Biaxial flexural modulus of antibiotic-impregnated orthopedic bone cement

Uniaxial/biaxial flexure strengths and elastic properties of resin-composite block materials for CAD/CAM

OBJECTIVE

Comparing strengths under different loading conditions provides useful information on the mechanical behaviour of restorative materials under multiaxial masticatory loading in the oral cavity. The aims of this study was to investigate the flexural strengths and the reliability of resin-composite blocks for CAD/CAM by uniaxial and biaxial flexure tests and to compare the elastic properties measured by different methods including digital image correlation (DIC).

METHODS

Four resin-composite blocks for CAD/CAM, namely, VE (Vita Enamic), LU (Lava Ultimate), MD (Mazic Duro), and CS (Cerasmart), were investigated. Beam specimens (4.0×1.4×18.0mm³) and disks (12-14mmϕ×1.5mm) were prepared to determine the uniaxial (three-point bending) and biaxial (ball-on-ring, BOR) flexural strengths and flexural moduli. A compression test (8×4×18mm³) with DIC analysis was utilized to measure the elastic modulus and Poisson's ratio. Data were analysed by a 2-parameter Weibull function and ANOVA with Scheffe's test.

RESULTS

The mean uniaxial and biaxial strengths and Weibull moduli of the specimen groups were as follows: uniaxial VE (140.1±7.0, 24.1), LU (159.1±6.3, 31.5), MD (144.9±13.3, 13.6), and CS (165.4±16.9, 11.2) and biaxial VE (153.6±10.4, 19.0), LU (231.0±29.3, 9.7), MD (148.9±23.8, 7.4), and CS (249.7±22.4, 13.8). Although the ranking of both sets of strength data remained unchanged, the strength reliability was significantly affected by the loading; the Weibull moduli of the specimens decreased when they were subjected to biaxial tests (except for that of CS). The elastic modulus values of the materials varied significantly under the different test loadings, although they were in the same order regardless of the test method: VE>>LU≈MD>CS. The DIC technique yielded elastic moduli that were in good agreement with those measured by the uniaxial flexure test.

SIGNIFICANCE

The flexural strength, reliability, and elastic modulus of resin-composite block materials differed with the uniaxial and biaxial flexural loading and the test method. The different behaviours under both loadings should be considered in the evaluation of the mechanical performance of those materials.

EFFECT OF ANTIBIOTICS AUGMENTATION AND STORAGE CONDITION ON IMPACT RESISTANCE OF ORTHOPEDIC BONE CEMENT

Antibiotic-impregnated poly(methyl methacrylate) (PMMA) bone cement has been successfully used to treat infected joint arthroplasties and surgeons have advocated the use of antibiotic-treated bone cement to prevent possible infections in joint replacement surgeries. However, there is a concern that this addition may adversely affect the mechanical properties of the bone cement. In most cases, the addition of antibiotics to bone cement has been reported to lower its mechanical strength. The uniaxial, biaxial and three/four point bending tests of antibiotic-impregnated bone cement have been extensively performed and well documented. However, only a few documents have focused on the impact strength of bone cement. The present study reports the impact tests of control and antibiotic loaded bone cements at different temperatures and aging conditions. According to the results, the addition of gentamicin or vancomycin significantly reduced the samples' impact strength. Moreover, the samples aged in saline at 23[Formula: see text]C were more resistant than the samples aged in air at 23[Formula: see text]C. Furthermore, raising the storage temperature from 23[Formula: see text]C to 37[Formula: see text]C significantly lowered the bone cement's impact strength in both control and antibiotic loaded samples.

Mechanical effects, antimicrobial efficacy and cytotoxicity of usnic acid as a biofilm prophylaxis in PMMA

Experiments were performed to test the null hypothesis that the addition of a natural occurring antibiotic would not alter mechanical properties of polymethylmethacrylate (PMMA). Compression and four-point bending tests were used to assess mechanical properties of zirconium dioxide bearing bone cement (Type Zr) and barium sulfate bearing bone cement (Type Ba), mixed with the antibiotic usnic acid ("usnic"), used to create a surface resistant to biofilm formation. Addition of usnic had a statistically significant effect on the material properties. Compressive and bending strengths decreased as usnic was added and Type Zr was stronger than Type Ba although material properties remained above recommended minima. With implications of liver toxicity with large doses of usnic taken as a dietary supplement, cytotoxicity tests using bone cement coupons were performed and showed very little or no toxicity in primary cultures of rabbit skin derived fibroblasts. A simple test of usnic's efficacy as a biofilm prophylaxis in PMMA was also conducted. Bone cement coupons with usnic were tested for their effectiveness against methicillin resistant Staphylococcus aureus. Diminished biofilm formation on usnic-containing coupons indicated that usnic can be an effective anti-microbial agent.

Surfactant-stabilized emulsion increases gentamicin elution from bone cement

BACKGROUND

Liquid antimicrobial use for antimicrobial-loaded bone cement is limited because of decreased strength and small volume that can be loaded. Emulsifying the liquid antimicrobial into the monomer may address both issues.

QUESTIONS/PURPOSES

We determined the effect of using a surfactant-stabilized emulsion on antimicrobial release, compressive strength, and porosity.

METHODS

We made 144 standardized test cylinders from emulsified antimicrobial-loaded bone cement (three batches, 72 cylinders) and control antimicrobial-loaded bone cement made with antimicrobial powder (three batches, 72 cylinders). For each formulation, five specimens per batch (n = 15) were eluted in infinite sink conditions over 30 days for gentamicin delivery; five specimens per batch were axially compressed to failure after elution of 0, 1, and 30 days (n = 45); and two noneluted specimens and two gentamicin delivery specimens from each batch (n = 12) were examined under scanning electron microscopy for porosity. Antimicrobial release and compressive strength were compared across cement type and time using repeated-measures ANOVA.

RESULTS

Emulsified antimicrobial-loaded bone cement released four times more antimicrobial than control. Compressive strength of emulsified antimicrobial-loaded bone cement was less than control before elution (58.1 versus 81.3 MPa) but did not decrease over time in elution. Compressive strength of control antimicrobial-loaded bone cement decreased over 30 days in elution (81.3 versus 73.9 MPa) but remained stronger than emulsified antimicrobial-loaded bone cement. Porosity was homogeneous, with pores ranging around 50 μm.

CONCLUSIONS

Emulsified antimicrobial-loaded bone cement has homogeneous porosity with increased drug release but a large loss of strength.

CLINICAL RELEVANCE

Liquid antimicrobials are released from emulsified antimicrobial-loaded bone cement, but increased strength is needed before this method can be used for implant fixation.