A clinical way to non-invasively assess dental implant stability is important for long-term success of the implant. Dental implants are typically screw shaped prosthetics which fuse with the surrounding jaw bone through a process known as osseointegration, where newly formed bone is deposited on the implant surface, forming a direct structural connection. Following sufficient healing, the implant is used to hold a dental restoration in place, which serves to replace the function and appearance associated with the missing tooth. The risk of implant failure is generally highest before any osseointegration has taken place, which has resulted in the development of various techniques to measure implant stability. Many of these techniques, developed over the last few decades, relate the stability of an implant to the stiffness of the bone-implant interface.

The Advanced System for Implant Stability Testing (ASIST) is a recently developed device that was shown to evaluate the stability of bone anchored hearing aid implants as well as natural teeth. The device couples an impact technique with an analytical model of the system, such that the measured signal can be correlated with the analytical response by determining the model parameters, including the interfacial stiffness, which minimizes the Euclidean norm between the model response and fitted data as quantified by an R² value. This stiffness is non-dimensionalized and reported as the ASIST Stability Coefficient (ASC). The current work presents the development of the ASIST towards dental implant systems. The device was evaluated using in vitro laboratory testing with polyurethane foam as an artificial bone substitute. A refined analytical model was also developed, which accounts for the different mechanical properties of the cortical and cancellous bone layers.

It was found that the ASIST was able to consistently estimate the interfacial stiffness on a given implant installation with various abutments and crowns. This provides evidence that the analytical model is able to account for the geometric and inertial properties of different system components, and that ASIST approach can isolate the stiffness of a given interface. Further tests were done to evaluate the correlations between the ASC and other methods of measuring stability. This includes the commercially available Osstell® device, in addition to the insertion torque (IT) and the force required to pull the implant out of its socket. The ASIST was able to detect differences in stability corresponding to changes in substrate properties and implant bonding. Additionally, the ASIST was found to have several advantages over the Osstell® device. Compared to the Osstell® device, the ASIST was shown to retain its sensitivity across a wider range of stability, and possessed a stronger correlation to the insertion torque and pullout force.

To better reflect the physiological structure of bone, the analytical model was then further refined to model the mechanical properties of the cortical and cancellous layers and used to evaluate the effects of cortical density and thickness on primary stability. The ASIST was then compared to the Osstell® in terms of their correlations to IT and pullout strength. Compared to the ISQ, the ASC showed stronger correlations with IT and pullout values. This implies that the analytical model is an accurate representation of the implant’s mechanical stability, and can potentially be used to measure the stability of implants in a clinical setting.

This work shows that the ASIST device is mainly sensitive to changes in the interface conditions, and possesses several advantages over current measurement techniques. The ASIST shows promising preliminary results as a method of measuring dental implant stability. With further research into the device’s performance with implant systems in real bone, the device could potentially provide clinicians with an improved non-invasive method of measuring the stability and health of dental implants over time.