Orthodontic expander including a left frame (T1) and a right frame (T2). The left frame (T1) and right frame (T2) respectively include a left body (1) and a right body (2) provided with structure for their anchorage to the teeth of a dental arch. The bodies (1.2) have through holes (10) oriented in an expansion direction (d). The frames (T1, T2) are slidingly mounted along the expansion direction (d) by guides (4) inserted in the holes (10) of the bodies (1.2). The distance (h) between the bodies (1, 2) is adjusted by a screw (5) screwed into the body (2) of one of the frames. The screw (5) has an operating head (51) positioned between the bodies (1.2) Elastic plates are positioned and acting between the frames (T1, T2) and can be activated or reactivated by acting on the screw (5) which compresses them to activate or reactivate them when desired.