2B is a frontal view of an alternate retaining system;FIG. 2C is a frontal view of an alternate retaining system;FIG. 3 is a schematic, cross-sectional view of another retaining system in a sagittal plane;FIG. 4 is a schematic, cross-sectional view of another retaining system in a sagittal plane;FIG. 4A is a frontal view of the retaining system of FIG. 4;FIG. 5 is a schematic, cross-sectional vie