After multiple sintering, if the phenomenon of yellow insulation zirconium beads is found, please observe whether the heating element peeling phenomenon in time. If peeling is slight, please replace the zirconium beads air-fired (1600 degree) primary heating equipment. If peeling is serious, please replace the heating element. After replacing the new heating element, please air burn (1600 degrees) once to ensure that the surface of the heating element formed intact protective film. Then the denture sintering.