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Compressive strength measurements were conducted on 32 macroporous biphasic calcium phosphate (MBCP) samples to evaluate the influences and interactions of five synthesis factors: chemical composition, percentage of macropores, mean size of macropores, isostatic compaction pressure, and sintering temperature. These parameters were varied simultaneously between two limit levels. Experiments used a factorial design method (FDM) allowing optimization of the number of samples as well as statistical analysis of results. FDM showed that compressive strength, in a defined experimental area, can be described by a first-order polynomial equation in which the percentage of macroporosity and sintering temperature are the major influences. This study leads up to an isoresponse line diagram that will allow the manufacture of some classes of MBCP with fitted compressive strength.
This study compared three mechanical properties of two recently introduced core materials, a light-activated glass ionomer cement (VariGlass VLC) and a fluoride-release dual cure composite resin (FluoroCore), with those of a conventional silver-reinforced glass-ionomer cement (Miracle Mix). Seventy-two samples (eight per product for each property) were prepared for testing diametral tensile strength, flexural strength, and compressive strength. The specimens were cured, stored for 24 hours at 37 degrees C in 100% humidity, and tested with the use of an Instron universal testing machine. The results of this study indicate that the diametral tensile strength, flexural strength, and compressive strength of the FluoroCore and VariGlass VLC materials were significantly higher than those of the conventional Miracle Mix. The values obtained with FluoroCore material were consistently higher than those obtained with VariGlass VLC material.
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Three thoracic (T5-T7) and three lumbar (L1-L3) vertebral bodies and the anterior parts of both iliac crests were removed from 44 normal individuals aged 15-87 years who had died suddenly. Small, cylindrical samples of trabecular bone (length 5 mm, diameter 7 mm) from T6, L1, and L3 and from the standard site for iliac crest biopsies were compressed in an Alwetron-250 materials testing machine. Whole vertebral bodies from T5, T7, and L2 with cut planoparallel end-plates were compressed in an Instron materials testing machine. The maximum compressive stress value sigma max of the whole vertebral bodies and of the vertical vertebral trabecular bone decreased with age with almost parallel linear regression lines. At any age the sigma max for whole vertebral bodies was about 1.6 MPa (1 MPa = 100 N/cm2) higher than for the trabecular bone. The average cross-sectional area of the vertebral bodies increased by 25-30% from the age of 20 to 80 years. The anisotropic properties of the vertebral trabecular bone (expressed as the ratio between the vertical and horizontal sigma max) increased markedly with age. A highly significant positive correlation was observed between the vertical vertebral trabecular bone sigma max (X) and the total vertebral body sigma max (y = 0.90x + 1.75, r = 0.88, P less than 0.01). The slope was not significantly different from 1, whereas the intercept was positive (P less than 0.01). The average total vertebral body sigma max (range 1.5-7.8 MPa) could be predicted from mechanical tests on horizontal iliac crest bone biopsies with standard error of estimate (SEE) of 0.92 MPa.(ABSTRACT TRUNCATED AT 250 WORDS)
Compressive strength is widely used as the criterion of strength of glass-ionomer dental cements, despite the difficulties in interpretation of the findings. With the introduction of light-cured glass-ionomer cements, which can be used only in thin layers, the question arises of how test specimens should be prepared for the measurement of compressive strength. A suggested method has been to prepare test pieces by building them up in layers, an approach which is examined critically in the current paper. Two different conventional (acid-base) glass-ionomers were studied with the use of layered and unlayered specimens of dimensions 6 mm (height) x 4 mm (diameter) and 12 mm (height) x 6 mm (diameter). While smaller samples gave the same value of compressive strength as larger specimens, layered specimens gave significantly lower values of compressive strength for both sizes. In view of these findings, and since the layered specimens are tedious to prepare, we conclude that compressive strength is unsatisfactory as a criterion of strength for light-cured glass-ionomer cements.
The compressive strength of five different amalgams was measured at one hour, six hours, 24 hours, and seven days, and X-ray diffraction analysis was carried out for each amalgam at the same times in order to investigate the early strength characteristics of the amalgams in relation to the formation of different phases. At 24 hours all tested amalgams reached about 90% or more of their seven-day compressive strength, but the increase in the early compressive strength from one hour to 24 hours varied between different amalgams. Two of the five amalgams tested reached about 90% of their seven-day compressive strength at six hours. A significant correlation was found between the ratio of early compressive strength to seven-day compressive strength, and the X-ray diffraction intensity ratio (ratios of one-, six- and 24 hour intensity to seven-day intensity) for the gamma 1 phase, indicating that the increases in early compressive strength are mainly dependent upon the formation of gamma 1.
In the present study, the compressive strength of four representative dental investment materials was compared. The whole investigation was divided in three experiments. In the first one the effect of different ways of mixing on the compressive strength of the investments was examined. In the second the compressive strength of investments mixed mechanically under vacuum was compared: a) two hours after mixing, b) at the highest heating temperature and c) at room temperature after the heating procedure. In the third experiment, a comparison was made between the compressive strength of investments at the highest heating temperature. The investments were mixed mechanically under vacuum but half of the specimens were placed in a pressure device during setting. From the results obtained the following conclusions were made: a) Mixing mechanically under vacuum increases the compressive strength of the investments, b) the compressive strength of phosphate-bonded investments increases at the highest temperature of the heating procedure and c) the use of a pressure device during the setting of the investments results also in an increased compressive strength.
In this study, we investigated compressive strength of various luting cements and composite resin cores in both dry and wet condition, and then influences of repeating load on compressive strength in wet condition of distilled water at 37 degrees C. As frequency of repeating load increased, compressive strength of all materials decreased. It means that the repeated load cycling test used in this study is adequate for evaluating durability of various dental materials. The results were as follows: 1. In the condition of no loading in both dry and wet condition, resin cement indicated the highest compressive strength of all cements examined and was followed by glass ionomer cement, zinc phosphate cement and polycarboxylate cement. Glass ionomer cement was notably influenced in wet condition. 2. After 10,000 cycles of loading in wet condition, resin cement indicated the highest compressive strength again and was followed by glass ionomer cement, polycarboxylate cement and zinc phosphate cement. In particular, compressive strength of zinc phosphate cement decreased remarkably. 3. In the condition of no loading, visible light-cured composite resin core was superior to chemical one. Visible light one was notably influenced in wet condition. 4. After 10,000 cycles of loading, visible light-cured composite resin core was superior to chemical one.
Compressive strength measurement and microstructure studies of standard, diamond bur-ground, and fracture surfaces of durapatite cones were reported. The compressive strength measurements of durapatite cones were variable and strongly dependent on the test method. The fracture force ranged from 1090 to 3692 N and the calculated compressive strengths ranged from 113 (16,333 psi) to 389 mN/m2 (56,462 psi). The outer surface of durapatite cones was rough, irregular, and dense. Sharp fracture lines occurred along the longitudinal axis of the cones. Isolated porosity was seen in the fracture surface of one specimen. Grinding hydroxyapatite cones using a high-speed diamond bur with water spray produced a surface grinding feature, an irregular surface topography, and microcracks. The microcrack directions were perpendicular to the direction of the diamond bur cutting features.
Setting reactions and compressive strengths of a self-hardening calcium phosphate cement (CPC) were investigated. The CPC consists of tetracalcium phosphate (TTCP) and anhydrous dicalcium phosphate (DCPA). The cement specimens were prepared by mixing 0.7 g of the powder (TTCP 72.9 wt% + DCPA 27.1 wt%) with 0.175 mL of the liquid (25 mmol/L H3PO4 and 1.32 mmol/L sodium fluoride). The specimens were removed from the molds at pre-determined time intervals after being mixed, and their compressive strengths were measured. Immediately afterward, the fractured specimens were rapidly frozen in ethanol (-80 degrees C), lyophilized, and examined by powder x-ray diffraction and scanning electron microscopy (SEM). The results showed that (1) hydroxyapatite was the only reaction product; (2) the reaction was nearly completed within four h, during which both the reaction product and compressive strength increased linearly with time, resulting in a strong correlation between the two; and (3) fully set CPC consisted primarily of small rod-like crystals and some platy crystals.
The compressive strength of 98 specimens of motion segments of human thoracolumbar spines was measured. In addition, the density of the trabecular bone in the midplane of the vertebrae was assessed by quantitative computed tomography (QCT); the size of the vertebral endplates was measured by CT as well. The results show that the compressive strength of thoracolumbar vertebrae can be predicted from the product of density and end-plate area, with an error of estimate of 1 kN. The data of the experiment allow for an in vivo prediction of the strength of vertebrae to quantify the risk of fracture in physically very demanding tasks, to support expert opinion in trauma cases, or to assist in therapeutic decisions in cases of severe osteoporosis.
The present study compares the compressive strength after one week of some conventional glass-ionomer restorative materials with that of glass ionomers reinforced by the addition of ceramic-coated silver or dental amalgam alloy particles to the aluminosilicate glass powder. Apart from the commercially available Ketac Silver and Miracle Mix, experimental mixtures of Fuji II glass-ionomer powder, the old as well as the new version, with various amounts of either a spherical or lathe-cut amalgam alloy were investigated. For the conventional glass ionomers, the mean compressive strength based on all measurements amounts to 159.9 +/- 4.5 MPa. Both formulations of Fuji II have a comparable strength after one-week maturation. The compressive strength of Ketac Silver does not differ significantly from that of Ketac Fill or from that of the conventional glass ionomers investigated. The effect of admixing amalgam alloy on the compressive strength is found to be determined by the shape and the amount of the alloy particles. Moreover, both parameters are interactive with the formulation of the Fuji glass ionomer used for preparation of the mixture. The results indicate that when dental amalgam alloy is added to the glass ionomer, lathe-cut particles are to be preferred but only in an amount up to 20% by weight.
The one-hour compressive strength of 22 commercially available dental amalgams has been measured. Large differences between different alloys were observed. It was recognized that an intermediate one-hour compressive strength is probably the most desirable in view of the other properties which are involved.
Articular cartilage provides the smooth bearing surfaces in freely moving (synovial) joints. Its mechanical properties are important because structural failure of cartilage is closely associated with joint disorders, including osteoarthritis. Some mechanical properties of cartilage are well characterized, but little is known about its compressive strength. A technique for measuring cartilage compressive strength is evaluated, and an overview of experiments which relate strength to stiffness and tissue hydration is given. Specimens of bovine articular cartilage-on-bone, approximately 15 mm square, were loaded on a hydraulic materials testing machine using flat impermeable indentors. Linear-ramp loading/unloading cycles of 1 s duration, and of increasing severity, were applied until failure was evident on force-displacement graphs. Some specimens were tested following a 30 min period of creep loading. Inkstaining and histology were used to locate the site of initial damage to each specimen. Specimen failure occurred first in the cartilage surface layer at a nominal applied stress of 14-59 MPa (mean 35.7 MPa). Mechanical properties were little affected by specimen or indentor size, provided both remained within defined limits, and compressive strength could be measured to an accuracy of approximately +/- 5 per cent. Compressive stiffness was a significant predictor of strength, but only if it was measured at high levels of stress. Strength increased following creep-induced water loss, and initial mechanical damage could propagate under moderate cyclic loading. This technique for measuring cartilage compressive strength has potential for investigating the causes of cartilage failure in vivo.
This in vitro study investigated the compressive strength of five commercially available calcium hydroxide based lining materials and a resin bonded zinc oxide/eugenol material under varying conditions of temperature and relative humidity and at various ++time intervals after mixing. The results of the study showed that the calcium hydroxide liners could be consistently ranked in order with Dycal most frequently having the highest and either Life or Renew having the lowest compressive strength at all time intervals examined. Under simulated clinical conditions all the materials tested with the exception of Life and Renew had sufficient compressive strength 3 minutes after mixing to withstand the force of amalgam condensation.
The purpose of this investigation was to examine the effects of thermocycling upon the compressive strength and abrasive wear resistance of three commercial composites Fulfil, P-50 and Herculite-XR. Specimens of each material were divided into five treatment groups comprising a control, and four different cycling and storage regimes. Tests for compressive strength and wear resistance were carried out. Prior to testing all specimens were stored in distilled water for 1 week. Three groups were stored at a temperature of 37 degrees C and the remaining two at 60 degrees C. Thereafter all groups that were thermocycled were subjected to 750 cycles of a thermocycling regime consisting of the cycle ACAB where A and B represent the fixed temperatures of 37 degrees C and 5 degrees C, and C, depending upon the treatment group, either 50 degrees C or 60 degrees C. One-way analyses of variance upon the compressive strength and wear factor data following the treatments highlighted significant differences in the mean compressive strength for all materials (Fulfil (P < 0.05), P-50 and Herculite-XR (P < 0.01)) and in the wear factor values for only Fulfil and P-50 (P < 0.001). Surprisingly, thermocycling P-50 with an upper temperature limit of 50 degrees C had catastrophic consequences upon the measured properties. It is concluded that some of the observed behaviour may have potentially detrimental consequences upon the long-term clinical durability of the materials tested.