Novel resin modified glass-ionomer cements with improved flexural strength and ease of handling

Poly(acrylic acid-co-itaconic acid) copolymers containing pendent methacrylates were synthesized and used to formulate redox-initiated in situ cured glass-ionomer cements (GICs) by mixing with reactive glass fillers (Fuji II LC). Various formulations for the redox initiator were studied, and flexural strength (FS) was used as a screening tool for optimization. Effects of molecular weight (MW), grafting ratio, comonomer, polymer content in the liquid composition, powder/liquid (P/L) ratio, and aging on FS were investigated. The results show that the in situ cured GICs demonstrated higher FS (89.6-123.2 MPa), as compared to commercial Fuji II LC GIC (57.1 MPa). The optimal concentrations for redox initiators were found to be 0.15% (by weight) for K₂S₂O₈ and 0.2% for ascorbic acid (or 0.6% for microencapsulated ascorbic acid), respectively. Effects of MW, grafting ratio, P/L ratio and polymer content in the liquid formulation were significant. During aging, the cement showed an increase in strength over 24 h and then no change for time periods up to six months. SEM analysis supports the strength data associated with the formulations. The exotherm and setting time suggest that novel redox-initiated resin-modified GICs hold promise as biocompatible and workable cement for orthopedic applications.     

Synthesis of amino acid-containing polyacids and their application in self-cured glass-ionomer cement

Six methacrylate or acrylate derivatives of natural amino acids were synthesized and characterized. Based upon these monomers, six terpolymers [poly(acrylic) acid-co-itaconic acid-co-amino acid] were prepared and characterized. The synthesized polymers were used to formulate glass-ionomer cements (GICs) using Fuji II glass filler. The effects of the molecular weight (MW) and powder/liquid (P/L) ratio were evaluated. Scanning electron microscopy (SEM) was used to examine the fracture surfaces of the selected cement specimens. Results show that all the amino acid modified GICs exhibited higher compressive strengths (CS, 193-236 MPa) and much higher flexural strengths (FS, 55-71 MPa) as compared to commercial Fuji II GIC (191 in CS and 16 in FS). Both MW and P/L ratio affected the strength of the formed cement. It was important to find the optimal MW and P/L ratio to obtain the highest FS. In this study, optimized MW (number average) of the polyacids and P/L ratio were around 50,000 and 2.7/1, respectively. The microstructures of the fracture surfaces helped to explain the strength differences among the materials tested in the study. SEM analysis suggests that more integrated microstructures and fewer defects can lead to higher FS.     

SYNTHESIS OF POLY(ACRYLIC ACID-CO-ITACONIC ACID) IN CARBON DIOXIDE–METHANOL MIXTURES

ABSTRACT

High fluidity solvents, such as supercritical fluids, have several advantages over traditional solvents as polymerization media, such as offering a more environmentally-friendly reaction media, providing increased reaction rates, and simplifying the separation and purification of polymers. In this study, a traditional glass-ionomer polymer, poly(acrylic acid-co-itaconic acid) (PAA/IA) was synthesized by using mixtures of CO₂ and methanol as the reaction solvent and was characterized by ¹H-NMR, FT-IR, GPC, and viscometry. The mechanical and working properties of the glass-ionomer cements, prepared by mixing aqueous solutions of the polymers with Fuji II glass powder, were evaluated for compressive strength (CS), diametral tensile strength (DTS) and flexural strength (FS), as well as setting time and working time. The results showed that the polymerization reaction in CO₂/methanol mixtures was faster and had higher conversion than the polymerization reaction in water. The glass-ionomer formulations made from the copolymer prepared under SC conditions showed higher CS, comparable FS and DTS compared with those made from the same polymer prepared in water. Both of the synthesized copolymers had significantly higher CS and FS than Fuji II. The working properties of PAA/IA made in CO₂/methanol met the requirement of ANSI/ADA No. 96.     

PREPARATION AND EVALUATION OF ACRYLIC ACID,ITACONIC ACID,AND N-METHACRYLOYLGLUTAMIC ACID COPOLYMERS FOR USE IN GLASS-IONOMER TYPE DENTAL RESTORATIVES

A series of copolymers containing various molar ratios of acrylic acid, itaconic acid and N-methacryloylglutamic acid were prepared in aqueous solution, using standard free-radical polymerization conditions. Specimens for mechanical property studies were prepared by mixing water solutions of the copolymers (50:50, wt:wt) with a commercial, calcium-fluoroaluminosilicate glass powder, with curing or hardening achieved by salt-bridge formation. The glass powder used in the formulation(s) was the same as that used in Fuji II (GC America) glass-ionomer. The working and setting times of the various formulations were evaluated. The compressive strength was used as the basic screening property to find the optimum molar ratio of the three monomers. The diametral tensile strength, flexural strength and Knoop surface hardness of the cured materials were also determined. All mechanical properties were measured after the specimens were conditioned in distilled water for 7 days at 37°C. Based on the compressive strength (CS), poly (AA-co-IA-co-MGA) with a monomers ratio of 8:1:1, respectively, showed the highest CS (269.9 MPa). The 8:1:1 copolymer with different molecular weights were also prepared to evaluate the effect of MW on the compressive strength. The optimum MW copolymer gave a glass-ionomer having the compressive strength improved by 30%, compared to Fuji II (293.9 MPa vs. 224.9 MPa). The same polymer solution was also mixed with glass powders used in other commercial glass-ionomers, i. e., Ketac-Molar (ESPE, Seefeld, Germany), α-Fil and α-Silver (DMG, Hamburg, Germany) to produce conventional glass-ionomers test specimens. The mechanical properties of these materials were also obtained and compared to the Fuji II, Ketac-Molar, α-Fil and α-Silver controls.     

Improved Flexural Strength of N-Vinyl-Pyrrolidone Modified Acrylic Acid Copolymers for Glass-Ionomers

Abstract

The flexural strengths of N-vinylpyrrolidone modified glass-ionomer cements were investigated. The optimal molar ratio of the monomers in copolymers, composed of the three components acrylic acid, itaconic acid and N-vinylpyrrolidone, was determined using a SAS statistical program. The copolymers were prepared using a free-radical polymerization process. The viscosities of aqueous solutions of these polymers were determined. Cements were formed by the reaction of these solutions with glass particles. Flexural strength (FS) was used as the basic screening property to find the optimum molar ratio. Statistical models were applied to predict the optimum molar ratios. All strength values were recorded on the specimens conditioned in distilled water at 37°C for 7 days. The optimal molar ratio for these copolymers was 7:1:3 for poly(acrylic acid-co-itaconic acid-co-N-vinylpyrrolidone), based on flexural strength and viscosity. The effect of molecular weight (MW) on FS was also evaluated. Copolymer with a MW of 10, 800 (M_n) showed 85% higher FS than the Ketac-Molar (KM) system, along with a reasonable working viscosity.     

NEW MATRIX RESINS FOR GLASS POLYALKENOATES OR GLASS-IONOMERS WITH PENDANT AMINO ACID RESIDUES

The monomers N-acryloyl (AGA) and N-methacryloylglutamic acid (MGA) have been prepared and copolymerized with acrylic acid (AA) and itaconic acid (IA) to make polyelectrolytes for evaluation in glass polyalkenoates or glass-ionomers. It was shown that poly(AA-co-IA-co-AGA) and poly(AA-co-IA-co-MGA), having a monomers ratio, respectively, of 7:3:3 could be formulated with glass powders used in Fuji II (GC America), α-Silver (DMG-Hamburg), α-Fil (DMG-Hamburg) and Ketac-Molar (ESPE, Seefeld, Germany) to produce conventional glass-ionomers with improved compressive strength (CS), flexural strength (FS) and fracture toughness (FT), compared to Fuji II, α-Silver, α-Fil and Ketac-Molar controls. Since MGA is much easier to produce in high yields than AGA, it was important to show that MGA could be used as well as AGA to produce new matrix resins for glass-ionomers. Furthermore, we demonstrated that both the 7:3:3 AGA and MGA copolymers could be reacted with 2-isocyanatoethyl methacrylate (IEM) to produce intermediates useful for formulating visible light-curable (VLC) glass-ionomers with improved CS, FS and FT, compared to two com-mercial VLC materials Fuji II^TM LC and Vitremer^TM Tricure. Here again, it was found that MGA could be used as well as AGA to prepare improved materials. We also demonstrated that poly(AA-co-MGA) could be used to formulate glass-ionomers with improved properties. Further, we demonstrated that small amounts of MGA could be used as a reactive diluent in VLC formulations such as Fuji II^TM LC, Vitremer^TM Tricure, and an experimental VLC formulation to improve their mechanical properties, adhesion to tooth structure, and fluoride release.     

Formulation of Visible Light-Curable Glass-Ionomer Cements Containing N-Vinylpyrrolidone

Abstract

The best graft ratio of the light-curable N-vinylpyrrolidone (NVP) modified terpolymers (LC NVPM TPs) with the molar ratio of 8:2:1 (acrylic acid:itaconic acid:NVP) and the optimal formulation for this light-curable glass-ionomer cement, based on the best graft ratio, were determined. Statistical models were utilized to predict the optimal formulations. The terpolymer was prepared using a free-radical polymerization reaction. The LC NVPM TPs were produced by grafting 2-isocyanatoethyl methacrylate (IEM) onto the terpolymer. Cements were formed by both light-curing and the reaction with glass particles. Compressive strength was used as the basic screening property to find the optimal formulation. Diametral tensile and flexural strengths were also used to evaluate the mechanical properties. The strength values were recorded on the specimens conditioned in distilled water at 37&C for 24 hours or 7 days. The best graft ratio for IEM in this system was 15% of the terpolymer by a molar ratio. The optimal formulation was found to be at the weight ratio of 55:15:30 [LC NVPM TP:2-hydroxyethyl methacrylate (HEMA): H₂O]. Stress-strain curves showed that a relatively high amount of water in the formulation led to higher elastic modulus and proportional limit and lower malleability, whereas a relatively high amount of HEMA gave the opposite results. The light-curable NVP modified glass-ionomer cements showed statistically significantly higher values in compressive, diametral tensile, and flexural strengths than the commercial Vitremer^TM.     

Synthesis, formulation and evaluation of novel zinc-calcium phosphate-based adhesive resin composite cement

Three novel adhesive oligomers having carboxylic acid and methacrylate groups were synthesized, characterized and used to formulate composite bone cements with newly synthesized zinc-calcium-silicate phosphate. The optimal formulation was determined based on types of oligomer, oligomer/diluent ratio, initiator concentration, and filler level using compressive strength (CS) and curing time (CT) as screening tools. Shrinkage, exotherm and aging of the formed composite cements were also evaluated. Results show that the experimental cement was 186% higher in CS, 16% higher in diametral tensile strength, similar in flexural strength, 56% less in exotherm and 64% less in shrinkage, as compared to conventional polymethylmethacrylate cement. The optimal concentrations for initiators were found to be 1.5% (by weight) for both benzoyl peroxide and N,N^′-dimethyl-p-toluidine. With increasing initiator concentration, diluent content and zinc oxide content in the cement formulation, CS of the cement increased but curing time decreased. Shrinkage and exotherm of the cement decreased with increasing filler level. CS was not proportional to an increase of filler level and CT increased with an increase of filler level. During aging, the cement showed an increase of strength over 24 h and then no change for over nine months. It appears that this novel cement may be a potential candidate for orthopedic restoration if its biological performance is good and the formulation is optimized.     

Microhardness of N-Vinylpyrrolidone Modified Glass-Ionomer Cements

ABSTRACT

The water soluble N-vinylpyrrolidone (NVP) monomer was used to prepare poly(N-vinylpyrrolidone-co-itaconic acid-co-acrylic acid) glass-ionomer copolymers, using a free-radical polymerization process. NVP modified terpolymer was mixed with glass powders from four commercial glass ionomer systems. Microhardness from the set cement was measured and compared to several commercial glass-ionomer systems. The Knoop hardness number (KHN) values were recorded on polished specimens conditioned for 48 hours and 7 days. One-way analysis of variance and Tukey-Kramer tests were used to determine the significant differences among the materials tested in each group. Among the four commercial cements, Ketac-Molar (KM) showed the highest value and α-Silver (AS) snowed the lowest value in KHN. Fuji II (F2) and α-Fil (AF) showed much the same values in KHN. At the same P/L ratio, NVP modified glass-ionomers showed higher KHN values than the AS, similar to the AF and F2, and lower than the KM. The effect of P/L ratios was evident and highest KHN values for each group were basically presented by the one with a higher P/L ratio. Higher P/W ratio did not improve the KHN for the AS and KM group, but improved the F2 group.     

Syntheses and evaluation of biodegradable multifunctional polymer networks

The biodegradable, injectable and in situ crosslinkable polymer networks based upon di(propylene fumarate)-dimethacrylate (DPFDMA) and polycaprolactone trimethacrylate (PCLTMA), were prepared and characterized. The polymer networks were initiated by photopolymerization. The initial compressive (CS) and diametral tensile strengths (DTS) of the networks materials were determined and used to evaluate the effects of PCLTMA/DPFDMA ratios on the degradation behavior. The networks exhibited initial DTS values ranging from 2.5 to 9.3 MPa and CS values ranging from 1.8 to 146.0 MPa. The increase of PCLTMA in the formulation led to an increase in viscosity and DTS. The degree of conversions and polymerization shrinkage of the resins ranged from 60% to 72% and 5.1% to 6.4%, respectively. After 6 month, PCL300TMA/DPFDMA resins at a ratio of 100/0, 75/25 and 25/75 lost 70%, 87% and 46% of their initial CS, respectively, while PCL900TMA/DPFDMA and PCL300TMA/PCL900TMA resins at 75/25 lost 100% and 83% of their initial CS, respectively.     

Syntheses and evaluation of novel biodegradable amino acid based anhydride polymer resins and composites

A novel synthetic biodegradable oligomer based upon methacrylated aminocaproyl maleamic acid (MACMA), was synthesized and characterized. Injectable and in situ crosslinkable polymer networks were formulated by copolymerization of MACMA with triethyleneglycol dimethacrylate (TEGDMA). In addition, composites composed of MACMA, TEGDMA and beta-tricalcium phosphate (β-TCP) were prepared. The networks and composites were initiated by photo- and redox-polymerization, respectively. The initial compressive (CS) and diametral tensile strengths (DTS) of these materials were determined and used to evaluate the effects of MACMA/TEGDMA ratios on the degradation behavior of the materials. The neat resin networks exhibited initial CS values ranging from 6.7 to 284.2 MPa and the composites demonstrated initial DTS values ranging from 2.8 to 20.8 MPa and CS values ranging from 19.1 to 119.5 MPa. During the course of degradation the polymer neat resins lost 51%, 69% and 61% of their initial CS after 3 weeks for the MACMA/TEGDMA ratios at 25/75, 50/50 and 75/25, respectively. The resin with the MACMA/TEGDMA ratio of 75/25 completely degraded after 6 months. The composite with the MACMA/TEGDMA ratio of 25/75 exhibited a significant increase in CS after an initial decrease for 7 days and then lost 57% of its initial CS after 3 months. The composite composed of poly(MACMA) homopolymer showed a complete degradation after 21 days.     

Magnesium-substituted calcium phosphate cements with (Ca + Mg)/P = 2

The introduction of magnesium ions into bone calcium phosphate cements (CPCs) increases the strength and biodegradation rate of the materials. Cement powders with the (Ca + Mg)/P ratio of 2 and the degree of magnesium substitution for calcium of 0, 10, 20, and 40 wt % were used in the study. Sodium phosphate-based solutions were used as the cement fluids. Depending on the magnesium content, CPCs based on magnesium-substituted apatite and whitlockite phases were obtained. The phase composition, setting time, strength, and microstructure of the cements were determined. An increase in the acidity of the cement liquid was found to give cements with a greater content of amorphous phase and more homogeneous structure, resulting in higher strength.     

The First Step in Standardizing an Artificial Aging Protocol for Dental Composites—Evaluation of Basic Protocols

The clinical performance of a dental restoration is strongly influenced by the complex and dynamically-changing oral environment; however, no standard procedure exists to evaluate this lifetime. This research provides an in-depth analysis of the effect of different aging procedures on the flexural strength (FS), diametral tensile strength (DTS) and hardness (HV) of selected dental materials (Resin F, Flow-Art and Arkon). Material structure was evaluated by scanning electron microscopy. It was found that each aging protocol had some influence on the tested properties, with continual erosion and degradation being observed. Greater mechanical degradation was observed for Resin F (neat resin) after the applied aging protocols, suggesting that a resin matrix is more susceptible for degradation. The most aggressive aging protocol was Protocol 5: 0.1 M NaOH, seven days, 60 °C. Further studies on the effect of artificial aging on dental materials should include a study of the thermal and chemical factors. A standardized aging procedure is crucial for improving the resistance of dental resin composite to oral conditions and their clinical performance.     

NOVEL TRIMETHACRYLATES: SYNTHESIS,CHARACTERIZATION, AND EVALUATION OF NEW MONOMERS FOR IMPROVED DENTAL RESTORATIVES

ABSTRACT

Two novel trimethacrylates, i.e., 1,1,1-tri-[4-(methacryloxyethoxy)-phenyl] ethane (TMPE) and 1,1,1-tri-[4-(2-methyl-2-methacryloxyethoxy)-phenyl]ethane (TMMPE), have been synthesized by reacting methacryloyl chloride with the corresponding hydroxyl intermediates. Both trimethacrylate monomers, having a low viscosity of 11.5 and 13.1 Pa.S, respectively, were blended with TEGDMA at three different weight ratios, i.e., 90/10, 70/30, and 50/50. The mixtures were made visible light-curable (VLC) by the addition of camphorquinone (0.5 wt%) and N,N-dimethyl-aminoethyl methacrylate (1.0 wt%). In addition to evaluation as cured neat resins, VLC formulations with 70% by wt. of silanated microfiller were also prepared and evaluated. The control in both cases was a VLC formulation of BisGMA/TEGDMA (70/30 and 50/50 wt/wt). These new, formulated resins have both improved physical properties and higher double bond conversion than the BisGMA control, as well as decreased linear polymerization shrinkage (LPS). The neat resin having 70/30 (wt/wt) ratio of TMPE/TEGDMA (T7T3, Table 2) exhibited a compressive strength (CS) of 496 (±51) MPa compared to the 70/30 (wt/wt) ratio of BisGMA/-TEGDMA control having 425(±27) MPa. A filled resin having a 90/10 (wt/wt) ratio of TMPE/TEGDMA exhibited a flexural strength (FS) of 122.6(±23) MPa, compared with a similar filled BisGMA/TEGDMA (70/30, wt/wt) resin exhibiting 112.7(±19) MPa. These and other results suggest that these new trimethacrylates have potential application in formulating dental composites with improved performance.     

甲基丙烯酸甲酯/苯乙烯在硅片表面的RAFT接枝聚合

将3-(2-二硫代苯甲酸基丙酰氧基)丙基二甲基甲氧基硅烷化学键合于硅片表面.以甲基丙烯酸甲酯和苯乙烯为单体,在硅片表面进行可逆加成-断裂链转移(RAFT)接枝聚合.X-射线光电子能谱仪证实聚甲基丙烯酸甲酯(PMMA)、聚苯乙烯(PS)、苯乙烯/甲基丙烯酸甲酯的共聚物(poly(MMA-co-St))都接枝到硅片表面.但3个体系表现出不同的性质,甲基丙烯酸甲酯的RAFT聚合可控性差,分子量比设计分子量大得多,分子量分布指数宽,接枝密度仅为0·03chains/nm2;苯乙烯均聚合的活性/可控性好、分子量分布窄,接枝密度提高到0·21chains/nm2;共聚合体系综合了两个均聚体系的优点,分子量分布较窄,接枝密度最高为0·31chains/nm2,聚合物膜厚随转化率、数均分子量基本呈线性增长.     

化学-物理法制备聚乙烯醇/壳聚糖/纳米羟基磷灰石复合水凝胶及其性能

采用化学 物理交联法制备了聚乙烯醇/壳聚糖/纳米羟基磷灰石（PVA/CS/n-HA）复合水凝胶材料。 通过对比其含水率、拉伸强度、红外光谱和TG谱图,探讨了PVA含量及戊二醛加入量对材料性能的影响。 结果表明,m(PVA)∶m（CS+n-HA）=5∶1,戊二醛质量分数为2%时,复合水凝胶材料具有较好的综合性能：含水率为82.0%、拉伸强度为2.14 MPa、断裂伸长率为343.26%;同步热分析表明,25~140 ℃,仅存在水分的蒸发,直至360 ℃材料才发生分解,说明材料的热稳定性良好;红外分析表明,CS与戊二醛发生了交联反应。     

丙烯酸β-羟丙酯与聚氯乙烯膜的紫外光接枝改性

采用液相接枝方法 ,在紫外线辐照下 ,合成了一系列丙烯酸 β-羟丙酯 (β -HPAT) /聚氯乙烯接枝膜。讨论了引发剂浓度、单体浓度、光照时间、光照强度对接枝率的影响。结果表明 ,引发剂浓度为 6 .5 1× 10 -3 mol/L ,单体浓度 2 .0mol/L ,光照时间为 2 .0h ,且光照强度越强时 ,接枝率最大。接枝膜的结构特征通过FT -IR光谱进行了确证 ,最后 ,对接枝膜进行TGA分析 ,结果表明聚氯乙烯经过表面改性后 ,表面极性增大 ,热稳定性大大提高。     

聚甲基丙烯酸-对-甲氧基偶氮苯烷氧基酯的合成及柔性间隔基对液晶行为的影响

通过甲基丙烯酸钾盐与溴化物的反应合成了一系列柔性间隔基长度不同的甲基丙烯酸 对 甲氧基偶氮苯烷氧基酯（ＰＭＡＡＺＯｎ,ｎ＝２,３,４,５,６）,然后聚合成相应的聚合物．用１Ｈ ＮＭＲ和ＩＲ表征了聚合物的结构,ＧＰＣ测定了分子量,ＤＳＣ和偏光显微镜观测了液晶高分子的相行为和织构．研究了间隔基长度对织构、相变和热力学性质的影响,观测到聚合物的ＴＮＩ随间隔基的长度变化表现出的奇偶效应．     

原位沉析法制备壳聚糖棒材的研究

以壳聚糖凝胶膜为模板,将壳聚糖溶液与NaOH凝固液隔离,利用膜渗透原位沉析法制备了高性能的壳聚糖棒材(d=4.5mm),其弯曲强度、弯曲模量和剪切强度分别为92.4MPa,4.1GPa和36.5MPa.扫描电子显微镜(SEM)分析结果表明,原位沉析法制备的壳聚糖棒材具有同心筒状层叠结构,并对其成型机理进行了探讨.     

Hydration mechanisms of supersulfated cement

Considerable attention has been given to special cements, capable of reducing CO₂ emissions, energy and limestone consumption. Supersulfated cements are made of blast furnace slag (GBFS), calcium sulfate (CS), and small quantities of activator, but achieving their optimal proportions is complex. In this paper, the effects of the both CS and alkali activator (KOH) contents were studied. The main results showed that the compressive strength, heat of hydration, and consumption of anhydrite phase were strongly influenced by the alkaline content, while low calcium sulfate or alkaline content increased the formation of CSH. The instability of ettringite was verified: with low CS, the probable hypothesis was its conversion into monosulfate due to the scarcity of sulfate; with high CS, it was associated with intense, rapid consumption of anhydrite with high KOH content, followed by the precipitation of ettringite on the surface of slag grains and its conversion into monosulfate.