The shelf life of ASDs: 2. Predicting the shelf life at storage conditions

Amorphous solid dispersions (ASDs) are a widely used formulation technology for poorly water-soluble active pharmaceutical ingredients (API). Depending on the API-polymer combination and API load in the ASD, the amorphous API might be thermodynamically metastable and crystallize over time. The crystallization onset is one critical factor that can define the shelf life of the ASD. Thus, for ASD formulations, long-term stability against crystallization of the API is of particular interest. This work presents a method for predicting the long-term physical stability of ASDs (crystallization onset time). The new approach combines the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation with classical nucleation theory. The shelf life predicted using the new approach depends on supersaturation (determined with PC-SAFT), viscosity (determined with WLF equation or Arrhenius equation) and two specific model parameters k' and B. The latter were fitted to a few fast crystallization-kinetics measurements above the glass transition of the ASD. An additional crystallization-kinetics measurement below the glass-transition temperature of the ASD was used to determine the Arrhenius parameters. Once all parameters are determined for a given API/polymer combination and manufacturing method, they are valid for any API load, temperature, and RH. The proposed approach allows predicting the shelf life (crystallization onset) of a potential ASD in early stage of development within a few days. It was successfully verified for ASDs stored at 25 °C and 10% RH or 60% RH.

Influence of pectin and hemicelluloses on physical properties of bacterial cellulose

The properties of bacterial cellulose (BC)-based films produced by in situ biosynthesis with various polysaccharides (water-soluble pectin, arabinan, rhamnogalacturonan I, arabinoxylan, xyloglucan, glucomannan) were investigated. The addition of the polysaccharides to the bacterial growth environment changed the composition of the films by incorporating characteristic monosaccharides. BC-based films contained up to 26.7 % of non-cellulosic polysaccharides. The applied modification had a clear impact on water sorption and caused a decrease in the thermal stability of most BC films, which was connected with the depletion of geometrical dimensions of cellulose nanofibers observed with AFM. The FT-IR and Raman spectra demonstrated a decrease in % Iα of cellulose films, most notably for xyloglucan and glucomannan, as well as a change in their degree of crystallinity and the length of cellulose chains. The addition of xyloglucan had the most pronounced effect on film hardening; the other additives had a similar but lesser effect.

Evaluation of flexible three-dimensionally printed occlusal splint materials: An in vitro study

OBJECTIVE

To evaluate and compare the mechanical properties, water sorption, water solubility, and degree of double bond conversion of three different commercially available three-dimensional (3D) printing resins used for the fabrication of flexible occlusal splints.

METHODS

A digital printer was used to generate specimens from the evaluated splint materials (KeySplint Soft, IMPRIMO LC Splint flex, and V-Print splint comfort). The specimens were equally divided and tested either dry or after water storage at 37 °C for 30 days. A three-point bending test was used to assess flexural strength, elastic modulus, and fracture toughness. A two-body wear test was performed using a dual-axis chewing simulator. Water sorption and water solubility were measured after 30 days. The degree of double bond conversion was determined by FTIR-spectrometry. All data for the evaluated properties were collected and statistically analyzed.

RESULTS

Both material and storage conditions had a significant effect on the flexural strength (P < 0.001), elastic modulus (P < 0.001), fracture toughness (P < 0.001), and wear (P < 0.001). The highest water sorption was noticed with IMPRIMO LC Splint flex (1.9 ± 0.0 %), while V-Print splint comfort displayed the lowest water solubility (0.2 ± 0.0 %). For the degree of conversion, it was statistically non-significant among the different materials (P = 0.087).

SIGNIFICANCE

Different flexible 3D-printed splints available in the market displayed variations in the evaluated properties and clinicians should consider these differences when choosing occlusal device materials. Among the tested flexible splint materials, KeySplint Soft had the greatest flexural strength, elastic modulus, fracture toughness, wear resistance, and degree of conversion. It also showed the lowest water sorption.

The effect of varying monocalcium phosphate and polylysine levels on dental composite properties

OBJECTIVES

The aim was to quantify effects of polylysine (PLS, 2 or 5 wt%) and monocalcium phosphate (MCP, 4 or 8 wt%) on properties of dental composites.

METHODS

Light-activated, lower surface polymerisation kinetics versus sample depth (1-4 mm) of 4 formulations were quantified using ATR-FTIR. Water sorption and solubility (at 1 week) were assessed following ISO/4049. PLS release (over 1 month) and biaxial flexural strength (over 6 months) of fully-cured, water-immersed, 1 mm thick discs were determined. Surface mineral precipitation, following immersion in simulated body fluid (SBF), was assessed by SEM. Z250 was used as a conventional composite comparator.

RESULTS

With 40s light exposure, increasing depth (from 1 to 4 mm) led to enhanced delay before polymerisation (from 3 to 17s) and decreased final conversion (72-66%) irrespective of PLS and MCP level. Increasing PLS and MCP raised solubility (4-13 μg/mm3). Water sorption (between 32 and 55 μg/mm3) and final PLS release (8-13% of disc content) were raised primarily by increasing PLS. Higher PLS also reduced strength. Strength reached minimum values (69-94 MPa) at 3 months. Surface mineral deposition was enhanced by increased MCP. For Z250, polymerisation delays (3-6s) and final conversions (55-54%) at 1-4 mm depth, solubility (0 μg/mm3), water sorption (16 μg/mm3) and strength (180 MPa) were all significantly different.

CONCLUSION

Delay time increased whilst final conversion decreased with thicker samples. Higher PLS enhances its percentage release, but lower level is required to keep water sorption, solubility and mechanical properties within ISO 4049 recommendations. Doubling MCP raises solubility and enhances minerals reprecipitation with minimal mechanical property compromise.

Bonding performance of experimental HEMA-free two-step universal adhesives to low C-factor flat dentin

OBJECTIVES

Experimental two-step universal adhesives (2-UAs) providing a particle-filled hydrophobic adhesive resin with a significant film thickness to hydrophobically seal the adhesive interface were designed and synthesized. This study aimed to characterize their interfacial interaction with dentin, to determine whether the 2-UA formulations achieve durable bonding to low C-factor flat dentin and to measure their water sorption.

METHODS

Bonding effectiveness of 2-UAs that combine a 10-MDP-based primer with hydrophobic adhesive resins differing only for filler (BZF-21, BZF-29, and BZF-29_hv) were comparatively investigated with the commercial adhesive Clearfil SE Bond 2 (C-SE2, Kuraray Noritake). Adhesive-dentin interfaces were characterized with TEM. Adhesive-resin disks were immersed in distilled water at 37 °C for 1 week, 6 months and 1 year to measure water sorption and solubility. 'Immediate' and 'aged' micro-tensile bond strength (μTBS) of the adhesives applied in etch-and-rinse (E&R) and self-etch (SE) bonding mode to low C-factor flat dentin were measured. Statistical analyses involved linear mixed-effects (LME) modelling and Kruskal-Wallis testing (p < 0.05).

RESULTS

TEM revealed that E&R hybrid layers were more sensitive to aging than SE hybrid layers. Lower water sorption was recorded for all UAs compared with C-SE2. The immediate μTBS of BZF-21 and BZF-29 was not significantly different from that of C-SE2. The 1-year aged μTBS of all 2-UAs was significantly lower than that of C-SE2, except for BZF-29 applied in E&R mode. A significant reduction in μTBS upon 1-year aging was recorded for BZF-21 and BZF-29 applied in E&R mode. A significant difference in μTBS between E&R and SE bonding modes was recorded for all adhesives except BZF-21.

SIGNIFICANCE

Experimental 2-UAs with a hydrophobic adhesive-resin design produced± 20-μm thick adhesive-resin layers, absorbed less water and resulted in bonding performance that was more aging-resistant when applied in SE than in E&R bonding mode. The silica-filled BZF-29 2-UA revealed the most comparable bonding performance with C-SE2 in a low C-factor condition (flat dentin).

Preparation of a fluorinated dental resin system and its anti-adhesive properties against S. mutans

OBJECTIVES

The purpose of this study was to characterize physicochemical properties and investigate anti-bacterial adhesion effect of dental resins containing fluorinated monomers.

METHOD

Fluorinated dimethacrylate FDMA was mixed with commonly used reactive diluent triethylene- glycol dimethacrylate (TEGDMA) and fluorinated diluent 1 H,1 H-heptafluorobutyl methacrylate (FBMA) separately at a mass ratio of 60 wt./40 wt. to prepare fluorinated resin systems. Double bond conversion (DC), flexural strength (FS) and modulus (FM), water sorption (WS) and solubility (SL), contact angle and surface free energy, surface element concentration, and anti-adhesion effect against Streptococcus mutans (S. mutans) were investigated according to standard or referenced methods. 2,2-bis[4-(2-hydroxy-3-methacryloy-loxypropyl)-phenyl]propane (Bis-GMA)/TEGDMA (60/40, wt./wt.) was used as control.

RESULTS

Both fluorinated resin systems had higher DC than Bis-GMA based resin (p < 0.05); compared with Bis-GMA based resin (FS, FDMA/TEGDMA resin system had higher FS (p < 0.05) and comparable FM (p > 0.05), while FDMA/FBMA resins system had lower FS and FM (p < 0.05). Both fluorinated resin systems had lower WS and SL than Bis-GMA based resin (p < 0.05), and FDMA/TEGDMA resin system had the lowest WS (p < 0.05) in all experimental resin systems. Only FDMA/FBMA resin system showed lower surface free energy than Bis-GMA based resin (p < 0.05). When the surface was smooth, FDMA/FBMA resin system had lower amount of adherent S. mutans than Bis-GMA based resin (p < 0.05), while after the surface became roughness, FDMA/FBMA resin system had comparable amount of adherent S. mutans as Bis-GMA based resin (p > 0.05).

SIGNIFICANCE

Resin system prepared exclusively with fluorinated methacrylate monomers reduced the S. mutans adhesion due to their increased hydrophobicity and decreased surface energy., while flexural properties of it should be improved.

Disagreements Between Calorimetric and Van't Hoff Enthalpies of Adsorption: A New Langmuir-like Model to Account for the Effect of Solvent Displacement Stoichiometry

The reported inconsistencies between calorimetry and the van't Hoff equation hinder the utility of thermodynamics in pharmaceutical research. In ligand binding or adsorption assays, it is believed that the van't Hoff equation falls short because of the lack of stoichiometric treatment in the equilibrium constant. A new modified Langmuir-Like equation that accounts for the stoichiometry of solute adsorption and solvent displacement is proposed in this work. The performance of the model was evaluated by studying the adsorption of phenobarbital from aqueous solutions by commercial activated carbon. The amount of water occupying the adsorption sites was estimated by graphical analysis of the 'knee point' of water-vapor adsorption isotherms and was found to correlate well with the relative percentage of hydroxyl and carbonyl surface groups. It was found that one phenobarbital molecule displaces 2-6 water molecules from the adsorption site. It is shown that adsorption enthalpy was not affected by the adjustment for stoichiometry, supporting the notion that the van't Hoff enthalpy is intrinsic and is independent of the stoichiometry of solvent displacement in Langmuir-based binding. The widely reported disparities between the van't Hoff and calorimetric enthalpies are unlikely to be from a stoichiometric origin.

Gravimetric analysis of stability of polymeric materials during exposure to chemical disinfectants at different temperatures

The goal of this study was to evaluate the impact of thermal and chemical aging processes on high-density polyethylene (HDPE), low-density polyethylene (LDPE), unplasticized polyvinyl chloride (U-PVC), and high-impact polyvinyl chloride (Hi-PVC) pipes. The materials were exposed to 1-10 ppm chemical disinfectants [chlorine dioxide (ClO₂) and hypochlorite (HOCl)] at 40-80 °C for 1200 h. The diffusion properties of the materials were systematically analyzed based on the change in their sorption characteristics and activation energies according to the Arrhenius model. Moreover, the structural changes were analyzed with scanning electron microscopy (SEM), Fourier transform infrared (FTIR) radiation, and thermogravimetric analysis (TGA). The results show that the materials have Fickian characteristics in the aging environment. Specifically, the water sorption rates of HDPE and LDPE increase first and then decrease after reaching saturation (Ms); those of U-PVC and Hi-PVC its increasing continuously with different rate. This behavior of materials was prominent for ClO₂ at high temperature and disinfectant dose because of polymeric chains crosslinking and rearrangement, extraction of monomers, and stable compounds removal during aging under exposed conditions. The deleterious effects decreased the activation energies of the materials and increased the concentrations of carbonyl groups [CO] via the formation of ketones, aldehydes, and carboxylic acids. The decomposition temperature increased with the changes in the material morphology and elemental contents under the investigated conditions. Moreover, LDPE and Hi-PVC were more severely affected in the thermal aging process with 10 mg.L^-1 ClO₂ at 80 °C.

Color changes of dental zirconia immersed in food and beverage containing water-soluble/lipid-soluble pigments

The present study examined color changes in the tooth-colored restorative materials, zirconia (3Y-TZP), resin composite, and porcelain. The colors (CIELab) of these materials were measured using a spectrophotometer. Specimens were immersed in black tea or curry for 1 and 7 days, after which colors were re-assessed. Color differences (∆E^*ab) before and after immersion were calculated. Specimens after the 7-day immersion were ultrasonically cleaned, and colors were measured again to assess the color recovery rate. The surface free energy, roughness, and water sorption/solubility of each material were also evaluated. Specimens were observed under a scanning electron microscope. The ∆E^*ab of 3Y-TZP was the smallest with both immersions. Resin composite had the smallest recovery rate. The surface free energy and roughness of 3Y-TZP were smaller than those of porcelain. 3Y-TZP and porcelain showed almost no sorption during the 7-day period. The present results revealed that 3Y-TZP exhibited the strongest resistance to discoloration.

Modeling of composite sorption isotherm for stratum corneum

Equilibrium water sorption in stratum corneum (SC) is considered by treating it as a biocomposite with two main phases, namely, corneocytes and lipids. To validate the rule of mixtures for the individual phase sorption isotherms, a new flexible fitting model is introduced by accounting for characteristic features observed in the variations of the thermodynamic correction factors corresponding to the individual sorption isotherms. The comparison of the model fitting performance with that of the five-parameter Park's model shows a remarkably good ability to fit experimental data for different types of sorption isotherms. The effect of the lipids content on the variance of the composite sorption isotherm of stratum corneum is highlighted. The sensitivity analysis reveals that for the typical water content 20-30 wt%, which corresponds to the SC in a stable condition, the sensitivity of the composite sorption isotherm to the variation of the lipids content on dry basis is predominantly positive and sufficiently small. The good agreement observed between the experimental sorption isotherm for SC and the composite isotherm, which is based on the rule of mixtures for the individual phase sorption isotherms, yields a plausible conclusion (hypothesis) that the corneocytes-lipids mechanical interaction during unconstrained swelling of the SC membrane in the in vitro laboratory experiment is negligible.

Coulometric titration of water content and uptake in CAD/CAM chairside composites

OBJECTIVES

This study aimed to evaluate the water content and uptake of CAD/CAM chairside composites over 60 days using coulometric Karl Fischer (KF) titration.

METHODS

Rectangular plates (10 ×10×1 mm³ of thickness) were cut from the blocks of composites Cerasmart 270 (CS), Katana Avencia (KA), Grandio Blocs (GB), and Lava Ultimate (LU). Specimens were stored in distilled water for up to 60 days at 37 °C, and non-stored specimens were used as a control (n = 5). Specimens were isothermally heated at 200 °C, and the water content was evaporated and transferred to the titration cell throughout a nitrogen gas flow. The KF coulometer determined the percentage of water in each specimen. Data were analyzed by 2-way ANOVA and Tukey`s test (α = 0.05).

RESULTS

The water content of non-stored specimens ranged from 0.29 to 1.66 wt% (6.9-32.9 μg/mm³) for GB and LU, respectively. The water content increased underwater storage (0.82-2.96 wt% after 60 days). The extend of water sorption (11.9-26.1 μg/mm³) among the materials was directly related to their base water content. No additional water content increase was observed after 7 (LU and KA) or 21 (GB and CS) days. Measuring the water content in wt% or μg/mm³ affected the ranking of materials when KA and CS were analyzed.

SIGNIFICANCE

Composites with higher base water content also presented higher water sorption. KF titrationshowed to be a reliable method to measure the water sorption of composites, including their base water content.

Comparative Evaluation of Water Sorption, Solubility, and Microhardness of Zirconia-reinforced Glass Ionomer, Resin-modified Glass Ionomer, and Type IX Glass Ionomer Restorative Materials: An In Vitro Study

The challenge that practicing dentists face every day is to decide which dental material is best suited for each dental treatment. New glass-ionomer cement (GIC) formulations have been introduced in order to overcome the drawbacks of conventional ones thereby catering to the needs of the pediatric population.

Aim and objective

The study aimed to evaluate and compare water sorption, solubility, and microhardness of zirconia-reinforced glass ionomer, resin-modified glass ionomer, type IX glass ionomer cements.

Materials and methods

90 specimens were prepared in total of which 45 cylindrical specimens with dimensions of (6 × 4) mm and 45 disks with (10 × 2) mm were prepared from Zirconomer, RMGIC, and Type IX GIC restorative materials, each material having 30 specimens (15 disks, 15 cylinders). After taking the initial weight (W1), the 45 cylinders (15 of each material) were immersed in artificial saliva at 37°C for 28 days after which the weights W2 and W3 were weighed. The other 45 disks (15 of each material) were subjected to microhardness test under microhardness tester. Results were subjected to ANOVA and Tuckey's post hoc test.

Results

Zirconomer showed the maximum resistance to water sorption and solubility followed by RMGIC and type IX GIC with a significant p value of < 0.001 difference. For microhardness, Zirconomer showed the highest value with a significant p value of < 0.001 difference. But, there was no significant difference between RMGIC and Type IX GIC depicting almost equal strength.

Conclusion

Water sorption, solubility, and microhardness of Zirconomer were significantly high in comparison to the other groups and it can be used as a posterior restorative material for stress-bearing areas.

Clinical Significance

As pediatric dentistry demands restorations to be completed frequently in less than ideal conditions, Zirconomer has shown to be better than RMGIC and conventional GIC probably because of the improvisation in the GIC properties.

How to cite this article

Bethapudy DR, Bhat C, Lakade L, et al. Comparative Evaluation of Water Sorption, Solubility, and Microhardness of Zirconia-reinforced Glass Ionomer, Resin-modified Glass Ionomer, and Type IX Glass Ionomer Restorative Materials: An In Vitro Study. Int J Clin Pediatr Dent 2022;15(2):175-181.

Study of the water sorption and barrier performances of potato starch nano-biocomposites based on halloysite nanotubes

The barrier performances, in terms of water vapor sorption properties, gas and water barrier performances were analyzed on different starch-based nano-biocomposites. These multiphase systems were elaborated by melt blending starch and halloysite nanotubes at different contents with different plasticizers (glycerol, sorbitol and a mix of both polyols). The influence of the composition was investigated onto the structure, morphology, water sorption and barrier performances. As recently reported, halloysite nanoclay is a promising clay to enhance the properties of plasticized starch matrix. The barrier performances of nanofilled starch-based films were examined through gas and water permeabilities, diffusivity and water affinity. Glycerol-plasticized starch films give fine and more homogeneous nanofiller dispersion with good interfacial interactions, compared to sorbitol ones (alone or mixed), due to stronger and more stable hydrogen bonds. Tortuosity effects linked to the halloysite nanotubes were evidenced by gas transfer analysis, and exacerbated by the good interactions at interfaces and the resulting good filler dispersion. The influence of morphology and interfacial interactions towards water affinity was highlighted by moisture barrier properties. This was a key factor on the reduction of water diffusion and uptake with nanoclay content. A preferential water transfer was observed as a function of a plasticizer type in relation with the phenomenon of water plasticization in the nanocomposite systems.

Characterization of occlusal splint materials: CAD-CAM versus conventional resins

AIM

The aim of this in vitro study was to assess the mechanical properties of five commercially available subtractive computer-aided design and computer-aided manufacturing (CAD-CAM) milled splint materials, as well as to compare them with conventional heat-polymerized and autopolymerizing resins used in the construction of conventional splints.

MATERIAL AND METHODS

Five CAD-CAM milled (ProArt CAD Splint, Therapon Transpa, Temp Premium Flexible Transpa, Cast, and Aqua), one autopolymerizing (Palapress), and one heat-polymerized (Paladon 65) resin materials were evaluated. Flexural strength, E-modulus, Vickers hardness, fracture toughness, fracture work, water sorption, and water solubility were measured. Samples were evaluated after dry and water storage for 30 days at 37 °C. Data were collected and statistically analyzed.

RESULTS

Under both storage circumstances, the flexural strength values of Paladon 65, Therapon Transpa, Temp Premium Flexible Transpa, and Aqua were statistically non-significant (P=0.055). The polycarbonate-based CAD-CAM material Temp Premium Flexible Transpa had the highest statistically significant values of the fracture toughness and fracture work (P<0.001). Moreover, it exhibited the lowest percentages of water sorption and water solubility among the investigated materials (P<0.001). All of the CAD-CAM materials exhibited dry elastic moduli greater than Palapress and lower than Paladon 65. One of the CAD-CAM materials, Cast, had the highest dry Vickers hardness value, which was non-significant when compared to Therapon Transpa (P=0.762).

CONCLUSION

CAD-CAM polycarbonate-based splint materials exhibit higher fracture toughness and fracture work as well as lower water sorption and solubility than polymethyl methacrylate-based ones. The mechanical characteristics of the assessed CAD-CAM milled splint materials were not typically superior to those of the conventional heat-polymerized resin. However, some of them outperformed the autopolymerizing acrylic resin in terms of flexural strength, surface microhardness, water sorption, and water solubility.

Effect of sealer coating on hardness and water sorption data of soft denture lining materials

Soft denture lining (SDL) are acrylic or silicone based materials that can be cured with heat or auto polymerization process, which is commonly used in removable prosthodontics to reline the intaglio (interior) surface of the denture. Loss of softness due to aging process is caused by loss of plasticizer and other soluble component. However, water sorption causes changes in structure and increased materials hardness, thus need frequent replacement of the materials. To extend the durability of the SDL, sealer coating (SC) was used. In this data, sealant coating acts as mechanical barrier to prevent water sorption and solubility of the chemical component to preserved material hardness. This article provides the data of sealant coating effect on hardness and water sorption of acrylic-based and silicone-based SDL materials was arranged in 4 test group: pristine and coated acrylic SDL and pristine silicone SDL and coated silicone SDL. Shore Hardness test was carried out using a Shore A Durometer and water sorption data were presented. Accordingly, the data was statistically analyzed for comparison using independent T-test for shore A hardness and water sorption.

Water sorption and diffusion in cellulose acetate: The effect of plasticisers

The conservation of cellulose acetate plastics in museum collections presents a significant challenge, due to the material's instability. Several studies have led to an understanding of the role of relative humidity (RH) and temperature in the decay process. It is well established that a major decay mechanism in cellulose acetate museum objects is the loss of plasticiser, and that the main decay mechanism of the polymer chain involves hydrolysis reactions. This leads to the loss of sidechain groups and the breakdown of the main polymer backbone. However, interactions between these decay mechanisms, specifically the way in which the loss of plasticiser can modify the interaction between cellulose acetate and water, has not yet been investigated. This research addresses the role of RH, studying the sorption and diffusion of water in cellulose acetate and how this interaction can be affected by plasticiser concentration using Dynamic Vapour Sorption (DVS).

Mechanical degradation of contemporary CAD/CAM resin composite materials after water ageing

OBJECTIVE

The aim of the present study was to assess the effect of water storage on the quasi-static properties and cyclic fatigue behavior of four contemporary CAD/CAM resin composite materials.

METHODS

The CAD/CAM resin composites Grandio Blocs, Lava^TM Ultimate, Cerasmart^TM and Brilliant Crios, as well as the direct resin composite Grandio SO, were evaluated. Rectangular plates were cut from the blocks or fabricated using a silicon mold to obtain specimens for fracture toughness (K_Ic, n = 10), biaxial strength (σ₀, n = 30) and cyclic fatigue testing (n = 30). Half of the specimens was stored for 24 h in dry conditions and the other half was aged for 60 days in distilled water at 37 °C. K_Ic was determined using the Compact-Tension (C(T)) method and σ₀ and cyclic fatigue were tested using the Ball-on-Three-Balls assembly. Additional disc-shaped specimens (n = 5) were produced to obtain water sorption curves of the materials. Weibull statistics and two-way ANOVA with Tukey's post-hoc test were used for data assessment.

RESULTS

The highest water sorption was observed for Lava^TM Ultimate (42.6 μg/mm³), whereas Grandio SO displayed the lowest uptake (14 μg/mm³). A statistically significant drop in K_Ic and σ₀ was measured for all materials after water storage, except for the σ₀ of Cerasmart^TM. Water ageing had a dissimilar effect on the cyclic fatigue behavior, increasing the slow crack growth susceptibility of Lava^TM Ultimate, but decreasing it for Cerasmart^TM and Brilliant Crios.

SIGNIFICANCE

Contemporary CAD/CAM resin composites are susceptible to water driven degradative processes, although differences in filler content and resin matrix constitution play an important role in how it impacts their mechanical properties.

Glass transition and crystallization of solid model system of jujube slice as influenced by sugars and organic acids

To understand the specific contributions of amorphous sugars and organic acids to the quality of food matrix, the solid model system of jujube slice skeleton (JSS) was firstly established. Effects of fructose (F), glucose (G), malic acid (M) and citric acid (C) on the glass transition temperature (T_g) and crystallization of JSS were studied. JSS-F/G/M/C blends were prepared by osmosis in the solution at a range of 0 ~ 32 g/100 g. Sugars reduced the T_g in the system, structure of JSS-G/M blends was changed from "amorphous glassy" to "amorphous rubbery" by increasing the osmotic solute concentration. T_g was decreased from 50.8 to 14.0 °C when JSS was osmosed in a 4 g/100 g fructose solution. Organic acids induced their crystallization in JSS. The crystallinity of JSS-M immersed in 32 g/100 g osmotic solution concentration was increased from 2% to 75%. Fructose presented greater influence on the adverse quality of jujube slices.

Combining crystalline and polymeric excipients in API solid dispersions - Opportunity or risk?

Amorphous solid dispersions (ASDs) are often metastable against crystallization of the active pharmaceutical ingredient (API) and thus might undergo unwanted changes during storage. The crystallization tendency of ASDs is influenced by the API crystallization driving force (CDF) and the mobility of the molecules in the ASD. Low molecular weight-excipients are known to stabilize amorphous APIs in so-called co-amorphous formulations. Due to their success in stabilizing co-amorphous APIs, low-molecular weight excipients might also enhance the stability of polymeric ASDs. In this work, we investigated the potential of combined low-molecular weight excipient/polymer formulations with in-silico tools and validated the predictions with long-term stability tests of the most promising excipient/polymer combinations. The considered critical quality attributes for the ASDs were the occurrence of amorphous phase separation, API CDF, and molecular mobility in the ASD. As an example, carbamazepine/polyvinylpyrrolidone ASDs were investigated combined with the excipients fructose, lactose, sucrose, trehalose, saccharin, tryptophan, and urea. Although all excipients had a negative impact on the ASD stability, saccharin still turned out to be the most promising one. Long-term stability studies with ASDs containing either saccharin or tryptophan verified -in agreement to the predictions- that API crystallization occurred faster than in the reference ASDs without additional excipient. This work showed that the addition of crystalline excipients to polymeric ASDs might not only offer opportunities but might also bear risks for the long-term stability of the ASD, even though the crystalline excipient stabilizes the polymer-free API. Consequently, excipients should be evaluated based on the thermodynamic phase behavior of the individual mixture of API/polymer/excipient, rather than based on pure-component properties of the excipient only. In-silico predictions proposed in this work remarkably decrease the number of screening tests for identifying suitable formulation excipients.

Color stability of provisional restorative materials with different fabrication methods

PURPOSE

The aim of this study was to investigate and compare the color stability of provisional restorative materials fabricated by 3D printing, dental milling, and conventional materials.

MATERIALS AND METHODS

For the experimental groups, two commercially available 3D-printing provisional resins (E-Dent 100; EnvisionTEC GmbH, Germany & VeroGlaze™; Stratasys®, USA), two dental milling blocks (PMMA Disk; Yamahachi Dental Co., Japan & Telio®CAD; Ivoclar Vivadent AG, Liechtenstein), and two conventional materials (Alike™; GC Co., Japan & Luxatemp automix plus; DMG, Germany) were used. The water sorption and solubility test were (n=10, respectively) carried out according to ISO4049:2000 (International Standards Organization, Geneva, Switzerland). For the color stability test (n=10), coffee and black tea were used as staining solutions, and the specimens were stored for 12 weeks. Data were analyzed by one-way ANOVA and Tukey's HSD using SPSS version 22.0 (SPSS Inc. Chicago, IL, USA) (P<.05).

RESULTS

Alike and Veroglaze showed the highest values and Luxatemp showed the lowest water sorption. In the color stability test, the ΔE of conventional materials varied depending on the staining solution. PMMA milling blocks showed a relatively low ΔE up to 4 weeks, and then significantly increased after 8 weeks (P<.05). 3D-printed materials exhibited a high ΔE or a significant increase over time (P<.05).

CONCLUSION

The degree of discoloration increased with time, and a visually perceptible color difference value (ΔE) was shown regardless of the materials and solutions. PMMA milled and 3 D-printed materials showed more rapid change in discoloration after 8 weeks.

Effect of mechanical interaction on the hydration of mixed soy protein and gluten gels

Mixed gels of plant proteins are being investigated for use as meat analogues. Juiciness is an important characteristic for the acceptability of meat analogues. The juiciness is assumed to be governed by the hydration properties, or water holding capacity, of the gel (WHC). We analysed the WHC of single-phase gels of respectively soy protein and gluten by applying Flory-Rehner theory. This enabled us to describe the WHC of more the complex mixed gels. The WHC of mixed soy protein - gluten gels is shown not to be a linear combination of their constituents. At high volume fractions, soy forms a continuous network and swells similarly to pure soy without being hindered by gluten. However, increasing gluten content leads to a gradual decrease in soy swelling. This is due to the mechanical interaction between soy and gluten. We propose that gluten-rich gels have a continuous gluten network that entraps soy and hinders its swelling. The elastic moduli of the gluten network were extracted from WHC data, and are in reasonable agreement with experimentally determined moduli. A better understanding of the effect of mixed gel composition on WHC is valuable for the development of the next generation meat analogues.

Viscosity of ASDs at humid conditions

Many amorphous solid dispersions (ASDs) are thermodynamically unstable. Thus, the active pharmaceutical ingredient (API) might crystallize over time. The crystallization kinetics and therewith the long-term stability of ASDs depends on the storage conditions temperature and relative humidity (RH) as they determine the molecular mobility of the API in the polymer. To quantify the molecular mobility, the rheological behavior of two different ASDs with ibuprofen and either poly(vinyl acetate) or poly(vinylpyrrolidone-co-vinyl acetate) was analyzed as function of temperature and relative humidity by means of an oscillatory rheometer. The plasticizing effect of ibuprofen and absorbed water on the zero-shear viscosity of the polymer could be fully explained by the reduction of the glass-transition temperature of the mixture compared to the one of the pure polymer. Moreover, this work proposes an approach to predict the zero-shear viscosity of an ASD based on only the temperature dependence of the zero-shear viscosity of the pure polymer as well as the predicted water content in the ASD at certain RH using the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT).

Influence of 10-MDP concentration on the adhesion and physical properties of self-adhesive resin cements

Objectives

Self-adhesive resin cements contain functional monomers that enable them to adhere to the tooth structure without a separate adhesive or etchant. One of the most stable functional monomers used for chemical bonding to calcium in hydroxyapatite is 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP). The aim of this study was to evaluate the influence of the10-MDP concentration on the bond strength and physical properties of self-adhesive resin cements.

Materials and Methods

We used experimental resin cements containing 3 different concentrations of 10-MDP: 3.3 wt% (RC1), 6.6 wt% (RC2), or 9.9 wt% (RC3). The micro-tensile bond strength of each resin cement to dentin and a hybrid resin block (Estenia C&B, Kuraray Noritake Dental) was measured, and the fractured surface morphology was analyzed. Further, the flexural strength of the resin cements was measured using the three-point bending test. The water sorption and solubility of the cements following 30 days of immersion in water were measured.

Results

The bond strength of RC2 was significantly higher than that of RC1. There was no significant difference between the bond strength of RC2 and that of RC3. The water sorption of RC3 was higher than that of any other cement. There were no significant differences in the three-point bending strength or water solubility among all three types of cements.

Conclusions

Within the limitations of this study, it is suggested that 6.6 wt% 10-MDP showed superior properties than 3.3 wt% or 9.9 wt% 10-MDP in self-adhesive resin cement.

Water sorption, antimicrobial activity, and thermal and mechanical properties of chitosan/clay/glycerol nanocomposite films

Chitosan-based nanocomposites films with different clay loadings (0, 5, 10, 15 wt %), with (10, 20, 30 wt%) and without glycerol as plasticizer, were prepared by solution casting. The effects of the addition of clay and glycerol on the thermal, mechanical, water absorption, and antimicrobial activity properties of chitosan/clay nanocomposites films were investigated in this study. XRD results indicated that the intercalated structure was obtained in the chitosan/clay nanocomposites with and without glycerol. The thermal stability of the chitosan was significantly enhanced by the presence of clay and glycerol. It was found that the addition of clay into the chitosan improved significantly the tensile strength and tensile modulus. The highest values in strength and stiffness were achieved for the chitosal/clay nanocomposites with 5 wt% of clay and 20 wt% of glycerol. The addition of both clay and glycerol reduced drastically the ductility of chitosan. The best water resistance was obtained for the chitosan film containing 5 wt% of clay and 20 wt% of glycerol. The chitosan/clay nanocomposite film had potential for application of alternative food packing materials.

Tracking of enzymatic biomass deconstruction by fungal secretomes highlights markers of lignocellulose recalcitrance

BACKGROUND

Lignocellulose biomass is known as a recalcitrant material towards enzymatic hydrolysis, increasing the process cost in biorefinery. In nature, filamentous fungi naturally degrade lignocellulose, using an arsenal of hydrolytic and oxidative enzymes. Assessment of enzyme hydrolysis efficiency generally relies on the yield of glucose for a given biomass. To better understand the markers governing recalcitrance to enzymatic degradation, there is a need to enlarge the set of parameters followed during deconstruction.

RESULTS

Industrially-pretreated biomass feedstocks from wheat straw, miscanthus and poplar were sequentially hydrolysed following two steps. First, standard secretome from Trichoderma reesei was used to maximize cellulose hydrolysis, producing three recalcitrant lignin-enriched solid substrates. Then fungal secretomes from three basidiomycete saprotrophs (Laetisaria arvalis, Artolenzites elegans and Trametes ljubarskyi) displaying various hydrolytic and oxidative enzymatic profiles were applied to these recalcitrant substrates, and compared to the T. reesei secretome. As a result, most of the glucose was released after the first hydrolysis step. After the second hydrolysis step, half of the remaining glucose amount was released. Overall, glucose yield after the two sequential hydrolyses was more dependent on the biomass source than on the fungal secretomes enzymatic profile. Solid residues obtained after the two hydrolysis steps were characterized using complementary methodologies. Correlation analysis of several physico-chemical parameters showed that released glucose yield was negatively correlated with lignin content and cellulose crystallinity while positively correlated with xylose content and water sorption. Water sorption appears as a pivotal marker of the recalcitrance as it reflects chemical and structural properties of lignocellulosic biomass.

CONCLUSIONS

Fungal secretomes applied to highly recalcitrant biomass samples can further extend the release of the remaining glucose. The glucose yield can be correlated to chemical and physical markers, which appear to be independent from the biomass type and secretome. Overall, correlations between these markers reveal how nano-scale properties (polymer content and organization) influence macro-scale properties (particle size and water sorption). Further systematic assessment of these markers during enzymatic degradation will foster the development of novel cocktails to unlock the degradation of lignocellulose biomass.

Mechanical and hydrolytic degradation of an Ormocer®-based Bis-GMA-free resin composite

OBJECTIVES

The aim of the study was to evaluate the mechanical stability of bisphenol A-glycidyl methacrylate (Bis-GMA) and Ormocer-based resin composites before and after water absorption and to examine water saturation.

MATERIAL AND METHODS

Disc-shaped specimens of the Bis-GMA (Grandio SO, Voco) and the Ormocer-based (Admira Fusion, Voco) dental resin composites were produced, stored in water, and weighed after pre-determined times to measure the absorbed water. Bend bars were produced and stored for 24 h in dry conditions as well as in distilled water for 14 days or 60 days at 37 °C. The initial flexural strength (FS) under quasi-static loading and flexural fatigue strength (FFS) under cyclic loading were determined under 4-point bending. Fracture toughness (K_Ic) of both composites was measured using the single-edge-V-notch-beam (SEVNB) technique after the same storage conditions under 3-point bending.

RESULTS

Within the first 14 days, storage conditions did not affect the initial FS of Grandio SO, while a significant drop in initial FS was observed for Admira Fusion after 2 weeks in water and most of the water was absorbed within this time. FFS for the Bis-GMA composite was not reduced before 2 months in water, whereas for the Ormocer®-based composite, there has been a significant decrease in strength after cyclic fatigue already at 2 weeks of water storage. K_Ic of Admira Fusion decreased significantly after both storage periods, while K_Ic of Grandio SO decreased only significantly after 2 weeks of water storage.

CONCLUSION

All mechanical properties of the Bis-GMA composite were superior to those of the Ormocer®-based material, except water sorption.

CLINICAL SIGNIFICANCE

Water storage seems to have a much more pronounced effect on the mechanical properties of Ormocer®-based dental composites in comparison to Bis-GMA-based composites.

Plasticizing of chitosan films with deep eutectic mixture of malonic acid and choline chloride

Chitosan (CS) films containing deep eutectic solvent (DES) based on malonic acid (MA) and choline chloride (ChCl) were successfully prepared by solution casting method by using DES content ranging from 0 to 82 wt%. A strong interaction of CS with the components of DES was demonstrated by analyses of water sorption isotherms, atomic force microscopy and FTIR results. The plasticizing effect of the MA and ChCl mixture on the CS matrix was shown by static bulk mechanical measurements, thermal analysis and quantitative nanomechanical mapping (QNM). Elongation at break increased from 3 to 62% at increase of DES content from 0 to 67 wt%, while further increase of DES content led to the decreasing of maximal elongation. Introduction of DES into CS films led to the appearance of glass transition temperature in the region +2 - -2.3 °C. QNM results indicated homogeneity of the films containing up to 75 wt% of DES.

Water-associated attributes in the contemporary dentin bonding milieu

OBJECTIVES

The water-associated attributes of resin-dentin interfaces created by contemporary adhesives are important determinants of bond integrity and stability. In the present work, these attributes were estimated from the perspectives of causality, to examine the behavior of the first and most-recently launched versions of universal adhesives when applied in either the etch-and-rinse mode or the self-etch mode.

METHODS

The immediate cause of interfacial permeability and the time-dependent cause of water sorption were investigated in conjunction with the intermediate effect of interface degradation and the more long-term effect of loss of mechanical strength, before and after thermomechanical cycling. The results were compared with control etch-and-rinse and self-etch adhesives.

RESULTS

Although the introduction of this new class of universal adhesives has brought forth significant changes to the dental adhesion arena, including more application options, reduced bonding armamentarium and increased user friendliness, the water-associated attributes that are critical for making resin-dentin bonds more durable to environmental challenges and less susceptible to degradation have remained unchanged at large, when compared with benchmarks established by former classes of adhesives.

CONCLUSION

It appears that the current trend of adhesive development has brought forth significant changes but lacks the vigor that demarcates progress and technological sublimity.

CLINICAL SIGNIFICANCE

The advent of the user friendly universal adhesives has brought forth significant changes to the dental adhesion arena. However, the elements that are critical for making resin-dentin bonds more durable to environmental challenges and less susceptible to degradation have remained unchanged at large.

Comparison Of Solubility And Water Sorption Of Two Different Soft Lining Material

BACKGROUND

Soft denture lining materials play a very important role in Removable Prosthodontics because of their ability to provide a cushioning effect for maintaining the health of traumatized, swollen and deformed mucosa through absorption and equal redistribution of stresses over the entire area covered by denture, thus eliminating the distortion of oral mucosa. The objective of this investigation is to quantify and relate the mean solubility and water sorption of acrylic resin based permanent soft liner with a silicone based permanent soft liner.

METHODS

Two different permanent soft denture liners, i.e., acrylic and silicone based are selected for this study, 30 samples of each material are prepared in the form of circular disks of the 30 disks, and three subgroups of ten disks each are made for the two materials. Initially the processed disks will be weighed 3 times daily with an analytical balance until a constant weight is achieved. This initial weight of each specimen is denoted by W1. Each subgroup of 10 specimens is immersed in 250 ml of 37 °C distilled water in a sealed polyethylene container. First subgroup is tested after 1 week, second after 4 weeks and third after 6 weeks of immersion.

RESULTS

Ever soft has higher solubility (1.67mg/cm2 ±0.26 mg/cm2laboratory-processed) and sorption (0.84 mg/cm2 ±0.35 mg/cm2laboratory-processed) than Molloplast B (0.40 mg/cm2 ±0.08 mg/cm2solubility and 0.27 mg/cm2 ±0.16 mg/cm2 sorption) after 6 weeks of immersion.

CONCLUSIONS

It is therefore concluded that Molloplast B may provide better clinical success based on its lower solubility and water sorption.

Evaluation of the water sorption of luting cements in different solutions

OBJECTIVE

To evaluate and compare the water sorption of three luting cements in three different solutions: distilled water and artificial saliva with different pH values (7.4 and 3.0).

MATERIALS AND METHODS

Resin-modified glass-ionomer cement (GC Fuji Plus) and two resin cements (Multilink Automix and Variolink II) were used. A total of 45 specimens - 15 specimens (15x1 mm) for each cement were prepared according to ISO standard 4049:2009. The water sorptions of the cements were calculated by weighing the specimens before and after immersion and desiccation.

RESULTS

. Nonparametric statistic methods were applied. GC Fuji Plus cement showed significantly higher values of water sorption in all three solutions of both resin cements (p<0.009) and significantly higher values of sorption in artificial saliva pH 3.0. Multilink Automix showed significantly higher values of water sorption compared with Variolink II in artificial saliva pH 7.4, and higher values of sorption in this solution compared with pH value 3.0.

CONCLUSION

Water sorption values are mainly influenced by the proportion of hydrophilic matrix, the type and composition of filler, and the pH value of solutions.

Water sorption in microfibrillated cellulose (MFC): The effect of temperature and pretreatment

Water sorption behavior of two different microfibrillated cellulose (MFC) films, produced by delamination of cellulose pulp after different pretreatment methods, is examined at various temperatures (16-65°C) and up to 70% RH. The effect of drying temperature of MFC films on the water uptake is also investigated. The obtained solubility isotherms showed the typical downward curvature at moderate RH, while no upturn is observed at higher RH; the uptakes are in line with characteristic values for cellulose fibers. Enzymatically pretreated MFC dispersion showed lower solubility than carboxymethylated MFC, likely due to the different material structure, which results from the different preparation methods The experimental results are analyzed by Park and GAB models, which proved suitable to describe the observed behaviors. Interestingly, while no significant thermal effect is detected on water solubility above 35°C, the uptake at 16 and 25°C, at a given RH, is substantially lower than that at higher temperature, indicating that, in such range, sorption process is endothermic. Such unusual behavior for a cellulose-based system seems to be related mainly to the structural characteristics of MFC films, and to relaxation phenomena taking place upon water sorption. The diffusion kinetics, indeed, showed a clear Fickian behavior at low temperature and RH, whereas a secondary process seems to occur at high temperature and higher RH, leading to anomalous diffusion behaviors.

A quality by design (QbD) twin-Screw extrusion wet granulation approach for processing water insoluble drugs

In this study, a Quality by Design (QbD) approach was used to identify the effect of formulation parameters in a twin screw wet extrusion granulation process for the manufacturing of ibuprofen (IBU) granules with increased dissolution rates. A fractional factorial Design of Experiment (DoE) was used to investigate the effect of the excipient composition, binder amount and liquid to solid (L/S) ratio (independent variables) on drug dissolution rates, median particle size diameter and specific surface area (dependent variables). The intra-granular addition of the binder in inorganic/polymer blends processed with ethanol as granulating liquids facilitated the formation of granules at various particle sizes. DoE regression analysis showed that all formulation parameters affect the dependent variables significantly. The enhanced dissolution rates were attributed not only to the IBU particle size reduction and adsorption in the porous inorganic network but also to the high specific surface area of the produced granules. Dynamic vapour sorption showed increased water absorption for granules with small particle size distribution and high specific surface area.

A Comparative Evaluation of Sorption, Solubility, and Compressive Strength of Three Different Glass Ionomer Cements in Artificial Saliva: An in vitro Study

Aim

To evaluate and compare the sorption, solubility, and compressive strength of three different glass ionomer cements in artificial saliva - type IX glass ionomer cement, silver-reinforced glass ionomer cement, and zirconia-reinforced glass ionomer cement, so as to determine the material of choice for stress-bearing areas.

Materials and methods

A total of 90 cylindrical specimens (4 mm diameter and 6 mm height) were prepared for each material following the manufacturer’s instructions. After subjecting the specimens to thermocycling, 45 specimens were immersed in artificial saliva for 24 hours for compressive strength testing under a universal testing machine, and the other 45 were evaluated for sorption and solubility, by first weighing them by a precision weighing scale (W1), then immersing them in artificial saliva for 28 days and weighing them (W2), and finally dehydrating in an oven for 24 hours and weighing them (W3).

Results

Group III (zirconomer) shows the highest compressive strength followed by group II (Miracle Mix) and least compressive strength is seen in group I (glass ionomer cement type IX-Extra) with statistically significant differences between the groups. The sorption and solubility values in artificial saliva were highest for glass ionomer cement type IX - Extra-GC (group I) followed by zirconomer-Shofu (group III), and the least value was seen for Miracle Mix-GC (group II).

Conclusion

Zirconia-reinforced glass ionomer cement is a promising dental material and can be used as a restoration in stress-bearing areas due to its high strength and low solubility and sorption rate. It may be a substitute for silver-reinforced glass ionomer cement due to the added advantage of esthetics.

Clinical significance

This study provides vital information to pediatric dental surgeons on relatively new restorative materials as physical and mechanical properties of the new material are compared with conventional materials to determine the best suited material in terms of durability, strength and dimensional stability.

This study will boost confidence among dental surgeons in terms of handling characteristics, cost effectiveness and success rate.

This study will help clinically and scientifically; pediatric dental surgeons to use this material in stress-bearing areas in pediatric patients.

How to cite this article

Bhatia HP, Singh S, Sood S, Sharma N. A Comparative Evaluation of Sorption, Solubility, and Com-pressive Strength of Three Different Glass Ionomer Cements in Artificial Saliva: An in vitro Study. Int J Clin Pediatr Dent 2017;10(1):49-54.

Discoloration of various CAD/CAM blocks after immersion in coffee

Objectives

This study evaluated color differences (ΔEs) and translucency parameter changes (ΔTPs) of various computer-aided design/computer-aided manufacturing (CAD/CAM) blocks after immersion in coffee.

Materials and Methods

Eight CAD/CAM blocks and four restorative composite resins were evaluated. The CIE L^*a^*b^* values of 2.0 mm thick disk-shaped specimens were measured using the spectrophotometer on white and black backgrounds (n = 6). The ΔEs and ΔTPs of one day, one week, and one month immersion in coffee or water were calculated. The values of each material were analyzed by two-way ANOVA and Tukey's multiple comparisons (α = 0.05). The ΔEs after prophylaxis paste polishing of 1 month coffee immersion specimens, water sorption and solubility were also evaluated.

Results

After one month in coffee, ΔEs of CAD/CAM composite resin blocks and restorative composites ranged from 1.6 to 3.7 and from 2.1 to 7.9, respectively, and ΔTPs decreased. The ANOVA of ΔEs and ΔTPs revealed significant differences in two main factors, immersion periods and media, and their interaction except for ΔEs of TEL (Telio CAD, Ivoclar Vivadent). The ΔEs significantly decreased after prophylaxis polishing except GRA (Gradia Block, GC). There was no significant correlation between ΔEs and water sorption or solubility in water.

Conclusions

The ΔEs of CAD/CAM blocks after immersion in coffee varied among products and were comparable to those of restorative composite resins. The discoloration of CAD/CAM composite resin blocks could be effectively removed with prophylaxis paste polishing, while that of some restorative composites could not be removed.

Water-Vapor Sorption Processes in Nanoporous MgO-Al2O3 Ceramics: the PAL Spectroscopy Study

The water-vapor sorption processes in nanoporous MgO-Al2O3 ceramics are studied with positron annihilation lifetime (PAL) spectroscopy employing positron trapping and positronium (Ps)-decaying modes. It is demonstrated that the longest-lived components in the four-term reconstructed PAL spectra with characteristic lifetimes near 2 and 60-70 ns can be, respectively, attributed to ortho-positronium (o-Ps) traps in nanopores with 0.3- and 1.5-1.8-nm radii. The first o-Ps decaying process includes "pick-off" annihilation in the "bubbles" of liquid water, while the second is based on o-Ps interaction with physisorbed water molecules at the walls of the pores. In addition, the water vapor modifies structural defects located at the grain boundaries in a vicinity of pores, this process being accompanied by void fragmentation during water adsorption and agglomeration during water desorption after drying.

Phase behaviour and non-monotonic film drying kinetics of aluminium chlorohydrate-glycerol-water ternary solutions

We study the drying and film formation of a model ternary system comprising an inorganic salt (aluminium chlorohydrate, ACH), a humectant (glycerol) and water. Employing viscometric, X-ray diffraction, calorimetric, dynamic vapour sorption, spectroscopic, gravimetric and adhesion measurements, we examine the roles of humectant concentration, temperature and relative humidity (RH) in the phase behaviour and kinetics of film formation. Equilibrium film compositions are found to be non-monotonic with glycerol content. Around 15:4 ACH:glycerol mass ratio, films exhibit enhanced, albeit slower, desiccation, with water content lower than that of binary ACH-water solutions. At higher glycerol content, drying is faster, yet the resulting films have higher water content and remain tackier. Water adsorption/desorption is shown to be fully reversible, and share a similar non-monotonic kinetic dependence on glycerol composition. These findings are rationalised in terms of the competitive binding of water and glycerol to ACH, the overall miscibility and glass formation within the ternary system. Our study is relevant to a range of salt formulations, employed in a variety of commercial applications, including lyoprotectants and personal care products.

Application of superabsorbent polymers (SAP) as desiccants to dry maize and reduce aflatoxin contamination

The ability of superabsorbent polymers (SAP) in drying maize and controlling aflatoxin contamination was studied under different temperatures, drying times and SAP-to-maize ratios. Temperature and drying time showed significant influence on the aflatoxin formation. SAP-to-maize ratios between 1:1 and 1:5 showed little or no aflatoxin contamination after drying to the optimal moisture content (MC) of 13 %, while for ratios 1:10 and 1:20, aflatoxin contamination was not well controlled due to the overall higher MC and drying time, which made these ratios unsuitable for the drying process. Results clearly show that temperature, frequency of SAP change, drying time and SAP-to-maize ratio influenced the drying rate and aflatoxin contamination. Furthermore, it was shown that SAP had good potential for grain drying and can be used iteratively, which can make this system an optimal solution to reduce aflatoxin contamination in maize, particular for developing countries and resource-lacking areas.

Evaluation of the physical properties of dental resin composites using optical fiber sensing technology

OBJECTIVES

The characterization of the physical properties of dental resin composites is fraught with difficulties relating to significant intra and inter test parameter variabilities and is relatively time consuming and expensive. The main aim of this study was to evaluate whether optical fiber Bragg grating (FBG) sensing system may become a viable tool to study dental material characteristics. Of particular focus was the potential for the system to demonstrate a multi parameter all-in-one feature.

METHODS

A miniature FBG was embedded in six different dental resin composites and employed as a sensor to evaluate linear polymerization shrinkage, thermal expansion and water sorption. Six commercially available dental composites with different filler types and volume are evaluated. The tests are repeated with three sets of samples. The curing characteristics and residual strain gradient exhibited by the cured dental composites were also observed and commented.

RESULTS

Among the studied samples, SDR shows lowest polymerization shrinkage, while Beautifil FO3 shows the highest. The results also show clear distinction between particle filler type and fiber reinforcement based composites in their polymerization shrinkage properties. The agreement of the results with existing literatures show that FBG based system provides accurate results. Polymerization shrinkage rate of the samples are also obtained. Thermal expansion of the composites are measured using the FBG sensing method for the first time and is correlated with resin type, volume, filler type and glass transition temperature. The water sorption characteristics of the dental composite are also successfully measured using the FBG sensing method. The high level of repeatability and the low standard deviations shown in the results indicate good reliability with the use of FBG sensors.

SIGNIFICANCE

This study demonstrates how optical fiber technology can provide simple and reliable methods of measuring the critical physical properties of dental composites. In addition due to the embedding and preservation of the sensor within the samples multiple parameters can be tested for with the same sample. These features are expected to greatly assist material science researchers in dentistry as well as other biomedical fields. Of some interest the phenomenon of stress relaxation of dental composite at higher temperature was observed.

Role of moisture on the physical stability of polymorphic olanzapine

The focus of this study was the understanding of the hydrate transformations of anhydrous olanzapine Forms I and II (the most common polymorphs) upon exposure to different moisture conditions (11, 53, 75, 93% RH) and direct contact with water (e.g. aqueous slurry) and the impact of hydration on the aqueous dissolution rates of the polymorphs. The kinetics of reversible transformations (anhydrate-hydrate phases) and the identification of polymorphs were evaluated by differential scanning calorimetry, thermogravimetry, infrared (DRIFT) and X-ray powder diffraction. The results showed that anhydrous Forms I and II have undergone water vapor phase induced transformations at 93% and 75% RH, respectively. At 93% RH Forms I and II showed to hydrate into dihydrates D and B, respectively, the latter with a higher hydration rate. The conversion of Form I into the dihydrate D showed to affect the dissolution rate of olanzapine (f2<50). As slurries both forms showed to hydrate into a mixture of two different Forms - dihydrate B and higher hydrate. The study provided an understanding of the conversion pathways of the different forms when they were exposed to humid air or aqueous environments, resembling the transformations that might occur during processing, storage or during the persecution of dissolution tests to assess the quality of dosage forms delivering olanzapine.

Water loss from litchi (Litchi chinensis) and longan (Dimocarpus longan) fruits is biphasic and controlled by a complex pericarpal transpiration barrier

In litchi and longan fruits, a specialised pericarp controls water loss by a protective system consisting of two resistances in series and two water reservoirs separated by a barrier. In the fruits of litchi (Litchi chinensis) and longan (Dimocarpus longan), the pericarp is solely a protective structure lacking functional stomata and completely enclosing the aril that is the edible part. Maintaining a high water content of the fruits is crucial for ensuring the economic value of these important fruit crops. The water loss rates from mature fruits were determined and analysed in terms of the properties of the pericarps. Water loss kinetics and sorption isotherms were measured gravimetrically. The pericarps were studied with microscopy, and cuticular waxes and cutin were analysed with gas chromatography and mass spectrometry. The kinetics of fruit water loss are biphasic with a high initial rate and a lower equilibrium rate lasting for many hours. The outer and inner surfaces of the pericarps are covered with cuticles. Litchi and longan fruits have a unique type of transpiration barrier consisting of two resistances in series (endo- and exocarp cuticles) and two reservoirs of water (aril and mesocarp). The exocarp permeability controls the water loss from fresh fruits while in fruits kept for an extended time at low relative humidity it is determined by the endo- and exocarp permeabilities. Permeances measured are within the range for typical fruit cuticles. The findings may be used to design optimal postharvest storage strategies for litchi and longan fruits.

Color stability, water sorption and cytotoxicity of thermoplastic acrylic resin for non metal clasp denture

PURPOSE

The aim of this study was to compare the color stability, water sorption and cytotoxicity of thermoplastic acrylic resin for the non-metal clasp dentures to those of thermoplastic polyamide and conventional heat-polymerized denture base resins.

MATERIALS AND METHODS

Three types of denture base resin, which are conventional heat-polymerized acrylic resin (Paladent 20), thermoplastic polyamide resin (Bio Tone), thermoplastic acrylic resin (Acrytone) were used as materials for this study. One hundred five specimens were fabricated. For the color stability test, specimens were immersed in the coffee and green tee for 1 and 8 weeks. Color change was measured by spectrometer. Water sorption was tested after 1 and 8 weeks immersion in the water. For the test of cytotoxicity, cell viability assay was measured and cell attachment was analyzed by FE-SEM.

RESULTS

All types of denture base resin showed color changes after 1 and 8 weeks immersion. However, there was no significant difference between denture base resins. All specimens showed significant color changes in the coffee than green tee. In water sorption test, thermoplastic acrylic resin showed lower values than conventional heat-polymerized acrylic resin and thermoplastic polyamide resin. Three types of denture base showed low cytotoxicity in cell viability assay. Thermoplastic acrylic resin showed the similar cell attachment but more stable attachment than conventional heat-polymerized acrylic resin.

CONCLUSION

Thermoplastic acrylic resin for the non-metal clasp denture showed acceptable color stability, water sorption and cytotoxicity. To verify the long stability in the mouth, additional in vitro studies are needed.

Resin-based composites show similar kinetic profiles for dimensional change and recovery with solvent storage

OBJECTIVES

To investigate the sorption, solubility, mass change and hygroscopic expansion (solvent swelling) of resin-composites after long term storage in different solvents.

METHODS

Eight materials were studied: two bulk-fill flowable materials (SDR and Venus bulk fill, V-BF), a packable bulk-fill material (Tetric Evoceram bulk-fill, TET-BF), a fiber reinforced material (Ever X posterior, EVX), a nano-hybrid conventional material (Tetric Evoceram, TET) and micro-hybrid conventional materials (G-aenial anterior, GA-P and posterior, GA-A). Three groups of disk shaped specimens were prepared using split stainless steel molds. Each group was stored, respectively, in: water, 75% ethanol/water and methyl ethyl ketone (MEK). The total storage time was 180 d plus a reconditioning time of 120 d. A non-contact laser scanning micrometer was used to measure the diametral changes.

RESULTS

Significant differences were found in the sorption and solubility of the materials. Generally, MEK stored specimens had the highest values followed by 75% ethanol/water then water. A similar trend was found with the mass and volume changes (except for EVX). V-BF showed the highest sorption (98.1μg/mm(3)) and solubility (10μg/mm(3)) after MEK storage. Mass and volume changes showed near-linear correlation, with high Pearson coefficients (0.86-0.99).

SIGNIFICANCE

Generally the materials were most greatly affected by MEK storage compared to the other two solvents. The glass-fiber-reinforced EVX, however, was most affected by water immersion. The pattern of change/recovery behavior of the materials, during solvent challenge, was similar to the pattern of viscoelastic creep/recovery behavior of resin-composite materials.

Influence of humidity on the phase behavior of API/polymer formulations

Amorphous formulations of APIs in polymers tend to absorb water from the atmosphere. This absorption of water can induce API recrystallization, leading to reduced long-term stability during storage. In this work, the phase behavior of different formulations was investigated as a function of relative humidity. Indomethacin and naproxen were chosen as model APIs and poly(vinyl pyrrolidone) (PVP) and poly(vinyl pyrrolidone-co-vinyl acetate) (PVPVA64) as excipients. The formulations were prepared by spray drying. The water sorption in pure polymers and in formulations was measured at 25°C and at different values of relative humidity (RH=25%, 50% and 75%). Most water was absorbed in PVP-containing systems, and water sorption was decreasing with increasing API content. These trends could also be predicted in good agreement with the experimental data using the thermodynamic model PC-SAFT. Furthermore, the effect of absorbed water on API solubility in the polymer and on the glass-transition temperature of the formulations was predicted with PC-SAFT and the Gordon-Taylor equation, respectively. The absorbed water was found to significantly decrease the API solubility in the polymer as well as the glass-transition temperature of the formulation. Based on a quantitative modeling of the API/polymer phase diagrams as a function of relative humidity, appropriate API/polymer compositions can now be selected to ensure long-term stable amorphous formulations at given storage conditions.

Effect of intrinsic pigmentation on the tear strength and water sorption of two commercially available silicone elastomers

The purpose of this study was to evaluate the water sorption and tear strength of two commercially available silicone elastomers. Silicone test specimens with the dimension of 150 mm × 150 mm × 3 mm were prepared for cosmesil M511 silicone (Cosmedica Ltd, Cardiff, UK) and biomed silicone (MP Sai Enterprises, Mumbai, India). Sixty test specimens were divided equally into two groups-I and II. Group I and II were further subdivided into A, B, and C with 10 specimens each. Subgroup A represented the control group (without colorant), test specimens in subgroup B (incorporated with intrinsic pigments) were evaluated for tear strength, and subgroup C specimens, incorporated with intrinsic pigments were evaluated for water sorption. Students's t test was performed. Among the control group, cosmesil M511 silicone showed more tear strength with the mean of 11.42 ± 0.73 compared to biomed silicone which showed 6.64 ± 0.70. The tear strength values increased for both silicones after intrinsic pigmentation. Cosmesil M511 silicone showed more water sorption compared to biomed silicone. Medical grade cosmesil M511 silicone had better tear strength values compared to biomed silicone.

Qualitative and quantitative assessment of water sorption in natural fibres using ATR-FTIR spectroscopy

In the field of composite materials, natural fibres appear to be a viable replacement for glass fibres. However, in humid conditions, strong hydrophilic behaviour of such materials can lead to their structural modification. Then, understanding moisture sorption mechanisms in these materials is an important issue for their efficient use. In this work, the water sorption on three natural fibres (flax, hemp and sisal) was studied using Fourier transformed infrared spectroscopy. The spectral information allowed both qualitative and quantitative analyses of the moisture absorption mechanisms. The main chemical functions involved in the water sorption phenomenon were identified. The absolute water content of the fibres was also determined by using a partial least square regression (PLS-R) approach. Moreover, typical sorption isotherm curves described by Park model were fitted as well as water diffusion kinetics. These last applications confirmed the validity of the FTIR spectra based predictive models.

The relationship between cyclic hygroscopic dimensional changes and water sorption/desorption of self-adhering and new resin-matrix composites

OBJECTIVES

This study evaluated the relationship between mass changes and hygroscopic dimensional changes during water sorption/desorption cycles in new resin composites.

METHODS

A silorane posterior composite (Filtek(®) Silorane, FS), two micro-fine hybrid composites (GC Gradia Direct Anterior, GDA; GC Gradia Direct Posterior, GDP), a universal composite (GC Kalore, GCK), and a self-adhering flowable composite (Vertise(®) Flow, VF) were evaluated. 25 (n=5) disk specimens (15mm×2mm) were prepared according to ISO 4049. Water sorption was measured gravimetrically. Hygroscopic expansions were measured by a laser micrometer regularly during 150 d water storage and 40 d recondition periods, all at 37°C. Data were analyzed by repeated measures ANOVA, one-way ANOVA and Tukey's post hoc test (p<0.05).

RESULTS

Mass changes after 150 d water immersion ranged from 0.68% (±0.02) for FS to 2.83% (±0.11) for VF and the corresponding hygroscopic expansions were from 0.74% (±0.05) for FS to 4.79% (±0.18) for VF. The differences were significant for all materials (p<0.001), except mass changes between GCK and GDP, as well as hygroscopic changes between GCK and GDA. The relationship between hygroscopic expansions and mass changes was initially non-linear and then tended toward linear behavior. But at the late stage of water sorption the hygroscopic expansion of GCK and VF was slightly sigmoidal with respect to their mass changes.

SIGNIFICANCE

Relationships between hygroscopic expansion and mass change were determined for some diverse resin-matrix composites. The initial non-linearity for all materials suggests a lower expansion rate due to occupancy of internal free volume by water ingress. The silorane composite FS showed statistically the lowest mass change and hygroscopic dimensional change.

The evaluation of water sorption/solubility on various acrylic resins

OBJECTIVES

The absorption of water by acrylic resins is a phenomenon of considerable importance since it is accompanied by dimensional changes, a further undesirable effect of absorbed water in acrylic resins to reduce the tensile strength of the material. Solubility is also an important property because it represents the mass of soluble materials from the polymers.

METHODS

Ten acrylic resin-based materials were evaluated: two heat cure acrylic resins (De Trey QC-20, Meliodent Heat Cure) and eight self cure acrylic resins (Meliodent Cold, Akrileks, Akribel, Akribel Transparent, Vertex Trayplast, Formatray, Dentalon Plus, Palavit G). To evaluate water sorption and water solubility, thirty square-shaped specimens (20x20x1.5 mm) were fabricated from the wax specimens. One way ANOVA test, Tukey test and Pearson correlation coefficient performed for data.

RESULTS

Water sorption mean values varied from 11.33+/-0.33 to 30.46+/-0.55 mug/mm(3). Water solubility mean values varied from -0.05+/-0.23 to 3.69+/-0.12 mug/mm(3). There was statistically significant difference between mean values of the materials (P<.05). There was no linear correlation between sorption and solubility values.

CONCLUSIONS

The results of the water sorption and water solubility values of both self-cured and heat-cured acrylic resins were in accordance with the ISO specification. No correlation found between water sorption and water solubility values.