A considerable number of clinical case studies and observations concerning the treatment of tooth displacement by use of thermoformed appliances is to be found in the dental-medical literature. But until the presenr day, the forces generated by invisible aligners are hardly taken into account at all in the literature. The present study aimed to measure and compare the strength delivery of thermoformed appliances from three different materials , with the same thickness, on a lower lateral incisor in conjuction with vestibular and lingual tipping. Beside the aimed therapeutic forces it was always possible to observe forces, which did not correspond to the intended dental movement. In this connection it is primarily a matter of intrusive forces. The forces delivered by the materials investigated were mostly higher than those stated in the literature.
