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PubMed2005

Synthesis of bioactive PMMA bone cement via modification with methacryloxypropyltri-methoxysilane and calcium acetate.

Bone cement consisting of polymethylmethacrylate (PMMA) powder and methylmethacrylate (MMA) liquid is clinically used for fixation of implants such as artificial hip joints. However, it does not show bone-bonding ability, i.e., bioactivity. The lack of bioactivity would be one of factors which cause loosening between the cement and the implant. The present authors recently showed the potential of bioactive PMMA-based bone cement through modification with gamma-methacryloxypropyltrimethoxysilane (MPS) and calcium acetate. In this study, the effects of the kinds of PMMA powder on setting time, apatite formation and compressive strength were investigated in a simulated body fluid (Kokubo solution). The cement modified with calcium acetate calcined at 220 degrees C could set within 15 min when the PMMA powder had an average molecular weight of 100,000 or less. The addition of calcium acetate calcined at 120 degrees C in the PMMA powder required a much longer period for setting. The modified cements formed an apatite layer after soaking in the Kokubo solution within 1 day for cement starting from PMMA powder with a molecular weight of 100,000 or less. Compressive strengths of the modified cements were more than 70 MPa for cements starting from 100,000 and 56,000 in molecular weight. After soaking in Kokubo solution for 7 days, the modified cement consisting of PMMA powder of 100,000 in molecular weight showed a smaller decrease in compressive strength than that consisting of 56,000 in molecular weight. These results indicate that bioactive PMMA cement can be produced with appropriate setting time and mechanical strength when PMMA powders with a suitable molecular weight are used. Such a type of design of bioactive PMMA bone cement leads to a novel development of bioactive material for bone substitutes.

Acetates↗
PubMed2006

In vitro inhibition of coagulase-negative staphylococci by vancomycin/aminoglycoside-loaded cement spacers.

BACKGROUND: Successful treatment of allograft infections by the temporary implantation of an antibiotic-loaded polymethylmethacrylate cement spacer depends on the diffusion of antibiotics out of the cement and inhibition of bacterial growth in the surrounding tissue. We investigated with an in vitro model how long antibiotics are released by the cement and if gentamicin-resistant coagulase-negative staphylococci (CNS) are inhibited by vancomycin mixed with the gentamicin-loaded cement. MATERIALS AND METHODS: Four formulations of antibiotic-loaded cement disks, i.e. gentamicin, tobramycin, vancomycin and tobramycin combined with vancomycin, respectively, were used to test the inhibition of eight isolates of Staphylococcus epidermidis and two reference strains of Staphylococcus aureus by an agar diffusion test on Mueller-Hinton (MH) agar similar to the routine laboratory disk diffusion method. Moreover, cement spacer cylinders loaded with gentamicin alone or combined with vancomycin were submerged in MH agar for weeks and the capacity to inhibit five different isolates of S. epidermidis was measured. RESULTS: The size of the inhibition zones around the antibiotic-loaded cement disks correlated with the minimal inhibitory concentration (MIC) of the antibiotics against the tested strains. All five strains of S. epidermidis were inhibited by vancomycin-loaded cement spacers for at least 30 days. However, two gentamicin-resistant S. epidermidis strains with MICs of 4 mg/l and 16 mg/l could not be inhibited longer than 3 days by the gentamicin-loaded cement spacer. CONCLUSION: The in vitro data suggest that antibiotic-loaded cement spacers inhibit susceptible bacteria for 4-6 weeks. The addition of vancomycin to commercial aminoglycoside-loaded cements might be helpful in allograft infections in tumor patients to inhibit a broad range of bacteria including gentamicin-resistant CNS very commonly found in such infections.

Aminoglycosides↗
PubMed2006

In vitro biodegradation of three brushite calcium phosphate cements by a macrophage cell-line.

Depending upon local conditions, brushite (CaHPO4 x 2 H2O) cements may be largely resorbed or (following hydrolysis to hydroxyapatite) remain stable in vivo. To determine which factors influence cement resorption, previous studies have investigated the solution-driven degradation of brushite cements in vitro in the absence of any cells. However, the mechanism of cell-mediated biodegradation of the brushite cement is still unknown. The aim of the current study was to observe the cell-mediated biodegradation of brushite cement formulations in vitro. The cements were aged in the presence of a murine cell line (RAW264.7), which had the potential to form osteoclasts in the presence of the receptor for nuclear factor kappa B ligand (RANKL) in vitro, independently of macrophage colony stimulating factor (M-CSF). The cytotoxicity of the cements on RAW264.7 cells and the calcium and phosphate released from materials to the culture media were analysed. Scanning electron microscopy (SEM) and focused ion beam (FIB) microscopy were used to characterise the ultrastructure of the cells. The results showed that the RAW264.7 cell line formed multinucleated TRAP positive osteoclast-like cells, capable of ruffled border formation and lacunar resorption on the brushite calcium phosphate cement in vitro. In the osteoclast-like cell cultures, ultrastructural analysis by SEM revealed phenotypic characteristics of osteoclasts including formation of a sealing zone and ruffled border. Penetration of the surface of the cement, was demonstrated using FIB, and this showed the potential demineralising effect of the cells on the cements. This study has set up a useful model to investigate the cell-mediated cement degradation in vitro.

Animals↗
PubMed2006

Porosity of different dental luting cements.

OBJECTIVE: The aim of this in vitro study was to compare open porosity and pore size distribution of different types of luting cements (zinc phosphate and polycarboxylate produced by Harvard Cement, Great Britain, glass-ionomer product GC Fuji I, GC Corporation, Japan, and Panavia F, resin based composite cement, Kurraray Co. Ltd. Japan) using mercury intrusion porosimetry and use it as an additional parameter for ranging the quality of cements used in prosthetics. METHOD: Samples were hand mixed in accordance with the manufacturer's instructions and formed in cylindrical test specimens. Density of samples was determined using a pycnometer while porous structure was estimated using high pressure mercury intrusion porosimeter enabling estimation of pore diameters in interval 7.5-15,000 nm. RESULTS: The polycarboxylate cement posses the highest porosity and specific pore volume among investigated cements. By comparison of the results obtained for zinc phosphate and glass-ionomer cement, it can be observed that according to some textural properties zinc phosphate cement is better choice (smaller specific pore volume and absence of macropores larger than 1 microm) while according to other textural properties the glass-ionomer has advantage (smaller porosity). The resin based composite cement poses the most desired porous structure for prosthetic application among the investigated cements (the lowest porosity and specific pore volume and all identified pores are smaller than 20 nm). SIGNIFICANCE: Based on results of this study, it is possible to estimate the efficiency of luting cements to protect the interior of tooth from penetration of oral fluids, bacteria and bacterial toxins into unprotected dentine.

Dental Cements↗
PubMed2005

The effect of three-dimensional shape optimization on the probabilistic response of a cemented femoral hip prosthesis.

Probabilistic analyses allow the effect of uncertainty in system parameters on predicted model performance measures to be determined. Furthermore, using performance functions to describe a failure event, the probability of failure can be quantified. The effect of three-dimensional prosthesis shape optimization on the probabilistic response and failure probability of a cemented hip prosthesis system is investigated. Random variables include joint and muscle loading, cortical and cancellous bone and PMMA bone cement elastic properties, and strength parameters describing failure of the bone cement and the prosthesis-bone cement interface. Several performance functions describing the bone cement and prosthesis-cement interface are used to compute the probability of failure. When evaluated deterministically, most performance functions indicated a safe design, with the exception of interface tensile failure. However, when evaluated probabilistically, finite probabilities of failure were computed, some significant. The most likely mode of failure before shape optimization was prosthesis-bone cement interface tensile failure with a predicted probability of failure of 97.9%. Deterministic prosthesis shape optimization reduced the probability of failure for all performance functions and reduced prosthesis-bone cement interface tensile failure by 31.7%. Probability sensitivity factors indicate that the uncertainty in the joint loading, cement strength, and implant-cement interface strength have the greatest effect on the computed probability of failure. Implant shape optimization results in a more robust implant design that is less sensitive to uncertainties in joint loading, which cannot be easily controlled, and more sensitive to cement and interface properties, which are easier to modify.

Cementation↗
PubMed2005

A comparative FEA of the debonding process in different concepts of cemented hip implants.

Debonding of the stem-cement interface and damage accumulation in the cement mantle are basic events that contribute to the long-term failure of cemented hip reconstructions. In this work, a numerical study with these two processes coupled is presented. On the one hand, debonding of the stem-cement interface was simulated by means of a cohesive surface theory that was implemented into an interface finite element. This interface model includes a tensile-shear behavior law, the fatigue failure of the interface, and the friction evolution between both surfaces. On the other hand, damage accumulation in the cement was formulated through the theory of continuum damage mechanics, considering cement damage due to tension, creep under compression, crack closure effects, non-linear damage accumulation and cement residual stresses appearing during polymerisation. This methodology was applied to simulate and compare the degradation process of the cement and stem-cement interface in four different concepts of design: Exeter, Charnley, Elite Plus and ABG II stems. As the actual mechanical properties of the surface of each specific prosthesis are not known, we assumed the same for all of them, distinguishing between polished and matt surfaces. With this assumption, the predicted results showed that the debonding process is very different for each implant depending on the stem geometry. Lower cement deterioration was obtained for the Exeter and ABG II stems, while the lowest stem-cement interface debonding was produced in the Exeter and the Elite Plus stems.

Biomechanical Phenomena↗
PubMed2001

Current cementing techniques in hip hemi-arthroplasty.

To assess the use of modern cementing techniques in hip hemi-arthroplasty a postal questionnaire was sent during 1998 to all British Orthopaedic Training Association (B.O.T.A.) members regarding use of cement, type of cement, bone preparation and cementing technique. The results of this survey were compared to a similar survey in 1994 to assess any change in practice. Two hundred and eighty-six trainees responded to the 1998 survey, 352 to the 1994 survey. The use of uncemented prostheses had decreased from 31.3 in 1994 to 21.7% in 1998. Normal viscosity Palacos cement remains the most common cement in use, 64.3% in 1998. The use of antibiotic loaded cement has increased from 53.7 in 1994 to 67.9% in 1998. For bone preparation 47.3% of trainees in 1998 used a modern technique (syringe irrigation/pulsed lavage, brushing, gauze packing) compared to 35.1% in 1994. Modern cement insertion (retrograde gun, cement restriction and sustained pressure) was carried out by 39.3% in 1998 compared to 28.5% in 1994. Overall 27.2% of trainees used modern cementing techniques in hip hemi-arthroplasty, compared to 19.4% in 1994. Modern cementing techniques are used by a minority of British orthopaedic trainees, but in comparison to 1994 their use has increased.

Arthroplasty, Replacement, Hip↗
PubMed2000

Tissue responses of calcium phosphate cement: a study in dogs.

The in vivo properties of a new kind of calcium phosphate cement were investigated in this study. Calcium phosphate cement was implanted as paste into femoral bone and dorsal muscle of dogs for 3 and 6 months, and as prehardened form into thigh muscles of dogs for 1, 2 and 6 months. Histology was performed on thin un-decalcified sections. No foreign body reaction, no inflammation and no necrosis were found both in bony site and in muscles. There was no connective tissue layer between the cement and bone when cement paste was implanted in the bone. A creeping substitution of cement by bone, in which osteoclast-like cells resorbed the cement as if the cement is a part of bone and new bone was formed directly on the resorption line of calcium phosphate cement, was found. Bone formation was found histomorphologically in pores and deep rugged surface of cement samples (both paste and prehardened form) implanted in muscles of dogs. The induced bone was also identified with backscattered scanning electron microscopy (BSE) and by energy-dispersive X-ray micro-analysis (EDX). The results suggest that the calcium phosphate cement used in this study is biocompatible, resorbable in a manner of creeping substitution, osteoconductive and osteoinductive. It seems that an ideal bone substitute can be developed by using this type of calcium phosphate cement.

Absorbable Implants↗
PubMed2001

Staphylococcus aureus biofilm formation on different gentamicin-loaded polymethylmethacrylate bone cements.

In this in vitro study, the formation of a Staphylococcus aureus biofilm on six gentamicin-loaded bone cements (CMW1, CMW3, CMW Endurance, CMW2000, Palacos, and Palamed) was determined in a modified Robbins device over a 3 days time span and related with previously (Van de Belt et al., Biomaterials 21 (2000) 1981) measured kinetics of antibiotic release by these cement brands. The influence of gentamicin release on biofilm formation was quantified by expressing the number of colony-forming units on gentamicin-loaded cement relative to the number of viable organisms on unloaded cement of the same brand. Biofilms formed on all gentamicin-loaded cements, despite the release of antibiotics, followed a consistent pattern in time with a maximum number of colony-forming units per unit cement area found between 24 and 30 h after inoculation. None of the gentamicin-loaded cements showed a reduction in biofilm formation relative to unloaded cements within 6 h after inoculation, whereas only gentamicin-loaded CMW1 and Palacos reduced biofilm formation 24 h after inoculation. Alternatively, CMW Endurance, CMW2000, and Palamed did not exhibit any initial reductions in biofilm formation, but effects started after 72, 48, and 72 h, respectively. Biofilm reduction by gentamicin-loaded CMW3 lasted the longest from 24 to 72 h. Interestingly, each cement seemed to have a different "window-of-effectiveness" with regard to reduction in biofilm formation that did not relate with the gentamicin-release kinetics. Summarising, this study demonstrates that although gentamicin loading of bone cements yields reductions in biofilm formation, S. aureus is able to grow on gentamicin-loaded bone cements.

Biocompatible Materials↗
PubMed2001

Distribution of fluoride in glass ionomer cement determined using SIMS.

The uptake by glass ionomer cement of ions (particularly fluoride) from solutions in which the cements have been immersed has been extensively reported. The concentrations within the cement often greatly exceed those in the immersing solution. The distribution of these ions has not been determined. The aim of this study is to use SIMS to investigate the levels of ions within the cement at different depths below the immersed surface of the cement. K+ and F were the ions studied and uptake was into a cement containing neither K nor F (LG30) and one containing F (AH2). The surface was analysed using a Cameca ims4f instrument employing a 14.5 keV Cs+ primary ion beam. This was calibrated on cements made from a series of glasses in which fluorine content was systematically substituted for oxygen (without other elemental changes). XPS, which is very much a surface technique, was used in confirmatory role with respect to the SIMS analysis. Cement discs were made from LG30- and AH2-based cements. After maturation for 72 h these were immersed in 0.275% KF solution for 24 h. SIMS analysis indicated appreciable surface F concentration on LG30 and on AH2 an enhanced F concentration. In contrast, K was not detected on the LG30 surface and only at a low level on AH2. These results were confirmed by XPS. Using the ion beam of the SIMS to sputter away cement enabled the F depth profile on LG30 to be measured to 10 microm. Over this distance the F content drops from 6.2 mmol/g at 0.2 microm from the surface to 0.2 mmol/g at 10 microm. No K was detected down to 13 microm from the surface. From the results of this study, it can be concluded that SIMS is an appropriate tool for further investigation of the distribution of ions uptaken by glass ionomer cements.

Anions↗
PubMed1991

Compressive behavior of human bone-cement composites.

Current surgical practice in the implantation of cemented total joint arthroplasties generally creates a zone of variable thickness in which polymethylmethacrylate (PMMA) is intermixed with trabecular bone. The authors' objectives in these experiments were to characterize the compressive mechanical properties of this bone-cement composite material. They found that the mechanical properties of bone-cement composite specimens, fabricated under in vitro conditions that would promote nearly complete cement filling, are closer to the properties of trabecular bone than to those of cement. For both low-viscosity cement (LVC) and PMMA specimens, with the cement introduced by either hand-packing or pressurized injection at periods of 2 and 7 minutes, the compressive strengths ranged from 29 MPa to 50 MPa and the compressive moduli from 539 MPa to 1,210 MPa. Cement volume fractions achieved using different filling methods ranged from 76% to 87%. In contrast to previous studies of bone-cement composites using high-density bovine bone, neither mechanical properties nor filling parameters correlated significantly with bone porosity measured prior to filling. The authors expect that the mechanical properties of bone-cement regions created at surgery under less than these ideal in vitro filling conditions will only approach their values as an upper limit. Thus, bone-cement composites created in situ at surgery will also exhibit mechanical properties well below previously assumed values.

Aged↗
PubMed1997

Effect of sodium bicarbonate amount on in vitro indomethacin release from self-setting carbonated-apatite cement.

PURPOSE: In the present study, to develop a drug delivery system with higher bioactivity in hard tissues by using the self-setting bioactive carbonate apatite cement, we have investigated the effects of sodium bicarbonate content on the in vitro drug release from a self-setting bioactive carbonate apatite cement containing indomethacin (IMC). METHODS: The cement powder systems constituted an equimolar mixture of tetracalcium phosphate (Ca4(PO4)2O) and dicalcium phosphate dihydrate (CaHPO4.2H2O), hydroxyapatite (HAP, Ca10(PO4)6(OH)2) seed crystals and sodium bicarbonate. Two types of 2% IMC loaded-cements were prepared as follows, one containing 0% HAP seed crystal and 0-10% sodium bicarbonate, and the other containing 40% HAP seed crystal and 0-10% sodium bicarbonate. The drug release profiles from 2% IMC loaded-cements were measured in simulated body fluid at pH 7.25 and 37.0 degrees C. RESULTS: The drug release profiles from the cement matrix systems with or without seed crystals were estimated using a moment analysis computer program. The mean drug release time (MDT) and the time required for 50% drug release of the cement containing 0 and 40% seed crystal decreased with an increase of sodium bicarbonate. Furthermore, after the drug release the total pore volume of the cement matrix, as measured by mercury porosimetry, increased with an increase of sodium bicarbonate. CONCLUSIONS: MDT and T50's were a function of adding the amount of sodium bicarbonate. The results of the relationship between the micropore distribution, total volume of pores after drug release and drug release supported the hypothesis that the variation in drug release from the cements resulting from the addition of sodium bicarbonate was mainly due to an increase in the diffusion of the drug in the micropores of the cement by dissolution or erosion of the cement matrix.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2000

Early failure of modern cemented stems.

In the late 1970s, improved cement technique was introduced in an attempt to address the problem of early cemented stem loosening. Subsequently, numerous centers reported stem survival rates of >95% beyond 10 years. Long-term cemented stem fixation was believed widely to be consistently obtainable in most patients. Despite the widespread clinical success of these early cemented stems, numerous changes were introduced in stem design and cement technique. In more recent years, a surprising number of series of early failures of cemented stems have been reported. Some designs consistently have had a high early failure rate. Others have failed infrequently, but the failures have occurred early and with extensive osteolysis. Numerous causes have been proposed, including poor cement technique, undersized broaches, increased stem offset, decreased stem length, rough surface finish, and circular stem cross-section. Failures often are multifactorial and defy a simple explanation based on a single parameter. Results of cemented stems are more variable than previously appreciated. There are nuances of cemented stem design, cement technique, and patient selection that can lead to early failure and that are not understood completely at present. Given the availability of many cemented designs with proven records of clinical success, new design features should be introduced prudently with extensive premarket testing, limited clinical release, and careful postmarket surveillance.

Arthroplasty, Replacement, Hip↗
PubMed2004

Comparison of various vacuum mixing systems and bone cements as regards reliability, porosity and bending strength.

BACKGROUND: There are several vacuum mixing systems on the market which are arbitrarily used with various bone cements in clinical work. Hardly any studies have been done on the performance and handling of these systems in combination with different cement brands. MATERIAL AND METHODS: We therefore tested 6 vacuum mixing systems (Palamix, Summit, Cemvac, Optivac, Vacumix, MixOR) in combination with 6 cement brands (Palacos R, Simplex P, CWM 1, CWM 2000, Palamed G, VersaBond) concerning their reliability, user-friendliness, porosity and bending strength. RESULTS: Our study indicated that each system has weak points. The preparation of the mixed cement for gun injection can present problems. If cement collection under vacuum fails, porosity is increased. Manual collection without a vacuum carries the risk of intermixing air. For comfortable and effective retrograde cement application, cement guns should have a stable connection with the cartridge and a high piston stroke. There are marked differences between the systems as regards overall porosity when all tested cements are considered (range 2-18%), and between the cements when all tested systems are considered (range 2-17%). All test samples exceeded the required bending strength of 50 MPa, according to ISO 5833. Palaces specimens showed excessive plastic deformation in the bending test. INTERPRETATION: There are better and worse mixing system/cement combinations for a given system and a given cement. Systems with cement collection under vacuum reduce porosity best.

Bone Cements↗
PubMed2006

Estimation of the optimum loading of an antibiotic powder in an acrylic bone cement: gentamicin sulfate in SmartSet HV.

BACKGROUND: In some countries, commercially available antibiotic powder-loaded acrylic bone cement is routinely used in joint replacement, while, in others, "off-label" formulations are used in selected procedures (where the antibiotic powder is blended manually with the powder of a plain cement in the operating room/theater by either the surgeon or approved personnel). In the latter situation, an arbitrary rather than a rational approach is used for deciding on the amount of the antibiotic that is blended with the cement powder (herein referred to as "the antibiotic powder loading"). METHODS AND RESULTS: The first objective of this study was to present two methods for estimating the optimum loading of gentamicin sulfate powder that may be blended manually with the powder of a commercially available acrylic bone cement, ABC (Wopt). The second objective was to define the challenges associated with each of these methods. The loading (W) was optimized with respect to two key properties of the cured cement that were obtained simultaneously, namely (1) fatigue life in phosphate-buffered saline solution (PBS) at 37 degrees C, and (2) the rate of elution of the gentamicin from the cement (E) in that medium. Three sets of specimens were used, containing 2.25, 4.25 and 11.50 wt/wt% of the gentamicin that was blended manually with the cement powder. The fatigue tests involved determining the number of cycles at which a specimen fractured (Nf) when subjected to fully-reversed tension-compression sinusoidal load, +/- 15 MPa at 2 Hz. E was determined from the concentration of gentamicin in the PBS solution when the specimen fractured, using fluorescence polarization immunoassay for the measurement. Consistent with a priori expectations, it was found that, with increase in W, Nf decreased while E increased. Two approaches for obtaining an estimate of Wopt are described, a mathematical method and an empirical one, that lead to Wopt values of 6.50 wt/wt% and 4.78 wt/wt%, respectively. Thus, this antibiotic loading ranges from about the same to about 92% greater than that in SmartSet GHV Gentamicin, which is a commercially available bone cement used clinically and which has the same composition as SmartSet HV except for the presence of gentamicin sulfate in its powder (blended in by the manufacturer). INTERPRETATION: We present and critically compare two rational methods of determining the optimum loading of an antibiotic powder in an acrylic bone cement, which should serve as a guide when using "off-label" antibiotic powder-loaded acrylic bone cements in cemented joint replacements.

Anti-Bacterial Agents↗
PubMed1996

Mechanical effects of stem cement interface characteristics in total hip replacement.

Stem cement debonding is 1 of the most common forms of fixation failure and is thought to be a prelude to gross loosening of a total hip reconstruction. However, the immediate consequences of debonding remains a matter of controversy. The dynamic effects of stem cement debonding in total hip reconstruction were analyzed using 3-dimensional finite element techniques. Stem cement interface conditions were assumed as completely bonded or unbonded, with or without friction. The dynamic effects were accounted for, as presented by the stance and swing phases of the gait cycle. It was found that both cyclic micromotions at the stem cement interface and stresses in the cement mantle were effectively reduced by friction. The friction cases produced failure probabilities of the cement mantle that were relatively close to the one generated by the bonded stem. The probability of mechanical failure of the cement bone interface decreased after debonding and decreased more with reduced stem cement friction. These results show that, although a firm and lasting bond between stem and cement may be desirable for preventing cement failure, the mechanical effects of a debonded stem are less detrimental than were assumed earlier. For straight tapered stem shapes subjected to the loading conditions described, a polished stem may be desirable for the cement bone interface mechanics.

Bone Cements↗
PubMed2005

Vertebroplasty by use of a strontium-containing bioactive bone cement.

STUDY DESIGN: A review of the laboratory and clinical data for a new strontium-containing hydroxyapatite bioactive bone cement. OBJECTIVES: To compare the properties of the strontium-containing bioactive bone cement with those of polymethyl methacrylate (PMMA) and hydroxyapatite (HA) bone cements. SUMMARY OF BACKGROUND DATA: Vertebroplasty and kyphoplasty using conventional PMMA bone cements have been effectively used to treat osteoporotic spine fractures with good short- and medium-term results. However, PMMA has some undesirable properties, including its high setting temperature, lack of osseointegration, and large stiffness mismatch with osteoporotic bone. These properties are responsible for some postoperative complications. METHODS: Strontium-containing hydroxyapatite (Sr-HA) bioactive bone cement consists of a filler blend of strontium-containing hydroxyapatite, fumed silica and benzoyl peroxide; and a resin blend of bisphenol A diglycidylether methacrylate, triethylene glycol dimethacrylate, poly(ethylene glycol) methacrylate, and N, N-dimethyl-p-toluidine. Its properties, including mechanical strength, setting temperature, biocompatibility, and osseoinduction, were compared with other cements in vitro and in vivo. Early clinical results are presented. RESULTS: The Sr-HA cement has a setting time of 15 to 18 minutes, a maximum setting temperature of 58 degrees C, a compressive strength of 40.9 MPa, bending strength of 31.3 MPa, and a bending modulus of 1,408 MPa. The bending strength and modulus are closer to human cancellous bone. Sr-HA cement promotes osteoblast attachment and mineralization in vitro and bone growth and osseointegration in vivo. In a pilot study, 23 cases of osteoporotic fractures treated with this cement with a mean follow-up of 18 months suggest that it is as effective as PMMA in relieving pain. DISCUSSIONS: Oral strontium has been shown to induce new bone formation and is effective in reducing fracture risk in osteoporosis. Our data suggest that strontium delivered locally has the same effect; thus, the combination of strontium with HA in a cement with a low setting temperature, adequate stiffness, and low viscosity makes this a good bioactive cement for vertebroplasty and kyphoplasty.

Animals↗
PubMedDate not supplied

The influence of chemical activation on hardness of dual-curing resin cements.

During the cementation of metallic restorations, the polymerization of dual-curing resin cements depends exclusively on chemical activation. This study evaluated the influence of chemical activation compared with dual-curing (chemical and light activation), on the hardness of four dual-curing resin cements. In a darkened environment, equal weight proportions of base and catalyst pastes of the cements Scotchbond Resin Cement, Variolink II, Enforce and Panavia F were mixed and inserted into moulds with cavities of 4 mm in diameter and 2 mm in height. Subsequently, the cements were: 1) not exposed to light (chemical activation = self-cured groups) or 2) photoactivated (dual-curing = dual-cured groups). The Vickers hardness number was measured at 1 hour, 24 hours and 7 days after the start time of cements' spatulation. For all the cements, the hardness values of self-cured groups were lower than those of the respective dual-cured groups at 1 hour and 24 hours. At 7 days, this behavior continued for Variolink II and Panavia F, whilst for Scotchbond Resin Cement and Enforce there was no statistical difference between the two activation modes. All cements showed a significant increase in their hardness values from 1 hour to 7 days for both activation modes. Of the self-cured groups, Scotchbond Resin Cement and Variolink II presented the highest and the lowest hardness values, respectively, for all three times tested. Within the limitations of this study, up to the time of 24 h, chemical activation alone was unable to promote similar hardness as to that obtained with dual-curing.

Analysis of Variance↗