Novel light-cured resins and composites with improved physicochemical properties.

OBJECTIVES: The aim of this study was to determine the effect of two new diluent agents (Bis-GMA analogues), at different dilution levels and filler contents on relevant physicochemical properties of several novel resins and composites containing Bis-GMA as matrix. Composites using TEGDMA as diluent were used as control. METHODS: Twenty formulations were prepared combining three monomer mixtures (Bis-GMA/TEGDMA, Bis-GMA/CH(3) Bis-GMA and Bis-GMA/CF(3) Bis-GMA), at three dilution levels (85/15, 10/90, 0/100) and two percentages of filler loading (silanated barium aluminosilicate glass): 0%, 10%, 35%. Preliminary rheological testing was performed in order to obtain the viscosity of the resin samples. Resins and composites were then inserted into molds and light-cured (500mW/cm(2)). The properties evaluated were: (1) homogeneity of curing (HC), using FTIR or Vickers microindentor, (2) microhardness, by a Vickers microindentor, (3) depths of cure and oxygen inhibitor effect (OIE), quantified by scraping, (4) water contact angle on the materials surface, (5) water sorption and solubility, performed by the Oysaed-Ruyter method and (6) scanning electron microscopy analysis of the specimens surfaces. Data were analyzed by ANOVA and Student-Newman-Keuls tests (p<0.05). RESULTS: Materials with CH(3) Bis-GMA and CF(3) Bis-GMA exhibited less hydrophilicity, water sorption and solubility. Bis-GMA dilution induced an increase in depth of cure and promoted a higher OIE, particularly when the diluent was TEGDMA. Filler loading reduced the OIE and increased hydrophobicity of the resins. SIGNIFICANCE: CH(3) Bis-GMA may be considered as good candidate to be used as diluent because when replacing TEGDMA-induced lower hydrolytic degradation and increase in HC.     

Fabrication and evaluation of Bis-GMA/TEGDMA dental resins/composites containing nano fibrillar silicate.

OBJECTIVE: To investigate the reinforcement of Bis-GMA/TEGDMA dental resins (without conventional glass filler) and composites (with conventional glass filler) with various mass fractions of nano fibrillar silicate (FS). METHODS: Three dispersion methods were studied to separate the silanized FS as nano-scaled single crystals and uniformly distribute them into dental matrices. The photo-curing behaviors of the Bis-GMA/TEGDMA/FS resins were monitored in situ by RT-NIR to study the photopolymerization rate and the vinyl double bond conversion. Mechanical properties (flexural strength, elastic modulus and work-of-fracture) of the nano FS reinforced resins/composites were tested, and analysis of variance (ANOVA) was used for the statistical analysis of the acquired data. The morphology of nano FS and the representative fracture surfaces of its reinforced resins/composites were examined by SEM/TEM. RESULTS: Impregnation of small mass fractions (1% and 2.5%) of nano FS into Bis-GMA/TEGDMA (50/50 mass ratio) dental resins/composites improved the mechanical properties substantially. Larger mass fraction of impregnation (7.5%), however, did not further improve the mechanical properties (one way ANOVA, P>0.05) and may even reduce the mechanical properties. The high degree of separation and uniform distribution of nano FS into dental resins/composites was a challenge. Impregnation of nano FS into dental resins/composites could result in two opposite effects: a reinforcing effect due to the highly separated and uniformly distributed nano FS single crystals, or a weakening effect due to the formation of FS agglomerates/particles. SIGNIFICANCE: Uniform distribution of highly separated nano FS single crystals into dental resins/composites could significantly improve the mechanical properties of the resins/composites.     

The application of fluorinated aromatic dimethacrylates and diacrylates to light-cured composite resins. 1. Improvement of transmittance of composite

To improve the transmittance of light-cured composite resins, the matching of the refractive indices of the matrix monomer and filler were examined. Eight fluorinated aromatic dimethacrylates and diacrylates with a low refractive index were synthesized. Three of these monomers had a poor solubility to TEGDMA. The depths of cure and the other physical properties of eight experimental composites prepared from one of five fluorinated monomers, TEGDMA and UDMA were determined compared with those of the control composites prepared from Bis-GMA or Bis-MEPP/ and TEGDMA in the same ratio. These composites contained 70 wt% of silanized silica filler. The depths of cure of the experimental composites except for one were significantly greater than those of the control composites. The mechanical properties of the experimental composites were comparable to those of the control composites with a few exceptions, but the difference in the mechanical properties between these exceptional composites and the control was small. The water sorption of the experimental composites was markedly lower than that of the composite containing Bis-GMA and comparable to that of the composite containing Bis-MEPP. These five fluorinated monomers are considered useful as the matrix monomer of light-cured composite resins.     

The effect of resin matrix composition on the polymerization shrinkage and rheological properties of experimental dental composites.

OBJECTIVES: This study was undertaken to evaluate the effect of the resin matrix composition of experimental composites on their polymerization shrinkage and rheological properties. METHODS: Six experimental composites consisting of varying ratios of Bis-GMA, TEGDMA, and UDMA were made. All composites had the same amount of filler (barium-aluminum-silicate glass, 76.5 wt.%) and initiator concentrations (camphorquinone, 1.7 wt.%). To investigate the effects of different resin matrices on the polymerization shrinkage, a newly developed measurement method was used. Using a rotational rheometer, a dynamic oscillatory shear test was undertaken to evaluate the rheological properties, including the storage shear modulus (G'), loss shear modulus (G'), loss tangent (tandelta), phase angle (delta), and complex viscosity (eta*) of the experimental composites as a function of frequency (0.1-10Hz). RESULTS: The polymerization shrinkage and complex viscosity of the experimental composites ranged from 2.61 to 3.88 vol.% and from 3.8 to 181.4Pas, respectively. The experimental composite composed of 17.5% Bis-GMA and 4.4% TEGDMA showed the lowest shrinkage and highest viscosity. The composite composed of 8.7% Bis-GMA and 13.1% TEGDMA showed the highest shrinkage and lowest viscosity. With increasing TEGDMA content, the polymerization shrinkage increased but the viscosity decreased. The substitution of UDMA for TEGDMA reduced the shrinkage level but increased viscosity. There was an inverse relationship between the polymerization shrinkage and complex viscosity. All experimental composites exhibited pseudoplasticity. SIGNIFICANCE: Within the limitations of this study, resin matrix composition significantly affected the volumetric shrinkage and rheological properties of the experimental composites.     

Hydrolytic stability of experimental hydroxyapatite-filled dental composite materials.

OBJECTIVES: The purpose of this study was to analyze the behavior in water, related to mechanical properties, of experimental composites for dental restoration. METHODS: The studied materials were composed of a visible-light-curing monomer mixture (Bis-GMA and TEGDMA or HEMA) and micrometric, nanometric or a mixture of both sizes hydroxyapatite particles as a reinforcing filler. Filler particles were modified with a coupling agent (citric, hydrosuccinic, acrylic or methacrylic acid or silane). The hydrolytic stability of the evaluated materials was studied through total elution and water-uptake tests. Percent net-mass variation was daily monitored and analyzed as a function of time. Mechanical performance was examined through flexural properties and Vickers hardness. Morphological surface changes were observed with scanning electron microscopy. ANOVA statistical analysis was performed (P<0.05). RESULTS: In general, the use of HEMA instead of TEGDMA did not substantially worsen the composite quality. Dental composites containing only nanometric particles of hydroxyapatite as a filler are unsuitable for clinical performance. Midway-filled composite resins loaded with micro-HAP particles, coated with citric, acrylic or methacrylic acid displayed low percent elution and water-uptake values. Mechanical properties were similar or even superior to those measured for silane treated particles. SIGNIFICANCE: More research is needed to further improve the interaction of nano-HAP particles with the polymeric matrix, either as a single filler or, preferentially, mixed with micro-HAP, that will allow to increase the total loading of reinforcing filler and, hence, to improve the mechanical properties.     

Properties of eight methacrylated beta-cyclodextrin composite formulations.

OBJECTIVES: Methacrylated beta-cyclodextrins (MCDs) are novel candidate dental monomers if all or some of the hydroxyl groups of beta-cyclodextrin are substituted with methacrylate groups. The main objective of this study was to evaluate mechanical properties of a number of composite formulations having MCDs as novel dental comonomers. The properties determined were flexural strength (FS), volumetric shrinkage (VS), and degree of conversion (DC). METHODS: A mass fraction of 50% of MCD monomers was mixed with a mass fraction of 50% each of a series of dimethacrylate or monomethacrylate diluent comonomers to produce consistent formulations of a workable viscosity. For comparison a resin mixture of a mass fraction of 50% Bis-GMA and a mass fraction of 50% triethyleneglycol dimethacrylate (a typical dental resin mixture) was also studied. The mixtures were activated with camphorquinone and ethyl 4-dimethylamino benzoate. One part by mass of each activated resin formulation was mixed with three parts by mass of glass filler. Samples for the FS tests were prepared in (2 x 2 x 25) mm3 molds by light-curing the composites for 2 min on each side. The cured samples were immersed in 37 degrees C water for 24 h, and FS was measured with an Instron machine at a crosshead speed of 0.5 mm/min. VS was measured by a computer-controlled mercury dilatometer. DC was measured by near-infrared spectroscopy. RESULTS: The properties of the MCD-based composites depended on the kind of diluent used. With these MCD monomers, diluents of triethyleneglycol dimethacrylate, 1,10-decamethylenediol dimethacrylate, or benzyl methacrylate yielded the best composite properties. SIGNIFICANCE: Although not yet fully optimized, MCD-based composite formulations containing triethyleneglycol dimethacrylate, 1,10-decamethylenediol dimethacrylate, or benzyl methacrylate yielded flexural strength and volumetric shrinkage values were comparable to those of the Bis-GMA/triethyleneglycol dimethacrylate controls. These findings lend support for further development and evaluations of polymerizable cyclodextrin derivatives for use in dental materials.     

In vitro wear, surface roughness and hardness of propanal-containing and diacetyl-containing novel composites and copolymers based on bis-GMA analogs.

OBJECTIVE: To evaluate the effect of two additives, aldehyde or diketone, on the wear, roughness and hardness of bis-GMA-based composites/copolymers containing TEGDMA, propoxylated bis-GMA (CH(3)bis-GMA) or propoxylated fluorinated bis-GMA (CF(3)bis-GMA). METHODS: Fifteen experimental composites and 15 corresponding copolymers were prepared combining bis-GMA and TEGDMA, CH(3)bis-GMA or CF(3)bis-GMA, with aldehyde (24 mol% and 32 mol%) or diketone (24 mol% and 32 mol%) totaling 30 groups. For composites, hybrid treated filler (barium aluminosilicate glass/pyrogenic silica; 60 wt%) was added to monomer mixtures. Photopolymerization was affected by 0.2 wt% each of camphorquinone and N,N-dimethyl-p-toluidine. Wear (W) test was conducted in a toothbrushing abrasion machine (n=6) and quantified using a profilometer. Surface roughness (R) changes, before and after abrasion test, were determined using a rugosimeter. Microhardness (H) measurements were performed for dry and wet samples using a Knoop microindenter (n=6). Data were analyzed by one-way ANOVA and Tukey's test (alpha=0.05). RESULTS: Incorporation of additives led to improved W and H values for bis-GMA/TEGDMA and bis-GMA/CH(3)bis-GMA systems. Additives had no significant effect on the W and H changes of bis-GMA/CF(3)bis-GMA. With regard to R changes, additives produced decreased values for bis-GMA/CH(3)bis-GMA and bis-GMA/CF(3)bis-GMA composites. Bis-GMA/TEGDMA and bis-GMA/CH(3)bis-GMA copolymers with additives became smoother after abrasion test. SIGNIFICANCE: The findings correlate with additives ability to improve degree of conversion of some composites/copolymers thereby enhancing mechanical properties.     

Investigation of Mechanical Properties of Experimental Bis‐GMA/TEGDMA Dental Composite Resins Containing Various Mass Fractions of Silica Nanoparticles

Purpose: Mechanical properties of dental composite resins need to be improved in order to enhance their performance for applications in direct restorations. Application of nanoparticles in this field is a recent development. The aim of this study was to investigate the mechanical properties of experimental composites containing various mass fractions of silica nanoparticles. Materials and Methods: Experimental composites were composed of a visible‐light‐curing monomer mixture (70 wt% Bis‐GMA and 30 wt% TEGDMA) and silica nanoparticles of a size ranging from 20 nm to 50 nm modified with γ‐methacryloxy propyl trimethoxy silane (γ‐MPS) as reinforcing filler. The composites were classified into four groups according to their filler mass fractions ranging from 20% to 50%. Following the same preparation procedure, a conventional composite was also fabricated consisting of a mass percentage of 60% silica fillers having particle sizes ranging from 10 μm to 40 μm in the same organic matrix, which served as control. Ten specimens were prepared of each experimental group and also of the control. Fracture toughness was measured using single‐edge notched bend (SENB) specimens. Specimen fracture surfaces were mounted on aluminum stubs with carbon cement, sputter‐coated with gold and examined under scanning electron microscopy (SEM). Flexural strength was evaluated through a standard three‐point bending test and Vickers microhardness test was performed to investigate the hardness of the samples. Results: Filler mass fraction had a significant effect on composite properties. Fracture toughness, flexural strength, and hardness of composites at filler mass fraction of 40% of silica nanoparticles were (mean ± SD) 1.43 ± 0.08 MPa.m^1/2, 149.74 ± 8.14 MPa, and 62.12 ± 3.07 VHN, respectively; relevant values for composites at 50% mass fraction of silica nanoparticles were 1.38 ± 0.07 MPa.m^1/2, 122.83 ± 6.13 MPa, and 70.69 ± 3.67 VHN, respectively, all of which were significantly higher than 1.07 ± 0.06 MPa.m^1/2, 104.61 ± 8.73 MPa, and 52.14 ± 4.02 VHN of the control, respectively (Tukey's multiple comparison test; family confidence coefficient = 0.95). Measured values for composites at 20% mass fraction of silica nanoparticles were 0.94 ± 0.06 MPa.m^1/2, 103.41 ± 7.62 MPa, and 42.87 ± 2.61 VHN, respectively; relevant values for composites at 30% mass fraction of silica nanoparticles were 1.16 ± 0.07 MPa.m^1/2, 127.91 ± 7.05 MPa, and 51.78 ± 3.41 VHN, respectively. Conclusions: Reinforcement of dental composite resins with silica nanoparticles resulted in a significant increase in the evaluated mechanical properties in comparison with the conventional composite. The filler mass fraction played a critical role in determining the composite's mechanical properties.     

Effect of propionaldehyde or 2,3-butanedione additives on the mechanical properties of Bis-GMA analog-based composites

ObjectivesThe purpose of this study was to evaluate the effect of two additives, propionaldehyde/aldehyde or 2,3-butanedione/diketone, on mechanical properties of Bis-GMA-based composites containing TEGDMA, propoxylated Bis-GMA (CH₃Bis-GMA) or propoxylated fluorinated Bis-GMA (CF₃Bis-GMA).MethodsThree control composites, Bis-GMA/diluent monomer (25/75 mol%), and six test composites, Bis-GMA/diluent monomer/aldehyde or diketone (17/51/32 mol%) were prepared. All composites contained hybrid treated filler (barium aluminosilicate glass/pyrogenic silica; 60 wt%), and 0.2 wt% each of camphorquinone and N,N-dimethyl-p-toluidine. Degree of conversion (DC%), flexural strength (FS), modulus of elasticity (E), modulus of resilience (R) and diametral tensile strength (DTS) were determined. DC% (n = 3) was investigated by FT-IR. For FS and E, beam-shaped specimens (25 mm × 2 mm × 2 mm) were prepared (n = 6), stored for 7 days in 37 °C deionized water and tested on an Instron utilizing a three-point loading jig (0.5 mm/min). The R-values were obtained from the following equation: R = (FS)²/2E. For DTS, cylindrical specimens (4 mm × 8 mm) were prepared (n = 6), stored for 7 days in 37 °C deionized water and diametrically loaded on an Instron (0.5 mm/min). Data were analyzed by one-way ANOVA and Tukey's test (α = 0.05).ResultsIncorporation of additives led to an increase in DC%, FS and E for Bis-GMA/TEGDMA and Bis-GMA/CH₃Bis-GMA systems. R-values for all systems were unaffected by addition of additives. They had no significant effect on DC% or mechanical properties of Bis-GMA/CF₃Bis-GMA.SignificanceThe findings correlate with the ability of additives to improve degree of conversion of some composite systems thereby enhancing mechanical properties.     

核壳纳米纤维增强牙科树脂基体的力学性能与界面研究

目的研究PAN—PMMA核壳纳米纤维对牙科光固化树脂基体力学性能的增强效果。方法通过静电纺丝法制备PAN—PMMA核壳纳米纤维,同时将纳米纤维分别按1wt％、2wt％、3wt％和5wt％的质量比直接纺入Bis—GMA／TEGDMA光固化树脂单体制成纳米纤维树脂复合物。空白组是Bis—GMA／TEGDMA纯光固化树脂。在万能力学测试机上用三点弯曲法测试各组的弯曲强度、模量及断裂功,用SPSS软件进行统计学分析。SEM观察各组样条断面纤维与树脂界面及纤维分散状态。结果2wt％纳米纤维增强组弯曲强度和模量及断裂功较空白组分别增加了25％、74％、47％,统计学分析有显著性差异（P〈0．05）;SEM结果显示断面拔出的纤维表面粗糙,纤维分散均匀,有较好的界面形成。结论2wt％质量比的PAN—PMMA核壳纳米纤维可以提高光固化树脂基质的力学性能。     

Development of dental composite resin utilizing low-shrinking and low-viscous monomers

To lower the viscosity of composite resins, experimental composite resins were produced using low-viscosity monomer mixtures of newly developed polyfunctional acrylates, and the mechanical and physical properties of the hardened composites were investigated. Mechanical (i.e., compressive, diametral tensile, and bending) strength of a polymer obtained from one new monomer mixture without fillers was similar to that of a bis-GMA/TEGDMA (2/1 weight ratio) based polymer. As for the hardened composites, the mechanical strength of composites produced using the new monomer mixtures showed a different tendency from that of bis-GMA based composites. Further, even the viscosity of composite pastes with high filler content was markedly lower than that of bis-GMA based composites. In terms of setting shrinkage, the composites consisting of new monomer mixtures exhibited significantly smaller shrinkage than the bis-GMA based composites, and decreased with increase in filler content.     

Influence of additives on the properties of Bis-GMA/Bis-GMA analog comonomers and corresponding copolymers.

OBJECTIVES: The purpose of this study was to evaluate the effect of two additives: propionaldehyde (aldehyde) and 2,3-butanedione (diketone) on the properties of Bis-GMA diluted with TEGDMA and the synthesized Bis-GMA analogs, propoxylated Bis-GMA (CH(3)Bis-GMA) and propoxylated fluorinated Bis-GMA (CF(3)Bis-GMA). METHODS: Nine experimental comonomers were prepared combining Bis-GMA and TEGDMA, CH(3)Bis-GMA, CF(3)Bis-GMA, with aldehyde (32mol%) and diketone (32mol%). Photopolymerization was effected by using Camphorquinone (0.2wt%) and N,N-dimethyl-p-toluidine (0.2wt%). Experimental comonomer viscosity (Brookfield viscometer), polymerization shrinkage (gravimetrically), degree of conversion (FT-IR) and contact angles (contact angle goniometer) were determined. Comonomer and copolymer T(g)s (DSC and Fox equation) were also evaluated. Data were analyzed by one-way ANOVA and Tukey test (alpha=0.05). RESULTS: Bis-GMA/CH(3)Bis-GMA and Bis-GMA/CF(3)Bis-GMA with additives exhibited lower viscosities (p<0.01). Inclusion of additives into the comonomer systems did not produce significant increase in polymerization shrinkage (p>0.05). A significant increase in degree of conversion was shown for Bis-GMA/TEGDMA and Bis-GMA/CH(3)Bis-GMA with additives (p<0.01). Additives reduced contact angle and comonomer T(g) values, whereas the corresponding copolymers with additives showed an increase in T(g). SIGNIFICANCE: Use of novel comonomer systems with the addition of aldehyde and diketone functional groups would improve dental resin composite properties.     

Evaluation of highly reactive mono-methacrylates as reactive diluents for BisGMA-based dental composites

ObjectivesThis study evaluates the performance of highly reactive novel monomethacrylates characterized by various secondary moieties as reactive diluent alternatives to TEGDMA in BisGMA filled dental resins. We hypothesize that these monomers improve material properties and kinetics over TEGDMA because of their unique polymerization behavior.MethodsThe cure rates and final double bond conversion of the resins were measured using real-time FTIR spectroscopy. The glass transition temperature and storage modulus of the formed polymers were measured using dynamic mechanical analysis. Flexural modulus and flexural strength values were obtained using a three-point bending flexural test.ResultsPolymerization kinetics and polymer mechanical properties were evaluated for the novel resin composites. It was observed that upon the use of novel monomethacrylates as reactive diluents, polymerization kinetics increased by up to 3-fold accompanied by increases in the extent of cure from 5% to 13% as compared to the BisGMA/TEGDMA control. Polymer composites formed from resins of BisGMA/novel monomethacrylates exhibited comparable T_g values to the control, along with 27–37% reductions in the glass transition half widths indicating the formation of more homogeneous polymeric networks. The BisGMA/monomethacrylate formulations exhibited equivalent flexural modulus and flexural strength values relative to BisGMA/TEGDMA.SignificanceFormulations containing novel monovinyl methacrylates exhibit dramatically increased curing rates while also exhibiting superior or at least comparable composite polymer mechanical properties. Thus, these types of materials are attractive for use as reactive diluent alternatives to TEGDMA in dental formulations.     

The effect of comonomer composition, silane heating, and filler type on aqueous TEGDMA leachability in model resin composites

Experimental composites using either bisGMA/TEGDMA or UEDMA/ TEGDMA matrices, quartz or barium glass fillers, and 2 different filler silanization methods were evaluated regarding monomer leachability in distilled water. The leached amount was detected and quantified using gas chromatography. The results showed that twice as much TEGDMA is leached from a bisGMA/TEGDMA based composite than from an UEDMA/ TEGDMA based composite, when both contain 50 wt% TEGDMA. The hypothesis suggested that the higher degree of cure of UEDMA/TEGDMA based composites would be reflected in a lower monomer leaching value, and this hypothesis was supported by the findings. Whether such a correlation exists within groups of UEDMA/TEGDMA based matrices having different degrees of cure was not determined and needs to be investigated in future studies. Variables such as filler composition and silane treatment did not affect the leaching values of TEGDMA in water. That finding suggests that future studies should target differences in matrices, and that the need for considering effects of filler composition and silane treatment methods should not receive the same priority.     

Mechanical properties of visible light-cured resins reinforced with hydroxyapatite for dental restoration.

OBJECTIVES: The purpose of this study was to measure and analyze the mechanical properties of several composite materials designed for dental restoration. METHODS: The materials were composed of a visible light-curing monomer mixture (either Bis-GMA+TEGDMA or Bis-GMA+HEMA) as a matrix and hydroxyapatite (either microscopic or nanoscopic particles) as a reinforcing filler. The surface of the hydroxyapatite particles was modified by using a coupling agent (citric, malic, acrylic or methacrylic acid). Five specimens of 14 different composites were prepared for each mechanical test: flexural strength, Young's modulus and Vickers hardness. Mean values and standard deviations were calculated, and ANOVA and Student Newman Keuls multiple comparison tests were applied (P < 0.05). RESULTS: The addition of 50-60 wt% of hydroxyapatite particles to the unfilled monomer mixtures led to the increase of both Young's modulus and surface hardness of the material, while the flexural strength decreased. In general, when microscopic instead of nanoscopic hydroxyapatite was used as a reinforcing filler, mechanical properties were favored. The mechanical properties were also improved by adding citric, acrylic or methacrylic acid as a coupling agent. CONCLUSIONS: An adequate surface modification of the hydroxyapatite particles conferred enhanced mechanical properties to the final dental composite. Microscopic-hydroxyapatite particles are preferred to nanoscopic ones.     

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

ObjectivesThe purpose of this study was to characterize physicochemical properties and investigate anti-bacterial adhesion effect of dental resins containing fluorinated monomers.MethodFluorinated 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.ResultsBoth 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).SignificanceResin 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.     

Dimethacrylate monomers with varied fluorine contents and distributions.

OBJECTIVES: There are many unique properties associated with fluorinated polymers that make these materials attractive for use in the challenging oral environment. This study was devised to better define the influence of fluorine content and its structural distribution on properties of fluorinated resins and composites, especially with regard to their water-related and mechanical properties. METHODS: A series of fluorinated dimethacrylate monomers was prepared by reaction of aromatic diepoxides with fluoroalcohols and subsequent conversion of the resulting diols to the methacrylates. Composites based on monomer systems comprised of the fluorinated monomers with 1,10-decamethylene dimethacrylate and reinforced with silanized quartz filler were evaluated for conversion, water contact angle, water sorption and diametral tensile strength. RESULTS: By selection of reactants, fluorine was introduced as trifluoromethyl groups, extended fluoroalkyl pendant chains, or combinations of the two. Photopolymerization conversion among the experimental composites was generally equal to or greater than that of a conventional Bis-GMA/TEGDMA composite. While the water contact angles generally increased with fluorine content, no correlation was obtained between fluorine content and water sorption of the composites. The mechanical strength of the fluorinated composites showed a general decline with increasing fluorine content and consistent variations due to specific structural features. SIGNIFICANCE: A versatile route to fluorinated dimethacrylates with diverse structural and fluorine distribution patterns is presented. Composites from these monomers are very hydrophobic but have relatively low mechanical strength. The monomers described can be considered as useful additives to moderate the water sorption of conventional resins. However, the results of this study point to specific fluorinated resin structures that are expected to provide a more optimal balance between hydrophobicity and mechanical strength that will improve the long-term performance of dental composites.     

The effect of ceramic and porous fillers on the mechanical properties of experimental dental composites.

OBJECTIVES: The purpose of this study was to investigate the effect of ceramic fillers (containing leucite crystals) and their porosity on the mechanical properties of a new experimental dental composite in order to compare with the properties of composites containing conventional glass fillers. METHODS: In this study, experimental composites were prepared by mixing the silane-treated fillers with monomers. Experimental composites were divided into four groups according to their filler type, amount and porosity. The monomers were composed of 70% Bis-GMA and 30% TEGDMA by weight for all groups. Glass and leucite-containing-ceramic were prepared as different filler types. In order to make fillers porous, leucite-containing-ceramic fillers were treated with HF acid. Camphorquinone and DMAEMA were used as photo initiator system. Post-curing was done for all groups before mechanical testing. Degree of Conversion of composites was measured using FTIR spectroscopy. The diametral tensile strength (DTS), flexural strength and flexural modulus were measured and compared among the groups. RESULTS: The results showed that the stronger and more porous filler has a positive effect on flexural strength. Porosity of filler increased flexural strength significantly. No significant difference was found in DTS tests among the groups. Flexural modulus was affected and increased by using ceramic fillers. The type of the filler affected the DC of the composite and DC increased by post-curing. SIGNIFICANCE: Flexural strength is one of the most important properties of restorative dental materials. Higher flexural strength can be achieved by stronger and more porous fillers. Investigation into the effect of filler on dental material properties would be beneficial in the development of restorative dental material.     

Correlation between Surface Roughness and Microhardness of Experimental Composites with Varying Filler Concentration

Aim: The purpose of this study was to investigate the influence of the surface roughness on the surface microhardness of experimental composites with varying filler concentration. Materials and methods: Experimental resin composites were formulated by mixing Bis-GMA and TEGDMA in a 50/50% weight ratio and CQ/EDAB were added to make the material photosensitive. Silanized glass particles were incorporated in the resin blend in two concentrations: C50 with 50% and C75 with 75% in weight ratio. The surface roughness and the surface microhardness measurements were determined after every three finishing procedures with #280-, #600- and #1200-grit wet sandpapers, respectively. The data were analyzed statistically by Two Way ANOVA and Tukey's test, and comparisons were conducted using the Spearman's correlation test (p > 0.05). Results: The surface roughness and surface microhardness were negatively associated (r = - 0.68) and the finishing procedures of both composites resulted in harder and smoother surfaces than the initial ones. Additionally, in a smooth circumstance, the higher content of fillers has not resulted in a composite with better microhardness and smoothness. Conclusion: Finishing procedures decreased the surface roughness and consequently improved the surface microhardness of the composites evaluated. Clinical significance: Finishing and polishing procedures are effectives in reducing the surface roughness amplitude of composite materials and in improving their surface microhardness. Thus a microhardness test and any hardness evaluation must be conducted only after a properly finished and polished surface is achieved. Keywords: Laboratory research, Composite resins, Surface properties, Hardness, Roughness, Nanoparticles. How to cite this article: Munchow EA, Correa MB, Ogliari FA, Piva E, Zanchi CH. Correlation between Surface Roughness and Microhardness of Experimental Composites with Varying Filler Concentration. J Contemp Dent Pract 2012;13(3):299-304. Source of support: Nil Conflict of interest: None declared.     

Effect of filler properties in composite resins on light transmittance characteristics and color

The purpose of this investigation was to examine the effect of filler particle size and shape as well as filler content on light transmittance characteristics and color of experimental composite resins. A mixture of 30 mol% Bis-GMA and 70 mol% TEGDMA was prepared as a base monomer and to which a photoinitiator (camphorquinone) and a co-initiator (N,N-dimethylaminoethyl methacrylate) were added. Four different irregular- and spherical-shaped filler types with an average particle size of 1.9-11.1 microm were added to the mixture in three different filler contents of 20, 30, and 40 vol%. Light transmittance characteristics including light diffusion characteristics of the materials were evaluated. Color values and color differences among filler contents of the materials were also determined. Materials containing smaller and irregular-shaped fillers showed higher light transmittance and diffusion angle distribution with a sharper peak, as compared with those containing larger and spherical-shape fillers. It was also found that there was a significant correlation between the specific surface area of fillers and the color difference of the materials containing the fillers. Our results indicated that the shape of filler particles, as well as particle size and filler content, significantly affected the light transmittance characteristics--including light diffusion characteristics--and color of composite resins.