The influence of fixation in formalin on the measurement of stability of implants using resonance frequency analysis and Periotest M®: a study in a dog.

Resonance frequency analysis (RFA) and Periotest® have been widely used to evaluate measurements of the stability of implants in clinical studies and animal experiments. In animals, these measurements are often made after bone has been fixed in formalin. However, it is not yet clear how this fixation influences RFA and Periotest®, and our aim was to clarify this using the implant stability quotient (ISQ) and Periotest® value (PTV). Six titanium implants were placed, 3 into each femur, of one male dog (a beagle/labrador cross). After 2 months blocks of bone were harvested, each block containing 3 implants, and were fixed in 10% neutral formalin. Measurements were made before fixation (time 0) then at 4h, and 1, 7, 14, 21, and 28 days. ISQ values of 6 implants were evaluated 3 times on the short and long axes, as were PTV. ISQ ranged from 67.5 to 79.3 and tended to increase with time. ISQ at 7-28 days were significantly higher than that at time 0. PTV ranged from -7.7 to -7.8 and did not differ significantly among fixation times. These results suggest that fixation of bony tissue in formalin might affect ISQ, so it might be preferable to measure ISQ during the early stages of fixation.