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Results for “Compressive Strength”

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PubMed2006

Femoroplasty--augmentation of the proximal femur with a composite bone cement--feasibility, biomechanical properties and osteosynthesis potential.

BACKGROUND: Analogous to vertebroplasty, cement-augmentation of the proximal femur ("femoroplasty") could reinforce osteoporotic bones. This study was to evaluate (i) the feasibility of femoroplasty with a composite cement (Cortoss), (ii) its influence on femoral strength by mechanical testing and (iii) the feasibility of stable osteosynthesis of the augmented fractured bones. METHODS: Nine human cadaveric femora were augmented with a composite bone cement, the surface heat generation monitored, and then tested biomechanically against their native contralateral control to determine fracture strength. Subsequently, thirteen reinforced and fractured femora were osteosynthetized by different implants and tested against their osteosynthetisized, non-augmented contralateral control. FINDINGS: Cement could be injected easily, with a moderate temperature rise. A positive correlation between BMD and fracture load and a significant increase in fracture load (+43%) of the augmented femora compared to their native controls (6324 N and 4430 N, respectively) as well as a significant increase in energy-to-failure (+187%, 86 N m and 30 N m, respectively) was found. Osteosynthesis was possible in cement-augmented femora. Osteosynthetisized femora showed equivalent strength to the intact controls. INTERPRETATION: Augmentation of the proximal femur with composite bone cement could be of use in prophylaxis of fractures in osteoporotic femurs. Osteosynthesis of the fractured augmented bones is a challenging procedure but has a good chance to restore strength.

Biomechanical Phenomena↗

PubMed1998

Fluoride release and re-uptake in direct tooth colored restorative materials.

OBJECTIVES: Glass ionomers may be "recharged" through topical fluoride (F-) treatments; however, this reported "recharging," may be attributed to surface changes after F- treatment. This study examined differences in F- release and re-uptake among dual-cured and chemically-cured glass ionomers, and a photo-cured F- releasing composite. A secondary goal was to determine if tensile strength or surface roughness changed due to F- release, or F- re-uptake and re-release. METHODS: In Phase 1, initial surface roughness and diametral tensile strength were measured. F- release was measured for 30 days. Strength and roughness were then remeasured. In Phase 2, surface roughness was measured, then materials were treated with a 5000 ppm neutral F- gel, the same gel without F-, or phosphoric acid. F- release was measured for 30 days, then final surface roughness and strength were determined. RESULTS: Significant differences were found in amount and rate of F- release, and F- re-uptake and re-release among study materials and enamel controls (p < 0.001). The amount and rate of F- re-release after NaF treatment differed significantly from F- release after acid treatment in glass ionomers, although both groups showed increased F- release after surface treatment (p < 0.001). There were no significant changes in tensile strength or surface roughness after F- release or F- re-uptake and re-release as determined by ANOVA. SIGNIFICANCE: The results of this in vitro study indicate that applications of neutral 5000 ppm F- gel to aged glass ionomer restorations results in a significant fluoride uptake and subsequent release. The data suggest that the application of neutral fluoride gel to glass ionomer restorations in situ may result in increases in oral fluoride concentrations, without affecting the restoration's surface roughness or tensile strength.

Analysis of Variance↗

PubMed2002

Measurement of physical strength of pharmaceutical extruded pellets.

This paper describes a novel and simple method for measuring the physical strength of pharmaceutical pellets prepared by extrusion granulation. Pharmaceutical powders composed of lactose, cornstarch, and microcrystalline cellulose were kneaded with purified water and dry binder (hydroxypropylcellulose), then extruded through a dome-type extrusion granulator. The physical strength of the dried extruded pellets was measured with a novel system: pellets and grinding alumina media were both fed into a ball mill pot and then "grinding degree" was measured as defined by the ground fine powder fraction after being rotated in the pot. The grinding conditions such as grinding time and number of alumina balls were optimized. The measured physical strength and pellet strength measured with a typical strength tester was compared. Quantitative relationships between the strength and the physical properties of the pellets such as friability and disintegration time were also investigated. It was found that the newly developed system could easily and accurately evaluate the physical strength of extruded pellets and could also predict the various physical properties.

Compressive Strength↗

PubMed2004

A study of age-related architectural changes that are most damaging to bones.

Osteoporosis-related bone damage causes major socioeconomic problems. For efficient use of therapeutic agents, it is necessary to be able to reliably identify patients with high propensity for nontraumatic fracture. Age-related bone loss imposes several architectural changes in bone; one of the few ways to estimate damage due to individual changes, and hence determine the most serious types of damage, is via the analysis of suitable mathematical models. Anatomical sites such as the vertebral body, proximal femur, and distal radius are locations where most age-related fractures occur. The inner porous (or trabecular) bone from these sites, which resemble disordered cubic networks, play a significant role in load transmission at these sites. Analysis of a mathematical model of porous bone is used to show that perforation of elements of the network is the most damaging architectural change to a bone. We also show that an expression for bone strength, derived on this basis, can capture changes in strength caused by the inclusion of other features like thinning of trabecular bone and the anisotropy of the network. We finally argue that bone density, which is currently the most routinely used diagnostic, cannot be a reliable surrogate for bone strength.

Aging↗

PubMed2004

Microstructure and strength of extruded porous HA ceramics.

The paper discusses the influence of sintering temperature on the microstructure and strength of hydroxyapatite ceramics prepared using the extrusion process. The average pore diameters observed were in the range of approximately 150mm to 300mm whereas the compaction strength was found to be around 120-160 MPa.

Bone Substitutes↗

PubMed1988

A hypothesis on the mechanism of trauma of lung tissue subjected to impact load.

When a compressive impact load is applied on the chest, as in automobile crash or bomb explosion, the lung may be injured and show evidences of edema and hemorrhage. Since soft tissues have good strength in compression, why does a compression wave cause edema? Our hypothesis is that tensile and shear stresses are induced in the alveolar wall on rebound from compression, and that the maximum principal stress (tensile) may exceed critical values for increased permeability of the epithelium to small solutes, or even fracture. Furthermore, small airways may collapse and trap gas in alveoli at a critical strain, causing traumatic atelectasis. The collapsed airways reopen at a higher strain after the wave passes, during which the expansion of the trapped gas will induce additional tension in the alveolar wall. To test this hypothesis, we made three new experiments: (1), measuring the effect of transient overstretch of the alveolar membrane on the rate of lung weight increase; (2) determining the critical pressure for reopening collapsed airways of rabbit lung subjected to cyclic compression and expansion; (3) cyclic compression of lung with trachea closed. We found that in isolated rabbit lung overstretching increases the rate of edema fluid formation, that the critical strain for airway reopening is higher than that for closing, and that these critical strains are strain-rate dependent, but independent of the state of the trachea, whether it is open or closed. Furthermore, a theoretical analysis is presented to show that the maximum principal (tensile) stress is of the same order of magnitude as the maximum initial compressive stress at certain localities of the lung.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2004

Influence of different adhesive resin cements on the fracture strength of aluminum oxide ceramic posterior crowns.

STATEMENT OF PROBLEM: The influence of different types of adhesive resin cements on the long-term prognosis of aluminum oxide ceramic posterior crowns is unclear. PURPOSE: The purpose of this study was to evaluate the fracture resistance of aluminum oxide ceramic on maxillary posterior crowns cemented with different resin luting agents before and after cyclic thermomechanical loading. Material and methods Forty-eight maxillary first molars were prepared and restored with standardized aluminum oxide ceramic (In-Ceram Alumina) crowns. The test specimens were randomly divided into 3 groups (n=16). The crowns were luted with an acrylic resin cement (Super-Bond C&B, control, Group SB) and 2 composite luting agents (Panavia F, Group PV; and Rely X Unicem, Group RX). Half of the specimens were exposed to thermomechanical fatigue in a masticatory simulator. All specimens were tested for fracture strength (N) using quasistatic loading. The Wilcoxon rank sum test was used to compare the fracture strength (alpha=.05). RESULTS: All specimens survived the exposure to the simulator. The following median fracture strength values were obtained without/with thermomechanical fatigue loading: Group SB, 2726 N/2673 N; Group PV, 2520 N/2083 N; and Group RX, 2036 N/2369 N. The fracture strength in Group PV after thermomechanical fatigue loading was significantly lower compared to the fracture strength in Group PV without artificial aging (P =.016), as well as significantly lower compared to Group SB with artificial aging (P =.003). CONCLUSION: Within the limitations of this study, all tested cements are capable of successfully luting aluminum oxide ceramic crowns. The fracture strength of Group PV after artificial aging was comparatively low.

Compressive Strength↗

PubMed2006

Fracture strength of two oxide ceramic crown systems after cyclic pre-loading and thermocycling.

The aim of the present study was to investigate the fracture resistance of zirconia crowns and to compare the results with crowns made of a material with known clinical performance (alumina) in away that reflects clinical aspects. Sixty crowns were made, 30 identical crowns of alumina and 30 of zirconia. Each group of 30 was randomly divided into three groups of 10 crowns that were to undergo different treatments: (i) water storage only, (ii) pre-loading (10 000 cycles, 30-300 N, 1 Hz), (iii) thermocycling (5-55 degrees , 5000 cycles) + pre-loading (10 000 cycles, 30-300 N, 1 Hz). Subsequently, all 60 crowns were subjected to load until fracture occurred. There were two types of fracture: total fracture and partial fracture. Fracture strengths (N) were: group 1, alumina 905/zirconia 975 (P = 0.38); group 2, alumina 904/zirconia 1108 (P < 0.007) and group 3, alumina 917/zirconia 910 (P > 0.05). Total fractures were more frequent in the alumina group (P < 0.01). Within the limitations of this in vitro study, it can be concluded that there is no difference in fracture strength between crowns made with zirconia cores compared with those made of alumina if they are subjected to load without any cyclic pre-load or thermocycling. There is, however, a significant difference (P = 0.01) in the fracture mode, suggesting that the zirconia core is stronger than the alumina core. Crowns made with zirconia cores have significantly higher fracture strengths after pre-loading.

Aluminum Oxide↗

PubMed2000

In vitro repair of all-ceramic and fibre-reinforced composite crowns.

Shear bond strength between fibre reinforced composite and all-ceramic frameworks and veneering/repair composites was investigated after different surface treatments for evaluating the possibility of a repair. Then, 24 crowns were adhesively luted on human teeth and artificially aged. Repair quality was characterized by a loading to fracture test, where undamaged crowns were compared to repaired crowns. To simulate repeated damage, aging and repair, the procedure was performed three times for each crown. A combined silicate-silane treatment of the fibre-reinforced composite frameworks and the hydrofluoric acid etching of the ceramic showed good repair qualities and a sufficient fracture strength for clinical application.

Analysis of Variance↗

PubMed2006

Predictions of tensile strength of binary tablets using linear and power law mixing rules.

There has recently been an increased interest in predicting the tensile strength of binary tablets from the properties of the individual components. In this paper, measurements are reported for tensile strength of tablets compressed from single-component and binary powder mixtures of lactose with microcrystalline cellulose (MCC), and lactose with two types of silicified microcrystalline cellulose (SMCC and SMCC-HD), which are different in compressibility. Measurements show the tensile strength increases with the relative density for single powders, and both with the relative density and the mass fraction of cellulose in the mixtures. It was also observed, for binary mixtures compacted at 50 and 150 MPa, that there was a slight variation in porosity with the mass fraction of celluloses. The predictions of the tensile strength of binary tablets from the characteristics of the single-components was analysed with the extended Ryshkewitch-Duckworth model by assuming both linear and power law mixing rules for the determination of the parameters "tensile strength at zero porosity and bonding capacity constant". As consequence, four models were analysed and compared with measurements using criteria based on the standard deviation from the mean values. Results showed a good prediction using a linear mixing rule combined with the power law. However, as the predictions of these models depend on the powders and the porosity range for the characterization of single-components, none of them can be systematically considered as being the best to predict binary behaviour from data for individual powders.

Cellulose↗

PubMed2003

Properties of elastomeric calcium phosphate cement-chitosan composites.

OBJECTIVE: Self-hardening calcium phosphate cements (CPC) have been shown to be efficacious in a number of clinical applications. For some applications it is desirable to have CPC in a non-rigid resorbable elastomeric matrix. In the present study, chitosan was evaluated as the matrix for preparing CPC-chitosan composites. METHODS: Cement specimens were prepared by mixing CPC powder (an equimolar mixture of tetracalcium phosphate and dicalcium phosphate anhydrous) with a chitosan solution at a powder/liquid ratio of 2-2.5. The setting time was measured by a Gilmore needle method. A standard three-point flexural test was used to fracture the specimens at a crosshead speed of 0.5 mm/min. Powder X-ray diffraction analysis was used to determine the conversion of the CPC to hydroxyapatite. RESULTS: The CPC-chitosan composites were more stable in water than conventional CPC. They did not disintegrate even when placed in water immediately after mixing. The CPC-chitosan paste hardened within 10 min in all cases. The 1d mean flexural modulus (GPa) for the control CPC was 5.3 (0.3) (mean (standard deviation); n=5), and that for CPC-chitosan composites were between 2.7 (0.3) and 4.7 (0.3). The 1d mean flexural strength (MPa) for the control was 16.6 (1.9), and that for the CPC-chitosan ranged from 4.5 (0.5) and 12.0 (1.0) (n=5). Chitosan did not interfere the conversion of CPC components to hydroxyapatite. SIGNIFICANCE: This study demonstrates that CPC-chitosan composites are stable in a wet environment and have acceptable mechanical strengths for clinical applications.

Biocompatible Materials↗

PubMed2002

Patients with laxity of the distal radioulnar joint after distal radial fractures have impaired function, but no loss of strength.

Laxity of the distal radioulnar (DRU) joint after distal radial fractures has a worse general outcome in patients before the usual age for development of osteoporosis. The hypothesis for this study was that patients with laxity also have less strength during supination and pronation. An apparatus for measuring strength in supination and pronation was constructed and validated. 20 patients were chosen from a cohort of 76 patients who had had distal radial fractures 6 years ago. The stability of the DRU-joint was tested manually by 2 examiners and the test's reliability was good. The DRU-joint was lax in 6 patients. No differences were found between patients with stable and lax DRU-joints as regards isometric grip strength, strength in supination or pronation or radiographic characteristics. However, subjectively evaluated hand function was impaired in those with lax DRU-joints. This was noted on the subjective part of the Gartland and Werley score and 13 questions concerning everyday activities. In conclusion, DRU-joint laxity was associated with impaired hand function, but no loss of strength in forearm rotation after distal radial fractures in non-osteoporotic patients.

Adult↗

PubMed1996

The biomechanics of cartilage load-carriage.

This paper presents a review and critical appraisal of the more recent attempts to understand the fundamental mechanisms of load-carriage in articular cartilage. In the first section the question is addressed as to how the intrinsic strength of the matrix is developed with respect to its ultrastructure. In the second part we examine various models proposed to explain the response of the matrix to externally applied compressive forces in terms of its unique physico-chemical properties.

Biomechanical Phenomena↗

PubMed2007

Bone formation after damaging in vivo fatigue loading results in recovery of whole-bone monotonic strength and increased fatigue life.

Bone has a remarkable capacity for self-repair. We previously reported a woven bone response after damaging in vivo fatigue loading of the rat ulna that led to a rapid recovery of whole-bone strength. In the current study we asked: does the bone response in the 12 days after damaging fatigue loading result in a bone that has normal fatigue properties? The right forelimbs of 52 adult rats were subjected to a single bout of in vivo fatigue loading. Nonloaded left forelimbs were used as controls. Ulnar geometric properties were assessed by peripheral quantitative computed tomography (pQCT) and ex vivo mechanical properties were assessed by three-point bending. On day 0, ulnae from loaded forelimbs had a 15-20% reduction in stiffness and ultimate force versus controls (p < 0.10), indicative of structural damage. On day 12, bone area at the midshaft was increased by 27% (p < 0.001) and microCT scans revealed periosteal woven bone at this site. This bone response led to a recovery of the monotonic properties of loaded ulnae at day 12 versus control (stiffness, p = 0.73; ultimate force, p = 0.96). Importantly, fatigue testing ex vivo at day 12 demonstrated significantly greater fatigue life in in vivo loaded ulnae versus controls (p < 0.001). Additionally, the slope of the fatigue-life curve was significantly less in loaded versus control ulnae (p < 0.002). We conclude that woven bone "repair" of a bone damaged by fatigue loading restores whole-bone strength and enhances resistance to further damage by repetitive loading.

Animals↗

PubMed1998

Effect of glass fiber reinforcement on some mechanical properties of autopolymerizing polymethyl methacrylate.

PURPOSE: This study investigated the different effects of quantitative percentages of glass fiber intensity on the transverse strength, maximum deformation, and the modulus of elasticity of acrylic resin. MATERIALS AND METHODS: Fifty-four specimens were formed in a specially designed mold to produce identical specimens in accordance with the manufacturer's recommendations. Six percentages of glass fiber reinforcement in loose random form were studied. Each glass fiber treatment percentage (0%, 1%, 2%, 5%, 10%, 15%) was related to the total powder/liquid mass. RESULTS: The results indicated that 1% glass fiber treatment enhanced the transverse strength of the tested specimen. Maximum deformation at failure in the tested treatment groups was found to be different. The interaction of glass fiber concentration on fracture strength and deformation was significant (p < 0.0001). CONCLUSION: The 1% glass fiber concentration was found to give the best fracture strength and deformation results. Significantly higher glass fiber percentages was found to weaken the resin.

Analysis of Variance↗

PubMedDate not supplied

Zoledronic acid improves the mechanical properties of normal and healing bone.

OBJECTIVE: To determine the effects of the bisphosphonate zoledronic acid on the mechanical properties of normal and regenerating bone in a rabbit model of distraction osteogenesis. BACKGROUND: Bisphosphonate therapy is used for treating osteoporosis and, more recently, to enhance bone healing and reduce stress-shielding osteoporosis in distraction osteogenesis. METHODS: Thirty eight rabbits underwent 14 days of distraction osteogenesis on the right rear limb. They received either zero, one or two doses of intravenous zoledronic acid. Four point bending tests were performed to collect mechanical data. RESULTS: The peak load capacity of the regenerating bone was significantly increased by bisphosphonate therapy, but a similar trend in normal bone was not significant. The energy absorbed to failure did not vary significantly in either group. CONCLUSIONS: These data suggest that bisphosphonate therapy has a beneficial effect on the load capacity of regenerating bone, without increasing the brittleness of either new or existing bone. RELEVANCE: Zoledronic acid administration may be a potentially valuable adjunct to distraction osteogenesis treatment, to enhance bone strength, thus reducing refracture complications.

Animals↗

PubMed2005

Bonding of ceramic insert to a laboratory particle filler composite.

The push-out bond strength of cylindrical ceramic inserts (CI) to particulate filler resin composite (VC) was evaluated in this study. Various surface treatments to improve the adhesion of CI to resin composite were tested. Additionally, the effect of fiber-reinforced composite (FRC) laminate encapsulation around CI was tested. Feldspathic porcelain CI with a diameter of 3.1 mm was bonded to VC. Adhesive resin was used for bonding. In group 1, no surface treatment of CI was done. In group 2, CI was encapsulated with a thin layer of woven glass FRC. In group 3, the surface of the CI was tribochemically silica coated and silanized. In group 4, the surface of the CI was grit-blasted with 50 microm aluminum oxide and etched with hydrofluoric acid. In group 5, the grit-blasted CI was encapsulated with a layer of FRC. The specimens (n = 6/group) were either dry stored or thermocycled in water (6000 x 5-55 degrees C). The push-out test was carried out with a universal material testing machine. The highest push-out strength was achieved in group 5 (20.4 MPa) and the lowest in group 2 (11.5 MPa). ANOVA revealed that both surface treatment and storage condition had a significant effect on push-out strength (p < 0.05). We conclude that the additional glass FRC encapsulation can be used to increase the bond strength of insert to composite.

Acrylic Resins↗

PubMed2005

Cortical and trabecular load sharing in the human vertebral body.

UNLABELLED: The biomechanical role of the vertebral cortical shell remains poorly understood. Using high-resolution finite element modeling of a cohort of elderly vertebrae, we found that the biomechanical role of the shell can be substantial and that the load sharing between the cortical and trabecular bone is complex. As a result, a more integrative measure of the trabecular and cortical bone should improve noninvasive assessment of fracture risk and treatments. INTRODUCTION: A fundamental but poorly understood issue in the assessment of both osteoporotic vertebral fracture risk and effects of treatment is the role of the trabecular bone and cortical shell in the load-carrying capacity of the vertebral body. MATERIALS AND METHODS: High-resolution microCT-based finite element models were developed for 13 elderly human vertebrae (age range: 54-87 years; 74.6 +/- 9.4 years), and parameter studies-with and without endplates-were performed to determine the role of the shell versus trabecular bone and the effect of model assumptions. RESULTS: Across vertebrae, whereas the average thickness of the cortical shell was only 0.38 +/- 0.06 mm, the shell mass fraction (shell mass/total bone mass)-not including the endplates-ranged from 0.21 to 0.39. The maximum load fraction taken by the shell varied from 0.38 to 0.54 across vertebrae and occurred at the narrowest section. The maximum load fraction taken by the trabecular bone varied from 0.76 to 0.89 across vertebrae and occurred near the endplates. Neither the maximum shell load fraction nor the maximum trabecular load fraction depended on any of the densitometric or morphologic properties of the vertebra, indicating the complex nature of the load sharing mechanism. The variation of the shell load-carrying capacity across vertebrae was significantly altered by the removal of endplates, although these models captured the overall trend within a vertebra. CONCLUSIONS: The biomechanical role of the thin cortical shell in the vertebral body can be substantial, being about 45% at the midtransverse section but as low as 15% close to the endplates. As a result of the complexity of load sharing, sampling of only midsection trabecular bone as a strength surrogate misses important biomechanical information. A more integrative approach that combines the structural role of both cortical and trabecular bone should improve noninvasive assessment of vertebral bone strength in vivo.

Aged↗