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PubMed2000

Influence of silanization and filler fraction on aged dental composites.

The effect of silanization and filler fraction on the mechanical properties of aged dental composites was investigated. Experimental composites (75/25 Bis-GMA/TEGDMA resin reinforced with 0, 12.6, 30.0, and 56.5 vol% 8 microm silanized/unsilanized BaSiO6) were fabricated into 4.7 mm diameter x 2.2 mm thick discs and 3.5 mm diameter x 7.3 mm thick discs for diametral tensile and compressive tests, respectively. The effect of immersion in 75% ethanol at 37 degrees C for 0-30 days on the diametral tensile strength (DTS) and compressive strength (CS) of the samples was evaluated and analysed by ANOVA and Tukey LSD test. The fracture interface between filler and resin matrix was then examined by scanning electron microscope. Results and subsequent statistical evidence from DTS (18.6+/-7.6 MPa, silanized versus 11.7+/-2.6 MPa, unsilanized) and CS (85.1+/-29.7 MPa, silanized versus 56.0+/-11.3 MPa, unsilanized) strongly implies that silanization may greatly enhance the mechanical properties of the resin composites. Furthermore, it also shows that both DTS and CS increased proportionally as the filler fraction of the composites increased. However, in the unsilanized groups, DTS decreased (up to 40%) as the filler fraction increased, and CS showed no relevance to the filler fraction at all. As for the influence of aging, it was found that both DTS and CS showed a significant decrease after immersion in 75% ethanol, and silanization heavily correlated with the filler fraction of aged-resin composites. Microscopic examination of the fractured samples showed that failure primarily occurred within the resin matrix per se for silanized composites and adjacent to the filler particles for unsilanized composites. All the evidence points to the conclusion that mechanical properties of aged-resin composites can be greatly influenced by silanization and the filler fraction.

Analysis of Variance↗
PubMed2002

The effects of eugenol and epoxy-resin on the strength of a hybrid composite resin.

The compatibility of different dental materials (root canal sealer and composite core build-up restoratives) is an important factor for a successful restoration. The aim of this in vitro study was to determine the effects on compressive and diametral tensile strength of a classical chemical cure composite resin (Henry Schein Composite Anterior-Posterior dental restorative) when in contact with either eugenol or an epoxy-resin (EZ-Fill) in a variety of situations: (a) eugenol or epoxy-resin added during mixing of a composite resin before curing; (b) vapor exposure to cured samples; and (c) specimens placed directly in eugenol or epoxy-resin (after curing). Compressive strengths and diametral tensile strengths were tested for each group. Only the addition of eugenol during mixing with the composite resin (directly before curing) resulted in specimens that were unable to be tested, because they did not achieve a full cure or hardness. For all other groups, there were no significant differences with respect to either compressive strength (p = 0.17) or diametral tensile strength (p = 0.39). Group 1 (mixed directly with eugenol) was found to be statistically different from groups 2 through 7.

Analysis of Variance↗
PubMed1980

Alumina as a filler for bone cement: a feasibility study.

A composite bone cement of Alcoa A-10 Alumina and very finely ground poly(methyl methacrylate) beads (PMMA) was fabricated. It was tested in an attempt to improve on the conventionally used pure PMMA bone cement. By knowing the densities of the powders and their volumes, the mass of each was calculated for the most efficient packing of PMMA and Al2O3 powders and a 65% PMMA: 35% Al2O3 ratio by weight composition was determined. This was tested, as well as the pure cement so comparisons could be made. Cylinders for the strength tests were also made of silane treated Al2O3. The compositions were tested for compressive and tensile strengths. The pure PMMA, composite and silane treated composite had compressive strengths of 79.64 +/- 13.0, 83.17 +/- 4.8, and 71.52 +/- 8.6 MPa and the tensile strengths were 6.69 +/- 0.6, 5.12 +/- 0.3, and 7.12 +/- 0.5 MPa respectively. Also the 65%-35% PMMA-Al2O3 composite required 64% less monomer for mixing than did the pure cement which is thought to be better for tissue healing. The maximum temperature attained from room temperature was 110 degrees-115 degrees C for both cements. The composite took 6.5 min longer to reach its peak temperature than did the pure cement. The bone cements were implanted for one week in a rabbit and both compositions seemed acceptable by the tissue.

Aluminum↗
PubMed2004

[The influence of Ce on microstructures and mechanics performances of Ti-Fe-Mo-Mn-Nb-Zr alloys].

The influences of Ce on the microstructure and mechanics performances of Ti-Fe-Mo-Mn-Nb-Zr alloys were studied and presented in this paper. The microstructure of no-Ce Ti-Fe-Mo-Mn-Nb-Zr alloy was thick, long and dendritic, and the microstructure of alloy was fined by Ce. With the increase in Ce wt%, the microstructure became equiaxial gradually. Hardness decreased with the increase in Ce wt%. The compression yield strength became greater with the increasing of Ce wt%, but after the Ce wt% increased to a certian degree, the compression yield strength became smaller with the further increasing of Ce wt%. This phenomenon was explained in the light of bond energy and X-ray diffraction experiment. X-ray diffraction experiment showed that the alloys were beta-Ti.

Alloys↗
PubMed1998

Temporary dental restorative materials for military field use.

New temporary dental restorative materials are an important military requirement. This study compares the critical properties of the currently used temporary material, reinforced zinc oxide-eugenol (ZOE), with those of a glass ionomer restorative material (GI), a high-viscosity modified glass ionomer material (MGI), and two resin-modified glass ionomer materials (RMGIs). Properties tested included compressive and tensile strength, rigidity, hardness, bond strength, working and setting times, and storage stability. Ranked results for compressive strength, rigidity, and hardness were MGI > GI > RMGI > ZOE; for tensile strength they were RMGI > MGI > GI > ZOE; and for storage stability they were ZOE > MGI > GI > RMGI. Working and setting times were all within reasonable clinical limits, and bond strength was heavily dependent on tooth surface preparation. Although none of the materials tested met all of the ideal requirements, the high-viscosity glass ionomer material offers the most promise for military field use.

Composite Resins↗
PubMed2000

Mechanical performance of standard and cannulated 4.0-mm cancellous bone screws.

The mechanical performance of bone screws is determined by their pull-out strength (holding power), compressive force, stripping torque, yield bending moment, ultimate bending moment, and fatigue strength. These parameters are related to the parameters of the screw design, including major thread diameter, minor thread diameter, thread length, pitch, shaft diameter, cannulation diameter, and material properties. The goal of the study was to theoretically predict the static performance of five 4.0-mm, 45-46-mm-long, cancellous, partially threaded standard and cannulated bone screws and compare the predictions with experimental measurements. A secondary goal was to determine if cannulation of the bone screw diminished its mechanical performance. The predicted values for pull-out force, compressive force, and stripping torque were determined by the thread length, major thread diameter, and thread shape factor. The screws with the largest major thread diameter and longest thread length had the greatest pull-out force, compressive strength, and stripping torque. However, when correcting for the thread length, a higher thread shape factor compensated for a smaller major diameter. The coefficient of determination (r2) for the correlation between the predicted and measured pull-out force improved from 0.75 to 0.90 when the theoretical model included the thread shape factor. The yield and ultimate bending moments are a function of the section modulus and material properties of the screw. The Ace solid screw had the greatest section modulus and yield and ultimate bending moments. The experimental data support the theoretical models for predicting the mechanical performance of bone screws. The design of the bone screws can be optimized on the basis of theoretical modeling. The strong correlation between the predicted and measured parameters allows comparison between bone screws without repeated experimental tests. Theoretical and experimental results show that cannulation of the bone screw did not inherently diminish its mechanical performance.

Biomechanical Phenomena↗
PubMed2006

The physical-mechanical performance of the new Ketac Molar Easymix compared to commercially available glass ionomer restoratives.

OBJECTIVES: To evaluate the time dependence of physical-mechanical performance of glass ionomer restoratives. METHODS: The physical-mechanical properties of Ketac Molar Easymix in comparison to four handmix glass ionomer restoratives were evaluated by testing the compressive and flexural strength, acid erosion and solubility. By testing the properties in the early and late setting phase it was determined how fast the level of material characteristics is achieved. IR spectroscopy was used for monitoring the acid-base reaction. RESULTS: The compressive strength after 1 and 24h setting time show that Ketac Molar Easymix and Fuji IX demonstrate a significantly higher performance. Ketac Molar Easymix exhibits by far the highest flexural strength 1h after start of setting. After 24h, it remains at this high level and only Vitro Molar and Fuji IX come close. Ketac Molar Easymix and Fuji IX show the lowest solubility in neutral media after 24h and 7d. It is remarkable that the solubilities of Ionofil Molar, Vitro Molar and Vidrion R stored in water for 24h are higher than those of Ketac Molar Easymix and Fuji IX obtained after 7d water immersion. In acidic media Ketac Molar Easymix is least prone to acid erosion. CONCLUSIONS: For clinical success of a filling material the early achievement of a high physical-mechanical performance is mandatory to minimize the risk of early damage to a restoration. With the high flexural strength reached after 1h combined with the lowest susceptibility for acid-attack and solubility in water, Ketac Molar Easymix, from 3M ESPE, provides the best performance of any materials tested.

Analysis of Variance↗
PubMed2003

Vertebral body replacement with an expandable cage for reconstruction after spinal tumor resection.

OBJECT: The authors report their clinical experience with expandable cages used to stabilize the spine after vertebrectomy. The objectives of surgical treatment for spine tumors include a decrease in pain, decompression of the neural elements, mechanical stabilization of the spine, and wide resection to gain local control of certain primary tumors. Most of the lesions occur in the anterior column or vertebral body (VB). Anterior column defects following resection of VBs require surgical restoration of anterior column support. Recently, various expandable cages have been developed and used clinically for VB replacement (VBR). METHODS: Between January 2001 and June 2003, the authors treated 15 patients who presented with primary spinal tumors and metastatic lesions from remote sites. All patients underwent vertebrectomy, VBR with an expandable cage, and anterior instrumentation with or without posterior instrumentation, depending on the stability of the involved segment. The correction of kyphotic angle was achieved at an average of 20 degrees. Pain scores according to the visual analog scale decreased from 8.4 to 5.2 at the last follow-up review. Patients whose Frankel neurological grade was below D attained at least a one-grade improvement after surgery. All patients achieved immediate stability postsurgery and there were no significant complications related to the expandable cage. CONCLUSIONS: The advantage of the expandable cage is that it is easy to use because it permits optimal fit and correction of the deformity by in vivo expansion of the device. These results are promising, but long-term follow up is required.

Adult↗
PubMed1999

[Compression biliodigestive anastomosis: the morphological characteristics of its dynamics of formation].

The method of the compressive biliodigestive anastomosis formation, using implant and the apparatus for its performance, was elaborated. An experimental investigation on 30 rabbits was done. An optimal strength of compression while doing the tissues connection was 0.002-0.004 N/m2. Minimal traumaticity, preservation of sufficient blood flow of the tissues connected, delineation of the healing zone from the intestinal contents and bile, the absence of chronic inflammation in anastomotic tissues are the advantages of compressive biliodigestive anastomosis, promoting early restoration of the intestinal and gallbladder wall, the formation of functionally full value anastomosis, which is not stenotizes cicatricially.

Anastomosis, Surgical↗
PubMed2003

Quantitative computed tomography-based finite element models of the human lumbar vertebral body: effect of element size on stiffness, damage, and fracture strength predictions.

This study investigated the numerical convergence characteristics of specimen-specific "voxel-based" finite element models of 14 excised human cadaveric lumbar vertebral bodies (age: 37-87; M = 6, F = 8) that were generated automatically from clinical-type CT scans. With eventual clinical applications in mind, the ability of the model stiffness to predict the experimentally measured compressive fracture strength of the vertebral bodies was also assessed. The stiffness of "low"-resolution models (3 x 3 x 3 mm element size) was on average only 4% greater (p = 0.03) than for "high"-resolution models (1 x 1 x 1.5 mm) despite interspecimen variations that varied over four-fold. Damage predictions using low- vs high-resolution models were significantly different (p = 0.01) at loads corresponding to an overall strain of 0.5%. Both the high (r2 = 0.94) and low (r2 = 0.92) resolution model stiffness values were highly correlated with the experimentally measured ultimate strength values. Because vertebral stiffness variations in the population are much greater than those that arise from differences in voxel size, these results indicate that imaging resolution is not critical in cross-sectional studies of this parameter. However, longitudinal studies that seek to track more subtle changes in stiffness over time should account for the small but highly significant effects of voxel size. These results also demonstrate that an automated voxel-based finite element modeling technique may provide an excellent noninvasive assessment of vertebral strength.

Adult↗
PubMed1992

Effects of moisture content and endodontic treatment on some mechanical properties of human dentin.

The objective of this study was to determine whether significant differences exist between the mechanical properties of human dentin from treated pulpless teeth and dentin from normal vital teeth. Dentin specimens (n = 262) were obtained from 54 freshly extracted normal vital human teeth and 24 treated human pulpless teeth. These specimens were subjected to different experimental conditions (wet, air dried, desiccated, and rehydrated). Compression, indirect tensile, and impact tests were conducted to measure the mechanical properties of those specimens. All data obtained were analyzed with t tests. The results showed that the dehydration of dentin increases the Young's modulus, proportional limit (in compression), and especially the ultimate strength (in both compression and tension). Substantial dehydration changes the fracture characteristics of dentin specimens under static compressive and indirect tensile loadings. The measurements of impact-breaking energies of desiccated dentin were not found to be significantly decreased. The compressive and tensile strengths of dentin from treated pulpless teeth obtained in this study do not appear to be significantly different from those of normal dentin (p > 0.05), while the mean values of Young's modulus and proportional limit in compression tests appear to be lower. Fifty percent of the dentin specimens from treated pulpless teeth exhibit greater plastic deformation than normal dentin in compression. The results of this study do not support the theory that dehydration after endodontic treatment per se weakens dentin structure in terms of compressive and tensile strengths. Other mechanical properties of treated pulpless teeth, however, may not be the same as those of normal vital teeth.

Dental Pulp Devitalization↗
PubMed1990

Effect of compression speed on the tensile strength of tablets of binary mixtures containing aspirin.

Mixtures of aspirin with sodium chloride, sucrose, Starch 1500 or Emcompress have been compressed to two maximum upper punch pressures at two compression speeds. Non-linear relationships between tensile strength and composition, and tablet porosity and composition were found in all cases. Tablets of the individual materials compressed at fast speed showed either little change or a reduction in tensile strength when compared with those compressed at slow speed. For mixtures of aspirin with Starch 1500, tablets compressed at fast speed were weaker and more porous than those compressed at slow speed. However, some mixtures of aspirin with sodium chloride, sucrose or Emcompress gave tablets with greater tensile strength and lower porosity when prepared at fast compression speed compared with tablets prepared at slow speed. This behaviour was attributed to the modification of the consolidation behaviour of the aspirin by the second material.

Aspirin↗
PubMed1976

The rate of development of strength in base forming materials for dental amalgam.

Eleven base forming materials used under amalgam restorations were examined for the rate of development of their compressive and tensile strengths. Materials from three categories were compared. Under in vitro conditions of testing, it was found that, immediately after a state of clinical set had been reached, the quick-setting zinc oxide-eugenol materials possessed strengths significantly greater than the calcium hydroxide cements but significantly weaker than the zinc phosphate cements. Calcium hydroxide cements possessed the lowest compressive strength to tensile strength ratio and modified zinc oxide-eugenol materials the highest.

Calcium Hydroxide↗
PubMed2004

A study on the effect of drying techniques on the mechanical properties of pellets and compacted pellets.

Microcrystalline cellulose (MCC) pellets produced by a standard extrusions/spheronisation process with a 40% ethanol/water mixture as the fluid component, were dried by four different techniques, namely: freeze-drying, fluid-bed drying, hot air oven drying and desiccation with silica-gel to less than 5% (w/w) water content. A 1.0-1.18mm size fraction of the dried pellets were characterised structurally and mechanically in terms of, shape, density/porosity (open and closed), pore volume/pore volume distribution, surface area, surface tensile strength, shear strength, deformability, linear strain and elastic modulus. An amount of 600, 700 and 750mg of the same size fraction of each pellet batch were compacted to the same tablet thickness and the tensile strength and volumetric elastic recovery of the resulted compacts were determined. Analysis of variance was used to assess the significance of the drying process on the property of the pellets and their compacts. The drying process did not influence the shape of the pellets, but all the other properties were affected to some extent. Pellets dried by freeze-drying were more porous, with most of the pores open to the atmosphere and had a higher surface area than pellets dried by the other methods. Pellets dried by desiccation contained the highest proportion of closed pores. The decrease in tensile strength of the pellets, which occurred with the increase in porosity could presumably be due to ease of crack initiation and propagation between the MCC fibres. The weaker pellets broke instantly before they were subjected to appreciable strain. The porous pellets needed a higher compressing pressure and work of compaction to produce tablets of the same mass and dimensions. This reflected their compressibility, i.e. relative decrease in volume of the pellet bed during compression. The strength and volumetric elastic recovery of the compacts increased with the increase of their porosity. The drying techniques, which produced porous, deformable and weak pellets, produced stronger tablets. The value of the volumetric elastic recovery of the compacts was also observed to increase with the value of compaction pressure.

Cellulose↗
PubMed2000

Critical evaluation of known bone material properties to realize anisotropic FE-simulation of the proximal femur.

PURPOSE: In a meta-analysis of the literature we evaluated the present knowledge of the material properties of cortical and cancellous bone to answer the question whether the available data are sufficient to realize anisotropic finite element (FE)-models of the proximal femur. MATERIAL AND METHOD: All studies that met the following criteria were analyzed: Young's modulus, tensile, compressive and torsional strengths, Poisson's ratio, the shear modulus and the viscoelastic properties had to be determined experimentally. The experiments had to be carried out in a moist environment and at room temperature with freshly removed and untreated human cadaverous femurs. All material properties had to be determined in defined load directions (axial, transverse) and should have been correlated to apparent density (g/cm(3)), reflecting the individually variable and age-dependent changes of bone material properties. RESULTS: Differences in Young's modulus of cortical [cancellous] bone at a rate of between 33% (58%) (at low apparent density) and 62% (80%) (at high apparent density), are higher in the axial than in the transverse load direction. Similar results have been seen for the compressive strength of femoral bone. For the tensile and torsional strengths, Poisson's ratio and the shear modulus, only ultimate values have been found without a correlation to apparent density. For the viscoelastic behaviour of bone only data of cortical bone and in axial load direction have been described up to now. CONCLUSIONS: Anisotropic FE-models of the femur could be realized for most part with the summarized material properties of bone if characterized by apparent density and load directions. Because several mechanical properties have not been correlated to these main criteria, further experimental investigations will be necessary in future.

Anisotropy↗
PubMed1977

Plastic flow during compression of directly compressible fillers and its effect on tablet strength.

The effects of the duration of the overall compression cycle and of the duration of the maximum compressive force on tablet strength were studied using an instrumented rotary tablet press. Various direct compression fillers were evaluated. Increasing the overall compression cycle duration to 10 sec resulted in significantly greater tablet tensile strengths with microcrystalline cellulose and compressible starch fillers but not with lactose or compressible sugar. Increasing the duration of the maximum compressive force to 20 sec significantly increased the tensile strength in all cases, but microcrystalline cellulose and compressible starch tablets were affected more than lactose or sugar tablets. The maximum compressive force decayed with time for all fillers but at a greater rate with microcrystalline cellulose and compressible starch. This behavior was attributed to differences in the extent of plastic flow. The decay curves were analyzed using the Maxwell model.

Calcium Phosphates↗
PubMed2005

Calcium phosphate cement composites in revision hip arthroplasty.

Loosening of the femoral component in a total hip arthroplasty with concomitant bone loss can pose a problem for revision surgery due to inadequate structure in the remaining femur. While impaction allografting has shown promise, it has also shown serious complications, especially with moderate to severe bone loss. It may be possible to stabilize the graft layer with a bioresorbable cement to improve clinical results. This study examines the mechanical properties of a potential morsellized bone-bioresorbable composite. Morsellized bone was mixed with a commercially available bioresorbable cement (alpha-BSM, Etex Corp.) in compositions of 0%, 25%, 50% and 75% bone. Unconfined compression and diametral tensile and confined compression tests were performed to determine the composite mechanical properties. The composition containing 50% bone tended to exhibit the highest uniaxial strengths, as well as the highest confined compression modulus. The uniaxial compressive strength and stiffness of this composition was in the range of cancellous bone. Uniaxial compressive modulus decreased with increasing bone fraction whereas elongation exhibited the opposite trend. Bone fraction had a significant effect on compressive strength (p < 0.0001), compressive modulus (p < 0.0001), elongation (p < 0.01), tensile strength (p < 0.0001) and confined compressive modulus (p = 0.04). The addition of a bioresorbable cement to the allograft layer may improve the properties of the layer, preventing early subsidence seen in some clinical studies of impaction allografting, and therefore improving the clinical results. Further testing is required to evaluate the in vitro mechanical performance, as well as in vivo remodelling characteristics.

Aged↗