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PubMed1995

The effect of adhesive luting agent-dentinal surface interactions on compressive strength of two types of all-ceramic crowns.

This research compared the compressive strength of two types of all-ceramic crown (Hi-Ceram and Duceram) as affected by selected luting cements (Zn phosphate, glass ionomer and composite resin cement). Thirty crowns of similar size and shape were constructed (15 crowns of each tested material) to fit a standard posterior tooth preparation. Five crowns from each material were cemented by one of the tested cements. The cemented crowns were loaded until catastrophic failure. A two-way analysis of variance was performed and showed that the type of utilized cement had a significant effect on the compressive strength being that Panevia Ex. resin cement the most effective one followed by glass ionomer and then finally zn phosphate cement. Statistical analysis also showed that Hi-Ceram crowns were more resistant to occlusal load than Duceram.

Aluminum Oxide↗
PubMed1994

Differences between the tensile and compressive strengths of bovine tibial trabecular bone depend on modulus.

The conflicting conclusions regarding the relationship between the tensile and compressive strengths of trabecular bone remain unexplained. To help resolve this issue, we compared measurements of the tensile (n = 22) and compressive (n = 22) yield strengths, and yield strains, of trabecular bone specimens taken from 38 bovine proximal tibiae. We also studied how these failure properties depended on modulus and apparent density. To enhance accuracy, trabecular orientation was controlled, and each specimen had a reduced section where strains were measured with a miniature extensometer. We found that the mean yield strength was 30% lower for tensile loading. However, the difference between individual values of the tensile and compressive strengths increased linearly with increasing modulus and density, being negligible for low moduli, but substantial for high moduli. By contrast, both the tensile and compressive yield strains were independent of modulus and density, with the yield strain being 30% lower for tensile loading. Thus, the difference between the tensile and compressive strengths of bovine tibial trabecular bone depends on the modulus, but the difference between yield strains does not. This phenomenon may explain in part that conflicting conclusions reached previously on the tensile and compressive strengths of trabecular bone since the mean modulus has varied among different studies. Realizing that our data pertain only directly to bovine tibial trabecular bone for longitudinal loading, our results nevertheless suggest that failure parameters based on strains may provide more powerful and general comparisons of the failure properties for trabecular bone than measures based on stress.

Animals↗
PubMed1997

Experimental correlation between T2* and ultimate compressive strength in lumbar porcine vertebrae.

RATIONALE AND OBJECTIVES: The authors used magnetic resonance (MR) imaging to investigate the correlation between T2* measurements of trabecular bone and the ultimate compressive strength of lumbar porcine vertebrae. METHODS: Five pigs that weighted 25-32 kg were sacrificed and imaged with a 1.5-T MR system. T2* of the lumbar vertebrae was measured from gradient-echo images. The vertebrae were individually compressed at a fixed speed in the direction of the spine until crushed. The maximum load a vertebra could resist was recorded. RESULTS: T2* ranged from 7.1 to 14.5 msec. T2* determined from 5-mm coronal sections differed from that determined from axial and sagittal sections (P < .05). Between 2.9 and 5.4 kN of force (296-550 kg) was needed to crush a vertebra. A linear correlation between the ultimate compressive strength and T2* of all vertebrae was observed for all imaging planes and section thicknesses (P < .001, except for 10-mm sagittal images, for which P < .002). The T2* determined for the axial plane showed the best correlation with the ultimate compressive strength (r = -0.83). CONCLUSION: The correlation between T2* values and vertebral strength indicates that MR imaging may potentially be used to predict fracture risks in patients.

Animals↗
PubMed2006

Compressive strength recovery by composite onlays in primary teeth. Substrate treatment and luting agent effects.

OBJECTIVES: To evaluate 1% NaOCl treatment and two resin luting agent effects on compressive strength recovery in composite onlays on primary teeth and to analyze the fractures type. METHODS: Forty sound primary molars crowns were prepared in the standard machine and randomly divided into four groups (n=10): G1 (1% NaOCl/ 30 min+EnForce); G2 (without 1% NaOCl EnForce); G3 (1% NaOCl/ 30 min+Rely X); G4 (without 1% NaOCl+Rely X). The onlays were made using Z250 composite on plaster models. Ten sound teeth were used as control group (CG). All groups were submitted to compression mechanic test in a universal test machine INSTRON at 1mm/min cross-head speed. After that, the data (kgf) were submitted to ANOVA test (alpha=0.05). Finally, the fracture types were classified in a crescent scale (1-5) related with severity degree and submitted to Fisher's Exact Test (p<0.05). Scanning electronic microscope analysis was done in order to illustrate the fractures sites. RESULTS: The values of compressive strength of experimental groups did not differ each others neither from control group (p>0.05). The results from fracture type showed that types 5 and 4 fractures (most severe) present the highest percentage to experimental groups. Conversely, the CG showed higher percentage of fracture types 2 and 3. CONCLUSIONS: This research found that the composite onlays recovered the compressive strength compared to sound teeth, regardless of the substrate treatment and cement agent used. Nevertheless, no group showed similar type of fractures to CG, which had more frequency of less severe fracture types.

Acetone↗
PubMedDate not supplied

Risk of vertebral insufficiency fractures in relation to compressive strength predicted by quantitative computed tomography.

Vertebral insufficiency fractures may result from excessive loading of normal and routine loading of osteoporotic spines. Fracture occurs when the mechanical load exceeds the vertebral compressive strength, i.e., the maximum load a vertebra can tolerate. Vertebral compressive strength is determined by trabecular bone density and the size of endplate area. Both parameters can be measured non-invasively by quantitative computed tomography (QCT). In 75 patients compressive strength (i.e., trabecular bone density and endplate area) of the vertebra L3 was determined using QCT. In addition, conventional radiographs of the spines were analysed for the prevalence of insufficiency fractures in each case. By relating fracture prevalence to strength, three fracture risk groups were found: a high-risk group with strength values of L3 less than 3 kN (kilo Newton) and a fracture risk of 100%, an intermediate group with strength values from 3 to 5 kN and a steeply increasing risk with decreasing strength, and a low-risk group with strength values greater than 5 kN and a fracture risk near 0%. Biomechanical measurements and model calculations indicate that spinal loads of 3 to 4 kN at L3/4 will be common in everyday activities. These data and the results described above suggest that spines with strength values of L3 less than 3 kN are at an extremely high risk of insufficiency fractures in daily life. Advantages of fracture risk assessment by strength determination over risk estimation based on clinically used trabecular bone density measurements are discussed.

Adult↗
PubMed1993

Effect of luting media on the compressive strengths of two types of all-ceramic crown.

This study evaluated the effect of selected luting media on the compressive strength of two types of all-ceramic crown. Tooth preparation was standardized; each preparation had a shoulder width of approximately 1.2 mm, and all internal preparation angles were rounded. Hi-Ceram and Dicor all-ceramic crowns were fabricated and cemented into the preparations with zinc phosphate, glass-ionomer, or composite resin cement. Coronal compressive fracture strengths were determined, using a set of unrestored teeth as a control. There were no statistically significant differences among the mean compressive strengths of the three luting media, and there was no statistically significant difference between the mean compressive strength of Dicor and that of the natural tooth control.

Aluminum Oxide↗
PubMed2005

Effects of TiO2, ZrO2 and Al2O3 dopants on the compressive strength of tricalcium phosphate.

Tricalcium phosphate (TCP) powders synthesised using the Ca(NO3)2 and Ca(OH)2 routes were doped with TiO2, ZrO2 and Al2O3 in order to increase their compressive strength. An ultimate compressive strength (UCS) of 255 +/- 6 MPa was achieved for approximately 10 vol% TiO2 doping compared to 30 +/- 3 MPa for an un-doped control processed and tested in the same manner. Higher levels of TiO2 doping resulted in smaller increases in UCS with 30 and 50 vol% achieving 213 +/- 9 and 178 +/- 15 MPa, respectively. Very small amounts of Al2O3 doping (< 0.5 vol%) also resulted in a stronger materials. However, under the processing conditions employed, higher levels of Al2O3 and ZrO2 doping resulted in no beneficial effect on the UCS. Polyvinyl alcohol (PVA) was used as binding agent to facilitate processing. As expected, higher levels of PVA were associated with smaller increases in UCS. Powders synthesised using the Ca(OH)2 route had smaller particle size and resulted in larger increases in UCS compared to the Ca(NO3)2-synthesised powders. Although some powders contained alpha and beta-TCP phases, no other calcium phosphate, CaO, CaTiO3 or CaZrO3 phases were detected. In conclusion, a significant increase in the UCS of TCP was achieved by doping with approximately 10 vol% TiO2 which is expected to have little or no effect on the bioactivity or bioresorbability of the material.

Aluminum Oxide↗
PubMed1999

Lumbar vertebral body compressive strength evaluated by dual-energy X-ray absorptiometry, quantitative computed tomography, and ashing.

Bone densitometry with DXA (dual energy X-ray absorptiometry) and QCT (quantitative computed tomography) techniques are used for in vivo assessment of bone strength and thereby prediction of fracture risk. However, only few in vitro studies have investigated and compared these techniques' ability to determine vertebral compressive strength. The aim of the present study was to (1) assess the predictive value of DXA, QCT, and pQCT (peripheral QCT) for vertebral bone compressive strength assessed by mechanical testing; (2) describe both linear and power relationship between density and strength; and (3) evaluate whether gender-related differences in the above relations were present. The material comprised human lumbar vertebrae L3 from 51 women and 50 men (age range: 18 to 96 years). The study showed that both DXA and CT techniques (QCT and pQCT) have a high predictive value for vertebral strength. The DXA BMD had a high correlation with maximum compressive load (r2 = 0.86). The QCT and pQCT had high correlations with maximum compressive stress (r2 = 0.75 and r2 = 0.86, respectively). The correlation between ash density of the biomechanically tested specimen and maximum compressive stress was r2 = 0.88. There were no differences between linear and power fit in the degree of determination between density and strength. There was no gender-related difference in the relationship between volumetric density and maximum compressive stress. In conclusion, it was demonstrated that DXA, QCT, and pQCT are ex situ equally capable of predicting vertebral compressive strength with a degree of determination (r2) between 75% and 86%. No differences were found between linear and power analysis of the relationship between density and strength, and no difference was found in the density strength relationship between women and men.

Absorptiometry, Photon↗
PubMed1991

An evaluation of dental stones after repeated exposure to spray disinfectants. Part I: Abrasion and compressive strength.

This study investigated the effect of repeated applications of spray disinfectants on gypsum surfaces. Types III and IV gypsum products were evaluated in combination with iodophor, acid glutaraldehyde, phenol, and water spray. Results demonstrated greater resistance to abrasion with increasing numbers of water or disinfectant spray applications. Acid glutaraldehyde spray decreased the compressive strength of type III stone by 26%, phenol increased the compressive strength of type IV stone by 18%, and iodophor had no significant effect on either stone relative to compressive strength.

Aerosols↗
PubMed2006

Long-term compressive strength and some other properties of controlled low strength materials made with pozzolanic cement and Class C fly ash.

Controlled low strength material (CLSM) is a flowable mixture that can be used as a backfill material in place of compacted soils. CLSM (or flowable fill) require no tamping or compaction to achieve its compressive strength and typically has a load carrying capacity much higher than that of compacted soils, but can be proportioned to allow future excavation. In this study, several different CLSM mixtures containing Class C fly ash (FA) obtained from Soma Thermal Power Plant in Turkey, crushed limestone sand (CLS), and a minimal amount of pozzolanic cement (PZC) were produced. The mass of PZC was kept constant for all mixtures at 5% of FA by mass. The mechanical and physical properties of CLSM mixtures such as unconfined compressive strength, water absorption by capillarity and EP toxicity were investigated by a series of laboratory tests. CLSM mixtures with low PZC contents and high Class C FA and CLS contents can be produced with excellent flowability and low unconfined compressive strengths in the range of 1.16-2.80 MPa at 365-days age when re-excavation at later ages might be needed. The results presented here show a new field of application for Soma FA in CLSM mixtures, resulting in great advantages in waste minimization, as well as, conservation of resources and environment.

Absorption↗
PubMed1991

Compressive strength mapping of femoral head trabecular bone.

The purpose of this study was to develop a test protocol and complete a relative three-dimensional mapping of the local trabecular bone compressive strengths in healthy and osteoarthritic femoral heads. Five fresh frozen cadaveric femoral heads were compared to five fresh frozen osteoarthritic femoral heads obtained from patients undergoing total hip replacement. Each femoral head was coronally sectioned into eight 5 mm slices, which were compression-tested at 20 sites using a hydraulic testing machine. The results of the femoral head compressive strengths were normalized, mapped, and evaluated. The test protocol produced reproducible results and allowed the determination of diseased portions of osteoarthritic bone. The regions of high compressive strength were similar for normal and diseased bone and were located in the superior medial portions of the head. Ultimate stress was higher in diseased bone than in normal bone, while the yield point and stiffness of diseased bone was lower than for healthy bone.

Biomechanical Phenomena↗
PubMed2005

The effects of boric acid and phosphoric acid on the compressive strength of glass-ionomer cements.

OBJECTIVES: Both boric acid (H3BO3) and phosphoric acid (H3PO4) are components of dental cements, commonly incorporated into glass (as ingredients in the melt) and occasionally added to the powder or liquid components. This study investigated the effect of boric acid addition to an experimental glass-ionomer powder and the effect of phosphoric acid addition to a glass-ionomer liquid on the 24-h compressive strength. METHODS: Boric acid powder was added in various concentrations to an experimental glass-ionomer powder and, separately, phosphoric acid was added to an experimental glass-ionomer liquid. Powders and liquids were dosed into capsules at various powder:liquid ratios and cements thus formed were assessed for 24-h compressive strength. RESULTS: Incorporation of boric acid in glass-ionomer powder resulted in a pronounced decrease (p < 0.05 at 1% boric acid) in compressive strength. Addition of phosphoric acid produced initially stronger cements (up to 13% increase at 1% phosphoric acid) before also declining. SIGNIFICANCE: The incorporation of less than 2% w/w phosphoric acid in glass-ionomer liquids may improve cement strengths without compromising clinical usefulness. The incorporation of boric acid in glass-ionomer cements is contraindicated.

Boric Acids↗
PubMed2002

Knoop hardness depth profiles and compressive strength of selected dental composites polymerized with halogen and LED light curing technologies.

After the first light-emitting diode (LED) light curing units (LCUs) became available commercially, a comparison of mechanical properties between materials polymerized with conventional halogen lamps and this new technology was required. This study, therefore, investigated the curing performance of two conventional commercial halogen LCUs (Translux CL, Spectrum800), a custom-made LED LCU prototype, and one of the first commercially available LED LCUs (LUXoMAX). The Spectrum800 was adjusted to a similar irradiance to the custom-made LED LCU prototype. Both technologies were compared by measuring compressive strength and Knoop hardness depth profiles for selected dental composites polymerized for 20 or 40 s. Four dental composites (Z100, Spectrum TPH, Solitaire2, and Definite) were used. Two of these composites (Solitaire2 and Definite) contain co-initiators in addition to the standard photoinitiator camphorquinone. In general, the material hardness obtained with the LUXoMAX was statistically significantly (p < 0.05) lower at the depths of 0.1, 1.0, 1.9, and 3.1 mm, for all composites and curing times, than for the other three LCUs. The LED LCU prototype achieved, with one exception, up to a depth of 1.9 mm a material hardness for the composites Z100, Spectrum TPH and Solitaire2 that was not statistically significant different (p < 0.05) from the hardness obtained with the halogen LCUs. At a greater depth (3.1 mm), however, the LED LCU prototype showed statistically significantly lower hardness values than the halogen units. The compressive strength test showed at a 95% confidence level that similar compressive strengths were achieved with the LCUs LUXoMAX and Spectrum800, and the Translux and LED LCU prototype.

Composite Resins↗
PubMed1988

Prediction of the compressive strength of vertebral bodies of the lumbar spine by quantitative computed tomography.

The ultimate compressive strength of 36 thoracolumbar vertebrae was determined experimentally. In addition, the trabecular bone mineral content was measured by single energy quantitative computed tomography. The areas of fractured endplates were also determined by computed tomography. The results show that a linear relationship exists between the compressive strength and the product of bone density and endplate area. These data allow an in vivo prediction of vertebral body strength using a noninvasive method with a standard error of estimate amounting to less than 0.95 kN.

Adult↗
PubMed1994

Compressive strength and setting temperatures of mixes with various proportions of plaster to stone.

The compressive strength and setting temperature of different proportions of stone to plaster were measured. The water/powder ratio was 40:100 for all combinations. According to the experimental data, samples of stone to plaster in the ratios of 1:1, 1:3, and 1:4 gave an increased compressive strength of 10.3 MPa compared with the strength of plaster alone (8.3 MPa), possibly because of the low amounts of dental stone in the mix. The lowest amount of heat generated (lowest setting temperature) was recorded by the samples made with the ratio of stone/plaster equal to 1:1, which gave a setting temperature of 43 degrees C. Thus, the mix made with this ratio of stone to plaster may be the material of choice for filling the upper half of the flask during complete denture construction.

Calcium Sulfate↗
PubMed2004

Compressive strength of glass ionomer cements with dental antibacterial agents.

Glass ionomer cements have been suggested for obturating carious teeth that have been prepared with dental hand instruments. In such cases, carious dentine may be inadvertently or deliberately left in situ. The residual bacteria may, over time, lead to secondary caries and restoration failure. Benefit may be gained from combining antibacterial agents with the glass ionomer cement to control residual bacteria. The aim of this study was to investigate the effects on the compressive strength of glass ionomer cement combined with oral antibacterial agents. Cationic antibacterial agents; chlorhexidine hydrochloride, cetylpyridinium chloride and cetrimide were added to the powder and benzalkonium chloride, a liquid, to the liquid of Fuji IX glass ionomer cement. These were prepared to concentrations of 1, 2 and 4 per cent by weight of the glass ionomer cement and compared to Fuji IX with no antibacterial agent. Test specimens were subjected to a compressive force to failure. Multiple analysis of variance showed highly significant reductions in compressive strength (p < 0.01) between the test materials and control group apart from one per cent benzalkonium chloride. Increasing concentration of the antibacterial agent had increasing adverse effects on the physical properties. The addition of the antibacterial agents tested to Fuji IX reduces the seven-day compressive strength which may affect the clinical performance of the material.

Analysis of Variance↗
PubMed2004

[A biomechanical study on cervical spinal posture and prior loading history affecting spinal compressive strength].

OBJECTIVE: The purpose of this study is to investigate the effect of cervical spinal posture and prior loading history on spinal compressive strength. METHODS: Twelve human cadaver cervical spines were harvested and dissected into 24 motion segments containing 2 vertebrae and the intervertebral discs (C3,4 and C5,6). Compressive loads were applied on so that the effects of 2 loading conditions (dehydrated, superhydrated) and 2 postures (neutral trunk, flexed) could be examined. Dissection techniques and X-rays were used to determine the tissue injuries. RESULTS: Specimens had a lower ultimate compressive strength (P <0.001) in flexed posture than in neutral trunk posture. Under the injury loading in neutral trunk posture, superhydrated specimens had a lower strength (29%, P <0.01) than dehydrated specimens did. CONCLUSION: The spine may be more prone to injury early in the morning when the discs are at highest level of hydration and the cervical spine is in fully flexed posture.

Biomechanical Phenomena↗