A Comprehensive Study on Implant Stability Quotient (ISQ) in View of Resonance Frequency and Spectrum Analysis.

PURPOSE: This experimental study investigated how well implant stability quotient (ISQ) represents resonance frequency. Benchtop experiments on standardized samples, mimicking a premolar section of a mandible, were conducted to correlate an ISQ value and a resonance frequency to synthetic bone density and an incremental insertion torque. A frequency spectrum analysis was performed to check the validity of the resonance frequency analysis (RFA). MATERIALS AND METHODS: Branemark Mk III implants with dimensions ∅4 Å~ 11.5 mm were placed in Sawbones test models of five different densities (40, 30, 40/20, 20, 15 PCF). An incremental insertion torque was recorded during implant placement. To perform stability measurements, the test models were clamped partially in a vise (unclamped volume 10 Å~ 20 Å~ 34 mm). A MultiPeg was attached onto the implants, and a Penguin RFA measured ISQ. Simultaneously, motion of the MultiPeg was monitored via a laser Doppler vibrometer and processed by a spectrum analyzer to obtain the resonance frequency. Tightness of the clamp was adjusted to vary the resonance frequency. A statistical analysis produced a linear correlation coefficient 𝑅 among the measured ISQ, resonance frequency, and incremental insertion torque. RESULTS: The resonance frequency had high correlation to the incremental insertion torque (𝑅 = 0.978), confirming the validity of using RFA for this study. Measured ISQ data were scattered and had low correlation to the resonance frequency (𝑅 = 0.214) as well as the incremental insertion torque (𝑅 = -0.386). The spectrum analysis revealed simultaneous presence of multiple resonance frequencies. CONCLUSIONS: For the designed benchtop tests, resonance frequency does indicate implant stability in view of Sawbones density and incremental insertion torque. ISQ measurements, however, do not correlate well to the resonance frequency, and may not reflect the stability when multiple resonance frequencies are present simultaneously.

Challenges of Using Resonance Frequency Analysis to Identify Stability of a Dental Implant Placed in the Mandible.

PURPOSE: This numerical study examined the efficacy and challenges of using resonance frequency analysis to identify the stability of implants placed in mandibles. The study also examined the feasibility of using angular stiffness as an alternative index to quantify dental implant stability in mandibles. MATERIALS AND METHODS: A finite element model consisting of a mandible, an implant, an abutment, and a bonding layer (between the implant and the mandible) was created in commercially available software ANSYS. The level of osseointegration was modeled by varying the stiffness of the bonding layer. Three sets of boundary conditions were imposed on the mandible: fixed, rotationally free, and rotationally restrained. Three implant locations were studied: central, premolar, and molar positions. An alternative abutment mimicking SmartPeg and eight different implant lengths were also included. A modal analysis and a static analysis were conducted to calculate resonance frequencies and angular stiffness, respectively. RESULTS: Two types of vibration modes were found. One was jawbone modes, for which the mandible deformed significantly but not the bonding layer. Resonance frequencies of the jawbone modes were not sensitive to the level of osseointegration. The other was implant modes, for which the bonding layer deformed significantly but not the mandible. Among multiple implant modes obtained, only one was trackable as the level of osseointegration increased. The resonance frequency of the trackable implant mode was very sensitive to the implant location as well as boundary conditions, but not as much to the level of osseointegration. In contrast, angular stiffness was sensitive to the level of osseointegration but not as much to boundary conditions. CONCLUSION: The efficacy of using resonance frequency analysis to quantify the stability of a dental implant is questionable. Its high sensitivity to implant locations and boundary conditions as well as its low sensitivity to the level of osseointegration cause huge uncertainties in correlating measured resonance frequencies to implant stability. Angular stiffness is a much more reliable indicator because of its high sensitivity to the level of osseointegration and low sensitivity to boundary conditions.

Method to examine how geometry affects the release and retention of alpine touring boot-binding systems.

OBJECTIVES: Develop a method to examine the effects of component geometry and force-deflection on the release process of Tech/Pin alpine touring (AT) ski boots and bindings. DESIGN AND METHODS: For seven AT boots, we measured the critical geometric dimensions of the metal inserts at the toe region of the boots. Binding geometry (including the pins and rocker arms) and the force-angular deflection curves of typical AT bindings were measured. A kinematic model was derived to predict the contact force between the metal inserts of the AT boots and the pins of the AT bindings, dependent on angular displacement of the binding rocker arms. By combining the kinematic model, the force-angular deflection curves, and moment equilibrium, we determined the force and binding rotation angle needed to release the AT boot in a direction normal to the ski. RESULTS: The metal AT boot insert geometry and AT binding pin geometry and dimensions can affect significantly the contact states and kinematics of release. Two load-deflection curves of similar peak loads can result in significantly different maximal forces and angles to release the binding, even when the geometry and dimensions of the binding pins and boot inserts remain unchanged. CONCLUSIONS: The geometry and dimensions of the binding (pins and rocker arm) and the boot inserts define the kinematics of the binding release. The model can be used to test the effects of varying parameters on the release and retention characteristics of Tech/Pin boot-binding systems to optimize the release and retention characteristics.

A Critique of Resonance Frequency Analysis and a Novel Method for Quantifying Dental Implant Stability in Vitro.

PURPOSE: This study assessed the ability of resonance frequency measurements to differentiate the stability of implants with different lengths and diameters, and in different densities of bone. Another objective was to identify an alternative parameter capable of quantifying dental implant stability, thus facilitating greater sensitivity for efficacious detection of compromised or failing implants. MATERIALS AND METHODS: Implants of two different diameters (4 and 5 mm) and six different lengths were individually placed in synthetic bone blocks of three different densities (15, 40/20, and 40 pounds per cubic foot) in combination with two different abutments (short and tall) to evaluate their stability. Resonance frequency measurements were obtained via Osstell ISQ and experimental modal analysis (EMA). The resonance frequency measurements were further confirmed via finite element analysis (FEA) using commercially available software ANSYS. RESULTS: Resonance frequencies measured via Osstell ISQ and EMA did not change with respect to the length of the implants. The FEA also confirmed the measured results. FEA simulations further indicated that angular stiffness at the neck of the implant (ie, the base of the abutment) varied considerably with respect to the implant length and diameter. Moreover, the calculated angular stiffness was independent of the type of abutment used. CONCLUSION: The results obtained from resonance frequency analyses did not accurately represent dental implant stability. Changes to implant length and diameter did not affect resonance frequencies. In contrast, angular stiffness at the neck of the implant represented a superior index for quantifying dental implant stability. It not only successfully differentiated stability of implants of both varying lengths and diameters, but also produced quantitative data that was independent of the type of abutments used.

Asymmetries in wing inertial and aerodynamic torques contribute to steering in flying insects.

Maneuvering in both natural and artificial miniature flying systems is assumed to be dominated by aerodynamic phenomena. To explore this, we develop a flapping wing model integrating aero and inertial dynamics. The model is applied to an elliptical wing similar to the forewing of the Hawkmoth Manduca sexta and realistic kinematics are prescribed. We scrutinize the stroke deviation phase, as it relates to firing latency in airborne insect steering muscles which has been correlated to various aerial maneuvers. We show that the average resultant force production acting on the body largely arises from wing pitch and roll and is insensitive to the phase and amplitude of stroke deviation. Inclusion of stroke deviation can generate significant averaged aerodynamic torques at steady-state and adjustment of its phase can facilitate body attitude control. Moreover, averaged wing angular momentum varies with stroke deviation phase, implying a non-zero impulse during a time-dependent phase shift. Simulations show wing inertial and aerodynamic impulses are of similar magnitude during short transients whereas aerodynamic impulses dominate during longer transients. Additionally, inertial effects become less significant for smaller flying insects. Body yaw rates arising from these impulses are consistent with biologically measured values. Thus, we conclude (1) modest changes in stroke deviation can significantly affect steering and (2) both aerodynamic and inertial torques are critical to maneuverability, the latter of which has not widely been considered. Therefore, the addition of a control actuator modulating stroke deviation may decouple lift/thrust production from steering mechanisms in flapping wing micro aerial vehicles and increase vehicle dexterity through inertial trajectory shaping.

Direct Intracochlear Acoustic Stimulation Using a PZT Microactuator.

Combined electric and acoustic stimulation has proven to be an effective strategy to improve hearing in some cochlear implant users. We describe an acoustic microactuator to directly deliver stimuli to the perilymph in the scala tympani. The 800 µm by 800 µm actuator has a silicon diaphragm driven by a piezoelectric thin film (e.g., lead-zirconium-titanium oxide or PZT). This device could also be used as a component of a bimodal acoustic-electric electrode array. In the current study, we established a guinea pig model to test the actuator for its ability to deliver auditory signals to the cochlea in vivo. The actuator was placed through the round window of the cochlea. Auditory brainstem response (ABR) thresholds, peak latencies, and amplitude growth were calculated for an ear canal speaker versus the intracochlear actuator for tone burst stimuli at 4, 8, 16, and 24 kHz. An ABR was obtained after removal of the probe to assess loss of hearing related to the procedure. In some animals, the temporal bone was harvested for histologic analysis of cochlear damage. We show that the device is capable of stimulating ABRs in vivo with latencies and growth functions comparable to stimulation in the ear canal. Further experiments will be necessary to evaluate the efficiency and safety of this modality in long-term auditory stimulation and its ability to be integrated with conventional cochlear implant arrays.