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Results for “Compressive Strength”

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PubMed1976

Modulus of elasticity and strength properties of dental cements.

The modulus of elasticity of commercial dental cements was determined by an optical strain gauge method. Values of compressive and tensile strengths also were measured. Of the cements of primary consistency tested, a noneugenol zinc oxide cement had the lowest mechanical properties. A zinc phosphate cement had the highest value of compressive strength and modulus, but a zinc polyacrylate cement had the highest tensile strength. A zinc polyacrylate cement base had the highest tensile strength, but a zinc phosphate cement base had the highest compressive strength and modulus of elasticity. A calcium hydroxide liner had higher mechanical properties than an unmodified ZOE liner.

Dental Cements↗

PubMed2005

Femur strength index predicts hip fracture independent of bone density and hip axis length.

INTRODUCTION: Proximal femoral bone strength is not only a function of femoral bone mineral density (BMD), but also a function of the spatial distribution of bone mass intrinsic in structural geometric properties such as diameter, area, length, and angle of the femoral neck. Recent advancements in bone density measurement include software that can automatically calculate a variety of femoral structural variables that may be related to hip fracture risk. The purpose of this study was to compare femoral bone density, structure, and strength assessments obtained from dual-energy X-ray absorbtiometry (DXA) measurements in a group of women with and without hip fracture. METHODS: DXA measurements of the proximal femur were obtained from 2,506 women 50 years of age or older, 365 with prior hip fracture and 2,141 controls. In addition to the conventional densitometry measurements, structural variables were determined using the Hip Strength Analysis program, including hip axis length (HAL), cross-sectional moment of inertia (CSMI), and the femur strength index (FSI) calculated as the ratio of estimated compressive yield strength of the femoral neck to the expected compressive stress of a fall on the greater trochanter. RESULTS: Femoral neck BMD was significantly lower and HAL significantly higher in the fracture group compared with controls. Mean CSMI was not significantly different between fracture patients and controls after adjustment for BMD and HAL. FSI, after adjustment for T score and HAL, was significantly lower in the fracture group, consistent with a reduced capacity to withstand a fall without fracturing a hip. CONCLUSION: We conclude that BMD, HAL, and FSI are significant independent predictors of hip fracture.

Absorptiometry, Photon↗

PubMed1991

Physical properties of stainless-steel and silver-reinforced glass-ionomer cements.

The purpose of this study was to compare specific physical properties of an experimental stainless-steel-reinforced glass-ionomer cement with those of two commercially available silver-reinforced cements. Properties evaluated were compressive and diametral tensile strengths (one and 24 h), percent solubility in 0.01 mol/L lactic acid over 23 h, and working and setting times. Cylindrical specimens 6 mm (diameter) x 12 mm were prepared and maintained in distilled water at 37 +/- 2 degrees C and then tested on an MTS mechanical testing machine with a cross-head displacement rate of 0.5 mm/min for the diametral tensile strength test and 1.0 mm/min for the compressive strength test. ANOVA and Tukey's Studentized Multiple Range Test indicated significant differences between the experimental and commercially available cements for both compressive and tensile strengths at one and 24 h (p less than 0.01). The experimental stainless-steel-reinforced cement appeared to be significantly stronger in both tensile and compressive strengths than either of the commercially available cements. Working and setting times--as well as acid solubility of the experimental cement--also compared favorably with those of the commercial cements. Results suggest that the stainless-steel-reinforced glass-ionomer cement possesses strength properties that should lead to a stronger, more fracture-resistant restorative filling material when compared with those presently available.

Analysis of Variance↗

PubMed1998

Hydroxyapatite fiber reinforced poly(alpha-hydroxy ester) foams for bone regeneration.

A process has been developed to manufacture biodegradable composite foams of poly(DL-lactic-co-glycolic acid) (PLGA) and hydroxyapatite short fibers for use in bone regeneration. The processing technique allows the manufacture of three-dimensional foam scaffolds and involves the formation of a composite material consisting of a porogen material (either gelatin microspheres or salt particles) and hydroxyapatite short fibers embedded in a PLGA matrix. After the porogen is leached out, an open-cell composite foam remains which has a pore size and morphology defined by the porogen. By changing the weight fraction of the leachable component it was possible to produce composite foams with controlled porosities ranging from 0.47 +/- 0.02 to 0.85 +/- 0.01 (n = 3). Up to a polymer:fiber ratio of 7:6, short hydroxyapatite fibers served to reinforce low-porosity PLGA foams manufactured using gelatin microspheres as a porogen. Foams with a compressive yield strength up to 2.82 +/- 0.63 MPa (n = 3) and a porosity of 0.47 +/- 0.02 (n = 3) were manufactured using a polymer:fiber weight ratio of 7:6. In contrast, high-porosity composite foams (up to 0.81 +/- 0.02, n = 3) suitable for cell seeding were not reinforced by the introduction of increasing quantities of hydroxyapatite short fibers. We were therefore able to manufacture high-porosity foams which may be seeded with cells but which have minimal compressive yield strength, or low porosity foams with enhanced osteoconductivity and compressive yield strength.

Biocompatible Materials↗

PubMed1987

Failure stress criteria for composite resin.

In previous work (Peters and Poort, 1983), the stress distribution in axisymmetric models of restored teeth was analyzed by finite element analysis (FEA). To compare the tri-axial stress state at different sites, they calculated the Von Mises equivalent stress and used it as an indication for weak sites. However, the use of Von Mises' theory for material failure requires that the compressive and tensile strengths be equal, whereas for composite resin the compressive strength values are, on the average, eight times larger than the tensile strength values. The objective of this study was to investigate the applicability of a modified Von Mises and the Drücker-Prager criterion to describe mechanical failure of composite resin. In these criteria, the difference between compressive and tensile strength is accounted for. The stress criteria applied to an uni-axial tensile stress state are compared with those applied to a tri-axial tensile stress state. The uni-axial state is obtained in a Rectangular Bar (RB) specimen and the tri-axial state in a Single-edge Notched Bend (SENB) specimen with a chevron notch at midspan. Both types of specimens, made of light-cured composite, were fractured in a three-point bend test. The size of the specimens was limited to 16 mm x 2 mm x 2 mm (span, 12 mm). Load-deflection curves were recorded and used for linear elastic FEA. The results showed that the Drücker-Prager criterion is a more suitable criterion for describing failure of composite resins due to multi-axial stress states than are the Von Mises criterion and the modified Von Mises criterion.

Composite Resins↗

PubMed2005

Fracture patterns of the adolescent porcine spine: an experimental loading study in bending-compression.

STUDY DESIGN: To expose functional spinal units from adolescent porcine to mechanical flexion-compression and extension-compression to failure. The biomechanical, radiologic, magnetic resonance imaging, and histologic characteristics are described. OBJECTIVES: The aim of the present study was to investigate the fracture pattern of functional spinal units from adolescent porcine lumbar spines in in vitro compression loading and bending. SUMMARY OF BACKGROUND DATA: In several studies, it has been shown that the adolescent spine, especially the vertebral growth zones, is vulnerable to trauma. A high frequency of abnormalities affecting the spine has been found among athletes participating in sports with high demands on the back. The etiology of these abnormalities is still a controversial issue. METHODS: Sixteen functional spinal units obtained from eight adolescent male pigs were used. Eight functional spinal units were exposed to flexion-compression and eight functional spinal units to extension-compression loading to failure. They were examined with plain radiography and magnetic resonance imaging before and after the loading. The functional spinal units were finally examined macroscopically and histologically. RESULTS: Fractures/separations were seen in the growth zone anteriorly and more frequently, posteriorly in functional spinal units exposed to flexion-compression. In the extension-compression group, such injuries occurred only anteriorly. Only large fractures could be seen on plain radiographs and on magnetic resonance imaging. Macroscopically, a fracture/separation could be seen in 15 cases and histologically in all 16 cases. The median angle at failure for the flexion group was 17 degrees (range, 12-19) and for the extension group 17 degrees (range, 13-19 degrees). The median ultimate compression load in the flexion-compression group was 1894 N (range, 1607-3138 N) and in the extension-compression group 1801 N (range, 1158-2368 N). CONCLUSIONS: The weakest part of the growing porcine lumbar spine, when compressed into flexion- or extension-compression, was the growth zone. The injury was more extensive in extension loading than during flexion loading. Growth zone injuries of the adolescent spine may go undetected on plain radiographs and magnetic resonance imaging.

Age Factors↗

PubMed1989

[Properties of titanium dioxide-polymer composite with titanate coupling agents].

Titanium dioxide-polymethacrylate composites were prepared with triethyleneglycol dimethacrylate (TEGDMA), 1,6-bis(methacryloxy-2-ethoxycarbonylamino)-2,4,4-trimeth ylexane (UDMA) and rutile structure titanium dioxide. The coupling agents used were isopropyldimethacrylisostearoyl titanate (KR7), isopropyltri (dioctylphosphate) titanate (KR12) and 4-methacryloxyethyl trimellitate anhydride (4-META). Compressive and transverse strengths of composites were determined under various experimental conditions. Compressive strength of composite with KR 7-treated titanium dioxide was higher than that with untreated titanium dioxide. Transverse strength of the composite with 4-META-treated titanium dioxide was higher than that with untreated titanium dioxide. Both compressive and transverse strengths increased when the titanium dioxide was treated with the mixture of KR7 and 4-META. Scanning electron microscopic observations of fractured composite surfaces showed titanium dioxide polymer interface failure with untreated specimens and polymer cohesive fracture with KR7 + 4-META-treated specimens. The results suggest that titanium dioxide treated with both KR7 and 4-META is useful as a pigment of the opaque material of fixed prosthodontic composite.

Composite Resins↗

PubMed1996

A biomechanical model of the lumbar spine during upright isometric flexion, extension, and lateral bending.

STUDY DESIGN: Task-specific and subject-specific lumbar trunk muscle function, muscle geometry, and vertebral density data were collected from 16 men. A biomechanical model was used to determine muscle strength and the compressive forces acting on the lumbar spine. OBJECTIVES: To develop an anatomic biomechanical model of the low back that could be used to derive task-specific muscle function parameters and to predict compressive forces acting on the low back. Several model-specific constraints were examined, including the notion of bilateral trunk muscle anatomic symmetry, the influence of muscle lines of action, and the use of density-derived vertebral strength for model validation. SUMMARY OF BACKGROUND DATA: Clinical and basic science investigators are currently using a battery of diverse biomechanical techniques to evaluate trunk muscle strength. Noteworthy is the large variability in muscle function parameters reported for different subjects and for different tasks. This information is used to calculate forces and moments acting on the low back, but limited data exist concerning the assessment of subject-specific, multiaxis, isometric trunk muscle functions. METHODS: A trunk dynamometer was used to measure maximum upright, isometric trunk moments in the sagittal (extension, flexion) and coronal (lateral flexion) planes. Task- and subject-specific trunk muscle strength or "gain" was determined from the measured trunk moments and magnetic resonance image-based muscle cross-sectional geometry. Model-predicted compressive forces obtained using muscle force and body force equilibrium equations were compared with density-derived estimates of compressive strength. RESULTS: Individual task-specific muscle gain values differed significantly between subjects and between each of the tasks they performed (extension > flexion > lateral flexion). Significant differences were found between left side and right side muscle areas, and the lines of action of the muscles deviated significantly from the vertical plane. Model-predicted lumbar compressive forces were 38% (lateral flexion) to 73% (extension) lower that the L3 vertebral compressive strength estimated from vertebral density. CONCLUSION: The present study suggests that biomechanical models of the low back should be based on task-specific and subject-specific muscle function and precise geometry. Vertebral strength estimates based upon vertebral density appear to be useful for validation of model force predictions.

Adult↗

PubMedDate not supplied

Adhesive strength between fiber-reinforced composites and veneering composites and fracture load of combinations of these materials.

PURPOSE: This study examined the influence of the adhesive strength between fiber-reinforced composites (FRC) and veneering composites on the fracture load of combinations of these materials. MATERIALS AND METHODS: Six materials were used. An experimental material called BR-100, Vectris, and FibreKor were the types of FRC. Estenia, Targis, and Sculpture were used as veneering composites. With the Estenia/BR-100 combination, the surface of the FRC was subjected to three different conditions before veneering. Ten specimens of each combination were fabricated and divided into two groups: One group was stored in 37 degrees C distilled water for 24 hours, and the other was thermocycled (4 degrees C/60 degrees C, 10,000 cycles). Adhesive strength between FRCs and veneering composites was determined using the compressive shear strength test. In addition, fracture loads of laminate specimens were determined. RESULTS: Good adhesive strength was obtained by leaving an unpolymerized layer on the surface of the FRC or by performing silane and bonding treatment. In the Estenia/BR-100 combination, when the adhesive strength was low, the fracture load of the laminate specimens was also low. However, the difference in fracture load was not as large as that seen in adhesive strength. The fracture load of each laminate specimen was significantly lower after thermocycling. CONCLUSION: The adhesive strength between the FRCs and veneering composite had an effect on the fracture load of the combination.

Adhesiveness↗

PubMed1991

Mechanical properties of bone cement. Importance of the mixing technique.

The compressive and shear strength and the modulus of elasticity were studied in three different bone cements (CMW, Simplex P, and Zimmer low-viscosity cement). One hundred four specimens were prepared by either a conventional manual mixing technique or mechanical vibration. Mechanical mixing gave a significant increase in shear strength for CMW and Simplex P. The compressive strength of Simplex P and Zimmer low-viscosity cement was significantly improved by mechanical mixing. The scatter of the results was significantly reduced by mechanical mixing. The modulus of elasticity was significantly increased by mechanical mixing for the three cements. The uniformity of the bone cement mass seems to be increased by a standardized mechanical mixing technique.

Bone Cements↗

PubMed2006

[Testing of anisotropic modulus and fluid characteristic of Chinese femur and tibia].

The tension moduls and compression modulus of Chinese tibia and femur of male in three different directions, namely axial, circumferential and radial directions, were tested in our experiments. The measured compression moduli are 5.8 +/- 0.34, 3.4 +/- 0.17, 2.1 +/- 0.18 GPa respectively for femur, and 6.1 +/- 0.36, 3.5 +/- 0.17, 2.1 +/- 0.18 GPa respectively for tibia; the measured tension moduli are 15.6 +/- 1.21, 9.8 +/- 0.73, 5.4 +/- 0.52 GPa respectively for femur, and 16.7 +/- 1.09, 10.3 +/- 0.70, 5.6 +/- 0.49 GPa respectively for tibia. The tension and compression ultimate strengths of femur and tibia were tested, too. The measured compression ultimate strengths are 150 +/- 9.3, 111 +/- 6.5, 110 +/- 7.1 MPa respectively for femur, and 191 +/- 12.3, 140 +/- 6.3, 123 +/- 8.3 MPa respectively for tibia; the measured tension ultimate strengths are 115 +/- 9.6, 82 +/- 6.8, 78 +/- 7.3 MPa respectively for femur, and 143 +/- 8.7, 110 +/- 8.3, 97 +/- 6.4 MPa respectively for tibia. Furthermore, the stress-relaxation experiments were conducted. The relation between loading and time during the experiments were obtained by the method of curve fitting. They meet the logarithm function: F = A * B(log t); A is the initial load, and B is the fitting material parameter. For femur, B is equal to 0.985; for tibia, B is equal to 0.987.

Anisotropy↗

PubMed2007

Geometric indices of bone strength are associated with physical activity and dietary calcium intake in healthy older women.

UNLABELLED: A population-based study on 1008 postmenopausal women identified that the 24% of women achieving high levels of PA and CI had 3.4-4.4% higher femoral bone strength in axial compression and 1.7-5.2% in bending than those achieving low levels, indicating that lifestyle factors influence bone strength in the proximal femur. INTRODUCTION: Extensive research has shown that increased physical activity (PA) and calcium intake (CI) decrease the rate of bone loss; however, there is little research on how these lifestyle variables affect bone geometry. This study was designed to investigate the effects of modifiable lifestyle variables, habitual PA and dietary CI, on femoral geometry in older women. MATERIALS AND METHODS: Femoral geometry, habitual PA, and dietary CI were measured in a population-based sample of 1008 women (median age+/-interquartile range, 75+/-4years) enrolled in a randomized controlled trial (RCT) of calcium supplementation. Baseline PA and CI were assessed by validated questionnaires, and 1-year DXA scans (Hologic 4500A) were analyzed using the hip structural analysis technique. Section modulus (Z), an index of bending strength, cross-sectional area (CSA), an index of axial compression strength, subperiosteal width (SPW), and centroid position, the position of the center of mass, were measured at the femoral neck (NN), intertrochanter (IT), and femoral shaft (FS) sites. These data were divided into tertiles of PA and CI, and the results were compared using analysis of covariance (ANCOVA), with corrections for age, height, weight, and treatment (calcium/placebo). RESULTS AND CONCLUSIONS: PA showed a significant dose-response effect on CSA all hip sites (p<0.03) and Z at the narrow neck and intertrochanter sites (p<0.02). For CI, there was a dose-response effect for centroid position at the intertrochanter (p=0.03). These effects were additive, such that the women (n=240) with PA in excess of 65.5 kcal/day and CI in excess of 1039 mg/day had significantly greater CSA (NN, 4.4%; IT, 4.3%; FS, 3.4%) and Z (NN, 3.9%; IT, 5.2%). These data show a favorable association between PA and aspects of bone structural geometry consistent with better bone strength. Association between CI and bone structure was only evident in 1 of 15 variables tested. However, there was evidence that there may be additive effects, whereby women with high levels of PA and CI in excess of 1039 mg/day had significantly greater CSA (NN, 0.4%; FS, 2.1%) and Z (IT, 3.0%) than women with high PA but low CI. These data show that current public health guidelines for PA and dietary CI are not inappropriate where bone structure is the health component of interest.

Aged↗

PubMed2006

Effect of diameter of the drill hole on torque of screw insertion and pushout strength for headless tapered compression screws in simulated fractures of the lateral condyle of the equine third metacarpal bone.

OBJECTIVE: To compare variables for screw insertion, pushout strength, and failure modes for a headless tapered compression screw inserted in standard and oversize holes in a simulated lateral condylar fracture model. SAMPLE POPULATION: 6 pairs of third metacarpal bones from horse cadavers. PROCEDURE: Simulated lateral condylar fractures were created, reduced, and stabilized with a headless tapered compression screw by use of a standard or oversize hole. Torque, work, and time for drilling, tapping, and screw insertion were measured during site preparation and screw implantation. Axial load and displacement were measured during screw pushout. Effects of drill hole size on variables for screw insertion and screw pushout were assessed by use of Wilcoxon tests. RESULTS: Drill time was 59% greater for oversize holes than for standard holes. Variables for tapping (mean maximum torque, total work, positive work, and time) were 42%, 70%, 73%, and 58% less, respectively, for oversize holes, compared with standard holes. Variables for screw pushout testing (mean yield load, failure load, failure displacement, and failure energy) were 40%, 40%, 47%, and 71% less, respectively, for oversize holes, compared with standard holes. Screws could not be completely inserted in 1 standard and 2 oversize holes. CONCLUSIONS AND CLINICAL RELEVANCE: Enlarging the diameter of the drill hole facilitated tapping but decreased overall holding strength of screws. Therefore, holes with a standard diameter are recommended for implantation of variable pitch screws whenever possible. During implantation, care should be taken to ensure that screw threads follow tapped bone threads.

Animals↗

PubMed1995

The biomechanical properties of deep freezing and freeze drying bones and their biomechanical changes after in-vivo allograft.

This study measured the physical properties in bending of the rat femur and compression of the rat first tail vertebra subjected to deep freezing at -80 degrees C for 2 weeks, 6 weeks, 12 weeks and freeze drying. This study also measured the mechanical changes after in vivo allograft of fresh bone, deep freezing(2, 6, 12 weeks) and freeze drying. Analysis for deep freezing groups showed a mean 7.2% decrease in bending strength and 11.0% decrease in compressive strength when compared with the control group, but there was no statistical difference in the duration of deep freezing. The groups of in vivo graft after deep freezing showed 23.1% and 22.2% decrease in bending and compressive strength. There was no statistical difference in the duration of deep freezing. The freeze drying group showed a 9.7% decrease in bending strength and no significant difference in compressive strength. The group of in vivo graft after freeze drying showed a 30.1% and a 41.3% decrease in bending and compressive strength. The above results suggested that there would be some mechanical limitation in using freeze dried graft for supporting implants.

Animals↗

PubMed1989

[Production of denture by preform compression molding method. Part 3. Retentive strength of artificial teeth].

A preform compression molding method to make a polysulfone denture has been reported. Retentive strength of artificial teeth to the denture base was examined to select artificial teeth for the compression molding method. Ceramic teeth with metal pins and polysulfone teeth heated at above 140 degrees C were retained to the denture base by useful retentive strength. Acrylic teeth on which the adhesive was used were also retained by useful strength. Each of the teeth, acrylic teeth, ceramic teeth and polysulfone teeth, could be used in the compression molding method.

Acrylic Resins↗

PubMed2005

Liquid gentamicin in bone cement: a laboratory study of a potentially more cost-effective cement spacer.

BACKGROUND: Liquid gentamicin is approved by the Food and Drug Administration, is readily available, and is much less costly than tobramycin, the more commonly used antibiotic in cement spacers. The purpose of the present study was to test the mechanical properties, elution characteristics, and antibacterial activity of liquid gentamicin in an acrylic bone cement spacer. METHODS: Standardized specimens consisting of Palacos cement combined with liquid gentamicin, powdered tobramycin, or no antibiotic were fashioned, and the three groups were tested with regard to compressive and tensile strength, elution characteristics (with use of radioimmunoassays), and antibacterial activity (with use of bioassays). RESULTS: The ultimate compression strength decreased by 49% (from 64.65 +/- 3.89 MPa to 32.96 +/- 3.33 MPa) and the ultimate tension strength decreased by 46% (from 35.85 +/- 2.97 MPa to 19.20 +/- 0.36 MPa) when the specimens containing 480 mg of liquid gentamicin were compared with the controls. The addition of tobramycin had no significant effect compared with the controls. The majority of gentamicin was released from the cement during the initial twenty-four hours (mean concentration, 26.4 mcg/mL). The mean concentrations at three and six weeks were 4.15 and 0.65 mcg/mL, respectively. The bioassays confirmed the bactericidal activity of the gentamicin released from the cement. CONCLUSIONS: Liquid gentamicin in bone cement is potent and bactericidal. Although the mechanical properties of the cement are significantly diminished by the addition of liquid gentamicin, the temporary nature of the cement spacer makes its use potentially worthwhile given the substantial cost savings to the hospital and the patient.

Anti-Bacterial Agents↗

PubMed2003

Calcium hypochlorite as a disinfecting additive for dental stone.

STATEMENT OF PROBLEM: Dental casts come into direct contact with impression materials and other items that are contaminated by saliva and blood from a patient's mouth, leaving the casts susceptible to cross-contamination. Topical methods of disinfecting casts are difficult to control, while immersion methods are potentially destructive. Thus, an additional method to control cross-contamination between patients and laboratory personnel is needed. PURPOSE: This study was undertaken in an attempt to develop a dental stone with disinfecting properties and adequate compressive and tensile strengths. MATERIAL AND METHODS: Calcium hypochlorite [Ca(OCl)(2)] in aqueous solution in concentrations from 0 to 1.5% was tested as a disinfecting additive to type V dental stone. The compressive and tensile strength properties of the modified stone were measured (MPa) using a universal testing machine at a consistency similar to unmodified stone. Strength data were analyzed by 1-way ANOVA and post hoc Tukey-Kramer procedure (alpha < or =.05). To measure the disinfecting ability, the effect on Bacillis subtilis bacteriophage phi29 was tested in triplicate to find the minimum concentration at which no phage was detected. Additionally, 3 impressions were disinfected with CaviCide, and 3 impressions rinsed in water served as controls. RESULTS: In general, the effect of adding the disinfectant to the stone was a decrease in strength. Exceptions were the dry compressive strength, for which there was a significant increase in strength (P=.048) at 0.5%, and the wet compressive and wet tensile strength, which showed no significant difference between the 1.5% and the control. When Ca(OCl)(2) was added at the concentration 0.5% (2765 ppm available chlorine), the gypsum had acceptable mechanical properties; dry compressive strength was 78.86 +/- 4.12 MPa, and dry tensile strength was 10.64 +/- 1.27 MPa, compared to control values of 67.85 +/- 6.28 and 13.41 +/- 1.24 MPa, respectively. At concentrations of 0.3% and higher (36 1650 ppm of available chlorine), calcium hypochlorite was able to completely inactivate phi29. CONCLUSION: It is possible to prepare a type V dental stone that contains a disinfectant, has adequate mechanical properties, and will reduce numbers of residual microorganisms. For example, stone mixed with water containing 0.5% Ca(OCl)(2) meets these criteria.

Analysis of Variance↗

PubMed2006

The influence of montmorillonite clay reinforcement on the performance of a glass ionomer restorative.

OBJECTIVES: A pristine calcium montmorillonite (Ca-MMT) and an organically modified 12-amino-dodecanoicacid treated montmorillonite (ADA-MMT) clay were evaluated to determine the reinforcement effect on the performance of a glass ionomer (GI) restorative ChemFil Superior (Dentsply DeTrey, Kanstanz, Germany) to assess the potential as a posterior filling material. METHODS: Mean compressive fracture strengths and standard deviations were determined for groups of 30 cylindrical specimens with 0.5-2.5 wt.% Ca-MMT and ADA-MMT additions to either the powder or the liquid elements of the GI. Working characteristics were assessed using an oscillating rheometer, the interlayer d-spacings (d(001)) of each MMT clay was determined using X-ray diffraction (XRD) and the set cement structure was determined by scanning electron microscopy (SEM). RESULTS: The addition of up to 1.0 wt.% ADA-MMT resulted in a significant increase in the mean compressive fracture strength of the GI utilising the one-way ANOVA and Tukey test comparisons at P<0.05. When Ca-MMT clay was added to the GI a significant reduction in mean strength was recorded (P<0.05). MMT clay addition to the powder and liquid element of the GI in excess of 1.0 wt.% resulted in no significant differences in working characteristics although increases in setting times were evident for MMT addition up to 1.0 wt.%. XRD patterns identified the d(001) peaks for Ca- and ADA-MMT at 2 theta angles of 8.44 degrees and 5.07 degrees and d(001) spacings of 1.04 and 1.74 nm, respectively. CONCLUSIONS: The increased interlayer d-spacings recorded for ADA-MMT clay demonstrates that the clay had expanded layers which may have provided an increased opportunity for the polyacrylic acid chains of the GI restorative to diffuse into the MMT galleries. It is postulated that the increased interlayer d-spacings for the ADA-MMT clay had a positive reinforcing effect on the GI compared with the Ca-MMT clay where no increased performance was identified. The study has highlighted the potential for increasing the performance of GI restoratives when using an organically modified clay as a reinforcement which could increase the potential of GIs as posterior filling materials.

Aluminum Silicates↗