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PubMed1995

Effect of disinfectant on the dimensional stability, compressive strength and hardness on dental stone.

In this investigation it was planned to study the effect of disinfection time on the dimensional stability, compressive strength and hardness of gypsum die materials. Measurements of specimens treated with disinfectant were compared with the corresponding measurements of control specimens. The results of this study indicated that there was no difference in the dimensional stability, compressive strength and hardness. Therefore using the disinfectants will not affect gypsum die material.

Calcium Sulfate↗
PubMed1997

[The compressive strength, tensile strength, flexural strength and micro-hardness of Plat-II Castable Ceramics].

In preparation for the clinical use of Plat-II Castable Ceramics (PCC-II), we tested its compressive strength, tensile strength, flexural strength and microhardness. The flexural strength was tested by the three-point bending test. The result showed that the compressive strength was 541.7 MPa; the tensile strength 42.5 MPa; the flexural strength 142.0 MPa; the modulus of elasticity 61.4 GPa; and the micro-hardness 499.6 kg/mm3. The strength anol micro-hardness of PCC-II materials were better than those of human enamel. So PCC-II is applicable to restorations in dentistry.

Ceramics↗
PubMed1985

In vitro characteristics of tobramycin-PMMA beads: compressive strength and leaching.

Antibiotic-impregnated polymethylmethacrylate (PMMA) bone cement beads have been used as a local drug delivery system for the treatment of bone and soft tissue infections. The beads deliver a high local level of antibiotic with a decreased risk of toxic systemic levels. This study was undertaken to determine the antibiotic release characteristics of tobramycin-impregnated beads over time and to determine the compressive strength of these beads. Acrylic resin (PMMA) bone cement beads were prepared with three different concentrations of tobramycin. The beads were tested for compressive strength, and their antibiotic release characteristics were determined over a 21 day period by radioimmunoassay and by biological testing against a variety of bacteria. The compressive strength of the beads was found to be adequate to avoid fragmentation during their clinical use. There was gradual release of tobramycin from the beads over the entire 21 days, but the release was most marked during the first 48 hours. There was antibiotic activity against both gram-negative and gram-positive organisms, except Enterococcus, for the entire 21 day period. The release of tobramycin followed a curvilinear relationship and was directly related to the initial antibiotic concentration of the bead. Tobramycin-impregnated polymethylmethacrylate beads may represent a reliable method of local antibiotic delivery with sustained activity against a broad spectrum of organisms.

Bone Cements↗
PubMed1989

The effect of placement technique upon the compressive strength and porosity of a composite resin.

This paper examines the effect of two placement techniques upon the compressive strength and level of porosity of specimens of a composite resin. Those specimens prepared by a condensation technique had a significantly lower mean compressive strength (P less than 0.05) and value of Weibull modulus (P less than 0.05) than specimens prepared using a smearing technique. No significant differences in the overall mean percentage area occupied by porosity and mean number of pores were demonstrated (P greater than 0.05) between the two placement techniques. Specimens prepared using the smearing technique, however, had significantly smaller mean maximum pore diameters (P less than 0.05) than those prepared using the condensation technique. It is therefore desirable when placing composite resins to reduce to a minimum handling procedures that are likely to influence the levels of porosity within the material.

Composite Resins↗
PubMed1993

Investigation on the compressive strength of several gypsum products dried by microwave oven with different programs.

Different programs in a microwave oven were selected to dry several gypsum products. A type III dental stone (Moldano), a type IV high-strength dental stone (Glastone) and a type III partial denture casting investment (Multi-vest) were selected. Specimens of the products were dried by microwave radiation set at the lowest and highest power levels for 5 and 15 minutes. The dried specimens were tested at intervals of 2, 4, 24, and 48 hours for compressive strength. Specimens dried in ambient room air were used as the control group. A statistical analysis of the test results was performed with Student's t-test at p < or = 0.05 level. Microwave radiation at the highest power level resulted in a decrease in the compressive strength of type IV dental stone (Glastone), whereas the values of the other gypsum products did not differ at any time interval from values attained for the air-dried specimens. The 2-hour low power test of the investment (Multi-vest) had a higher compressive strength than the air-dried specimens after 24 hours.

Air↗
PubMed1991

Incorporation of adhesive liners in amalgam: effect on compressive strength and creep.

This study evaluated the effects of two adhesive resin liners (Panavia EX and Amalgambond) on the compressive strength and creep rate of a single composition high-copper amalgam alloy (Tytin). Cylindrical specimens were prepared by dead-loading or hand-condensing amalgam in a Teflon mold which was unlined, lined with Panavia EX, or lined with Amalgambond. Compressive strength specimens were tested at 1 hour, 24 hours, and 7 days after preparation. Creep specimens were tested at 7 days. The adhesive resin liners did not significantly affect the strength of the Tytin specimens prepared by dead-loading (P greater than 0.05). The Panavia EX significantly reduced the strength of the Tytin specimens prepared by hand-condensing (P less than 0.05). The creep rate was not significantly affected by either resin liner.

Analysis of Variance↗
PubMed2001

Spinal posture and prior loading history modulate compressive strength and type of failure in the spine: a biomechanical study using a porcine cervical spine model.

OBJECTIVE: The purpose of this study was to investigate the effect of posture and loading history on the compressive strength and site of failure in the spine. DESIGN: An in vitro experiment was performed using a porcine cervical model that provided a homogeneous population of young healthy spines. BACKGROUND: The distribution of stresses amongst the many load bearing tissues of the spine is altered throughout the day by posture and the history of loading, but it is not clear how this modulates tissue damage or the risk of injury. METHODS: 48 porcine cervical spines were harvested and dissected into motion segments containing two vertebrae and the intervening disc (C3/4 and C5/6). Compressive loads and rotational torques (flexion/extension) were applied so that the effects of four loading histories (hydrated, neutral dehydration, flexed dehydration, superhydrated) and two failure postures (neutral, flexed) could be examined. Levels of dehydration were based on those reported over the course of a day. Dissection techniques and X-rays were used to document tissue damage. RESULTS. Specimens had a lower yield point (43--63%) and ultimate compressive strength (23--47%) when in a flexed posture than when in a neutral posture. When injured in a neutral posture, superhydrated specimens had a lower strength (22--29%) than dehydrated specimens. Loading history also modulated the site of failure. CONCLUSIONS: The spine may be more prone to injury early in the morning when the discs are at their greatest level of hydration and/or when they are in a fully flexed posture.

Animals↗
PubMed2000

Effects of four mixing methods on setting expansion and compressive strength of six commercial phosphate-bonded silica investments.

Six commercial phosphate-bonded silica investments were mixed with four different mixing methods such as hand, two conventional blade-driven vacuum mixers and a new planetary mixing device, and examined for their setting expansion and compressive strength. The two properties often altered, depending upon the mixing method and the investment. The setting expansion of three investments were significantly affected by the mixing method while those of the other three were not. Compressive strength of all six investments varied by changing the mixing method. It is emphasized here that a mixing method and mixing condition must be properly set for each investment to improve the fit of the final metallic castings. This study also suggests that the planetary mixing device is a useful substitute for conventional blade-driven vacuum mixers.

Compressive Strength↗
PubMed2004

[Orthogonal test analysis of compressive strength of porous hydroxylapatite prepared by gel-casting process].

Porous hydroxylapatite (HA) has excellent osseous inductive ability. It has been prepared by gel-casting process, which is feasible and can make complex ceramic material. According to the result of orthogonal test based on the compressive strength, the order and the level of the factors, including monomer HA, initiator MBAM, catalyst APS and water, were dealt with. The effects of drying and sintering technique on the properties of porous hydroxylapatite were also researched. The results showed that the order of every factor in the gel-casting process is as follows, AM-APS, MBAM, H2O. Based on the determined level of each factor, the suitable slurry constituents and drying and sintering technologies were selected, and the porous hydroxylapatite with compressive strength of 6-7 MPa was produced.

Biocompatible Materials↗
PubMed2003

Finite element models predict in vitro vertebral body compressive strength better than quantitative computed tomography.

The correlation between bone mineral density and vertebral strength is not based on mechanical principles and thus the method cannot reflect the effects of subtle geometric features and densitometric inhomogeneities that may substantially affect vertebral strength. Finite element models derived from quantitative computed tomography (QCT) scans overcome such limitations. The overall goal of this study was to establish that QCT-based "voxel" finite element models are better predictors of vertebral compressive strength than QCT measures of bone mineral density with or without measures of cross-sectional area. QCT scans were taken of 13 vertebral bodies excised from 13 cadavers (L1-L4; age: 37-87 years; M = 6, F = 7) and used to calculate bone mineral density (BMD(QCT)). The QCT voxel data were converted into linearly elastic finite element models of each vertebra, from which measures of vertebral stiffness and strength were computed. The vertebrae were biomechanically tested in compression to measure strength. Vertebral strength was positively correlated with the finite element measures of strength (r(2) = 0.86, P < 0.0001) and stiffness (r(2) = 0.82, P < 0.0001), the product of BMD(QCT) and vertebral minimum cross-sectional area (r(2) = 0.65, P = 0.0008), and BMD(QCT) alone (r(2) = 0.53, P = 0.005). These results demonstrate that highly automated "voxel" finite element models are superior to correlation-based QCT methods in predicting vertebral compressive strength and therefore offer great promise for improvement of clinical fracture risk assessment.

Adult↗
PubMed1996

Effect of wet and dry cellulose ring liners on setting expansion and compressive strength of a gypsum-bonded investment.

Effective setting expansion of gypsum-bonded investments is influenced by many variables. The purpose of this study was to determine the effect of using either water-saturated or dry cellulose ring lining material on (1) the fit of castings on a steel die and (2) the compressive strengths of investment cores using either type of liner. The mean gingival space in the water-saturated liner group was 0.241 +/- 0.048 mm and was 0.071 +/- 0.029 mm in the dry liner group (p < 0.001). The compressive strengths of investment cores from the dry liner group were 36.5% greater than those of cores from the water-saturated liner group. The results demonstrated that the use of dry liners may improve the fit of castings to dies.

Calcium Sulfate↗
PubMed1999

[Determination of high temperature compressive strength and refractory degree of die material compatible with slip casting core of sintered titanium powder].

OBJECTIVE: The refractory die is the precondition for developing slip casting core of sintered powder. This study is to determine the high temperature properties of the refractory die material compatible with slip casting core. METHODS: To prepare three cylindrical specimens (phi 10 x 15 mm) and determine their compressive strength at 1000 degrees C: to make four specimens in flat-topped cone for determining the practical refractory degree by decreasing the pressing temperatures in a sequence of 1420, 1400, 1350 and 1100 degrees C. RESULTS: The compressive strength of this material was 17.8 MPa at 1000 degrees C. Its practical refractory degree was higher than 1100 degrees C. CONCLUSION: The high temperature properties of the refractory die material that we developed meet the demand of slip casting core of sintered powder.

Compressive Strength↗
PubMed1990

Compressive strength of autologous and allogenous bone grafts for thoracolumbar and cervical spine fusion.

The selection of the bone graft type for stabilization of spinal fusion depends on availability, the clinical situation, and the desired mechanical stability. The authors determined the potential immediate postoperative compressive strength of various types of bone grafts under axial compression on a material testing machine. The fibular strut graft (5,070 +/- 3,250 N, mean +/- standard deviation [SD]) was significantly stronger (P less than 0.05) than the anterior (1,150 +/- 487 N) and posterior (667 +/- 311 N) iliac crest grafts, and the rib grafts (452 +/- 192 N). Hydroxyapatite grafts with a pore size of 200 mu were significantly stronger (P less than 0.05) than those with a pore size of 500 mu (1,420 +/- 480 N versus 338 +/- 78 N). Ethylenoxide sterilization had no significant effect on the immediate compressive strength. Bicortical and tricortical Bailey-Badgley and Cloward bone grafts also were compared. Results showed that all cervical graft types may be sufficiently strong to support sizable loads.

Aged↗
PubMed1994

[Effect of aging on compressive strength of lumbar trabecular bone in hemodialyzed and non-hemodialyzed patients].

In order to clarify the effect of aging and bone mineral content on the compressive strength of lumbar trabecular bone, the third lumbar vertebral body (L3) was analyzed by mechanical and chemical tests in hemodialyzed (HD) and non-hemodialyzed (non-HD) patients. L3 was removed from 40 non-HD patients and 10 HD patients at autopsy. Cylindrical trabecular bone samples from L3 were analyzed by compression test, relaxation test and Brinel's test. Bone mineral content was based on Ca, P and Mg measured after incineration of the samples. In non-HD patients, a significant age-related decrease was observed in both Brinel's hardness (HBS) (r = -0.470) and Young's modulus (Qo) (r = -0.527), and there was a significant increase in age and viscoelasticity (B) (r = 0.439). HBS and Qo in about 50 percent of HD patients were larger than those in non-HD patients. C-PTH in HD patients showed a significant positive correlation with HBS and with Qo. Bone Ca content of the 50-69-year-old non-HD patients was 81 percent of that in the patients in their 40s and the content in the patients aged over 70 years was 55.5 percent of that in the patients in their 40s. In non-HD patients, the P/Ca and Mg/Ca weight ratios of bone were nearly constant regardless of age or sex. However, bone P/Ca and Mg/Ca weight ratios were relatively large in 80 percent of the HD patients. Bone Ca content exhibited a significant positive correlation with HBS (r = 0.399) and with bone mineral density measured by quantitative computed tomography (QCT) (r = 0.819). In conclusion, it was indicated that bone mineral content and compressive strength of trabecular bone decreased with aging, and that biomechanical competence in HD patients was much more prominent along with elevated C-PTH.

Adult↗
PubMed1979

The compressive strength of lumbar vertebrae.

Values for the compressive breaking load of lumbar vertebrae at physiological strain rates show enormous scatter across the population, ranging from 0.8 kN to nearly 16 kN. Increase in strength was found at faster strain rates, but differences in compressive strength between upper and lower lumbar vertebrae were not significant. Hydraulic strengthening does not appear to contribute to the compressive strength at the strain rates studied.

Adolescent↗
PubMed1988

Comparison of the compression strength of human vertebral bodies with the mass and density of apatite: a study by 31P NMR spectroscopy.

The force needed to fracture individual human thoracic and lumbar vertebral bodies is compared with the mass and density of apatite. 31P NMR spectrometry was used to quantify the apatite, because it permits the mineral content of bone to be determined noninvasively with minimal nonspecific interference from the organic matrix or from variations in composition of the marrow. Experiments were performed with bones of similar structure and function from a single individual with no history of trabecular fractures, to compensate for the effects of the other variables that affect bone strength. The coefficient of correlation between compression strength and the volume density (i.e., g/cm3) of apatite was 0.95. The correlation of strength with the mass (i.e., grams) of apatite in a vertebral body also was reasonably good, r = 0.82, but correlations with areal density (i.e., g/cm2) and linear density (i.e., g/cm) were much poorer.

Apatites↗
PubMedDate not supplied

Compressive strength of calcium carbonate and hydroxyapatite implants after bone-marrow-induced osteogenesis.

Natural coral and structurally similar porous hydroxyapatite (HA) have been used as bone substitutes. They are not osteoinductive but bone formation can be induced by marrow cells, even in extraosseal sites. In our previous study we induced bone formation in porous coral and HA after having implanted the materials in intramuscular pockets in rat. New bone formed only in HA or coral implants soaked with marrow cells; fibrous tissue ingrowth alone was observed in the controls (without marrow). In the present study we examined the effect of tissue ingrowth on the mechanical properties of coral and HA implants obtained in a similar process to that used before. At 12 weeks the compressive strength of HA was higher in the marrow group than in the controls; it was also higher than that of the wet unimplanted material. The HA blocks did not show resorption. Coral resorbed quickly and lost its compressive strength, which was originally higher than in HA. At three weeks the marrow group was stronger than the control specimens. After six weeks only the marrow group, but not the controls, could be tested. Bone ingrowth seemed to maintain the strength of the coral implant even if it was dissolving. The mechanical strength of both materials was comparable to that of cancellous bone.

Animals↗
PubMed1976

Bone compressive strength: the influence of density and strain rate.

The compressive strength of bone is proportional to the square of the apparent density and to the strain rate raised to the 0.06 power. This relationship is applicable to trabecular and compact bone, and provides clinical guidelines for predicting bone strength on the basis of x-ray and densitometric examination.

Animals↗