A root assembly (3) includes an implant body (31) and a positioning device (32) connected to the implant body (31). The implant body (31) has a positioning hole (312) formed through one end thereof and an engaging portion (311) opposite to the positioning hole (312). The positioning hole (312) has an end edge. The positioning device (32) has a positioning seat (321) where an artificial tooth (4) is attached and a positioning unit (322) extending through and out of the positioning seat (321). A first recognition portion (3211) is formed on the positioning seat (321). The location of the first recognition portion (3211) of the positioning seat (321) corresponding to the end edge of the positioning hole (312) can recognize that the positioning device (32) is exactly positioned on the implant body (31), thereby preventing the positioning device (32) from loosening.
