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PubMed1998

Differential effects of bone mineral content and bone area on vertebral strength in a swine model.

Since the biomechanical competence of a vertebral body may be closely related to the content and distribution of the bone mineral, we have evaluated the effects of projected vertebral bone area (BA) and bone mineral parameters [bone mineral content (BMC) or bone mineral density (BMD)] on their biomechanical competence. We used dual-energy X-ray absorptiometry (DXA) to assess the bone mineral parameters of 36 swine thoracic vertebrae (T1-T12) and 15 lumbar vertebrae (L1-L5) after removal of the posterior elements. The failure load, compressive stress, and the stored strain energy of these vertebral bodies were assessed by a uniaxial compressive test using an MTS 810 testing system. Multiple regression analysis showed a significantly negative effect of BA and significantly positive effect of BMC on the biomechanical competence (compressive stress, r2 = 0.67, P < 0.0001; failure load, r2 = 0.75, P < 0.0001). However, the stored strain energy was only related to the BMC (r2 = 0.35, P < 0.0001). The contributory effects of BMC and BA on the biomechanical competence were not equal. The effects of BMC was larger than BA in determining the failure load and stored strain energy, whereas the reverse was found for the compressive stress. Using the log-transformed parameters as the regressors resulted in similar results. These results suggested the differential effects of BA and BMC in determining the biomechanical competence of vertebral bodies. We recommend the use of both parameters instead of BMD alone for evaluation of the vertebral biomechanical competence.

Absorptiometry, Photon↗
PubMed2004

Preparation of novel mesoporous carbons for the adsorption of an inflammatory cytokine (IL-1 beta).

Mesoporous carbons derived from two types of sulphonated styrene divinylbenzene copolymers (Macronet MN500HS and CT275, Purolite International Ltd) were produced and their adsorptive capacity for the proinflammatory cytokine IL-1 beta (MW 14.4 kDa) determined. The carbons produced had surface areas from 400 to 1200 m(2)g(-1) and pore volume between 0.2 and 1.4 cm(3)g(-1). The mechanical strength of the carbon beads with surface area values up to 800 m(2)g(-1) were robust. The highest adsorption value of IL-1 beta was 150 ng g(-1) for a mesoporous carbon with surface area around 900 m(2)g(-1) and pore volume around 1.3 cm(3)g(-1). However, there was a trade-off between adsorptive capacity and mechanical strength. When used in conjunction with existing treatment modalities, the materials produced have the potential to enhance the removal of uraemic toxins.

Adsorption↗
PubMed2005

Effect of heating temperature on the sintering characteristics of sewage sludge ash.

This study investigated and analyzed the effects of the heating temperature on the properties of the sintered sewage sludge ash. The results indicated that the water absorption rate of the sintered sewage sludge ash samples decreased when the firing temperature was increased from 800 to 900 degrees C. When the heating temperature reached 1000 degrees C, the absorption rate decreased significantly. The bulk density of the sewage sludge ash samples increased by 2.3g/cm3 when the heating temperature was increased from 900 to 1000 degrees C, indicating that the densification was affected by heating. The porosity of the sintered sewage sludge ash samples ranged from 36% to 39% when the heating temperature ranged from 600 to 900 degrees C. The least porosity occurred at 1000 degrees C; the sintered samples were well densified. When the temperature was between 900 and 1000 degrees C, the strength appeared to increase significantly, reaching 2040 kgf/cm2, implying an advance in densification due to sintering. The SEM observations were in general agreement with the trends shown by the density data.

Absorption↗
PubMed2001

Anisotropic elasticity of cortical and cancellous bone in the posterior mandible increases peri-implant stress and strain under oblique loading.

The aim of this study was to compare implant-bone interface stresses and peri-implant principal strains in anisotropic versus isotropic three-dimensional finite element models of an osseointegrated implant in the posterior mandible. We obtained anisotropic (transversely isotropic) elastic constants for mandibular bone and derived equivalent isotropic constants by averaging over all possible spatial orientations. A finite element model was constructed using ten-node tetrahedral p-elements, providing curved edges where necessary and increasing the accuracy of the results in regions of high stress gradients. Perfect bonding was assumed at the implant-bone interface. An oblique load was applied at the coronal aspect of the crown with 100 N vertical and 20 N bucco-to-lingual components. Implant-bone interface stresses exceeded reported bond strengths and principal strains reached yield strain levels in the cortical crest. Anisotropy increased what were already high levels of stress and strain in the isotropic case by 20 to 30% in the cortical crest. In cancellous bone, anisotropy increased what were relatively low levels of interface stress in the isotropic case by three- to four-fold to exceed bond strength levels. Anisotropy has subtle, yet significant effects on interface stresses and peri-implant strains and careful consideration should be given to its use in finite element studies of dental implants.

Alveolar Process↗
PubMedDate not supplied

Investigation of the dry and wet fatigue properties of three all-ceramic crown systems.

PURPOSE: The aim of this study was to investigate the influence of fatigue on the fracture strength of In-Ceram (Vita Zahnfabrik), Optimal Pressable Ceramic (Opc, Jeneric Pentron), and IPS Empress (Ivoclar-Vivadent) in both wet and dry environments. MATERIALS AND METHODS: Twenty-six crown shapes measuring 8.0 mm in diameter and 8.5 mm in height were fabricated for each ceramic system. For each ceramic system, 10 specimens were tested for fracture strength without fatiguing. A second group (8 specimens) was submitted to a fatigue and fracture test in dry conditions, and a third group (8 specimens) was fatigued and fractured in a wet environment using a mechanical testing machine (Instron). The results were statistically analyzed using a Mann-Whitney test. RESULTS: The results indicated that: (1) The facture strength for In-Ceram was significantly stronger than IPS Empress. No difference was found between In-Ceram and Opc, and Opc and IPS Empress. (2) The strength of the three ceramic systems decreased significantly after fatiguing in both dry and wet environments compared with the nonfatigued specimens. No difference was found between fatiguing in dry and wet environments. (3) For the three systems fatigued in a dry environment and then fracture tested, In-Ceram and Opc were significantly stronger than IPS Empress, but no difference was found between the three systems fatigued in a wet environment. CONCLUSION: Significant differences in the fracture strengths of the different systems investigated may be seen that result from both the nature of the system and the environment in which the specimens were fatigued.

Aluminum Oxide↗
PubMed2000

The effect of sandblasting treatment on endurance properties of titanium alloy hip prostheses.

Sandblasting is a procedure of increasing surface roughness. This treatment is common in the orthopedic field. An increased roughness may affect the endurance limit of the material. This study investigates the effect on the endurance limit of the Ti6Al4V due to two different sandblasting treatments: fine sandblasting and coarse sandblasting. Twenty hip stems, 10 finely sandblasted and 10 coarsely sandblasted, were tested under sinusoidal fluctuating bending. The staircase method was used to estimate the endurance limit of the material. The results show an important reduction in the endurance properties up to 40% for the coarsely sandblasted specimens. The failures of the sandblasted specimens were not due to material defects. Rather, the decreased endurance strength of the sandblasted stems was caused by surface defects, which act as crack initiators. By modulating the roughness with an appropriate sandblasting treatment, it is possible to limit the reduction in the endurance limit of the alloy.

Alloys↗
PubMed2000

Consolidation behavior of an experimental, cross-linked polyalkyl ammonium polymer.

The effect of various factors (i.e., particle size, lubricant, moisture, and excipients) on the tableting properties of DMP 504 powder, an experimental, cross-linked polyalkyl ammonium polymer, was studied using an instrumented single-punch tablet press. The results indicate that plastic deformation is the primary consolidation mechanism for DMP 504. Lubrication of DMP 504 with magnesium stearate resulted in negative interaction in compactibility. The increase in tablet hardness with increase in water content of DMP 504 (up to 2.5%) could be attributed to the lubricating effect of water. Increasing the water content above the optimum moisture range (i.e., 2.5% to 4.0%) caused a drastic reduction in tablet crushing strength due to the hydrodynamic resistance. A mixture of DMP 504 with microcrystalline cellulose or starch led to a positive interaction with respect to compactibility. A deviation in tablet strength from the linear interpolated value did not correspond to a deviation in tablet thickness. The improved compactibility for the mixture of DMP 504 and microcrystalline cellulose or starch is not related directly to the facilitated densification.

Chemistry, Pharmaceutical↗
PubMed2004

Adaptations to free-fall impact are different in the shafts and bone ends of rat forelimbs.

Impact exercise can have beneficial effects on the growing skeleton. To understand what changes it promotes in the shafts and ends of weight-bearing bones, we measured the effects of impact from repetitive free falls in growing rats. Fischer 344 female rats, 6.5 wk old, were assigned to one of three groups (n = 10 each). Controls were not dropped, whereas those subjected to impact were dropped from 30 or 60 cm. Rats in both free-fall groups were dropped 10 times per day for 8 wk. Leg bones were mechanically tested, and their cross-sectional area (CSA), cross-sectional moments of inertia, and volumetric bone mineral density (BMD) were measured by peripheral quantitative computed tomography. In the shafts of the forelimbs, but not the hindlimbs, free-fall impact resulted in greater ultimate breaking force, minimum and maximum second moments of area, and CSA but not BMD. In the bone ends of the forelimb and tibial bones, trabecular BMD increased but CSA did not. Landing from 30 and 60 cm produced peak impact forces of 12.0 and 16.7 times the standing forefoot weight for each front leg and of 4.5 and 7.7 times the standing hind foot weight for each hind foot. Overall, free-fall impact affected the forelimbs by increasing trabecular bone density in the bone ends and improving the strength at the shaft as a result of geometric improvements. These results indicate that adaptation to impact may occur by different mechanisms in bone end and shaft regions.

Adaptation, Physiological↗
PubMed2004

Men are more fatigable than strength-matched women when performing intermittent submaximal contractions.

The purpose of this study was to compare the time to task failure for a series of intermittent submaximal contractions performed with the elbow flexor muscles by men and women who were matched for strength (n = 20, 18-34 yr). The fatigue task comprised isometric contractions at 50% of maximal voluntary contraction (MVC) torque (6-s contraction, 4-s rest). The MVC torque was similar for the men and women [64.8 +/- 9.2 (SD) vs. 62.2 +/- 7.9 N.m; P > 0.05]. However, the time to task failure was longer for the women (1,408 +/- 1,133 vs. 513 +/- 194 s; P < 0.05), despite the similar torque levels. The mean arterial pressure, heart rate, and rating of perceived exertion started and ended at similar values for the men and women, but the rate of increase was less for the women. The rate of increase in the average of the rectified electromyogram (AEMG; % peak MVC) for the elbow flexor muscles was less for the women: the AEMG was greater for the men compared with the women at task failure (72 +/- 28 vs. 50 +/- 21%; P < 0.05), despite similar AEMG values at the start of the fatiguing contraction (32 +/- 9 vs. 36 +/- 13%). These results indicate that for intermittent contractions performed with the elbow flexor muscles 1) the sex difference in time to task failure was not explained by the absolute strength of the men and women, but involved another mechanism that is present during perfused conditions, and 2) men required a more rapid increase in descending drive to maintain a similar torque.

Adult↗
PubMed2004

Correlation between the strength of glass ionomer cements and their bond strength to bovine teeth.

This study examined the possible correlation between the strength of glass ionomers and their adhesive strength to bovine teeth. The shear bond strengths of three different brands of glass ionomer mixed at four different P/L ratios to bovine teeth were measured 24 hours after the cement specimens were prepared. The correlation between shear bond strength and mechanical strength reported in our previous study was also examined. No significant (p > 0.05) increases in the bond strength to bovine teeth were found in any of the cements when the mixing ratio increased. The present study showed no significant (p > 0.05) correlation between mechanical strength of cement and its bond strength to bovine teeth. Rather than trying to increase the strength of the cement, it would be more effective to enhance the adhesive bond strength through procedures such as surface conditioning or cleaning of the tooth structure when glass ionomers are used as luting agents.

Adhesiveness↗
PubMed2003

Mechanical consequences of different scenarios for simulated bone atrophy and recovery in the distal radius.

Metabolic bone diseases such as osteoporosis usually cause a decrease in bone mass and a deterioration of bone microarchitecture leading to a decline in bone strength. Methods to predict bone strength in patients are currently based on bone mass only. It has been suggested that an improved prediction of bone strength might be possible if structural changes are taken into account as well. In this study we evaluated which structural parameters (other than bone mass) are the best predictors for changes in bone mechanical properties of the human radius after different bone atrophy scenarios and whether the original strength of the affected bone can be recovered if bone loss is restored by thickening of the remaining structures. To answer these questions, a human radius was measured with a microcomputer tomography scanner to extract the full three-dimensional architecture of the distal radius at an isotropic resolution of 80 microm. Eight models with modified bone architecture were created and the mechanical variations due to these modifications were studied using microfinite element (micro-FE) simulations. In four models mass was lowered by 20%, either by reducing cortical thickness, trabecular thickness, or number of trabeculae or by overall thinning of structures. In the other four models bone mass was restored to the original value using a trabecular bone thickening procedure. The micro-FE analyses revealed that most load was carried by the cortical bone. For this reason, bone strength was affected most in the reduced cortical thickness model. For the same reason, the trabecular bone atrophy scenarios, all of which affected bone strength in a very similar way, resulted in less dramatic bone strength reduction. The restoration of bone mass did not recover the original bone strength. These findings demonstrate that the importance of different parameters for the prediction of bone strength also depends on the mechanical loading. This could explain why results of earlier studies on the importance of structural parameters can be inconsistent and site-dependent.

Adult↗
PubMed1992

Strength of roots before and after endodontic treatment and restoration.

The resistance to fracture of mandibular premolar roots before and after endodontic and restorative procedures was tested. Seven treatment groups were evaluated. A Universal testing machine was used to apply vertical and lateral (45-degree) forces. Overall, the untreated roots showed the highest resistance to fracture. Factors of importance to prevent fracture were found to be (a) the amount of remaining tooth structure; (b) strength of post and core; and (c) bonding between core material and dentin. These factors suggest that a composite core following the use of EDTA to remove the smear layer may be a successful treatment when sufficient tooth structure remains.

Bicuspid↗
PubMed2001

Validation of finite element analysis in dental ceramics research.

STATEMENT OF PROBLEM: In vitro dental materials strength testing of ceramic restorations primarily has involved mechanical evaluations of simplified models. The finite element method (FEM) provides a mathematic analysis to predict strength values, but neither methodology is without the potential for errors. PURPOSE: The purpose of this study was to demonstrate the advantages of combining mechanical testing results and FEM data to determine the strengths of a layered ceramic beam when the layered materials and positions are varied. MATERIAL AND METHODS: Eight finite element 5 x 20 x 1-mm layered beams were modeled. Four of the modeled beams were of the same layered arrangements as physical specimens from a previously published study. The remaining 4 modeled beams provided intermediate layered arrangements not evaluated in the earlier study. A force in newtons was applied in the center of the top layer of each beam until fracture. finite element analysis was performed, and the data were compared with mechanical strength test results from the earlier study. RESULTS: The FEM data of the 8 models demonstrated a linear decrease in load-bearing capacity as the layer thickness of the core material decreased and the layer thickness of the veneer material increased. The progressively decreasing values for the FEM beams were 170, 144, 140, 134, 72, 43, 34, and 27 N. The mean load-bearing capacities of 3 of the 4 mechanically tested beams compared favorably with the FEM data. The strength of the fourth mechanically tested beam, a veneer/core layered arrangement, was 110 N, which was lower than the corresponding FEM value (140 N). The 110 N value fell outside the decreasing linear progression for load, indicating that the FEM data were more accurate and reliable than the mechanical data. CONCLUSION: No one perfect method exists for testing the strength of dental materials. The best approach is to use the results from both mechanical testing and finite element analysis, which together may provide more reliable and valid data than either method alone.

Aluminum Oxide↗
PubMed2000

Evaluation of a new method of small fragment fixation in a medial malleolus fracture model.

OBJECTIVE: To evaluate a new method of small fragment fixation in a medial malleolus fracture model. DESIGN/METHODS: The authors measured the pullout strength, resistance to shear stress, and speed of insertion of 4.0-millimeter partially threaded cancellous screws, 2.4-millimeter smooth K-wires, and a small fragment fixation system with 2.2-millimeter threaded K-wires. Pullout strength was tested in eighty-one synthetic foam blocks and resistance to shear stress in thirty synthetic tibias by use of a servohydraulic testing machine. Six randomized time trials with the threaded K-wires and cancellous screws were also conducted. RESULTS: Pullout strength increased with increasing foam density, increasing insertion depth, and varied with fixation method (p < 0.05). Maximum pullout strengths were as follows: partially threaded cancellous screws, 730+/-4 Newtons; threaded K-wires, 316+/-12 Newtons; and smooth K-wires, 172 +/-5 Newtons. Percent difference in pullout strength between the partially threaded cancellous screw and threaded K-wire diminished with increased depth of insertion and increased foam density. Offset axial load to initiate fracture displacement in a synthetic tibia model averaged 1540+/-138 Newtons for the partially threaded cancellous screws, 1,318+/-117 Newtons for the threaded K-wires, and 1,287+/-121 Newtons for the smooth K-wires (p > 0.05). Average time of fixation of a medial malleolar fragment by orthopedic surgeons with a variety of experience levels in a synthetic tibia with two threaded K-wires (114+/-8 seconds) was significantly faster (p < 0.05) than with two partially threaded cancellous screws (207+/-20 seconds). CONCLUSIONS: Threaded K-wires show substantial pullout strength and similar resistance to offset axial load when compared with partially threaded cancellous screws. These threaded K-wires offer an alternative for the internal fixation of medial malleolus fractures.

Bone Screws↗
PubMed1997

Anterior instrumentation of the thoracolumbar spine. A biomechanical comparison.

STUDY DESIGN: To evaluate the fatigue strength and stiffness of four anterior thoracolumbar fixation devices using a corpectomy model without load-sharing bone graft to test the devices under the worst case scenario of instability. OBJECTIVES: To gain a more thorough understanding of the biomechanical qualities of anterior fixation devices to improve clinical application and design. SUMMARY OF BACKGROUND DATA: For many surgeons, the anterior approach has become the treatment of choice for patients with compression of the spinal cord, whether it is caused by trauma, tumor, or infection. When stabilization is needed, anterior fixation devices have been advocated for many years to avoid the additional approach required for posterior fixation. Many of these devices, however, have an unacceptably high rate of hardware failure. Recently, several new devices for anterior fixation have been marketed with purported advantages in fatigue life and ease of use. METHODS: Four implants, the Synthes Anterior Thoracolumbar Locking Plate, the Kaneda device, a Texas Scottish Rite Hospital anterior construct, and the Z-Plate were attached to vertebral models and tested for stiffness in multiple planes on a modified Materials Testing System machine. They then were fatigued to failure on an Instron testing machine. RESULTS: The Anterior Thoracolumbar Locking Plate was the stiffest in axial compression, lateral flexion, and torsion. The Texas Scottish Rite Hospital anterior construct was the least stiff in flexion-extension, with no significant differences in the stiffness of the anterior thoracolumbar locking plate, that of the Kaneda device, and that of the Z-Plate. Fatigue life exceeded 80,000 cycles for the anterior thoracolumbar locking plate and averaged 26,472 cycles for the Z-Plate, 6915 cycles for the Teas Scottish Rite Hospital construct, and 4419 cycles for the Kaneda device. CONCLUSIONS: The significantly greater fatigue life of the Anterior Thoracolumbar Locking Plate and the Z-Plate may predict a lower incidence of hardware failure than with previous anterior devices. This has been confirmed in preliminary clinical studies with the Z-Plate. Further clinical studies are needed to show if these lower failure rates will continue over a long-term period.

Compressive Strength↗
PubMed1997

An investigation of new metal framework design for metal ceramic restorations.

STATEMENT OF PROBLEM: Metal ceramic restorations have been implicated in the discoloration of associated gingival tissues. Attempts to remedy this by altering the design of the metal frameworks for such restorations may lead to unacceptable decreases in fracture resistance. PURPOSE: This study evaluated a new metal framework design for metal-ceramic restorations. MATERIAL AND METHODS: Twenty artificial crowns were fabricated with various degrees of facial metal reduction; 0, 1, 2, and 3 mm. The study was conducted in two parts. The first part evaluated changes in light transmission into adjacent root tissue. A light box was fabricated so sample crowns could be illuminated on a mounted natural tooth. The root of the tooth remained outside the light box, and the light transmitted through the crowns into root tissue was measured with a light meter. The second part of the study evaluated changes in fracture strength. The sample crowns were subjected to a vertical load until fracture with use of an Instron machine at a crosshead speed of 1 mm per minute. The load at fracture was recorded. RESULTS: Results indicated a statistically significant increase in light transmission with 1 mm framework reduction or greater, and fracture strengths did not decrease with up to 1 mm of framework reduction. A 1 mm facial axial reduction of the metal framework may be indicated for anterior metal-ceramic restorations.

Analysis of Variance↗
PubMed2005

Are scaling laws on strength of solids related to mechanics or to geometry?

One of the largest controversial issues of the materials science community is the interpretation of scaling laws on material strength. In spite of the prevailing view, which considers mechanics as the real cause of such effects, here, we propose a different argument, purely based on geometry. Thus, as happened for relativity, geometry could again hold an unexpected and fundamental role.

Biocompatible Materials↗
PubMed2002

Strength-duration testing of the external anal sphincter in females with anorectal dysfunction.

PURPOSE: The strength-duration test has been suggested as a means of assessing external anal sphincter function. This study was designed to investigate this claim by comparing the strength-duration test with established measures of external anal sphincter function. METHODS: Forty-nine females undergoing diagnostic anorectal testing (manometry, rectal sensation, electromyogram, pudendal nerve terminal motor latency, and endoanal ultrasound) also had the strength-duration test performed (which was repeated for each patient after a short rest period). RESULTS: The strength-duration test was repeatable. Statistically significant correlations were found between this test at pulse durations of 3 ms, 1 ms, and 0.3 ms with electromyographic activity of the external anal sphincter and with pressure in the anal canal during voluntary contraction. Significant correlations were found for durations of 100 ms, 30 ms, 10 ms, and 3 ms with the pudendal nerve terminal motor latency on the right and for the 3 ms and 0.3 ms durations with latency on the left. There were no correlations between the strength-duration test and resting pressure in the anal canal. CONCLUSION: The strength-duration test significantly correlates with the established measures of external anal sphincter function and its innervation. Therefore, this simple test appears to provide a simple measure of external anal sphincter denervation.

Adult↗