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At least 73 records · Page 4Linked to original sources
PubMed2001

Castability and resistance of ceramometal bonding in Ni-Cr and Ni-Cr-Be alloys.

STATEMENT OF PROBLEM: Because of its pathogenic potential, the importance of the use of beryllium with Ni-Cr alloys must be determined. PURPOSE: This study compared fundamental properties for the clinical use of Ni-Cr alloys, determining the advantage of the addition of beryllium, despite the involved risks. MATERIAL AND METHODS: Two Be-free commercial alloys (Vera Bond II and Wiron 99) and 1 Be-free experimental alloy (E3) with Nb and/or Mo in their formulations and 1 experimental Ni-Cr alloy (E4) with 1.1% Be were submitted to ceramometal bonding resistance, castability, and hardness tests. RESULTS: Analysis of variance showed significant differences (P=.05) between Vera Bond II and Wiron 99 (Be-free) and the E4 alloy for the castability test. Vera Bond II, Wiron 99, and E4 presented higher castability values than E3. There were no statistically significant differences for the ceramometal bonding resistance test. The Kruskal-Wallis test showed significant differences (P=.01) among the alloys with Rockwell 30 T values for the hardness test. CONCLUSION: Within the limitations of this study, the presence of Be in Ni-Cr alloys was not necessary to guarantee the castability and the ceramometal bond resistance of the alloys tested.

Analysis of Variance↗
PubMed1977

[Recrystallization process in the 20 carat dental gold alloy (author's transl)].

An annealing process of the 20 carat dental gold alloy was studied by hardness testing, electrical resistivity measurement and optical microscopic observation. The material was cold rolled to 67.4% and 90.7% in reduction and subsequently annealed in the temperature range from 300 degrees to 500 degrees C. Microscopic observation, electrical resistivity and hardness testing revealed that the annealing process were three distinguishable stages, recovery, recrystallization and grain boundary migration. Activation energies, the order of the reaction involved, and frequency factors for various annealing processes were established.

Crystallization↗
PubMed1995

Mechanical properties of the binary titanium-zirconium alloys and their potential for biomedical materials.

Mechanical properties of titanium-zirconium binary alloys were investigated in order to reveal their possible use for new biomedical materials and to collect useful data for alloy design through a hardness test, a tensile test, and optical microscopy. The hardness of the alloy containing 50% zirconium was approximately 2.5 times as large as the hardness of pure titanium and pure zirconium. Tensile tests showed a similar tendency. No changes between hardness of as cast specimens and as homogenized specimens were observed, nor were changes in microstructures noted. Comparisons between the Ti-6Al-4V alloy and the Ti-Zr-6Al-4V alloy indicated that a titanium-zirconium alloy could provide a base material for a new biomedical alloy. From these results, it was concluded that new alloys for biomedical materials should be designed as titanium-zirconium base alloys.

Alloys↗
PubMedDate not supplied

Temperature change and hardness with different resin composites and photo-activation methods.

This study verifies whether there is any temperature change during photoactivation of two resin composites (Filtek Z250 and Filtek Flow) with three different light curing methods (conventional halogen light curing unit, light emitting diodes curing unit and xenon plasma arc curing unit) and the relationship of temperature change with resin composite hardness. A type-K thermocouple registered the temperature rise peak in an elastomer mold during photoactivation. After photoactivation, the specimens were submitted to Knoop hardness test performed by an indenter (HMV-2000) under a load of 50g for 15 seconds. Both the temperature change data and results of the Knoop hardness test were submitted to ANOVA and Tukey's test at the 5% significance level. No statistical differences in temperature rise were recorded for the different composites following processing by light curing unit (p>0.05). The conventional halogen source produced statistically higher temperatures (p<0.05) than the other units. The plasma arc source promoted statistically lower (p<0.05) Knoop hardness values and temperature changes than the other light curing units.

Composite Resins↗
PubMed2005

Fracture toughness measurement of dental ceramics using the indentation fracture method with different formulas.

This study examined fracture toughness (KIC) measurements obtained using the indentation fracture (IF) method with a view to improving their reliability. The KIC values of five dental ceramics were measured using the IF method with five different formulas, and the single-edge precracked beam (SEPB) method was used as a control. The elastic moduli of the dental ceramics were evaluated by dynamic hardness test. Load conditions of the dental ceramics that produced a median/radial crack for the IF method formulas were investigated. Based on the resultant c/a and P/c1.5 values, the indentation load (P) required for median/radial crack occurrence varied greatly from 29.4 to 196 N depending on the ceramic used. Among the five formulas, none of the KIC values obtained by the IF method with Miyoshi's formula differed significantly (p > 0.05) from the values obtained using SEPB method. These results suggested that, after an appropriate indentation load is determined, reliable KIC values for small dental ceramic specimens can be easily obtained using the IF method if Miyoshi's formula is used in combination with the dynamic hardness test.

Algorithms↗
PubMed2006

Effect of bleaching agents on the microhardness of tooth-colored restorative materials.

STATEMENT OF PROBLEM: There is no consensus concerning the effect of bleaching gels on microhardness of restorative materials. Information about the effect of whitening strips on microhardness of restorative materials is also limited. PURPOSE: The purpose of this study was to evaluate the effect of a bleaching gel and a whitening strip on the microhardness of 3 tooth-colored restorative materials. MATERIAL AND METHODS: Forty cylindrical specimens (6 x 2 mm) of each restorative material, including a nanohybrid composite resin (Grandio), a polyacid-modified composite resin (Dyract eXtra), and a glass-ionomer cement (Ionofil Molar AC), were prepared and stored in distilled water at 37 degrees C for 24 hours. The specimens were then polished using medium, fine, and superfine polishing disks and stored in 37 degrees C distilled water for 7 days. Specimens were divided into 4 groups (n=10). One group was selected for baseline Vickers hardness measurements (load 100 g, dwell time 20 seconds) of the top surfaces. The other 3 groups were treated for 21 days with 1 of the following: distilled water (control), bleaching gel (10% carbamide peroxide), or whitening strip (14% hydrogen peroxide). The top surfaces of the treated specimens were also subjected to the same hardness testing performed for the baseline specimens. Data were analyzed with 2-way analysis of variance and Tukey Honestly Significant Difference tests (alpha=.05). RESULTS: There were no significant differences in microhardness between the test groups of each restorative material. However, significant differences in microhardness were observed among restorative materials. For all test groups, composite resin showed the highest hardness values, whereas glass-ionomer cement presented the lowest (P<.05). CONCLUSION: The bleaching products used in this study did not adversely affect the microhardness of the restorative materials.

Acrylic Resins↗
PubMed1997

Depth of cure of light-cured composite resin with light-curing units of different intensity.

An increase in light intensity is known to produce greater surface hardness of composite resin. The purpose of this study was to determine the depth of cure produced by two light-curing units with different light intensity outputs. Two light-curing units were selected, the one producing 600 mW/cm2 and the other 300 mW/cm2. Five metal plates with thicknesses 1, 2, 3, 4 and 6 mm were selected and 20 holes of 5 mm diameter were drilled through each plate. Each hole was slightly over filled with composite resin (Z100, 3M), covered with a polyester strip, compressed, and light-cured; 10 samples on each plate with the 300 mW/cm2 unit and 10 samples with the 600 mW/cm2 unit. The bases of all samples were subjected to Vickers Hardness testing immediately and one hour after curing. Results were analysed with the Student-t-test. There was a decrease in Vickers Hardness with every increase in depth. Significant differences were found between all the immediate and one hour groups, between the 300 and 600 mW/cm2 light intensities at 2 mm depth and the 2 mm and 3 mm groups. Increments of light-curing composite resin should not exceed 2 mm; optimal hardness only developed after one hour; at a depth of 2 mm an increase in light intensity produced a significant increase in Vickers Hardness; beyond 2 mm depth the increased light intensity did not produce a significant increase in Vickers Hardness.

Chemical Phenomena↗
PubMed2003

Effect of prepartum zeolite A supplementation on renal calcium excretion in dairy cows around calving and evaluation of a field test kit for monitoring it.

In a prospective, longitudinal study ten pregnant dry cows were randomly assigned as either experimentals or controls. The experimental period was from 28 days before expected calving until calving. Experimental cows were allocated 800 g of zeolite A daily during week 2 and 3 before expected calving. The zeolite A was given continuously via a feed dispenser. The daily calcium intake was calculated to be 60 g. Daily urine samples were obtained before, during and after the period of zeolite A supplementation. Urine pH was measured immediately whereas the remaining of samples was stored at C until analysis for calcium and creatinine. Urinary calcium/creatinine ratio was used as a measure of renal calcium excretion. Zeolite A supplementation did not affect urine pH. Renal calcium excretion peaked at the first day of supplementation, whereupon it decreased steadily to a level comparable to pre-exposure level. This could be explained by a sudden draw of calcium from the readily mobilizable pool in the bone. A commercial available water hardness test kit was evaluated as a possible cow-side test for monitoring renal calcium excretion. The repeatability of the analysis was acceptable (CV = 9.3). The accuracy of the test was good. When compared to laboratory derived urinary calcium/creatinine ratios of the same samples, a distinct linear relationship could be shown (Y = 7.9E-7 + 1.9E-8). It was therefore concluded that the water hardness test was able to monitor renal calcium excretion with an acceptable accuracy.

Aluminum Silicates↗
PubMed1996

Hardness, strength, and ductility of prefabricated titanium rods used in the manufacture of spark erosion crowns.

Depending on the size of the prepared tooth spark eroded and milled, Procera crowns (Nobelpharma AB, Göteborg, Sweden) are manufactured from one of five diameters of pure titanium rods. In this study microindentation hardness tests were performed on the outer 400 microns and center of 10 samples for each type of rod. Five tensile samples were also machined for each of the diameters and tested in tension in a universal testing machine. Cast titanium samples were similarly prepared and tested. Some significant differences in hardness and considerable differences in strength and ductility were identified between the prefabricated rods. In comparison, cast titanium was significantly harder and stronger but less ductile.

Analysis of Variance↗
PubMed2005

Mechanical strength and optimal site of placement of a threaded bone screw assessed on the basis of the screw breakage for non-union of the scaphoid: a biomechanical study.

We have performed the surgical procedure on the patients with the fracture of the scaphoid using mini-acutrak screws (ACUMED, Inc.). A 25-year-old man was injured in a fall. Surgical treatment for non-union of the scaphoid using a mini-acutrak screw was performed. However, this screw was broken, despite the absence of any obvious trauma mechanism. A structural examination was performed with a metal microscope and a hardness test was performed. A hardness evaluation was conducted on this broken screw and similar screws. Cannulated screws having diameters of 2.7 and 3.5 mm were also evaluated in the strength test as controls for comparison. The breakage of screw occurred due to fatigue. The screw provides the strength equivalent to that of a 3.5 mm cannulated screw but the bending strength of the head end portion in which the breakage occurred was assumed to be the strength of about one-third that of the intermediate portion.

Adult↗
PubMed1984

On the nature of the opaque and translucent enamel regions of some macropodinae (Macropus giganteus, Wallabia bicolor and Peradorcas concinna).

Teeth of three macropod species, M. giganteus, W. bicolor and P. concinna, have been studied using the techniques of light microscopy, scanning- and transmission-electron microscopy and hardness measurement. Light microscope observations showed that the teeth of these species had a translucent enamel region close to the dentine and an outer opaque enamel region at the tooth's surface. These regions were not related to the presence or absence of tubules which are a characteristic feature of marsupial enamel. Hardness tests showed that the opaque enamel was softer than the translucent enamel. Scanning electron microscope observations revealed that there was no correlation between any particular prism packing or orientation and the opaque and translucent enamel regions. Transmission electron microscope observations showed that the translucent enamel region consisted of well defined prisms and well packed, lath-like crystals, whereas the opaque enamel was disrupted by voids (which ranged in size from enlarged micropores to about 2 microns in diameter in extreme cases) between crystals and some randomly oriented, loosely packed crystals. This disruption within the opaque enamel region was more common at prism boundaries but pockets of disrupted enamel were also found within prisms and interprismatic regions. The opacity of the enamel was caused by scattering of light from the voids. The ultrastructure of the opaque enamel region indicated that this region was hypomineralized; hardness tests and polarized light microscope observations were consistent with these results.

Animals↗