Purpose: To investigate the influence of milling parameters on the durability during in-vitro aging-simulation, and fracture force of resin-based composite crowns. Materials and Methods: Identical molar crowns (n=8 per group) were milled from resin-based composite crowns (Grandio, VOCO, Germany) with different processing speed (soft, normal, fast) or level of details (very high, high, low) form 98mm discs. To investigate the influence of cooling, one group was milled wet. The influence of polishing was tested in two groups. All crowns were adhesively bonded on standardized resin-based composite molars. Aging was performed with thermal cycling and mechanical loading (2x3000x5°C/55°C, 2min, H20 dist., 1.2x106 force 50N). Fracture forces were determined (v=1mm/min, Z010, Zwick, Germany). Statistics: Pearson-correlation, one-way ANOVA, Bonferroni post-hoc-tests (α=0.05). Results: All crowns survived TCML without any failures. The fracture values varied between 1237.3 +/- 326.7N and 3308.6 +/- 655.8N. Significant (p<0.001) differences between the individual manufacturing approaches were detected. Failure was categorized as a fracture of the crown and partial loosening of the crown. No different failure pattern was observed between the tested systems. Conclusion: A medium level of detail seems to be ideal to achieve highest fracture forces. No relationship existed between machining speed and fracture force. Fracture force was not affected by wet grinding. In individual cases, polishing reduced crown fracture values, due to reduced wall thickness.