Purpose: The Periotest is an electronic instrument that has been advocated for the measurement of implant stability and osseointegration. The aims of this investigation were to establish the relationship between contact time and PTV values when the Periotest was used to assess implants in vivo and in vitro, and to investigate the influence of the striking height of the Periotest handpiece and the length of implant abutment. Materials and Methods: The accelerometer signal from a Periotest was captured and compared with the resulting PTV value. In vitro measurements of PTV and contact time were performed on a 3-mm abutment that had been attached to a 15-mm implant luted into an aluminum block, and were repeated on a patient in vivo. Further measurements were made of the abutments of six implants in turn in the maxilla of the same patient. The standard abutment lengths on the implants were 3, 4 (x 2), 5.5 (x 2), and 7 mm. Results: The results indicated that there was a linear relationship between contact time and PTV value for implants measured in vitro and in vivo. Greater scatter of the in vivo data was attributed to test and patient variables including striking position, distance, and damping as a result of the presence of soft tissues. There was a linear relationship between the PTV value and the striking height for implant measurements in vivo and in vitr Conclusion: It can be concluded that the sensitivity of the Periotest to clinical variables including striking height and handpiece angulation limit the application of the instrument as a clinical diagnostic aid to measure implant stability