Masks for the Reduction of Methyl Methacrylate Vapor Inhalation

BACKGROUND

Exposure to methyl methacrylate vapor (MMA) presents an occupational risk to orthopedic surgeons and ancillary personnel in the operating room. The purpose of this study was to identify a disposable face mask to reduce MMA organic vapor inhalation in the operative suite.

METHODS

First, the effectiveness of MMA vapor filtration was determined in the laboratory. A section of activated carbon impregnated filter face mask (Model 8514, 3M Inc.) was exposed to 150 ppm MMA vapor and MMA ppm of filtered air was monitored until MMA vapor was detectable. The face mask was then worn as directed in the operating room during routine cement mixing during total knee arthroplasty to determine the exposure to MMA vapors during the procedure both with and without the activated carbon impregnated filter face mask.

RESULTS

The activated carbon impregnated face mask was effective in reducing MMA vapor inhalation to non-detectable levels for up to 40 minutes in the laboratory at steady-state exposure of 150 ppm MMA vapor as well as throughout cement mixing and curing in the operative suite during routine total knee arthroplasty.

CONCLUSIONS

An activated carbon impregnated face mask offers a solution for the orthopedic surgeon and supporting personnel who wish to limit their exposure to MMA vapors due to health concerns.Level of Evidence: III.

Visualization of calcium phosphate cement in teeth by zero echo time 1 H MRI at high field

¹ H magnetic resonance imaging (MRI) by a zero echo time (ZTE) sequence is an excellent method to image teeth. Calcium phosphate cement (CPC) materials are applied in the restoration of tooth lesions, but it has not yet been investigated whether they can be detected by computed tomography (CT) or MRI. The aim of this study was to optimize high-field ZTE imaging to enable the visualization of a new CPC formulation implanted in teeth and to apply this in the assessment of its decomposition in vivo. CPC was implanted in three human and three goat teeth ex vivo and in three goat teeth in vivo. An ultrashort echo time (UTE) sequence with multiple flip angles and echo times was applied at 11.7 T to measure T₁ and T₂ * values of CPC, enamel and dentin. Teeth with CPC were imaged with an optimized ZTE sequence. Goat teeth implanted with CPC in vivo were imaged after 7 weeks ex vivo. T₂ * relaxation of implanted CPC, dentin and enamel was better fitted by a model assuming a Gaussian rather than a Lorentzian distribution. For CPC and human enamel and dentin, the average T₂ * values were 273 ± 19, 562 ± 221 and 476 ± 147 μs, respectively, the average T₂ values were 1234 ± 27, 963 ± 151 and 577 ± 41 μs, respectively, and the average T₁ values were 1065 ± 45, 972 ± 40 and 903 ± 7 ms, respectively. In ZTE images, CPC had a higher signal-to-noise-ratio than dentin and enamel because of the higher water content. Seven weeks after in vivo implantation, the CPC-filled lesions showed less homogeneous structures, a lower T₁ value and T₂ * separated into two components. MRI by ZTE provides excellent contrast for CPC in teeth and allows its decomposition to be followed.

Importance of the PMMA viscoelastic rheology on the reduction of the leakage risk during osteoporotic bone augmentation: A numerical leakage model through a porous media

Osteoporotic fractures poses one of the most problematic health issues that affects millions of people by weakening their bones (Osteoporosis). Polymethylmethacrylate (PMMA) cement is usually used to augment the bone and stabilize the fractures. Despite the benefit of using PMMA, it might cause a leakage where the cement undesirably access the surrounding tissues or vessels and lead to a serious complications. Consequently, it is important to study the leakage phenomenon and associated geometric and operation interactions. Although the experimental leakage models have been reported in many studies, a representative numerical leakage model is not exist. Therefore, the objectives of the present paper are to: (a) to develop and validate a representative numerical leakage model; and (b) to investigate numerically and analytically the importance of the rheological parameters (viscosity and relaxation time) on the cement flow to reduce the risk of leakage. ANSYS Polyflow was utilized to implement a 2D numerical leakage model to study the interaction of complex rheological parameters of the cement with the operational and geometrical structure of the representative porous media. In this model, the cement (represented by the upper-convected Maxwell model) flows from the entrance (tip of an 8 gauge cannula) through a porous media with a leakage path (blood vessels) toward the output (Bottom side). The verified and validated numerical leakage model showed the importance of the elastic and viscous part of the cement to control the uniformity of the distributed cement and augmentation pressure, respectively. Moreover, increasing the flow rate can lead to reduce the risk of leakage since the elastic effect will increase. Geometrical parameters of the porous media has a minor effect on changing the elasticity and subsequently on the uniformity of the distributed cement. In conclusion, Cement rheological parameters are found to be the most influential parameters to reduce the risk of leakage by controlling the uniformity of the distributed cement and the augmentation pressure.

Interface micromechanics of transverse sections from retrieved cemented hip reconstructions: an experimental and finite element comparison

In finite element analysis (FEA) models of cemented hip reconstructions, it is crucial to include the cement-bone interface mechanics. Recently, a micromechanical cohesive model was generated which reproduces the behavior of the cement-bone interface. The goal was to investigate whether this cohesive model was directly applicable on a macro level. From transverse sections of retrieved cemented hip reconstructions, two FEA-models were generated. The cement-bone interface was modeled with cohesive elements. A torque was applied and the cement-bone interface micromotions, global stiffness and stem translation were monitored. A sensitivity analysis was performed to investigate whether the cohesive model could be improved. All results were compared with experimental findings. That the original cohesive model resulted in a too compliant macromechanical response; the motions were too large and the global stiffness too small. When the cohesive model was modified, the match with the experimental response improved considerably.

Evaluation of colloidal silica suspension as efficient additive for improving physicochemical and in vitro biological properties of calcium sulfate-based nanocomposite bone cement

In the present study new calcium sulfate-based nanocomposite bone cement with improved physicochemical and biological properties was developed. The powder component of the cement consists of 60 wt% α-calcium sulfate hemihydrate and 40 wt% biomimetically synthesized apatite, while the liquid component consists of an aqueous colloidal silica suspension (20 wt%). In this study, the above mentioned powder phase was mixed with distilled water to prepare a calcium sulfate/nanoapatite composite without any additive. Structural properties, setting time, compressive strength, in vitro bioactivity and cellular properties of the cements were investigated by appropriate techniques. From X-ray diffractometer analysis, except gypsum and apatite, no further phases were found in both silica-containing and silica-free cements. The results showed that both setting time and compressive strength of the calcium sulfate/nanoapatite cement improved by using colloidal silica suspension as cement liquid. Meanwhile, the condensed phase produced from the polymerization process of colloidal silica filled the micropores of the microstructure and covered rodlike gypsum crystals and thus controlled cement disintegration in simulated body fluid. Additionally, formation of apatite layer was favored on the surfaces of the new cement while no apatite precipitation was observed for the cement prepared by distilled water. In this study, it was also revealed that the number of viable osteosarcoma cells cultured with extracts of both cements were comparable, while silica-containing cement increased alkaline phosphatase activity of the cells. These results suggest that the developed cement may be a suitable bone filling material after well passing of the corresponding in vivo tests.

Microspheres of Collagen/β-TCP with an Open Network Fibrillar Structure Strengthened by Chitosan

A novel method of preparing collagen/beta-tricalcium phosphate microspheres with chitosan as the mechanical strength enhancer has been developed in this study. The process involved firstly droplet formation by discharging a mixture of collagen, beta-tricalcium phosphates and alginate into an aqueous solution of CaCl(2) by extruding through an air jet-syringe at 4 degrees C. The gel beads thus formed were collected and subsequently coated with chitosan to stabilize the surface of gel bead. Collagen within the gel beads was then reconstituted while the entrapped alginate was liquefied and drained by incubating in phosphate buffer at 37 degrees C. Microspheres comprised of fibrillar collagen and well-dispersed beta-tricalcium phosphate particulates were obtained by this process. And the mechanical strength of these microspheres was significantly enhanced by chitosan coating. These chitosan-coated collagen/beta-tricalcium phosphate microspheres have an open fibrillar network structure with a great potential for future application as biodegradable bone grafting materials.

Control of methyl methacrylate during the preparation of orthopedic bone cements

The use of methyl methacrylate (MMA) bone cement during orthopedic procedures has been seen as a potential exposure hazard to health care professionals. However, that assessment is based on a number of investigations with problems in experimental design, analysis, and data interpretation. The current investigation quantified differences in MMA vapors produced during the preparation of competing bone cements using various methods of preparation. Unlike previous investigations, this effort employs modern validated sampling and analytical methods, and considers the affect of censored results. Measurements of sufficient quality and number were collected to allow for a statistical treatment of the data. The ability of two controlled preparation techniques to reduce MMA emissions were compared with a traditional open container. The results confirmed that the preparation of bone cement releases MMA vapors into the breathing zone of the preparer. One preparation technique (Stryker Bowl) controlled emissions during mixing and curing and affected a 73% reduction in measured MMA concentrations. In addition to mixing and curing, the second technique (UltraMix System) also controlled the MMA during pouring of the monomer and affected a 90% reduction in MMA concentrations. An ANOVA test of interaction indicates that the reductions are attributable to the preparation technique regardless of the type of cement being used. Both a Fisher's PLSD and Games/Howell post hoc test of the results indicate that the mean differences between the uncontrolled open container and the controlled preparation techniques are significant (p < 0.05).

An evaluation of GC-MS and HPLC-FD methods for analysis of protein binders in paintings

Two chromatographic methods have been compared for analysis of protein-binding media used in paintings, namely, HPLC with fluorescence detection and GC-MS. The proteins were hydrolyzed to the corresponding amino acids (AAs) by gaseous HCl and the AAs were derivatized with methyl chloroformate, followed by GC-MS or by HPLC after derivatization with the AccQ fluorescence reagent. The hydrolysis, derivatization reactions and the chromatographic procedures have been optimized and applied to standard binding media, model and real samples of paintings. The methods have been compared and critically evaluated.

Cemented Cup Stability during Lever-Out Testing after Acetabular Bone Impaction Grafting with Bone Graft Substitutes Mixes Containing Morselized Cancellous Bone and Tricalcium Phosphate-Hydroxyapatite Granules

Bone defects after failed total hip arthroplasty can be reconstructed with impacted morselized bone grafts and a cemented cup. In the near future the amount of bone grafts available for surgical purposes will be insufficient. Ceramic calcium phosphates [tricalcium phosphate (TCP) and hydroxyapatite (HA)] have been widely considered as potential bone graft substitutes or bone graft extenders. In the past, mechanical experiments have been performed to determine implant stability of bone grafts and ceramic TCP-HA granules mixes under a compressive load. However, in-vivo migration studies suggest that shear loading may be equally important. This in-vitro study investigated the initial stability of cups reconstructed with various mixes of bone grafts and ceramic TCP-HA granules in a lever-out situation, where shearing is the predominant loading mode. It was found that the cups reconstructed with mixes of bone graft and TCP-HA granules exhibited greater mechanical stability than the cups reconstructed with bone grafts only. It is concluded that from a mechanical standpoint, when considering shear force resistance, 50–50 per cent volume mix and 25–75 per cent volume mix of morselized cancellous bone graft and TCP-HA granules both provide adequate initial cup stability and can be used for acetabular reconstructions with the bone impaction grafting technique.

[Cemented total knee arthroplasties]

INTRODUCTION

The aseptic loosening of cemented total knee arthroplasties is still an unsolved problem. In this regard, the hydrolysis resistance in the metal-to-bone cement interface is of major importance.

MATERIAL AND METHODS

Cemented pre-treated tibia components coated by means of a silica/silane interlayer system of the model "Columbus PS" were dynamically loaded with the help of a knee-simulator similar to DIN ISO 14243. After loading, the components were microscopically analysed concerning debonding in the metal-to-bone cement interface as well as with regard to cement mantle defects. These data were matched with uncoated "Columbus PS" components. Unloaded coated and uncoated tibia components acted as a control.

RESULTS

In comparison with uncoated tibia components, the pre-treated and coated ones yielded a highly significant reduction of cement defects (p < 0.01) as well as a significant reduction of debonding in the metal-to-bone cement interface (p < 0.05).

CONCLUSION

By means of the silica/silane interlayer system for cemented tibia components, a hydrolytic debonding in the metal-to-bone cement interface with subsequent mechanical loosening and consecutive early cement mantle failure can be significantly reduced. This could lead to an increased long-term stability of the metal-to-bone cement compound with decreased aseptic loosening in clinical use.

Mechanical and histological evaluation of a PMMA-based bone cement modified with gamma-methacryloxypropyltrimethoxysilane and calcium acetate

Polymethylmethacrylate (PMMA) bone cement is widely used for prosthetic fixation in orthopaedic surgery; however, the interface between bone and cement is a weak zone. We developed a bioactive PMMA cement through modification with gamma-methacryloxypropyltrimethoxysilane (MPS) and calcium acetate. The purpose of this study was to compare the handling, mechanical and histological properties of the modified bone cement with those of the conventional cement. The modified specimens exhibited higher bonding strength between bone and implant. Histological observation and micro-focus X-ray computed tomogram (micro-CT) images showed that the modified cement exhibited osteoconduction, which the conventional PMMA bone cement lacked. The modification was found to be effective in enabling osteoconduction with PMMA bone cement, thus providing stable fixation for a long period after implantation.

Effects of porosity on the fatigue performance of polymethyl methacrylate bone cement: an analytical investigation

Porosity has been shown to affect the fatigue life of bone cements, but, although vacuum mixing is widely used to reduce porosity in the clinical setting, results have been mixed and the effects of porosity are not well understood. The aim of this study was to investigate the effects of porosity using stress analysis and fracture mechanics techniques. The stress concentrations arising at voids in test specimens were found using analytical solutions and boundary element methods. The fatigue life of specimens containing voids of various sizes was predicted using fracture mechanics techniques. For spherical voids that do not occupy a significant proportion of the cross-section, the resulting stress concentration is independent of void size and too small to account for the observed crack initiation. Cracks must therefore initiate at additional stress raisers such as radiopacifier particles or additional voids. For large voids, the stress increases as the remaining cross-section of the specimen decreases, and this may account for much of the observed reduction in fatigue strength in hand-mixed cement. Although crack initiation may be largely independent of void size, there is an effect on crack growth rate. Cracks are predicted to grow faster around larger voids, since they remain in the stress concentration around the void for longer. This effect may account for the relationship between porosity and fatigue life that has been observed in samples without large voids. Since porosity appears to affect crack growth more than initiation, it may be less damaging in high-cycle clinical fatigue, which may be predominantly initiation controlled, than in short laboratory tests.

Validation of the small-punch test as a technique for characterizing the mechanical properties of acrylic bone cement

This paper examines the validity of using the small-punch test technique as a means of quantifying the mechanical properties of acrylic bone cement under different test conditions. The elastic moduli calculated using the small-punch test method were compared with data measured using the international standard for acrylic bone resin, ISO 5833. Conclusions from the study indicate that the small-punch test is a reproducible miniature specimen test method that can be used to characterize the mechanical properties of retrieved acrylic bone cement as used in total joint replacement surgery. Moreover, the test conditions were found to influence the elastic modulus of acrylic bone cement. The test temperature had a greater effect on the elastic behaviour of the bone cement than the test medium.

Biomechanical properties of bone cement with addition of cefuroxime antibiotic

Antibiotic-loaded bone cement has been used as prophylaxis against infection in total joint replacement surgery. Its effect on the mechanical strength of cement is a major concern as high dose of antibiotic was associated with a significant reduction in mechanical strength of bone cement. However, the cut-off antibiotic that weakens the mechanical strength of cement remains to be determined. This study was undertaken to observe the changes in the mechanical properties of bone cement with gradual increments of Cefuroxime antibiotic. Cefuroxime at different doses: 0, 1.5, 3.0 and 4.5gm were added to a packet of 40gm bone cement (Simplex P) and study samples were prepared by using third generation cementing technique. Mechanical impact, flexural and tensile strength were tested on each sample. Significant impact and tensile strength reduction were observed after addition of 4.5 gm of Cefuroxime. However, flexural strength was significantly reduced at a lower dose of 3.0 gm. The maximum dose of Cefuroxime to be safely added to 40mg Surgical Simplex P is 1.5gm when third generation cementing technique is used. Further study is needed to determine whether it is an effective dose as regards to microbiological parameters.

A procedure and criterion for bone cement fracture toughness tests

Nowadays, two procedures, based on the recommendation of two American standards (ASTM E399 and ASTM D5045), are used to determine the fracture toughness, KIC, of bone cement. However, there is a lack of knowledge about the equivalence of the two testing methods applied to bone cement. Additionally, in spite of the recommendation of several authors to introduce a rejection criterion for specimens based on the size of defects found in the fracture surface, no data are available about the effect of porosity within the material on the KIC of bone cement.

The aims of this study were to verify whether the KIC values calculated for bone cement using the two procedures are comparable and whether macroporosity within the tested samples affects the KIC value of bone cement, and, if so, to establish a rejection criterion for specimen selection. Samples of pure polymethyl methacrylate (PMMA) were tested by both procedures. Additionally, samples showing defects (macroporosity) of different sizes and located in different positions within the specimen were tested. The KIC value determined following the ASTM E399 procedure was 13 per cent lower than that calculated following the ASTM D5045 procedure. In the first series a lower data scatter was observed. Also, the presence of macroporosity on the fracture surface of the specimen affected the KIC value of bone cement. Therefore, the mechanical behaviour of samples was affected by defects within the material. Since it is possible to mould specimens without macroporosity, it seems recommendable to reject specimens with macroporosity on the fracture surface before calculating the KIC value of bone cement.

Calcium phosphate cement composites in revision hip arthroplasty

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

Modified PMMA cements for a hydrolysis resistant metal-polymer interface in orthopaedic applications

Amongst the many factors influencing the long-term stability of cemented hip prostheses, the interface between the implant and bone cement is considered to be one of the most susceptible to failure. Osteolysis and loosening of the implant can occur by the interaction of mechanically and/or hydrolytically induced bond failure of the metal-cement interface. In this work, an improvement of the hydrolysis resistance of the titanium-bone cement interface was obtained by cement modification with a bifunctional coupling agent combined with a tribochemical TiO2-modification of the metal surface. Methacryloxypropyl-trimethoxysilane was added as coupling agent to the PMMA monomer in concentrations between 5 and 20 wt.% followed by the testing the shear bond strength of PMMA/titanium joints before and after ageing in physiological saline solution. It was found that the hydrolysis resistance of the metal-PMMA interface could be significantly improved by the modification of the cement. At the same time, the mechanical properties (compressive and bending strength) of the modified cement were not altered by the addition of the coupling agent. The advantage of the modification of the cement matrix is an easy clinical applicability of the procedure maintaining the processing and implantation techniques of the cement material.

The self-setting properties and in vitro bioactivity of tricalcium silicate

In this study, tricalcium silicate (Ca(3)SiO(5)), as a new promising injectable bioactive material, was employed to investigate its physical and chemical properties for an injectable bioactive cement filler. The workable Ca(3)SiO(5) pastes with a liquid to powder (L/P) ratio of 0.8--.2 mlg(-1)could be injected for 15--60 min (nozzle diameter 2.0mm). The setting process yielded cellular structures with compressive strength of 6.4--20.2 MPa after 2--28 days. The in vitro bioactivity of Ca(3)SiO(5) paste was investigated by soaking in simulated body fluid (SBF) for various periods. The result showed that the Ca(3)SiO(5) paste could induce hydroxyapatite (HA) formation and dissolve slowly in SBF. The result of indirect cytotoxicity evaluation indicated that Ca(3)SiO(5) paste had a stimulatory effect on cell growth in a certain concentration range. The exothermic process showed that Ca(3)SiO(5) had lower heat evolution rate during the hydration as compared to calcium phosphate cement (CPC). Our results indicated that Ca(3)SiO(5) paste was bioactive and dissolvable, and it is a progressive candidate for further investigation as injectable tissue repairing substitute.

Surface pretreatment for prolonged survival of cemented tibial prosthesis components: full- vs. surface-cementation technique

Background

One of few persisting problems of cemented total knee arthroplasty (TKA) is aseptic loosening of tibial component due to degradation of the interface between bone cement and metallic tibial shaft component, particularly for surface cemented tibial components. Surface cementation technique has important clinical meaning in case of revision and for avoidance of stress shielding. Degradation of the interface between bone cement and bone may be a secondary effect due to excessive crack formation in bone cement starting at the opposite metallic surface.

Methods

This study was done to prove crack formation in the bone cement near the metallic surface when this is not coated. We propose a newly developed coating process by PVD layering with SiO_x to avoid that crack formation in the bone cement. A biomechanical model for vibration fatigue test was done to simulate the physiological and biomechanical conditions of the human knee joint and to prove excessive crack formation.

Results

It was found that coated tibial components showed a highly significant reduction of cement cracking near the interface metal/bone cement (p < 0.01) and a significant reduction of gap formation in the interface metal-to-bone cement (p < 0.05).

Conclusion

Coating dramatically reduces hydrolytic- and stress-related crack formation at the prosthesis interface metal/bone cement. This leads to a more homogenous load transfer into the cement mantle which should reduce the frequency of loosening in the interfaces metal/bone cement/bone. With surface coating of the tibial component it should become possible that surface cemented TKAs reveal similar loosening rates as TKAs both surface and stem cemented. This would be an important clinical advantage since it is believed that surface cementing reduces metaphyseal bone loss in case of revision and stress shielding for better bone health.

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.

Gas chromatography-mass spectroscopy analysis of emissions from cement when using ultrasonically driven tools

BACKGROUND

Ultrasonically driven tools have been used to reduce the incidence of complications during cement removal at revision hip replacement operations. These have been shown to be safe and effective in various ways, but produce fumes.

METHODS

Using gas chromatography-mass spectroscopy, we analyzed the fumes produced during the use of these ultrasonic tools for the removal of bone cement, both in the laboratory and during actual surgery.

RESULTS

Benzene, styrene, methylmethacrylate, xylene, toluene, isopropyl alcohol and dichlorobenzene were some of the substances isolated from the fumes in the laboratory. Styrene and methylmethacrylate were the main components. Concentrations of all the above components taken from the breathing zone of the operating staff during actual surgery were well below the safety limits.

INTERPRETATION

The use of ultrasonic tools for cement removal appears to be safe.

Damage accumulation, fatigue and creep behaviour of vacuum mixed bone cement

The behaviour of bone cement under fatigue loading is of interest to assess the long-term in vivo performance. In this study, uniaxial tensile fatigue tests were performed on CMW-1 bone cement. Acoustic emission sensors and an extensometer were attached to monitor damage accumulation and creep deformation respectively. The S-N data exhibited the scatter synonymous with bone cement fatigue, with large pores generally responsible for premature failure; at 20 MPa specimens failed between 2 x 10(3) and 2 x 10(4) load cycles, while at 7 MPa specimens failed from 3 x 10(5) load cycles but others were still intact after 3 x 10(6) load cycles. Acoustic emission data revealed a non-linear accumulation of damage with respect to time, with increasing non-linearity at higher stress levels. The damage accumulation process was not continuous, but occurred in bursts separated by periods of inactivity. Damage in the specimen was located by acoustic emissions, and allowed the failure site to be predicted. Acoustic emission data were also used to predict when failure was not imminent. When this was the case at 3 million load cycles, the tests were terminated. Creep strain was plotted against the number of load cycles and a linear relationship was found when a double logarithmic scale was employed. This is the first time a brand of cement has been characterised in such detail, i.e. fatigue life, creep and damage accumulation. Results are presented in a manner that allows direct comparison with published data for other cements. The data can also be used to characterise CMW-1 in computational simulations of the damage accumulation process. Further evidence is provided for the condition-monitoring capabilities of the acoustic emission technique in orthopaedic applications.

Fluoride-containing acrylic bone cement in total hip arthroplasty. Randomized evaluation of 97 stems using radiostereometry and dual-energy x-ray absorptiometry

Ninety patients (97 hips) scheduled for total hip arthroplasty were stratified to fixation of the femoral component using fluoride-containing cement or Palacos with gentamicin. Whole polyethylene Reflection and press-fit Trilogy cups were used. All patients received Spectron EF stem. The micromotions of the stem were measured with radiostereometric analysis and the periprosthetic bone mineral density with automatic and manual dual-energy x-ray absorptiometry (DEXA) analysis. At 2 years, the choice of cement did not influence the subsidence or rotations of the stem. The DEXA analysis revealed more loss of periprosthetic bone mineral density in fluoride cement group. We speculate that forming of fluorapatite crystals, toxic effects of the fluoride, or lower radiopacity of the fluoride cement might explain this finding. According to our study with 2-year of follow-up, there is no obvious advantage of addition of fluoride to acrylic bone cement when used to fixate the femoral component in total hip arthroplasty.

Premixed rapid-setting calcium phosphate composites for bone repair

Although calcium phosphate cement (CPC) is promising for bone repair, its clinical use requires on site powder-liquid mixing. To shorten surgical time and improve graft properties, it is desirable to develop premixed CPC in which the paste remains stable during storage and hardens only after placement into the defect. The objective of this study was to develop premixed CPC with rapid setting when immersed in a physiological solution. Premixed CPCs were formulated using the following approach: Premixed CPC = CPC powder + nonaqueous liquid + gelling agent + hardening accelerator. Three premixed CPCs were developed: CPC-monocalcium phosphate monohydrate (MCPM), CPC-chitosan, and CPC-tartaric. Setting time for these new premixed CPCs ranged from 5.3 to 7.9 min, significantly faster than 61.7 min for a premixed control CPC reported previously (p < 0.05). SEM revealed the formation of nano-sized needle-like hydroxyapatite crystals after 1 d immersion and crystal growth after 7 d. Diametral tensile strength for premixed CPCs at 7 d ranged from 2.8 to 6.4 MPa, comparable to reported strengths for cancellous bone and sintered porous hydroxyapatite implants. Osteoblast cells attained a normal polygonal morphology on CPC-MCPM and CPC-chitosan with cytoplasmic extensions adhering to the nano-hydroxyapatite crystals. In summary, fast-setting premixed CPCs were developed to avoid the powder-liquid mixing in surgery. The pastes hardened rapidly once immersed in physiological solution and formed hydroxyapatite. The cements had strengths matching those of cancellous bone and sintered porous hydroxyapatite and non-cytotoxicity similar to conventional non-premixed CPC.

Bone-cement interface of the glenoid component: stress analysis for varying cement thickness

BACKGROUND

Although shoulder arthroplasty is an accepted treatment for osteoarthritis, loosening of the glenoid component, which mainly occurs at the bone-cement interface, remains a major concern. Presently, the mechanical effect of the cement mantel thickness on the bone-cement interface is still unclear.

METHODS

Finite element analysis of a prosthetic scapula was used to evaluate the effect of cement thickness on stresses and micromotions at the bone-cement interface. The glenoid component was all-polyethylene, keeled and flat back. Cement mantel thickness was gradually increased from 0.5 to 2.0 mm. Two glenohumeral contact forces were applied: concentric and eccentric. Two extreme cases were considered for the bone-cement interface: bonded and debonded.

FINDINGS

Within cement, stress increased as cement thickness decreased, reaching the fatigue limit below 1.0 mm. Bone stress was below its ultimate strength and was minimum between 1.0 and 1.5mm. Interface stress was close to the interface strength, and also minimum between 1.0 and 1.5 mm. Both the decentring of the load and the debonding of the interface increased the stress.

INTERPRETATION

A cement thinning weakens the cement, but also the bone-cement interface, along the back-keel edges. Conversely, a cement thickening rigidifies the cemented implant, consequently increasing interfacial stresses and micromotions. To avoid both excessive cement fatigue and interface failure, an ideal cement thickness has been identified between 1.0 and 1.5 mm.

Development of a strontium-containing hydroxyapatite bone cement

A new route was developed to synthesis a new type of strontium-containing hydroxyapatite (Sr-HAP) bone cement with precursors of tetracalcium phosphate (TTCP), strontium hydrogen phosphate (DSPA), dicalcium phosphate (DCPA), phosphate acid and water. The processing parameters and fundamental properties including pH value, setting time, compressive strength of final hardened body and the cytotoxicity for serial extracts of each cements were investigated. The result shows that the final product of the cement after setting for 24h is nonstoichiometic Sr-containing hydroxyapatite (Ca(10-m-x)Sr(x) square(m)(HPO4)y(PO4)6-y(OH)2-2m square2m, 0<x<1, nSr-HAP) and no other harmful impurities were detected. The pH value of Sr-containing cement pastes approaches to 7.0-7.6 when they are mixed with a ratio of 1:1 of powder to liquid (P/L) in weight. The setting time of the cement pastes is 4-11 min for the initial one and 10-17 min for the final one when the concentration of diluted phosphate is in a range of 0.5-1.0 mol/l. The compressive strengths of the hardened cements with different molar ratios of Sr/(Sr+Ca) after subjected an immersion in simulated body fluid (SBF) increase uniformly from 1 day to 5 days, where they get maximum values, respectively, but then decrease till to 2 weeks. Especially for the CPC-1, with a Sr/(Sr+Ca) molar ratios of 5% in cement powder composition, the largest compressive strength gained at 5 days is 66.57 MPa and the lowest one gained at 2 weeks is 44.75 MPa, which matches the value of human bones and can be expected to use in clinic application in repairing the nonloading sites on account of the positive result of cytotoxicity test of the extracts of Sr-containing calcium phosphate cement (Sr-CPC).

Comparative study on the properties of acrylic bone cements prepared with either aliphatic or aromatic functionalized methacrylates

Bone cements prepared with methacrylic acid (MAA) and diethyl amino ethyl methacrylate (DEAEM) were compared with formulations employing 4-methacryloyloxybenzoic acid (MBA) and 4-diethyaminobenzyl methacrylate (DEABM) as comonomer. The influence of these new aromatic monomers on various physicochemical, setting and mechanical properties was assessed. Surface characterization demonstrated that bone cements prepared with any of the functionalized monomers exhibited increasing hydrophilicity with monomer concentration and that the aromatic monomers provided more hydrophilic cements than their aliphatic counterparts for low concentrations of the functional monomer. It was also found that bone cements prepared with high amounts of the acidic aliphatic monomer provided the highest exotherm of reaction and their setting times were shorter than MBA based cements. On the other hand, DEABM containing bone cements exhibited shorter setting times than DEAEM formulations and slightly higher peak temperatures. In general, it was found that the glass transition temperature increased with the presence of acidic comonomer and decreased when alkaline comonomers were present, especially aliphatic ones. When aromatic methacrylates were used at 0.05 molar fraction, the highest tensile and compressive strength were achieved i.e. 46 and 118 MPa for MBA and 51 and 108 MPa for DEABM formulations. A further increase in the aromatic monomer concentration led to cements of low mechanical properties due to solubility problems as revealed by SEM.

Identifying enzyme activities within human saliva which are relevant to dental resin composite biodegradation

Esterase activities similar to those of cholesterol and pseudocholine esterases (CE and PCE, respectively) have been detected within whole human saliva. Since commercial CE has been shown to possess distinct activity relative to PCE for select components in dental composites, it is hypothesized that esterases isolated from human saliva will also show selectivity towards specific monomer elements within the composites. The objective of this work was to carry out the isolation of these activities from whole human saliva and study their individual effects on resin monomers such as Bis-phenyl glycidyl dimethacrylate (aromatic structure) and triethylene glycol dimethacrylate (hydrophilic structure), and on cured composites containing the latter monomers. Human saliva samples were processed, fractionated on a gel filtration column and assayed for CE and PCE-like activity. Selected fractions were incubated at 37 degrees C with the above monomers and select commercial composites. Degradation was monitored using high-performance liquid chromatography. The fraction with the highest cholesterol esterase-like character preferentially degraded the aromatic monomer and significantly degraded more of the composite's material relative to a fraction containing low amounts of the cholesterol esterase activity but elevated pseudocholine esterase-like activity. Hence, it was concluded that select salivary esterases had preferences for distinct composite resin components.

Analysis of the shelf life of a two-solution bone cement

Two-solution bone cement consists of methyl methacrylate monomer and poly(methyl methacrylate) polymer dissolved together to yield a viscous solution. Two solutions are used such that the initiator, benzoyl peroxide (BPO), is placed in one solution and the activator, N,N, dimethyl-para-toluidine, is placed in the other. This approach to bone cement provides for a simplified use during surgery and eliminates some of the sources of porosity formation. However, the BPO-containing solution cement will spontaneously polymerize over time and will limit the useful shelf life of this component of the system. The activator-containing component is much more stable and is not as susceptible to spontaneous polymerization. In making two-solution cements, it is envisioned that antibiotics may be incorporated and that the polymer may be sterilized using gamma(gamma)-irradiation. Therefore, this study investigated the shelf life of the initiator-containing solution bone cement and studied the effects of initiator concentration, gamma-irradiation, gentamicin addition, and the role of storage temperature. Isothermal differential scanning calorimetry (Iso-DSC) techniques were used to monitor the polymerization of BPO-containing solutions. It was found that the shelf life was highly temperature dependent and followed an Arrhenius expression where refrigeration storage (4 degrees C) yielded approximately a 12-month storage time, while 70 degrees C storage results in setting in about 5-7 min. gamma-irradiation and gentamicin addition did not significantly affect the shelf life. Initiator concentration affected storage time with higher levels resulting in shorter shelf life.

Study on modelling of PMMA bone cement polymerisation

This contribution is concerned with the modelling of PMMA-based bone cement polymerisation process and the associated heat effect. While existing models use description in terms of the so-called polymerisation fraction to fit the experimental data, the new model is constructed in such a way as to mimic the chemical processes taking place in the cement dough. The important phenomena are identified and the mathematical formulation is proposed.

Development of high-viscosity, two-paste bioactive bone cements

Self-curing two-paste bone cements have been developed using methacrylate monomers with a view to formulate cements with low polymerization exotherm, low shrinkage, better mechanical properties, and improved adhesion to bone and implant surfaces. The monomers include bis-phenol A glycidyl dimethacrylate (bis-GMA), urethane dimethacrylate (UDMA) and triethylene glycol dimethacrylate (TEGDMA) as a viscosity modifier. Two-paste systems were formulated containing 60% by weight of a bioactive ceramic, hydroxyapatite. A methacroyloxy silane (A174) was used as a coupling agent due to its higher water stability in comparison to other aminosilanes to silanate the hydroxyapatite particles prior to composite formulation. A comparison of the FT-infrared spectrum of hydroxyapatite and silanated hydroxyapatite showed the presence of the carbonyl groups ( approximately 1720 cm(-1)), -C=C-( approximately 1630 cm(-1)) and Si-O- (1300-1250 cm(-1)) which indicated the availability of silane groups on the filler surface. Two methods of mixing were effected to form the bone cement: firstly by mixing in an open bowl and secondly by extruding the two pastes by an auto-mixing tip using a gun to dispense the pastes. Both types of cements yielded low polymerization exotherms with good mechanical properties; however, the lower viscosity of UDMA allowed better extrusion and handling properties. A biologically active apatite layer formed on the bone cement surface within a short period after its immersion in simulated body fluid, demonstrating in vitro bioactivity of the composite. This preliminary data thus suggests that UDMA is a viable alternative to bis-GMA as a polymerizable matrix in the formation of bone cements.

Factors influencing calcium phosphate cement shelf-life

Long-term stability during storage (shelf-life) is one major criterion for the use of a material as medical device. This study aimed to investigate the ageing process of beta-tricalcium phosphate/monocalcium phosphate cement powders when stored in sealed containers at ambient conditions. This kind of cement type is of interest because it is forming dicalcium phosphate dihydrate (brushite) when set, which is in contrast to hydroxyapatite resorbable in physiological conditions. The stability of cements was checked by either measuring the phase composition of powders as well as the setting time and compressive strength when mixed with sodium citrate as liquid. Critical factors influencing ageing were found to be temperature, humidity and the mixing regime of the powders. Mechanically mixed cement powders which were stored in normal laboratory atmosphere (22 degrees C, 60% rel. humidity) converted to dicalcium phosphate anhydrous (monetite) within a few days; this could be mechanistically related to a dissolution/precipitation process since humidity condensed on the particles' surfaces and acted as reaction medium. Various storage conditions were found to be effective in prolonging cement stability which were in order of effectiveness: adding solid citric acid retardant>dry argon atmosphere=gentle mixing (minimal mechanical energy input) low temperature.

Static and fatigue mechanical behavior of bone cement with elevated barium sulfate content for treatment of vertebral compression fractures

The use of bone cement to treat vertebral compression fractures in a percutaneous manner requires placement of the cement under fluoroscopic image guidance. To enhance visualization of the flow during injection and to monitor and prevent leakage beyond the confines of the vertebral body, the orthopedic community has described increasing the amount of radiopacifier in the bone cement. In this study, static tensile and compressive testing, as well as fully reversed fatigue testing, was performed on three PMMA-based bone cements. Cements tested were SimplexP with 10% barium sulfate (Stryker Orthopedics, Mahwah, NJ) which served as a control; SimplexP with 36% barium sulfate prepared according to the clinical recommendation of Theodorou et al.; and KyphX HV-R with 30% barium sulfate (Kyphon Inc., Sunnyvale, CA). Static tensile and compressive testing was performed in accordance with ASTM F451-99a. Fatigue testing was conducted in accordance with ASTM F2118-01a under fully reversed, +/-10-, +/-15-, and +/-20-MPa stress ranges. Survival analysis was performed using three-parameter Weibull modeling techniques. KyphX HV-R was found to have comparable static mechanical properties and significantly greater fatigue life than either of the two control materials evaluated in the present study. The static tensile and compressive strengths for all three PMMA-based bone cements were found to be an order of magnitude greater than the expected stress levels within a treated vertebral body. The static and fatigue testing data collected in this study indicate that bone cement can be designed with barium sulfate levels sufficiently high to permit fluoroscopic visualization while retaining the overall mechanical profile of a conventional bone cement under typical in vivo loading conditions.

Modulation of porosity in apatitic cements by the use of α-tricalcium phosphate—calcium sulphate dihydrate mixtures

Calcium phosphate bone cements are injectable biomaterials that are being used in dental and orthopaedic applications through minimally invasive surgery techniques. Nowadays, apatitic bone cements based on alpha-tricalcium phosphate (alpha-TCP) are of special interest due to their self-setting behaviour when mixed with an aqueous liquid phase. In this study, a new method to improve osteointegration of alpha-TCP-based cements is presented. This method consists in the modification of the cement's powder phase with different amounts of calcium sulphate dihydrate (CSD). The resulting hardening properties of the new biphasic cements are a combination between the progressive hardening due to the main alpha-TCP reactant and the progressive dissolution of the CSD phase, which render a porous material. It was observed that the maximum compressive strength of Biocement-H (45 MPa) decreased as the amount of CSD increased in the cement powder mixture ( approximately 30 MPa for 25 wt% of CSD). It was also observed that after complete dissolution of the CSD phase a porous apatitic structure appears with a mechanical compressive strength suitable for cancellous bone applications (10 MPa).

Evaluation of chitosan/beta-tricalcium phosphate microspheres as a constituent to PMMA cement

Two methods, a traditional emulsion technique and a high voltage electrostatically modified encapsulation system, were used to fabricate degradable chitosan/beta -tricalcium phosphate (beta-TCP) microspheres. The two distinct kinds of microspheres both exhibited good sphericity and the beta-TCP was trapped well inside the chitosan gel. The microspheres prepared by high voltage electrostatic system exhibited a rougher outer surface and narrower size distribution. These microspheres were then used as an added constituent to commercially available PMMA bone cement. Four modified cement composites that were prepared with different composition ratios of the two kinds of chitosan/beta-TCP microspheres that were made from emulsion technique (C1P1 and C2P1) and from a process by a high voltage electrostatic system (EC1P1 and EC2P1) were compared with the PMMA cement (Pure P). The characteristics of these materials indicate that with the addition of chitosan/beta-TCP microspheres as a constituent into the PMMA cement significantly decreases the curing peak temperature. Furthermore, the setting time increases from 3.5 min to 9 min, as compared to the PMMA cement. These changes could be beneficial for the handling of the bone cement paste and causing less damage to the surrounding tissues. Understandably, the presence of chitosan/beta-TCP microspheres in the prepared composites reduced the ultimate compressive strength and bending strength. From the degradation test and SEM observations, the modified chitosan/beta -TCP/PMMA composites could be degraded gradually and create rougher surfaces that would be beneficial to cell adherence and growth.

High-strength apatitic cement by modification with superplasticizers

This study reports on a novel method to improve the strength of apatitic bone cements. The liquid phase of Biocement-H was modified with commercial superplasticizers. The results showed that small additions, i.e. 0.5 vol%, in the aqueous liquid phase improved the maximum compressive strength of Biocement-H (35 MPa) by 71%, i.e. 60 MPa. Moreover, the addition of high amounts of superplasticizers, i.e. 50 vol.%, allowed for a significant reduction of the liquid-to-powder ratio from 0.32 to 0.256 mL/g, without affecting the maximum strength and/or the workability of the cement. These results open up new ways to develop injectable and high-strength apatitic bone cements for load-bearing applications.

Alkali ion substituted calcium phosphate cement formation from mechanically activated reactants

Potassium and sodium containing nanoapatite cements were produced from Ca2KNa(PO4)2 by prolonged high energy ball milling of the compound for up to 24 h. This mechanical treatment resulted in the decrease of the crystal size and a partial amorphisation of the cement reactant as shown by X-ray diffraction analysis and the appearance of strong exothermic peaks in differential scanning calorimetry measurements. The pH of water saturated with Ca2KNa(PO4)2 was 12.5 when the material was mechanically activated but was only 9.5 for the untreated compound suggesting an increase in solubility following milling. The cements set following mixing with a 2.5% Na2HPO4 solution in clinically acceptable times between 5-12 min and showed compressive strengths of up to 11 MPa after 24 h setting. The strong alkaline pH value of the cements may provide antimicrobial potential for an application in dentistry as pulp capping agents or cavity liners or for the treatment of infected bone sites.

Injectability of calcium phosphate pastes

A theoretical model was developed to assess ways to improve the injectability of calcium phosphate pastes. The theoretical results were then compared to experimental data obtained on calcium phosphate slips. The theoretical approach predicted that the injectability of a cement paste could be improved by an increase of the liquid-to-powder ratio, and a decrease of the particle size and the plastic limit (PL) of the powder. The theoretical results were confirmed by experimental data. Interestingly, an increase of the viscosity of the mixing liquid with small additions of xanthan had a positive effect on the paste injectability. This effect could be due to a change of the PL of the powder or to the lubricating effect of the polymer.

Cement from magnesium substituted hydroxyapatite

Brushite cement may be used as a bone graft material and is more soluble than apatite in physiological conditions. Consequently it is considerably more resorbable in vivo than apatite forming cements. Brushite cement formation has previously been reported by our group following the mixture of nanocrystalline hydroxyapatite and phosphoric acid. In this study, brushite cement was formed from the reaction of nanocrystalline magnesium-substituted hydroxyapatite with phosphoric acid in an attempt to produce a magnesium substituted brushite cement. The presence of magnesium was shown to have a strong effect on cement composition and strength. Additionally the presence of magnesium in brushite cement was found to reduce the extent of brushite hydrolysis resulting in the formation of HA. By incorporating magnesium ions in the apatite reactant structure the concentration of magnesium ions in the liquid phase of the cement was controlled by the dissolution rate of the apatite. This approach may be used to supply other ions to cement systems during setting as a means to manipulate the clinical performance and characteristics of brushite cements.

Influence of P/L ratio and peroxide/amine concentrations on shrinkage-strain kinetics during setting of PMMA/MMA biomaterial formulations

This study investigated the effects on polymerisation shrinkage-strain for two unmodified powder and liquid formulations of polymethyl methacrylate (PMMA), methyl methacrylate (MMA) dough-type systems, by varying the powder/liquid (P/L) ratio. Furthermore, the shrinkage-strain effects for the 1.0:1.0 P/L ratio of adding additional amounts of amine and benzoyl peroxide (BPO) were studied. The rationale was the continuing importance of bone cements and the renewed interest in acrylic biomaterials, based on MMA and PMMA co-polymers, as used in new fibre-reinforced systems, where low P/L ratios may be important. Shrinkage-strain is directly related to extent of monomer conversion and has intrinsic importance related to interfacial disruption. Shrinkage-strain kinetics were determined using the "bonded disk" method. The first series of experiments studied two unmodified self-curing materials (MEA and PAL), where specimens with different P/L ratios by volume (3.0, 2.5, 2.0, 1.5 and 1.0 to 1.0) were mixed for 60s. In these formulations, final shrinkage-strain values correlated positively with P/L ratios, rather than negatively, as would be expected from fully polymerised material. This highlights a problem of under-polymerisation through deviation from an optimum or recommended P/L ratio. When an additional 1.0% BPO was added in the powder, final shrinkage-strain values correlated negatively rather than positively, with P/L ratio for both products, except at ratio 1.0:1.0. Specimens mixed at 1.0:1.0 P/L ratio, with increasing amounts of BPO and amine resulted in higher final shrinkage-strain values, indicative of more complete polymerisation. Shrinkage-strain and optimum polymerisation are related, but clinically rather antagonist properties with respect to effective biomaterial utilisation and performance. In both design and surgical application of these polymethacrylate formulations, possible adverse effects of changing P/L ratio, producing either excessive shrinkage-strain or under-polymerisation, must be understood and where possible controlled.

Formation of apatitic calcium phosphates in a Na-K-phosphate solution of pH 7.4

Poorly crystalline, apatitic calcium phosphate powders have been synthesized by slowly adding a Na- and K-containing reference phosphate solution with a pH value of 7.4 to an aqueous calcium nitrate solution at 37 degrees C. Nano-particulated apatitic powders obtained were shown to contain small amounts of Na and K, which render them more similar in chemical composition to that of the bone mineral. Precipitated and dried powders were found to exhibit self-hardening cement properties when kneaded in a mortar with a sodium citrate- and sodium phosphate-containing starter solution. The same phosphate solution used in powder synthesis was found to be able to partially convert natural, white and translucent marble pieces of calcite (CaCO3) into calcium-deficient hydroxyapatite upon aging the samples in that solution for 3 days at 60 degrees C. Sample characterization was performed by using scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, inductively-coupled plasma atomic emission spectroscopy, and simultaneous thermogravimetry and differential thermal analysis.

Dynamic creep and mechanical characteristics of SmartSet GHV bone cement

The restrained dynamic creep behaviour and mechanical properties of SmartSet GHV bone cement have been investigated at both room temperature and body temperature. It was found that the bone cement behaves significant differently at room temperature from that at body temperature. The test temperature had a strong effect on the creep performance of the bone cements with a higher creep rate observed at body temperature at each loading cycle. For both temperatures, two stages of creep were identified with a higher creep rate during early cycling followed by a steady state creep rate. The relationship between creep deformation and loading cycle can be expressed by a Hyperb 1 model. As a visco-elastic material, the sensitivity of bone cement to the temperature change was evident during mechanical testing. Compared to the mechanical strength at room temperature, a decreased value was demonstrated at body temperature. The bending modulus was very sensitive to the change in testing temperature, where a reduction of 52% was recorded. A significant reduction in compressive and bending strength, 31 and 23% were recorded respectively. The effect of temperature on bending strength was less apparent, where only 13% reduction was exhibited at body temperature compared to room temperature.

Importance of the Peridural Membrane in Percutaneous Vertebroplasty

OBJECTIVE

The peridural membrane is a fibrous membrane that lies anterior to the posterior longitudinal ligament and attaches to its deep layer. It spans the width of the vertebral body and encircles the bony canal around the outside of the dura. The purpose of this study was to determine if the peridural membrane helps contain posterior cement leakage during percutaneous vertebroplasty.

METHODS

Compression fractures were experimentally created in cadaveric spines. The bodies were stabilized using bipedicular injection of cement, and injection was continued until cement was evident beyond the posterior border of the vertebral body. The vertebral segments were then dissected and the extravasated cement localized anatomically.

CONCLUSIONS

All extravasated cement was constrained by the peridural membrane, and no direct contact of the cement with the dura was seen.

On the Importance of Considering Porosity When Simulating the Fatigue of Bone Cement

Fatigue cracking in the cement mantle of total hip replacement has been identified as a possible cause of implant loosening. Retrieval studies and in vitro tests have found porosity in the cement may facilitate fatigue cracking of the mantle. The fatigue process has been simulated computationally using a finite element/continuum damage mechanics (FE/CDM) method and used as a preclinical testing tool, but has not considered the effects of porosity. In this study, experimental tensile and four-point bend fatigue tests were performed. The tensile fatigue S-N data were used to drive the computational simulation (FE/CDM) of fatigue in finite element models of the tensile and four-point bend specimens. Porosity was simulated in the finite element models according to the theory of elasticity and using Monte Carlo methods. The computational fatigue simulations generated variability in the fatigue life at any given stress level, due to each model having a unique porosity distribution. The fracture site also varied between specimens. Experimental validation was achieved for four-point bend loading, but only when porosity was included. This demonstrates that the computational simulation of fatigue, driven by uniaxial S-N data can be used to simulate nonuniaxial loadcases. Further simulations of bone cement fatigue should include porosity to better represent the realities of experimental models.

Mechanical properties of two orthodontic adhesive materials polymerized with halogen and plasma curing

OBJECTIVES

The aim of this study is to compare the efficiency of two polymerization techniques (halogen curing--Astralis 7 and plasma curing--Flipo), with two orthodontic adhesive materials (Enlight, a composite resin, and Fuji Ortho LC, a glass ionomer cement).

METHODS

The efficiency of the polymerization techniques was shown by two mechanical tests. The hardness test was carried out on the exposed and non-exposed surfaces using 10 x 4 x 3-mm samples, polymerized either by halogen curing (40 seconds) or by plasma curing (5 seconds). The three-point bending tests were carried out on 2 x 2 x 25-mm samples polymerized as above. The samples were kept 1 hr at room temperature, then for 24 hrs in distilled water at 37 degrees C.

RESULTS

Whatever the polymerization technique used, the results are similar for hardness and flexion, with the exception of the hardness tests carried out after polymerization with the Flipo light on the surface not directly exposed.

CONCLUSION

In orthodontic practice, both polymerization techniques can be used. But a multi-bracket session can be long, and the reduction of time spent in the chair obtained by using plasma lamps seems to make this technique preferable.

A 3D analysis of mechanically stressed dentin?adhesive?composite interfaces using X-ray micro-CT

Dentin bonding systems (DBS) have been developed in order to bond restorative materials (i.e. composite) to tooth tissues when function and integrity have to be re-established. Adhesion to dentin results from the penetration of DBS into the demineralised substrate constituted by a conditioned collagen network. The long-term stability of a restored tooth is mainly affected by the seal of the restorative material on the dental structures. Although leakage through the dentin-DBS interface has been widely reported, 3D investigation technique and accurate non-destructive measurements of leakage as functions of mechanical cycling have never been provided. To address these issues, the properties of the material interface are analysed using micro-tensile static and dynamic tests, assisted by the finite element modelling and by the X-ray computed micro-tomography. The dual energy absorption technique, with the synchrotron beam light, has been developed to investigate, in a non-destructive manner, the effect of mechanical cycling on leakage of a silver nitrate staining solution at the dentin-DBS interface. The effect of the pulpal roof on the stress distribution in the coronal dentin-DBS-composite interface has been investigated and the level at which the state of stress can be assumed to be uniform within acceptable limits has been defined. The tensile static and dynamic results suggest that the adhesive strength for the multi-step DBS resulted significantly higher than the other investigated DBS. Imaging results indicate that 3D leakage occurs radially at the dentin-adhesive interface through the interface itself rather than through the unconditioned dentin bulk; moreover, the dynamic tensile loading allows a more diffuse staining penetration.

A radiographic study of the detection limits of bone-cement remnants in total joint arthroplasty

Management of an infected hip prosthesis typically requires that all associated cement be removed. In the absence of gross mantle loosening, the surgeon frequently resorts to intraoperative radiographs to assess the completeness of removal. For this reason, we undertook a study to determine limits of detection of retained cement by routine radiography. Polymethyl methacrylate bone-cement beads (Simplex-P; Stryker-Howmedica-Osteonics, Allendale, NJ) were fashioned into graduated sizes and placed within cadaver medullary canals using 2 different methods. Standard radiographic images were obtained. Individually and independently, we viewed these images and proposed the limit of resolution to be 2.4 to 3.2 mm. It is difficult to remove all cement based on radiographs alone. These results suggest a need to use techniques that permit visualization of the canal to ensure adequate cement removal.