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PubMed2006

Compressive shear bond strength of core buildup materials.

New tooth-colored restorative materials have been developed with the goal of replacing amalgam. These restoratives are marketed as packable composite and ormocer. The purpose of the present study was to compare the compressive shear bond strengths of these new materials with that of hybrid composite and amalgam as core materials. Standardized core buildups were made on four groups of extracted molars, with 10 teeth per group. Three tooth-colored restorative materials (Filtek Z 250, Filtek P 60, and Definite) and an amalgam (SDI Permite) were used. Specimens were placed in a special jig at a 45-degree angle. The compressive shear bond strength was obtained using a universal testing machine. The Kruskal-Wallis test was used to compare the groups, and pairwise comparisons were made by Mann-Whitney U test (P < .05). Filtek P 60, a packable composite resin, had the greatest compressive shear bond strength values in all instances, and the ormocer (Definite) had the lowest. The strengths of packable composite, hybrid composite, and amalgam as core materials were not significantly different (P > .05).

Acrylic Resins↗

PubMed2003

Role of pericellular matrix in development of a mechanically functional neocartilage.

The role of the chondrocyte pericellular matrix (PCM) was examined in a three-dimensional chondrocyte culture system to determine whether retention of the native pericellular matrix could stimulate collagen and proteoglycan accumulation and also promote the formation of a mechanically functional hyaline-like neocartilage. Porcine chondrocytes and chondrons, consisting of the chondrocyte with its intact pericellular matrix, were maintained in pellet culture for up to 12 weeks. Sulfated glycosaminoclycans and type II collagen were measured biochemically. Immunocytochemistry was used to examine collagen localization as well as cell distribution within the pellets. In addition, the equilibrium compressive moduli of developing pellets were measured to determine whether matrix deposition contributed to the mechanical stiffness of the cartilage constructs. Pellets increased in size and weight over a 6-week period without apparent cell proliferation. Although chondrocytes quickly rebuilt a PCM rich in type VI collagen, chondron pellets accumulated significantly more proteoglycan and type II collagen than did chondrocyte pellets, indicating a greater positive effect of the native PCM. After 5 weeks in chondron pellets, matrix remodeling was evident by microscopy. Cells that had been uniformly distributed throughout the pellets began to cluster between large areas of interterritorial matrix rich in type II collagen. After 12 weeks, clusters were stacked in columns. A rapid increase in compressive strength was observed between 1 and 3 weeks in culture for both chondron and chondrocyte pellets and, by 6 weeks, both had achieved 25% of the equilibrium compressive stiffness of cartilage explants. Retention of the in vivo PCM during chondrocyte isolation promotes the formation of a mechanically functional neocartilage construct, suitable for modeling the responses of articular cartilage to chemical stimuli or mechanical compression.

Animals↗

PubMed1999

Coagulation Kinetics and Mechanical Behavior of Wet Alumina Green Bodies Produced via DCC.

Ceramic green bodies can be produced by enzyme-catalyzed reactions from suspensions with high solids loading. There are two ways of destabilizing an electrostatically stabilized suspension: shifting the pH to the isoelectric point (IEP) or increasing the ionic strength. Both can be done via the urease-catalyzed decomposition of urea. The properties of wet green bodies produced by these two methods were compared using compressive strength measurements. Ionic-strength samples needed 24 h or more to achieve sufficient strength because the high urea concentrations required for these slurries inhibit the enzyme. Due to the long coagulation time and to the weak attractive forces formed, the particles can rearrange. This causes the wet green strength and the Young's modulus of these bodies to be considerably higher than those of the pH shift bodies. For the latter, coagulation needs only about one hour, and the interparticle attractive forces are strong. pH shift bodies are more or less insensitive to vibration, whereas ionic-strength bodies tend to flow under oscillatory stress. Copyright 1999 Academic Press.

Journal Article↗

PubMed1996

Biodegradable bone cement compositions based on acrylate and epoxide terminated poly(propylene fumarate) oligomers and calcium salt compositions.

The synthesis of biodegradable bone cement compositions is presented. These bone cement compositions can be applied as a putty-like mixture and harden to a strong material in a bone fracture. They degrade from the site of application to allow the ingrowth of new bone for complete healing of the bone fracture. The bone cement is composed of a solid particulate phase dispersed in an initially liquid polymeric phase, which can be hardened by cross-linking. The polymeric phase is a low-molecular-weight liquid poly(propylene fumarate) (PPF) containing double bonds available for cross-linking. The solid particulate phase consists of calcium carbonate and tricalcium phosphate. PPF oligomers of Mw = 1800 and Mn = 750 were prepared from the condensation of non-volatile bis(2-hydroxypropyl fumarate) and propylene-bis(hydrogen maleate) trimers. PPF terminated divinyl and diepoxide derivatives were obtained from the reactions between PPF diol and acryloyl chloride or epichlorhydrin, respectively. Putty-like cement compositions were prepared from a mixture of 30 wt% polymer phase containing benzoyl peroxide-dimethyl toluidine as polymerization catalyst and 70 wt% calcium salts. The divinyl and diepoxide terminated PPF oligomers provided a high strength composition of between 30 and 129 MPa which is suitable for bone cement applications. In vitro hydrolysis of the composites showed little weight loss with the compressive strength remaining above 20 MPa after 4 weeks in buffer solution. Compositions of the PPF oligomers cross-linked without calcium salts showed a gradual weight loss (10-65 wt% after 4 weeks) when placed in buffer solution followed by high water absorption (18-200 wt% after 4 weeks), with the epoxide terminated PPF being the least to degrade or absorb water.

Acrylates↗

PubMed1997

Optimal selection and preparation of fresh frozen corticocancellous allografts for anterior interbody lumbar spinal fusion.

To determine the effect of graft preparation on graft strength, corticocancellous grafts suitable for anterior interbody fusion were obtained from six cadavers using five different donor bone sites with different graft sectioning orientations and locations. Graft compression strength was determined in simulated physiological loading. The distal tibia and femoral head lumbar interbody grafts are significantly stronger than grafts prepared from other corticocancellous donor sites. Graft fabrication by cutting perpendicular to the long axis and closer to the long bone ends results in increased graft strength.

Adult↗

PubMed1999

Physical properties and self-setting mechanism of calcium phosphate cements from calcium bis-dihydrogenophosphate monohydrate and calcium oxide.

An apatitic calcium phosphate cement was developed from calcium bis-dihydro-genophosphate monohydrate (or monocalcium phosphate monohydrate, MCPM) and calcium oxide (CaO). The powder had a Ca/P molar ratio of 1.67, and the liquid was either pure water or 0.25 M-1 M sodium phosphate buffer, pH 7.4. The influence of the powder-to-liquid (P/L) ratio on the setting time and the mechanical strength were studied. The best results were obtained for the 1 M phosphate buffer with a P/L ratio of 1.53; the setting time was 7 min and the compressive strength was 25 MPa after 24 h and 33 MPa after 11 d. The mechanism and kinetics of the setting reaction were investigated by X-ray diffraction, differential scanning calorimetry, 31P magic angle spinning-nuclear magnetic resonance and infrared spectrometry. The setting reaction was found to be biphasic: in the first step, during the mixing time, MCPM reacted with CaO immediately to give calcium hydrogenophosphate dihydrate (or dicalcium phosphate dihydrate, DCPD) which, in the second step, reacted more slowly with the remaining CaO to give hydroxyapatite. The conversion of the starting materials to hydroxyapatite was complete within 24 h when the liquid was water, but was slower and incomplete with the phosphate buffers. Of the starting materials, 30% remained after 3 d.

Journal Article↗

PubMed2006

Habitual use of the primate forelimb is reflected in the material properties of subchondral bone in the distal radius.

Bone mineral density is directly proportional to compressive strength, which affords an opportunity to estimate in vivo joint load history from the subchondral cortical plate of articular surfaces in isolated skeletal elements. Subchondral bone experiencing greater compressive loads should be of relatively greater density than subchondral bone experiencing less compressive loading. Distribution of the densest areas, either concentrated or diffuse, also may be influenced by the extent of habitual compressive loading. We evaluated subchondral bone in the distal radius of several primates whose locomotion could be characterized in one of three general ways (quadrupedal, suspensory or bipedal), each exemplifying a different manner of habitual forelimb loading (i.e. compression, tension or non-weight-bearing, respectively). We employed computed tomography osteoabsorptiometry (CT-OAM) to acquire optical densities from which false-colour maps were constructed. The false-colour maps were used to evaluate patterns in subchondral density (i.e. apparent density). Suspensory apes and bipedal humans had both smaller percentage areas and less well-defined concentrations of regions of high apparent density relative to quadrupedal primates. Quadrupedal primates exhibited a positive allometric effect of articular surface size on high-density area, whereas suspensory primates exhibited an isometric effect and bipedal humans exhibited no significant relationship between the two. A significant difference between groups characterized by predominantly compressive forelimb loading regimes vs. tensile or non-weight-bearing regimes indicates that subchondral apparent density in the distal radial articular surface distinguishes modes of habitually supporting of body mass.

Absorptiometry, Photon↗

PubMed1984

Strength of polymethylmethacrylate increased by vacuum mixing.

The mechanical strength of high and low viscosity gentamicin-containing cement was analysed using three different mixing procedures: hand, vibration, and vacuum stirring. Vacuum mixing improved the flexural and compression strength and the modulus of elasticity by 15-30 per cent, especially for high viscosity cement.

Bone Cements↗

PubMed2001

Compression, compaction, and disintegration properties of low crystallinity celluloses produced using different agitation rates during their regeneration from phosphoric acid solutions.

The tabletting characteristics of low crystallinity celluloses (LCPC)-LCPC-700, LCPC-2000, and LCPC-4000-prepared using agitation rates of 700, 2000, and 4000 rpm, respectively, during their regeneration from phosphoric acid, were evaluated and compared with those of Avicel PH-102 and Avicel PH-302. The mean deformation pressure values calculated from the linear region of the Athy-Heckel curves indicated LCPC-4000 to be the most ductile material. The area under the Athy-Heckel curve for LCPC-4000 was 330 MPa, whereas LCPC-700 and LCPC-2000 showed a corresponding value similar to that of Avicel PH-102 and Avicel PH-302 (192-232 MPa). The tensile strength of LCPC and Avicel compacts increased linearly with increasing applied pressures. A comparison of the area under the tensile strength-compression pressure curves indicated that LCPC-4000 formed the strongest tablets. The strengths of LCPC-700 and LCPC-2000 compacts, in contrast, were slightly lower than that of Avicel PH-302 and Avicel PH-102, respectively. The compacts of both LCPC-4000 and Avicel PH-102 were intact in water for 6 hours, whereas LCPC-2000 and Avicel PH-302 compacts disintegrated in 4 minutes and 2 minutes, respectively. In conclusion, LCPC-4000 was the most ductile material and exhibited the highest compression and compaction characteristics. The corresponding properties of LCPC-700 and LCPC-2000, in contrast, were comparable to that of Avicel PH-102 or Avicel PH-302.

Cellulose↗

PubMed1997

Composite titanium dental implant fabricated by electro-discharge compaction.

An electro-discharge compaction (EDC) fabrication window was established for producing commercially pure porous titanium dental implants of 4 mm diameter and 7 mm length with a solid titanium cap. The optimum input energy was in the range of 0.58-0.87 kJ g-1 for a powder column of 0.500 g. Input energy greater than 0.58 kJ g-1 resulted in an implant torque strength exceeding 30 N-cm (the retaining screw tightening torque), while input energy greater than 0.72 kJ g-1 exceeded 46.7 N-cm torque strength (at this level the retaining screw failed prior to the implant). The integrity of the internally threaded hole and hexagonal head of the cap were maintained throughout the EDC process. The EDC process did not after the strength and/or microstructure of the components, and the bead-cap interface was stronger than the bead-bead interface. EDC implants produced within the aforementioned window have sufficient compressive strengths and other physical properties to meet the requirement for titanium dental implants.

Biocompatible Materials↗

PubMed1997

[The development of light-curing soft denture liner].

In this study, a visible light-curing soft denture liner was developed, and 6 methacrylate polyurethane elastomer and a diluent were synthesised, their effect on tensile strength, compression set, Shore A hardness, absorption and solubility were also investigated. The results showed that the elastomer made of polyethylene adipate or polybutylene ether glycol possessed the highest tensile strength and hardness, the elastomer made of polypropylene ether glycol showed low tensile strength and low shore A hardness, the elastomer made of hydroxyl-terminated liquid polybutadiene rubber had a moderate tensile strength and hardness.

Denture Liners↗

PubMedDate not supplied

[Relation between distribution of roentgen density and tensile strength to pressure and tension in the shaft center of the human tibia].

Investigations on 12 tibiae of 6 male corpses (68-81 years). In radiographs of cross-sectional slices from the middle of the shaft, the distribution of the density has been investigated by the method of Konermann (1971) and calibrated by a staircase of aluminium. In samples, taken from the positions anterior, medial, posterior and lateral, proximally and distally of the cross-section, tensile and compressive strength has been determined. From the results is concluded, that there exists functional adaptation of mechanical stress in the central part of the tibia with the following pattern: adaptation to tension at the locations anterior and medial, and adaptation to compression at the locations posterior and lateral. At the compression-side there is an additional adaptation by increased density.

Absorptiometry, Photon↗

PubMed1998

Assessment of cancellous bone quality in severe osteoarthrosis: bone mineral density, mechanics, and microdamage.

The role of bone microdamage (microscopic cracks or microcracks and ultrastructural collagen matrix and bone mineral damage) in diseases such as osteoarthrosis and osteoporosis is poorly understood. Microdamage accumulation in vivo is influenced by age and cyclic loading, therefore, it would be useful if the burden of microdamage in bone could be assessed by noninvasive measures such as the radiological measurement of bone mineral density (BMD). The aim of this study was to investigate the relationship between BMD, compressive strength and stiffness, and microdamage in the cancellous bone of the proximal femur in patients with severe osteoarthrosis. Trabecular bone core samples, from the intertrochanteric region of the femur, were obtained from 34 patients, with a mean age of 70.3 +/- 11.1 years, undergoing total hip arthroplasty for osteoarthrosis. Cores selected from contact X-ray images were used for BMD measurement, compressive mechanical testing or left untested (uncrushed), en bloc staining for microdamage, and bone histomorphometry. The study shows a strong dependence of both the elastic modulus and ultimate failure stress of the bone samples on BMD and a significant relationship between the elastic modulus and trabecular anisotropy (Tr. An). In multiple linear regression, BMD and Tr. An together account for about 70% of the variance in the elastic modulus. Then including microcrack crack density (Cr.Dn) and damage volume fraction (DxV/BV) variables, Tr. An alone accounts for a relatively small amount of the variation (8.5%) in ultimate failure stress and elastic modulus. The Cr.Dn accounts for more of the variation in the ultimate failure stress than in the elastic modulus (50% vs. 7%). In this experiment, data for Cr.Dn provide a measure of damage associated with the ultimate failure of cancellous bone. In specimens that were not mechanically tested, in vivo microcrack accumulation increases exponentially with age. In conclusion, data from this study suggest that BMD and Cr.Dn are the major determinants of cancellous bone strength, whereas BMD and Tr. An are major determinants of cancellous bone stiffness. In bone specimens subjected to compressive testing there was no relationship between microdamage and BMD, suggesting that BMD cannot be used to monitor changes in the mechanical properties of bone due to microdamage accumulation.

Absorptiometry, Photon↗

PubMed1992

Alternative crown systems. Is the metal-ceramic crown always the restoration of choice?

The metal-ceramic crown system still is selected the most frequently because of its strength and versatility. The ability to select metals for color or strength for single units or fixed partial dentures gives great flexibility, but when esthetics of the anterior region are a prime concern, the all-ceramic crown is still an excellent choice. Choice of which all-ceramic system to use is dependent on the strength demands, esthetic needs, amount of tooth structure that can be preserved, and laboratory support available. Where good tooth structure remains but some color, contour, or incisal length changes are desired, the porcelain laminate veneer is an outstanding esthetic and restorative choice. When good labial tooth structure remains but lingual structure is inadequate, a partial veneer gold crown can be an excellent esthetic choice. If moderate tooth structure is lost or moderate staining is present, the Dicor crown is a superb choice. In those instances in which heavy staining is present, a foil or core system should be considered to completely block out the background colors. As the occlusal forces become more of a factor, selection of a restorative system will depend more on strength than esthetic demands. The aluminous porcelain jacket crown still offers great strength and esthetics at a reasonable price. When most of the color is on the surface of the teeth, or when there is a high translucency to the teeth, Dicor can provide very esthetic results, and the Dicor Plus crown offers the opportunity to develop intrinsic shading. When greater strength is required, selection of a foil and core system is suggested, as might be a system that provides a stronger core material, like Alceram or Inceram. These stronger core materials will render improved flexural and compressive strengths, but some increases in brightness may occur with the increased alumina content of the cores. The future in ceramic restorative dentistry may be in the computer-generated crown if ways to develop internal coloring and layered building can be developed and cost can be controlled. Ceramic crowns are best limited to the anterior region of the mouth where occlusal forces normally are less than those found in the posterior region. In selected cases, in which there is no evidence of parafunctional habits, and when the dentist and technician are well versed in functional occlusion and have maximum restorative control of the occlusion, posterior ceramic restorations will be successful. It is important to remember in these cases that porcelain is harder than enamel and very strong in compression.(ABSTRACT TRUNCATED AT 400 WORDS)

Aluminum Oxide↗

PubMed1976

[Studies on the application of apatite to dental materials. (I) --Apatite ceramics-- (author's transl)].

Apatite ceramics is composed of hydroxyapatite [Ca10(PO4)6(OH)2] sintered at high temperature. It is known that hydroxyapatite is the main component of bone and tooth minerals. There are two synthetic methods for the apatite powder. One is so called wet synthetic method: Synthesis by the reaction of Ca++ and PO4--- in the aqueous solution of approximately pH 7.0, the other is dry method: Synthesis by the solid state reaction at high temperature. The apatite powder stable below 1400 degrees C was prepared by the latter method in this work. After passing through a sieve, this powder was cold-pressed and then sintered at 1000 degrees C to 1300 degrees C in air. Biological apatite powders were also perpared as a reference. It was found that any apatite ceramics having porosity in the range of 5 to 50% could be obtained under the various sintering conditions. Compressive strength of these apatite ceramics increased with the reduction of the porosity, and those with porosity less than 20% were more than 100 kg/cm2. Vickers hardness was measured. This result showed the same tendency as that of compressibility. Hardness of the apatite ceramics with 90% relative density was almost the same or more as that of enamel. Solubility of the synthetic apatite powder in distilled water and aqueous solution of lactic acid (pH 4.0) was nearly the same as biological apatites. The dissolution rate decreased with the reduction of porosity of the ceramics. It was certified that hot pressing technique was extremely effective to obtain high density ceramics (more than 95% of density) and thus low parosity apatite ceramics. From the facts as described above, it is understood that sintered pure hydroxy-apatite is an excellent ceramics of high mechanical strength.

Apatites↗

PubMed1999

Fractal analysis of proximal femur radiographs: correlation with biomechanical properties and bone mineral density.

Conventional radiography and fractal analysis were used to quantify trabecular texture patterns in human femur specimens and these measures were used in conjunction with bone mineral density (BMD) to predict bone strength. Radiographs were obtained from 51 human femur specimens (25 male, 26 female). The radiographs were analyzed using three different fractal geometry based techniques, namely semi-variance, surface area and Fourier analysis. Maximum compressive strength (MCS) and shear stress (MSS) were determined with a material testing machine: BMD was measured using quantitative computed tomography (QCT). MCS and MSS both correlated significantly with BMD (MCS: R = 0.49-0.54; MSS: R = 0.69-0.72). Fractal dimension also correlated significantly with both biomechanical properties (MCS: R = 0.49-0.56; MSS: R = 0.47-0.54). Using multivariate regression analysis, the fractal dimension in addition to BMD improved correlations versus biomechanical properties. Both BMD and fractal dimension showed statistically significant correlation with bone strength. The fractal dimension provided additional information beyond BMD in correlating with biomechanical properties.

Adult↗

PubMed1996

Anteroposterior and lateral spinal DXA for the assessment of vertebral body strength: comparison with hip and forearm measurement.

Spinal bone mineral density (BMD) is traditionally measured by dual-energy X-ray absorptiometry (DXA) in the anteroposterior (AP) projection which includes both the vertebral body and the posterior elements in the measurement. The posterior elements, however, contribute little to the compressive strength of the spine. It has therefore been suggested that spinal BMD measured in the lateral projection, including only the vertebral body in the measurement, might be more appropriate for the prediction of fracture risk. To date little clinical evidence has been presented to support this assumption. To address the issue, we measured vertebral, hip and forearm BMD in situ in 14 human cadavers and remeasured BMD in vitro in excised vertebrae. Lateral spinal measurements were performed in the decubitus position. Fracture force and other biomechanical measures were determined for 32 vertebrae in a mechanical testing machine and compared with BMD values in situ and in vitro. Correlations of BMD with vertebral fracture force were r = 0.48/0.51 (in situ/in vitro) for the AP spinal measurements, r = 0.45/0.71 (in situ/in vitro) for the lateral spinal measurements, and r = 0.64 and r = 0.53 for total hip and forearm measurements in situ, respectively. Thus, despite an apparent diagnostic advantage in vitro, lateral spinal BMD measurement was not superior to AP measurement when performed in situ. This observation corresponds well with previous clinical findings and is probably due to the larger accuracy error in the lateral than in the AP projection resulting from a lower ratio of bone to soft tissue. The high correlation between hip BMD and vertebral fracture force suggests that hip measurement may prove as useful for vertebral fracture risk assessment as spinal measurement in any projection, especially in the elderly with a high prevalence of degenerative changes in the spine.

Absorptiometry, Photon↗

PubMed1993

Early strength and adaptability of amalgam in relation to coherence time.

The minimum mixing time required to give a coherent mix of a dental amalgam ("coherence time") was determined for eleven representative materials using two different amalgamators. The effect of mixing these amalgams at various multiples of their coherence time on early compressive strength and adaptability was determined. It was found that the two amalgamators gave different coherence time values for the alloys, but that the strength data for any given alloy was similar for a given multiple of coherence time. Longer mixing tended to yield amalgams of greater early strength, but reduced the adaptability of the mixed material.

Analysis of Variance↗