A new method for determining the ogden parameters of soft materials using indentation experiments.

A full understanding of the material properties of skin tissue is crucial for exploring its tribo-mechanical behaviour. It has been widely accepted that the mechanical behaviour of skin tissue for both small and large deformations can be accurately described using a hyperelastic model, such as the one developed by Ogden. However, obtaining these Ogden parameters for in-vivo skin by in-vivo experiments no matter the indentation or suction tests is a significant challenge. The mathematical model used to describe the material behaviour during the test should consider not only the material nonlinearity but also the geometrical confinement of the tissue, the large deformations induced, and the fact that the specimens are relatively thin. A range of contact models is available to describe the contact behaviour during the indentation test. However, none of them can be used for hyperelastic materials with small thickness under large deformations. Simultaneously explaining material nonlinearity and geometric nonlinearity, either through theoretical equations or numerical calculations, poses a significant challenge. In this research, we propose a pragmatic method to obtain Ogden parameters for in-vivo skin tissue by combining experimental indentation results and numerical simulations. The indentation tests were used to obtain the force-indentation depth curves, while the numerical simulations were used to obtain the strain fields. The method assumes the material behaviour of specimens can be linearized in each small deformation increment, and the contact model developed by Hayes can be applied to accommodate each increment. Then, the linear elastic behaviour in each increment can be described by the elastic modulus E which were obtained using Hayes model, and the principal stresses in each increment were subsequently obtained using Hooke's law. By combining all stress fields, overall stress-strain curves can be constructed, from which the hyperelastic Ogden parameters can be obtained. A second numerical simulation of the hyperelastic indentation was then performed using the obtained Ogden parameters, allowing a comparison of the experimental and simulated relationships between force and indentation.

Approach for contact medical device development via integrated testing, skeletal muscle modeling, and finite element analysis.

Development of novel medical devices for the treatment of musculoskeletal pain associated with neuro-muscular trigger points requires a model for relating the mechanical responses of in vivo biological tissues to applied palliative physical pressures and a method to design treatments for optimal effects. It is reasonable to hypothesize that the efficacy of therapeutic treatment is proportional to the maximum tensile strain at trigger point locations. This work presents modeling of the mechanical behavior of biological tissue structures and treatment simulations, supported by indentation experiments and finite element (FE) modeling. The steady-state indentation responses of the tissue structure of the posterior neck were measured with a testing device, and an FE model was constructed using a first-order Ogden hyperelastic material model and calibrated with the experimental data. The error between experimental and FE-generated displacement-load curves was minimized via a two-stage optimization process comprised of an Optimal Latin Hypercube design-of-experiments analysis and a Bayesian optimization loop. The optimized Ogden model had an initial shear modulus (µ) of 5.16 kPa and a deviatoric exponent (α) of 11.90. Another FE model was developed to simulate the deformation of the tissue structures in the posterior neck adjacent to the C3 vertebrae in response to indentation loading, in order to determine the optimal location and angle to apply an indentation force for maximum therapeutic benefit. The optimal location of indentation was determined to be 28° lateral from the sagittal plane along the surface of the skin, measured from the centerline of the spine, at an angle of 8° counterclockwise from the surface normal vector. The optimized spatial orientation of the indentation corresponded to the average of the maximum principal strain across the deep muscle region of the model.

Validation of a double-semicircular notched configuration for mechanical testing of orthodontic thermoplastic aligner materials.

The potential of using specimens with a double-semicircular-notched configuration for performing tensile tests of orthodontic thermoplastic aligner materials was explored. Unnotched and double-semicircular-notched specimens were loaded in tension using a universal testing machine to determine their tensile strength, while finite element analysis (FEA) and digital image correlation (DIC) were used to estimate stress and strain, respectively. The shape did affect the tensile strength, demonstrating the importance of unifying the form of the specimen. During the elastic phase under tension, double-semicircular-notched specimens showed similar behavior to unnotched specimens. However, great variance was observed in the strain patterns of the unnotched specimens, which exhibited greater chance of end-failure, while the strain patterns of the double-semicircular-notched specimens showed uniformity. Considerable agreement between the theoretical (FEA) and practical models (DIC) further confirmed the validity of the double-semicircular-notched models.

Cyclic Fatigue and Torsional Strength of a New Thermally Treated Reciprocating System.

OBJECTIVE: This study evaluated the resistance to cyclic fatigue and the torsional strength of Prima One Gold® and WaveOne Gold® reciprocating systems. METHODS: Cyclic fatigue was tested in an artificial canal with 60º curvature, a 5 mm radius of curvature at 22°C (n=10) and 36.5°C (n=10). The torsional strength test followed ISO 3630-1, measuring torque and deflection angle until fracture (n=10). The t-test was used to compare the two groups, and the significance level was set at 5%. RESULTS: The Prima One Gold group presented greater resistance to cyclic fatigue at room temperature (P=0.001) and body temperature (P<0.001). For the torsional resistance test, the Prima One Gold group had a lower maximum torque value (P=0.029), despite having a greater deflection angle (P<0.001). CONCLUSION: The Prima One Gold group showed greater resistance to cyclic fatigue regardless of temperature and a greater deflection angle. The WaveOne Gold group showed a greater maximum torque value than the Prima One Gold group.

Evaluation of Wear Properties of Four Bulk-Fill Composites: Attrition, Erosion, and Abrasion.

PURPOSE: Wear and increased surface roughness are among the reasons for failure of posterior composite restorations. Considering the widespread use of bulk-fill composites in the posterior region, information about their wear resistance is imperative. The aim of this study was to compare the wear and surface roughness of four bulk-fill composite resins with a conventional composite. METHODS: Thirty composite discs (4 mm × 10 mm) were fabricated from EverX Posterior (GC), X-tra fil (Voco), Filtek Bulk-Fill Posterior (3M, USA), SonicFill 2 (Kerr), and Z250 (3M) composites. The baseline weight and surface roughness of specimens were measured. For the assessment of the attrition wear, the specimens were placed in a chewing simulator (Mechatronik). pH cycling was performed to erode the composite discs. They were then placed in a tooth brushing simulator machine (Dorsa) for abrasion wear. Finally, the weight and surface roughness of the specimens were measured. Data were compared using one-way ANOVA (alpha ≤ 0.05). RESULTS: One-way ANOVA showed that the mean weight changes were significant after attrition, abrasion, and erosion (P = 0.019), but changes in surface roughness were not significant (P ≥ 0.05). The results of Tukey's test showed no significant difference between the bulk-fill composites and Z250 regarding weight loss (P ≥ 0.05), but the weight loss of X-tra fil was significantly greater than that of EverX (P = 0.007) and Filtek Bulk-Fill (P = 0.005). CONCLUSIONS: Considering the limitations of this study, it appears that the wear and surface roughness of bulk-fill composites are within the acceptable range and are not different from those of a conventional composite.

Laboratory Reconstructions of Real-world Bicycle Helmet Impacts.

The best way to prevent severe head injury when cycling is to wear a bike helmet. To reduce the rate of head injury in cycling, knowing the nature of real-world head impacts is crucial. Reverse engineering real-world bike helmet impacts in a laboratory setting is an alternative to measuring head impacts directly. This study aims to quantify bike helmet damage using computed tomography (CT) and reconstruct real-world damage with a custom, oblique test rig to recreate real-world impacts. Damaged helmets were borrowed from a helmet manufacturer who runs a helmet warranty program. Each helmet was CT-scanned and the damage metrics were quantified. Helmets of the same model and size were used for in-lab reconstructions of the damaged helmets where normal velocity, tangential velocity, peak linear acceleration (PLA) and peak rotational velocity (PRV) could be measured. The damage metrics of the in-lab dropped helmets were quantified using the same CT scanning process. For each case, a multiple linear regression (MLR) equation was created to define a relationship between the quantified damage metrics of the in-lab tested helmets and the associated measured impact velocities and kinematics. These equations were used to predict the impact kinematics and velocities from the corresponding real-world damaged helmet based on the damage metrics from the original damaged helmet. Average normal velocity (3.5 m/s), tangential velocity (2.5 m/s), PLA (108.0 g), PRV (15.7 rad/s) were calculated based on a sample of 23 helmets. Within these head impact cases, five notes reported a concussion. The difference between the average PLA and PRV for concussive cases versus other impacts were not significantly different, although the average impact kinematics for the concussive cases (PLA = 111.4 g, PRV = 18.5 rad/s) were slightly higher than the remaining cases (PLA = 107.1 g, PRV = 15.0 rad/s). The concussive cases were not indicative of high magnitude impact kinematics.

Development, manufacturing, and preliminary validation of a reusable half-face respirator during the COVID-19 pandemic.

INTRODUCTION: The COVID-19 pandemic has led to widespread shortages of N95 respirators and other personal protective equipment (PPE). An effective, reusable, locally-manufactured respirator can mitigate this problem. We describe the development, manufacture, and preliminary testing of an open-hardware-licensed device, the "simple silicone mask" (SSM). METHODS: A multidisciplinary team developed a reusable silicone half facepiece respirator over 9 prototype iterations. The manufacturing process consisted of 3D printing and silicone casting. Prototypes were assessed for comfort and breathability. Filtration was assessed by user seal checks and quantitative fit-testing according to CSA Z94.4-18. RESULTS: The respirator originally included a cartridge for holding filter material; this was modified to connect to standard heat-moisture exchange (HME) filters (N95 or greater) after the cartridge showed poor filtration performance due to flow acceleration around the filter edges, which was exacerbated by high filter resistance. All 8 HME-based iterations provided an adequate seal by user seal checks and achieved a pass rate of 87.5% (N = 8) on quantitative testing, with all failures occurring in the first iteration. The overall median fit-factor was 1662 (100 = pass). Estimated unit cost for a production run of 1000 using distributed manufacturing techniques is CAD $15 in materials and 20 minutes of labor. CONCLUSION: Small-scale manufacturing of an effective, reusable N95 respirator during a pandemic is feasible and cost-effective. Required quantities of reusables are more predictable and less vulnerable to supply chain disruption than disposables. With further evaluation, such devices may be an alternative to disposable respirators during public health emergencies. The respirator described above is an investigational device and requires further evaluation and regulatory requirements before clinical deployment. The authors and affiliates do not endorse the use of this device at present.

An apparatus for rapid and nondestructive comparison of masks and respirators.

The SARS-CoV-2 global pandemic has produced widespread shortages of certified air-filtering personal protection equipment and an acute need for rapid evaluation of breathability and filtration efficiency of proposed alternative solutions. Here, we describe experimental efforts to nondestructively quantify three vital characteristics of mask approaches: breathability, material filtration effectiveness, and sensitivity to fit. We focus on protection against aqueous aerosols >0.3 µm using off-the-shelf particle, flow, and pressure sensors, permitting rapid comparative evaluation of these three properties. We present and discuss both the pressure drop and the particle penetration as a function of flow to permit comparison of relative protection for a set of proposed filter and mask designs. The design considerations of the testing apparatus can be reproduced by university laboratories and medical facilities and used for rapid local quality control of respirator masks that are of uncertified origin, monitoring the long-term effects of various disinfection schemes and evaluating improvised products not designed or marketed for filtration.

Measurement of filtration efficiencies of healthcare and consumer materials using modified respirator fit tester setup.

During the current SARS-CoV-2 pandemic there is unprecedented demand for personal protective equipment (PPE), especially N95 respirators and surgical masks. The ability of SARS-CoV-2 to be transmitted via respiratory droplets from asymptomatic individuals has necessitated increased usage of both N95 respirators in the healthcare setting and masks (both surgical and homemade) in public spaces. These precautions rely on two fundamental principles of transmission prevention: particle filtration and droplet containment. The former is the focus of NIOSH N95 testing guidelines, and the latter is an FDA guideline for respirators and surgical masks. While studies have investigated droplet containment to provide guidance for homemade mask production, limited work has been done to characterize the filtration efficiency (FE) of materials used in home mask making. In this work, we demonstrate the low-cost (<$300) conversion of standard equipment used to fit-test respirators in hospital and industrial settings into a setup that measures quantitative FEs of materials based on NIOSH N95 guidelines, and subsequently measure FEs of materials found in healthcare and consumer spaces. These materials demonstrate significant variability in filtration characteristics, even for visually similar materials. We demonstrate a FE of 96.49% and pressure drop of 25.4 mmH20 for a double-layer of sterilization wrap used in surgical suites and a FE of 90.37% for a combination of consumer-grade materials. The excellent filtration characteristics of the former demonstrate potential utility for emergent situations when N95 respirators are not available, while those of the latter demonstrate that a high FE can be achieved using publicly available materials.

Significant correlation of bone material strength index as measured by the OsteoProbe with Vickers and Rockwell hardness.

The bone material strength index (BMSi), as measured by the OsteoProbe, is significantly correlated with Vickers hardness and Rockwell (RW) hardness measurements on conventional materials. The Vickers and RW measurements were carried out according to American Society for Testing and Materials standard test methods, and OsteoProbe measurements followed published standardized testing methods. The correlations between the BMSi and RW hardness, r = 0.93, and between the BMSi and Vickers hardness, r = 0.94, are comparable with the correlation between RW and Vickers hardness, r = 0.87. The correlation between the BMSi and RW is significant at p < 0.01, and the correlation between the BMSi and Vickers hardness is significant at p < 0.01. These results show that the indentation measurement performed by the OsteoProbe may be considered as a type of hardness measurement comparable to widely used conventional methods, with specific applications targeted by its portable and narrow design.

Evaluation of the force degradation and deformation of the open-closed and open springs of NiTi: An in vitro study.

OBJECTIVE: The aim of this study was to evaluate the force degradation and deformation over time of an open-closed and open coil spring. MATERIAL AND METHODS: 40 NiTi springs were divided into 2 groups according to the manufacturer (20 specimens per group): Morelli™ (Sorocaba, SP, Brazil) and Orthopli™ (Philadelphia, PA, USA). Then, they were subdivided into 2 groups according to the type of spring (n=10): open spring and open-closed spring. The springs were submitted to the initial compression test in a Universal Test Machine (Instron) in 43.3% of the initial length and analyzed in 3 points (0.5mm, 3.25mm and 6.5mm). After this, the springs were activated with a 240 gf and those maintained for 4 weeks in artificial saliva in the oven at 37°C, and analyzed by a new compression test with the same initial parameters. Scanning Electron Microscopy/Energy Dispersive X-Ray Spectroscopy (SEM/EDS) analyzed the spring's morphology. Two-way repeated measures Analysis of Variance was applied for each brand and extension of compression. Student t-test with correction of Bonferroni was used to compare open spring vs open-closed springs and pairwise t-test was used to compare initial vs final period. The level of significance was set at 95% in all tests. The most representative images were selected (SEM/EDS). RESULTS: The Orthopli™ open-closed spring showed a statistically higher deformation (14.52±0.37) in relation to open spring (14.85±0.19) after 4 weeks (P<0.05). No statistical difference was observed between the types of Morelli™ springs (P>0.05). Orthopli™ open-closed spring showed force values statistically higher than the open spring in the initial and final time (P<0.05). Regardless of the type of spring, the initial force was significantly higher than the final force (P<0.05). CONCLUSIONS: The orthodontist should not rely on the indicated force range without considering the type of spring (open or open-closed), the manufacturer and the amount of compression of the spring.

An observational ergonomic tool for assessing the worn condition of slip-resistant shoes.

Worn shoes are known to contribute to slip-and-fall risk, a common cause of workplace injuries. However, guidelines for replacing shoes are not well developed. Recent experiments and lubrication theory suggest that the size of the worn region is an important contributor to the shoe tread's ability to drain fluid and therefore the under-shoe friction. This study evaluated a simple test for comparing the size of the worn region relative to a common object (AAA and AA battery) as a means of determining shoe replacement. This study consisted of three components involving slip-resistant shoes: Experiment #1: a longitudinal, mechanical, accelerated wear experiment; Experiment #2: a longitudinal experiment where the same shoes were tested after each month of worker use; and Experiment #3: a cross-sectional experiment that exposed participants to a slippery condition, while donning their own worn shoes. The COF (Experiments #1 and #2); under-shoe fluid pressure (all experiments); and slip severity (Experiment #3) were compared across outcomes (fail/pass) of the battery tests. Larger fluid pressures, lower coefficient of friction, and more severe slips were observed for shoes that failed the battery tests compared with those passing the tests. This method offers promise for assessing loss in friction and an increase in slip risk for slip-resistant shoes.

Novel degradation flow-through chamber for in vitro biomaterial characterization.

The characterization of degradation of biodegradable materials for tissue regeneration is classically carried out in three steps: in vitro degradation analysis, in vitro cell culture, and in vivo animal experiments. Each step involves an increasing complexity and should serve a more sophisticated material selection, which serves as an orientation to clinical studies and the final application in patients. Recently, the usefulness of degradation analyses is being discussed. In this context, the aim of this work is to increase the importance of in vitro degradation analysis by using flowing media to move closer to the in vivo situation. In the long term, this should lead to a more sensitive biomaterial characterization as well as to a replacement of time-consuming static or quasi-dynamic incubation experiments. The practicability of the novel chamber is demonstrated in context of a degradation study of silica/collagen/calcium phosphate composites in flowing media with physiological (2.4 mM) and lowered (0.5 mM) calcium ion concentrations. This is done by comparison with static and quasi-dynamic incubation experiments. In order to keep all media regimes comparable to each other, for the dynamic experiment, a flow rate was chosen equivalent to the medium exchange in quasi-dynamic incubation. Under flow-through conditions, there is a clearly decreased tendency to lower the calcium concentration, so that a concentration close to the physiological initial situation can be continuously maintained.

Single particles as resonators for thermomechanical analysis.

Thermal methods are indispensable for the characterization of most materials. However, the existing methods require bulk amounts for analysis and give an averaged response of a material. This can be especially challenging in a biomedical setting, where only very limited amounts of material are initially available. Nano- and microelectromechanical systems (NEMS/MEMS) offer the possibility of conducting thermal analysis on small amounts of materials in the nano-microgram range, but cleanroom fabricated resonators are required. Here, we report the use of single drug and collagen particles as micro mechanical resonators, thereby eliminating the need for cleanroom fabrication. Furthermore, the proposed method reveals additional thermal transitions that are undetected by standard thermal methods and provide the possibility of understanding fundamental changes in the mechanical properties of the materials during thermal cycling. This method is applicable to a variety of different materials and opens the door to fundamental mechanistic insights.

Design and evaluation of a laboratory-based wheelchair castor testing protocol using community data.

Wheelchair castors fail frequently causing physical, social and economic consequences for wheelchair users. These failures occur in spite of established wheelchair test methods and regulations, suggesting that the existing tests may not be sufficient to screen poorly designed castors. An expert stakeholder group, convened by the International Society of Wheelchair Professionals (ISWP), noted castor failures as a high priority and recommended that a new castor testing system should be developed. In a previous study, the effect of shock exposure on castor durability was studied. The current paper extends the previous work and focuses on the development of a castor testing protocol based on shock, corrosion and abrasion exposure data collected in the community. The testing protocol was applied to 8 different castor models tested under four conditions: shock, corrosion + shock, abrasion + shock and abrasion + corrosion + shock. For each model, a total of n = 8 samples were evaluated across the four conditions. Results demonstrate that corrosion and abrasion reduced castor durability between 13% to 100% depending on the model. Importantly, the inclusion of corrosion and abrasion resulted in changes in the failure modes for 75% of the tested models and two-thirds of the altered failure modes are associated with increased risk of injury for wheelchair users. These results suggest that corrosion and abrasion present in the community reduce castor durability, thus supporting their inclusion in the castor testing protocol and potentially other wheelchair standards.

Influence of novel design alteration of pedicle screw on pull-out strength: A finite element study.

BACKGROUND: We conducted a finite element study to assess the effectiveness of a novel pedicle screw design with two alterations in the distal and proximal portions. METHODS: Finite element (FE) models of 24 vertebrae were constructed using computed tomographic data. Pull-out strength of 4 different pedicle screws were compared. The basic screw design was a dual threaded one (PS0), in which the proximal portion is double-threaded (cortical thread), and the distal portion is single-threaded (cancellous thread). In PS1, the inter-thread double-core shape was added to PS0 in the distal portion. Compared to PS0, in PS2, the proximal portion was elongated by 5 mm. PS3 had both PS1 and PS2 features. In addition, the 24 vertebrae were classified into 3 groups based on volumetric bone mineral density (vBMD) of the vertebral body: low <120 mg/cm3, moderate 120-170 mg/cm3, and high >170 mg/cm3. RESULTS: The mean pull-out strengths (±SD) were 1137 ± 500 N, 1188 ± 520 N, 1191 ± 512 N, and 1242 ± 538 N for PS0, PS1, PS2, and PS3, respectively. In PS1, there was significant difference in the incremental ratio of pull-out strength to PS0 between the low and high vBMD groups (3.7 ± 1.6% vs. 5.0 ± 1.0%, p = 0.006). In PS2, there was a significant difference in the incremental ratio to PS0 between the moderate and high vBMD groups (7.6 ± 4.0% vs. 3.3 ± 1.8%, p < 0.001). In PS3, there was a significant difference in the incremental ratio to PS0 between the moderate and high vBMD groups (12.1 ± 4.8% vs. 8.5 ± 2.1%, p = 0.003). CONCLUSIONS: The two design alterations showed the combined additive effect in the PS3 design. The moderate vBMD group has a balanced bone property to reflect the combined effects of the PS1 and PS2 design alterations.

A device for measuring sternal bone connectivity using vibration analysis techniques.

OBJECTIVES: Stability of bone splitting sternotomy is essential for normal healing after open cardiac surgery. Mechanical vibration transmittance may offer a means for early detection of separation of bone (diastasis) in the sternotomy and prevent further complications. This article describes the technical implementation and validation of vibration analysis-based prototype device built for measuring sternal bone connectivity after sternotomy. METHODS: An in-house built measurement system, sternal vibration device, consisting of actuator, sensor, and main controller and signal acquisition unit was designed and manufactured. The system was validated, and three different test settings were studied in mockups (polylactide rods in ballistic gel) and in two human sternums: intact, stable wire fixation, and unstable wire fixation with a gap mimicking bone diastasis. The transmittance of vibration stimulus across the median sternotomy was measured. RESULTS: The validation showed that the force produced by the actuator was stable, and the sensor could be calibrated to precisely measure the acceleration values. The vibration transmittance response to material cut and sternotomy was evident and detectable in the 20 Hz to 2 kHz band. The transmittance decreased when the connectivity between the sternal halves became unstable. The trend was visible in all the settings. CONCLUSION: Technical solutions and description of validation process were given. The device was calibrated, and the vibration transmittance analysis differentiated intact and cut polylactide rod. In the sternum, intact bone, wire fixation with exact apposition, and with a gap were identified separately. Although further studies are needed to assess the accuracy of the method to detect different levels of diastases, the method appears to be feasible.

Mechanical Analysis of Notch-Free Pre-Bent Rods for Spinal Deformity Surgery.

STUDY DESIGN: Experimental study of spinal rod as per the American Society for Testing Materials (ASTM) F2193 methodology for static and dynamic four-point bending. OBJECTIVE: The hypotheses underlying this study were that the notch-free, curved rod would have a significantly higher ultimate load and fatigue strength compared with conventional notched curved rods. This study aimed to analyze the mechanical properties of notch-free curved rods compared with conventional notched rods. SUMMARY OF BACKGROUND DATA: The goal of instrumented spinal fusion in the management of spinal deformities is to realign the spine and maintain the correction and stability in order to obtain arthrodesis. Although rod curvature could play an important role, intraoperative contouring of the straight rod induces notches into the rod, leading to decreased fatigue strength. METHODS: Commercially produced titanium alloy (ϕ6.0 mm) and cobalt chromium alloy (ϕ5.5 mm) spinal rods were assessed by four-point bending tests in accordance with the ASTM F2193. RESULTS: Static four-point bending tests for the curved spinal rods showed that cobalt chromium alloy rods had significantly higher stiffness compared with titanium alloy rods. Notch-free cobalt chromium alloy rods had a significantly higher ultimate load than the conventional notched cobalt chromium alloy and titanium alloy rods. The dynamic four-point bending test showed that force/displacement at a minimum force at 2,500,000 cycles was larger in the notch-free cobalt chromium alloy rod than in the notched cobalt chromium alloy rod. CONCLUSION: The notch-free curved cobalt chromium alloy rod is likely to maintain its curvature after spinal deformity surgery with a decreased risk of breakage and could overcome the problems of the conventional notched rod such as breakage and spring-back. LEVEL OF EVIDENCE: N/A.

3D printed clamps improve spine specimen fixation in biomechanical testing.

This study presents an anatomically customizable fixation technique for biomechanical spine experiments using a 3D printed clamping system. The aim of this study is to evaluate the feasibility and compare the fixation rigidity of the novel technique to PMMA potting with and without screw augmentation. For this purpose, 16 thoracic and lumbar functional spine units of bovine, porcine, ovine and human cadavers (4 each) were consecutively fixed with all three techniques and loaded in six degrees of freedom. The combined relative movement between the cranial and caudal vertebral body and their corresponding fixtures were recorded using a 3D motion capture system. The 3D printed clamps did provide multiple advantages, showed no failures and the fixation rigidity was superior to potting in all loading directions and superior to screw-augmented potting in two of six loading directions (p < 0.05). In conclusion, the here proposed novel fixation method showed equal to superior properties in comparison to both other methods used in this study. When considering all characteristics of 3D printing, 3D printed fixtures can be an effective alternative to potting.

Comparative Evaluation of Fluoride Release From Two Different Glass Ionomer Cement and a Novel Alkasite Restorative Material - An in Vitro Study

Abstract Objective: To compare the fluoride release from Conventional Glass Ionomer Cement (GIC), Resin Modified GIC (RMGIC), and Cention N Alkasite Material. Material and Methods: Forty- five disc-shaped specimens of three different restorative materials (Conventional GIC, RMGIC, and Alkasite material) were made and divided into 3 groups (n=15). Fluoride release was evaluated at the end of Day 1, 7, 14, and Day 28 using fluoride ion-selective electrode. Intergroup and Intra-group analysis was done using One-way ANOVA with a Post-hoc test. A p-value of <0.05 was considered statistically significant. Results: Cention showed more fluoride release (in parts per million) than GIC and RMGIC at increased time duration. However, at the end of day 1, there was lesser fluoride release with Cention, as compared with the other groups. Conclusion: The new Alkasite restorative material showed promising results in terms of fluoride release and is better than GIC and RMGIC at increased time duration.