Resonant Frequency Measurement of Dental Implants Using an Impulse Method

Objectives: The purpose of this study was to measure resonant frequency (RF), system transfer function and decay constants of vibration of dental implants in vivo  during the healing phase of osseointegration.

Method: Input impulses were delivered to the implant using a miniature instrumented hammer and the resulting vibrations were measured by an accelerometer attached to the implant.

Results: Nine subjects and eighteen implants, both maxillary and mandibular, were followed from implant placement to prosthesis placement four to twelve months later. An initial decrease in  RF was observed in 75% of the trials with a minimum 30 to 60 days post implantation followed by a rise usually well above the immediate post implantation measurement. On average RF values were 2500 Hz. (day 0), 1500 Hz. (day 40), 3500 Hz. (day 80) and 4000 Hz. (day 120).This impulse method also allows studies of the ratio of output acceleration amplitude to the input impulse amplitude (i.e. system transfer function). We correlate transfer function rise with RF rise. For example in a particular implant the transfer functions were 2.50 x 10⁵ (kg s)^-1 at RF of 2450 Hz., 5.00 x 10⁵ (kg s)^-1 at RF of 2800 Hz. and 7.50 x 10⁵ (kg s)^-1 at RF of 3300 Hz.

Conclusion: This study demonstrates that an impulse method of implant vibration can produce data that reflect changes occurring at the bone implant interface during osseointegration.