An expandable, intervertebral spacer includes a top component and a base component in engagement with the top component, the base component defining at least one channel for receiving a hardening material, and placement of the hardening material within the channel causes the top component to move between a first position in which the top component is a first distance from the base component and a second position in which the top component is a second distance from the base component, the second distance being greater than the first distance. The hardening material can be removed from the channel by a flexible coring tool, and the top component forced toward the base component to collapse the spacer.