Testing procedures There are a number of methods used to gauge the level of osseointegration and the subsequent stability of an implant. One widely used diagnostic procedure is percussion analysis, where a dental instrument is tapped against the implant carrier. The nature of the ringing that results is used as a qualitative measure of the implant’s stability. An integrated implant will elicit a higher pitched "crystal" sound, whereas a non-integrated implant will elicit a dull, low-pitched sound. Another method is a reverse torque test, in which the implant carrier is unscrewed. If it fails to unscrew under the reverse torque pressure, the implant is stable. If the implant rotates under the pressure it is deemed a failure and removed. This method comes at the risk of fracturing bone that is mid-way in the process of osseointegration. It is also unreliable in determining the osseointegration potential of a bone region, as tests have yielded that a rotating implant can go on to be successfully integrated. A non-invasive and increasingly implemented diagnostic method is resonance frequency analysis (RFA). A resonance frequency analyzer device prompts vibrations in a small metal rod temporarily attached to the implant. As the rod vibrates, the probe reads its resonance frequency and translates it into an implant stability quotient (ISQ), which ranges from 1–100, with 100 indicating the highest stability state. Values ranging between 57 and 82 are generally considered stable, though each case must be considered independently. Osseoperception One of the peculiarities of osseointegrated prostheses is that mechanical events at the prosthesis (e.g. touch) are transferred as vibrations through the bone. This “osseoperception” means that the prosthesis user regains a more accurate sense of how the prosthesis is interacting with the world. Users of bone-anchored lower limb prostheses report, for example, that they can tell which type of soil they are walking on due to osseoperception. Recent research on users of bone-anchored upper and lower limb prostheses showed that this osseoperception is not only mediated by mechanoreceptors but also by auditory receptors. This means that, rather than just feeling mechanical influences on the device, users also hear the movements of their prosthesis. This joint mechanical and auditory sensory perception is likely responsible for the improved environment perception of users of osseointegrated prostheses compared to traditional socket suspended devices. It is not clear, however, to what extent this implicit sensory feedback actually influences prosthesis users in everyday life.