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Results for “Compressive Strength”

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At least 253 records · Page 14Linked to original sources

PubMed1976

The effect of cold temperature mixing on the properties of zinc phosphate cement.

A series of proprietary zinc phosphate cements were evaluated after mixing on glass slabs at three different temperatures, 23 degrees, 6 degrees and -10 degrees C. Working time, setting time, diametral tensile strength, compressive strength and solubility were investigated. From the results of the tests the following conclusions were made: 1) As the temperature of the mixing slab was decreased, the amount of powder required to maintain a constatnt viscosity increased. 2) Compressive, tensile, and solubility values remained constant as the temperature of the mixing slab was decreased provided a consistent viscosity was maintained. 3) Mixing zinc phosphate cement substantially below the dew point is an acceptable practice provided the powder/liquid ratio is modified accordingly. 4) Although the setting time of zinc phosphate cement generally remained constant at temperatures below 6 degrees C, the working time continued to increase at -10 degrees C. 5) Mixing zinc phosphate cemment on a cold mixing slab increases the working time on the glass slab and decreases the setting time in an oral environment. Both of these alterations are clinically beneficial to the orthodontist.

Cold Temperature↗

PubMed1989

Effect of temperature and ageing on the mechanical properties of dental polymeric composite materials.

Evaluation of the mechanical properties of some dental composite materials, Compact, Finesse and Prisma-Fil based on bisphenol glycidyl methacrylate resin was undertaken by applying compression, tension and hardness tests. The effects of temperature and ageing times on these properties were studied. There was a marked increase in the mechanical properties (compressive strength, diametral tensile strength, compressive elastic modulus and hardness) for all the investigated composites with increase of both temperature and time. This was explained in terms of the influence of temperature on the polymerization rate of the materials. The improvement in the mechanical properties of the samples, kept at 37 degrees C, was attributed to further and continued polymerization of the polymer content of their resin system. Such mechanical improvement was verified by the regression equation of linearity versus both temperature and time.

Chemical Phenomena↗

PubMed1986

The effect of resin formulation on the degree of conversion and mechanical properties of dental restorative resins.

The goal of this study was to determine the effects of resin formulation variables, such as diluent concentration, catalyst type and concentration and cure mode, on the degree of conversion of carbon double bonds and mechanical properties of dental restorative resins. Diametral tensile strength, compressive strength, hardness, flexural modulus and strength, and dynamic mechanical properties were tested, and the results were correlated to the degree of conversion results obtained by infrared analysis. The results showed a significant correlation between increased mechanical properties and higher degrees of conversion. Enhanced conversions were achieved by incorporating higher diluent and lower inhibitor concentrations into the resins. Ambient temperature properties were similarly enhanced by lower inhibitor concentrations, but were not enhanced by higher diluent concentration. Dynamic mechanical properties testing at oral and elevated temperatures elucidated possible differences in resin microstructure and network quality. The storage moduli decreased over the dental temperature range and was lower at all temperatures for resins with lower conversions. The glass transition temperature was also lower in resins with poorer conversions, suggesting that these resins may be more unstable at oral temperatures than more highly converted resins. Dynamic mechanical properties were most closely correlated to degree of conversion in these polymeric systems.

Acrylic Resins↗

PubMed2004

Self-reinforced composites of bioabsorbable polymer and bioactive glass with different bioactive glass contents. Part I: Initial mechanical properties and bioactivity.

Spherical bioactive glass 13-93 particles, with a particle size distribution of 50-125 microm, were combined with bioabsorbable poly-L,DL-lactide 70/30 using twin-screw extrusion. The composite rods containing 0, 20, 30, 40 and 50 wt% of bioactive glass were further self-reinforced by drawing to a diameter of approximately 3 mm. The bioactive glass spheres were well dispersed and the open pores were formed on the composite surface during drawing. The initial mechanical properties were studied. The addition of bioactive glass reduced the bending strength, bending modulus, shear strength, compression strength and torsion strength of poly-L,DL-lactide. However, the strain at maximum bending load increased in self-reinforced composites. Initially brittle composites became ductile in self-reinforcing. The bioactivity was studied in phosphate buffered saline for up to 12 days. The formation of calcium phosphate precipitation was followed using scanning electron microscopy and energy dispersive X-ray analysis. Results showed that the bioactive glass addition affected the initial mechanical properties and bioactivity of the composites. It was concluded that the optimal bioactive glass content depends on the applications of the composites.

Biocompatible Materials↗

PubMed1994

Mechanical and bond strength properties of light-cured and chemically cured glass ionomer cements.

The purpose of this study was to evaluate the mechanical and bond strength properties of a commercially available light-cured glass ionomer cement and of a chemically cured glass ionomer cement. Sixty recently extracted human molars were randomly divided into six equal groups, and the bond strengths of the two cement types were evaluated at 1 hour, 24 hours, and 7 days. Stainless steel lingual buttons were bonded to prepared enamel surfaces, and the samples were placed in a water bath at 37 degrees C until testing. The shear bond strength of each sample was determined with a universal testing instrument. The mechanical strength properties of the two cements were then evaluated. The transverse flexural strength, compressive strength, rigidity, and diametral tensile strength were tested for each cement at 1 hour, 24 hours, and 7 days. The results of the mechanical property strength tests were then compared with the results of the bond strength tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMed1997

[Preliminary evaluation of plastic crown restoration supported by osseointegrated implants].

This study was to evaluate the feasibility of plastic crown restoration supported by osseointegrated implants. The following conclusions were drawn from this study: plastic crown gave better biomechanical consideration than porcelain fused to metal (PFM) crown in osseointegrated prostheses, but plastic crown gave worse wearability, tensile strength, compression strength and flexuaral strength than PFM crown. After restoration the disadvantages of the plastic crown were beyond the clinical acceptable range. It showed plastic crown designed dental prothetic implantation was unfeasible.

Crowns↗

PubMed1989

[Influences of remelting on physical properties of denture base metal alloys].

This research was designed in order to evaluate the mechanical properties, such as tensile strength, compressive strength, surface hardness and the elongation and reduction percentages of the length, of the metal specimens prepared from first, second and third generation castings of a denture base metal. The results revealed only a proportional decrease on surface hardnesses of the specimens casted from first, second and third meltings. While the other properties of all specimens had showed no significant differences between themselves, it was concluded that the denture base metals could be melted and used again at least three times.

Dental Alloys↗

PubMedDate not supplied

Mechanical properties of an improved visible light-cured resin-modified glass ionomer cement.

This study investigates the mechanical properties (hardness, flexural strength and compressive strength) of a new light-cured resin-modified glass ionomer cement (Fuji II LC Improved). Effects of the increased powder:liquid ratio on mechanical properties and the correlation between different mechanical properties were also studied. Mechanical properties of the cement at manufacturer's recommended powder:liquid ratio (F), 2% (F2) and 4% (F4) increased powder weight were measured after one day, one week and one month storage in distilled water at 37 degrees C. Hardness testing (KHN; n = 5) was done with a digital microhardness tester (load = 500 g, dwell time = 15 seconds). Flexural and compressive strength testing (MPa; n = 5) were conducted based on ISO 4049 and BS6039, respectively. Results were analyzed using ANOVA/Scheffe's test (p < 0.05) and Pearson's correlation (p < 0.01). The maximum mechanical properties of Fuji II LC Improved were achieved at one week. The hardness, flexural and compressive strength at one week was significantly higher than at one day. A decrease in all mechanical properties was observed at one month. Mechanical properties were significantly affected by increased powder:liquid ratio. After one month storage, significance was as follows: Hardness--F, F2 > F4; Flexural strength--F4 > F, F2 and F > F2; Compressive strength--F, F2 > F4 and F2 > F. A significant very strong and negative correlation was observed between flexural and compressive strengths (r = 0.97).

Compressive Strength↗

PubMed1992

Mechanical properties of dental base materials.

The compressive strengths and compressive moduli of seven base materials (Dycal, VLC Dycal, Time-line, Vitrabond, Ketac Bond, Fuji Lining LC, XR-Ionomer) were measured at 7 minutes, 24 hours, and 90 days using 9 mm by 4 mm cylindrical specimens prepared in hollow Teflon tubes. The 24-hour and 90-day specimens were maintained for 1 hour at 37 degrees C with relative humidity greater than 30%, then placed in distilled water at 37 degrees C until testing. After grinding the ends of the specimens flat, the cylinders of base material were loaded at 1.0 mm/min in an Instron. The compressive strengths of Timeline, a resin based material, at 7 minutes, 24 hours, and 90 days were not significantly different. Timeline had significantly greater compressive strengths of all time periods than the other six materials. The compressive strength of both Dycal and VLC Dycal decreased significantly between the 24-hour and 90-day periods. Of the three photosensitive GI base/liners tested, Fuji Lining LC had significantly higher compressive strengths in all three time periods. At 7 minutes, Timeline demonstrated a significantly higher compressive modulus than any other product. Ketac Bond had a significantly higher compressive modulus at 24 hours and 90 days.

Analysis of Variance↗

PubMed2006

Novel biobased nanocomposites from soybean oil and functionalized organoclay.

Novel biobased nanocomposites have been prepared by the cationic polymerization of conjugated soybean oil (CSOY) or conjugated LoSatSoy oil (CLS) with styrene (ST) and divinylbenzene (DVB), and a reactive organomodified montmorillonite (VMMT) clay as a reinforcing phase. This filler has been prepared by the cationic exchange of sodium montmorillonite with (4-vinylbenzyl)triethylammonium chloride in aqueous solution. The nanostructures of the nanocomposites have been determined by using wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM), respectively. The results from WAXD and TEM indicate that a heterogeneous structure consisting of intercalation and partial exfoliation or an intercalation structure exists in the nanocomposites, depending on the amount of VMMT in the polymer matrix. The thermal, mechanical, and organic vapor barrier properties of the nanocomposites have been evaluated by dynamic thermal analysis, thermogravimetric analysis, mechanical testing, and toluene absorption. A significant improvement is observed in the thermal stability, the dynamic bending storage modulus, the compressive modulus, the compressive strength, the compressive strain at failure, and the vapor barrier performance for the CSOY-- and CLS-based nanocomposites with 1-2 wt % VMMT loading, where some individual exfoliated silicate platelets occur. For example, the CLS-based nanocomposite with 1-2 wt % VMMT exhibits increases of 100-128%, 86-92%, and 5-7% in compressive modulus, compressive strength, and compressive strain at failure, respectively. CLS with higher unsaturation and reactivity affords nanocomposites with higher thermal stability and higher mechanical properties than CSOY.

Aluminum Silicates↗

PubMed2002

Thermoplastic composites for veneering posterior teeth-a feasibility study.

OBJECTIVES: This pilot study was conducted to explore selected commercially-available thermoplastic composites that potentially had physical properties superior to currently available dental systems for restoring esthetic posterior crowns. METHODS: Polyurethane, polycarbonate, and poly(ethylene/tetrafluoroethylene) (ETFE) composites and unfilled polyurethane specimens were injection molded to produce shapes adaptive to five standardized mechanical tests. The mechanical testing included abrasive wear rate, yield strength, apparent fracture toughness (strength ratio), flexural strength, and compressive strength. RESULTS: Compared to commercially available dental composites, abrasion wear rates were lower for all materials tested, yield strength was greater for the filled polycarbonates and filled polyurethane resins, fracture toughness testing was invalid (strength ratios were calculated for comparison of the pilot test materials), flexural strength was roughly similar except for the filled ETFE which was significantly greater, and compressive strength was lower. SIGNIFICANCE: Commercially available thermoplastic resin composites, such as polyurethane, demonstrate the potential for development of an artificial crown material which exceeds the mechanical properties of currently available esthetic systems, if compressive strength can be improved.

Analysis of Variance↗

PubMed2005

Effects of combined elcatonin and alendronate treatment on the architecture and strength of bone in ovariectomized rats.

We examined the combined effects of elcatonin (ECT) and alendronate (ALN) on bone mass, architecture, and strength in ovariectomized (OVX) rats. Fifty female Sprague Dawley rats, aged 13 weeks, were divided into Sham, OVX, OVX+ECT, OVX+ALN, and OVX+ECT+ALN groups (n = 10). Immediately after ovariectomy, ECT was administered at a dose of 15 units (U)/kg three times a week, and ALN was administered daily at a dose of 2.0 microg/kg, subcutaneously for 12 weeks. The three-dimensional architecture of the bone in the distal femoral metaphysis was analyzed using a microfocus X-ray computed tomography system (microCT), and bone strength was measured using a material-testing machine. Trabecular bone volume (BV/TV) and number (Tb.N) were significantly greater in the OVX+ECT and OVX+ALN groups than in the OVX group. In the OVX+ECT+ALN group, BV/TV and Tb.N were significantly greater when compared with those in the OVX+ECT and OVX+ALN groups. Trabecular thickness (Tb.Th) was significantly greater in the OVX+ECT+ALN group than in the OVX+ALN group. With regard to bone strength, the compression strength in the femoral metaphysis was significantly lower in the OVX group than in the Sham group. The reduction of compression strength was slightly lower in the OVX+ECT and OVX+ALN groups. In the OVX+ECT+ALN group, the compression strength in the femoral metaphysis significantly increased when compared with the OVX and OVX+ECT groups. These results suggest that the combined treatment of ECT and ALN does not alter the individual effects of each drug and that it exerts an additive effect on trabecular architecture and bone strength in OVX rats.

Alendronate↗

PubMed1996

In vitro degradation of a poly(propylene fumarate)-based composite material.

We investigated the in vitro degradation of a novel degradable polymeric composite material being developed to function as a temporary replacement for trabecular bone. This material is based on a mixture of poly(propylene fumarate) cross-linked by N-vinyl-pyrrolidone and includes sodium chloride and beta-tricalcium phosphate. Using an in vitro test in simulated body fluids, the compressive strengths and compressive moduli of two composite materials increased with degradation time and remained above the minimum values acceptable for trabecular bone substitutes. A compressive strength of 21.3 (+/- 0.4) MPa and a compressive modulus of 696 (+/- 53) MPa were measured after twelve weeks for a composite material with initial strength of 18.0 (+/- 4.6) MPa and initial modulus of 113 (+/- 40) MPa. This unexpected phenomenon may prove to be useful for orthopaedic applications.

Biocompatible Materials↗

PubMed1999

Storage stability of dental luting agents.

STATEMENT OF PROBLEM: Mechanical properties are considered to be important to the clinical success of dental cements. Storage time of dental luting agents (dental cements) before use and at the manufacturer may have substantial effects on their properties. PURPOSE: This study observed and investigated the changes in the properties of water-based dental luting agents over time and on exposure to various environmental conditions. METHODS AND MATERIAL: Properties of zinc phosphate, zinc polycarboxylate, and glass-ionomer luting agents were recorded at baseline and at intervals past 84 months, whereas the materials were exposed to controlled storage conditions as well as various conditions typical of clinical situations. Tests included viscosity, diametral tensile strength, ultimate compressive strength, rigidity, hardness, and working/setting times. RESULTS: Viscosity increased over 24 to 60 months for the acidic polymer liquids (zinc polycarboxylate and glass ionomer). Tensile and compressive strengths began to decrease after 36 months for all cements, most acutely for glass ionomer. CONCLUSION: Changes in critical properties on aging may not be noticed by the clinician and yet may impact clinical success. These data emphasize the importance of storage stability for perishable dental materials and portend the need for standardized tests.

Analysis of Variance↗

PubMed1997

In vitro evaluation of a glass-ceramic restorative material.

The aim of the present study was to evaluate the clinically relevant properties of the recently introduced ceramic material IPS Empress, which is marketed for all-ceramic restorations. The following parameters were investigated: three- and four-point bending strength, bi-axial flexure strength, compressive and diametral tensile strength, compressive strength and marginal fit of full crowns. The results show that this material is a highly developed glass-ceramic with physical properties making this dental material well suitable for adhesively luted restorations.

Adhesives↗

PubMed1991

Physical and mechanical properties of calf lumbosacral trabecular bone.

The physical and mechanical properties of calf lumbar and sacral trabecular bone were determined and compared with those of human trabecular bone. The mean tissue density (1.66 +/- 0.12 g cm-3), equivalent mineral density (169 +/- 36 mg cm-3), apparent density (453 +/- 89 mg cm-3), ash density (194 +/- 59 mg cm-3), ash content (0.6 +/- 0.05%), compressive strength (7.1 +/- 3.0 MPa) and compressive modulus (173 +/- 97 MPa) of calf trabecular bone are similar to those of young human. There were moderate, positive linear correlations between apparent density and equivalent mineral density, ash density, and compressive strength; and between compressive strength and equivalent mineral density (R2 ranging from 0.35 to 0.48, p less than 0.001). Apparent density, ash density, and equivalent mineral density did not differ significantly in different regions. In contrast to humans, the compressive strength increased from posterior, near the facet, to the anterior vertebral body. These comparisons of physical and mechanical properties, as well as anatomical comparisons by others, indicate that the calf spine is a good model of the young non-osteoporotic human spine and thus useful for the testing of spinal instrumentation.

Animals↗

PubMed1999

Mechanical properties of dental luting cements.

STATEMENT OF PROBLEM: Dental luting cements fail by microcrack formation and bacterial ingress or by gross failure and crown dislodgment. Both of these failure modes are related to mechanical properties and deformation. PURPOSE: This study evaluated those mechanical properties of cements. METHODS AND MATERIAL. Elastic modulus for 8 representative cements (zinc phosphate, polycarboxylate, glass ionomer, encapsulated glass ionomer, resin-modified glass ionomer, resin composite, and adhesive resin composite) was measured by using a nondestructive technique and evaluated for cement type and storage time (1 hour, 1 day, 1 week, 1 month, 1 year) by 2-way ANOVA (P <.05). Compressive properties (proportional limit, resilience, and toughness), ultimate strengths (compressive, diametral tensile, and flexural), and flexural toughness were determined and evaluated by 2-way ANOVA for 2 crosshead testing rates (5 and 0.5 mm/min) and cement type (P <.05). RESULTS: Cements varied with respect to elastic moduli, compressive proportional limit, compressive resilience, compressive strength, compressive toughness, diametral tensile strength, flexural strength, and flexural toughness. Storage time affected the elastic moduli of different materials in different ways. Elastic moduli of polycarboxylate and glass ionomer cements increased over time, whereas the other materials changed little after the first day. Crosshead rate only significantly affected compressive proportional limit and resilience. CONCLUSIONS: Luting cements differed considerably with respect to mechanical properties.

Adhesives↗

PubMed2006

Effects of degradation and porosity on the load bearing properties of model hydroxyapatite bone scaffolds.

Degradation of three types of model hydroxyapatite (HA) scaffolds was studied after in vitro degradation in a sodium acetate buffer (pH 4). Degradation was evaluated using compression testing, scanning electron microscopy (SEM), inductively coupled plasma (ICP) analysis, and weight measurements. Scaffolds were fabricated with a solid freeform fabrication (SFF) technique based on the robotic deposition of colloidal pastes. Scaffolds had a macrostructure resembling a lattice of rods. Scaffolds contained either macropores (270 or 680 microm in the x-y direction and 280 microm in the z-direction) and micropores (1-30-microm pores and pores <1 microm) or only macropores pores (270 microm in the x-y direction and 280 microm in the z-direction). A computer-aided design (CAD) program controlled the size and distribution of macropores; micropores were created by polymethylmethacrylate (PMMA) microsphere porogens (1-30-microm pore diameter) and controlled sintering (pores <1 microm). Percent weight loss of the scaffolds and calcium and phosphorus ion concentrations in solution increased as the degradation period increased for all scaffold types. After degradation, compressive strength and compressive modulus decreased significantly for those scaffolds with microporosity. For scaffolds without microporosity, the changes in strength and modulus after degradation were not statistically significant. The compressive strength of scaffolds without microporosity was significantly greater than the scaffolds with microporosity.

Bone Substitutes↗