Effect of resin hydrophilicity and temperature on water sorption of dental adhesive resins

This study examined the effects of copolymer hydrophilicity and temperature on water sorption and solubility characteristics of five copolymer blends of increasing degree of hydrophilicity using gravimetric measurements. Six resin disks (15 mm in diameter x 1 mm in thickness) were prepared from each copolymer blend and were stored in deionised water at 23, 37 and 55 degrees C. Water sorption and solubility of the resin disks were measured before and after water immersion and desiccation. Multiple regression analysis of water sorption was performed on two independent variables, copolymer hydrophilicity and temperature. Maximum water sorption increased significantly with Hoy's total cohesive energy density (delta(t)), Hoy's solubility parameter for polar forces (delta(p)) and hydrogen bonding (delta(h)), but was not influenced by temperature. However, a significant positive relationship was observed between diffusion coefficients (obtained using Fick's law of diffusion) and temperature. The water absorption activation energy was 10 kJ/mol for the most hydrophilic copolymer blend R5 and 35-51 kJ/mol for copolymer blends R1-R4. The positive relationship between maximum water uptake and copolymer hydrophilicity suggests that water molecules diffuse through the polymer matrices by binding successively to the polar sites via hydrogen bonding. Such water sorption may determine the durability of resin-dentine bonds.     

Evaluation of the effect of water-uptake on the impedance of dental resins

Electrical impedance spectroscopy (EIS) offers a quantitative method of measuring the stability of resin films in aqueous solution over time. PURPOSE: The purpose of this study was to measure the EIS of five experimental dental adhesive films (ca. 17 microm thick) of increasing hydrophilicity (ranked by their Hoy's solubility parameters), and how much these values change over 3 weeks in aqueous buffer. METHODS: The resin films were placed in a U-shaped chamber and a pair of Ag-AgCl electrodes was used for EIS. The EIS results were confirmed by immersing the films in 50% AgNO3 for 24 h to trace the distribution of any water absorption into the resins by TEM observations. RESULTS: The resistance (Rr) of the resins 1-4 films increased most during the first day, and varied from 1x10(11) ohm for resin 1, to 40Omega for resin 5 at day 1. The day 1 Rr values of resins 1-4 were inversely proportional to their Hoy's solubility parameter for hydrogen bonding forces. Electrical impedance values of resins 1-3 and 5 varied widely but were relatively constant over time, while those of resin 4 decreased more than 99% from day 1 to 21 (p<0.05). Capacitance (Cr) of films of resins 1-4 all increased over the first day and then were relatively unchanged over the 20 days (except for resin 4 that continued to increase) and were between 0.01 and 1 nF. Silver uptake by TEM revealed the development of water-filled branching structures that formed in resins 4 and 5 over time.     

Application of hydrophobic resin adhesives to acid-etched dentin with an alternative wet bonding technique

Hydrophilic dentin adhesives are prone to water sorption that adversely affects the durability of resin-dentin bonds. This study examined the feasibility of bonding to dentin with hydrophobic resins via the adaptation of electron microscopy tissue processing techniques. Hydrophobic primers were prepared by diluting 2,2-bis[4(2-hydroxy-3-methacryloyloxy-propyloxy)-phenyl] pro- pane/triethyleneglycol dimethacrylate resins with known ethanol concentrations. They were applied to acid-etched moist dentin using an ethanol wet bonding technique that involved: (1) stepwise replacement of water with a series of increasing ethanol concentrations to prevent the demineralized collagen matrix from collapsing; (2) stepwise replacement of the ethanol with different concentrations of hydrophobic primers and subsequently with neat hydrophobic resin. Using the ethanol wet bonding technique, the experimental primer versions with 40, 50, and 75% resin exhibited tensile strengths which were not significantly different from commercially available hydrophilic three-step adhesives that were bonded with water wet bonding technique. The concept of ethanol wet bonding may be explained in terms of solubility parameter theory. This technique is sensitive to water contamination, as depicted by the lower tensile strength results from partial dehydration protocols. The technique has to be further improved by incorporating elements of dentin permeability reduction to avoid water from dentinal tubules contaminating water-free resin blends during bonding.     

Solvent and water retention in dental adhesive blends after evaporation

This study examined the extent of organic solvent and water retention in comonomer blends with different hydrophilicity (Hoy's solubility parameter for hydrogen bonding, delta(h)) after solvent evaporation, and the extent of tracer penetration in polymerised films prepared from these resins. For each comonomer blend, adhesive/solvent mixtures were prepared by addition of (1) 50 wt% acetone, (2) 50 wt% ethanol, (3) 30 wt% acetone and 20 wt% water and (4) 30 wt% ethanol and 20 wt% water. The mixtures were placed in glass wells and evaporated for 30-60s for acetone-based resins, and 60-120 s for ethanol-based resins. The weight of the comonomer mixtures was measured before and after solvent evaporation. Resin films were prepared for transmission electron microscopy (TEM) after immersion in ammonical silver nitrate. The percentages of solvent and water retained in the comonomer mixtures, and between the acetone and ethanol groups were measured gravimetrically and were statistically compared. In comonomer-organic solvent mixtures, the percentage of solvent retained in acetone and ethanol-based mixtures increased significantly with hydrophilicity of the comonomer blends (P < 0.05). In resin-organic solvent-water mixtures, significantly more solvent and water were retained in the ethanol-based mixtures (P < 0.0001), when compared to acetone-based mixtures after 60s of air-drying. TEM revealed residual water being trapped as droplets in resin films containing acetone and water. Water-filled channels were seen along the film periphery of all groups and throughout the entire resin films containing ethanol and water. The addition of water to comonomer-ethanol mixtures results in increased retention of both ethanol and water because both solvents can hydrogen bond to the monomers.     

Study of water sorption,solubility and modulus of elasticity of light-cured dimethacrylate-based dental resins

Polydimethacrylate resins were prepared by photopolymerization of Bis-GMA, TEGDMA, UDMA or Bis-EMA (4) monomer, initiated by camphoroquinone/N,N-dimethylaminoethyl methacrylate system. The study of physical properties of these resins showed that TEGDMA seems to create the most dense polymer network, which however is the most flexible (0.74GPa), absorbs the highest amount of water (6.33 wt%) and releases the lowest amount of unreacted monomer (2.41 microg/mm(3)). UDMA and Bis-EMA (4) create more rigid networks, which absorb lower water and release higher unreacted monomer than TEGDMA. Bis-EMA (4) absorbs the lowest water amount (1.79 wt%) and releases the highest amount of unreacted monomer (14.21 microg/mm(3)). Bis-GMA leads to the formation of the most rigid network (1.43 GPa), which absorbs lower water than the resin made by TEGDMA but higher than the resin made by UDMA and Bis-EMA (4). Copolymers of Bis-GMA with the other monomers were also prepared, using various monomer combinations and molar ratios. Copolymers Bis-GMA/TEGDMA (50/50 and 70/30 wt%) showed significantly higher values for Young's modulus (1.83 and 1.78 GPa) than those predicted by the linear dependence of the values on the copolymer composition. Gradual replacement of TEGDMA with UDMA or/and Bis-EMA (4) in copolymerization with Bis-GMA resulted in more flexible resins with lower water sorption and higher solubility values, depending on the TEGDMA content.     

Water-sorption kinetics of dental polymeric resin under tensile stressing conditions.

Water sorption tests were conducted on unfilled poly(methyl methacrylate) samples in distilled water at 5, 37, and 60 degrees C under three different tensile stress ratios (sigma appl/sigma ys = 0%, 5%, and 10%). Each sample was placed in a modified Hoffman open-side tubing clamp and subjected to four-point bending at pre-determined stress level for 1 day, 3 days, 1 week, 2 weeks, and 4 weeks. Water sorption was measured by weight change calculations, without accounting for any weight loss due to solubility of uncured monomer. A generalized diffusion equation can be used to express both stress-free and stress conditions; D = D0exp[-E (sigma)/kT]. It was found that the activation energy for water sorption diffusion was linearly related to applied stress ratios; i.e., E = 1.15 sigma appl/sigma ys + 10.76 (kJ/mol), with the correlation coefficient r = 0.97. Since the proportional pre-exponential constant, D0, is independent of temperature, it is speculated that the loading percentage of reinforcing filler elements in composite resin materials can be related to this constant.     

Trifunctional methacrylate monomers and their photocured composites with reduced curing shrinkage,water sorption,and water solubility

Novel trifunctional methacrylates, 1,1,1-tris[4-(2'-acetoxy-3'-methacryloyloxypropoxy)phenyl]ethane (Ac-THMPE) and 1,1,1-tris[4-(2'-acetoxy-3'-methacryloyloxypropoxy)phenyl]methane (Ac-THMPM), have been prepared by acetylation of the hydrophilic hydroxyl groups of 1,1,1-tris[4-(2'-hydroxy-3'-methacryloyloxypropoxy)phenyl]ethane (THMPE) and 1,1,1-tris[4-(2'-hydroxy-3'-methacryloyloxypropoxy)phenyl]methane (THMPM), respectively, for use as dental monomers. Decrease in monomer viscosity resulted from the acetylation. Unfilled resins and composites based on the four trimethacrylates were evaluated for photopolymerization conversion, water contact angle, and curing shrinkage. Water sorption, water solubility, and flexural strength of the composites prepared from the trimethacrylate were measured. Those data obtained for the trimethacrylate-containing materials were compared with control 2,2-bis[4-(2'-hydroxy-3'-methacryloyloxypropoxy)phenyl]propane (bis-GMA)-based materials in order to evaluate the applicability of the trimethacrylates as dental monomers. The acetylation of hydroxyl groups appeared to be an effective method to decrease curing shrinkage, water sorption, and water solubility of the dental composites. When compared with the bis-GMA composite, the composites based on Ac-THMPM and Ac-THMPM showed much lower curing shrinkage, water sorption, and water solubility, along with approximately equal conversion and flexural strength.     

Water sorption, solubility and effect of post-curing of glass fibre reinforced polymers.

Different polymer matrices are used for dental glass fibre composites. The aims of this study were to determine water sorption and solubility of glass fibre composites with different polymer matrices. In addition, the effect of post-curing of matrix polymers with heat on the water sorption and solubility values was investigated. Commercial one-phase and two-phase (powder-liquid) monomer systems were used in polymer matrix of E-glass fibre composite. Rhombic unreinforced and fibre reinforced test specimens were polymerized by autopolymerization or by light only, or additionally post-cured with heat. Water sorption and solubility determination method was based on ISO/DIS 1567-1997 draft for international standard with 7 d immersion time. In addition, water sorption was measured at second time for 30 d immersion time to determine saturation time of test specimens by water. Five test specimens of unreinforced polymer and reinforced polymer were tested and the quantity of fibres was determined by combustion analysis. Water sorption values of different brands of polymer matrices ranged from 0.9 to 8.3 wt% (P < 0.001, ANOVA). High sorption values were explained by microscopic voids in the polymer matrix and by composition of polymer matrix. Solubility values ranged from 0.02 to 2.5 wt% (P < 0.001, ANOVA). Generally, fibre inclusion and post-curing of polymer matrix reduced water sorption and solubility. The results of this study suggest that the water sorption and solubility of fibre composites varies according to the brand of polymer matrix and homogenity of polymer matrix. Water sorption of polymer matrix might influence hydrolytic stability of polymer-glass fibre composite.     

Water sorption characteristics of light-cured dental resins and composites based on Bis-EMA/PCDMA

The water uptake characteristics of resins and composites based on an ethoxylated bisphenol A glycol dimethacrylate (Bis-EMA) and a polycarbonate dimethacrylate (PCDMA) were studied in detail. Polydimethacrylate resins were prepared by photopolymerization of the neat monomers and mixtures of them with various weight ratios, using the camphoroquinone/N,N-dimethylaminoethyl methacrylate system as initiator, while the composites were prepared from the light-curing of commercial samples (Sculpt-It and Alert). Water sorption/desorption was examined both in equilibrium and dynamic conditions in two adjacent sorption-desorption cycles. The equilibrium water uptake from all resins was very small with a trend to increase as the amount of PCDMA was increased. The inverse effect was observed in the solubility values. The composites studied exhibited also very low water uptake values in comparison to other composite materials reported in the literature. It was also observed that the equilibrium uptake decreased with increasing filler loading. Slightly larger equilibrium water uptake and much smaller solubility values were obtained during the second sorption-desorption cycle in comparison to the first one. Concerning the sorption rate data, it was observed that the resin materials followed Fickian diffusion during almost the whole sorption or desorption curve, while the composites showed this behavior until only M(t)/M( infinity ) congruent with 0.5. The diffusion coefficients calculated for the resins were larger than those of the composites and always higher during desorption compared to sorption. The values of the diffusion coefficients for both resins and composites were in the same order of magnitude with the values of the corresponding materials reported in the literature.     

Synthesis and characterization of N-isopropyl, N-methacryloxyethyl methacrylamide as a possible dental resin

In this study, N-isopropyl, N-methacryloxyethyl methacrylamide (NIMM) is proposed as a possible reactive diluent in place of triethylene glycol dimethacrylate (TEGDMA) for dental resin mixtures. Real-time infrared spectroscopy was used to monitor the double-bond conversion as a function of irradiation time, and mixtures of 50/50wt% bis-GMA/NIMM were found to reach final conversions (95%) that were 1.5 times greater than bis-GMA/TEGDMA (65%) under visible light irradiation. In addition, samples cured to these conversions were tested with dynamic mechanical analysis. The bis-GMA/NIMM mixture (100% converted) was found to have a higher glass transition temperature and modulus at body temperature than a comparable bis-GMA/TEGDMA mixture (60% converted). Finally, the water sorption and solubility of bis-GMA/NIMM were determined to be higher than the bisGMA/TEGDMA comparison, but the values were still within the range of the ISO 9000s standard. These results suggest that bis-GMA/NIMM mixtures are a viable alternative to conventional dental resins since a greater degree of monomer conversion is obtainable without sacrificing physical and mechanical properties.     

NIR-spectroscopic investigation of water sorption characteristics of dental resins and composites.

A near infrared (NIR) method using the 5200 cm(-1) absorption of water has been employed to examine water absorbed in photopolymerized dental resins and composites in the form of 0.01-cm- to 0.15-cm-thick specimens. The concentration, c [mol L(-1)], of absorbed water in specimens of thickness t [cm] was calculated by means of Beer's law, A = e ct. A is the NIR absorbance and e is the absorptivity of absorbed water. e depends on the environment of the water molecule and it is necessary to estimate e for water in each material. Water sorption was determined gravimetrically and correlated to the absorbance in the NIR spectrum. Once the relationship between e and water content was known for a material, water sorption was determined rapidly on very thin specimens for faster equilibration. Where dissolution of the specimen occurred, the solubility behavior of the specimen was evaluated from a comparison of NIR and gravimetric measurements. The NIR absorptivity, e, of water absorbed in a polymeric medium was found to be inversely related to the degree of hydrophilicity and hydrogen bonding capability of the polymer. The presence of water clusters in a polyethylene oxide methacrylate polymer was inferred from convex-up curvature in the plot of e vs. water content.     

Sorption kinetics of ethanol/water solution by dimethacrylate-based dental resins and resin composites

In the present investigation the sorption-desorption kinetics of 75 vol % ethanol/water solution by dimethacrylate-based dental resins and resin composites was studied in detail. The resins examined were made by light-curing of bisphenol A glycol dimethacrylate (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA), urethane dimethacrylate (UDMA), bisphenol A ethoxylated dimethacrylate (Bis-EMA), and mixtures of these monomers. The resin composites were prepared from two commercial light-cured restorative materials (Z100 MP and Filtek Z250), the resin matrix of which is based on copolymers of the above-mentioned monomers. Ethanol/water sorption/desorption was examined in both equilibrium and dynamic conditions in two adjacent sorption-desorption cycles. For all the materials studied, it was found that the amount of ethanol/water sorbed or desorbed was always larger than the corresponding one reported in literature in case of water immersion. It was also observed that the chemical structure of the monomers used for the preparation of the resins directly affects the amount of solvent sorbed or desorbed, as well as sorption kinetics, while desorption rate was nearly unaffected. In the case of composites studied, it seems that the sorption/desorption process is not influenced much by the presence of filler. Furthermore, diffusion coefficients calculated for the resins were larger than those of the composites and were always higher during desorption than during sorption. Finally, an interesting finding concerning the rate of ethanol/water sorption was that all resins and composites followed Fickian diffusion kinetics during almost the whole sorption curve; however, during desorption the experimental data were overestimated by the theoretical model. Instead, it was found that a dual diffusion-relaxation model was able to accurately predict experimental data during the whole desorption curve. Kinetic relaxation parameters, together with diffusion coefficients, are reported for all resins and composites.     

Preparation of new low viscosity urethane dimethacrylates for dental composites

Abstract

Urethane-based polymers are very biocompatible in many biomedical applications. This study reports the synthesis of new low viscosity urethane dimethacrylates and evaluation of the formed composites. New urethane dimethacrylates were synthesized and formulated to form the composites. Compressive strength was used as a primary tool to evaluate the mechanical property. Water sorption, solubility, degree of conversion, flexural strengths and shrinkage were also investigated. It was found that liquid urethane dimethacrylates could be synthesized by derivatizing isocyanates with asymmetrical methacrylates. By eliminating diluent triethylene glycol dimethacrylate, the new urethane dimethacrylate-composed composites showed significantly higher modulus, lower water sorption, lower solubility and lower shrinkage, as compared to commercial BisGMA- and UDMA-based ones.     

Use of electrochemical impedance spectroscopy to evaluate resin-dentin bonds

Electrochemical impedance spectroscopy (EIS) offers a potentially nondestructive quantitative method for measuring the stability of resin films and or resin-bonded dentin over time. The purpose of this study was to measure the electrical impedance of five experimental dental adhesives of increasing hydrophicities as 30-microm films and as resin-bonded coatings on acid-etched dentin. Resin films or resin-coated dentin disks were placed in U-shaped chambers containing pairs of Ag-AgCl electrodes in 0.1M KCl. Electrical impedance spectra were run at day 0, 1, 7, 14, and 21 days. All resin films and resin-bonded dentin showed increases in capacitance during the first day of storage in electrolyte. This was usually associated with an increase in the pore resistance of the resins. Generally, resin-bonded dentin gave lower impedance values than their respective resins (resins 1-4) but solvated resin 5 bonded to water-saturated dentin gave higher capacitance and impedance values than resin 5 films. However, solvated resin 5 films gave higher impedance values than resin 5-bonded dentin. This behavior was confirmed by TEM examinations of silver uptake into films of neat resin 5 vs. ethanol-solvated resin 5, where water tree-like structures seen in the former were not seen in the latter. EIS is useful in examining changes in the capacitance and electrical impedance of very hydrophilic, ionic methacrylate resins. Its utility in detecting degradation in resin-bonded dentin interfaces remains to be determined in longer term studies.     

Mechanical and antibacterial properties of benzothiazole-based dental resin materials

A synthesized benzothiazole containing mono-methacrylate monomer BTTMA was incorporated into Bis-GMA/TEGDMA dental resin system with a series of mass concentration from 5 to 30 wt.% as an antibacterial agent. The influence of BTTMA on physicochemical properties of dental resin system, such as double bond conversion (DC), volumetric shrinkage (VS), flexural strength (FS) and modulus (FM), water sorption (WS) and solubility (SL) were investigated. Direct contact testing and agar diffusion testing were used to evaluate the antibacterial activity of BTTMA containing dental resin. The results showed that BTTMA could endow dental resin with significant antibacterial activity when its concentration reached a certain amount (20 wt.%), and the antibacterial activity of BTTMA containing dental resin was mainly attributed to the immobilized BTTMA instead of the unreacted leachable BTTMA. BTTMA had no negative effect on physicochemical properties of dental resin, and even some BTTMA containing dental resins had advantages like higher DC, lower VS and WS when compared with control resin. Therefore, BTTMA could be considered as a suitable antibacterial agent in dental material, but much more researches concerned about biocompatibility should be done in future to prove whether it could be applied in clinic.     

Effect of resin hydrophilicity and water storage on resin strength

This study evaluated the change in the ultimate tensile strength (UTS) of five polymerised resin blends of increasing hydrophilicity, after ageing in distilled water or silicon oil. Resin blocks were prepared from each resin blend by dispensing the uncured resin into a flexible, embedding mould, containing multiple cavities. The resins were polymerised in the moulds under nitrogen at 551.6 kPa and light-activated at 125 degrees C for 10 min. After dry ageing for 24 h at 37 degrees C, the middle third of each resin specimen was trimmed into an 'I' shape. Fifteen control specimens were randomly selected from each resin blend for baseline UTS evaluation. The UTS of the experimental specimens were determined after 1, 3, 6 and 12 months of ageing in water or oil. The UTS of each group of resins at different storage periods in water or oil were analysed using the Friedman multiple ANOVA on ranks and Dunn's multiple comparison tests at 95% confidence level. Significant reduction (p < 0.01) in UTS was observed in Groups II-V resins after 12-month storage in water, while the most hydrophobic Group I resin showed no significant change (p > 0.05) in the same period. The percentage reduction in UTS increased with the hydrophilicity of the resin blends. Long-term water storage of hydrophilic resin blends such as those employed in dentine adhesives, resulted in a marked reduction in their mechanical strength that may compromise the durability of resin-dentine bonds.     

Physical Properties of a Hybrid and a Nanohybrid Dental Light-Cured Resin Composite

This work was aimed at the study of some physical properties of two current light-cured dental resin composites, Rok (hybrid) and Ice (nanohydrid). As filler they both contain strontium aluminosilicate particles, however, with different size distribution, 40 nm–2.5 μm for Rok and 10 nm–1 μm for Ice. The resin matrix of Rok consists of UDMA, that of Ice of UDMA, Bis-EMA and TEGDMA. Degree of conversion was determined by FT-IR analysis. The flexural strength and modulus were measured using a three-point bending set-up according to the ISO-4049 specification. Sorption, solubility and volumetric change were measured after storage of composites in water or ethanol/water (75 vol%) for 1 day, 7 or 30 days. Thermogravimetric analysis was performed in air and nitrogen atmosphere from 30 to 700°C. Surface roughness and morphology of the composites was studied by atomic force microscopy (AFM). The degree of conversion was found to be 56.9% for Rok and 61.0% for Ice. The flexural strength of Rok does not significantly differ from that of Ice, while the flexural modulus of Rok is higher than that of Ice. The flexural strengths of Rok and Ice did not show any significant change after immersion in water or ethanol solution for 30 days. The flexural modulus of Rok and Ice did not show any significant change either after immersion in water for 30 days, while it decreased significantly, even after 1 day immersion, in ethanol solution. Ice sorbed a higher amount of water and ethanol solution than Rok and showed a higher volume increase. Thermogravimetric analysis showed that Rok contains about 80 wt% inorganic filler and Ice about 75 wt%.     

Sorption and solubility testing of orthodontic bonding cements in different solutions

To evaluate and compare the solubility and sorption of orthodontic bonding cements after immersion in different solutions, five different cements were used: a fluoride-containing resin composite, a light-cured glass ionomer cement, a light-cured resin composite, a paste-paste chemically cured resin composite, and a liquid-paste chemically cured resin composite. Five different solutions were employed: distilled water, artificial saliva, an alcohol-free mouthrinse solution (Orthokin), a 5% alcohol mouthrinse solution (Perioaid), and a 75% ethanol/water solution. Five disc specimens (15 mm x 0.85 mm) were used for each experimental condition. Materials were handled following manufacturers' instructions and were ground wet with silicon carbide paper. Solubility and sorption of the materials were calculated by means of weighing the samples before and after immersion and desiccation. Data were analyzed by two-way ANOVA and Student-Newman-Keuls test (p < 0.05). The light-cured glass ionomer cement showed the lowest solubility and the highest sorption values. When using alcohol-containing solutions as storage media, solubility of the paste-paste chemically cured resin composite increased, and sorption values for the tested chemically cured resin composites were also increased. The use of alcohol-free mouthrinses does not affect sorption and solubility of orthodontic cements. The chemically cured (paste-paste) composite resin cement, requiring a mixing procedure, was the most affected by immersion in alcohol-containing solutions.     

三种义齿软衬材料吸水性和溶解性的实验研究

我们对自凝水凝胶、自凝型丙烯酸酯和SDG－A硅橡胶三种义齿软衬材料进行吸水性和溶解性的实验探讨。采用的方法是将各材料制成直径50mm,厚1mm,表面平整光滑的园子,干燥24h后称重（m1）。再分别浸在人工唾液和蒸馏水溶液中保持7d和28d,称湿重（m2）,继续干燥后称重（m3）,最后计算材料的吸水值、吸水率和溶解率,统计学分析处理。结果显示：在人工唾液中7d和28d的吸水率,水凝胶为28.62%和24.96%,自凝型丙烯酸酯为1.89%和1.65%,SDG－A硅橡胶为0.25%和0.29%;溶解率分别为0.56%和0.51%,0.74%和0.83%,以及0.10%和0.12%。在蒸馏水中7d和28d的吸水率,水凝胶为30.15％和27.85％,自凝型丙烯酸酯为3.64％和6.17％,SDG－A硅橡胶为0.83％和0.98％;溶解率分别为0.79%和1.16%,0.86％和1.01％,以及0.10％和0.14％。结论是三种义齿软衬材料的吸水率大小依次为水凝胶＞丙烯酸酯＞硅橡胶。丙烯酸树脂由于含有一定量的增塑剂,其溶解率高于其他两种材料;浸泡溶液中增加离子成份可能对材料的吸水性能和溶解性能都有不同程度的影响;水凝胶材料的高吸水性能对临床实际意义还有等进一步研究。     

Water absorption characteristics of dental microfine composite filling materials: II. Experimental materials

Water absorption characteristics have been studied in terms of diffusion coefficient equilibrium uptake, and solubility as a function of the volume loading of pyrolytic silica filler, for two different resins. Equilibrium uptake decreased with filler loading, but if calculated on the original volume of monomer present gave consistent values for each resin. Triethylene glycol dimethacrylate based materials had much higher water uptake and diffusion coefficients than the urethane dimethacrylate resins. Furthermore the former exhibited higher concentration dependance of the diffusion coefficient. Diffusion coefficients were sensibly independent of filler loading.