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PubMed1997

Setting reaction and hardening of an apatitic calcium phosphate cement.

The combination of self-setting and biocompatibility makes calcium phosphate cements potentially useful materials for a variety of dental applications. The objective of this study was to investigate the setting and hardening mechanisms of a cement-type reaction leading to the formation of calcium-deficient hydroxyapatite at low temperature. Reactants used were alpha-tricalcium phosphate containing 17 wt% beta-tricalcium phosphate, and 2 wt% of precipitated hydroxyapatite as solid phase and an aqueous solution 2.5 wt% of disodium hydrogen phosphate as liquid phase. The transformation of the mixture was stopped at selected times by a freeze-drying techniques, so that the cement properties at various stages could be studied by means of x-ray diffraction, infrared spectroscopy, and scanning electron microscopy. Also, the compressive strength of the cement was measured as a function of time. The results showed that: (1) the cement setting was the result of the alpha-tricalcium phosphate hydrolysis, giving as a product calcium-deficient hydroxyapatite, while beta-tricalcium phosphate did not participate in the reaction; (2) the extent of conversion of alpha-TCP was nearly 80% after 24 hr; (3) both the extent of conversion and the compressive strength increased initially linearly with time, subsequently reaching a saturation level, with a strong correlation observed between them, indicating that the microstructural changes taking place as the setting reaction proceeded were responsible for the mechanical behavior of the cement; and (4) the microstructure of the set cement consisted of clusters of big plates with radial or parallel orientations in a matrix of small plate-like crystals.

Bone Cements↗
PubMed1993

High-strength dental gypsum prepared by cold isostatic pressing.

Powder of a dental plaster (Moldabaster, Bayer) was compacted by cold isostatic pressing (CIP) at 300 MPa for 10 min and immersed in water for 1 h. The compressive strength of the CIP-processed material was compared with that of conventionally processed material. The green block of plaster before water immersion was carvable with a green density and green strength of 50% and 5 MPa, respectively. The compressive strength of the CIP-processed gypsum after 24 h was three times higher than that of conventionally processed, 103 compared with 29 MPa, and the microhardness (Vickers hardness number, VHN) of CIP-processed materials was 40 compared with 12 VHN. An increase of density was also recorded. It seems that the CIP process produced a dense and pore-free gypsum with a composite-like structure. The high-strength gypsum processed by CIP may extend the applications of this material in the medical field as implant materials.

Biomechanical Phenomena↗
PubMed2002

[Biomechanical study on the composite of allogenic decalcified bone matrix gelatin and bone cement].

OBJECTIVE: To evaluate the biomechanical properties and structural characteristics of various composites of partially decalcified allogenic bone matrix gelatin and bone cement at different ratios. METHODS: According to Urist method, partially decalcified allogenic bone matrix gelatin was prepared and mixed with bone cement at different ratios of 0, 400, 500, and 600 mg/g. Then the comparisons of these composites were performed in microstructure, ultimate compression strength and ultimate bending strength properties. RESULTS: The electronic microscope showed that the bone particles and bone cement were distributed evenly in the composite, irregularly connecting by multiple points; with the increase of bone particles and decrease of bone cement in the composite, there were more and more natural crevices, varying from 100 microns to 400 microns in width, in the biomaterials. Of all the composites with the ratios of 0, 400, 500, and 600 mg/g, the measurements of ultimate compression strength were (71.7 +/- 2.0) MPa, (46.9 +/- 3.3) MPa, (39.8 +/- 4.1) MPa, and (32.2 +/- 3.4) MPa, respectively; and the measurements of ultimate bending strength were (65.0 +/- 3.4) MPa, (38.2 +/- 4.0) MPa, (33.1 +/- 4.3) MPa and (25.3 +/- 4.6) MPa, respectively. CONCLUSION: The composite of partially decalcified allogenic bone matrix gelatin and bone cement has a good biomechanical property and could be easily fabricated and re-shaped, which make it available to be used clinically as an idea bone graft biomaterial.

Biomechanical Phenomena↗
PubMed2006

An experimental study on the biomechanical properties of the cancellous bones of distal femur.

OBJECTIVE: To study the comprehensive biomechanical properties of the cancellous bone of distal femur through a series of mechanical tests, and provide relevant subjects with the basic technical data. BACKGROUND: The study on bone mechanics is a commonly used approach to evaluate the biomechanical competency of bone. The biomechanical properties of bone have come to be the precondition of the further research of these relevant clinical subjects. METHOD: In this paper, comprehensive items of mechanical properties of the cancellous bones of distal femur were conducted, and many valuable test results were obtained through a series of mechanical tests, which comprised tensile test, compression test, torsion test, shear test, bending test and impact test. The specimens were extracted from the normal corpses of Chinese donors died from acute head injury. As another key problem in this kind of experiment, the sampling and fixing method of cancellous bones specimens was developed and optimized in this research. RESULT: A series of the experimental data of mechanical properties of cancellous bones were obtained in the tests, these experimental data include tensile strength, compression strength, yield tensile strength, modulus of elasticity, torsion strength, shear strength, torsion modulus, bending strength, yield shear limit and impact toughness, which can reflect the complex mechanical competency of bone, being of great value and practice in clinic and further research on cancellous bones. The mechanical properties of the cancellous bones of distal femur were analyzed and discussed. CONCLUSION: The biomechanical properties of the cancellous bones have a close relationship with individual difference. Comprehensive items of the mechanical properties of the bone can evaluate the mechanical performance of the bone better, and can provide more valuable data to relevant research.

Adult↗
PubMed2003

Biomechanical study of human cadaveric lumbar spine reinforced by newly developed hydroxyapatite bone cement.

The compression strength of the lumbar spine reinforced by newly developed hydroxyapatite (HA) bone cement was evaluated using a mechanical testing machine. Sixteen cadaveric lumbar vertebrae obtained from nine subjects (five men, four women) were used. The specimens were randomly divided into two groups. In group A ( n = 8), HA bone cement was injected into the vertebral body through curetted pedicles using specially designed needles and then pushed into the vertebral body by the surgeon's finger, simulating open surgery. In group B ( n = 8) the cement was injected using 16-gauge Ostycut biopsy needles via the pedicles through both sides, simulating percutaneous injection. The initial ultimate compression strength of the specimens was 28.6 +/- 13.4 MPa in group A and 25.2 +/- 12.6 MPa in group B. The value after reinforcement was 35.6 +/- 12.9 MPa in group A and 30.4 +/- 14.8 MPa in group B. There was no significant difference between the ultimate strength of the intact specimen and that after reinforcement. The present study demonstrated biomechanical characteristics of vertebral body fractures reinforced with newly developed HA bone cement.

Biocompatible Materials↗
PubMed1995

Fractures of posterior teeth: a review and analysis of associated factors.

PURPOSE OF STUDY: To examine factors which may predispose to tooth fracture, and to assess the compressive strengths of foods and sweets which are associated with tooth fracture in vivo. POPULATION STUDIED: Consecutive dental patients presenting with one or more fractured posterior teeth at the surgeries of three general dental practitioners, over a four-month period. METHOD: A pro forma was designed to elicit information on the factors associated with tooth fracture and the nature and extent of such fractures. Three general dental practitioners were requested to complete a pro forma for each patient presenting with a fractured posterior tooth over a four-month period. Foods and sweets considered to be associated with tooth fracture were identified and their compressive strengths tested. FINDINGS: A total of 129 cases of fractured posterior teeth were recorded, of which 48% occurred in the mandibular arch and 52% in the maxillary arch. In the mandible, 75% of tooth fractures occurred in molars while in the maxillary arch 50% occurred in molars. In 57% of cases assessed, no identifiable causative item was noted. Forty-five per cent of fractures were in teeth which had been restored on three or more surfaces. Compressive forces of 0.16KN to 2.2KN were obtained for food items implicated in tooth fractures. CONCLUSION: As mesio-occlusodistal restorations were identified as a major predisposing factor to tooth fracture in this study, with mandibular first molar teeth particularly affected, placement of cuspal coverage restorations may be considered to be a justifiable preventative measure in teeth identified as being at risk.

Adolescent↗
PubMed2005

The effect of the antimicrobial peptide, Dhvar-5, on gentamicin release from a polymethyl methacrylate bone cement.

The objective of this study was to investigate the release mechanism and kinetics of the antimicrobial peptide, Dhvar-5, both alone and in combination with gentamicin, from a standard commercial polymethyl methacrylate (PMMA) bone cement. Different amounts of Dhvar-5 were mixed with the bone cement powders of Osteopal and the gentamicin-containing Osteopal G bone cement and their release kinetics from the polymerized cement were investigated. Additionally, the internal structure of the bone cements were analysed by scanning electron microscopy (SEM) of the fracture surfaces. Secondly, porosity was investigated with the mercury intrusion method and related to the observed release profiles. In order to obtain an insight into the mechanical characteristics of the bone cement mixtures, the compressive strength of Osteopal and Osteopal G with Dhvar-5 was also investigated. The total Dhvar-5 release reached 96% in the 100 mg Dhvar-5/g Osteopal cement, whereas total gentamicin release from Osteopal G reached only 18%. Total gentamicin release increased significantly to 67% with the addition of 50mg Dhvar-5/g, but the Dhvar-5 release was not influenced. SEM showed an increase of dissolved gentamicin crystals with the addition of Dhvar-5. The mercury intrusion results suggested an increase of small pores (< 0.1 microm) with the addition of Dhvar-5. Compressive strength of Osteopal was reduced by the addition of Dhvar-5 and gentamicin, but still remained above the limit prescribed by the ISO standard for clinical bone cements. We therefore conclude that the antimicrobial peptide, Dhvar-5, was released in high amounts from PMMA bone cement. When used together with gentamicin sulphate, Dhvar-5 made the gentamicin crystals accessible for the release medium presumably through increased micro-porosity (< 0.1 microm) resulting in a fourfold increase of gentamicin release.

Antimicrobial Cationic Peptides↗
PubMed2004

Effects of MgO-CaO-P2O5-Na2O-based additives on mechanical and biological properties of hydroxyapatite.

In this research, we improved densification, hardness, and compression strength of synthetic hydroxyapatite (HAp) ceramics by introducing small quantities of MgO-CaO-P(2)O(5)-Na(2)O-based sintering additives. Biological properties of HAp were not altered by this procedure. Phase analyses were performed by using a Philips Xpert fully automated diffractometer with Co K-alpha radiation to understand the influence of additives on phase purity in the final products. All compositions were characterized at green and sintered densities to understand the influence of additives on densification. Some of the compositions showed >40% increase in Vickers microhardness compared with pure HAp processed under the same conditions. Improvement in compression strength was also detected in some compositions. In vitro biological testing used a modified human osteoblast cell line to test biocompatibility, cell attachment, and cell proliferation. All these compositions were nontoxic and biocompatible. Our results indicate that MgO-CaO-P(2)O(5)-Na(2)O-based sintering additives can be used to improve both mechanical and biological properties of HAp ceramics.

Biocompatible Materials↗
PubMed1993

Bone ingrowth and mechanical properties of coralline hydroxyapatite 1 yr after implantation.

A previous study of coralline hydroxyapatite as a bone-graft substitute was extended from 4 to 12 months to determine better the relationships between implantation time, bone ingrowth and mechanical properties. The model consisted of a 10 x 30 mm window defect in the shaft of the canine radius (a cortical site), and a 10 mm diameter cylindrical defect in the head of the humerus (a cancellous site). In the new study, these two defects were made bilaterally in eight dogs, and filled with block-form coralline hydroxyapatite. The radius defects were supported by a metal fixation plate which was removed after 9 months. After 12 months, the dogs were killed and the left-side implants were analyzed histomorphometrically and mechanically. The right-side radius and humerus were reserved for structural analysis. The results were combined with those previously measured after 4, 8, 12 and 16 wk of implantation. In the cortical site, bone ingrowth increased from 52% at 16 wk to 74% at 1 yr. In the cancellous site, bone ingrowth was 38% after 4 wk, then fell monotonically, reaching 17% at 1 yr. Bending and compressive strength and stiffness of the radius implants increased throughout the post-implantation year, but compressive strength and stiffness of the humerus implants did not change after the first 2-4 months. Mechanical properties were strongly correlated to bone ingrowth in the cortical, but not the cancellous, site. The volume fraction of the coralline hydroxyapatite material diminished significantly with time in the cortical, but not the cancellous, site.

Animals↗
PubMed2000

[Physical properties of apatite bone cement].

Some properties of the apatite bone cement which is composed of alpha-tricalcium phosphate and hydroxyapatite for use as a biomaterial were investigated. The powder of cement was synthesized from calcium phosphate, calcium carbonate and dicalcium phosphate by solid reaction. Several kinds of citric acid solutions were used for hardening. When the liquid for hardening was 30% (w/w) citric acid solution, the setting time was about six minutes, the compressive strength of hardened bodies was 24.96 MPa, and the solubility was about 1.4 wt%. The compressive strength was increased by the addition of Na or K salt. Especially, when copolymer of acrylic acid/itaconic acid was added to the liquied, the strength was increased about three times, but the setting time was significantly shortened. The results of this study indicate that the apatite bone cement is a potentially highly useful biomaterial for dental and medical applications.

Apatites↗
PubMed2004

Effect of added gelatin on the properties of calcium phosphate cement.

This study investigates the effect of gelatin on the setting time, compressive strength, phase evolution and microstructure of calcium phosphate cement. The composite cement powder (about 18 wt% gelatin, and 82 wt% alpha-tricalcium phosphate) was prepared from the solid compound obtained by casting a gelatin aqueous solution containing alpha-tricalcium phosphate. 5 wt% of CaHPO(4) x 2H(2)O were added to the powder before mixing with the liquid phase. Two cement formulations were prepared using two different liquid/powder ratios, and their properties compared with those of control samples, prepared without gelatin. The final setting time increases from 10 min to more than 45 min when the L/P ratio increases from 0.3 to 0.4 ml/g. The presence of gelatin accelerates the setting reaction, and improves the mechanical properties of the cements. The compressive strength increases with the setting reaction up to 10.7-14.0 MPa for the gelatin cements, whereas the control samples exhibit much lower values. The improved mechanical properties of the composite cements with respect to the controls can be related to their reduced total porosity and more compact microstructure.

Biocompatible Materials↗
PubMed1992

Implications of architecture for the pathogenesis and prevention of vertebral fracture.

Rapid loss of cancellous bone after menopause occurs by a mechanism that removes some structural elements completely, leaving those that remain more widely separated and less well connected. Slow loss of cancellous bone continues by a mechanism that reduces the thickness of the structural elements that survive the initial phase of rapid loss. Both processes have advanced further in patients with vertebral compression fracture due to osteoporosis, than in healthy subjects of similar age; whether this is because they began sooner, proceeded more rapidly or continued for longer is unknown. This overall concept, first developed about ten years ago, has now been confirmed by a variety of different methods including node-strut analysis, star volume and the change in curvature with profile dilation. Because part of the architectural contribution to compressive strength is captured by non-invasive densitometric methods, and the contribution of cortical bone to compressive strength is significant, it has been difficult to demonstrate an independent architectural component of bone fragility by in vitro comparison of structural measurements with biomechanical testing. Nevertheless, three independent clinical studies, comparing subjects with and without vertebral fracture, have each strongly suggested an independent architectural contribution to fracture risk. Complete removal of structural elements is initiated by focal perforation of trabecular plates, but the mechanism of perforation remains controversial.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1999

The effect of strontium oxide in glass-ionomer cements.

The reaction of strontium oxide powder with poly(acrylic acid) has been studied both alone and within glass-ionomer cements. Reaction was found to be slow and the strontium-carboxylate structure was found to be partially covalent in character, as determined by Fourier transform infrared spectroscopy (FTIR). These are similar to the structures formed by calcium in glass-ionomer cements, but are different from typical monomeric strontium carboxylates, which tend to be purely ionic. Strontium oxide powder introduced in two types of glass-ionomer cements, slowed down the setting reaction at both 21 degrees C and 37 degrees C, but at low levels (5 wt %), increased the compressive strength in both cement formulations studied. However, at higher levels, it was found to decrease the compressive strength. This study confirms the view that strontium is a cement-forming ion; but concludes that, except at very low levels, strontium oxide powder does not improve the properties of glass-ionomer cements.

Journal Article↗
PubMed1983

Fluoride content related to the elemental composition, mineral density and strength of bone in healthy and chronically diseased persons.

The fluoride (F) content of bone was determined and compared to the elemental composition, mineral density and compressive strength in bone specimens from the crista iliac of 88 subjects who had died suddenly, and from 50 subjects who had died as the result of chronic immobilizing diseases. The elemental composition of bone was determined using an atomic absorption spectrophotometer, mineral density using gamma-ray attenuation, compressive strength using a strain transducer, and F content using an ion-selective electrode. The increase of F content with age was not statistically significantly different between the groups. The Ca content of bone decreased more with age in post-menopausal women who had suffered from chronic diseases than in women who had died suddenly. The same was true for the negative correlation coefficient between Ca and F. A similar trend was found for mineral density. This does not support the idea that the F concentration obtained produces any effect that would clearly prevent bone loss in post-menopausal women when compared to those who had died suddenly. In both groups F content was correlated with Zn and Mn; in the sudden-death group Zn concentration explained 12.9% of the F concentration. The relation between Zn and F may be important in the formation and structure of biological apatite.

Adolescent↗
PubMed2001

Mechanical augmentation of the vertebral body by calcium phosphate cement injection.

The effectiveness of transpedicular calcium phosphate cement (CPC) injection as a new treatment for osteoporotic compression fracture of vertebrae was evaluated by measuring the compressive strength and the mode of failure in vertebrae experimentally injected with CPC. Forty-five human cadaver vertebrae were divided into three groups: a control group; group A, in which CPC was injected into the upper half of the vertebral body; and group B, in which CPC was injected into the whole vertebra. The load-displacement curve characteristically had two peaks in group A, and decreased rapidly after failure in group B. The failure site was the cancellous bone immediately below the cranial endplate in the control group, cancellous bone immediately below the CPC injection area in group A, and in the CPC injection area in group B. Although mechanical strength was greatest in those vertebrae in which the entire cancellous bone was replaced with CPC, the compressive strength of the vertebrae was also increased by partial replacement of cancellous bone with CPC injection. In terms of mode of failure and mechanical gradient with adjacent vertebrae, there were several advantages for those vertebrae in which the cranial half of the cancellous bone was replaced with CPC.

Aged↗
PubMed1988

Mechanical strength of trabecular bone at the knee.

Interest in the biomechanical properties of trabecular bone has expanded in response to the problems related to total and partial joint replacement with the knee joint constituting a main focus of attention. This relatively recent development has left a number of fundamental problems unanswered, especially related to the machining, storage and testing of trabecular bone specimens. Nevertheless, these studies have contributed to the understanding of the mechanical function of trabecular bone. Regarding the role of trabecular bone at the knee joint, the following conclusions may be emphasized (conclusions drawn from the author's previous studies (I-X) are shown in italics): (1) Trabecular bone is almost exclusively responsible for the transmission of load at the proximal tibial epiphysis from the knee joint to the metaphysis. The peripheral shell surrounding the epiphysis is not composed of cortical bone and plays a negligible role in load transmission. (2) The compressive strength and stiffness of trabecular bone is primarily dependent upon the apparent density, trabecular architecture and the strength of the bone material. Direct and indirect sources suggest that the true material strength of trabecular bone is less than that of cortical bone. The epiphyseal trabecular architecture, featuring a marked polarity with alignment of primary trabeculae at right angles to the joint surface, is responsible for functional anisotropy which points to the axial compressive properties as the more important mechanical parameters. (3) Tensile and shear properties are of special relevance to mechanical loosening of implants. These properties may be derived from the apparent density, and a close empirical relation to the axial compressive strength and stiffness is suggested. (4) The foam-like structure of trabecular bone is the basis for the large energy absorptive capacity. (5) The pattern of axial compressive stiffness and strength at the normal proximal tibia differs little among individuals. Supporting the medial tibial plateau is a large high strength area with maximal strength centrally and slightly anteriorly, while laterally there is a restricted area of relatively high strength posteriorly with a lower maximal value than medially. Bone strength is significantly reduced within ten millimeters of the subchondral bone plate, and this reduction continues distally at the lateral condyle. At both condyles strength is reduced towards the periphery with very low values being obtained at the margins of the condyles and at the intercondylar region. Absolute bone strength values are influenced by the level of physical activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Arthritis, Rheumatoid↗
PubMed2005

Chitin-based tubes for tissue engineering in the nervous system.

The purpose of this study was to investigate chitin and chitosan as potential materials for biodegradable nerve guides. Transparent chitin hydrogel tubes were synthesized, for the first time, from chitosan solutions using acylation chemistry and mold casting techniques. Alkaline hydrolysis of chitin tubes resulted in chitosan tubes, with the extent of hydrolysis controlling the resulting amine content. This, in turn, impacted compressive strength and cell adhesion. Chitosan tubes were mechanically stronger than their chitin origins, as measured by the transverse compressive test, where tubes having degrees of acetylation of 1%, 3%, 18% (i.e. chitosan) and 94% (i.e. chitin) supported loads at a 30% displacement of 40.6 +/- 4.3, 25.3 +/- 4.5, 10.6 +/- 0.8, and 8.7 +/- 0.4 g, respectively. However, the chitin processing methodology could be optimized for compressive strength, by either incorporating reinforcing coils in the tube wall, or air-drying the hydrogel tubes. Chitin and chitosan supported adhesion and differentiation of primary chick dorsal root ganglion neurons in vitro. Chitosan films showed significantly enhanced neurite outgrowth relative to chitin films, reflecting the dependence of nerve cell affinity on the amine content in the polysaccharide: neurites extended 1794.7 +/- 392.0 microm/mm(2) on chitosan films vs. 140.5 +/- 41.6 microm/mm(2) on chitin films after 2 days of culture. This implies that cell adhesion and neurite extension can be adjusted by amine content, which is important for tissue engineering in the nervous system. The methods for easy processing and modification of chitin and chitosan described herein, allow the mechanical properties and cyto-compatibility to be controlled and provide a means for a broader investigation into their use in biomedical applications.

Animals↗