Powder-liquid Ratio Research Articles

Expansion of Gutta-percha in contact with various concentrations of zinc oxide-eugenol sealer: A three-dimensional volumetric study using spiral computed tomography.

Aim:The purpose of this study was to evaluate the three-dimensional expansion of Gutta-percha (GP), at various powder/liquid ratios, of a zinc oxide-eugenol (ZOE)-based sealer using spiral computed tomography (SCT).Materials and Methods:Thirty-five freshly extracted human mandibular premolars were selected for this study. Cleaning and shaping were performed in all the teeth initially with hand K-files up to #25 and finally with RaCe rotary instruments (25/06). Teeth were randomly divided into five groups of 7 teeth each. Specimens were scanned using SCT. They were then viewed both cross-sectionally and longitudinally, with a constant thickness of 1 mm/slice. The volume of root canal in each tooth was estimated. Obturation was performed by GP points (25/04) and ZOE-based root canal sealer in all groups with different powder-liquid ratio. Groups 1, 2, 3, and 4, had powder/liquid ratio of 1:1, 1:2, 1:3, and 1:4, respectively, while in the control group, no sealer was used. The obturation was performed by sealer coated single cone GP. A second SCT scan was performed to determine the volume of GP and sealer in all four groups 1 day after obturation. The third and fourth SCT scans were taken 7 and 30 days after obturation, respectively. The mean volume of GP per group was calculated. Data were statistically analyzed using one-way ANOVA. Inter-group comparisons were done using Scheffe post hoc multiple comparisons test.Results:All groups with sealer showed expansion of GP at both 7th day and 30th day, which was statistically significant from the GP volume at 1st day. Groups 2 and 3 with powder/liquid ratio of 1:2 and 1:3 gave the highest mean volume values during 30 days period and showed significant expansion in comparison with Groups 1 and 4 with powder/liquid ratio of 1:1 and 1:4, respectively.Conclusion:Increasing the ratio of eugenol in sealer resulted in the volumetric expansion of GP. However, further studies should be performed to confirm the expansion of GP, leading to the achievement of fluid impervious seal.

Predicting composition–property relationships for glass ionomer cements: A multifactor central composite approach to material optimization

Adjusting powder–liquid ratio (P/L) and polyacrylic acid concentration (AC) has been documented as a means of tailoring the handling and mechanical properties of glass ionomer cements (GICs). This work implemented a novel approach in which the interactive effects of these two factors on three key GIC properties (working time, setting time, and compressive strength) were investigated using a central composite design of experiments. Using nonlinear regression analysis, formulation–property relationships were derived for each property, which enabled prediction of an optimal formulation (P/L and AC) through application of the desirability approach. A novel aluminum free GIC was investigated, as this material may present the first clinically viable GIC for use in injectable spinal applications, such as vertebroplasty. Ultimately, this study presents the first series of predictive regression models that explain the formulation-dependence of a GIC, and the first statistical method for optimizing both P/L and AC depending on user-defined inputs.

Effect of Varying Curing Regimes and Powder-liquid Ratios on the Flexural Strength and Surface Porosities of Heat Cure Acrylic: An In-vitro Experiment

Objectives: To evaluate and compare the effect of varying curing regimes and powder-liquid ratios on flexural strength and surface porosities in heat cure acrylic denture base resin. Methodology: Heat cured acrylic specimens (18 x 10 x 3mm) were made according to four powder-liquid ratio groups(2.22, 2.00, 1.80 and student-ratio) and polymerized according to four different curing cycles. Each group consisted of 16 samples with a total of 64 acrylic discs. Curing cycles 1A and 1B initiated curing of specimens at room temperature followed by a terminal boil for 60 and 30 minutes respectively. Cycles 2A and 2B initiated curing at 70°C and 100°C respectively, without any terminal boil. All discs were tested for flexural strength by the ‘short beam’ testing method after immersion in water at 37°C for 28 days. Perimeter of each surfacepore was outlined and area of each pore was measured by a SEM. Total area of surface pores was calculated and expressed in percentage form. Results: Regression analysis indicated a very weak negative correlation (-0.085) between the powder-liquid ratios and the flexural strength values (p =0.252), indicating that variations in powder-liquid ratio does not affect the flexural strength of the acrylic specimens. Placing the curing assembly directly in the water bath at 100°C for 30 minutes showed the lowest over-all flexural strength and highest porosity percent, while immersing the flask in water bath at room temperature, gradually increasing the temperature from 70°C to 100°C and maintaining it for 60 minutes displayed the lowest over-all percent porosity and highest flexural strength values. A weak positive correlation (0.286) between the groups and percent porosity values (p=0.025) indicate a poor effect of powder-liquid ratio on porosities. Conclusions: Flexural strength and percent porosity of acrylic resins are affected more by changes in curing regimes rather than variations in powder-liquid ratio. Increasing the terminal boil period by 30 minutes had a significant effect on reducing percent porosity however did not enhance flexural strength of heat cure acrylic specimens.

The Effect of α-Tricalcium Phosphate Powder Preparation Methods on Cement Properties

The properties of calcium phosphate cements are influenced both by presence of setting aids in cement paste and also by surface properties and particle size distribution of solid phase. In this study the influence of α-tricalcium phosphate powder preparation methods on properties of cement are examined: milling, thermal treatment at temperatures up to 600°C and treatment with deionized water. The properties of cements based on prepared powders evaluated are: setting time, injectability and cohesion. The compressive strength of selected cement samples was determined. Thermal treatment improves injectability, but significantly prolongs setting time and reduces cohesiveness. Treatment of powder particles with deionized water increases setting time, but also significantly reduces injectability. It was not possible to significantly increase powder liquid ratio (from 1.75 to 2.00), if thermally treated powders were used. It was found that reduction of particle size, under certain conditions, can increase the injectability of cements. Powder preparation methods do not significantly affect the compression strength of cement, but fast setting upon the contact water based fluids is necessary to obtain cohesive cements.

Caries-preventive effect of sealants produced with altered glass-ionomer materials, after 2 years

ObjectivesThe aim of the present study was to investigate the caries-preventive effect of sealants produced with a high-viscosity glass-ionomer with an elevated powder-liquid ratio (ART), of having energy added to this glass-ionomer, and that of glass-carbomer, in comparison to that of resin composite sealants. MethodsThe randomized controlled trial covered 407 children, with a mean age of 8 years. At a school compound three dentists placed sealants in pits and fissures of high caries-risk children. Evaluation by two independent evaluators was conducted after 0.5, 1 and 2 years. The Kaplan–Meier survival method, ANOVA and t-test were used in analyzing the data. Results1352 first permanent molars were sealed. 6.6% of children and 6.8% of sealants dropped out within 2 years. 27 re-exposed pits and fissures, 20 in occlusal and 7 in smooth surfaces, in 25 children, developed a dentin carious lesion. The cumulative survival of dentin carious lesion-free pits and fissures in the glass-carbomer sealant group was statistically significantly lower (97.4%) than those in the high-viscosity glass-ionomer with energy supplied (99%) and the resin-composite (98.9%) sealant groups. There was no statistically significant difference in the cumulative survival of dentin carious lesion-free pits and fissures, between the high-viscosity glass-ionomer with (99%) and without (98.3%) energy supplied sealant groups, after 2 years. SignificanceThe survival of dentin carious lesion-free pits and fissures was high in all sealant types. More dentin carious lesions were observed in the glass-carbomer sealant group.

Factors affecting the mechanical properties of glass ionomer cements for luting -Effect of powder-liquid ratio on compressive strength and fracture toughness-

Factors affecting the mechanical properties of glass ionomer cements for luting -Effect of powder-liquid ratio on compressive strength and fracture toughness-

Development of remineralizing, antibacterial dental materials

Light curable methacrylate dental monomers containing reactive calcium phosphate filler (monocalcium phosphate monohydrate (MCPM) with particle diameter of 29 or 90 μm) and β-tricalcium phosphate (β-TCP) at 1:1 weight ratio in a powder:liquid ratio (PLR) of 1:1 or 3:1 and chlorhexidine diacetate (0 or 5 wt.%), were investigated. Upon light exposure, approximately 90% monomer conversion was gained irrespective of the formulation. Increasing the PLR promoted water sorption by the set material, induced expansion and enhanced calcium, phosphate and chlorhexidine release. Concomitantly, a decline in compressive and biaxial flexural strengths occurred. With a reduction in MCPM particle diameter, however, calcium and phosphate release was reduced and less deterioration in strength observed. After 24 h, the remaining MCPM had reacted with water and β-TCP, forming, within the set materials, brushite of lower solubility. This provided a novel means to control water sorption, component release and strength properties. Measurable chlorhexidine release was observed for 6 weeks. Both diffusion rate and total percentage of chlorhexidine release decreased with lowering PLR or by adding buffer to the storage solutions. Higher chlorhexidine release was associated with reduced bacterial growth on agar plates and in a biofilm fermenter. In cell growth media, brushite and hydroxyapatite crystals precipitated on the composite material surfaces. Cells spread on both these crystals and the exposed polymer composite surfaces, indicating their cell compatibility. These formulations could be suitable antibacterial, biocompatible and remineralizing dental adhesives/liners.

An investigation of thermal changes of various permanent dental cements

The aim of this study was to investigate and compare the temperature rises which occurred during the setting reactions of different permanent cements used to lute fixed partial prosthodontics. In this study, four cements were used. They were mixed in three different proportions: according to manufacturers' recommendations, at doubled powder ratio, and at doubled liquid ratio. With a thermocouple, the temperature rises which occurred during the setting reactions were measured. For each proportion, the measurement was repeated five times such that a total of 60 measurements were done for the four different cements. Data were analyzed using analysis of variance (ANOVA). ANOVA results showed that cement type and the interaction between cement type and the powder-liquid ratio were statistically significant factors (p<0.001). Similarly, the powder-liquid ratio was a statistically significant (p<0.01) factor. Among the dental cements tested, zinc phosphate cement showed the highest temperature rise during setting reaction, whereas glass ionomer cement showed the lowest.

Zinc-based glass polyalkenoate cements with improved setting times and mechanical properties

The suitability of glass polyalkenoate cements (GPCs) for skeletal applications is limited by the presence, in the glass phase, of the aluminium ion (Al 3+), a neurotoxin. The zinc ion (Zn 2+), a bacteriocide, has been incorporated into aluminium-free GPCs based on zinc silicate glasses. However, these GPCs have considerably shorter working times and poorer mechanical properties than their Al 3+-containing counterparts. Based on results for calcium phosphate cements, there is an indication that mixing a GPC with an organic compound, tricalcium citrate (TSC), may lead to cements with improved rheological and mechanical properties. We developed a range of Zn-based GPCs and determined their working times ( T w), setting times ( T s), compressive strength (CS) and biaxial flexural strengths (BFS). A GPC composed of 1 g of a calcium–zinc silicate glass (BT100) mixed with a 50 wt.% aqueous solution on polyacrylic acid (coded E9, M w 80,800) at a powder liquid ratio of 2:1.5 exhibited the best combination of T w, T s, CS and BFS. We also found that the addition of TSC (over the range 5–15 wt.%) to a GPC led to significant increases in both T w (from 40 ± 3 to 100 ± 4 s) and T s (from 70 ± 2 to 3000 ± 4 s) accompanied by changes in both CS and BFS that were affected by the duration of the aging time of the specimens in distilled water (for example, after aging for 7 days CS dropped from 62 ± 2 to 17 ± 1 MPa, while after aging for 30 days, BFS increased 27 ± 6 to 31 ± 7 MPa and then dropped to 17 ± 1 MPa). Future modification and characterization of the examined GPCs are needed before they may be considered as candidates for orthopaedic applications.

Synthesis and evaluation of novel light‐curable amino acid‐constructed glass–ionomer cements

AbstractPoly(alkenoic acid)s constructed with β‐alanine and glutamic acid were synthesized and grafted with glycidyl methacrylate (GM). The purified polymers were further formulated with water, acrylic acid (AA), and Fuji II LC glass filler to form photocurable dental cements. Compressive strength (CS) and flexural strength (FS) of the cement, and viscosity of the resin liquid were used as screening tools to find the optimal formulation. The specimens were conditioned in distilled water at 37°C for 24 h, prior to testing. The results show that the effects of grafting ratio, polymer content, powder liquid (P/L) ratio, initiator concentration, and light exposure time were significant, but the effect of molecular weight was not. Aging study shows that the experimental cement showed a constant increase in mechanical strength for up to 1 week and then kept constant over 1 month. The formulation with 50/25/25 (liquid composition of polymer/AA/water), 70% (grafting ratio of GM), 3.2/1 (P/L ratio) as well as 0.9% (camphorquinone) and 1‐min light exposure time were found to be the optimal. The experimental cement was 19% higher in CS, 47% higher in diametral tensile strength and 176% higher in FS, compared to Fuji II LC. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1587–1595, 2007

Mechanical Behavior of Glass Ionomer Cements as a Function of Loading Condition and Mixing Procedure

With a view to comparing conventional (CGIC) and resin-modified glass ionomer cements (RMGIC) in terms of mechanical properties, these materials were subjected to different loading conditions for evaluation. In addition, this study investigated the assumption that capsulated systems possess superior mechanical properties compared to the hand-mixed systems, owing to the former's better material homogeneity and a more precise adjustment of the powder-liquid ratio. In view of the aims of this study, the following mechanical properties were determined: strength and modulus of elasticity in flexural test, diametric tensile and compressive strengths, as well as variation of hardness and modulus of elasticity with depth. In all macroscopic strength tests, the RMGICs performed significantly better than the CGICs. In microhardness evaluation, the differences were levelled out. In particular, the mechanical properties of RMGICs were comparable to those of microfilled and packable composites. The effect of mixing was closely intertwined with material property. The tested CGICs performed better when they were hand-mixed, whereas RMGICs fared better in the capsulated form.

Effect of Powder-liquid Ratio on Shear Strength of Glass Ionomer Cements for Luting

Effect of Powder-liquid Ratio on Shear Strength of Glass Ionomer Cements for Luting

インプラント埋入後の暫間義歯における粘膜調整材の緩圧効果の検討

The main objective of this study was to examine the influence of the thickness and its longitudinal change within the limited denture space on the stress releasing effect for installed implants during the healing period of a two-stage procedure. As for the tissue conditioning material, Tissue Conditioner (Shofu, Kyoto, Japan) with the designated powder liquid ratio was used. The force transmitted to the implant with the material 5 min after the mixing was measured by a miniature pressure sensor in the position of the implant head (Kyowa, Tokyo, Japan). Measurements were repeated with the material preserved in the water for one and two weeks. Load of 2 kg was applied with a 3-mm diameter round tip using a static loading machine for 2 min to the center of the flat type denture model. The model consisted of denture, mucosa, tissue conditioning material and implant where the first three variables were changed as in the oral cavity. Influence of thickness of each variable was examined longitudinally. Force measured with any thickness of tissue conditioning material was smaller than that without the material. The stress releasing effect did not change with change of the longitudinal material property up to two weeks. Within the limitations of our study, it was suggested that the stress releasing effect of the tissue conditioning material for the installed implant was not influenced by the thickness or change of longitudinal property.

Effect of 10 wt% spherical silica filler addition on the various properties of conventional and resin-modified glass-ionomer cements

In this study, we evaluated the effects of 10 wt% spherical silica filler (SSF) addition on 24-h compressive strength, modulus of elasticity, water uptake, and immediate setting shrinkage of conventional glass-ionomer (Fuji II and Experimental) and resin-modified glass-ionomer (Fuji II LC EM) cements. The glass-ionomer cement powders were modified by being mixed with 10 wt% SSFs with an average particle diameter of 0.3 μm. The materials were mixed to consistencies similar to the flow of Fuji II mixed with a powder-liquid ratio of 2.7∶1 (w/w). The 24-h compressive strength, modulus of elasticity, water uptake, and immediate setting shrinkage were observed and the results compared with the original materials mixed with similar flow. The addition of SSF increased the compressive strength value to 1.1 times, while the increase of moduli of elasticity was 1.10 to 1.35 times. In general, the addition of SSF decreased the 24-h water uptake to 80–90% and reduced the immediate setting shrinkage to 70–79% of the original materials. The addition of 10 wt% SSF improved the characteristics of conventional and resin-modified glass-ionomer cement.

Gap formation of class V glass-ionomer restorations for high powder-liquid ratio and their mechanical properties: immediately vs. after 24-hour storage

Gap formation of class V glass-ionomer restorations for high powder-liquid ratio and their mechanical properties: immediately vs. after 24-hour storage

Development of a new calcium phosphate cement that contains sodium calcium phosphate

A cement powder consisting of sodium calcium phosphate, Na 3Ca 6(PO 4) 5, in addition to tetracalcium phosphate and β-tricalcium phosphate was prepared by pulverizing blocks of 4 wt% sodium-,11 wt% carbonate-containing apatite samples that were heated at 1700°C for 5 h. When mixed with 30 wt% malic acid or citric acid at a powder liquid ratio of 3:1, the cement set in 3 or 7 min at room temperature with compressive strength being around 52 or 27 MPa. In HeLa-cell cultures, the cement mixed with malic acid was less cytotoxic than the cement mixed with citric acid, which was far less cytotoxic than a commercial carboxylate cement used as a negative control, suggesting malic acid to be superior to citric acid as a liquid in this regard. Similar findings were also obtained with osteoclasts, of which culture experiments clearly suggested that the number of osteoclasts on the cement mixed with malic acid was significantly greater than that on the cement mixed with citric acid. Since osteoclastic response to substrates could be used as a maker in evaluating their bioresorbability associated with osteoclasts, the above finding may suggest that the cement that is to be mixed with malic acid would be more useful as bone substitutes.

Marginal Gap of Light-activated Glass Ionomers for Base/liner Immediately after Ligth-activation : Effect of Powder-liquid Ratio

Marginal Gap of Light-activated Glass Ionomers for Base/liner Immediately after Ligth-activation : Effect of Powder-liquid Ratio

Influence of Powder Liquid Ratio on Thermal Properties of Dental Cements

Influence of Powder Liquid Ratio on Thermal Properties of Dental Cements

Strength properties of three zinc phosphate cements mixed to two different consistencies.

When hand-mixing is used, clinicians mix zinc phosphate cement to consistencies which allow proper seating of restorations. Slump tests have indicated that the same two preferred consistencies (one for cementing a single unit restoration, the other for cementing a multiple unit restoration) could be obtained at different slab temperatures for three cements by mixing to certain powder-liquid ratios which were different for each cement. Each cement could be repeatedly mixed to the preferred consistency by using the appropriate powder-liquid ratio. The compressive and tensile strengths of the cements varied, although mixed to the same consistency. Selection of a cement for clinical use should be based on its strength properties when mixed to a preferred consistency.

Forces fracturing cements at die interfaces and their dependence on film thickness

Film thickness (FT) and retention of zinc phosphate, polycarboxylate and ionomer cement as a function of powder-liquid (P/L) ratio were determined for both non-vented and vented crowns and using a standard ADA/ANSI test. The effect of P/L ratio on FT was more dependent on the composition of the brand than on the type of cement. FT values obtained from the specification test usually lay between those obtained from the vented crowns and from the non-vented crowns. Higher consistency (higher P/L ratio) of the mix increased the FT. The relationship between FT of P/L ratio and retention is complex and dependent on the type of cement, brand, and on the technique used. Venting of the prepared crown lowered the FT and usually tended to increase retention.