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Results for “Compressive Strength”

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PubMed1995

Porcelain jacket crowns: diagnostic try-ins for optimal aesthetics.

All-ceramic restorations have gained patient acceptance and are increasingly utilized in aesthetic appearance-related restorations. This case report describes the utilization of a leucite-reinforced porcelain to fabricate all-porcelain crowns for maxillary anterior restorations for functional and aesthetic improvement. This particular porcelain system was selected for its high tensile strength, fracture resistance, and excellent marginal adaptation. The new generation adhesive agents combined with highly filled resin luting cements allow the clinicians to create an integral unit between the restoration and the natural tooth. This bond provides high compressive strength and low microleakage. The preparation procedure, the fabrication of tooth-colored wax crowns, the wax try-in procedure, and the laboratory technique of all-porcelain crown fabrication are discussed in detail, using intraoral photographs of the case to illustrate each applicable procedure. The learning objective of this article is to share the knowledge of all-porcelain restoration principles and application and to provide a detailed description and illustration of each clinical procedure.

Aluminum Silicates↗

PubMed2003

Local 3D scaling properties for the analysis of trabecular bone extracted from high-resolution magnetic resonance imaging of human trabecular bone: comparison with bone mineral density in the prediction of biomechanical strength in vitro.

RATIONALE AND OBJECTIVES: A novel, nonlinear morphologic measure [DeltaP(alpha)] based on local 3D scaling properties was applied to high-resolution magnetic resonance images (HR-MRI) of human trabecular bone to predict biomechanical strength in vitro. METHODS: We extracted DeltaP(alpha) and traditional morphologic parameters (apparent trabecular volume fraction, apparent trabecular separation) from HR-MR images of 32 femoral and 13 spinal bone specimens. Furthermore, bone mineral density (BMD) and maximum compressive strength (MCS) were determined. The morphologic measures were compared with BMD in predicting the biomechanical strength. RESULTS: In the vertebral (femoral) specimens, R2 for MCS versus DeltaP(alpha) was 0.87 (0.61) (P < 0.001). Correlation between BMD and MCS was 0.53 (P = 0.05) (0.79 [P < 0.001]) for the vertebral (femoral) specimens. For the femoral specimens, prediction of MCS could be improved further by combining BMD and morphologic parameters by multiple regression (R2 = 0.88). CONCLUSIONS: Morphologic measures extracted from HR-MRI considering local 3D-scaling properties can be used to predict biomechanical properties of bone in vitro. They are superior to 2-dimensional standard linear morphometric measures and, depending on the anatomic location, more reliably predict bone strength as measured by MCS than does BMD.

Adult↗

PubMed1993

Reduction of image noise in elastography.

Elastography is a method for imaging the elastic properties of compliant tissues which produces gray scale elasticity images called elastograms. The elastograms of phantoms with homogeneous elastic properties exhibit a noisy appearance. We demonstrate that this noisy appearance of the elastograms is due to the nonstationary relationship between the pre- and postcompression signals that results in an artifactual modulation of the strain estimates by the amplitude variations of the envelope of the rf signal. We have identified two methods to reduce the strain modulation artifact. The first method consists of reducing the signal amplitude swings within the observation windows by logarithmically or otherwise compressing the rf signal. The sensitivity of this method to amplitude compression strength and the ability to reduce the noise in the elastograms without affecting the spatial resolution are investigated through simulations. The second method to reduce the strain modulation artifact consists of temporal stretching of the signal obtained after physical compression to approximate the shape of the signal obtained before compression. In this paper, we discuss the first method. The results show that significant improvement in image noise can be obtained with logarithmic amplitude compression. This improvement is obtained in conjunction with improved spatial resolution.

Computer Simulation↗

PubMed2001

About the use of stoichiometric hydroxyapatite in compression - incidence of manufacturing process on compressibility.

Literature concerning calcium phosphates in pharmacy exhibits the chemical diversity of the compounds available. Some excipient manufacturers offer hydroxyapatite as a direct compression excipient, but the chemical analysis of this compound usually shows a variability of the composition: the so-called materials can be hydroxyapatite or other calcium phosphates, uncalcined (i.e. with a low crystallinity) or calcined and well-crystallized hydroxyapatite. This study points out the incidence of the crystallinity of one compound (i.e. hydroxyapatite) on the mechanical properties. Stoichiometric hydroxyapatite is synthesized and compounds differing in their crystallinity, manufacturing process and particle size are manufactured. X-Ray diffraction analysis is used to investigate the chemical nature of the compounds. The mechanical study (study of the compression, diametral compressive strength, Heckel plots) highlights the negative effect of calcination on the mechanical properties. Porosity and specific surface area measurements show the effect of calcination on compaction. Uncalcined materials show bulk and mechanical properties in accordance with their use as direct compression excipients.

Calcium↗

PubMed1998

A comparative study of trabecular bone properties in the spine and femur using high resolution MRI and CT.

The purpose of this study was to use high resolution (HR) magnetic resonance (MR) and computed tomography (CT) images combined with texture analysis to investigate the trabecular structure of human vertebral and femoral specimens and to compare these techniques with bone mineral density (BMD) in the prediction of bone strength. Twenty-nine bone cubes were harvested from 12 proximal femur cadaver specimens and 29 from 8 spines. HR MR and CT images were obtained, and texture analysis techniques were used to assess trabecular structure. Additionally, BMD, elastic modulus (EM), and maximum compressive strength were determined. R2 for EM versus texture measures computed in the MR images was higher (R2 = 0.27-0.64, p < 0.01) in the spine than in the femur specimens (R2 = 0.12-0.22, p < 0.05). R2 values were similar in the CT images. R2 for EM versus BMD was 0.66 (p < 0.01) in the spine and 0.61 (p < 0.01) in the femur specimens. In the MR images, texture measures combined with BMD in a multivariate-regression model significantly increased R2, while improvement was less significant in the CT images. Thus, texture analysis may provide additional information needed to analyze bone strength and quality.

Adult↗

PubMed2005

Mechanical properties and in vitro degradation of bioresorbable fibers and expandable fiber-based stents.

Bioresorbable polymeric support devices (stents) are being developed in order to improve the biocompatibility and drug reservoir capacity of metal stents, as well as to offer a temporary alternative to permanent metallic stents. These temporary devices may be utilized for coronary, urethral, tracheal, and other applications. The present study focuses on the mechanical properties of bioresorbable fibers as well as stents developed from these fibers. Fibers made of poly(L-lactide) (PLLA), polydioxanone (PDS), and poly(glycolide-co-epsilon-caprolactone) (PGACL) were studied in vitro. These fibers combine a relatively high initial strength and modulus together with sufficient ductility and flexibility, and were therefore chosen for use in stents. The effect of degradation on the tensile mechanical properties and morphology of these fibers was examined. The expandable stents developed from these fibers demonstrated excellent initial radial compression strength. The PLLA stents exhibited excellent in vitro degradation resistance and can therefore support body conduits such as blood vessels for prolonged periods of time. PDS and PGACL stents can afford good support for 5 and 2 weeks, respectively, and can therefore be utilized for short-term applications. The degradation resistance of the stents correlates with the profile of mechanical property deterioration of the corresponding bioresorbable fibers.

Absorbable Implants↗

PubMed1992

The biomechanical evaluation of intramedullary nails in distal femoral shaft fractures.

The biomechanical parameters (torsional rigidity and compressive strength) for three different intramedullary femoral nails, Küntscher (K), Brooker-Wills (BW), and Küntscher Interlocking (KI) were compared in this study. Fractures were created in the femoral shaft distal to the isthmus with sections removed so that pure torsional rigidity and resistance to compression could be measured. The standard K nail provided no torsional rigidity and only minimal resistance to longitudinal compression. The KI was significantly more rigid under compression than either the BW or the K. In torsional resistance the K nail was significantly weaker than either the BW or KI. The K nail does not provide significant resistance to compression or torsion for use in oblique or comminuted fractures. The BW nail probably provides enough resistance to rotation for use in distal fractures, but probably does not provide enough resistance to compression for use in fractures that are prone to shortening.

Biomechanical Phenomena↗

PubMed1997

Biomechanical evaluation of hydroxyapatite intervertebral graft and anterior cervical plating in a porcine cadaveric model.

The biomechanical properties of a porous hydroxyapatite (HA) intervertebral graft with or without anterior cervical plating were evaluated in cadaveric porcine cervical spine model using C3-4 discectomy and dissection of the posterior longitudinal ligament to cause instability. The experimental groups were intact (n = 11), instability (n = 11), autogenous bone implant (n = 6), HA graft implant (n = 5), autogenous bone with plating (n = 6), and HA graft with plating (n = 5). Porous HA with 40% porosity and scapular bone were used as grafts. The displacement rates of the cervical spine by compressive forces in the flexural, extensional, and lateral bending directions were evaluated using video-recording followed by computer-assisted analysis. The stiffness to compressive load was calculated from the load-displacement rate curve. The linear and non-linear coefficients of the Fung's equation were obtained based on the plot of Young's modulus against load. There were no statistical differences in the stiffness between the HA and autogenous bone graft in all directions. The two plating groups showed significantly increased stiffness in all directions. The non-linear coefficient value in Fung's equation was far larger in both HA and HA graft with plating groups than in the other groups in flexural compression. Porous HA graft has a compressive strength similar to autogenous graft in vitro, and anterior plating provides additional stiffness to the cervical spine. The larger non-linear coefficient value of the HA groups may represent the characteristic biomechanical brittleness of HA graft, but this is manifest only in flexural compression.

Animals↗

PubMed1986

Is there a relation between bone strength and percolation?

The thermal contraction temperature of collagen in partially demineralized bone was measured as a function of the volume fraction of the mineral phi m. Initially, the contraction temperature gradually increased with an increase in phi m and then rapidly increased in the vicinity of phi m = 0.17. The resisting force against the contraction stress caused by collagen, which corresponds to the compressive strength, was estimated from the thermal contraction temperature of partially demineralized bone. The phi m-dependence of the resisting force of partially demineralized bone was roughly explained in terms of the percolation theory which gives a good description of a sol-gel transition. This suggests that bone can be approximately regarded as a percolated structure of the mineral on a collagen matrix.

Animals↗

PubMed2005

Vertebroplasty by use of a strontium-containing bioactive bone cement.

STUDY DESIGN: A review of the laboratory and clinical data for a new strontium-containing hydroxyapatite bioactive bone cement. OBJECTIVES: To compare the properties of the strontium-containing bioactive bone cement with those of polymethyl methacrylate (PMMA) and hydroxyapatite (HA) bone cements. SUMMARY OF BACKGROUND DATA: Vertebroplasty and kyphoplasty using conventional PMMA bone cements have been effectively used to treat osteoporotic spine fractures with good short- and medium-term results. However, PMMA has some undesirable properties, including its high setting temperature, lack of osseointegration, and large stiffness mismatch with osteoporotic bone. These properties are responsible for some postoperative complications. METHODS: Strontium-containing hydroxyapatite (Sr-HA) bioactive bone cement consists of a filler blend of strontium-containing hydroxyapatite, fumed silica and benzoyl peroxide; and a resin blend of bisphenol A diglycidylether methacrylate, triethylene glycol dimethacrylate, poly(ethylene glycol) methacrylate, and N, N-dimethyl-p-toluidine. Its properties, including mechanical strength, setting temperature, biocompatibility, and osseoinduction, were compared with other cements in vitro and in vivo. Early clinical results are presented. RESULTS: The Sr-HA cement has a setting time of 15 to 18 minutes, a maximum setting temperature of 58 degrees C, a compressive strength of 40.9 MPa, bending strength of 31.3 MPa, and a bending modulus of 1,408 MPa. The bending strength and modulus are closer to human cancellous bone. Sr-HA cement promotes osteoblast attachment and mineralization in vitro and bone growth and osseointegration in vivo. In a pilot study, 23 cases of osteoporotic fractures treated with this cement with a mean follow-up of 18 months suggest that it is as effective as PMMA in relieving pain. DISCUSSIONS: Oral strontium has been shown to induce new bone formation and is effective in reducing fracture risk in osteoporosis. Our data suggest that strontium delivered locally has the same effect; thus, the combination of strontium with HA in a cement with a low setting temperature, adequate stiffness, and low viscosity makes this a good bioactive cement for vertebroplasty and kyphoplasty.

Animals↗

PubMed2007

Effects of teriparatide and alendronate on vertebral strength as assessed by finite element modeling of QCT scans in women with osteoporosis.

UNLABELLED: FE modeling was used to estimate the biomechanical effects of teriparatide and alendronate on lumbar vertebrae. Both treatments enhanced predicted vertebral strength by increasing average density. This effect was more pronounced for teriparatide, which further increased predicted vertebral strength by altering the distribution of density within the vertebra, preferentially increasing the strength of the trabecular compartment. INTRODUCTION: Teriparatide 20 microg/day (TPTD) and alendronate 10 mg/day (ALN) increase areal, measured by DXA, and volumetric, measured by QCT, lumbar spine BMD through opposite effects on bone remodeling. Using finite element (FE) modeling of QCT scans, we sought to compare the vertebral strength characteristics in TPTD- and ALN-treated patients. MATERIALS AND METHODS: A subset of patients (N = 28 TPTD; N = 25 ALN) from the Forteo Alendronate Comparator Trial who had QCT scans of the spine at baseline and postbaseline were analyzed. The QCT scans were analyzed for compressive strength of the L(3) vertebra using FE modeling. In addition, using controlled parameter studies of the FE models, the effects of changes in density, density distribution, and geometry on strength were calculated, a strength:density ratio was determined, and a response to bending was also quantified. RESULTS: Both treatments had positive effects on predicted vertebral strength characteristics. At least 75% of the patients in each treatment group had increased strength of the vertebra at 6 months compared with baseline. Patients in both treatment groups had increased average volumetric density and increased strength in the trabecular bone, but the median percentage increases for these parameters were 5- to 12-fold greater for TPTD. Larger increases in the strength:density ratio were also observed for TPTD, and these were primarily attributed to preferential increases in trabecular strength. CONCLUSIONS: These results provide new insight into the effects of these treatments on estimated biomechanical properties of the vertebra. Both treatments positively affected predicted vertebral strength through their effects on average BMD, but the magnitudes of the effects were quite different. Teriparatide also affected vertebral strength by altering the distribution of density within the vertebra, so that overall, teriparatide had a 5-fold greater percentage increase in the strength:density ratio.

Aged↗

PubMed2004

New percutaneously inserted spinal fixation system.

STUDY DESIGN: We describe a new percutaneous minimally invasive spinal fixation system based on pedicle screws and inflatable rods. The rods are inserted in a flexible state and harden following deployment. We test this system in terms of biocompatibility, ferromagnetism, magnetic resonance artifact production, bench top mechanical testing, ease of insertion within cadavers, potential thermal damage to paraspinous muscles in pigs, and long-term device tolerability in sheep. OBJECTIVES: To determine the safety and utility of this system before its use in human subjects. SUMMARY OF BACKGROUND DATA: Composite materials and epoxy compounds have been used safely in a variety of implanted medical devices for years with no signs of systemic toxicity or significant device failures. METHODS: Long-term biocompatibility test of system components was conducted according to International Standards Organization 10993 and Food and Drug Administration Blue Book Memorandum #G95-1 standards. Device components were assessed for magnetic deflection and torque and imaged in a 1.5 Tesla magnetic resonance unit. Full constructs of the system were tested for compression strength, torque, and fatigue per American Society for Testing and Materials F1717 standards. The system was deployed using C-arm fluoroscopic guidance in 11 cadavers and 2 live sheep. Further, the inflatable rods were tested for exothermic damage to paraspinous musculature in 2 pigs. RESULTS: All system components were found to be biocompatible, nonferromagnetic, and produce little magnetic resonance artifact. Compression and torque results for the new system were found to be comparable to standard metallic pedicle screw and rod fixation systems. However, the new system displayed a superior modulus of elasticity relative to standard surgical systems. The new system endured 5 million cycles of repetitive compressions without breakage or significant wear. All cadaver and sheep insertions were performed successfully. Sheep suffered no complications, and minimal blood loss occurred during device insertions. One of the animals killed at 6 months demonstrated no internal organ damage. The self-curing version of polymer used to inflate the flexible rods cured to approximately 53% of its final strength in 90 minutes with maximum external rod temperature of 40.5 C. and no adjacent thermal damage within porcine paraspinous musculature. CONCLUSIONS: The new spinal fixation system is biocompatible, uses a nontoxic polymer, is magnetic resonance compatible, displays favorable biomechanical characteristics, can be easily deployed percutaneously using simple fluoroscopic guidance, is well tolerated in living sheep, caused no muscular thermal damage, and could be used in humans within a reasonable operative time frame. The new system demonstrates the feasibility of percutaneously constructing composite structures in situ within the body.

Animals↗

PubMed2005

Bone tissue engineering with porous hydroxyapatite ceramics.

The main principle of bone tissue engineering strategy is to use an osteoconductive porous scaffold in combination with osteoinductive molecules or osteogenic cells. The requirements for a scaffold in bone regeneration are: (1) biocompatibility, (2) osteoconductivity, (3) interconnected porous structure, (4) appropriate mechanical strength, and (5) biodegradability. We recently developed a fully interconnected porous hydroxyapatite (IP-CHA) by adopting the "form-gel" technique. IP-CHA has a three-dimensional structure with spherical pores of uniform size that are interconnected by window-like holes; the material also demonstrated adequate compression strength. In animal experiments, IP-CHA showed superior osteoconduction, with the majority of pores filled with newly formed bone. The interconnected porous structure facilitates bone tissue engineering by allowing the introduction of bone cells, osteotropic agents, or vasculature into the pores. In this article, we review the accumulated data on bone tissue engineering using the novel scaffold, focusing especially on new techniques in combination with bone morphogenetic protein (BMP) or mesenchymal stem cells.

Animals↗

PubMed1976

[Radial nerve compression].

A new compression syndrome of the deep branch of the radial nerve is described, in which a sudden anterior displacement of a part of this nerve under maximal tension is followed by an axonotmesis. This happens in an area in which the deep branch of the radial nerve crossed some narrow structures which are unyielding and have more compression strength (tense cords of connective tissue Fig. 3). The operative finding of a torsion of the injured fascicles justifies the correctness of the immediate operative revision; otherwise the nerve regeneration would be impaired by the torted empty endoneural tubes. This description is a further constribution not observed before to the compression syndromes of the radial nerve, since in 1970 the author was able to give an explanation for the pathogenesis of compression palsies of the radial nerve, unclear up to that time but observed after forceful muscle contractions again and again since the beginning of this century. This observation gives the evidence that the occurrence of a peripheral compression lesion of nerves is not bound absolutely on the existence of a "physiological narrowness" (fibrous or osteofibrous tunnel etc.). This is also true for the median nerve.

Humans↗

PubMed1995

Characterization of vertebral strength using digital radiographic analysis of bone structure.

Bone mineral densitometry (BMD) is useful in predicting fracture risk, but, unfortunately, there is a significant degree of overlap in BMD measurements of patients who have a high risk of fracture and patients with a low risk of fracture. In this study, a method of characterizing trabecular bone structure in digitized radiographs of vertebrae is proposed and assessed. A significant correlation between bone "structure" and the compressive strength of vertebral bodies was found. The utility of the parameter for distinguishing between "weak" and "strong" bone samples was assessed using receiver operating characteristic (ROC) analysis. Using this analysis, the structural parameter produced an area under the ROC of 0.88 +/- 0.05, while a bone density measure produced an area of 0.79 +/- 0.07. The results suggest that the addition of a measure of bone structure to the conventional measures of bone density may prove useful in predicting the quality of bone when considering surgical or medical intervention for osteoporotic conditions.

Bone Density↗

PubMed1992

Amalcore strength recovery following refilling of access preparations with amalgam.

After endodontic treatment through an amalgam core, the recommended procedure is to replace the entire core. This study examined the strength achieved by restoring the access openings with dental amalgam and reported the type of failure during strength testing. Seventy-two Dispersalloy 8 x 8 mm cylindrical specimens were produced using controlled condensation pressures. The specimens were randomized in three groups: (1) controls, (2) 3 mm access preparations wetted with mercury-rich amalgam before restoration, and (3) 3 mm access preparations restored unwetted. The specimens tested for compressive strength were separated in two subsets. The unwetted group demonstrated significantly less strength than the control and wetted group (p less than 0.05), while the unwetted and wetted groups revealed significantly less strength than the control group (p less than 0.05). The mean diametral tensile strength recovery for the wetted and unwetted groups was 76% and 69%, respectively. The qualitative assessment of the fracture zones indicated that wetted specimens exhibited more fractures through the new amalgam core than the unwetted specimens (p less than 0.05). It would appear that amalgam refilling of access preparations through amalgam cores has clinical potential.

Dental Alloys↗

PubMed1977

[Studies on the contract of the casting. (II) Influence of core inside the cast (author's transl)].

A alloy has its constant coefficient of casting shrinkage, but its value is changed by casting conditions. This time, we studied with effect of core which exist inside the cast. The results obtained were as follows: 1. The more the strength of core material increases, the smaller the coefficient of casting shrinkage becomes. 2. The smaller the thermal expansion coefficient of core material in solid state, the smaller the casting shrinkage. 3. In case of Silver-Palladium-Gold casting alloy, its actual casting shrinkage (y) has a multiple correlation with the compressive strength (x1) of core material in high temperature, and with the difference (x2) of the original casting shrinkage of the alloy from the casting shrinkage of core material, that is, y = -0.0023x1 + 0.0087x2 + 1.4927 4. Silver-Indium casting alloy is hard to be influenced by the quality of core material, for the alloy has a small shrinkage force.

Dental Alloys↗

PubMed2004

Porous Ti-6Al-4V alloy fabricated by spark plasma sintering for biomimetic surface modification.

Porous compacts with both biological and biomechanical compatibilities and high strength were developed. Spherical powders of Ti-6Al-4V alloy, which were either as received or surface modified with the use of calcium ions by hydrothermal treatment (HTT), were fabricated by a spark plasma sintering process. The porous compacts of pure Ti were used as reference materials. Porosity was approximately 30%, and compressive strengths were 113 and 125 MPa for the as-received Ti alloy powders and those modified by the HTT process, respectively. The bending strength and elastic modulus of as-received Ti alloy powders were 128-178 MPa and 16-18 GPa, respectively. Each of the compacts was immersed in simulated body fluid (SBF). The amount of adsorption/precipitation of calcium phosphate through the compacts was measured by weight change and was observed by SEM. The compacts were covered with calcium phosphate after 2 weeks of immersion in SBF. The compacts of Ti alloy had plenty of precipitated apatite crystals, and modification by HTT accumulated more precipitation. Because calcium phosphate is a mineral component of bone, apatite, which is precipitated on the surface of the compacts, could adsorb proteins and/or drugs such as antibiotics. It is expected that a large amount of proteins and/or drugs could be impregnated when the porous compacts developed are used.

Alloys↗