A process for manufacturing a cap (4) which has at least one nominal breaking point (16) of a covering device for a bone defect site (2) and a device (1) for covering and/or reconstructing a bone defect site (2) are proposed, wherein through comparing a first data set which represents the affected bone defect site (2) in the actual condition with a second data set which represents the nominal condition of a regenerated bone at the bone defect site (2), wherein the second data set has been calculated or recorded at a time at which the bone at the site now to be regenerated was still a healthy bone (18) it is made possible that the regenerated bone produced through the regeneration of the bone defect point (2) has a shape which corresponds to the shape the bone had at the site to be regenerated when it was still healthy.