A filler instrument comprises a first chamber section having a first cross sectional area and a second chamber section having a second cross sectional area less than the first cross sectional area. The second chamber section communicates with the first chamber section. The first chamber section includes an inlet for receiving a material into the filler instrument, and the second chamber section includes an outlet for discharging the material from the filler instrument. A first plunger is sized to pass through the first chamber section and not the second chamber section. A second plunger is sized to pass through an interior bore of the first plunger and into the second chamber section. In use, the first plunger displaces material residing in the first chamber section through the second chamber section toward the outlet, and the second plunger displaces material residing in the second chamber section through the outlet.