An intervertebral spacer device includes first and second plates disposed in a spaced apart relationship, each plate having an inner surface and an outer surface, the inner surfaces of the opposing plates facing one another. The device also includes at least one restoring force providing element disposed between the inner surfaces of the plates, wherein a compressive load applied to the outer surfaces of the first and second plates is counteracted by the at least one restoring force providing element. The at least one restoring force providing element includes at least one slotted belleville washer having a convex shape when unloaded and a flatter shape when loaded, whereby one or more slots of the belleville washer widen when compressively loaded, and whereby the at least one slotted belleville washer is unloaded when no load is applied to the outer surfaces of the first and second plates, and is loaded when the compressive load is applied to the outer surfaces of the first and second plates. The second plate has an annular groove formed in the inner surface of the second plate, the device including a retaining wall and a retaining ring, whereby a wide end of the at least one belleville washer is captured by the retaining wall and the retaining ring for maintaining the wide end adjacent the inner surface of the second plate.