Thesis: Aim of this study was to compare newly developed and conventional retention systems by objective measurements of the clinical adhesion force of prostheses. Material and methods: The adhesion force was measured for each prosthesis with a specially developed device. Therefore the prosthesis was connected with a plate at the occlusal surface. A centered fastened loop served as a loose coupling with a dynamometer-box (Fa. Typ U2A, Hottinger Baldwin Measurements, Marlborough, USA), which avoids the prosthesis to stand on edge during the pull-off phase. The device was calibrated prior to each series of measurements. 10 consecutive measurements for each prosthesis were performed in a prospective clinical trial. Mean values were calculated and defined as adhesion force. Test group: 8 metal-free tapered crown prostheses (primary crown: ceramic, Empressâ 2; frame: fibre composite, Vectrisâ: Fa. Ivoclar Schaan-Liechtenstein) on 28 abutments (6 teeth, 22 implants). Control group: 12 conventional tapered crown prostheses on 58 abutments (24 teeth, 34 implants). Results: The relative standard deviation of the 10 single-measurements was 3,9 % on average. The average adhesion force of the test group (4,8N±1,7N) did not significantly differ from the control group (5,1N±2,9N); (Anova, p