beneficial impact on class III treatment [14,15,17] and furthermore suggested that it might also be a successful alternative to conventional appliances because of its expanding forces at the centre of resistance of the nasomaxillary complex [16-18]. For the practitioner it is of particular interest at what age a specific RME-modification should be preferred, whereby the aim would always be a maximum of therapeutic effectiveness while being minimal invasive. A study compared skeletal and dental effects of Hyrax-RME and Hybrid-RME in young adults with the same age (13-14 years) [19]. The only significant difference was that the bone thicknesses of the left first premolars significantly differed between groups. Although Hybrid-RME therefore seemed to have advantages over Hyrax-RME, it should be critically questioned if the insertion of mini-implants is justified, considering the fact, that Hyrax-RME was able to lead to a comparable skeletal and dental expansion at that age.