A temporospatial histomorphometric analysis of bone density adjacent to acid-etched self-tapping dental implants with an external hexagon connection in the female baboon.

OBJECTIVE: To characterize osseointegration as the percent of bone-implant contact (%BIC) along the surface (0.0 mm) as well as at surface profiles 0.5 mm and 1.0 mm lateral to the implant, determining any differences between early occlusally loaded and non-loaded implants. MATERIAL AND METHODS: In ten adult female baboons, 120 dental implants were randomly placed in opposing mandibular and maxillary locations. Eighty sites had two groups of healing (no load) of either 1 (n = 40) or 2 (n = 40) months leading to 3 months of functional loading. These sites received full acid-etched surface implants. The 40 control implants represented healing only periods (no load) for 1 (n = 10), 2 (n = 10), 4 (n = 10), and 5 (n = 10) months. These implants were of a vertically split surface texture design (acid-etched and machined). Block sections and photomicrographs were obtained. Blinded histometric analyses determined the %BIC via a superimposed template. RESULTS: The unloaded groups (1, 2, and 4 months) had higher %BIC compared to the 5-month group (p < 0.0001). The loaded groups exhibited mean bone densities of 59.2% and 55.5% (1-month healing at 0.5 mm and 1.0 mm, respectively) and 61.0% and 57.1% (2-month healing at 0.5 mm and 1.0 mm, respectively) with no significant difference between healing time (p = 0.4118). CONCLUSION: There was a lateral increase in %BIC in the loaded compared to unloaded groups. CLINICAL RELEVANCE: The decrease in bone densities at the 5-month unloaded group suggests that there is a critical earlier time period when dental implants should be placed into functional load.

Crestal bone loss due to abutment manipulation and an internal silver deposition implant design in a canine model.

OBJECTIVE: The study aimed to evaluate the effect of internal silver coating as a countermeasure to crestal bone loss around implants with or without multiple abutment disconnections/reconnections. MATERIALS AND METHODS: Following tooth extraction, 48 implants with connected healing abutments (24 implants internally coated with elemental silver) were placed in the mandible of eight beagle dogs. Two months after implant surgery one side of the mandible was randomly assigned to four abutment manipulations (disconnection/reconnection) on a weekly basis. At 4 months postoperative, biopsies were obtained and prepared for histomorphometric analysis. RESULTS: Healing abutment manipulation increased crestal bone remodeling when compared to no abutment manipulation (1.28 mm versus 0.92 mm, respectively), although the difference was not statistically significant (p = 0.0836). Overall, an internal silver coating did not provide a statistically sufficient implant treatment characteristic as a countermeasure to crestal bone loss (p = 0.7801). CONCLUSIONS: These findings indicate that the controlled variables explored here (abutment manipulation/internal silver coating) have a limited effect on initial crestal bone loss. CLINICAL RELEVANCE: Abutment manipulation during prosthetic work does not seem to harm the peri-implant soft and hard tissues.

Validation of a Biomechanical Injury and Disease Assessment Platform Applying an Inertial-Based Biosensor and Axis Vector Computation.

Inertial kinetics and kinematics have substantial influences on human biomechanical function. A new algorithm for Inertial Measurement Unit (IMU)-based motion tracking is presented in this work. The primary aims of this paper are to combine recent developments in improved biosensor technology with mainstream motion-tracking hardware to measure the overall performance of human movement based on joint axis-angle representations of limb rotation. This work describes an alternative approach to representing three-dimensional rotations using a normalized vector around which an identified joint angle defines the overall rotation, rather than a traditional Euler angle approach. Furthermore, IMUs allow for the direct measurement of joint angular velocities, offering the opportunity to increase the accuracy of instantaneous axis of rotation estimations. Although the axis-angle representation requires vector quotient algebra (quaternions) to define rotation, this approach may be preferred for many graphics, vision, and virtual reality software applications. The analytical method was validated with laboratory data gathered from an infant dummy leg's flexion and extension knee movements and applied to a living subject's upper limb movement. The results showed that the novel approach could reasonably handle a simple case and provide a detailed analysis of axis-angle migration. The described algorithm could play a notable role in the biomechanical analysis of human joints and offers a harbinger of IMU-based biosensors that may detect pathological patterns of joint disease and injury.

Assessing specific causation of mesothelioma following exposure to chrysotile asbestos-containing brake dust.

BACKGROUND: The question of whether chrysotile asbestos-containing brake dust can plausibly serve as a cause of mesothelioma in an exposed individual has become a matter of heated debate in the medical literature despite multiple international, federal, and state governmental agencies acknowledging a causal association. OBJECTIVES: We describe and provide an analysis of various industry and academic perspectives contributing to the debate. METHODS: A framework is presented for evaluating the general and specific causal relationship between brake dust exposure and mesothelioma utilizing the principles of forensic epidemiology, and by applying the Bradford-Hill criteria. RESULTS AND CONCLUSIONS: We conclude that there is a "net" of evidence favoring a causal relationship between brake dust-associated chrysotile exposure and mesothelioma. The industry-sponsored position that there is insufficient evidence to support a contiguous "chain" of causation is specious from both a methodologic and evidentiary perspective. Finally, we suggest a semiquantitative approach for the evaluation of individual causation in putative cases of mesothelioma with a history of significant brake dust exposure.

A stochastic model validated with human test data causally associating target vehicle Delta V, occupant cervicocranial biomechanics, and injury during rear-impact crashes.

Even at low to moderate-speeds, rear-end motor vehicle crashes have been strongly associated with occupant cervicocranial biomechanics that lead to head and neck injury. In this paper, we present the development of an analytic mechanics model of occupant head and neck motion as associated with modeled target vehicle Delta V during rear-end vehicular crashes. The inclusion of stochastic mechanical input variables further developed the model beyond the deterministic framework by reflecting aspects of the random nature of real-world crashes and the resulting injuries. This approach led to the characterization of 1000 crash simulations, quantifying Delta V and the resulting probabilistic occupant biomechanics. The model was validated through the direct comparison with 86 published human subject crash tests. Overall, the model slightly underestimated by -2.6% the magnitude of peak head accelerations identified in the literature. The utility of the model allows a forensic biomechanical investigator to customize some of the fundamental input crash parameters and appropriately explore the resulting vehicular mechanics and their direct influence on injury biomechanics.

Volumetric stress-strain analysis of optohydrodynamically suspended biological cells.

Ongoing investigations are exploring the biomechanical properties of isolated and suspended biological cells in pursuit of understanding single-cell mechanobiology. An optical tweezer with minimal applied laser power has positioned biologic cells at the geometric center of a microfluidic cross-junction, creating a novel optohydrodynamic trap. The resulting fluid flow environment facilitates unique multiaxial loading of single cells with site-specific normal and shear stresses resulting in a physical albeit extensional state. A recent two-dimensional analysis has explored the cytoskeletal strain response due to these fluid-induced stresses [Wilson and Kohles, 2010, "Two-Dimensional Modeling of Nanomechanical Stresses-Strains in Healthy and Diseased Single-Cells During Microfluidic Manipulation," J Nanotechnol Eng Med, 1(2), p. 021005]. Results described a microfluidic environment having controlled nanometer and piconewton resolution. In this present study, computational fluid dynamics combined with multiphysics modeling has further characterized the applied fluid stress environment and the solid cellular strain response in three dimensions to accompany experimental cell stimulation. A volumetric stress-strain analysis was applied to representative living cell biomechanical data. The presented normal and shear stress surface maps will guide future microfluidic experiments as well as provide a framework for characterizing cytoskeletal structure influencing the stress to strain response.

An evaluation of applied biomechanics as an adjunct to systematic specific causation in forensic medicine.

Biomechanical tests of post hoc probability have been proposed by prior authors as reliable tests of causation in forensic settings. Biomechanical assessment of injury kinetics and kinematics is a potentially important tool in forensic medicine, but there is also the potential for misapplication. The most reliable application is when biomechanical analysis is used to explain injury mechanisms, such as how an injury may have occurred. When a biomechanical analysis is used as a means of determining whether, rather than how an injury has resulted from a traumatic exposure, then a lack of reliability of the methodology limits its application in forensic medicine. Herein, we describe a systematic assessment of causation by adapting established general causation principles to specific causation scenarios, and how biomechanical analysis of injury mechanics is properly used to augment such an approach in conjunction with the principles of forensic epidemiology. An example calculation of relative risk associated with cervical spine injury is provided as a representative probabilistic metric for assessing causation. The statistical benefits and limitations of biomechanical analysis are discussed as an adjunct to forensic medicine.

Application of flexural and membrane stress analysis to distinguish tensile and compressive moduli of biologic materials.

Three-point bending is often used during the mechanical determination of tissue material properties. When taken to failure, the test samples often experience high deformations. The objective of this study was to present beam and plate theories as analytical tools for determining tensile and compressive elastic moduli during the transition from flexure to membrane stress states. Samples of cartilage, a highly flexible connective tissue having differing tensile and compressive moduli, were tested. Three-point bending tests were conducted on auricular (ear) and costal (rib) cartilage harvested from pigs. The influence of span length variation and Poisson's ratio assumptions were statistically assessed. Tensile elastic moduli of the ear (3.886 MPa) and rib (6.131 MPa) were derived from high-deformation bending tests. The functional assessment described here can be applied as a design input approach for tissue reconstruction and tissue engineering, considering both hard and soft tissue applications.

Affordance-Based Surgical Design Methods Considering Biomechanical Artifacts.

Surgical design in personalized medicine is often based on native anatomy, which may not accurately reflect the interaction between native musculoskeletal tissues and biomechanical artifacts. To overcome this problem, researchers have developed alternative methods based on affordance-based design. The design process can be viewed in terms of action possibilities provided by the (biological) environment. Here, we use the affordance-based approach to address possibilities for action offered by biomechanical artifacts. In anterior crucial ligament (ACL) reconstruction, the design goal is to avoid ligament impingement while optimizing the placement of the tibial tunnel. Although in the current rationale for tibial tunnel placement roof impingement is minimized to avoid a negative affordance, we show that tibial tunnel placement can rather aim to constrain the target bounds with respect to a positive affordance. We describe the steps for identifying the measurable invariants and provide a mathematical framework for the surgery affordances within the knee.

A case-control study of cerebellar tonsillar ectopia (Chiari) and head/neck trauma (whiplash).

PRIMARY OBJECTIVE: Chiari malformation is defined as herniation of the cerebellar tonsils through the foramen magnum, also known as cerebellar tonsillar ectopia (CTE). CTE may become symptomatic following whiplash trauma. The purpose of the present study was to assess the frequency of CTE in traumatic vs non-traumatic populations. STUDY DESIGN: Case-control. METHODS AND PROCEDURES: Cervical MRI scans for 1200 neck pain patients were reviewed; 600 trauma (cases) and 600 non-trauma (controls). Half of the groups were scanned in a recumbent position and half were scanned in an upright position. Two radiologists interpreted the scans for the level of the cerebellar tonsils. MAIN OUTCOMES AND RESULTS: A total of 1195 of 1200 scans were read. CTE was found in 5.7% and 5.3% in the recumbent and upright non-trauma groups vs 9.8% and 23.3% in the recumbent and upright trauma groups (p = 0.0001). CONCLUSIONS: The results described in the present investigation are first to demonstrate a neuroradiographic difference between neck pain patients with and without a recent history of whiplash trauma. The results of prior research on psychosocial causes of chronic pain following whiplash are likely confounded because of a failure to account for a possible neuropathologic basis for the symptoms.

An inverse method for predicting tissue-level mechanics from cellular mechanical input.

Extracellular matrix (ECM) provides a dynamic three-dimensional structure which translates mechanical stimuli to cells. This local mechanical stimulation may direct biological function including tissue development. Theories describing the role of mechanical regulators hypothesize the cellular response to variations in the external mechanical forces on the ECM. The exact ECM mechanical stimulation required to generate a specific pattern of localized cellular displacement is still unknown. The cell to tissue inverse problem offers an alternative approach to clarify this relationship. Developed for structural dynamics, the inverse dynamics problem translates measurements of local state variables (at the cell level) into an unknown or desired forcing function (at the tissue or ECM level). This paper describes the use of eigenvalues (resonant frequencies), eigenvectors (mode shapes), and dynamic programming to reduce the mathematical order of a simplified cell-tissue system and estimate the ECM mechanical stimulation required for a specified cellular mechanical environment. Finite element and inverse numerical analyses were performed on a simple two-dimensional model to ascertain the effects of weighting parameters and a reduction of analytical modes leading toward a solution. Simulation results indicate that the reduced number of mechanical modes (from 30 to 14 to 7) can adequately reproduce an unknown force time history on an ECM boundary. A representative comparison between cell to tissue (inverse) and tissue to cell (boundary value) modeling illustrates the multiscale applicability of the inverse model.

Mechanical stress analysis of microfluidic environments designed for isolated biological cell investigations.

Advancements in technologies for assessing biomechanics at the cellular level have led to discoveries in mechanotransduction and the investigation of cell mechanics as a biomarker for disease. With the recent development of an integrated optical tweezer with micron resolution particle image velocimetry, the opportunity to apply controlled multiaxial stresses to suspended single cells is available (Neve, N., Lingwood, J. K., Zimmerman, J., Kohles, S. S., and Tretheway, D. C., 2008, "The muPIVOT: An Integrated Particle Image Velocimetry and Optical Tweezers Instrument for Microenvironment Investigations," Meas. Sci. Technol., 19(9), pp. 095403). A stress analysis was applied to experimental and theoretical flow velocity gradients of suspended cell-sized polystyrene microspheres demonstrating the relevant geometry of nonadhered spherical cells, as observed for osteoblasts, chondrocytes, and fibroblasts. Three flow conditions were assessed: a uniform flow field generated by moving the fluid sample with an automated translation stage, a gravity driven flow through a straight microchannel, and a gravity driven flow through a microchannel cross junction. The analysis showed that fluid-induced stresses on suspended cells (hydrodynamic shear, normal, and principal stresses in the range of 0.02-0.04 Pa) are generally at least an order of magnitude lower than adhered single cell studies for uniform and straight microchannel flows (0.5-1.0 Pa). In addition, hydrostatic pressures dominate (1-100 Pa) over hydrodynamic stresses. However, in a cross junction configuration, orders of magnitude larger hydrodynamic stresses are possible without the influence of physical contact and with minimal laser trapping power.

A Deterministic Model of Human Motion Based on Algebraic Techniques and a Sensor Network to Simulate Shoulder Kinematics.

Limiting the quantitative characterization of ambulatory mobility to only the two-dimensional sagittal plane through the investigation of key kinematic parameters, may still inform scientists and bioengineers of critical elements of joint locomotion. This paper presents the initial validation of a deterministic biomechanical gait model that was derived from an inverse kinematic analysis of three-dimensional upper extremity movement. Algebraic methods were applied to generate shoulder flexion and extension angles during a single gait cycle during normal walking. The direct kinematic measurements from a motion capture system were analyzed and compared to the predicted measurements from the algebraic model for eight healthy, human subjects. The predicted results over all subjects varied from the actual joint angle measurements with a nominal amount of mean error (23%), while correlations were quite strong (mean R2 = 0.97). These findings indicate the potential value of deterministic modeling with algebraic techniques as an alternative to existing methods.

Analysis of bending behavior of native and engineered auricular and costal cartilage.

A large-deflection elasticity model was used to describe the mechanical behavior of cartilaginous tissues during three-point bending tests. Force-deflection curves were measured for 20-mm long x 4-mm wide x approximately 1-mm thick strips of porcine auricular and costal cartilage. Using a least-squares method with elastic modulus in bending as the only adjustable parameter, data were fit to a model based on the von Karman theory for large deflection of plates. This model described the data well, with an average RMS error of 14.8% and an average R(2) value of 0.98. Using this method, the bending modulus of auricular cartilage (4.6 MPa) was found to be statistically lower (p < 0.05) than that of costal cartilage (7.1 MPa). Material features of the cartilage samples influenced the mechanical behavior, including the orientation of the perichondrium in auricular cartilage. These methods also were used to determine the elastic moduli of engineered cartilage samples produced by seeding chondrocytes into fibrin glue. The modulus of tissue-engineered constructs increased statistically with time (p < 0.05), but still were statistically lower than the moduli of the native tissue samples (p > 0.05), reaching only about a third of the values of native samples.

Five-year survival distributions of short-length (10 mm or less) machined-surfaced and Osseotite implants.

BACKGROUND: In cases of reduced alveolar bone height, implants of short length (10 mm or less) may be employed although there is a perceived risk that because of their small stature they will be unable to tolerate occlusal loads and will fail to osseointegrate. PURPOSE: This report describes an analysis of prospective multicenter clinical studies evaluating the risk for failure of short-length implants, comparing dual acid-etched (DAE) Osseotite implants (Implant Innovations, Inc., Palm Beach Gardens, FL, USA) to machined-surfaced implants. MATERIALS AND METHODS: Admission criteria were the same for both data sets. Baseline variables of demographics including age, gender and smoking status, bone quality, location, implant dimensions, and types of prostheses were compared to ensure balance among groups. Cumulative survival rates (CSRs) were calculated with the Kaplan-Meier estimator. RESULTS: The implant data included 2294 implants for the DAE series and 2597 implants for the machined-surfaced series. Patient demographics showed similar percentages of occurrence for all variables. The distributions of implants between short- and standard-length data sets for baseline variables including width, location, and restorative type were similar, qualifying these data sets for comparison of the independent variable of length. Overall, there was a 2.2% difference in 5-year CSRs between the machined-surfaced short- and the standard-length implants. For these implants a 7.1% difference was observed in the posterior maxilla and an 8.5% difference in the anterior maxilla. For DAE implants the overall difference between "standards" and "shorts" was 0.7%, which is not statistically significant. CONCLUSION: In this analysis the difference in CSRs between short- and standard-length implants was greater for machined-surfaced implants than for DAE implants.

Direct assessment of profilometric roughness variability from typical implant surface types.

PURPOSE: Protocols for quantifying the surface roughness of implants are varied and dependent upon the roughness parameter produced by the particular measurement device. The objective of this study was to examine the accuracy and precision of typical roughness characterization instruments used in the dental implant industry. MATERIALS AND METHODS: The average roughness (Ra) was measured using 2 common surface characterization instruments: an interferometer and a stylus profilometer. Titanium disks were prepared to represent 4 typical dental implant surfaces: machined, acid-etched, hydroxyapatite-coated, and titanium plasma-sprayed. Repeated measurements from multiple sites on each surface were undertaken to establish statistical inferences. Qualitative images of the surfaces were also acquired using a laser scanning confocal microscope. After surface measurements were conducted, the disks were diametrically cut and cross-sectional profiles were examined using a scanning electron microscope (SEM) as a comparative measure of surface topography. An analysis of variance was applied to isolate the effects of the measurement site, measurement sequence, surface treatment, and instrument type on Ra values. RESULTS: The results indicated that surface treatment (P = .0001) and instrument (P = .0001) strongly influenced Ra data. By design, measurement site (diametrical: P = .9859; area: P = .9824) and measurement sequence (P = .9990) did not influence roughness. In the assessment of individual instrument accuracy, the interferometer was the most accurate in predicting SEM-based roughness (P = .6688) compared with the stylus (P = .0839). As a measure of aggregate precision over all measurements, the most repeatable instrument was the stylus (coefficient of variation [CV] = 0.108), followed by the interferometer (CV = 0.125) and SEM (CV = 0.273). DISCUSSION: These results indicate dependencies in accuracy and precision related to the surface characterization technique. CONCLUSION: Instrument variability may obscure functional correlations between implant surface topography and osseointegration.

Dual-etched implants loaded after 1- and 2-month healing periods: a histologic comparison in baboons.

The purpose of this study was to evaluate the effect of early loading of Osseotite dual acid-etched commercially pure titanium dental implants in an established baboon model. Implant sites were prepared by removal of premolars and first molars at maxillary and mandibular sites in 10 adult female baboons (Papio anubis). The resultant edentulous ridges were allowed to heal for 6 weeks. Following the placement of 80 implants, 2-mm healing abutments were placed on each implant and protruded through the mucosa after flap closure. Each implant was functionally loaded with a single crown after either 1 month (n = 40) or 2 months (n = 40) of implant healing. All implants were removed in block section after 3 months of functional loading and prepared for histologic evaluation. Photographs of histologic slides were digitized for data collection. The amount of osseous tissue contact along the implant surface in the buccolingual plane was determined using image analysis. The fraction of direct bone-tissue contact along a standardized region of each implant perimeter was calculated and compared using analysis of variance. Implants loaded after 1 month of healing had a mean of 76.6% + 14.4% bone contact, and implants loaded after 2 months of healing had a mean of 77.2% +/- 12.2% bone contact. Statistically, the 1- and 2-month groups were similar (P = .81). No implant failures were observed in either treatment group. Reducing the surgical healing time from 2 months to 1 month did not statistically affect the amount of bone observed at the tissue-implant interface in baboons under functionally loaded conditions.

A meta-analysis evaluating the risk for implant failure in patients who smoke.

Failure of dental implants to achieve osseointegration is often attributed to patient baseline variables, such as smoking. This meta-analysis examines outcomes of clinical studies that monitored the performance of machined-surfaced and Osseotite, implants; the analysis also isolates the effect of smoking. The implant data for the machined-surfaced implants are derived from three prospective multicenter studies (n = 2,614) and from six prospective studies (n = 2,274) for the Osseotite implants. All implant placement surgeries followed a two-stage surgical approach with an unloaded healing period of 4 to 6 months. An evaluation of the data sets (i.e., smokers vs nonsmokers) was first performed to determine the existence of imbalance in baseline variables, including patient demographics, bone quality, location, dimensions, and types of prostheses. Analysis of the distributions of these baseline variables showed similar proportionalities and therefore qualified the data sets for comparison of the cumulative success rates (CSR) of the implants on the basis of smoking. For the 2,117 nonsmoking, machined-surfaced implants, the 3-year CSR is 92.8%; for the 492 implants in the smoking group, the CSR is 93.5%. The 3-year CSR for 1,877 nonsmoking Osseotite implants is 98.4%; for the 397 smoking implants it is 98.7%. No difference is observed between the smoking groups and the nonsmoking groups in these patient populations. There is, however, a clinically relevant difference observed between the two implant types.

Biomechanical Analysis of Concealed Pack Load Influences on Terrorist Gait Signatures Derived from Gröbner Basis Theory.

This project examines kinematic gait parameters as forensic predictors of the influence associated with individuals carrying concealed weighted packs up to 20% of their body weight. An initial inverse dynamics approach combined with computational algebra provided lower limb joint angles during the stance phase of gait as measured from 12 human subjects during normal walking. The following paper describes the additional biomechanical analysis of the joint angle data to produce kinetic and kinematic parameters further characterizing human motion. Results include the rotational velocities and accelerations of the hip, knee, and ankle as well as inertial moments and kinetic energies produced at these joints. The reported findings indicate a non-statistically significant influence of concealed pack load, body mass index, and gender on joint kinetics (p>0.05). Ratios of loaded to unloaded kinematics, however, identified some statistical influence on gait (p<0.05). On-going studies are examining an additional subject cohort with greater pack loads in an effort to identify alterations in gait signatures as a counter-terrorism approach.

Novel computational approaches characterizing knee physiotherapy.

A knee joint's longevity depends on the proper integration of structural components in an axial alignment. If just one of the components is abnormally off-axis, the biomechanical system fails, resulting in arthritis. The complexity of various failures in the knee joint has led orthopedic surgeons to select total knee replacement as a primary treatment. In many cases, this means sacrificing much of an otherwise normal joint. Here, we review novel computational approaches to describe knee physiotherapy by introducing a new dimension of foot loading to the knee axis alignment producing an improved functional status of the patient. New physiotherapeutic applications are then possible by aligning foot loading with the functional axis of the knee joint during the treatment of patients with osteoarthritis.