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PubMed2006

Aromatic resin characterisation by gas chromatography-mass spectrometry. Raw and archaeological materials.

An analytical procedure based on alkaline hydrolysis, solvent extraction and trimethyl-silylation followed by gas chromatography-mass spectrometry (GC-MS) analysis was used to study the chemical composition of benzoe and storax resins, water-insoluble exudates of trees of the Styrax and Liquidambar genus. They are chemically characterised by having aromatic acids, alcohols and esters as their main components and are thus known as aromatic and/or balsamic resins. This analytical procedure allowed us to characterise the main components of the two resins and, even though cinnamic acid is the main component of both the resins, the presence of other characteristic aromatic compounds and triterpenes permitted us to distinguish between the two materials. All the compounds identified in benzoe resin were detected in an archaeological organic residue from an Egyptian ceramic censer (fifth to seventh centuries a.d.), thus proving that this resin was used as one of the components of the mixture of organic materials burned as incense. These results provide the first chemical evidence of the presence of benzoe resin in an archaeological material from Mediterranean area.

Archaeology↗

PubMed2006

Preparative separation of vitexin and isovitexin from pigeonpea extracts with macroporous resins.

Vitexin and isovitexin are a pair of isomeric compounds known as the major constituents in pigeonpea leaves and possess various pharmacological activities. In the present study, the preparative separation of vitexin and isovitexin with macroporous resins (Nankai Hecheng S & T, Tianjin, China) was studied. The performance and adsorption characteristics of eight macroporous resins including ADS-5, ADS-7, ADS-8, ADS-11, ADS-17, ADS-21, ADS-31 and ADS-F8 have been evaluated. The research results indicate that ADS-5 resin is most appropriate for the separation of vitexin and isovitexin. Langmuir and Freundlich isotherms were used to describe the interactions between solutes and resin at different temperatures, and the equilibrium experimental data were well fitted to the two isotherms. Column packed with ADS-5 resin was used to perform dynamic adsorption and desorption tests to optimize the separation process. The optimum parameters for adsorption were as follows: the concentration of vitexin and isovitexin in sample solution: 0.22 and 0.40mg/mL, respectively, processing volume: 3 BV, flow rate: 1mL/min, pH 4, temperature: 25 degrees C; for desorption: ethanol-water (40:60, v/v), 5 BV as an eluent, flow rate: 1mL/min. After one run treatment with ADS-5 resin, the contents of vitexin and isovitexin were increased 4.07-fold and 11.52-fold from 0.86%, 1.53% to 3.50% and 17.63%, the recovery yields were 65.03% and 73.99%, respectively. In conclusion, the preparative separation of vitexin and isovitexin can be easily and effectively achieved via adsorption and desorption on ADS-5 resin, and the method can be referenced for the separation of other flavone C-glucosides from herbal materials.

Adsorption↗

PubMed2005

Effects of polymerization shrinkage on the interfacial stress at resin-metal joint in denture-base: a non-linear FE stress analysis.

OBJECTIVES: The purpose of this study was to investigate the effects of polymerization shrinkage on stress at the interface between resin and metal in removable dentures. METHODS: Three-dimensional finite element models of a denture-base were studied, which consisted of acrylic occlusal rims with different heights and metal frameworks. A relaxation modulus of 1.5 GPa for the resin and a Young's modulus of 220 GPa for the metal were used as the material properties. Each model was constrained at the edge of the framework on the palatal vault. Surface-to-surface contact elements were used to calculate the interfacial stress in a direction perpendicular to the bond surface under a linear shrinkage ranging from 0.41 to 0.65%. The principal stress within the resin was also calculated. RESULTS: The maximum interfacial and principal stresses within the denture-base increased with resin shrinkage. Under the lowest linear shrinkage, the mean area percentages in the resin-metal joint that showed interfacial tensile stresses over 10 and 20 MPa were 63.4 and 0%, respectively. While under the highest linear shrinkage, these mean area percentages were 98.8 and 38.1%, respectively. Negligible differences in the stresses were shown by occlusal heights. SIGNIFICANCE: The polymerization shrinkage level has a significant influence on the residual stress at the resin-metal interface. Enhancement of the bond strength on the interface can reduce the failure probability at a resin-metal joint.

Acrylic Resins↗

PubMed2006

Assessing the aquatic hazard of commercial hydrocarbon resins.

Hydrocarbon resins are used to modify polymer products to achieve desired functional properties for a diverse range of products. These complex hydrocarbon-based mixtures are typically poorly soluble in water. However, resins may leach lower-molecular-weight monomers or impurities upon contact with water, thus posing a potential hazard to the aquatic environment. The bioavailability and toxicity of leachable constituents of four solid and three liquid resins were evaluated by analyzing water-accommodated fractions prepared with each resin, using biomimetic solid phase microextraction (SPME) techniques. Liquid resins exhibited concentrations of bioavailable constituents that were sufficiently elevated to cause acute toxicity to the aquatic organism Daphnia magna. All solid resins exhibited lower bioavailable concentrations of leachable constituents that were unlikely to pose an aquatic toxicity concern. Since observed toxicity of both resin types was generally consistent with bioavailable concentrations determined using SPME fiber measurements, it is concluded that this approach provides a convenient in vitro screening tool that can help reduce the use of animal testing in environmental hazard assessment of complex hydrocarbon-based substances.

Animal Testing Alternatives↗

PubMed2005

Thermographic investigation of contemporary resin-containing dental materials.

OBJECTIVES: To measure the temperature rise induced during visible light curing of modern resin-containing dental materials and the effect of dentine sections in reducing this temperature rise. METHODS: A variety of newly introduced resin-containing materials were investigated, including flowable, packable and conventional hybrid composites, as well as a compomer and a resin modified glass ionomer material. The resin was packed into polytetrafluoroethylene (PTFE) moulds and cured for 40s. Temperature rises on the undersurface of the curing resin were measured using the Thermovision 900 infra-red scanning system. In the second part of the study, extracted, caries free teeth were sectioned into dentine disks of three thicknesses (0.7, 1.4 and 1.9 mm). Composite samples were overlaid by the disks and the insulating effect of dentine measured. RESULTS: The maximum temperature increases were: 43.1 degrees C (flowable composite), 32.8 degrees C (conventional composite), 32.8 degrees C (RMGI), 23.3 degrees C (compomer) and 22.4 degrees C (packable composite). CONCLUSIONS: There was a quantifiable amount of heat generated in resin-containing material during light curing. Dentine sections were good thermal insulators that significantly reduced temperature rises associated with resin composite photocuring.

Analysis of Variance↗

PubMed2005

The effect of a layer of resin luting agent on the biaxial flexure strength of two all-ceramic systems.

STATEMENT OF PROBLEM: The influence of a layer of resin luting agent on the longevity of glass-ceramic crowns has been demonstrated in some laboratory and clinical studies. The mechanisms of glass-ceramic crown failure and the influence of the resin luting agent layer are still not clearly understood. PURPOSE: The objectives of this study were to examine the difference in biaxial flexure strength between 2 glass-ceramic dental materials and to examine the influence of a layer of resin luting agent on the characteristic strength of these materials. MATERIAL AND METHODS: Thirty-seven disks, 15 mm x 1.5 mm, each of IPS Empress and IPS Empress2, were fabricated according to the manufacturer's recommendations. The surface of each disk underwent acid etching and silanation. The disks from each group were arbitrarily divided into 2 subgroups. One subgroup of each material type was selected to receive a thin (approximately 0.1 mm) layer of resin luting agent (Nexus 2), whereas the other subgroups remained unaltered. Each disk was loaded, with the treated surface down, using a ball-on-ring biaxial configuration in a universal testing machine. The failure loads (N) were recorded, and the biaxial flexure strength for each disk was calculated. Characteristic Weibull parameters and a +/-95% confidence interval were determined. A 2-way analysis of variance (alpha=.05) on transformed fracture strength data was used to determine significant differences between groups. RESULTS: The Weibull characteristic strength of IPS Empress2 (213 MPa) was 75% higher than IPS Empress (122 MPa). The results also show that the application of a thin layer of resin luting agent significantly increased (P <.001) the characteristic strength of both IPS Empress and IPS Empress2 by 45.6% and 47.6%, respectively. The higher strength of the resin-coated specimens cannot be explained in terms of standard fracture mechanics alone. CONCLUSION: Results suggested that IPS Empress had significantly lower characteristic strength than IPS Empress2. A relatively thin layer of resin luting agent bonded to both IPS Empress and IPS Empress2 significantly increased the characteristic strength of the ceramics.

Aluminum Silicates↗

PubMed2005

The effect of chemical surface treatments of different denture base resins on the shear bond strength of denture repair.

STATEMENT OF PROBLEM: Fracture of a repaired denture base often occurs at the junction of the base and repair materials rather than within these materials. PURPOSE: The purpose of the study was to evaluate the shear bond strengths of 4 denture base acrylic resins following the use of 3 chemical solvents and to examine treated acrylic resin surfaces under a field emission scanning electron microscope (SEM). MATERIAL AND METHODS: Forty discs (15 mm in diameter and 3 mm thick) were fabricated for each denture base material (a conventionally molded, heat-polymerized [Meliodent, M], an injection-molded, heat-polymerized [SR-Ivocap, I], and a microwave-polymerized [Acron MC, A]) repaired with an autopolymerizing acrylic resin (Meliodent), for a total of 120 specimens, processed according to manufacturers' instructions, embedded in acrylic resin blocks, and divided into 4 groups of 10. One of the groups served as control and had no surface treatment. In the 3 experimental groups, specimen surfaces were treated with chemical etchants by immersion in acetone (ac) for 30 seconds, in methylene chloride (mc) for 30 seconds, or in MMA (mo) for 180 seconds, respectively. Then autopolymerizing acrylic resin (Meliodent) was placed on the treated surfaces using a brass ring (6 mm in diameter and 2 mm in height) to confine the material to a standardized dimension. After 24 hours of storage at 37 degrees C, the shear bond strength (MPa) of the specimens was measured in a universal testing machine. A 2-way analysis of variance and the Tukey HSD test were performed to identify significant differences (alpha=.05). The nature of the failure was noted as adhesive, cohesive, or mixed. The effect of the chemical treatments on the surface of base resins was examined under an SEM. RESULTS: Chemical treatments increased the bond strength of repair material significantly. Significant differences were found between the control and experimental groups (P<.001). In the control group, M showed the highest (16.7 MPa) bond strength, and A showed the lowest (9.4 MPa). No significant differences were detected between M (18.9 MPa) and A (19.9 MPa) with acetone treatment, or between M (19.3 MPa) and A (20.3 MPa) with methylene chloride treatment. The SEM observations showed that application of chemical etchants produced smoother surfaces than controls. CONCLUSION: Chemical treatment prior to denture base repair showed significant improvement on the bond strength of the base materials. Although the microwave-polymerized acrylic resin, A, showed the lowest shear bond strength compared to the control groups, the highest percentage increase was obtained with A after chemical treatments.

Acetone↗

PubMed2006

Impact strength and fracture morphology of denture acrylic resins.

STATEMENT OF PROBLEM: Microwave-polymerization cycles may affect the impact strength and fracture morphology of denture base acrylic resin, and the microstructural effects of these processes have not been fully determined. PURPOSE: This study evaluated the impact strength and fracture morphology of denture base acrylic resins processed by microwave energy and hot water bath. MATERIAL AND METHODS: Twenty specimens measuring 65 x 10 x 2.5 mm were fabricated from each of 4 acrylic resins processed according to the manufacturers' recommendations: Lucitone 550 (control; 9 hours at 74 degrees C); Onda Cryl (3 minutes at 360 W + 4 minutes pause + 3 minutes at 810 W); Acron MC (3 minutes at 500 W); and Vipi Wave (20 minutes at 180 W + 5 minutes at 540 W). The impact strength was evaluated in an impact testing machine using the Charpy method with a load (impact action) of 3.95 J. Mean values of impact strength were compared by Tukey honestly significant difference test (alpha = .05). Fractures were classified as brittle or intermediate. Fractographic analysis was performed for all fragments by angle analyses of crack propagation, and the microstructural morphology characterization was accomplished with scanning electron microscopy (SEM). Data from the fractography analysis were submitted to the Kruskal-Wallis test for angles and radius (alpha = .05). RESULTS: Significant differences (P < .001) were found in the impact strength for Vipi Wave and Acron MC acrylic resins, which demonstrated the lowest values (0.19 +/- 0.04 and 0.21 +/- 0.02, respectively). Most fractures were classified as brittle (Lucitone 55%; Onda Cryl 75%; Acron MC 90%; Vipi Wave 65%). Fractographic angle analysis of brittle fractures showed no differences among acrylic resins studied; however, angle values of intermediate fractures for Onda Cryl were lower in comparison with those from Lucitone 550 and Vipi Wave (P = .03). The SEM observations revealed that brittle fractures showed defined and organized crystallographic planes, whereas the intermediate fractures had a disorganized appearance. CONCLUSION: Within the limitations of this study, it was observed that impact strength in microwave-polymerized acrylic resins varies according to the period of irradiation. Acrylic resins exhibited a high number of brittle fractures, irrespective of the processing technique.

Acrylic Resins↗

PubMed2006

Influence of post-etching cleaning and connecting porcelain on the microtensile bond strength of composite resin to feldspathic porcelain.

STATEMENT OF PROBLEM: There are different methods to fabricate layered feldspathic porcelain restorations, including the refractory die technique and the hot-press technique. Standard adhesive protocol for such restorations requires etching and silanating the fitting surface of the porcelain. Variations in bond strength between porcelain and composite resin might result from the different fabrication methods for porcelain restorations. PURPOSE: The purpose of this study was to determine differences in microtensile bond strength between composite resin (used as a luting agent) and feldspathic porcelain generated from the refractory die technique using 2 different connecting porcelains and the hot-press technique. The effect of post-etching cleaning was also investigated. MATERIAL AND METHODS: Sixteen pairs of ceramic blocks (7 x 8 x 4 mm) were fabricated. Eight pairs were fabricated using feldspathic porcelain (D-B4) on refractory dies. For 4 pairs, the refractory dies were coated with a paste (Ducera Lay Connector Paste; group CON) as a connecting porcelain, and the other 4 pairs were coated with a clear translucent porcelain (CL-O; group CLO). Another 8 block pairs were fabricated using the hot-press technique (Authentic porcelain SL B00+; groups AUTH and AUTH-N). Surface conditioning of the ceramic blocks included airborne-particle abrasion followed by hydrofluoric acid etching (all groups), and post-etching cleaning with a brush/H3PO4 and ultrasonic bath immersion (cleaning not applied to group AUTH-N). All specimens were then silanated/heat dried, and blocks of the same porcelain were bonded to each other using an adhesive resin (Optibond FL) and a light-polymerizing composite resin (Z100). Specimens were stored in water for 24 hours. A nontrimming microtensile bond strength test was applied. Ten beams (0.9 x 0.9 x 8 mm) from each pair of blocks were selected for testing. Bond strength data (MPa) were analyzed with a Kruskal-Wallis test, and post hoc comparison was done using the Mann-Whitney U test (alpha = .05). Additional specimens (1 block per group) were also evaluated for the effect of conditioning steps and mode of fracture using optical microscopy and scanning electron microscopy (SEM) analysis. RESULTS: The mean microtensile bond strengths of CLO and AUTH groups were not significantly different from one another at 46.3 and 49.7 MPa, respectively. For both CON and AUTH-N groups, the mean bond strengths at 37.9 MPa and 24.1 MPa, respectively, were significantly different (P < .05) from the other 3 groups. Optical microscopy revealed a significant amount of white residue for all groups as a result of hydrofluoric etching. Cleaning with a microbrush and 37.5% phosphoric acid for 1 minute resulted in the removal of the crystalline debris. The SEM analysis of specimens cleaned by phosphoric acid brushing alone revealed microscopic deposits still contaminating the etched surface; those were efficiently removed after ultrasonic cleaning. The SEM analysis of fractured beams demonstrated a trend for more mixed-type failure in CON and AUTH-N specimens involving both the composite resin and the surface of the porcelain, whereas CLO and AUTH fractured surfaces were primarily confined to the composite resin. CONCLUSIONS: Increased resin bond strength to refractory-generated porcelain is obtained with CLO as the connecting porcelain compared to the CON paste. The AUTH porcelain exhibited the highest mean bond strength, but omission of post-etching cleaning resulted in the lowest bond strength.

Acid Etching, Dental↗

PubMed1991

Resin-bonded fixed partial dentures: a recall study.

A clinical recall program was initiated at the University of Minnesota to evaluate the longevity and factors affecting longevity of resin-bonded fixed partial dentures (FPDs). Of the 49 resin-bonded FPDs evaluated in the clinic, 43 were acid-etched metal, resin-bonded FPDs, four were combinations of resin-bonded and conventional FPDs, and two were composite resin pontics. None of the combination FPDs and one of the two composite resin pontics were judged as failed at the examination. Of the 43 acid-etched metal resin-bonded FPDs, 15 were found to be debonded (failure rate = 34.9%). The average length of service for the 43 FPDs was 47.3 months. The average time of placement to debondment was 33 months for the 15 debonded FPDs. The failure rate for maxillary FPDs and FPDs with two retainers were significantly lower than the failure rate for mandibular FPDs and FPDs with more than two retainers (p greater than 0.05). The clinical significance of the present study was discussed.

Adolescent↗

PubMed1978

The strength of multilayer and repaired composite resin.

Composite resin surfaces that formed against a plastic matrix or that polymerized while exposed to air were excellent substrates for the adhesion of new resin. Samples formed by the addition of composite resin to a cut surface had a tensile strength of one half of the cohesive strength of the resin. Coating the cut surface with a thin layer of unfilled resin enhanced bonding of the second composite resin layer. The use of a thin layer of unfilled catalyst resin as a bonding agent caused the most rapid development of strength and the greatest strength in samples tested after 7 days.

Adhesiveness↗

PubMed1978

Dimensional and occlusal changes in fluid resin dentures.

This study evaluated complete dentures processed with fluid acrylic resins. The dentures were constructed with the aid of a new flask and modified spruing procedures, with the teeth immobilized in the hydrocolloid mold, and with slight mechanical vibration provided during the pouring of the resin. The fluid resin dentures were compared with the dentures constructed by the compression-molding technique and processed with heat-curing acrylic resin. The results indicate that the fluid resin dentures underwent more processing shrinkage (0.617%) than the conventionally processed dentures (0.377%). However, the fluid resin dentures seemed to function as well as the heat-cured dentures. The excessive reduction in the vertical dimension of the occlusion usually observed with fluid resin dentures was minimized; the average cusp height reduction was -0.089 mm. Individual tooth movement, voids, visible porosity, and other surface deficiencies were eliminated.

Acrylic Resins↗

PubMed1996

Color stability: denture base resins processed with the microwave method.

Several quick heat-cured denture base resin systems and microwave processing resins have been introduced to provide easier and faster processing. The microwave processing method is the fastest of the heat-cured processing methods. Conventional acrylic resins processed with the microwave method seem to possess adequate physical properties, and one study indicated that a microwave acrylic resin was reasonably color stable under conditions of accelerated aging, although manufacturers do not recommend using them for microwave processing. The purpose of this study was to evaluate the color stability of seven conventional and one microwave heat-cured denture base materials processed with the microwave method. The samples were subjected to conditions of accelerated aging to test for color stability. The color stability was quantitatively measured and color measurements were made before weathering and at 300, 600, and 900 hours. The mean color change for each sample group was statistically analyzed with polynomial regression to determine the pattern of color change over time. The differences in color change for the acrylic resins were significant for all materials, but the color change for Lucitone Hy-pro was not noticeable on visual examination. The results of this study revealed that color changes occurred after accelerated aging in heat-cured denture base resins and Acron GC microwave acrylic resins processed with the microwave method. Hy-pro and TruTone materials exhibited the least color change; Hy-pro material was the most color stable material.

Acrylic Resins↗

PubMed1997

Effects of chemical disinfectants on the surface characteristics and color of denture resins.

PURPOSE: Because dentures are disinfected repeatedly and for various amounts of time, it was of clinical interest to determine whether chemical disinfectants altered the surface texture or inherent color. MATERIAL AND METHODS: Five chemical disinfectants (Clorox, Banicide, Cidex-7, Biocide, and Multicide) in combination with five denture resins (Dentsply reline material, Hygenic HyFlo, Hygenic Perm, Lucitone 199, and Triad VLC reline resin) were evaluated at four different times of immersion (10 minutes, 30 minutes, 24 hours, and 7 days). Changes from baseline for surface roughness and color were recorded. Surface roughness data were recorded with a surface analyzer. Color data in CIE L*a*b* color space were measured with a colorimeter. Data were analyzed with repeated-measures analysis of variance and single-factor analysis of variance. RESULTS: Although statistical differences were demonstrated among disinfectants and resins for both measured parameters, the magnitudes of change in color and roughness was most often clinically insignificant. CONCLUSIONS: One disinfectant (Multicide) cannot be used on all five resins, and the remaining four disinfectants can be used on any of the five resins for up to a period of 30 minutes. All resins tested can be immersed in the four remaining disinfectants for up to 30 minutes without appreciable alteration to surface texture or color. Lucitone 199 resin can be immersed in any of the four disinfectants for up to 7 days without perceivable color change.

Acrylic Resins↗

PubMed2002

Regulation of NaF release from bis-GMA/TEGDMA resin using gamma-methacryloxypropyltrimethoxysilane.

OBJECTIVES: The aim of this study was to evaluate the feasibility of regulation of NaF release from bis-GMA/TEGDMA resin using gamma-methacryloxypropyltrimethoxysilane (gamma-MPTS). METHODS: NaF powder was treated with gamma-MPTS to form a polysiloxane layer on its surface. The morphology and the composition of the NaF powder treated with gamma-MPTS were evaluated using scanning electron microscopy, infrared spectroscopy, contact angle measurement and X-ray photoelectron spectroscopy. Bis-GMA/TEGDMA resin containing 50 wt% NaF powder was prepared as a model resin and immersed in distilled water at 37 degrees C, and the amount of fluoride released from the resin was measured using a fluoride electrode. The mechanical strength in terms of diametral tensile strength before and after fluoride release was also measured, and statistically analyzed using one-way factorial ANOVA and Fisher's PLSD method. RESULTS: NaF powder was covered with hydrophobic gamma-MPTS delivered polysiloxane. A larger amount of fluoride was released at the initial stage from the resin containing NaF treated with no gamma-MPTS. However, fluoride release terminated in a relatively shorter period. In contrast, we observed a smaller amount of fluoride released for a longer period from the resin containing NaF treated with gamma-MPTS. SIGNIFICANCE: We found that gamma-MPTS treatment is useful for the regulation of NaF release from bis-GMA/TEGDMA resin. The mechanism of slow NaF release may be the formation of a hydrophobic polysiloxane layer on the surface of NaF powder and resulting slow water diffusion to NaF powder.

Analysis of Variance↗

PubMed2002

Development of a new photocurable composite resin with reduced curing shrinkage.

OBJECTIVE: This study was conducted to evaluate the potential of a novel trifunctional methacrylate as a component of a photocurable composite resin with reduced curing shrinkage. METHODS: Tris[4-(2'-hydroxy-3'-methacryloyloxypropoxy)phenyl]methane (TTEMA) was synthesized by reacting triphenylolmethane triglycidyl ether (TTE) with methacrylic acid in the presence of 4-(dimethylamino)pyridine. Photopolymerization reactivity and volumetric shrinkage of unfilled resins based on TTEMA were investigated by Fourier transform infrared spectroscopy and density measurements, respectively, and the results were compared with those for conventional dental monomers. A three-point bending test of the TTEMA-containing composite resin was carried out. RESULTS: TTEMA was easily prepared in a good yield of 89%. Unfilled resins of TTEMA and bis-GMA, each containing 40% TEGDMA, showed similar photopolymerization reactivity. TTEMA exhibited a very low photopolymerization shrinkage of 2.09%, and 3:2 TTEMA-TEGDMA unfilled resin revealed 10% lower shrinkage than a conventional bis-GMA system containing the same amount of TEGDMA. The flexural strength of a light-activated composite resin formulated with TTEMA is comparable to that of a bis-GMA composite resin under the same conditions. SIGNIFICANCE: TTEMA is promising for application as a photocurable dental monomer due to ease of synthesis, good polymerization reactivity, and relatively low curing shrinkage.

4-Aminopyridine↗

PubMed2003

Rheologic properties of flowable, conventional hybrid, and condensable composite resins.

OBJECTIVES: This research was undertaken to investigate the viscoelastic properties related to handling characteristics of five commercial flowable, two conventional hybrid and two condensable composite resins and to investigate the effect on the viscosity of filler volume fraction of composites. METHODS: A dynamic oscillatory shear test was used to evaluate the storage shear modulus (G'), loss shear modulus (G"), loss tangent (tan delta) and complex viscosity (eta(*)) of the composite resins as a function of frequency (omega)-dynamic frequency sweep test from 0.01 to 100 rad/s at 25 degrees C-using an Advanced Rheometric Expansion System. To investigate the effect on the viscosity of the composites of the filler volume fraction, the filler weight% and filler volume% were measured by the Archimedes' principle using a pyknometer. RESULTS: The complex viscosity eta(*) of flowable composites was lower than that of the hybrid composites and significant differences were observed between brands. The complex viscosity eta(*) of condensable composites was higher than that of hybrid composites. The order of complex viscosity eta(*) at omega=10 rad/s in order of decreasing viscosity was as follows, Synergy compact, P-60, Z-250, Z-100, Aeliteflo, Tetric flow, Compoglass flow, Flow it and Revolution. The complex viscosity of flowable composites, normalized with respect to Z-100, was 0.04-0.56 but Synergy compact was 2.158 times higher than that of Z-100. The patterns of the change of loss tangent (tan delta) of the composite resins with increasing frequency were significantly different between brands. Phase angles delta ranged from 30.9 to 78.1 degrees at omega=10 rad/s. All composite resins exhibit pseudoplastic behavior with increasing shear rate. The relationships between the complex shear modulus G(*), the phase angle delta, and the shear rate omega were represented by the frequency domain phasor form, G(*)(omega)=G(*)e(i delta)=G(*) 90 degree angle delta. Only a weak relationship was found between filler volume% and the viscosity of the composite resins. SIGNIFICANCE: This investigation shows that the viscoelasticity of composites in the same class is significantly different between brands. This rheologic property of composite resins influences the handling characteristics of the materials. The locus of frequency domain phasor plots in a complex plane is a valuable method of representing the viscoelastic properties of composite resins.

Barium Compounds↗

PubMed1999

Properties of fluoride-releasing light-activated resin cement.

OBJECTIVES: Fluoroaluminosilicate glass and poly(acrylic acid) in small water phase was incorporated into resin composite cements to reduce or prevent secondary caries around luted restorations. The purpose of this study was to investigate the physical properties and the amounts of fluoride released from four types of visible light-activated resin cements. METHODS: A powder was composed of silanized SiO2 filler and 4.5 wt.% (G-4.5), 9.5 wt.% (G-9.5) or 19.5 wt.% (G-19.5) fluoroaluminosilicate glass and 0.5 wt.% reducing agent. The 45.25 wt.% triethylene glycol dimethacrylate (TEGDMA), 45.25 wt.% 2-hydroxyethyl methacrylate (HEMA), 9 wt.% poly(acrylic acid) solution in water and 0.5 wt.% camphorquinone were contained in a liquid. The powder and liquid were mixed at a 3:1 ratio by weight and the three types of specimen disks were cured using a photo-curing lamp. The TEGDMA-based composite cement was used as control (G-0). The specimens were immersed in water at 37 degrees C for 24 h or 6 months and compressive strength (CS) and diametral tensile strength (DTS) were evaluated for the four experimental materials. Disks prepared from the four resin cements were also immersed in deionized distilled water at 37 degrees C, and the fluoride released was measured over a period of 24 weeks. RESULTS: G-9.5 specimens showed almost the same CS and DTS as G-4.5 and G-0 specimens and significantly higher values for both parameters than G-19.5 specimens after 6 months of water storage. The amount of fluoride released from the three fluoride-containing resin cements continued to increase over the entire experimental period. The fluoride release rates of G-9.5 and G-19.5 resin cements were almost the same and were significantly greater than that of the G-4.5 resin cement. SIGNIFICANCE: G-9.5 containing 9.5 wt.% fluoroaluminosilicate glass may be a clinically useful resin cement due to its favorable physical properties and fluoride release.

Analysis of Variance↗