In haptic mixed reality, touch feedback of the real environment is merged with virtual haptic stimuli, thus altering the haptic perception of objects. In our research, we explore the feasibility of using this paradigm for medical training systems. In this talk, an overview of the technique will be provided as well as application scenarios be outlined. In earlier work, we had explored the use of such haptic augmentation in the context of tissue palpation. More recently, we focused on the modification of surgical instruments, to provide augmentation during interaction with mock-up anatomical models; specifically, a prototype system of a modified surgical bone drill has been developed. The setup is capable of providing different stiffness augmentations, representing varying bone densities, based on twisted-string actuation.