Liquid-to-powder Ratio Research Articles

Resin tags formation by modified Renewal MI formulations in a carious dentine model.

To determine which components in a new restorative material (Renewal MI) improve its ability to form resin tags within demineralized dentine. Varied components included polylysine (PLS), monocalcium phosphate (MCP), powder to liquid ratio (PLR), 4-methacryloyloxyethyl trimellitate anhydride (4META), and polypropylene glycol dimethacrylate (PPGDMA). Urethane dimethacrylate (UDMA), containing PPGDMA (24 wt%) and 4META (3 wt%), was mixed with glass filler with MCP (8 wt%) and PLS (5 wt%). PLR was 3:1 or 5:1. Reducing MCP and/or PLS to 4 and 2 wt% respectively or fully removing MCP, PLS, 4META or PPGDMA gave 16 formulations in total. Renewal MI, Z250 (with or without Scotchbond Universal adhesive) and Activa were used as commercial comparators. Collagen discs were obtained by totally demineralizing 2 mm thick, human, premolar, coronal dentine discs by immersion in formic acid (4M) for 48 h. The restorative materials were then applied on top (n = 3), before dissolving the collagen in sodium hypochlorite (15%). SEM/EDX was employed to determine resin tags length, composition, and surface coverage. Tags were >400, 20 and 200 µm and covered 62, 55 and 39% of the adhesion interface for Renewal MI, Scotchbond and Activa, respectively. With experimental formulations, they were 200 and >400 µm long with high vs. low PLR and composed primarily of polymerized monomers. Percentages of the adhesion interface covered varied between 35 and 84%. Reducing PLS or MCP caused a decline in coverage that was linear with their concentrations. Reducing MCP had lesser effect when PLS or PLR were low. Removal of 4META caused a greater reduction in coverage than PPGDMA removal. PLS, MCP, 4META, PPGDMA and low PLR together enhance Renewal MI tags formation in, and thereby sealing of, demineralized dentine.

The effect of powder to liquid ratio on physical properties and fluoride release of glass ionomer cements containing pre-reacted spherical glass fillers.

The aim was to assess the effect of powder to liquid ratio (PLR) on setting time, fluoride release, and compressive strength of conventional glass ionomer cements (GICs) containing pre-reacted spherical glass fillers (SPG). GICs were prepared by mixing SPG with Fuji IX Universal liquid using PLR of 1:1, 1.5:1, 2:1, 2.5:1, 3:1. Setting time decreased from 221 to 51 s upon rising PLR. Increasing PLR decreased cumulative fluoride release (33 to 13 ppm). Diffusion coefficient of fluoride of experimental GICs (1.6-1.8×10-8 cm2/s) was comparable with that of Fuji IX Universal (1.6×10-8 cm2/s). Compressive strength of PLR 2:1 to 3:1 (93-140 MPa) were comparable with that of Fuji IX Universal (124 MPa). These results demonstrated that rising powder ratio reduced setting time, fluoride release, and compressive strength of GICs. However, the setting time and strength experimental GICs with PLR greater than 2:1 were in the acceptable range of the ISO standard.

Mg-P/c-SWCNT Bone Cement: The Effect of Filler on Setting Behavior, Compressive Strength and Biocompatibility

Improving the strength of bone cement is one of the critical goals in cement designing to maintain their integrity and stabilize connection between the cement and their surrounding tissue during the time that the cement has been replaced by matured bone tissue. To this aim, the authors decided to evaluate setting behavior and compressive strength of Magnesium Phosphate Cement (MPC) by adding car-boxylated Single-Walled Carbon Nanotubes (c-SWCNTs) and assess the biocompatibility of the composite cement. MPC containing 0 wt% to 0.5 wt% of c-SWCNTs at the Powder to Liquid Ratio (PLR) of 1 g-mL-1 to 2 g-mL-1 were produced. Adding c-SWCNTs to MPC postponed the setting time of the cement at the beginning of the cementation process and preserved the reaction with a high rate for a longer time. In addition, the compressive strength of MPC was enhanced to 28 MPa by adding 0.2 wt% c-SWCNTs because of producing cement with compact and uniform micro structure. In addition, cell behavior on MPC with/without c-SWCNTs indicated no cytotoxic effect alongside a suitable adhesion and proliferation of them.

Magnesium Phosphate Cement as Mineral Bone Adhesive.

Mineral bone cements were actually not developed for their application as bone-bonding agents, but as bone void fillers. In particular, calcium phosphate cements (CPC) are considered to be unsuitable for that application, particularly under moist conditions. Here, we showed the ex vivo ability of different magnesium phosphate cements (MPC) to adhere on bovine cortical bone substrates. The cements were obtained from a mixture of farringtonite (Mg3(PO4)2) with different amounts of phytic acid (C6H18O24P6, inositol hexaphosphate, IP6), whereas cement setting occurred by a chelation reaction between Mg2+ ions and IP6. We were able to show that cements with 25% IP6 and a powder-to-liquid ratio (PLR) of 2.0 g/mL resulted in shear strengths of 0.81 ± 0.12 MPa on bone even after 7 d storage in aqueous conditions. The samples showed a mixed adhesive–cohesive failure with cement residues on the bone surface as indicated by scanning electron microscopy and energy-dispersive X-ray analysis. The presented material demonstrated appropriate bonding characteristics, which could enable a broadening of the mineral bone cements’ application field to bone adhesives.

Injectable dicalcium phosphate bone cement prepared from biphasic calcium phosphate extracted from lamb bone

Quick setting and poor injectability due to liquid–solid phase separation have limited the clinical use of brushite and monetite cements. The presence of certain ions in the cement during the setting reaction moderate the setting time and properties of the cement. This study reports the preparation of injectable bone cement by using biphasic calcium phosphate (BCP) extracted from femur lamb bone by calcination at 1450 °C. EDX analysis infers the presence of Mg and Na ions as trace elements in BCP. X-ray diffraction patterns of the prepared cement confirmed the formation of brushite (DCPD) along with monetite (DCPA) as a minor phase. DCPA phase diminished gradually with a decrease in powder to liquid ratio (PLR). Initial and final setting time of 5.3 ± 0.5 and 14.67 ± 0.5 min respectively are obtained and within the acceptable recommended range for orthopedic applications. Exceptional injectability of ≈90% is achieved for all prepared bone cement samples. A decrease in compressive strength was observed with increase in the liquid phase of the cement, which is attributed to the higher degree of porosity in the set cement. Immersion of bone cement in simulated body fluid (SBF) for up to 7 days resulted in the formation of apatite layer on the surface of cement with Ca/P ratio 1.71, which enhanced the compressive strength from 2.88 to 9.15 MPa. The results demonstrate that bone cement produced from BCP extracted from femur lamb bone can be considered as potential bone substitute for regeneration and repair of bone defects.

Injectability of calcium phosphate pastes: Effects of particle size and state of aggregation of β-tricalcium phosphate powders

The present study discloses a systematic study about the influence of some relevant experimental variables on injectability of calcium phosphate cements. Non-reactive and reactive pastes were prepared, based on tricalcium phosphate doped with 5mol% (Sr-TCP) that was synthesised by co-precipitation. The varied experimental parameters included: (i) the heat treatment temperature within the range of 800–1100°C; (ii) different milling extents of calcined powders; (iii) the liquid-to-powder ratio (LPR); (iv) the use of powder blends with different particle sizes (PS) and particle size distributions (PSD); (v) the partial replacement of fine powders by large spherical dense granules prepared via freeze granulation method to simulate coarse individual particles. The aim was contributing to better understanding of the effects of PS, PSD, morphology and state of aggregation of the starting powders on injectability of pastes produced thereof. Powders heat treated at 800 and 1000°C with different morphologies but with similar apparent PSD curves obtained by milling/blending originated completely injectable reactive cement pastes at low LPR. This contrasted with non-reactive systems prepared thereof under the same conditions. Hypotheses were put forward to explain why the injectability results collected upon extruding non-reactive pastes cannot be directly transposed to reactive systems. The results obtained underline the interdependent roles of the different powder features and ionic strength in the liquid media on determining the flow and injectability behaviours.

Study on the Injectable Magnesium-calcium Phosphate Cements

Injectable magnesium-calcium phosphate cements (IMPC) was prepared using magnesium oxide (MgO), monopotassium phosphate (KH2PO4), β-tricalcium phosphate (β-TCP), glucose and phosphoric acid solution. The effects of liquid to powder ratio(LPR), contents of MgO and glucose on IMPC’s gelling and mechanical properties were investigated. The results showed that increase of LPR and glucose content resulted in increased IMPC setting time and injectability, and decreased compressive strength. With the MgO content decreasing, the setting time and the injectability were decreased, whereas the compressive strength was increased. To obtain optimal formula for the new IMPC, the MgO and glucose contents and LPR were selected based on orthogonal experiments, and the result was 26wt% MgO, 6wt% glucose and 0.30 mL/g LPR. The new IMPC has moderate hydration with low exothermic reaction and ideal hardening performance, indicating that it may be used as a novel bone adhesive material.

Direct and interactive influence of explanatory variables on properties of a calcium phosphate cement for vertebral body augmentation

We used the response surface methodology to investigate the direct and interactive effects of three explanatory variables on three properties of a calcium phosphate cement (CPC) for use in vertebroplasty (VP) and balloon kyphoplasty (BKP). The variables were poly(ethylene glycol) content of the cement liquid (PEG), powder-to-liquid ratio (PLR), and the amount of Na2HPO4 added to an aqueous solution of 4 wt/wt% poly(acrylic acid) (as the cement liquid) (SPC). The properties were injectability (I), final setting time (F), and 5-day compressive strength (UCS). We found that (1) there was an interactive effect between the variables on I and F but not on UCS; (2) the maximum I (98%) was obtained with PEG = 20 wt/wt% and PLR = 2 g mL(-1); (3) F = 15 min (the proposed optimum value for a CPC for use in VP and BKP) was obtained with PEG = 4 wt/wt% and PLR = 2.9 g mL(-1); and (4) the maximum UCS (39 MPa) was obtained with SPC = 0 and PLR = 3.5 g mL(-1).

Evaluation of the ultrasonication process for injectability of hydraulic calcium phosphate pastes

This study examined the use of ultrasonication to improve the injectability of an aqueous calcium phosphate paste. Ultrasonication was applied to the paste through the plunger of the delivery syringe. A factorial design of experiments with three investigated factors, liquid to powder ratio (LPR) (38%, 39% and 40%), the size of the delivery syringe (5 and 10ml) and the amplitude of the 20kHz power ultrasonication (0–30μm), was used in this study. The volume fraction of the extruded paste was used to quantify injectability. Small injectability improvements were observed with an increase in LPR and decrease in syringe size, which is consistent with previously published results. The improvements due to ultrasonication were significant and remarkable. For example, when using the 5ml syringe the injected volume fraction of the 38% LPR paste improved from 63.4±2.3% without ultrasonication to 97.3±2.4% with 30%. This result shows that ultrasonication is an effective solution to improve injectability.

Injectability and mechanical properties of magnesium phosphate cements

Up to now magnesium phosphate cements are mainly being utilized in wastewater treatment due to their adsorptive properties. Recently they also have been shown to have a high potential as degradable biocements for application as replacement materials for bone defects. In comparison to degradable calcium phosphate cements they have the advantage of setting at neutral pH, which is favorable in biological environment. In this study two parameters of the cement composition, namely powder-to-liquid ratio (PLR) and citrate content, were varied in order to optimize the injectability properties of the cement paste and the mechanical properties of the reaction product. These properties were determined by means of testing setting time and temperature, paste viscosity, and injectability as well as phase composition and compressive strength of the set cements. Best results were obtained, when the cements were prepared with a PLR of 2.5 and a binder liquid consisting of an aqueous solution of 3 mol/l diammonium hydrogen phosphate and 0.5 mol/l diammonium citrate.

Injectability of brushite-forming Mg-substituted and Sr-substituted α-TCP bone cements

The influence of magnesium- and strontium-substitutions on injectability and mechanical performance of brushite-forming alpha-TCP cements has been evaluated in the present work. The effects of Mg- and Sr-substitutions on crystalline phase composition and lattice parameters were determined through quantitative X-ray phase analysis and structural Rietveld refinement of the starting calcium phosphate powders and of the hardened cements. A noticeable dependence of injectability on the liquid-to-powder ratio (LPR), smooth plots of extrusion force versus syringe plunger displacement and the absence of filter pressing effects were observed. For LPR values up to 0.36 ml g(-1), the percentage of injectability was always higher and lower for Mg-containing cements and for Sr-containing cements, respectively, while all the pastes could be fully injected for LPR > 0.36 ml g(-1). The hardened cements exhibited relatively high wet compressive strength values (~17-25 MPa) being the Sr- and Mg-containing cements the strongest and the weakest, respectively, holding an interesting promise for uses in trauma surgery such as for filling bone defects and in minimally invasive techniques such as percutaneous vertebroplasty to fill lesions and strengthen the osteoporotic bone.

Influence of setting liquid composition and liquid-to-powder ratio on properties of a Mg-substituted calcium phosphate cement

The influence of four variables on various properties of a Mg-substituted calcium phosphate cement (CPC) was investigated. The variables were the heat treatment temperature of the precipitated powders, the composition of the setting liquid, the liquid-to-powder ratio (LPR), and the time over which hardened specimens were cured in air. The properties analysed were the phase composition of the starting powder, the initial setting time, the evolution of the storage shear modulus ( G′) and the loss shear modulus ( G″) with the cement paste curing time ( t), and the compressive strength. The presence of α-TCP in CPC facilitated the setting and hardening properties due to its progressive dissolution and the formation of brushite crystals. As far as the liquid composition is concerned, in cases where citric acid was used, adding a rheology modifier (10 wt.% polyethylene glycol or 0.5 wt.% hydroxyl propylmethylcellulose) to the acid led to an increase in the initial setting time, while an increase in the acid concentration led to a decrease in the initial setting time. The initial setting time showed to be very sensitive towards the LPR. The evolution of G′ and G″ with curing time reflected the internal structural changes of cement pastes during the setting process. The compressive strength of the wet-hardened cement specimens with and without Mg increased with curing time increasing, being slightly higher in the case of Mg-substituted CPC. The results suggest that Mg-substituted CPC holds a promise for uses in orthopaedic and trauma surgery such as for filling bone defects.

Mechanisms underlying the limited injectability of hydraulic calcium phosphate paste

Calcium phosphate (CaP) cements are being increasingly used for minimally invasive hard tissue implantation. Possible approaches to improve the bad injectability of hydraulic calcium phosphate pastes have been discussed and investigated in a number of recent publications. However, the liquid-phase separation mechanism leading to the limited injectability has not yet been addressed. Liquid-phase separation means that the liquid-to-powder ratio (LPR) of the extruded paste is higher than the LPR of the paste left in the syringe. The goal of this paper was to remedy this situation by looking at the liquid-phase migration occurring during the injection of a paste from a syringe through a cannula. Experimentally, it was seen that the liquid content of both the syringe paste and the extrudate decreased during the paste injection. Moreover, a high extrusion velocity, small syringe size, short cannula and high LPR favored a good injectability. These results could be partly explained in light of rheological measurements performed with the investigated paste.

The effect of varying liquid-to-powder ratio to zinc oxide and eugenol of rat pulpal respiration

A study was conducted to determine the effect of varying the liquid to-powder ratio of zinc oxide and eugenol placed in contact with rat pulp tissue. The pulp tissue was suspended in phosphate buffer saline solution (PBS) to which ¹⁴C-succinic acid had been added. The ¹⁴CO₂ produced was used as an index of the effect on pulpal respiration. Findings indicated that the thicker mix of zinc oxide and eugenol produced the least effect in depression of pulpal tissue respiration.