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At least 127 records · Page 7Linked to original sources
PubMed1990

[Deformation phenomena occurring during compression. III. Changes of maximal compression strength in quasi-static condition].

Four materials of different properties in respect of compressibility, lactose, sodium chloride, microcrystalline cellulose (Avicel PH 101) and so-called simple granulate were investigated. In function of time and that of actual pressing force decrease of axial force on upper punch were measured in quasi-state. Evaluating relations it was established that both pressing time and pressing force had influence on deformation structural changes occurring inside compressed form. Furthermore, summing up of results showed that useful conclusions could be drawn from diagrams--which represented decrease of force--to compressibility properties of materials too.

Cellulose↗
PubMed1995

Parathyroid hormone (1-34) increases vertebral bone mass, compressive strength, and quality in old rats.

Human parathyroid hormone 1-34 (PTH) exerts an anabolic effect on bone in younger rats. The aim of the present study was to examine the effect of PTH on vertebral bone in 2-year-old male rats. The rats were treated with daily injections of 15 nmol/kg PTH or vehicle (V) for 56 days. Tetracycline and calcein were injected on day 15 and day 40 of the treatment period, respectively. The PTH treatment did not influence the body weights of the rats, the volumes of whole vertebra, or the vertebral body heights. However, the PTH treatment induced profound changes in the bone structure. Histomorphometric analyses of the vertebral bodies (L-6) revealed an approximate doubling of the cancellous bone volume after PTH treatment from 24.6 +/- 1.3% to 54.9 +/- 2.0% (p < 0.001) as well as a doubling of the trabecular thickness while the bone surface/bone volume decreased by 60%. PTH treatment also increased bone formation as indicated by an increase in mineral apposition rate (from 0.42 +/- 0.01 to 0.89 +/- 0.01 microns/day, p < 0.01), increased mineralizing surface (from 7.8 +/- 1.4 to 43.8 +/- 1.9%, p < 0.01) and an increase in both volume-related and surface-related bone formation rates (5 and 11 times, respectively). The biomechanical properties were analyzed using standardized bone specimens from the vertebral bodies of L-4 by applying cranial-caudal compression in a materials testing machine. The PTH treatment induced a substantial increase in the strength of the vertebral body: ultimate load increased by 66%, ultimate stiffness by 47%, and energy absorption by 98%. The increase in vertebral body strength was also evident after normalizing the parameters to the cross sectional area and the ash content of the vertebral body specimens. PTH treatment increased ultimate stress from 26 +/- 3 to 44 +/- 3 N per mm2 (p < 0.01) and increased ultimate load normalized to ash content per mm specimen height from 59 +/- 4 to 72 +/- 4 N (mm/mg) (p < 0.05). The PTH treatment induced an increase in dry defatted bone density and ash density of both the vertebral body specimen (L-4) and the whole vertebra (L-5). In conclusion, PTH showed a remarkable ability to stimulate bone formation in the vertebral body of old rats. Furthermore, the biomechanical analysis revealed an enhanced compressive bone strength, even after correction for the increased bone mass, indicating an improved bone quality after the PTH treatment.

Aging↗
PubMed1998

Relation between image-based assessment of distal radius trabecular structure and compressive strength.

OBJECTIVE: To investigate the degree to which an image-based assessment of trabecular bone structure can predict bone strength. METHODS: Transaxial high-resolution magnetic resonance imaging (MRI) images and peripheral quantitative computed tomography (pQCT) images were obtained for a set of 9 isolated radii. Trabecular bone was segmented from fat, and indices relating to the connectivity of the bone network and the size of the marrow space were derived. Bone mineral density was also assessed in each radius by means of dual-energy x-ray absorptiometry and pQCT. Each bone was subjected to a mechanical load consistent with a fall from a standing height, and measures of density and trabecular structure were compared to the compressive load. RESULTS: In the 9 bones tested, measures of bone mineral density explained approximately 50% of the variability with load (0.52 < r2 < 0.57, p < 0.03), and indices relating to the size of the marrow spaces explained an additional 25% to 30% of the variance. This held true whether the indices quantifying the marrow space were derived from the MRI images (r2 = 0.70, p = 0.03) or the pQCT images (r2 = 0.82, p = 0.006). CONCLUSION: Our findings suggest that image-based assessments of trabecular bone structure relate to bone strength in vitro.

Absorptiometry, Photon↗
PubMed1983

Compressive strength of tibial cancellous bone. Instron and osteopenetrometer measurements in an autopsy material.

The topographic variation of proximal tibial cancellous bone strength was investigated in 12 knees from routine autopsies. Samples from eight knees were tested to compressive failure in an Instron material testing machine, and four knees were tested with the osteopenetrometer, an instrument developed for intraoperative measurement of bone strength. Ultimate stress, elastic modulus and energy absorption of the bone were calculated from the Instron-curves. Mechanical properties varied considerably from knee to knee, but the topographic patterns were remarkably constant. The medial condyle showed the highest strength, the intercondylar area the lowest. On the medial side the bone was strongest at the front, while on the lateral side the reverse was true. The two horizontal levels tested did not differ significantly. The osteopenetrometer measurements closely modelled the pattern of ultimate stress.

Adult↗
PubMed1994

Effects of glucocorticoids on skeletal growth in rabbits evaluated by dual-photon absorptiometry, microscopic connectivity and vertebral compressive strength.

The effects of corticosteroid on bone were examined in female growing rabbits treated with 0.7 mg/kg per day prednisolone for 5 months. The evolution of whole-body total bone mineral measured by dual-photon absorptiometry showed a significant difference between the prednisolone-treated group and the control group from the first to the fifth month. The histomorphometric profile of corticosteroid-induced osteoporosis was observed, in particular the lower bone volume and thinner and fewer trabecular plates. Mechanical tests are possible on rabbit vertebrae and showed a very significant difference in bone strength between the prednisolone-treated and control groups, and a good correlation between mechanical tests and histomorphometric or densitometric results. This bone corticosteroid model shows that vertebral compression tests are possible on rabbit lumbar vertebrae. It may contribute to a better evaluation of corticosteroid treatments.

Absorptiometry, Photon↗
PubMed1988

Iliac crest trabecular bone volume as predictor for vertebral compressive strength, ash density and trabecular bone volume in normal individuals.

Whole vertebral bodies (L2) and cylindrical trabecular bone samples from the central part of the first lumbar vertebral body (L1) were obtained from 42 normal individuals aged 15-87 years (27 females and 15 males). These bone samples were analyzed by a compression test, and maximum load and stress values were calculated from the load deformation curves. After the compression the ash density of the samples was estimated. For histomorphometric measurements trabecular bone samples from L1 (n = 42) and from the iliac crest (n = 25) were embedded undecalcified, cut in 8 microns sections and stained with Masson trichrome. Trabecular bone volume (TBV) was measured by means of point counting. A significant and parallel age-related decrease in TBV was found in the iliac crest and in the vertebral trabecular bone specimens (p less than 0.001). Highly significant positive correlations were observed between iliac crest TBV and the quantitative vertebral parameters: TBV and ash density (p less than 0.001). Furthermore, the iliac crest TBV was significantly correlated to the qualitative vertebral strength parameters: Vertebral trabecular bone stress, whole vertebral body stress and whole vertebral body load (p less than 0.001). Multiple regression analyses revealed that the vertebral trabecular bone strength was unrelated to bone volume when the influence of age was considered but significantly inversely correlated to age when bone volume was taken into account. This indicates that age-related structural changes other than bone mass affect the vertebral bone strength strongly.

Adolescent↗
PubMed1980

[Compression strength of human radii (author's transl)].

500 radius segments of a certain length of the corpses of 6 female and 36 male persons (medium age: 54.4 years) were chosen to determine the fracture load and the ultimate breaking stress by means of a machine testing the pressure power in a compression test. The mean fracture load is 7371 N and the average ultimate breaking stress 38 MPa. Fracture load and ultimate breaking stress of preserved specimens are significant higher than those of non preserved specimens. The bone, therefore, becomes more fragile by the preservation. Fracture load and ultimate breaking stress decrease distinctly with advancing years. The ends of the radii are clearly less capable of being strained than the middle parts of the shafts. The fracture load of the radius increases with the total length.

Adult↗
PubMed1998

Compressive strength of interbody cages in the lumbar spine: the effect of cage shape, posterior instrumentation and bone density.

One goal of interbody fusion is to increase the height of the degenerated disc space. Interbody cages in particular have been promoted with the claim that they can maintain the disc space better than other methods. There are many factors that can affect the disc height maintenance, including graft or cage design, the quality of the surrounding bone and the presence of supplementary posterior fixation. The present study is an in vitro biomechanical investigation of the compressive behaviour of three different interbody cage designs in a human cadaveric model. The effect of bone density and posterior instrumentation were assessed. Thirty-six lumbar functional spinal units were instrumented with one of three interbody cages: (1) a porous titanium implant with endplate fit (Stratec), (2) a porous, rectangular carbon-fibre implant (Brantigan) and (3) a porous, cylindrical threaded implant (Ray). Posterior instrumentation (USS) was applied to half of the specimens. All specimens were subjected to axial compression displacement until failure. Correlations between both the failure load and the load at 3 mm displacement with the bone density measurements were observed. Neither the cage design nor the presence of posterior instrumentation had a significant effect on the failure load. The loads at 3 mm were slightly less for the Stratec cage, implying lower axial stiffness, but were not different with posterior instrumentation. The large range of observed failure loads overlaps the potential in vivo compressive loads, implying that failure of the bone-implant interface may occur clinically. Preoperative measurements of bone density may be an effective tool to predict settling around interbody cages.

Biomechanical Phenomena↗
PubMed1989

The predictive value of quantitative computed tomography for vertebral body compressive strength and ash density.

Whole lumbar vertebral sections (L2 and L3) were obtained from 30 elderly individuals aged 43-95 years, mean 81 years (13 females, 17 males). None of the subjects had had malignant diseases. Quantitative computed tomography (QCT) was performed on an EMI 7070 scanner. One 8 mm slice parallel to the end-plates was obtained from the center of each vertebral body. The trabecular bone mass in each slice was outlined interactively by means of a tracer-ball. A CT-histogram was recorded inside this area, and average CT-values were expressed in Hounsfield Units (HU). The whole vertebral body (L2) was compressed in a materials testing machine. From the central part of L3, vertical cylindrical pure trabecular bone specimens were obtained. The biomechanical competence of these specimens was also assessed by means of a materials testing machine. Finally, all bone specimens were incinerated for determination of apparent ash-density. Highly significant positive correlations were found between average CT-values and (a) stress values of the trabecular bone (r = 0.81, p less than 0.001) and (b) ash-density of the pure trabecular bone (r = 0.81, p less than 0.001). Furthermore, a significant positive correlation was found between CT-values and (a) total vertebral body load (r = 0.72, p less than 0.001), (b) total vertebral body stress (load/cross-sectional area) (r = 0.55, p less than 0.001) and (c) ash-density of the whole vertebral body (r = 0.76, p less than 0.001). It is concluded that quantitative computed tomography gives valid predictions of both vertebral trabecular bone mass and mechanical competence.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2000

Whisker-reinforced dental core buildup composites: effect of filler level on mechanical properties.

The strength and toughness of dental core buildup composites in large stress-bearing restorations need to be improved to reduce the incidence of fracture due to stresses from chewing and clenching. The aims of the present study were to develop novel core buildup composites reinforced with ceramic whiskers, to examine the effect of filler level, and to investigate the reinforcement mechanisms. Silica particles were fused onto the whiskers to facilitate silanization and to roughen the whisker surface for improved retention in the matrix. Filler level was varied from 0 to 70%. Flexural strength, compressive strength, and fracture toughness of the composites were measured. A nano-indentation system was used to measure elastic modulus and hardness. Scanning electron microscopy (SEM) was used to examine the fracture surfaces of specimens. Whisker filler level had significant effects on composite properties. The flexural strength in MPa (mean +/- SD; n = 6) increased from (95+/-15) for the unfilled resin to (193+/- 8) for the composite with 50% filler level, then slightly decreased to (176+/-12) at 70% filler level. The compressive strength increased from (149+/-33) for the unfilled resin to (282+/-48) at 10% filler level, and remained equivalent from 10 to 70% filler level. Both the modulus and hardness increased monotonically with filler level. In conclusion, silica particle-fused ceramic single-crystalline whiskers significantly reinforced dental core buildup composites. The reinforcement mechanisms appeared to be crack deflection and bridging by the whiskers. Whisker filler level had significant effects on the flexural strength, compressive strength, elastic modulus, and hardness of composites.

Bisphenol A-Glycidyl Methacrylate↗