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PubMed1981

Polymer implant materials with improved X-ray opacity and biocompatibility.

Poly(methyl methacrylate) samples containing 28 wt% inorganic fillers such as zirconium oxide, barium sulphate, zinc oxide, magnesium oxide and tricalcium phosphate were prepared and studied for their suitability as implant materials by physical property tests, X-ray opacity measurement, cell culture, and animal implantations. Addition of inorganic fillers to poly(methyl methacrylate) increased the compressive strength but decreased the transverse strength. Zirconium oxide was found to be most suitable as an X-ray opaque filler, and tricalcium phosphate showed superior biocompatibility when added to poly(methyl methacrylate) in cell culture experiments. The zirconium oxide and tricalcium phosphate composites evoked no greater unfavourable tissue reaction in rats than pure poly(methyl methacrylate). From the physical and biological standpoints zirconium oxide is the radiopaque filler of choice to be incorporated in poly(methyl methacrylate) implant material and addition of tricalcium phosphate could improve it's biocompatibility.

Animals↗
PubMed1988

Mechanical and biological properties of apatite composite resins.

Well-crystallized hydroxyapatite was synthesized at 80 degrees C and pH 7.4, and mixed as filler with 2.2'(4-methacryloxydiethoxyphenyl) propane. BPO and DHPT were used as polymerization initiators. The compressive strength and Knoop hardness of the apatite composite resins increased with the increase of apatite content, and approached a plateau above an apatite-resin ratio (Ap/R) of 1. The thermal expansion coefficient of the composite with apatite-resin ratio Ap/R = 1 was almost equal to that of teeth. In tooth cavities, the composites seemed to adhere well to enamel without a bonding agent. The biocompatibility of the composites implanted hypodermically into rats appeared to improve with the increase of apatite content, and implants showed no significant inflammation after 1 wk and 4 wk.

Acrylates↗
PubMed1991

In vitro properties of a chitosan-bonded hydroxyapatite bone-filling paste.

A possible bone substitute material for dental treatment was developed and tested. The material is composed of powdered hydroxyapatite (HA), ZnO and CaO, kneaded into a chitosan sol to make a quick-hardening paste. A composition was found which showed neutral pH, short setting time, and relatively high compressive strength. The use of such a paste for the treatment of periodontal defects or the augmentation of edentulous alveolar ridges may alleviate problems now associated with the implantation of particulate HA, such as early migration of particles and recontouring of the implant.

Biocompatible Materials↗
PubMed1993

Development of a degradable composite for orthopaedic use: mechanical evaluation of an hydroxyapatite-polyhydroxybutyrate composite material.

This study evaluates the mechanical properties of a composite material comprising polyhydroxybutyrate with hydroxyapatite added in proportions varying from 0 to 50%. Among the three methods of production, injection moulding was found to result in the most satisfactory mechanical properties. The tensile and compressive strength and the modulus of elasticity of composite produced in this way fell within the range for fresh human bone from different anatomical sites. With the additional advantages of biocompatibility, biodegradability and the potential for piezoelectric stimulation of new local bone formation, it was concluded that the injection-moulded composite material has considerable potential for use in orthopaedic surgery, both as a material to construct certain orthopaedic implants and as an alternative to corticocancellous bone graft.

Biocompatible Materials↗
PubMed1994

Novel polyalkenoate (glass-ionomer) dental cements based on zinc silicate glasses.

Powdered zinc silicate glasses were investigated for cement formation with aqueous poly(acrylic acid). Alkali metal zinc silicate glasses and calcium zinc silicate glasses gave polyalkenoate cements which were hydrolytically unstable, whilst alumino-zinc-silicate glasses gave hydrolytically stable cements with short setting times (under 10 min) and high compressive strengths (above 90 MPa). The aluminium to silicon ratio was not important in determining the cement forming ability of the glass. The ability to form a cement was, instead, determined largely by the network connectivity of the glass.

Aluminum↗
PubMed1994

Chloride- and alkali-containing calcium phosphates as basic materials to prepare calcium phosphate cements.

Combinations of an alkali-containing calcium phosphate-like rhenanite, sodium whitlockite or calcium potassium phosphate and a chloride-containing calcium phosphate-like spodiosite or chloroapatite with or without additions of other calcium phosphates like monocalcium phosphate monohydrate, dicalcium phosphate or dicalcium phosphate dihydrate were made and mixed with water into pastes. The setting time of these pastes was determined. After soaking for a day in Ringer's solution at 37 degrees C the compressive strength and the diametral tensile strength were determined. Two of the combinations tried in this study resulted in the formation of cements at room temperature. One cement was of the type dicalcium phosphate, whereas the other gave octocalcium phosphate as the solid reaction product. The byproducts formed were an aqueous solution of NaCl and one of K2HPO4, respectively. Applications for bone repair and augmentation are envisaged.

Alkalies↗
PubMed1995

Amalgams made from liquid Hg-In.

The addition of indium to amalgam appears to reduce the mercury vapour above fillings during setting. In the present work the structure and the physical properties of amalgams with In additions to the mercury up to 30 vol.% have been investigated. No new phase or undissolved in could be detected by X-ray diffraction and scanning electron microscopy studies. Energy dispersive spectroscopy measured 4 at.% In in the gamma 1-phase of an amalgam with 20 vol.% In added to the mercury. At the same time, the Ag/Hg ratio was substantially increased compared with amalgam having no In addition. The compression strength decreased with increasing In content, and for amalgam with as much as 30 vol.% In added to the mercury, it fell below the minimum requirement of ISO 1559 (Alloys for dental amalgam, International Organization for Standardization, Geneva, 1986). An abrupt drop of the load at the onset of failure and cracks running through the gamma 1-phase, as well as the eta-phase, indicates embrittlement of these phases with increasing In content.

Alloys↗
PubMed1995

Mechanical properties and histological evaluation of sintered beta-Ca2P2O7 with Na4P2O7.10H2O addition.

The ultimate goal of implantation of biomaterials in the skeleton is to reach full integration of the non-living implant with the living bone. The biomaterial can be used much as a bone graft, resorbing or dissolving as bone growth occurs, and the end result is a new remoulded bone. Calcium pyrophosphate, Ca2P2O7, is one of the intermediate products of bone mineralization. beta-Dicalcium pyrophosphate (beta-DCP) doped with certain amounts of Na4P2O7.10H2O was prepared as the developed material. Na4P2O7.10H2O was used as a liquid-phase additive to improve the sintering process and promote physiological bioresorbability. Compressive strength and four-point bending strength were measured by the Bionix test system 858. The mechanical strength of the sintered beta-DCP increased with the addition of Na4P2O7.10H2O up to 5 wt%, but thereafter decreased. The microstructure and crystal structure were analysed by the techniques of SEM, EPMA, TEM and XRD. The relationship between the mechanical strength of the sintered bioceramics and the Na4P2O7.10H2O dopant was examined in terms of the presence of NaCa(PO3)3, grain growth and abnormal grain coalescence while the dopant increased. Preliminary in vivo evaluation was studied by rabbit femur condyle implantation. There was no inflammation or any toxic sign during the experimental period. The histological section of intraosseous implantation revealed that the new bone deposited directly on the surface of the material in the fourth week after operation. The implant gradually decreased in volume and was replaced by the surrounding regenerated bone in the rabbit condyle in vivo environment. The results led us to conclude that the developed material has great potential as a biodegradable bone substitute.

Animals↗
PubMed1991

Glass-ionomer cements in orthopaedic surgery: design of laboratory tests.

Recently, interest has been shown in the use of Glass-ionomer cement as a bone cement in orthopaedic surgery. This paper discusses the determination of working time, setting time and compressive strength for an experimental Glass-ionomer [GI] and the existing poly(methyl methacrylate) [PMMA] cement. Conventional test methods and some novel techniques are explored. Suggestions are made for new techniques which will allow the comparison of different types of cement. The effect of different storage media on cement stability has shown that both cements show a degree of instability dependent on the medium used. The properties reported for the GI cement suggest that it has the potential to be a new bone cement.

Bone Cements↗
PubMed1993

The effect of glass heat treatment on the properties of a novel polyalkenoate cement.

The effect of heat treating the glass component of a novel glass-ionomer (polyalkenoate) cement on cement properties has been determined, with specific reference to the reactivity of the glass, and the mechanical properties of the resultant cement. It has been shown that heat treatment is a suitable method of decreasing the glass reactivity and improving the handling characteristics of the mixed cement. Under some conditions, an increase in compressive strength was found, although the effect on tensile properties was not significant.

Glass Ionomer Cements↗
PubMed1994

Compliance of an apatitic calcium phosphate cement with the short-term clinical requirements in bone surgery, orthopaedics and dentistry.

An apatitic calcium phosphate cement was developed containing a nucleator in its powder and an accelerator in the liquid and having an initial setting time of 7.5 min and a final setting time of 12.5 min according to testing with Gillmore needles at room temperature. At body temperature the initial setting time is 6 min, after which the wound can be closed. The dough time (during which it can be deformed without damaging its microstructure) is 4 min. Therefore, the time lost during an operation with this material is 2 min. The product does not shrink or expand during setting, neither is there a thermal effect; it does not swell or disintegrate upon exposure to aqueous fluids after initial setting. Upon soaking in Ringer's solution the product obtains a final compressive strength of 40 MPa and 65% of that strength is reached within 6 h at body temperature. Cytotoxicity is absent. Applications are envisaged in bone surgery, orthopaedics and dentistry, a.o. for acceleration of the osseointegration of metal endoprostheses.

Biocompatible Materials↗
PubMed1990

An investigation of test-house variability in the mechanical testing of dental materials and the statistical treatment of results.

The suitability of a test for standard specification testing depends inter alia on the ability to repeat the tests in a reproducible manner at a number of test centres. This work involved the investigation of three tests currently proposed as standard specification tests for dental materials. It was found that one test (compressive strength of cements) is inappropriate for inclusion in standards due to an unacceptable variation in test results between test centres. The treatment of results suggested in standards should place less emphasis on the mean value of a relatively small number of test specimens and the use of a simple form of probability theory in which, say, 80 per cent of specimens are required to achieve a certain pass level. In some standards there may be a need to increase the numbers of test specimens significantly in order to achieve a more meaningful and reliable result. The use of Weibull statistics can be adopted as a means of identifying tests which are suitable for inclusion in standard specifications, although it is doubtful that a test at this level of sophistication is required or desirable for inclusion in the standards themselves.

Composite Resins↗
PubMed2004

In vitro degradation of three-dimensional porous poly(D,L-lactide-co-glycolide) scaffolds for tissue engineering.

In vitro degradation behaviors of three-dimensional tissue engineering porous scaffolds made from amorphous poly(D,L-lactide-co-glycolide) with three different formulations have been systematically investigated up to 26 weeks in phosphate buffer saline solution at 37 degrees C. The following properties of the scaffolds were measured as a function of degradation time: dimensions, weight, compressive strength and modulus, polymer molecular weight and its distribution, and pore morphology. Of special interest was the determination of mechanical properties in wet environment. The pH of the PBS media was also detected. According to the characteristic changes of the various properties of porous scaffolds, the degradation process is suggested to be roughly divided into three stages tentatively named as quasi-stable stage, decrease-of-strength stage, loss-of-weight and disruption-of-scaffold stage.

Biocompatible Materials↗
PubMed2005

Nucleation of biomimetic apatite in synthetic body fluids: dense and porous scaffold development.

The effectiveness of synthetic body fluids (SBF) as biomimetic sources to synthesize carbonated hydroxyapatite (CHA) powder similar to the biological inorganic phase, in terms of composition and microstructure, was investigated. CHA apatite powders were prepared following two widely experimented routes: (1) calcium nitrate tetrahydrate and diammonium hydrogen phosphate and (2) calcium hydroxide and ortophosphoric acid, but using SBF as synthesis medium instead of pure water. The characteristics of the as-prepared powders were compared, also with the features of apatite powders synthesized via pure water-based classical methods. The powder thermal resistance and behaviour during densification were studied together with the mechanical properties of the dense samples. The sponge impregnation process was used to prepare porous samples having morphological and mechanical characteristics suitable for bone substitution. Using this novel synthesis was it possible to prepare nanosized (approximately equal to 20 nm), pure, carbonate apatite powder containing Mg, Na, K ions, with morphological and compositional features mimicking natural apatite and with improved thermal properties. After sintering at 1250 degrees C the carbonate-free apatite porous samples showed a surprising, high compressive strength together with a biomimetic morphology.

Apatites↗
PubMed2005

In vitro degradation of porous poly(propylene fumarate)/poly(DL-lactic-co-glycolic acid) composite scaffolds.

This study investigated the in vitro degradation of porous poly(propylene fumarate) (PPF-based) composites incorporating microparticles of blends of poly(DL-lactic-co-glycolic acid) (PLGA) and poly(ethylene glycol) (PEG) during a 26-week period in pH 7.4 phosphate-buffered saline at 37 degrees C. Using a fractional factorial design, four formulations of composite scaffolds were fabricated with varying PEG content of the microparticles, microparticle mass fraction of the composite material, and initial leachable porogen content of the scaffold formulations. PPF scaffolds without microparticles were fabricated with varying leachable porogen content for use as controls. The effects of including PLGA/PEG microparticles in PPF scaffolds and the influence of alterations in the composite formulation on scaffold mass, geometry, water absorption, mechanical properties and porosity were examined for cylindrical specimens with lengths of 13 mm and diameters of 6.5 mm. The composite scaffold composition affected the extent of loss of polymer mass, scaffold length, and diameter, with the greatest loss of polymer mass equal to 15+/-5% over 26 weeks. No formulation, however, exhibited any variation in compressive modulus or peak compressive strength over time. Additionally, sample porosity, as determined by both mercury porosimetry and micro-computed tomography did not change during the period of this study. These results demonstrate that microparticle carriers can be incorporated into PPF scaffolds for localized delivery of bioactive molecules without altering scaffold mechanical or structural properties up to 26 weeks in vitro.

Biocompatible Materials↗
PubMed2005

Acrylic bone cements modified with beta-TCP particles encapsulated with poly(ethylene glycol).

Beta-tricalcium phosphate (beta-TCP) has been encapsulated with poly(ethylene glycol) (PEG) to improve the filler/cement interface, and it was later incorporated to a poly(methyl methacrylate) bone cement in order to obtain cements with improved stability in the long term. Size and size distribution of the agglomerates forming the initial powder was drastically changed after its dispersion in a PEG aqueous solution. Whereas the initial beta-TCP particles had a 584 microm average diameter, the treated particles (TCP-PEG) presented more than 60% of the particles in a range of 2-6 microm. The effect of adding the treated particles to an acrylic cement was evaluated in terms of curing parameters, in vitro behaviour and mechanical performance. The presence of the TCP-PEG particles did not affect either peak temperature or setting time, indicating a good homogeneity of polymerising mass in contrast to the effect observed with the plain beta-TCP particles, which gave rise to higher setting times. In vitro behaviour studies revealed hydration degree values of the modified cements comparable to that of PMMA cements. Early stages of water uptake was Fickian in nature for all the experimental formulations indicating that the water absorption followed a diffusion controlled mechanism. After 3 months of storage in SBF the experimental formulations presented values of compressive strength in the range 76-78 MPa, higher than the minimum required by ISO 5833 (70 MPa) and those of tensile strength in the range 42-48 MPa, higher than the minimum reported for commercial formulations (30 MPa), but no significant differences in the strengths and elastic modulus were observed with the treatment of the filler particles. This observation was confirmed by ESEM analysis of the tensile fracture surfaces, which revealed a rather good cohesion between the bioceramic particles with some gaps around them, independently of the type of particles. The themogravimetric analysis of dry and wet specimens showed a higher dissolution rate of the plain beta-TCP particles in comparison to the encapsulated ones, indicating that the PEG adsorbed on the surface of the TCP particles could be a way to control the resorbability of the bioceramic component.

Absorption↗
PubMed2005

Mechanical properties and osteoconductivity of porous bioactive titanium.

Porous bioactive titanium implants (porosity of 40%) were produced by a plasma-spray method and subsequent chemical and thermal treatments of immersion in a 5M aqueous NaOH solution at 60 degrees C for 24 h, immersion in distilled water at 40 degrees C for 48 h, and heating to 600 degrees C for 1 h. Compression strength and bending strength were 280 MPa (0.2% offset yield strength 85.2 MPa) and 101 MPa, respectively. For in vivo analysis, bioactive and nontreated porous titanium cylinders were implanted into 6mm diameter holes in rabbit femoral condyles. The percentage of bone-implant contact (affinity index) of the bioactive implants (BGs) was significantly larger than for the nontreated implants (CGs) at all postimplantation times (13.5 versus 10.5, 16.7 versus 12.7, 17.7 versus 10.2, 19.1 versus 7.8 at 2, 4, 8 and 16 weeks, respectively). The percentage of bone area ingrowth showed a significant increase with the BGs, whereas with the CGs it appeared to decrease after 4 weeks (10.7 versus 9.9, 12.3 versus 13.1, 15.2 versus 9.8, 20.6 versus 8.7 at 2, 4, 8 and 16 weeks, respectively). These results suggest that porous bioactive titanium has sufficient mechanical properties and biocompatibility for clinical use under load-bearing conditions.

Animals↗