A simple technique is described for in vivo assessing the interfacial rigidity between a dental root implant and the bone surrounding it. The method is based on estimating the frequency (10 to 150 KHz) and amplitude of the vibration of the implant induced by a small pulsed force. Application of the force to the implant and detection of the vibrational signal from the implant are performed by lightly touching it with two fine needles connected with piezoelectric elements. A distinct signal difference observed in animal tests of bioactive implant and nonbioactive one is shown to well agree with that obtained from corresponding ex vivo models.