Abstract: Expansion appliance for correcting tooth misalignments having the following features: a first member (1), a second member (2), a spindle (3) which, for changing the distance between the first (1) and the second member (2), engages the two members (1, 2) in such a way that the distance can be varied by a predeterminable limited magnitude in the longitudinal direction of the spindle (3) in the stationary condition of the latter. There are provided two parallel guide rods (21), located on both sides of the spindle (3). For guiding the member (1, 2) in straight alignment the guide rods (21) are received and guided in holes (20) in the two members (1, 2) which extend in parallel one to the other and each of which is open toward the respective other member (2, 1). A compression spring (2) is tensioned between at least one end of each guide rod (21) and the respective opposite end of the hole (20), this end of the hole (20) being closed.