusal surface, so as to avoid the medical source of occlusal trauma. The adjacent surface should not be left with the overhang of the filling material to prevent stimulation of the gums causing inflammation.