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Results for “Compressive Strength”

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At least 991 records · Page 55Linked to original sources

PubMed2001

Outcomes of allogenic cages in anterior and posterior lumbar interbody fusion.

Interbody lumbar fusions provide a proven logical solution to diseases of the intervertebral discs by eliminating motion of the segment. Historically, there are many techniques to achieve spinal fusion in the lumbar spine. These include anterior, posterior, and foramenal approaches, often in combination with various internal fixation devices. The surgeon's choice of the approach and mechanical or biological implant is dependent on the patient's specific pathology and anatomy, in addition to the experience and training of the surgeon in similar conditions. In the past decade, new mechanical spine implants/spacers have been designed to provide restoration of disc height and improve stabilization of the spine. The ability to radiographically assess the "biology" of bone incorporation in these mechanical (metal) spacers has become a significant limitation. The femoral ring allograft (FRA) and the posterior lumbar interbody fusion (PLIF) spacers have been developed as "biological cages" that permit restoration of the anterior column with machined allograft bone biological cages. Test results demonstrate that the FRA and PLIF spacers have a compressive strength of over 25,000 N. The pyramid-shaped teeth on the surfaces and the geometry of the implant increase the resistance to expulsion at clinically relevant loads (1053 and 1236 N). The technique of anterior column reconstruction with both the FRA and the PLIF biological cages have been previously reported. Clinical outcomes and experience with the FRA spacer (137 patients) and the PLIF spacer (13 patients) were reported on and did not reveal any evidence of bone cage resorption or infectious inflammatory process. There was clinical migration with one PLIF spacer, which was later revised with an anterior approach and a FRA spacer. The radiographic outcomes demonstrated that 94% arthrodesis was achieved with the biological spacer and additional posterior instrumentation. The clinical success of every spine fusion procedure is dependent on many factors such as the extent of the instability, the pathology, type of graft used, the patient's pathology/anatomy and lifestyle.

Biocompatible Materials↗

PubMed2005

Porous Ti6Al4V scaffolds directly fabricated by 3D fibre deposition technique: effect of nozzle diameter.

3D porous Ti6Al4V scaffolds were successfully directly fabricated by a rapid prototyping technology: 3D fibre deposition. In this study, the rheological properties of Ti6Al4V slurry was studied and the flow rate was analyzed at various pressures and nozzle diameters. Scaffolds with different fibre diameter and porosity were fabricated. ESEM observation and mechanical tests were performed on the obtained porous Ti6Al4V scaffolds with regard to the porous structure and mechanical properties. The results show that these scaffolds have 3D interconnected porous structure and a compressive strength which depends on porosity at constant fibre diameters and on the fibre diameter at constant porosity. These Ti6Al4V scaffolds are expected to be constructs for biomedical applications.

Alloys↗

PubMed2005

Preparation and in vitro investigation of chitosan/nano-hydroxyapatite composite used as bone substitute materials.

Chitosan/nano-hydroxyapatite composites with different weight ratios were prepared through a co-precipitation method using Ca(OH)(2), H(3)PO(4) and chitosan as starting materials. The properties of these composites were characterized by means of TEM, IR, XRD, burn-out test and universal matertial test machine. Additionally, in vitro tests were also conducted to investigate the biodegradability and bioactivity of the composite. The results showed that the HA synthesized here was poorly crystalline carbonated nanometer crystals and dispersed uniformly in chitosan phase and there is no phase-separation between the two phases. Because of the interactions between chitosan and n-HA, the mechanical properties of these composites were improved, and the maximum value of the compressive strength was measured about 120 MPa corresponding to the chitosan/n-HA composite with a weight ratio of 30/70. The specimens made of 30/70 chitosan/n-HA composite exhibit high biodegradability and bioactivity when being immersed in SBF solutions. The composite is appropriate to being used as scaffold materials for bone tissue engineering. (c) Springer Science + Business Media, Inc.

Biocompatible Materials↗

PubMed2005

Biological response to pre-mineralized starch based scaffolds for bone tissue engineering.

It is known that calcium-phosphate (Ca-P) coatings are able not only to improve the bone bonding behaviour of polymeric materials, but at the same time play a positive role on enhancing cell adhesion and inducing the differentiation of osteoprogenitor cells. Recently an innovative biomimetic methodology, in which a sodium silicate gel was used as a nucleative agent, was proposed as an alternative to the currently available biomimetic coating methodologies. This methodology is especially adequate for coating biodegradable porous scaffolds. In the present work we evaluated the influence of the referred to treatment on the mechanical properties of 50/50 (wt%) blend of corn starch/ethylene-vinyl alcohol (SEVA-C) based scaffolds. These Ca-P coated scaffolds presented a compressive modulus of 224.6 +/- 20.6 and a compressive strength of 24.2 +/- 2.20. Cytotoxicity evaluation was performed according ISO/EN 10993 part 5 guidelines and showed that the biomimetic treatment did not have any deleterious effect on L929 cells and did not inhibit cell growth. Direct contact assays were done by using a cell line of human osteoblast like cells (SaOS-2). 3 x 10(5) cells were seeded per scaffold and allowed to grow for two weeks at 37( composite function)C in a humidified atmosphere containing 5% CO(2). Total protein quantification and scanning electron microscopy (SEM) observation showed that cells were able to grow in the pre-mineralized scaffolds. Furthermore cell viability assays (MTS test) also show that cells remain viable after two weeks in culture. Finally, protein expression studies showed that after two weeks osteopontin and collagen type I were being expressed by SaOS-2 cells seeded on the pre-mineralized scaffolds. Moreover, alkaline phosphatase (ALP) activity was higher in the supernatants collected from the pre-mineralized samples, when compared to the control samples (non Ca-P coated). This may indicate that a faster mineralization of the ECM produced on the pre-mineralized samples was occurring. Consequently, biomimetic pre-mineralization of starch based scaffolds can be a useful route for applying these materials on bone tissue engineering.

Alkaline Phosphatase↗

PubMed2006

Optimisation of the composition of an acrylic bone cement: application to relative amounts of the initiator and the activator/co-initiator in Surgical Simplex P.

In cemented arthroplasties, the two-part self-curing acrylic bone cement is currently the only material used for anchoring the total joint replacement to the contiguous bone. In virtually all commercially available formulations of this cement, the agents used for the initiation and activation/co-initiation of the radical polymerisation reaction are benzoyl peroxide (BPO) and N, N dimethyl-para-toluidine (DMPT), respectively. There are no reports in the open literature on the rationale for the amounts of these and other constituents in the formulations of the cement. Given the concerns that have been raised in the literature regarding the effect of residual DMPT on the body, it is important to keep the starting amounts of BPO and DMPT as high and as low, respectively, as possible. In the present work, the focus is on the relative amounts of these two agents in the case of one widely used commercial formulation, Surgical Simplex(R) P. Thirty variants of this cement were formulated, covering three concentrations of the co-polymer/BPO (75%, 80%, and 85% of the mass of the powder) and DMPT amounts (ranging from 0.8 %v/v to 2.4% v/v.) The setting time (t(set)), the peak temperature reached during the cement polymerisation process (T(max)), and the ultimate compressive strength (UCS) of each of the formulations were determined in accordance with procedures specified in ISO 5833. A critical examination of all the results indicated that the optimum ratio of the concentration of the initiator (BPO embedded in the PMMA-sytrene co-polymer) to that of the activator/co-initiator (DMPT) in Surgical Simplex(R) P is 57.14 (80%w/w co-polymer + BPO per 1.4%v/v DMPT). The mean values of t(set), T(max), and UCS of this optimum formulation were determined to be 12.30 min, 68 degrees C, and 101 MPa, respectively, all of which are within the limits specified in ISO 5833. The commercially available formulation of this cement contains 2.5%v/v DMPT, while the optimum formulation, as found in the present work, has 44% less DMPT, which may translate to a smaller amount of residual DMPT that is available for elution into the periprosthetic tissue in a cemented arthroplasty, over the in vivo life of the joint replacement.

Adhesiveness↗

PubMed1988

External fixation of fractures of the tibia: clinical experience of a new device.

The performance of a new external fixator was assessed in 50 cases of various types of fractures of the tibia. The fixator comprises an adjustable single outrigger bearing offset pins which offers considerable versatility in its use. The angle at which the pins are offset gives the device considerable torsional and angulatory stability, but its compressive strength is low, allowing axial loading of the fracture during weight bearing. The incidence of complications such as non-union, malunion, and pin-track infection was low. The time to bony union was shorter in cases in which the fixator was applied without exposure of the fracture, compared with those in which the fracture was reduced under direct vision. The time to bony union was also slightly shorter in cases where external fixation was the primary form of treatment, compared with those receiving preliminary os calcis traction.

Adult↗

PubMed1983

The mechanical characteristics of cancellous bone at the upper femoral region.

Mechanical behaviour of trabecular bone at the upper femoral region of human bones has been studied by compression tests on trabecular bone specimens removed from normal femora obtained at autopsy. Compression tests were performed along three different axes of loading on wet specimens and high loading rates. Femoral head specimens proved to be the strongest for any axis of loading. Large variation in compressive strength and modulus of elasticity is seen within and between femoral bone samples. Anisotropy and differences in anisotropy for the different regions have been observed. A significant correlation between mechanical properties (sigma max - E) and bone mineral content of the specimen was found. Tests on whole bone structures demonstrate that removal of the central part of the trabecular bone at the proximal femur reduces the strength for impact loading considerably (+/- 50%).

Biomechanical Phenomena↗

PubMed1977

Fluoride release and physical properties of a fluoride-containing amalgam.

1. The amount and percentage of fluoride released from amalgam were less for the 1:1.6 alloy/mercury ratio than for the 1:1 ratio. 2. Higher fluoride concentrations resulted in a greater quantity but lower percentage of fluoride released from the amalgam. 3. Longer immersion times resulted in a greater amounts and percentages of released fluoride. However, the fluoride released per hour decreased with immersion time. 4. Immersion of the amalgam in lactic acid caused a greater release of fluoride than immersion in distilled water. 5. Disintegration of the amalgam was greater in lactic acid than in distilled water. The contribution of calcium fluoride to weight loss was greater in water than in lactic acid, indicating a corrosive effect for lactic acid. 6. The higher calcium fluoride content (2 per cent) decreased the compressive strength of the amalgam but did not alter the dimensional change.

Calcium Fluoride↗

PubMed1978

A comparison of properties for zinc phosphate cements mixed on room temperature and frozen slabs.

The following conclusions may be drawn from this study: 1. More powder may be incorporated into the cement liquid when the cement is mixed on a frozen slab rather than a room temperature slab. 2. A dramatic increase in the working time and decrease in setting time occur with frozen-slab mixes. 3. No statistically significant difference in compressive strength was found for the room temperature and frozen-slab mixes. 4. Solubility and disintegration values for room temperature and frozen-slab mixes of the three cements not containing fluoride were below the maximum limit of ADA Specification No. 8.

Chemical Phenomena↗

PubMed1980

Frozen-slab technique for mixing zinc phosphate cement for cast restorations.

The technique for handling zinc phosphate cement can be altered to achieve enhanced properties of the cement. The compressive strength of the material can be decreased. The film thickness can be maintained within acceptable limits, and the possibility of pulpal damage can be kept low by maintaining temperature changes in the cement similar to those obtained from a room temperature-slab technique. The technique advocated by this report is as follows: 1. Store the aluminum slab with vinyl covering in a freezer at -15 degrees C to -20 degrees C in a plastic bag to prevent ice formation on the surface. 2. Remove the slab when ready to mix. 3. Quickly wipe the slab clean. 4. Dispense twice as much powder and liquid as recommended on the slab. 5. Start timer. 6. Slowly incorporate the powder into the liquid over a large area of the slab for 2 minutes. 7. Allow the mix to remain on the slab. 8. The instrument for placing the cement can be placed under the slab. The casting can be placed on a corner of the slab. 9. At 10 minutes, place the cement into the casting(s) and seat. 10. Remove excess cement. 11. Clean the slab by rinsing in water and gently wiping. 12. Dry the slab, place it in the plastic bag, and return it to the freezer.

Aluminum↗

PubMed1982

Mechanical mixing of zinc oxide-eugenol cements.

An analysis of the data yielded the following conclusions: 1. The use of a gelatin capsule in a metal casing combines the advantages of mechanical mixing and those of a disposable system. 2. In comparison to conventional mixing by hand, equal results can be obtained with mechanical mixing. 3. Mixing time and the use of a glass pestle will influence the setting time and the film thickness, whereas the type of casing only affects the setting time. No clear correlation was found between the temperature rise during mixing and the setting time, but the total quantity of the mix can influence the setting time. 4. The compressive strength was barely affected by the various mixing conditions.

Chemical Phenomena↗

PubMed1984

An in vitro comparison of two dowel and core techniques for endodontically treated molars.

A laboratory study was designed to compare the shear-compressive strength of two post and core systems in mandibular molars. A buildup with cemented posts and an amalgam core proved to have greater strength than a system in which only amalgam was used to create a dowel and core. The addition of crowns to the buildups did not produce a significant increase in the shear strength of the specimens. Most specimens prepared by a specific restorative technique fractured in a consistent predictable pattern. The dentist should be aware of the incidence of lingual wall fractures in planning the restorations for endodontically treated molars. Careful evaluation of the remaining amount of tooth structure should influence the selection of the dowel and core technique.

Crowns↗

PubMed1985

Microwave oven drying of artificial stone.

The compressive strength of various artificial stones were tested using air, oven, and microwave oven drying methods to compare the three for drying refractory casts. The microwave oven can be used for rapid drying of refractory casts in removable partial denture construction. However, it should not be used for drying extremely wet casts.

Air↗

PubMed1985

Effects of porcelain-metal junction angulation on porcelain fracture.

The different porcelain-metal junction angulations from 45 to 135 degrees have no effect on the amount of compressive force required to fracture the porcelain. The compressive force required to fracture the samples was reduced by half when the contacts were placed 1 or 2 mm from the porcelain-metal junction. Nevertheless, even at 2 mm from the porcelain-metal junction, the compressive strength was approximately six times that of the average biting force. Therefore, clinical fractures are not the result of biting force but possibly the burnishing effect on the metal as the patient slides through the junction. An experiment designed to study a sliding force on the porcelain-metal junction is needed to understand the causes of fracture that originate there and to determine an optimum distance for the placement of occlusal contacts.

Bite Force↗

PubMed1989

Properties of a glass-ionomer/resin-composite hybrid material.

A small percentage of the liquid resin used in commercial dental composites was added to the liquid used in a commercial glass-ionomer restorative in order to produce a fluoride-containing hybrid restorative-type material that would adhere to dentin while being stronger, less brittle, and less sensitive to desiccation in the oral cavity than glass ionomer. Compressive strength, yield strength, elastic modulus, fracture toughness, and tensile strength were analyzed for this hybrid, light-cured material. In addition, the solubility in water, adhesion to dentin, and surface roughness were also examined in vitro. The results suggest that the early (one-hour) mechanical properties of the hybrid material exceed those of glass ionomer. In addition, the brittleness and solubility of the material are less than those of commercial glass ionomer, while adhesion to dentin is unaffected. Most importantly, surface crazing, a documented problem with some glass ionomers when they become desiccated, is alleviated with this hybrid formulation.

Composite Resins↗

PubMed1989

The effect of trituration time on the mechanical properties of four high-copper amalgam alloys.

Several manipulative variables have been shown to influence the physical properties of dental amalgam. Variation in trituration time has been reported to affect creep, compressive strength, and diametral tensile strength in various amalgams. Recent classification of amalgam alloys by particle microstructure reveals four categories: single-composition lathe-cut; single-composition spherical; lathe-cut and eutectic admixture; and lathe-cut and single-composition spherical admixture. The effect of variation of trituration times has not been studied for these newer high-copper alloys. A representative from each classification was selected and physical properties tested, with varied times for trituration utilized. Results showed little compromise in laboratory values for the properties tested. Additional laboratory and clinical trials are warranted, but this study supports the premise that clinicians may vary trituration time to improve handling characteristics without significantly affecting mechanical properties.

Copper↗

PubMed1993

In vitro characterization of visible light-cured glass ionomer liners.

The purpose of this study was to characterize the in vitro performance of three visible light-cured glass ionomer liners. The liners containing 2-HEMA showed significantly higher compressive strength, diametral tensile strength and Vickers hardness than the liner without 2-HEMA. Statistically significant differences were found in the optical properties of the materials tested. The liners containing 2-HEMA manifested higher shear strength at liner/composite than at dentin/liner interfaces. The acid-base reaction was significantly delayed after light exposure in all the liners tested. The liner without 2-HEMA presented the greatest maximum gap at the liner/dentin interface. Significant correlations were detected between the optical properties of the liners and the top-bottom differences in the extent of conversion, as well as between the maximum marginal gap at the dentin/liner interface and the bond strength with dentin and composite. These correlations suggest the following areas for further developments: incorporation of low molecular weight polyalkenoic acids or accelerating agents to increase the initial carboxylate yield, increase in total transmittance and reduction in diffuse reflectance to improve the in-depth conversion, and reinforcement of the dentin liner interface to prevent gap formation.

Analysis of Variance↗

PubMed1980

Bioceramics consisting of calcium phosphate salts.

After a discussion of the chemical considerations involved in the production of calcium phosphate ceramics, animal and clinical studies are reviewed. Specific conclusions are that although these ceramics have high compressive strengths, they are not suitable for joint replacements. Prevention of alveolar ridge resorption is a promising concept, and space-filling and use of aids for jaw-bone enlargement are proposed for routine clinical application.

Biocompatible Materials↗