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Results for “Elastic Modulus”

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PubMed1991

Anatomic correlates of aortic pulse wave velocity and carotid artery elasticity during atherosclerosis progression and regression in monkeys.

We noninvasively measured changes in average aortic stiffness in 79 cynomolgus monkeys being fed cholesterol progression, regression, and control diets by measuring pulse wave velocity (PWV) in 260 experiments during a 30-month period. Every 6 months, a group of monkeys was studied with invasive aortic PWV techniques and with ultrasonically determined pressure-strain elastic modulus (Ep) of the carotid artery, and then the group was killed so that morphometric evaluation of atherosclerosis severity could be made. After 6 months of a cholesterol progression diet, PWV decreased slightly from 6.2 +/- 0.1 to 5.7 +/- 0.1 m/sec, followed by an approximate linear increase to 8.8 +/- 1.2 m/sec after 30 months on the diet. The corresponding ratio of intimal (plaque) area to medial area (IA/MA) measured on perfusion-fixed cross-sections of the abdominal and thoracic aortas increased from 0.16 +/- 0.07 at 6 months to 1.23 +/- 0.22 at 30 months. Monkeys in the regression groups were fed the cholesterol progression diet for 18 months, followed by a chow diet for 6 or 12 months. In the first 6 months of the cholesterol regression diet, PWV continued to increase from 7.0 +/- 0.2 to 8.1 +/- 0.4 m/sec, and IA/MA was 1.24 +/- 0.18. However, after 12 months of the cholesterol regression diet, PWV decreased to 6.8 +/- 0.4 m/sec, and IA/MA was 0.90 +/- 0.18. The variability of the data demonstrates that PWV is not a simple function of atherosclerosis severity, and the best simple correlation was r = 0.69 (r2 = 0.48) between PWV and intimal area. However, multiple regression analysis of aortic PWV, systolic (SP) and diastolic (DP) blood pressures, and total plasma cholesterol concentration (TPC), all of which can be measured with minimally invasive techniques, improved the prediction of the IA/MA ratio through the following equation: IA/MA = 0.127 PWV-0.039 DP+0.023SP+0.0003TPC-0.292 (r = 0.81, r2 = 0.66). These data suggest that arterial stiffness in combination with minimally invasive parameters can be used to predict the severity of diffuse asymptomatic atherosclerosis in monkeys. However, more widespread application of these data to humans is uncertain because of biological variability and differences between animal models and human subjects.

Animals↗

PubMed1998

Influence of biochemical alterations on arterial stiffness in patients with end-stage renal disease.

The incremental elastic modulus of the common carotid and radial arteries is increased in patients with end-stage renal disease (ESRD), independently of blood pressure, wall stress, and the presence of atherosclerotic alterations. Whether biochemical factors may be involved in the arterial changes and related to renal dysfunction remain largely ignored. To assess this question, we measured aortic (carotid-femoral), upper-limb (carotid-radial), and lower-limb (femoral-tibial) pulse wave velocity (PWV) in 74 ESRD patients undergoing hemodialysis in comparison with 57 control subjects similar in age, sex ratio, and mean blood pressure. We evaluated arterial blood pressure by sphygmomanometry, aortic calcifications and cardiac mass by echography, and routine biochemical parameters, total plasma homocysteine, and plasma endothelin levels by standard techniques. In the population of patients with ESRD, on the basis of multiple stepwise regression analysis, aortic PWV was positively and independently correlated with systolic blood pressure (P<.0001), age (P<.0001), prevalence of aortic calcification (P=.0004), and the prevalence of diabetes mellitus (P=.0043). Upper-limb PWV was influenced exclusively by mean blood pressure (P<.0001). Lower-limb PWV was positively and independently correlated with plasma total homocysteine (P=.0004) and plasma endothelin (P=.0187) only. At any vascular site, PWV was not independently correlated with tobacco consumption; plasma levels of cholesterol, triglyceride, fibrinogen, or hemoglobin; body mass index; or the presence of bilateral nephrectomy. Finally, plasma homocysteine was independently correlated with cardiac mass (P=.0022). This study provides evidence that in ESRD patients, the stiffness of the arterial wall and cardiac mass are strongly influenced by biochemical factors related to the kidney alterations and are independent of age and blood pressure level. Increased plasma endothelin and homocysteine may be specifically involved in the vascular damage of lower limbs.

Adult↗

PubMed1977

Survival rates of patients with malignant melanoma of the skin.

This paper reports on cases of malignant melanoma of the skin diagnosed in Finland between 1963 and 1968. Sufficient data for estimating the survival was obtained in 691 cases. The ten-year relative survival rate for the entire series was 41% for males and 53% for females. This sex difference remained constant throughout the various divisions of the material. The ten-year relative survival rate of males with tumour in stage I was 52% and that of females 59%. The highest survival rate of stage I tumour in males was for the tumours of the lower extremities (77%) and in females for those in the head and neck (79%). The relative survival of patients with tumour of the trunk in stage I was lowest in both sexes (males 49%, females 45%). The ten-year relative survival rate of patients with a local recurrence was 33% in males and 27% in females. The relative ten-year survival rates of patients with superficial melanoma were 130% in males and 92% in females.

Female↗

PubMed1997

Increased stiffness of radial artery wall material in end-stage renal disease.

The incremental elastic modulus (Einc), which is the slope of the relationship between stress and strain of arteries, is a marker of vascular wall material stiffness. Isobaric Einc is reduced at the site of the radial artery in patients with essential hypertension and increased at the site of the common carotid artery in subjects with end-stage renal disease (ESRD). Whether the changes in Einc are influenced by the topography of the vessels, the composition of the arterial wall, and/or by the presence of ESRD is largely ignored. Radial artery Einc was measured in 19 patients with ESRD and compared with the Einc of 89 subjects with essential hypertension and 20 normotensive control subjects. Transcutaneous measurements of radial artery internal diameter and wall thickness (echo-tracking device) and digital pulse pressure (Finapres) were allowed to calculate Einc under operational (ie, at the mean arterial pressure of each group) and isobaric (100 mm Hg) conditions, as well as for a given wall stress. Internal diameter and pulsatile changes in diameter were identical in the three groups. Wall thickness and mean blood pressure were significantly elevated in subjects with hypertension but not in ESRD patients. Circumferential wall stress was identical in the three groups. For the same operational wall stress, and therefore at the operational mean arterial pressure of each group, Einc (kPa x 10[3]) was increased in patients with ESRD (5.53+/-4.0 versus 3.3+/-2.4 in control subjects; P<.05) and normal in subjects with essential hypertension (3.87+/-4.0). Under isobaric conditions, Einc was also significantly lower in subjects with hypertension and elevated in patients with ESRD. Thus, at the site of a medium-sized muscular artery constantly devoid of atherosclerosis, the stiffness of wall material is increased in patients with ESRD. The demonstrated alterations of the arterial wall are independent of the level of blood pressure and tensile stress and should be related to the status ESRD.

Blood Pressure↗

PubMed2000

[Cardiovascular impact of end-stage renal insufficiency in children undergoing hemodialysis].

Cardiac hypertrophy and arterial dysfunction have been described in end-stage renal disease (ESDR) in adults. The incremental elastic modulus (Einc), is a marker of vascular wall material stiffness and an independant predictor of cardiovascular mortality in adults with ESRD on hemodialysis. The relationship between arterial changes and the heart is unknown in the children with ESRD in the same conditions. Using a high-resolution vascular ultrasound and a computerized system of measurement (Iotec), we assessed noninvasively 10 ESRD patients (mean +/- SD, age, 11.5 +/- 4 years; blood pressure [BP], 120 +/- 10/63 +/- 4 mmHg) and 10 age-, sex-, and BP-matched controls (mean +/- SD, age, 11 +/- 4 years; BP, 114 +/- 8/58 +/- 8 mmHg). The systolic and diastolic diameter of the common carotid artery (CCA), the thickness of the wall (intima-media thickness, IMT), the cross sectional compliance (CSC), the cross sectional distensibility (CSD) and the (Einc) were determined. CSC and CSD were evaluated at the same level of pressure. The CCA pressure waveform was obtained by applanation tonometry to assess the reflected wave by the augmentation index (AI). Further the left ventricular mass index was assessed. The flow mediated dilation (FMD) (endothelium-dependent function) and the vasodilation induced by glyceryl-trinitrate (GTNMD) (GTN, an endothelium-independent dilator) were evaluated at the brachial artery site. Compared to control subjects, ESRD patients have mechanical artery dysfunction with lower CSC and CSD (0.11 +/- 0.04 vs 0.18 +/- 0.05 mm2.mmHg-1; p < 0.01; 0.43 +/- 0.10 vs 0.82 +/- 0.20 mmHg-1.10(-2); p < 0.001) and higher Einc (2.60 +/- 1.00 vs 1.40 +/- 0.30 mmHg.10(3); p < 0.001). Furthermore an earlier return of the reflected pulse wave (AI -0.24 +/- 0.08 vs -0.58 +/- 0.06; p < 0.005) is correlated to LV mass index (r = 0.55, P < 0.01) that is significantly increased (134 +/- 63 vs 69 +/- 25 g/m2; p < 0.005). These patients have an impaired FMD (4 +/- 2 vs 7 +/- 1%; p = 0.02) with a normal GTNMD. This study shows that early arterial dysfunction can occur in children with ESRD.

Adult↗

PubMed2002

Effect of core stiffness on the in vitro fracture of crowned, endodontically treated teeth.

STATEMENT OF PROBLEM: Dentin and core materials that substitute for missing dentin are dissimilar materials. A core material with a lower elastic modulus may deform more under applied stress and therefore result in reduced stress concentration at the core/dentin junction. PURPOSE: This in vitro study examined the effect of core stiffness on the fracture resistance and failure characteristics of a crowned, endodontically treated tooth under simulated occlusal load. MATERIAL AND METHODS: Forty extracted human mandibular premolars were divided equally into 4 groups and prepared for posts and cast crowns as follows: group 1 = cast post and core, cast crown; group 2 = preformed metal post, composite core, and cast crown; group 3 = preformed metal post, amalgam core, and cast crown; and group 4 (control) = preformed metal post, no core, and cast crown. All prepared teeth had 2 mm of sound dentin on which the cemented crown rested. A continuous load (kg) was applied to the buccal cusp at a 30-degree angle to the long axis of each tooth at a crosshead speed of 2 mm/min until failure. Collected data were subjected to 1-way analysis of variance with the Welch modification to compare groups (P<.05). RESULTS: Failure loads for the 4 test groups were as follows: 98.1 +/- 34.6 kg (group 1), 94.4 +/- 41.8 kg (group 2), 105.5 +/- 18.6 kg (group 3), and 101.1 +/- 55.3 kg (group 4). No significant difference in failure load values was found among the 4 groups. The primary mode of failure (80%) in all groups was an oblique radicular fracture, either apical to the post or at the post level. Horizontal fracture of the root and post was found in groups 1, 2, and 3 (20%). Loosening of the crown, post, and core was found only in group 2(20%). CONCLUSION: Within the limitations of this study, core stiffness did not affect the failure resistance of teeth restored with posts and cores and complete-coverage cast metal crowns. The dominant pattern of failure was unrepairable root fracture. Only the composite core exhibited repairable fractures.

Bicuspid↗

PubMed2004

Carotid artery stenting: is there a need to revise ultrasound velocity criteria?

OBJECTIVES: Ultrasound (US) velocity criteria have not been well-established for patients undergoing carotid artery stenting (CAS). A potential source of error in using US after CAS is that reduced compliance in the stented artery may result in elevated velocity relative to the native artery. We measured arterial compliance in the stented artery, and developed customized velocity criteria for use early after CAS. METHODS: US was performed before and within 3 days after CAS, and after 1 month in a subset of 26 patients. Post-procedural peak systolic velocity (PSV) and end-diastolic velocity (EDV) of the internal carotid artery (ICA), PSV/EDV ratio, and internal carotid artery to common carotid artery ratio (ICA/CCA) were recorded. These were compared with degree of in-stent residual stenosis determined at carotid angiography performed at the completion of CAS. Peterson's elastic modulus (Ep) and compliance (Cp) of the ICA were determined in a subgroup of 20 patients at the distal end of the stent and in the same region in the native ICA before stenting. RESULTS: Ninety CAS procedures were analyzed. Mean (+/-SD) angiographic residual stenosis after CAS was 5.4 +/- 9.1%, whereas corresponding PSV by US was 120.4 +/- 32.4 cm/s; EDV, 41.4 +/- 18.6 cm/s; PSV/EDV ratio, 3.3 +/- 1.2; and ICA/CCA ratio, 1.6 +/- 0.5. PSV was unchanged at 1 month. Post-CAS PSV and ICA/CCA ratio correlated most with degree of stenosis (P <.0001 for both). Only six patients demonstrated in-stent residual stenosis 20% or greater, but the standard US threshold of PSV 130 cm/s or greater (validated for >20% ICA stenosis in our laboratory) categorized 38 of 90 patients as having stenosis 20% or greater. Receiver operator curve analysis demonstrated that a combined threshold of PSV 150 cm/s or greater and ICA/CCA ratio 2.16 or greater were optimal for detecting residual stenosis of 20% or greater, with sensitivity 100%, specificity 98%, positive predictive value 75%, and negative predictive value 100%. After placement of a stent, the ICA demonstrated significantly increased Ep (1.2 vs 4.4 x 10(3) mm Hg; P =.004) and decreased Cp (9.8 vs 3.2 %mm Hg x 10(-2); P =.0004). CONCLUSIONS: Currently accepted US velocity criteria validated in our laboratory for nonstented ICAs falsely classified several stented ICAs with normal diameter on carotid angiograms as having residual in-stent stenosis 20% or greater. We propose a new criterion that defines PSV less than 150 cm/s, with ICA/CCA ratio less than 2.16, as the best correlate to a normal lumen (0%-19% stenosis) in the recently stented ICA. This was associated with increased stiffness of the stented ICA (increased Ep, decreased Cp). These preliminary results suggest that placement of a stent in the carotid artery alters its biomechanical properties, which may cause an increase in US velocity measurements in the absence of a technical error or residual stenotic disease.

Aged↗

PubMed1991

Influence of carboxylic anhydrides on selected mechanical properties of heat-cured resin composites.

Resin composites are still in need of improved abrasion resistance for them to be ideal restorative materials for use in large occlusal cavities. The present study proposes a concept for additional cross-linking of dental monomers, by which mechanical properties and possibly the resistance to abrasion of the resin composites are increased. Cyclic acid anhydrides were added as cross-linking agents to different monomer mixtures, which were then loaded with filler. The monomer mixtures were varied with respect to type and ratio of monomer and anhydride. For measurement of diametral tensile strength, flexural strength, modulus of elasticity, and modulus of resilience, specimens were initially cured by light and then post-cured for one h at 150 degrees C. Resin composites based on UEDMA and HEMA were found to be superior to BISGMA- and TEGDMA-based composites. Increases in mechanical properties were highest when unsaturated anhydrides were used. An optimal effect of anhydride addition was found in resin composites also containing methacrylamide. Such materials resulted in a 20% increase in the mechanical properties investigated.

Acrylamides↗

PubMed2002

Delayed, reduced or inhibited thrombin production reduces platelet contractile force and results in weaker clot formation.

Clot retraction is a thrombin-dependent, platelet-mediated contraction of the cellular clot mass. In this study, the effects of delayed, deficient and inhibited thrombin generation on the development of platelet contractile force (PCF) and clot elastic modulus (CEM) were measured. When normal citrated whole blood is clotted by the addition of exogenous thrombin (1 U/ml) and calcium (10 mmol/l), PCF and CEM start to develop within the first minute and begin to level off by 1200 s. If identical samples are clotted with batroxobin (0.21 microg/ml) and calcium (10 mmol/l), both PCF and CEM development are delayed approximately 5 min. After 1200 s of clotting, however, values in the batroxobin system approach those seen with exogenous thrombin. If the added calcium concentration is held constant at 10 mmol/l, increasing the exogenous thrombin concentration from 0 to 0.5 U/ml results in increased PCF and CEM values. Above 0.5 U thrombin, the effect plateaus. At exogenous calcium of 10 mmol/l, increasing batroxobin concentrations (0-0.210 microg/ml) caused a 75% increase in PCF and a 55% increase in CEM. The increase in CEM reached a plateau above 0.05 microg batroxobin/ml. The effects of varying calcium concentrations were evaluated at constant batroxobin (0.21 microg/ml) and thrombin (1 U/ml) concentrations. With thrombin, PCF and CEM increased by > 700% as CaCl2 increased from 0 to 5 mmol/l. Above 5 mmol/l, no additional increases occurred. With batroxobin, PCF did not develop at CaCl2 concentrations < or = 2.5 mmol/l. Above 2.5 mmol/l CaCl2, PCF values increased and at 10 mmol/l CaCl2 were equal to those seen with thrombin. CEM in batroxobin-mediated clots peaked at 10 mmol/l CaCl2 but were 40% less than the values found in thrombin-mediated clots. When the thrombin inhibitor P-PACK was added to the batroxobin system, dose-dependent decreases in PCF and CEM were noted. At 120 micromol/l, P-PACK totally suppressed PCF. PCF in blood from a factor VIII-deficient patient varied significantly when clotted with batroxobin versus thrombin. PCF development in factor VIII-deficient blood was normal with thrombin but is delayed and depressed with batroxobin. PCF values in factor VIII-deficient blood did not reach the thrombin value after 1200 s of clotting, and CEM was significantly less. These results confirm that PCF development is thrombin dependent and that delay or reduction of PCF development results in structurally weaker clots.

Adult↗

PubMedDate not supplied

Effect of thickness of flowable resins on marginal leakage in class II composite restorations.

Despite limited scientific evaluation, there is an increased use of low elastic modulus flowable resin composite (FRC) as a stress-relieving gingival increment in Class II restorations. This study compared marginal leakage in preparations with gingival margins in enamel or dentin/cementum (sub-CEJ and supra-CEJ) after FRC was used as a gingival increment to hybrid resin composite used alone. In addition, the extent of leakage around restorations with or without the use of FRC gingival increments when light curing the resin composites from occlusal direction only or buccal, lingual and occlusal directions was compared. Sixty extracted human molars were prepared with two identical Class II (MO and OD) preparations (30 were 1 mm sub-CEJ and 30 were 1 mm supra-CEJ) and randomly assigned to six groups. After etching, dentin-bonding agent was applied to all prepared tooth surfaces according to the manufacturer's specifications. One of three different thicknesses of FRC (0.5 mm, 1 mm or 2 mm) was placed on the gingival floor, cured and a hybrid resin composite was placed occlusally to complete the restoration. The control preparation on each tooth was restored in the same manner, except that a hybrid resin composite was used for both the gingival and occlusal increments. The restored teeth were thermocycled (300 cycles), then immersed in 50% silver nitrate prior to the hemi-section and measured for leakage under a light microscope. The data were evaluated using paired measures analysis of variance (ANOVA). Most of the occlusal margins showed no leakage, while almost every gingival margin demonstrated some silver nitrate penetration regardless of whether it was located sub or supra-CEJ, although significantly less leakage was found in restorations with supra-CEJ margins (p=0.0001). Among supra-CEJ restorations, there was a pronounced reduction in leakage as FRC thickness increased (p=0.0005). In the teeth restored with the gingival-margin located supra-CEJ, the 2 mm thickness FRC gingival increment showed significantly less leakage (p<0.01) compared with the 0.5 mm thickness of FRC gingival increment. The direction of the curing light did not affect the extent of leakage (p>0.05). The use of FRC material as a gingival increment sub-CEJ in posterior hybrid resin restorations produced no significant difference in leakage (p>0.05). The results of this study indicated that restorations located supra-CEJ (with gingival margins in enamel) with 2 mm thick FRC gingival increments demonstrated significantly less leakage than did those with 0.5 mm FRC. When the margin of the restoration was located sub-CEJ (in dentin/cementum), neither the thickness nor the presence of FRC as a gingival increment significantly influenced the marginal leakage.

Acid Etching, Dental↗

PubMed1985

Arterial regenerative activity after prosthetic implantation.

Factors modifying arterial regenerative activity were evaluated by replacing adult rabbit aortas with either absorbable polyglycolic acid (PGA) or nonabsorbable Dacron prostheses, 3.5 mm in internal diameter by 24 mm in length, woven to identical specifications including pore size, wall thickness, and elastic modulus, and were followed up for 12 months. At death, 48 PGA and 20 Dacron specimens were studied grossly and by arteriography, light microscopy, scanning and transmission electron microscopy, and by bursting strength determinations. There were no aortic-related deaths or transaortic hemorrhages. Both materials elicited a surrounding inflammatory reaction containing macrophages which transgressed the interstices of only the PGA prostheses. Between two and four weeks, circumferentially oriented smooth-musclelike myofibroblasts proliferated in the PGA inner capsule yielding a neointima 3.2 times thicker than Dacron's. Early ultrastructurally primitive cells progressively differentiated into these smooth-musclelike myofibroblasts. The few myofibroblasts later appearing with Dacron were radially oriented. After one month proliferation stopped in both groups and neointimal thickness became constant. The luminal surface in the PGA group was endothelial-like but was fibrinous in the Dacron group. All specimens withstood saline infusion at three to five times systolic pressure. These studies demonstrate great arterial regenerative potential and suggest hemodynamic and intercellular mitogens controlling it.

Animals↗

PubMed1996

Analysis of a biodegradable composite for bone healing.

A degradable L-PLA/calcium carbonate composite made of interconnecting phases was examined. This structure was used both to slow the degradation rate and to reduce the brittleness of the ceramic. Both in vitro and in vivo degradation studies were performed. Samples were incubated in buffered saline or placed in the dorsum of rats for 0, 1, or 4 weeks. Mechanical testing was performed on both groups, volume fraction of each component was determined for in vitro samples, and histology was performed on in vivo samples. Failure load, tensile strength, and elastic modulus significantly decreased during the 1st week for both groups. Continued decreases were seen at 4 weeks for in vitro samples but not for in vivo. Failure strain and tensile strength decreased only for in vitro specimens. PLA fraction significantly decreased during the 1st week and then stabilized. Histology showed that tissue ingrowth occurred at 4 weeks. The decrease in mechanical properties was probably a result of the decreased PLA fraction. The stabilization and even a slight increase in tensile strength and failure strain in the in vivo samples was probably due to the tissue ingrowth forming an implant-tissue composite.

Animals↗

PubMed1997

Assessment of wrought ASTM F1058 cobalt alloy properties for permanent surgical implants.

The behavior of the ASTM F1058 wrought cobalt-chromium-nickel-molybdenum-iron alloy (commonly referred to as Elgiloy or Phynox) is evaluated in terms of mechanical properties, magnetic resonance imaging, corrosion resistance, and biocompatibility. The data found in the literature, the experimental corrosion and biocompatibility results presented in this article, and its long track record as an implant material demonstrate that the cobalt superalloy is an appropriate material for permanent surgical implants that require high yield strength and fatigue resistance combined with high elastic modulus, and that it can be safely imaged with magnetic resonance.

Alloys↗

PubMed1998

Investigation of dual-staged polymerization and secondary forming of photopultruded, fiber-reinforced, methacrylate-copolymer composites.

To develop a dual-curing monomer system for the photopultrusion of reformable (soft) composites, a microhardness assay showed that in a blend with 2,2-Bis[4-2-hydroxy-3-methacryloxypropoxy)phenyl] propane (Bis-GMA), the substitution of methyl methacrylate (MMA) for triethylene glycol dimethacrylate (TEGDMA) delayed the onset of gelation during photopolymerization. Adding lauroyl peroxide permitted the completion of polymerization thermally. This system was used to form silicate-glass-fiber-reinforced composites, with varying degrees of conversion, by photopultruding over a range of pulling speeds. Sol-gel extractions demonstrated both fully soluble and insoluble matrices. For the soluble material, gel permeation chromatography elucidated a trimodal distribution of molecular weights that corresponded to MMA, Bis-GMA, and polymeric molecules with molecular weights in the tens of thousands. Composites with matrix solubilities above about 10% wt could be swaged after photopultrusion to change the cross section from circular to rectangular before thermal processing. The effect on the final elastic modulus was small (-44GPa, as measured in flexure for 57% vol-reinforced composites); but the final flexure strength was reduced by approximately 25% to a constant of about 1.2 GPa. Morphological characteristics that were seen in the circular-sectioned precursors were observed in the swaged rectangular products as well, including flaws when swaging was conducted at matrix solubilities above about 75%.

Biocompatible Materials↗

PubMed1998

The effect of an intramedullary carbon-fiber-reinforced liquid crystalline polymer implant on bone: an experimental study on rabbits.

A novel composite material with an ultra-high strength and a low elastic modulus called carbon-fiber-reinforced liquid crystalline polymer (LCP/CF) has been developed. We studied the effects of an intramedullary LCP/CF rod on bone in rabbits. A LCP/CF rod of 3.2 mm in diameter and 50 mm in length was introduced into the intramedullary canal of the right femur in ten rabbits weighing an average of 3.6 (3.1-4.2) kg. The follow-up intervals were 3 and 52 weeks. No signs of deformity or osteopenia were seen in the operated femurs in the radiographic, histological, and histomorphometric studies. Histologically, the implant was enclosed by cancellous bone in the metaphyseal area and by a thin cancellous bone cuff in medullary cavity. Bone was able to grow in direct contact with the LCP/CF rod. No signs of degradation of the implants or of adverse tissue reaction were seen. The intramedullary LCP/CF rod had no harmful effects on bone in rabbits. The biocompatibility of the LCP/CF appeared to be good. This novel composite material demonstrates properties that may be useful in orthopedic applications.

Animals↗

PubMed1998

In vitro aging of dental composites in water--effect of degree of conversion, filler volume, and filler/matrix coupling.

The purpose of this study was to evaluate the long-term effect of aging in water on the physical properties of experimental composites having systematically controlled differences in degree of conversion (DC), filler volume fraction (Vf), and percentage of silane-treated fillers. Composites were made with a 50% Bis-GMA:50% TEGDMA light-cured resin and a 1-2 microm (average size) strontium glass filler (+ 5 wt% SiO2 microfiller). For composites A-E, the DC was varied from 56-66% by changing the curing time; for D and F-I, the Vf was varied from 28-62 vol%; and for D and J-M, the percent of fillers with a silane coupling agent (gamma-MPS) was varied from 20-100%. Fracture toughness (KIc), flexure strength (FS), elastic modulus (E), and hardness (KHN) were tested after soaking in water at 37 degrees C for 1 day, 6 months, 1 year, and 2 years. The KIc was reduced 20-30% for all composites after 6 months, with minimal changes thereafter. The FS was reduced for several composites at 6 months, but only those with poor cure (A and B) were lower at 2 years than they were initially. The E was not reduced for most composites. Hardness was reduced for most composites after 6 months, but many returned to their original levels at 2 years. Long-term aging in water caused a reduction in the KIc, independent of composition, but had little effect on other properties, suggesting limited degradation of composites in water.

Composite Resins↗

PubMed1999

Mechanical properties of medical grade expanded polytetrafluoroethylene: the effects of internodal distance, density, and displacement rate.

Expanded polytetrafluoroethylene (e-PTFE) is used successfully in a multitude of biomedical and clinical applications. The success of this biomaterial is due to its microporous structure that allows biointegration for fixation, as well as overall mechanical integrity. The mechanical properties and degree of tissue ingrowth depend on the microstructure of the expanded polymer foam, yet little is known about the correlation of the internodal distance and other microstructural features with the monotonic tensile properties. Complete structure-property correlation can be used to provide invaluable knowledge for the design of biomedical devices. The purpose of this study was to investigate the monotonic tensile properties of e-PTFE over a range of medically relevant microstructural features and manufacturing parameters. The microstructural and manufacturing parameters considered were internodal distance, linear density, volumetric density, and reduction ratio. Additionally, the effect of displacement rate on mechanical properties was studied. We found that the ultimate stress and strain increased linearly with linear density (R2 = 0.88 and 0.67, respectively). Surprisingly, elastic modulus did not correlate with any parameter measured and only weak correlations were found between all properties and internodal distance. The yield and ultimate stresses increased with increasing displacement rate (R2 = 0.88 and 0.57, respectively). The findings from this study indicate that linear density is a better predictor of mechanical properties than internodal distance and may be the preferred parameter to control when specifying a material for implantation in load bearing situations.

Biocompatible Materials↗

PubMed2000

Alumina powder/Bis-GMA composite: effect of filler content on mechanical properties and osteoconductivity.

Three composites consisting of alumina powder dispersed in a bisphenol-a-glycidyl methacrylate (Bis-GMA) matrix were prepared and evaluated to assess the effect of alumina powder content on the mechanical properties and osteoconductivity of the composite. The alumina powder composites (APC) consisted of alumina powder (AL-P) as the inorganic filler dispersed in a Bis-GMA matrix that was solidified by a radical polymerization process. Prior to polymerization the AL-P was mixed with the monomers in proportions of 50%, 70%, and 80% by weight (APC50, APC70, and APC80). A fused silica-glass-filled composite containing 70% glass by weight (SGC70) was used as a control. The compressive and bending strengths, the elastic modulus in bending, and the bending strain of the composites increased as the AL-P content increased. We also evaluated the composites in vivo by implanting them into the medullary canals of rat tibiae. To compare the osteoconductivity of the composites, an affinity index was calculated for each composite; the affinity index equals the length of a bone in direct apposition to the composite and is expressed as a percentage of the total length of the composite surface. Microradiographic examination for periods of up to 26 weeks after implantation revealed that APC50, APC70, and APC80 all exhibited excellent osteoconductivity and made direct contact with the bone with no interposed soft tissues. However, the higher the AL-P content of the composite, the higher the osteoconductivity, especially at 4 weeks after the operation. Moreover, the amount of bone directly apposed to the composite surface increased with time. In contrast, little bone formation was seen on the surface of SGC70, even after 26 weeks. Observation by scanning electron microscope-energy dispersive X-ray microanalysis demonstrated that bone made direct contact with the APC surface through a layer containing calcium, phosphorus, and alumina powder. These results suggest that APC shows promise as a basis for developing mechanically strong and highly osteoconductive composites.

Aluminum Oxide↗