Diametral Compressive Strength Research Articles

Influence of filler content on physicomechanical and bonding properties of an experimental dental resin cement

AbstractTo investigate the effects of filler contents on the bonding and physicomechanical properties of experimental dental resin cements and the correlation between them, four groups were formulated with silicon dioxide filler in the following weight percentages: A: 40%, B: 50%, C: 60%, and D: 70%. LuxaCore dental resin cement was used as group E for commercial reference. For testing bond strength, resin cements were applied to the prefabricated dental fiber posts in the artificial teeth canal and photo cured, and then the microtensile bonding strength (BS) between posts and resin cement was measured in sticks of 1 × 1 mm2. For the mechanical properties, flexural strength (FS), diametral tensile strength (DTS), compressive strength (CS), and hardness (H) were tested according to the related standard. Water sorption and solubility were also determined. The results showed both bonding and physicomechanical strengths of the experimental resin cements varied to different extents with filler addition. Positive correlations existed respectively between the filler content and some mechanical properties (rFS = 0.964, rCS = 0.967, and rH = 0.959), whereas no significant correlations were found between the filler content and the other strength values tested in this study (rDTS = 0.321, rBS = 0.014), neither were between bond strength and mechanical properties. The effect of filler content on mechanical properties was more influential and prominent compared to that on bond strength. It is partial to compare properties and to predict clinical behaviors of resin materials based on a single in vitro test, and comprehensive evaluation is necessary. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Removal of lead from solution by combination of natural zeolite–kaolin–bentonite as a new low-cost adsorbent

Abstract Recently several kinds of low-cost adsorbents were developed for the extreme environmental and waste treatment processes. The adsorption capacity and physico-mechanical properties of adsorbent are basically affected by mixing ratio of the used materials. These requirements cause to apply the technique of experiment to optimize mentioned properties. In the present investigation commercial zeolite, bentonite and kaolin were used in experimental design algorithm due to their abilities in removal of heavy metal ions. Different amounts of used powders were mixed according to mixture design algorithm and shaped by extrusion technique in the form of Raschig ring. The test rings were calcined at 600 and 700 °C after drying in laboratory oven and characterized by determining porosity, diametrical compressive strength and adsorption capacity. In order to manufacture applicable adsorbent, the response surface analysis method was used to optimize mixing ratio of materials. The investigation was concluded that the strength and adsorption capacity can be simultaneously optimized by the addition of 66.67, 29.17 and 4.16 wt.% zeolite, bentonite and kaolin respectively. In the next part of work, the kinetics and adsorption isotherm of lead on selected composition was mathematically investigated. The Langmuir isotherm and pseudo second order kinetic model showed the acceptable accuracy in prediction of adsorption data. The possibility of lead immobilization by fabricated rings can be useful in industrial practice.

Can we add chlorhexidine into glass ionomer cements for band cementation?

To test if the addition of chlorhexidine digluconate (CHD) might influence the mechanical properties and antibacterial properties of two different conventional glass ionomer cements (GICs) used for band cementation. Two commercial brands of conventional GICs were used: Ketac Cem Easymix (3M/ESPE, St Paul, Minn) and Meron (Voco, Cuxhaven, Germany). The cements were manipulated in their original composition and also with 10% and 18% CHD in the liquid to create a total of six groups. Diametral tensile strength, compressive strength, microhardness, shear bond strength, and antibacterial effects in 5, 45, and 65 days against Streptococcus mutans were tested in all groups, and the data were submitted to statistical analyses. There were no significant differences between the groups of the same material in diametral tensile, compressive strength, and shear bond strength (P > .05). There was significant improvement in the microhardness to the Ketac Cem Easymix (P < .001). GICs with the addition of CHD showed significant inhibition of S. mutans growth in comparison with the control groups at the three time points evaluated (P < .001). The addition of 18% CHD resulted in higher bacterial inhibition (P < .001). The addition of chlorhexidine digluconate to conventional GICs does not negatively modify the mechanical properties and may increase the antibacterial effects around the GICs even for relatively long periods of time.

Microstructure and properties of polyhydroxybutyrate-calcium phosphate cement composites

AbstractThe biopolymer (polyhydroxybutyrate) microparticles-calcium phosphate composites were prepared by mechanical mixing of the basic composite components with the addition of hardening liquid after ethanol-composite mixture suspension moulding. The composite microstructures were more compact than the pure cement samples as confirmed by the lower values of specific areas and mesopore volumes. Both the specific areas and mesopore volumes decreased with soaking time in a simulated body fluid. The low polyhydroxybutyrate degradation in composites was found after soaking in simulated body fluid, which was terminated after one week. The formation of a dense apatite layer bonded directly to the surface of polyhydroxybutyrate microparticles was observed. The highest diametral tensile strength (13 MPa) and compressive strength (95 MPa) values of up to 50 % higher than in pure cement were measured in samples with 10 % of polyhydroxybutyrate. The addition of polyhydroxybutyrate microparticles had no effect on the setting time.

Polymeric calcium phosphate cements incorporated with poly‐γ‐glutamic acid: Comparative study of poly‐γ‐glutamic acid and citric acid

AbstractPolymeric calcium phosphate cements (PCPC) derived from biodegradable poly‐γ‐glutamic acid (γ‐PGA) were prepared in an attempt to improve the mechanical strength of calcium phosphate cement (CPC). The characteristics of the PCPCs were compared with those of cement incorporated with citric acid. The diametral tensile and compressive strengths of the CPC incorporated with γ‐PGA were significantly higher than that of cement incorporated with citric acid at equivalent concentrations (P &lt; 0.05). The maximal diametral tensile and compressive strengths of the CPC incubated for 1 week in physiological saline solution were approximately 18.0 and 50.0 MPa, respectively. However, the initial setting time of the PCPC was slower than that of CPC incorporated with citric acid. The formation of ionic complexes between calcium ions and γ‐PGA was observed using FTIR spectroscopy. Hydroxyapatite (HA) formation was retarded by γ‐PGA incorporation according to scanning electronic microscopy (SEM) and powder X‐ray diffraction (XRD) observations. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Urethane dimethacrylate oligomers for dental composite matrix: Synthesis and properties

AbstractTwo urethane poly(ethylene oxide) dimethacrylates based on polyether diol of variable length (Mn: 300 and 1000 g/mol), isophorone diisocyanate and 2‐hydroxyethyl methacrylate, were synthesized and characterized to be used as comonomers for dental composites. The polymerization process initiated with benzoyl peroxide/amine or camphorquinone/tertiary amine couple was followed by a combination of FTIR spectroscopy and fluorescence technique using a pyrene probe for the in situ monitoring of microscopic changes in the polymeric systems. Difference in the polymerization kinetics of the oligomers and low‐molecular‐weight monomer is presented in connection with the chemical structure of the urethane dimethacrylate, taken together with another partners (bisGMA, TEGDMA, filler) with effect on the mobility and reactivity of the formed polymeric network. The results suggest a higher reactivity of the oligomeric forms and are in agreement with the fluorescence measurements induced of the pyrene molecule, whosemonomer fluorescence emission significantly increased with irradiation time as the network formation occurred. Measurements of the contact angle showed the maintenance of the hydrophilic nature of these resins, while the values of polymerization shrinkage and diametral tensile and compressive strengths of the three specimens indicated that the incorporation of dimethacrylate urethane oligomers in the organic matrix (18 wt%) led to materials with good properties. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Polymeric Calcium Phosphate Cements Incorporated with Poly-γ-Glutamic Acid

Polymeric calcium phosphate cements (PCPC) derived from biodegradable poly-g-glutamic acid (g-PGA) were prepared in an attempt to improve the mechanical strength of calcium phosphate cement (CPC). The characteristics of the PCPCs were compared to those of cement incorporated with citric acid. The diametral tensile and compressive strengths of the CPC incorporated with g-PGA were significantly higher than that of cement incorporated with citric acid at equivalent concentrations (p&lt;0.05). The maximal diametral tensile and compressive strengths of the CPC incubated for 1 week in physiological saline solution were approximately 18.0 and 50.0 MPa, respectively. However, the initial setting time of the PCPC was much slower than that of CPC incorporated with citric acid. The formation of ionic complexes between calcium ions and g-PGA was observed using FT-IR spectroscopy. Hydroxyapatite (HA) formation was retarded by g-PGA incorporation according to scanning electronic microscopy (SEM) and powder X-ray diffraction (XRD) observations.

Diametral Tensile and Compressive Strengths of Several Types of Core Materials

Compressive and diametral tensile strengths (DTSs) of core materials are thought to be important, because cores usually replace a large bulk of tooth structure and should provide sufficient strength to resist intraoral tensile and compressive forces. This study was undertaken to compare the mechanical properties of materials used for direct core foundations. The differences between the compressive and DTSs of six core materials, including Duralloy (high-copper amalgam), Grandio (visible light-cured nanohybrid resin composite), Admira (organically modified ceramic), Filtek P60 (packable composite resin), Rebilda DC (dual-cure adhesive core material), and Argion Molar (silver-reinforced glass ionomer cement), were tested. A total of 120 specimens, half for the compressive strength (CS) test (6 mm in height, 4 mm in diameter) and the other half for the DTS test (6 mm in diameter, 3 mm in thickness), were prepared. The specimens were stored at room temperature in distilled water for 7 days. The Lloyd testing machine was used to load the specimens at a crosshead speed 0.5 cm/min, and the strength values were determined in MPa. The compressive and DTS test values (in MPa), respectively, of the materials were: Admira (361, 44); Filtek P60 (331, 55); Grandio (294, 53); Rebilda DC (279, 42); Duralloy (184, 40); and Argion Molar (107, 9). Kruskal-Wallis test was computed, and multiple comparisons test discerned many differences among materials (p < 0.05). Packable composite resin (Filtek P60), visible light cured nanohybrid resin composite (Grandio), and organically-modified ceramic (Admira) had higher compressive and DTS values than the other materials.

Transformations in CDHA/OCP/β‐TCP scaffold during ageing in simulated body fluid at 36.5°C

The transformations that took place in a scaffold composed of CDHA/OCP/beta-TCP by ageing in SBF at 36.5 degrees during 14 days were studied. A carbonated-apatite layer was formed during immersion in SBF on the surface of the scaffold and part of the OCP present in the inner core of the material was also transformed into apatite. The precipitated apatite layer exhibited the typical globular morphology characteristic of bioactive materials. The content of CDHA increased from 14 to 29 wt % at the expense of the content of OCP that decreased from 39 to 29 wt %. beta-TCP content dropped slightly from 47 to 42 wt %. Total porosity (from 56.1% +/- 0.6% to 62.4% +/- 0.5%) and real density (from 2.58 +/- 0.01 to 2.79 +/- 0.01 g/cm(3)) increased, and diametral tensile (from 2.1 +/- 0.3 to 0.9 +/- 0.1 MPa) and compressive strengths (from 8.5 +/- 1.0 to 6.8 +/- 0.6 MPa) decreased during ageing. The in vitro results showed that the scaffold composed of CDHA, OCP, and beta-TCP is bioactive and partially resorbable. It seems to be suitable for in situ bone regeneration procedures.

Effect of in situ spinel seeding on synthesis of MgO-rich MgAl2O4 composite

MgO-rich MgAl2O4 spinel was prepared by adopting solid-state reaction of commercially available sintered seawater magnesia and α-alumina. Starting materials were mixed in weight ratio (Al2O3: MgO) of 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, where the developed MgAl2O4 spinel crystal seed in calcined powder varied (5–50%) with respect to addition of MgO content and temperature. Around 70% spinellisation could be noticed in Al2O3: MgO (1:1) batch through double stage sintering. Densification and grain size of the sintered specimen was found to be greatly dependent on initial calcination temperature and content of primary spinel seed. The diametrical compressive strength of sintered specimen was ∼115 MPa for highest amount of spinel content. The hardness of MgO-rich spinel composite was varied with spinel addition.

Quantification of the compactibility of pharmaceutical powders

The purpose of this study is to investigate and to quantify the compactibility of pharmaceutical powders by a simple linear relationship between the diametral compressive strength of tablets and the applied compaction pressure. The mechanical strength of the tablets is characterized as the crushing force normalized with the dimension of the tablet and termed the specific crushing strength, SCS. The proposed model: SCS = Cp ∗ P + b estimates the slope of the regression line Cp as a dimensionless compactibility parameter and is reported with the corresponding standard deviation S Cp. The linear region of the compactibility profile is selected using the 95% predictability limits bordering the regression line. Eleven different materials were tested and acceptable fits to the linear model were observed in all cases. The ability of the model to discriminate between the investigated materials is excellent, in cases where the difference may be difficult to show a simple t-test is used as an inference tool. No difference was found between lactose tablets of different masses (500 and 1000 mg). A relationship between the compactibility parameter and the compressibility characterized by the Walker coefficient is demonstrated.

Preparation of macroporous alumina ceramics using wheat particles as gelling and pore forming agent

The present work reports a simple process for preparation of macroporous alumina ceramics from aqueous powder slurries using wheat particles as gelling and pore forming agent. Wheat particles incorporated in aqueous alumina slurries rapidly absorb water on heating and transform it into a strong gel. The gelled bodies did not undergo crack and warpage during drying. The dried green bodies showed diametrical compressive strength in the range 0.41–0.59 MPa and are amenable to machining operations such as milling, drilling and lathing. Pyrolytic removal of the pore former followed by sintering at 1600 °C produced alumina bodies with porosity 67–76.7% and diametrical compressive strength 2.01–5.9 MPa. Isotropic shrinkage was observed during sintering. Microstructure showed both large (200–800 μm) and small (less than 20 μm) pores. Small pores were uniformly distributed in the struts and walls of the large pores.

Temporary restorative resins using non-phthalate ester plasticizers

This study examined temporary restorative resins that use non-phthalate ester plasticizers. Three non-phthalate plasticizers were tested: tri-ethyl citrate (TEC), tri-butyl citrate (TBC), and di-butyl sebacate (DBS). The experimental resins were compared with resins that use a phthalate ester plasticizer (di-butyl phthalate, DBP) and commercial products (Dura Seal, Plast Seal, and Fit Seal). For the experimental resins, the ratio of plasticizer to PMMA/MMA resin was varied from 30 to 60% (wt). The mechanical properties of the experimental resins were evaluated using a modified diametral compressive strength and the resistance to explorer insertion. The strengths of the experimental resins with plasticizer concentrations ranging from 40 to 50% (TEC, TBC, and DBP) or from 30 to 40% (DBS), by weight, were equivalent to the strengths of commercial temporary restorative resins. A similar tendency was seen for the resistance to explorer insertion. The results suggest that new temporary restorative resins can be prepared by choosing the appropriate proportions of resin monomer and non-phthalate ester plasticizer.

Ultrasonic and Mechanical Behavior of Green and Partially Sintered Alumina: Effects of Slurry Consolidation Chemistry

Green and partially sintered compacts of {alpha}-Al{sub 2}O{sub 3} powder were made by filtration of aqueous suspensions under three conditions: (i) electrostatic stabilization without any organic additive, (ii) strong flocculation near the isoelectric point without any organic additive, and (iii) weak flocculation by the use of maltodextrin or oxalic acid additives. The authors evaluated relationships between the macroscopic and interparticle mechanical behavior of these compacts using model correlations with measurements of diametral compression, ultrasonic velocity, and ultrasonic attenuation. Although type iii green specimens were less dense than type i, type iii exhibited significant increases in velocity, macroscopic Young`s modulus, interparticle-contact stiffness, and diametral compressive strength, suggesting that the mechanism of stiffening/strengthening entailed interparticle bridging of maltodextrin or oxalic acid. These properties were significantly reduced upon heating type iii specimens to 500 C, suggesting that pyrolysis of surface-adsorbed maltodextrin and oxalic acid may have reduced the interparticle stiffness and strength. In contrast, negligible changes in these properties occurred upon heating type i specimens to the same temperature. Despite small increases in packing density, significant decreases in attenuation and significant increases in velocity, interparticle-contact stiffness, and Young`s modulus occurred upon heating all specimens to {ge}700 C, suggesting the formation of interparticle necksmore » by solid-state sintering.« less

Effect of filler fraction on strength, viscosity and porosity of experimental compomer materials

Objective. The primary goal is to develop a self-cured polyacid-modified resin composite with good mechanical and rheological properties. To achieve such a goal, the aim of this study is to determine how volume filler fraction (VFF) affects mechanical properties and viscosities of such materials containing different filler volumes. Methods. A series of self-cured polyacid-modified composites made from polyacid modified resins and TEGDMA, mixed with filler particles, were evaluated regarding compressive strength (CS), diametral compressive strength (DCS) and viscosity. The maximum filler content, which could be incorporated into the materials, was calculated from CS tests as well as from viscosity measurements using Mooney's equation. Porosity contents were also determined in an attempt to explain different failure behaviours. Results. The CS values peaked at 18.9 vol.% filler particles and declined afterwards for self-cured polyacid-modified resin composites cured in air. Using photopolymerisation and barium filler in the polyacid-modified resin composites resulted in the highest CS and DCS values. The viscosity increased continuously with increased VFF. VFF results determined experimentally and with Mooney's equation at shear rates of 0.01, 0.1, 1.0, and 10.0 s −1 revealed that the maximal filler fraction values were 54.9±1.8, 55.9±1.3, 56.3±0.9, and 56.8±0.8 vol.%, respectively. The largest porosity content occurred at a VFF value of 53 vol.% Conclusions. We conclude that an increase in filler fraction of the investigated experimental polyacid-modified resin composite materials above a certain value (20–30 vol.%) does not result in improved mechanical properties.

About the use of stoichiometric hydroxyapatite in compression – incidence of manufacturing process on compressibility

Literature concerning calcium phosphates in pharmacy exhibits the chemical diversity of the compounds available. Some excipient manufacturers offer hydroxyapatite as a direct compression excipient, but the chemical analysis of this compound usually shows a variability of the composition: the so-called materials can be hydroxyapatite or other calcium phosphates, uncalcined (i.e. with a low crystallinity) or calcined and well-crystallized hydroxyapatite. This study points out the incidence of the crystallinity of one compound (i.e. hydroxyapatite) on the mechanical properties. Stoichiometric hydroxyapatite is synthesized and compounds differing in their crystallinity, manufacturing process and particle size are manufactured. X-Ray diffraction analysis is used to investigate the chemical nature of the compounds. The mechanical study (study of the compression, diametral compressive strength, Heckel plots) highlights the negative effect of calcination on the mechanical properties. Porosity and specific surface area measurements show the effect of calcination on compaction. Uncalcined materials show bulk and mechanical properties in accordance with their use as direct compression excipients.

PHYSICAL PROPERTIES OF COMPOSITES CURED WITH CONVENTIONAL LIGHT OR ARGON LASER

ABSTRACT Objective: This study evaluated various physical properties of two resin composites polymerized by either an argon laser or a conventional visible light. Materials and Methods: A hybrid composite, Herculite XRV (Kerr Corp., Orange, California), and a microfill composite, Durafill VS (Kulzer, Wehrheim, Germany), were used in this study. Three physical properties, diametral tensile strength, compressive strength, and flexural strength, were tested. Five specimens of each composite resin were made for each set of physical properties tested, for a total of 18 groups and 90 specimens. Specimens were fabricated according to the American National Standards Institute and American Dental Association Specification No. 27 for each property tested. The composite was polymerized with either an argon laser (power density of 1000 mW/cm2) for 10 or 20 seconds or a conventional visible light (power density of 354 mW/cm2) for 40 seconds. Specimens were stored in water in light‐proof containers at 37°C for 7 days before testing with a Zwick (Atlanta, Georgia) universal testing machine. Results: The physical properties of Herculite XRV were not affected by the light source or exposure time. For Durafill VS, no significant differences were observed for the diametral tensile strength whether the argon laser or conventional light was used. However, the flexural strength of the microfill was significantly lower when polymerized with the argon laser a t 10 seconds compared with the two other curing methods (20‐second laser cure, 40‐second conventional cure). Also, the compressive strength of Durafill VS polymerized with the argon laser a t 10 seconds was significantly lower than when it was cured with the conventional light for 40 seconds. Conclusions: Hybrid and microfill resin composites cured with an argon laser for 20 seconds had physical properties comparable to composites polymerized with a conventional visible light unit for 40 seconds. Therefore, with adequate exposure time, the argon laser is a potential alternative to conventional visible light‐curing.

Gelcasting of alumina using urea–formaldehyde III. Machinable green bodies by copolymerisation with acrylic acid

The present work is an attempt to improve the gel strength, green body strength and green machinability characteristics of gelcast alumina bodies by co-polymerisation of urea-formaldehyde (UF) with acrylic acid. Methylol urea and acrylic acid in the pre-mix solution undergo simultaneous polymerisation at 80°C. The polyacrylic acid stabilises the UF condensation products through hydrogen bonding and prevent precipitation, resulting in a transparent gel. The gel when heated at 110°C forms a tough polymer which gives a peak at 1738 cm −1 in the infrared spectrum indicative of crosslinking of the methylol urea condensation products and polyacrylic acid through ester linkage. The alumina slurries prepared in the premix solution, gels within 10–15 min at 80°C. The green strength of the gelcast bodies increases with acrylic content. A binder composition containing >50% acrylic acid shows diametrical compressive strength >7 MPa. The green bodies show excellent machinability and are subjected to lathing, milling and drilling using conventional tools and equipments. The green bodies during machining show chip resistance and machined body has good surface finish. A near steady state binder removal profile is achieved by heating the samples under both dynamic and isothermal conditions. The debinderised bodies on sintering gave up to 97% theoretical density.

Influence of silanization and filler fraction on aged dental composites.

The effect of silanization and filler fraction on the mechanical properties of aged dental composites was investigated. Experimental composites (75/25 Bis-GMA/TEGDMA resin reinforced with 0, 12.6, 30.0, and 56.5 vol% 8 microm silanized/unsilanized BaSiO6) were fabricated into 4.7 mm diameter x 2.2 mm thick discs and 3.5 mm diameter x 7.3 mm thick discs for diametral tensile and compressive tests, respectively. The effect of immersion in 75% ethanol at 37 degrees C for 0-30 days on the diametral tensile strength (DTS) and compressive strength (CS) of the samples was evaluated and analysed by ANOVA and Tukey LSD test. The fracture interface between filler and resin matrix was then examined by scanning electron microscope. Results and subsequent statistical evidence from DTS (18.6+/-7.6 MPa, silanized versus 11.7+/-2.6 MPa, unsilanized) and CS (85.1+/-29.7 MPa, silanized versus 56.0+/-11.3 MPa, unsilanized) strongly implies that silanization may greatly enhance the mechanical properties of the resin composites. Furthermore, it also shows that both DTS and CS increased proportionally as the filler fraction of the composites increased. However, in the unsilanized groups, DTS decreased (up to 40%) as the filler fraction increased, and CS showed no relevance to the filler fraction at all. As for the influence of aging, it was found that both DTS and CS showed a significant decrease after immersion in 75% ethanol, and silanization heavily correlated with the filler fraction of aged-resin composites. Microscopic examination of the fractured samples showed that failure primarily occurred within the resin matrix per se for silanized composites and adjacent to the filler particles for unsilanized composites. All the evidence points to the conclusion that mechanical properties of aged-resin composites can be greatly influenced by silanization and the filler fraction.

Diametral tensile strength and compressive strength of a calcium phosphate cement: Effect of applied pressure

Diametral tensile strength and compressive strength of a calcium phosphate cement: Effect of applied pressure