Fixed space maintainers come in many designs.
A band-and-loop maintainer is made of stainless-steel wire and held in place by a crown or band on the tooth adjacent to the empty space. The wire is attached to the crown or loop and rests against the side of the tooth on the other end of the space.
A lingual arch is used on the lower teeth when the back teeth on both sides of the jaw are lost. A wire is placed on the lingual (tongue) side of the arch and is attached to the tooth in front of the open space on both sides. This prevents the front teeth from shifting backwards into the gap.
In the case of a lost second primary molar prior to the eruption of the first permanent molar, a distal shoe may be recommended. Because the first permanent molar has not come in yet, there is no tooth to hold a band-and-loop space maintainer in place. A distal shoe appliance has a metal wire that is inserted slightly under the gum and will prevent the space from closing.