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PubMed2006

The use of the coefficient of variation in detecting sincerity of effort: a meta-analysis.

The coefficient of variation (CV) is used to determine sincerity of effort of strength measurements. However, there is a controversy in the literature concerning its validity and effectiveness. We used a meta-analytic approach and calculated the effect size between maximal and submaximal efforts for the CV of grip, elbow flexion and knee extension. We summarized findings concerning stability, sensitivity and specificity of the CV. We found large effect sizes (d > or = 0.8) for all comparisons indicating that submaximal efforts were more variable than maximal efforts. We also found large error rates and low stability of the CV. The error rates and stability values of the CV are unacceptable from both a clinical and a medico-legal standpoint. Therefore, the use of the CV for assessing sincerity of effort needs to be questioned.

Compressive Strength↗
PubMed2004

Comparison of the mechanical properties of 2 prosthetic mini-implants.

Two prosthetic mini-implants (MTI and MDI), which have very similar shapes, are widely used. In this investigation, the mechanical and physical properties of 2 prosthetic mini-implants were investigated. The flexural properties were measured with a universal testing machine. The surface image was observed by SEM with EDX. X-ray analyses were performed. The maximum strength and proportion limit for the different implants differed significantly (P <0.01); however, elastic modulus did not differ significantly (P >0.01). Although the surface of the MTI was smooth, the MDI had a rough surface. The elemental analysis detected titanium (Ti) in the MTI, and Ti, aluminum, and vanadium in the MDI. From the x-ray diffraction pattern, the MTI, which is composed of pure titanium, had a narrow, sharp Ti (syn) peak, whereas the corresponding peak for the MDI was small and broad. Although the 2 devices have similar shapes and dimensions, their surfaces and mechanical properties differ greatly. MTI is easy to remove and wrought in clinical use, and MDI is excellent in flexural properties compared with MTI. (Implant Dent 2004;13:251-256)

Aluminum↗
PubMed2003

The Genesis stent: A new low-profile stent for use in infants, children, and adults with congenital heart disease.

Placement of intravascular stents that can reach adult size in infants and smaller children has been limited by the large profile and poor flexibility of currently available stents. In vitro and in vivo testing of the Genesis stent was performed to evaluate crimpability, predeployment flexibility, and radial strength. Comparisons were made to the Palmaz iliac and IntraStent (IS) LD stents. Nine physicians placed 30 Genesis stents in swine pulmonary and systemic arteries to evaluate stent deliverability/crimpability. Two swine were recovered and underwent a second catheterization 8 weeks later, where the stents (n = 8) were reexpanded to maximal size. Angiographic and intravascular ultrasound (IVUS) assessments were performed. In vitro testing revealed the Genesis stent to have superior crimpability, flexibility, and comparable radial strength to the Palmaz iliac stent, and superior crimpability and radial strength and comparable flexibility to the IS LD series. During in vivo testing, the physicians graded the Genesis stent superior to the Palmaz stent regarding crimpability and deliverability, and superior to the IS LD stent in regard to crimpability, and comparable to or superior in deliverability. In the chronic animals, the Genesis stent was expanded up to maximal diameter 8 weeks following implantation. Angiographic and IVUS revealed no fractures no in-stent restenosis. The Genesis stent can be easily delivered through smaller sheaths, which will facilitate their use in infants and smaller children with vascular stenosis.

Adult↗
PubMed2004

Compaction of crystallographic forms of pharmaceutical granular lactoses. II. Compacts mechanical properties.

It is well known that the choice of the crystal form affects the physicochemical properties such as compaction behaviour. In this work, the mechanical properties of compacts obtained from compaction of lactoses by using a micropress prototype are calculated. Tensile strength, Young's modulus, toughness and Brinell hardness were measured and used to compare the various crystalline forms: alpha-lactose monohydrate (LalphaM), anhydrous beta-lactose (LbetaA), anhydrous alpha-lactose (LalphaA) and partly amorphous lactose (FF). With all the mechanical properties measured, the lactoses could be differentiated. Then, the specific energy of failure G*(IC) was obtained from the toughness and the Young's modulus for each lactose. LalphaM showed small specific energy of failure due to its low toughness which is not balanced by its Young's modulus. The highest values were obtained with the two anhydrous forms, LalphaA and LbetaA. Finally, these mechanical properties were linked with general compaction behaviour and cohesive energy density which is a characterization at a molecular level.

Compressive Strength↗
PubMed1997

Strength of core build-up materials in endodontically treated teeth.

PURPOSE: To compare the in vitro strength of a reinforced glass ionomer and a light-cured glass ionomer used as an alternative to amalgam in core construction to restore endodontically treated mandibular molar teeth. MATERIALS AND METHODS: The root canals of 120 extracted human mandibular molar teeth were prepared chemomechanically and obturated with laterally condensed cold gutta-percha. The crown of each tooth was sectioned leaving only one cusp standing. Gutta-percha was removed from the pulp chamber in all teeth. The volume of the pulp chamber was measured and the teeth ranked in ascending order of chamber volume. The specimens were divided into six groups of 20, allocating teeth with similar chamber volumes into each group. In three of the groups, gutta-percha was removed from the coronal 3-4 mm of each root canal. The teeth were restored with one of three materials, a cermet cement (Ketac-Silver), a resin-reinforced glass ionomer (Vitremer), or amalgam (Contour). Core preparation was carried out after 48 hours, reducing each core height to 6 mm. The specimens were thermocycled for 24 hours and then mounted in dental stone. A control group of 20 unrestored human mandibular molars was mounted in cold cure acrylic. Each tooth was tested in a Nene machine with a compressive load applied at 90 degrees to the occlusal surface at a crosshead speed of 5 mm/minute. RESULTS: There was no statistically significant difference between the experimental groups (P > 0.05), but the control group was significantly stronger (P < 0.001). Extension of core material into the coronal root canal system did not increase the fracture resistance of any of the experimental materials. Regression analysis of the results revealed no correlation between the volume of the pulp chamber and the load to fracture.

Cermet Cements↗
PubMed2004

Preparation and characteristics of hybrid scaffolds composed of beta-chitin and collagen.

Hybrid scaffolds composed of beta-chitin and collagen were prepared by combining salt-leaching and freeze-drying methods. The chitin scaffold used as a framework was easily formed into desired shapes with a uniformly distributed and interconnected pore structure with average pore size of 260-330 microm. The mechanical strength and the rate of biodegradation increased with the porosity, which could be modulated by the salt concentration. In addition, atelocollagen solution was introduced into the macropores of the chitin scaffold to improve cell attachment. Web-like collagen fibers fabricated between pores of chitin were produced by a 0.1 wt% collagen solution, whereas a 0.5 wt% collagen solution only coated the surface of the chitin scaffold. After 3 days of culture, fibroblasts cultured in collagen-coated scaffolds were attached at the place where the collagen was fabricated, whereas cells did not attach and aggregate on the scaffold of chitin alone. After 14 days, the fibroblasts showed a good affinity to and proliferation on all collagen-coated chitins.

Absorbable Implants↗
PubMed2006

Study on the fracture strength of root reconstructed with post and core: alveolar bone resorbed case.

This study evaluated the influence of alveolar bone level on the fracture resistance of root restored with post and core. Forty-eight extracted human mandibular premolars were divided into six groups. Cast posts and cores were cemented (MN8 and MP8) or resin cores were built up with fiber posts and composite resin (FN8, FP8, FN4, and FP4). Post length was 8 mm (MN8, MP8, FN8, and FP8) or 4 mm (FN4 and FP4). Specimens were embedded 2 mm (MN8, FN8 and FN4) or 5 mm (MP8, FP8 and FP4) below cement-enamel junction. All specimens were loaded at 45 degrees to the long axis until fracture. With normal bone model, cast post and core (MN8) showed the highest fracture resistance (2262.4 N). However, in the resorbed bone model, there were no significant differences in fracture resistance between cast post and core and fiber post with composite resin.

Alveolar Bone Loss↗
PubMedDate not supplied

Evaluation and analysis of patient outcomes with an intrasegmental fixation system in lumbar spinal fusion.

BACKGROUND CONTEXT: A new spinal fixation system with polydirectional screws and modular links with interconnecting radial serrations has been developed. The system allows the linking of multiple points of fixation, two points at a time (intrasegmental fixation), thus eliminating the need for intraoperative contouring of rods or plates. PURPOSE: Evaluation of this new type of spine system was done through biomechanical studies, analysis of lumbar lordosis preservation postoperatively, and multicenter review of patient outcomes with a minimum of 1 year follow-up. STUDY DESIGN/SETTING: Biomechanical studies of the spine system were performed according to American Society for Testing and Materials (ASTM) standards. To evaluate the maintenance of lordosis, radiographs from the first 119 patients were reviewed by the authors. Analysis of patient outcomes consisted of a review of the first 259 patients who underwent spinal fusion surgery with the new spine system. PATIENT SAMPLE: Evaluation of patient outcomes consisted of 122 men and 137 women with an average age of 50+/-13 years (range, 22-96 years) and a mean follow-up of 20+/-6 months (range, 12-54 months). The patient population was at high risk for fusion failure, with 127 smokers (49%), 141 who had previous spine surgery (54%), 22 with osteoporosis (8%), 63 were obese (24%), and 32 with diabetes (12%). One hundred two patients (39%) had a one-level fusion, 105 patients (41%) had two levels fused, and 52 patients (20%) had three or more levels fused. The majority of patients (66%) were covered under workers' compensation. OUTCOME MEASURES/METHODS: Radiographic fusion was deemed successful when the presence of trabecular bridging bone from transverse process to transverse process was observed, as well as no fixation failure nor radiographic evidence of screw loosening. Clinical success was rated excellent, good, fair, or poor depending on the patients pain level, function, and pain medication intake. RESULTS: Biomechanical studies of this intrasegmental fixation system have shown it to be strong under both static and fatigue testing, with exceptional strength in compression bending. In evaluating preservation of lumbar lordosis, no statistically significant loss of lordosis was observed. Overall, radiographic fusion was noted in 229 of 259 patients (88%) and did not differ significantly (p>.10) by the number of levels fused. Clinically, 69 patients (27%) had an excellent result, 111 patients (43%) had a good result, 50 patients (19%) had a fair result, and 29 patients (11%) had a poor result. The high rate of successful patient outcomes did not differ significantly (p>.10) by the number of levels fused, or other patient or surgical variables, except for the satisfaction level of workers' compensation versus nonworkers' compensation. One hundred of 118 patients (85%) who were working before surgery returned to work at an average 9+/-4 months postoperatively (range, 2-20 months). The use of direct current (DC) stimulation in this population was reserved for patients with one or more risk factors for fusion failure and was noted to be of benefit. There were no recorded intraoperative complications, but postoperatively 5 device and 19 non-device-related complications (9%) were noted, which is comparable to other lumbar fusion series. CONCLUSIONS: The results of these analyses show consistent patient outcomes regardless of the number of levels fused with an intrasegmental system. This may be attributable to the increased biomechanical strength of the system at each segment, coupled with the ability of intrasegmental fixation to maintain sagittal plane balance through preservation of the patient's lordotic curve.

Adult↗
PubMed2005

Analytically derived material properties of multilaminated extracellular matrix devices using the ball-burst test.

Xenogeneic extracellular matrices (ECMs) have been shown to be effective as naturally occurring scaffolds for soft-tissue repair. As acellular tissue substitutes at the time of surgical implantation, ECMs are subjected to the mechanical forces and micro-environmental conditions representative of the anatomical location in which they are placed. Ideally such natural scaffolds would possess mechanical properties that allow for normal tissue function in and around the implant site. The ball-burst test was used to simulate biaxial forces and to determine the strength of the ECM scaffold under a relevant physiological loading condition. The ball-burst test, in itself, does not quantify intrinsic mechanical properties and therefore a methodology was developed to determine the maximum stress resultant tangent modulus (MSRTM) or the maximum stress tangent modulus (MSTM), stress to failure (sigma(f)), failure stress resultant (N(f)), ball-burst pressure (P), and maximum elongation (lambda(max)) from the raw ball-burst data obtained at a constant-rate of transverse. The analytical methodology was compared to finite element simulations and showed good correlation with the analytical solution presented. The proposed approximations were used to compute biaxial failure properties for a variety of multilaminate ECM devices with varying number of layers, disinfection and sterilization, and organ origin.

Animals↗
PubMedDate not supplied

Optimisation of the predictive ability of artificial neural network (ANN) models: a comparison of three ANN programs and four classes of training algorithm.

The purpose of this study was to determine whether artificial neural network (ANN) programs implementing different backpropagation algorithms and default settings are capable of generating equivalent highly predictive models. Three ANN packages were used: INForm, CAD/Chem and MATLAB. Twenty variants of gradient descent, conjugate gradient, quasi-Newton and Bayesian regularization algorithms were used to train networks containing a single hidden layer of 3-12 nodes. All INForm and CAD/Chem models trained satisfactorily for tensile strength, disintegration time and percentage dissolution at 15, 30, 45 and 60 min. Similarly, acceptable training was obtained for MATLAB models using Bayesian regularization. Training of MATLAB models with other algorithms was erratic. This effect was attributed to a tendency for the MATLAB implementation of the algorithms to attenuate training in local minima of the error surface. Predictive models for tablet capping and friability could not be generated. The most predictive models from each ANN package varied with respect to the optimum network architecture and training algorithm. No significant differences were found in the predictive ability of these models. It is concluded that comparable models are obtainable from different ANN programs provided that both the network architecture and training algorithm are optimised. A broad strategy for optimisation of the predictive ability of an ANN model is proposed.

Algorithms↗
PubMed2006

Augmentation of acrylic bone cement with multiwall carbon nanotubes.

Acrylic bone cement, based on polymethylmethacrylate (PMMA), is a proven polymer having important applications in medicine and dentistry, but this polymer continues to have less than ideal resistance to mechanical fatigue and impact. A variety of materials have been added to bone cement to augment its mechanical strength, but none of these augmentative materials has proven successful. Carbon nanotubes, a new hollow multiwalled tubular material 10-40 nm in diameter, 10-100 microm long, and 50-100 times the strength of steel at 1/6 the weight, have emerged as a viable augmentation candidate because of their large surface area to volume ratio. The objective of this study was to determine if the addition of multiwall carbon nanotubes to bone cement can alter its static or dynamic mechanical properties. Bar-shaped specimens made from six different (0-10% by weight) concentrations of multiwall carbon nanotubes were tested to failure in quasi-static 3-point bending and in 4-point bending fatigue (5 Hz). Analyses of variance and the 3-Parameter Weibull model were used to analyze the material performance data. The 2 wt % MWNT concentration enhanced flexural strength by 12.8% (p=0.003) and produced a 13.1% enhancement in yield stress (p=0.002). Bending modulus increased slightly with the smaller (<5 wt % MWNT) concentrations, but increased 24.1% (p<0.001) in response to the 10 wt % loading. While the 2 wt % loading produced slightly improved quasi-static test results, it was associated with clearly superior fatigue performance (3.3x increase in the Weibull mean fatigue life). Weibull minimum fatigue life (No), Weibull modulus (alpha), and characteristic fatigue life (beta) for bone cement augmented with carbon nanotubes were enhanced versus that observed in the control group. These data unambiguously showed that the bone cement-MWNT polymer system has an enhanced fatigue life compared to "control" bone cement (no added nanotubes). It is concluded that specific multiwall carbon nanotube loadings can favorably improve the mechanical performance of bone cement.

Biocompatible Materials↗
PubMed2004

Comparative in vitro assessment of the primary stability of cementless press-fit acetabular cups.

Long-term stable osseointegration of porous-coated acetabular cups depends on bony ingrowth within their porous surface. For ingrowth to take place, one must ensure rigid initial fixation of the implant, by means of screws or by impaction or using a threaded ring. Primary stability is a prerequisite for long term stability through bony ingrowth. We tested several cups commonly used in our department to assess their primary stability. The study was done using synthetic EP-Dur polyurethane resin blocks (Bayer, Leverkusen, Germany). The blocks were fixed at a 45 degrees angle to the horizontal. They were subsequently reamed using the appropriate reamers and the cups tested were impacted into the resin blocks. Eleven 52-mm cups were tested. The pull out force necessary to extract each cup was measured. The pull-out strength ranged from 7.63 to 55.46 Nm. We noted that the closer the cup was to a hemisphere, the better was the initial stability. The contact zone was at the periphery, and the greater the contact was with the resin, the better was the stability. Micromovements exceeding 150 microns prevent any bony ingrowth in vivo. Solid osseointegration can thus only be achieved if movements between implant and bone can be prevented. Our study indicated that initial fixation is essentially peripheral and that those cups that demonstrated the highest pull-out values also had the best peripheral contact. Our observations suggest that the geometry of the cup is more important than its surface macrostructure in terms of primary stability. To achieve stable fixation, we recommend using an oversized cup with a flattened dome to allow maximum peripheral contact.

Acetabulum↗
PubMedDate not supplied

The effect of a mouthrinse containing essential oils on dental restorative materials.

Mouthrinses that contain essential oils are effective for controlling plaque and periodontal disease. Recent studies have shown that such mouthrinses are effective at preventing the formation of biofilm in dental unit waterlines. However, there is no information in the literature regarding the effect of such mouthrinses on restorative materials used within the oral cavity. Specimens of three common restorative materials (a glass ionomer, a composite resin, and amalgam) were subjected to continuous exposure to Listerine and distilled water for 10 days; at that time, the strength, fluid sorption, and surface appearance of the specimens were compared. Specimens of the test materials also were placed in intraoral devices; volunteer patients wore these devices for 12 hours per day for a period of 10 days. During that time, the patients were instructed to rinse twice daily for 30 seconds with Listerine Cool Mint or a non-active mouthrinse. After 10 days, the specimens were salvaged from the devices and inspected by visible and SEM examination. This study indicates that routine use of mouthrinses containing essential oils (or even prolonged exposure to such mouthrinses) has no adverse effects on restorative materials that might be expected to react to such mixtures because of their chemical compositions. It was concluded that active mouthrinses do not appear to have any adverse effects on a variety of restorative biomaterials.

Absorption↗
PubMed2005

Effect of mineral content on the nanoindentation properties and nanoscale deformation mechanisms of bovine tibial cortical bone.

In this paper, a multitechnique experimental and numerical modeling methodology was used to show that mineral content had a significant effect on both nanomechanical properties and ultrastructural deformation mechanisms of samples derived from adult bovine tibial bone. Partial and complete demineralization was carried out using phosphoric and ethylenediamine tetraacetic acid treatments to produce samples with mineral contents that varied between 37 and 0 weight percent (wt%). The undemineralized samples were found to have a mineral content of approximately 58 wt%. Nanoindentation experiments (maximum loads approximately 1000 microN and indentation depths approximately 500 nm) perpendicular to the osteonal axis for the approximately 58 wt% samples were found to have an estimated elastic modulus of approximately 7-12 GPa, which was 4-6x greater than that obtained for the approximately 0 wt% samples. The yield strength of the approximately 58 wt% samples was found to be approximately 0.24 GPa; 3.4x greater than that of the approximately 0 wt% sample. These results are discussed in the context of in situ and post-mortem atomic force microscopy imaging studies which show clear residual deformation after indentation for all samples studied. The partially demineralized samples underwent collagen fibril deformation and kinking without loss of the characteristic banding structure at low maximum loads (approximately 300 microN). At higher maximum loads (approximately 700 microN) mechanical denaturation of collagen fibrils was observed within the indent region, as well as disruption of interfibril interfaces and slicing through the thickness of individual fibrils leading to microcracks along the tip apex lines and outside the indent regions. A finite element elastic-plastic continuum mechanical model was able to predict the nanomechanical behavior of all samples on loading and unloading.

Animals↗
PubMed1997

Influence of dentinal adhesives and a prefabricated post on fracture resistance of silver amalgam cores.

PURPOSE: Failures of silver amalgam cores for endodontically treated teeth have been attributed to the use of posts. The use of adhesive agents has been reported to improve the strength of silver amalgam restorations. The purpose of this study was to test the effects of two adhesive agents on the fracture resistance of silver amalgam cores with and without a post. MATERIAL AND METHODS: Sixty mandibular molars were restored with the use of silver amalgam, with or without one of the adhesive agents and/or a tapered prefabricated post. A universal testing machine, with a constant load rate of 0.5 mm/minute, was used to determine the force in kilograms at failure. RESULTS: The use of either adhesive agent with silver amalgam significantly increased the force at failure, and neither adhesive agent was significantly better than the other. Silver amalgam with a post and without an adhesive agent had the least resistance to fracture. CONCLUSIONS: The results indicated that endodontically treated mandibular molars restored with silver amalgam are more resistant to fracture when an adhesive agent is used.

Analysis of Variance↗
PubMed2005

Laboratory and field testing for utilization of an excavated soil as landfill liner material.

This study investigates the feasibility of using a silty soil excavated in highway construction as landfill liner material. The tests were conducted both at laboratory and in situ scales, and the soil was tested in pure and lime treated forms. Different levels of compaction energy were used. For the field study, a test pad was constructed and in situ hydraulic conductivity experiments were conducted by sealed double ring infiltrometers (SDRI). Laboratory testing revealed that while lime treatment improved the shear strength, it resulted in higher hydraulic conductivity values compared to pure soil. It was observed that leachate permeation did not change the hydraulic conductivity of the pure and lime treated samples. Laboratory hydraulic conductivities were on the order of 10(-9) m/s and met the 1.0E-08 m/s criterion in the Turkish regulations, which is one order of magnitude higher than the value allowed in most developed countries. SDRI testing, which lasted for 6 mo, indicated that lime treatment increased the hydraulic conductivity of pure soil significantly in the field scale tests. In situ hydraulic conductivities were on the order of 1E-08 and 1E-07 m/s, and exceeded the allowable value in the Turkish regulations. Undisturbed samples collected from the test pad were not representative of field hydraulic conductivities. Contrary to laboratory findings, higher compaction efforts did not result in lower hydraulic conductivities in field scales. The study verified the importance of in situ hydraulic conductivity testing in compacted liners.

Calcium Compounds↗
PubMed2004

Comparison of strength properties of normotensive and hypertensive rat pulmonary arteries.

A series of tests were conducted to quantify the difference in the mechanical properties of normo- and hypertensive pulmonary arteries. A bubble-test design was employed to measure the biaxial properties of a segment of artery. The test results compare the properties at multiple orientations of the trunk, right, and left pulmonary arteries from normal (Control) and monocrotaline-treated male Long-Evans wild rats that ranged in age from 8 to 17 weeks old, along with some preliminary results from hypoxic Long-Evans knock-out rats. Data show little difference between the stress-strain relationship of the control pulmonary arteries and that of the monocrotaline-treated pulmonary arteries. However, the preliminary results from the hypoxic pulmonary arteries show that the arterial material strains less before the onset of strain-stiffening behavior. The longitudinal orientation exhibits strain stiffening at lower strains than does the circumferential orientation. The differences between the left and right main arteries are minor. The trunk consistently demonstrates less stiffening in the region of larger strains for all conditions.

Animals↗
PubMed2004

["Shrinkage of cruciate ligaments"--a biomechanical study. Shrinkage of elongated cruciate ligaments using an application of radiofrequency energy].

The aim of this study was to evaluate structural properties of native and elongated bovine anterior cruciate ligaments after the application of bipolar radiofrequency. Using a material testing machine typical load-elongation curves were used to determine the initial strength of untreated (group 1, n = 20) and elongated cruciate ligaments (group 2, n = 20) after treatment with bipolar radiofrequency (ArthroCare). After the application of a cyclic loading protocol (1000 x 400 N) elongation, yield load, maximal load, and stiffness were determined. Native ligaments served as a control group (group 3, n = 20). In both groups 4 mm reduction in length was caused by the application of radiofrequency. Elongation was significantly higher; yield load, maximal load, and stiffness of cruciate ligaments treated with radiofrequency (groups 1 and 2) were significantly reduced after the application of a cyclic loading protocol in comparison to the control group (p < 0.05). Group 2 ligaments showed the lowest values. The application of radiofrequency weakens the biomechanical properties of native and elongated cruciate ligaments significantly. When radiofrequency energy is used to shrink elongated cruciate ligaments, a nonaggressive rehabilitation protocol should be applied.

Animals↗