Space maintenance
Keeping open the volume in which new bone is to form, against the pressure of the soft tissue above it, until bone fills it. One of the four PASS principles of bone regeneration: primary closure, angiogenesis, space maintenance, stability.
Bone forms slowly and only into space that is available to it. If the flap collapses onto the defect, or a resorbable membrane sags into it, the volume for new bone is lost before it can be filled. Space maintenance is the set of measures that prevent that: a graft material that supports the membrane, a membrane stiff enough to hold its shape (titanium-reinforced PTFE, titanium mesh), a tenting screw, or a block graft.
Wang and Boyapati listed it as the third of four PASS principles for predictable regeneration: Primary wound closure, Angiogenesis, Space maintenance and Stability of the wound and the graft. The 2020 review of guided bone regeneration restates the same framework.
Space maintenance and stability are related but distinct. A graft can maintain space and still be displaced; it can be stable and still be compressed. Volume stability, measured on CBCT, is the outcome that reflects both.
On this site
A mouldable particulate graft held in a carrier is one approach to space maintenance and stability; see how the composition is designed.