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At least 109 records · Page 6Linked to original sources
PubMed1993

Erosion and compressive strength of hybrid glass ionomer cements when light activated or chemically set.

It is claimed that light-activated hybrid glass ionomer cements offer advantages over the conventional glass ionomer lining materials. The compressive strengths and erosion rates of two hybrid glass ionomer lining cements, when light activated and chemically set, were compared with conventional glass ionomer cements. The results demonstrated that the erosion rates of the light-activated materials were comparable with those of the conventional materials. The conventional material, Ketac-Bond, was stronger than the light-activated hybrids. When the hybrid materials were allowed to set chemically alone, their performance was inferior to the conventional glass ionomer lining cements.

Glass Ionomer Cements↗
PubMed2001

Compressive strength of interocclusal recording materials.

Many materials are used for making interocclusal records to mount casts on dental articulators. The strength of these materials during the compressive forces encountered in the mounting process is important because any deformation will cause incorrect occlusal relationships. This investigation compared the deformation of 4 thicknesses (2 mm, 5 mm, 10 mm, 20 mm), when subjected to 25 N compressive force, of 3 interocclusal recording materials: condensation silicone, recording wax, and rubber-based polyvinylsiloxane. Significant differences were recorded for all materials of 20 mm, 10 mm and 2 mm thickness. However, there was no significant difference among the 5 mm groups. Interocclusal records should be made of a minimal thickness, using a recording material which exhibits minimal distortion during compression.

Analysis of Variance↗
PubMed1989

Increase in compressive strength of glass ionomer restorative materials with respect to time: a guide to their suitability for use in posterior primary dentition.

Glass ionomer restorative cements have been used in anterior restorations for a number of years but have not been considered strong enough for use in posterior restorations. The compressive strengths of a number of materials currently available were measured at 30 min, 1 hour and 24 hours. It was concluded that some of the materials might be considered for posterior restorations in deciduous teeth where no other considerations, such as radiopacity, apply.

Dental Cements↗
PubMed1984

Compressive strength of implanted porous replamineform hydroxyapatite.

Porous replamineform hydroxyapatite is a nontoxic, nonallergenic synthetic ceramic currently under investigation as an implant for restoration of atrophic edentulous ridges. Previous studies have demonstrated its capacity to permit the ingrowth of bone into its pores. Evaluation of the material was carried out to determine its eventual compressive strength following implantation. Bony penetration results in a significant increase in strength, judged to be sufficient for support of dentures.

Animals↗
PubMed1989

[Comparison of brush and moulding techniques in condensation of porcelain work, through shrinkage, compression strength and SEM images].

A general character of porcelain is the firing shrinkage which creates some problems in the fabrication of porcelain restorations. To overcome this matter, a well condensation which increases the strength of porcelain and decreases the shrinkage, is recommended. Taking this point into consideration, a moulding system is developed and it is found that pressing the porcelain in a mould, minimized the shrinkage, strengthened the structure and increased the compression strength. As a result we can say that this technique has important advantages in porcelain work.

Dental Casting Technique↗
PubMed2000

Ultrasonic parameters and relationship between compressive strength, microstructure of gall bladder stones.

Patients with symptomatic stones are at a great risk for complications and these complications are a major cause of morbidity. The gall bladder stones may have a complex structure and variable composition. In the present investigation stones have been grouped into three categories namely cholesterol, bilirubinate and mixed, and a correlation between the surface structure, ultrasonic parameters and compressive strength is estimated. A double-probe through-transmission technique was used for the ultrasonic parameters study, a universal testing instrument for hardness and a scanning electron microscope (SEM) for microstructure study. Gall bladder stones of mixed type with higher ultrasonic velocity, less attenuation and higher crushing strength were found to be more difficult to break in comparison to other types of stones. SEM of mixed type stones showed rough surface as compared to bilirubinate and cholesterol stones. The results obtained as well as the relationship might be useful in the design of a focussed ultrasonic 0lithotripter.

Cholelithiasis↗
PubMed1997

Ex vivo estimation of thoracolumbar vertebral body compressive strength: the relative contributions of bone densitometry and vertebral morphometry.

The estimation of vertebral fracture risk in individuals with suspected osteopenia is commonly based on measurements of lumbar spine bone density. The efficacy of vertebral size and deformity, as assessed by vertebral morphometry, in the prediction of fractures has been less studied. In an ex vivo investigation the regional relationships between vertebral size, vertebral deformity, bone density and compressive strength throughout the thoracolumbar spine were examined. In 16 vertebral columns (T1-L5) the bone mineral content (BMC) and bone mineral density (BMD) of each segment were measured using lateral projection dual-energy X-ray absorptiometry, and the vertebral cancellous density (VCD) and mid-vertebral cross-sectional area (CSA) measured using quantitative computed tomography. Vertebral body heights were determined from mid-sagittal CT scans, and vertical height ratios calculated for each segment. The failure load and failure stress of the isolated vertebral bodies were determined using a material testing device. Separate analyses were performed for the upper (T1-4), middle (T5-8) and lower (T9-12) thoracic, and lumbar (L1-5) segments. In all regions, failure load was strongly correlated with BMD (r = 0.82-0.86), moderately correlated with VCD (r = 0.60-0.71) and vertebral height (r = 0.22-0.49), and poorly correlated with the height ratios (r = 0.04-0.33). Failure stress was best predicted by BMD (r = 0.73-0.78) and VCD (r = 0.70-0.78) but was poorly correlated with all morphometric variables (r = 0.01-0.33). The segmental correlations between BMD and VCD ranged form r = 0.49 to r = 0.79. For all regions, BMD and VCD were included in the stepwise regression models for predicting failure load and failure stress. Either the mid-vertebral height or CSA were included in all the failure load models, while mid-vertebral height was included in only one of the failure stress models. The results suggest that vertebral deformity and size (as assessed by vertebral morphometry) make only a minor contribution to the prediction of vertebral strength additional to that provided by bone densitometry alone. The consistent regional relationships between variables appear to support the practice of global fracture risk assessment based on lumbar spine densitometry.

Adult↗
PubMed1998

[Effect of various cylinder diameters of implants for lumbar inter-corporeal spinal fusion on compressive strength on the FSU model].

Anterior lumbar interbody fusion (ALIF) has evolved as a minimally invasive technique for treating lumbar instability caused by degenerative lumbar disc disease. A practical surgical method is the lateral retroperitoneal approach in which cylindrical implants are inserted in the intervertebral space. The optimal diameter of these implants remains unclear. The purpose of this biomechanical study was to investigate the influence of implant diameter on selected mechanical properties of the functional spinal units (FSU). In fresh frozen bovine FSU the bone density was first determined and cylindrical implants were then inserted. The FSU were then tested under compression loading in a material-testing machine. A tendency of the "failure loads" to decrease with increasing cylinder diameter was observed. The study reveals a strong correlation between bone density and loading capacity, with higher loads being sustained by the more strongly mineralized bone. In contrast to homogeneous material, in an FSU, larger cylinder diameter does not result in an increase in compression strength.

Animals↗
PubMed1989

[Axial compressive strength of amalgam fillings in correlation with cavity preparation].

UNLABELLED: Different types of cavities were prepared in 96 model teeth: simple preparations without ledges and with Amalgapins, slots or a post; proximal box preparations with an occlusal ledge, and box preparations with or without Amalgapins or slots. The amalgam fillings were subjected to axial load by means of a Zwick machine until the filling or the tooth fractured. RESULTS: --Occlusal ledges and box preparations allow high load values. --Surprisingly high loads can be placed on simple preparations without ledges but with a post. --Preparations without ledges but with Amalgapins or slots rate lowest. --In box preparations and preparations with ledges, Amalgapins or slots fail to offer any significant increase in compressive strength.

Dental Amalgam↗
PubMed2001

Effect of endplate conditions and bone mineral density on the compressive strength of the graft-endplate interface in anterior cervical spine fusion.

STUDY DESIGN: Destructive compression tests and finite element analyses were conducted to investigate the biomechanical strength at the graft-endplate interface in anterior cervical fusion. OBJECTIVES: To investigate the effect of endplate thickness, endplate holes, and bone mineral density of the vertebral body on the biomechanical strength of the endplate-graft interface in an anterior interbody fusion of the cervical spine. SUMMARY OF BACKGROUND: Subsidence of the graft into the vertebral body is a well-known complication in anterior cervical fusion. However, there is no information in the literature regarding the compressive strength of the graft-endplate interface in relation to the endplate thickness, holes in the endplate, and bone mineral density of the vertebral body. METHODS: Biomechanical destructive compression tests and finite element analyses were performed in this study. Cervical vertebral bodies (C3-C7) isolated from seven cadaveric cervical spines (age at death 69-86 years, mean 79 years) were used for compression tests. Bone mineral density of each vertebral body was measured using a dual energy radiograph absorptiometry unit. Endplate thickness was measured using three coronal computed tomography images of the middle portion of the vertebral body obtained using a computer-assisted imaging analysis. Then each vertebral body was cut into halves through the horizontal plane. A total of 54 specimens, consisting of one endplate and half of the vertebral body, were obtained after excluding eight vertebrae with gross pathology on plain radiograph. Specimens were assigned to one of three groups with different endplate conditions (Group I, intact; Group II, partial removal; and Group III, complete removal) so that group mean bone mineral density became similar. Each endplate was slowly compressed until failure using an 8-mm-diameter metal indenter, and the load to failure was determined as a maximum force on a recorded force-displacement curve. The effect on the strength of the graft-endplate interface of various hole patterns in the endplate was studied using a finite element technique. The simulatedhole patterns included the following: one large central hole, two lateral holes, two holes in the anterior and posterior portion of the endplate, and four holes evenly distributed from the center of the endplate. Stress distribution in the endplate was predicted in response to an axial compressive force of 110 N, and the elements with von Mises stress greater than 4.0 MPa were determined as failed. RESULTS: The endplate thickness and bone mineral density were similar at all cervical levels, and the superior and inferior endplates had similar thickness at all cervical levels. There was no significant association between bone mineral density and endplate thickness. Load to failure was found to have a significant association with bone mineral density but not with endplate thickness. However, load to failure tends to decrease with incremental removal of the endplate, and load to failure of the specimens with an intact endplate was significantly greater than that of the specimens with no endplate. Finite element model predictions showed significant influence of the hole pattern on the fraction of the upper endplate exposed to fracture stress. A large hole was predicted to be more effective than the other patterns at distributing a compressive load across the remaining area and thus minimizing the potential fracture area. CONCLUSION: Results of this study suggest that it is important to preserve the endplate as much as possible to prevent graft subsidence into the vertebral body, particularly in patients with poor bone quality. It is preferable to make one central hole rather than multiple smaller holes in the endplate for vascularity of the bone graft because it reduces the surface area exposed to fracture stresses.

Aged↗
PubMed1999

Diametral and compressive strength of dental core materials.

STATEMENT OF PROBLEM: Strength greatly influences the selection of core materials. Many disparate material types are now recommended for use as cores. Cores must withstand forces due to mastication and parafunction for many years. PURPOSE: This study compared the compressive and diametral tensile strengths of 8 core materials of various material classes and formulations (light-cured hybrid composite, autocured titanium containing composite, amalgam, glass ionomer, glass ionomer cermet, resin-modified glass ionomer, and polyurethane). MATERIAL AND METHODS: Materials were manipulated according to manufacturers' instructions for use as cores. Mean compressive and diametral strengths with associated standard errors were calculated for each material (n = 10). Analyses of variance were computed (P <.0001) and multiple comparisons tests discerned many differences among materials. RESULTS: Compressive strengths varied widely from 61.1 MPa for a polyurethane to 250 MPa for a resin composite. Diametral tensile strengths ranged widely from 18.3 MPa for a glass ionomer cermet to 55.1 MPa for a resin composite. Some resin composites had compressive and tensile strengths equal to those of amalgam. CONCLUSION: Light-cured hybrid resin composites were stronger than autocured titanium containing composites. The strengths of glass ionomer-based materials and of a polyurethane material were considerably lower than for resin composites or amalgam.

Analysis of Variance↗
PubMed2001

Statin given perorally to adult rats increases cancellous bone mass and compressive strength.

Recently, it has been shown that statins increased cancellous bone formation and volume in 3-month-old rats and induced a minor decrease in osteoclast number. In the present study, one-year-old female rats were given simvastatin (10 mg/kg) or placebo daily for 3 months by a gastric tube. Specimens, 2.0 mm high, were cut transversely from the 5th lumbar vertebral body. The cancellous bone core diameters within the cortical shell of each specimen were delineated by a micro-CT scanner and then the cancellous bone was compressed in a materials testing machine between an upper and a lower platen with a diameter corresponding to the diameter of the cancellous bone core of each specimen. The cancellous bone volume was determined histomorphometrically on transverse sections. The cancellous bone volume in the simvastatin group (52.7 +/- 1.6%, mean value +/- SEM) was increased by 23% compared with the placebo group (42.8 +/- 1.7%). The compressive stress of the cancellous bone from the simvastatin group (31.8 +/- 2.7 MPa) was increased by 24% compared with the placebo group (24.1 +/- 1.9 MPa). No changes were found in cortical bone mass and strength after the statin treatment. In conclusion, statin given perorally to adult rats increased cancellous bone mass and increased cancellous bone compressive strength. The cancellous bone was found to possess normal biomechanical competence after the statin treatment.

Administration, Oral↗
PubMed1993

Compression strength of donor bone for posterior lumbar interbody fusion.

Forty-three blocks of allograft bone used clinically for posterior lumbar interbody fusion and twenty-three blocks of xenograft bone from goats and cows were tested in compression and compared with the clinical mechanical requirements of posterior lumbar interbody fusion. Variations in processing methods allowed evaluation of the effects of processing on mechanical strength. Fresh-frozen cancellous bone from Os Bone (Cleveland, OH) failed at an average load of 863 +/- 615 N. Fresh-frozen cancellous bone from the Mid American Tissue Center (Massilon, OH) failed at an average load of 3492 +/- 1720 N. Freeze-dried cancellous bone obtained from the American Red Cross failed at an average load of 1595 +/- 1031 N. Air-dried ethylene oxide sterilized cancellous bone from Os Bone failed at an average load of 1338 +/- 691 N. Air-dried ethylene oxide sterilized cancellous bone from Mid America failed at an average load of 1616 +/- 1157 N. Fresh-frozen tricortical bone from Mid America failed at an average load of 2257 +/- 1081 N. Air-dried ethylene oxide sterilized tricortical bone from Os Bone failed at an average load of 2474 +/- 1928 N. Air-dried ethylene oxide sterilized tricortical bone from Mid America failed at an average load of 2308 +/- 422 N. Bovine Surgibone from Unilab (Hillside, NJ) failed at an average load of 2967 +/- 399 N. Strength of bone in compression was not weakened by freeze drying, air drying, ethylene oxide sterilization, or by incubation at 37 degrees C for 1 week before testing.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
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↗