Critical Analysis of Dental Implant Stability Measurements In Vitro

Objectives: A clinical need exists for implant stability measurement systems that provide greater accuracy. Commercial devices measure natural-frequency-values (e.g., Osstell ISQ®) or contact-time (e.g., Periotest®) to estimate implant stability. Research tools, such as finite element analysis (FEA) and experimental modal analysis (EMA), are accurate methods to predict and measure natural-frequency-values, respectively, making them excellent tools for study of implant stability. This study sought to (a) evaluate accuracy and reliability of Osstell ISQ® and Periotest® by calibrating the devices with EMA and FEA via synthetic bone models (Sawbones®), and (b) use vibration theories to critically analyze operational principles of Osstell ISQ® and Periotest®.
Methods: Branemark implants (NobelBiocare, Switzerland) of lengths ranging from 7 to 18 mm were placed in artificial-bone models (Sawbones®) of different densities: hybrid(0.64/0.32g/cm³), high-density(0.64g/cm³), and low-density(0.24g/cm³) blocks to evaluate the effect of implant length on implant stability. Measurements made with Osstell® and Periotest® were compared with those of EMA and FEA
Results: Based on FEA simulations, natural-frequency-values of the test specimens had no correlation to implant length. High-density Sawbones®, however, resulted in higher natural-frequency-values. EMA confirmed the frequency trend predicted by FEA. Osstell ISQ® measurements showed no dependence on implant length. ISQ was highly scattered in low-density Sawbones®. Periotest® values (PTV) were too scattered to be conclusive.
Conclusions: 1. Natural-frequency-values were not affected by implant length but were influenced by simulated bone density. 2. Osstell ISQ® partially measured the frequency trend, but Periotest® did not. 3. The single-degree-of-freedom (SDOF) assumption made for the operation of Osstell ISQ® and Periotest® may limit their performance because the actual implant-abutment-bone system is substantially more complex than a SDOF. 4. Combined use of EMA and FEA can serve as an accurate benchmark to evaluate and calibrate commercial devices.