Self-activated orthodontic expander including a left frame and a right frame, where the left frame and right frame include, respectively, a left body and a right body, each having anchoring means for anchoring them to the teeth of a dental arch. The bodies have through holes oriented in a predetermined expansion direction, where the frames are slidably mounted along the expansion direction by guides inserted into the holes of the bodies. Elastic elements are arranged and acting between the frames. The guides are further constrained with each other by a bridge oriented orthogonally to the same guides and adapted to prevent the reciprocal movement of the guides.