A restraining element for preventing separation of a pipe joint used to join a bell end of a female plastic pipe to the male end of a mating pipe. The restraining element is formed from a compressible body of elastomeric material, the compressible body having a segmented metal ring located therein with gripping teeth for engaging an outer surface of the mating male pipe. The ring segments making up the segmented metal ring are oriented such that the gripping teeth of the ring segments are out of contact with and initially angled away from the outer surface of the male plastic pipe. The teeth of the annular gasket are forced into engagement with the exterior surface of the male plastic pipe as the pipe joint is assembled. The teeth are oriented to allow movement of the male pipe in a first direction relative to the female bell end opening during assembly, but to resist movement in a opposite direction after the pipe joint has been assembled.