Influence of ketones on selected mechanical properties of resin composites

Effects of adding silica particles on certain properties of resin-modified glass-ionomer cement

OBJECTIVE

This study was conducted to evaluate the effect of incorporation of silica particles with different concentrations on some properties of resin-modified glass ionomer cement (RMGIC): Microleakage, compressive strength, tensile strength, water sorption, and solubility.

MATERIALS AND METHODS

Silica particle was incorporated into RMGIC powder to study its effects, one type of RMGIC (Type II visible light-cured) and three concentrations of silica particles (0.06, 0.08, and 0.1% weight) were used. One hundred and twenty specimens were fabricated for measuring microleakage, compressive strength, tensile strength, water sorption, and solubility.

STATISTICAL ANALYSIS

One-way analysis of variance and Tukey's tests were used for measuring significance between means where P ≤ 0.05.

RESULTS

RMGIC specimens without any additives showed significantly highest microleakage and lowest compressive and tensile strengths.

CONCLUSION

Silica particles added to RMGIC have the potential as a reliable restorative material with increased compressive strength, tensile strength, and water sorption but decreased microleakage and water solubility.

Improving Composite Resin Performance Through Decreasing its Viscosity by Different Methods

The aim of this work was to present the different current methods of decreasing viscosity of resin composite materials such as (using flowable composites, lowering the viscosity of the monomer mixture, heating composites and applying sonic vibration) and furnish dentists with a basis that can provide criteria for choosing one or another to suit their therapeutic requirements. The four discussed methods proved that lowering composite viscosity improves its handling and facilitates its application to cavities with complicated forms, decreasing time for procedure and improving marginal adaptation. Other properties improved by decreasing composite resin viscosity were controversial between the four methods and affected by other factors such as composite brand and light cure unit.

Water sorption of CH3- and CF3-Bis-GMA based resins with additives

OBJECTIVES

To evaluate the effect of additives on the water sorption characteristics of Bis-GMA based copolymers and composites containing TEGDMA, CH3Bis-GMA or CF3Bis-GMA.

MATERIAL AND METHODS

Fifteen experimental copolymers and corresponding composites were prepared combining Bis-GMA and TEGDMA, CH3Bis-GMA or CF3Bis-GMA, with aldehyde or diketone (24 and 32 mol%) totaling 30 groups. For composites, barium aluminosilicate glass and pyrogenic silica was added to comonomer mixtures. Photopolymerization was effected by 0.2 wt% each of camphorquinone and N,N-dimethyl-p-toluidine. Specimen densities in dry and water saturated conditions were obtained by Archimedes' method. Water sorption and desorption were evaluated in a desorption-sorption-desorption cycle. Water uptake (%WU), water desorption (%WD), equilibrium solubility (ES; µg/mm³), swelling (f) and volume increase (%V) were calculated using appropriate equations.

RESULTS

All resins with additives had increased %WU and ES. TEGDMA-containing systems presented higher %WU, %WD, ES, f and %V values, followed by resins based on CH3Bis-GMA and CF3Bis-GMA.

CONCLUSIONS

Aldehyde and diketone led to increases in the water sorption characteristics of experimental resins.

Degree of conversion and color stability of the light curing resin with new photoinitiator systems

OBJECTIVES

This study investigated p-octyloxy-phenyl-phenyl iodonium hexafluoroantimonate (OPPI) as a photoinitiator, in combination with camphorquinone/amine photoinitiation systems, for use with di(meth)acrylate-based composite resins. The investigation determined if the inclusion of OPPI improved degree and rate of conversion, initial color and color stability of a representative composite resin dental material.

METHODS

Camphorquinone (CQ) and OPPI were combined in various proportions with the amine co-initiator 2-dimethylaminoethyl methacrylate (DMAEMA) and used at two levels in which CQ + OPPI + DMAEMA = 1 wt.% or 3 wt.% to photoinitiate a BisGMA/BisEMA/TEGDMA (37.5:37.5:25 wt.%) monomer blend.A total of eight groups (four groups for each level of total photoinitiator, 1% and 3%) were tested according to the following proportion of components in the photoinitiator system: Group C: CQ only. Group CO: CQ + OPPI (1:2). Group CA: CQ + DMAEMA (1:2). Group COA: CQ + OPPI + DMAEMA (1:1:1). Each monomer was polymerized using a quartz-halogen curing unit (Demetron 400, Demetron Research Corp., Danbury, CT) with an intensity of 400 mW/cm2 for 5 s, 20 s, 40 s, 60 s, 300 s and their conversion levels (DC) were determined at each exposure time using a Fourier transform infrared spectrophotometer (FTIR).To examine color stability, experimental composite resins were made by mixing 3.2% silanated barium glass (78 wt.%, average filler size; 1 microm) with each monomer system, except both CQ only group and 1% CO group, which were found to cure insufficiently to be able to prepare useful specimens. Disk-shaped samples (10 mm in diameter and 1.5 mm in thickness) were made and stored under the conditions of dry or saline solution at room temperature (25 degrees C) or 60 degrees C water bath. Each CIELAB scale was determined with a colorimeter (CHROMA METER CR-400) at the time of baseline (day after curing), 1 week, 2 weeks, and 4 weeks later.

RESULTS

The high level (3%) photoinitiated groups exhibited greater DC than the low level (1%) groups. In the 3% group, the COA group showed the fastest and the highest DC, while in the 1% group the CA and COA groups showed the greatest DC.In the color stability test, both CA groups were darker and more yellow than the CO and COA groups. Color was more stable in composite resins containing OPPI than those containing only the CQ and amine components. The least color change (greatest color stability) was found using 25 degrees C saline solution aging, and the most change (least color stability) occurred using 60 degrees C dry air aging.

SIGNIFICANCE

This study suggests that OPPI can be used to replace the amine in a given CQ/amine photoinitiator system to accelerate cure rate, increase conversion, reduce initial color and increase color stability.

Synthesis and evaluation of ethylene glycol 3-diethylamino-propionate methacrylate as a polymerizable amine coinitiator for dental application

OBJECTIVE

The primary objective of this study was to synthesize and characterize ethylene glycol 3-diethylamino-propionate methacrylate (EGDPM) as a polymerizable coinitiator to replace the commercial amine coinitiator. The 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]-propane (Bis-GMA) and triethylene glycol dimethylacrylate (TEGDMA) resin mixture was polymerized by camphorquinone/EGDPM initiator system under visible light irradiation. The mechanical properties, water sorption and solubility of cured samples were also evaluated.

METHODS

EGDPM was synthesized via Michael-Addition reaction and characterized using FTIR and 1H NMR spectroscopy. Photopolymerization kinetics of the dental resin mixtures were monitored by real-time IR (RTIR). The mechanical properties of cured samples were recorded by dynamic mechanical analyzer (DMA). And the water sorption and solubility of cured samples were detected according to ISO 4049.

RESULTS

Both the double bond conversion and the rate of polymerization of the resin mixtures increased as increasing the concentration of EGDPM but were lower than that of ethyl-4-dimethylaminobenzoate (EDMAB) and 2-(dimethylamine)ethyl methacrylate (DMEM) as a coinitiator at some concentration. When it served as diluent, the final double bond conversion was comparable to that of EDMAB, and the rate of polymerization was higher than that of DMEM. The modulus and T(g) of the cured samples were very close. Water sorption and solubility of the samples were almost the same except that of EGDPM as diluent.

CONCLUSIONS

EGDPM was synthesized by Michael-Addition reaction. It could be used as a potential coinitiator but not suitable as diluent for dental composite.

Sorption and solubility of resin-based restorative dental materials

OBJECTIVES

To measure the water sorption and solubility of different resin-based restorative dental materials.

METHODS

Eight commercial restorative materials were selected: two resin composites (Z100 and Prodigy), four polyacid-modified resin composites (Compoglass, Compoglass F, Dyract and Dyract AP), and two light-cured glass ionomers (Vitremer and Fuji II LC). Five disc specimens were prepared of each material, following the manufacturer's instructions, and were grounded wet with silicon carbide paper. Water sorption and solubility of the different materials were calculated by means of weighting the samples before and after water immersion and desiccation. Data were analyzed by one-way ANOVA and Student-Newman-Keuls tests (P<0.05).

RESULTS

Compoglass and Compoglass F showed the lowest values of water sorption and solubility, while Vitremer and Fuji II LC displayed the highest values. Solubility values of Prodigy, Z100, Dyract and Dyract AP did not show significant differences among them, while their water sorption values attained some differences and were lower for Prodigy followed by Dyract and Z100.

CONCLUSIONS

The attained water sorption and solubility values are mainly influenced by the generic type of material and variations occurring between materials of the same type may result from differences in resin matrix compositions.

Synthesis and photopolymerization of N,N'-dimethyl,-N,N'-di(methacryloxy ethyl)-1,6-hexanediamine as a polymerizable amine coinitiator for dental restorations

N,N'-dimethyl,-N,N'-di(methacryloxy ethyl)-1,6-hexanediamine (NDMH) was synthesized for the purpose of replacing both triethylene glycol dimethacrylate (TEGDMA) and the non-polymerizable amine which is added as a coinitiator in dental resin mixtures, 2,2-bis[4(2-hydroxy-3-methacryloxypropoxy)phenyl] propane (bis-GMA), camphorquinone (CQ) and ethyl-4-dimethylaminobenzoate (EDAB) were used as monomer, photoinitiator and coinitiator, respectively, in these model dental resin systems. Mixtures of bis-GMA/TEGDMA/CQ/EDAB and bis-GMA/TEGDMA/CQ/NDMH were found to reach final conversions of about 45%, slightly higher than his-GMA/NDMH/CQ (40%) under comparable visible light irradiation conditions. In addition, samples cured to these conversions were tested with dynamic mechanical analysis. The bis-GMA/TEGDMA/CQ/EDAB, his-GMA/TEGDMA/CQ/NDMH and bis-GMA/NDMH/CQ mixtures were found to have approximately the same glass transition temperature and modulus. Finally, the water sorption and solubility of bis-GMA/NDMH/CQ were higher than those of the bis-GMA/TEGDMA/CQ/EDAB, and bis-GMA/TEGDMA/CQ/NDMH. However, the values were still within the range of the ISO 9000's standards. These results suggest that NDMH is a viable alternative to conventional photocuring dental resins, serving both as a diluent and coinitiator, since there are no large differences in physical and mechanical properties when using NDMH to replace the amine coinitiator and TEGDMA diluent. The key advantage to this system is that the dimethacrylate NDMH can copolymerize with bis-GMA and TEGDMA, limiting the amount of extractable amine.

Development of a new photoinitiation system for dental light-cure composite resins

OBJECTIVES

The purpose of this study is to explore the synergistic effect of combining camphorquinone (CQ) with 1-phenyl-1,2-propanedione (PPD) as a new photoinitiator.

METHODS

A BisGMA, UDMA, TEGDMA monomer mixture was made light-curing with CQ and/or PPD plus 0.2 wt.% N,N-cyanoethyl-methylaniline (CEMA). Seventeen groups, three specimens each, were tested in which the concentrations of PPD and CQ were varied. The effect of photosensitizer type (CQ or PPD) and ratio (PPD/CQ) on degree of conversion (DC) was investigated using FTIR spectrophotometry. The results were analyzed by ANOVA and Student-Newman-Keuls' multiple range comparison. The absorption spectra of PPD and CQ were recorded by UV-Vis spectrophotometry. A blind color comparison of specimens containing combinations of the two photosensitizers was also undertaken.

RESULTS

Alone, PPD induces a DC which is not significantly different from that of CQ alone. In combination, CQ + PPD produces a DC that generally exceeds that produced by the same concentration of either used alone. The maximum DC occurs between PPD/CQ = 1:1 and 1:4. At total photosensitizer concentrations above 1.8 wt.%, DC is increased by PPD but depressed by CQ, which is evidence that different mechanisms are involved. PPD (lambda max approximately 410 nm) and CQ (lambda max approximately 468 nm) have different wavelength absorption ranges, resulting in a perceptibly lighter shade of yellow for PPD.

SIGNIFICANCE

1-phenyl-1,2-propanedione is a photosensitizer of potential value in reducing color problems associated with visible light cured dental resins. In combination with camphorquinone, it acts synergistically to produce a more efficient photoinitiation reaction.

Mechanical properties of resin composites with filler particles aligned by an electric field

OBJECTIVES

To explore possible enhancement of the mechanical properties of resin composites by aligning the filler particles.

METHODS

The resin for the composites consisted of urethane dimethacrylate (UDMA) and 1,6-hexanediol dimethacrylate (HDDMA) mixed in the ratio of 90 to 10; the filler was silica-zirconia in two particle sizes, 1.7 microns (P50), which was mixed with the resin in the volume fractions of 29 and 48 vol%, and 0.7 micron (Z100), which was mixed with the resin in the volume fractions of 37 and 57 vol%. Particle alignment was obtained by applying a 60 Hz AC electric field across the composite before the resin was photopolymerized. The stress-strain behavior and the elastic modulus of the hardened composite were measured along the alignment axis in compression.

RESULTS

The elastic moduli of the aligned composites increased by as much as 20%, and the maximum stress sustainable in compression before significant deformation occurred was elevated. An electric field strength of the order of 1 kV mm-1 was required to obtain sufficient alignment.

SIGNIFICANCE

Besides conferring a structure to resin composites that is more like that of the natural tooth, particle alignment increased some of the mechanical properties and may have improved durability.

Influence of UEDMA BisGMA and TEGDMA on selected mechanical properties of experimental resin composites

OBJECTIVES

This study was conducted to determine the effect of UEDMA, BisGMA and TEGDMA on selected mechanical properties of experimental resin composites.

METHODS

Thirty monomer mixtures of TEGDMA and BisGMA and/or UEDMA were produced. Five base monomer mixtures had the following molar relationships between TEGDMA and BisGMA: 30:70, 40:60, 50:50, 60:40 and 70:30. Monomer mixtures were then produced in which BisGMA was successively substituted by UEDMA, 10 mol% at a time. The resins were made light-curing and loaded with filler. Diametral tensile strength, flexural strength and modulus of elasticity were determined on 1 week old specimens. The results were analyzed by ANOVA and by response surface methodology.

RESULTS

The diametral tensile strength of the resin composites varied between 52 and 59 MPa, the flexural strength between 137 and 167 MPa, and the modulus of elasticity between 8.0 and 11.1 GPa. The statistical analyses showed that substitution of BisGMA or TEGDMA by UEDMA resulted in an increase in tensile and flexural strength, and that substitution of BisGMA by TEGDMA increased tensile, but reduced flexural strength. Further, it was found that, for a given content of UEDMA, variations in the ratio BisGMA/TEGDMA gave rise to a maximum in modulus of elasticity. The size of this maximum in modulus decreased with increasing content of UEDMA.

SIGNIFICANCE

Varying the relative amounts of UEDMA, BisGMA and TEGDMA has a significant effect on the mechanical properties of the resin composition. Thus, by selecting specific combinations of these components, it may be possible to design composites with properties that are tailor made to specific applications.

Retention of propanal and diacetyl in experimental resins

The degree of evaporation from experimental resins containing 0.40 mol% propanal or diacetyl was determined over a 6-month period at 60 degrees C. From the results the maximum evaporation possible, M infinity was calculated for each resin and was found to vary between 0.28% and 7.51% by weight. At low contents of propanal or diacetyl, M infinity 1 remained unchanged as compared with the control resins without additive. At higher contents of additive, M infinity increased significantly. In resins based on BisGMA and TEGDMA, propanal was retained to a lesser extent than diacetyl. In resins based on UEDMA and HEMA, propanal was retained to a greater extent than diacetyl. This study confirms that propanal and diacetyl become bound in the polymer structure, and theories as to the reaction mechanisms are presented.

Resin composites in dentistry: the monomer systems

The present review outlines the history of monomers used in resin composites, motivates further development, and highlights recent and ongoing research reported in the field of dental monomer systems. The monomer systems of most present-day resin composites are based on BisGMA, developed some 40 years ago, or derivatives of BisGMA. In the remaining resin composites, urethane monomers or oligomers are used as the basis of the monomer system. The main deficiencies of current resin composites are polymerization shrinkage and insufficient wear resistance under high masticatory forces. Both factors are highly influenced by the monomer system, and considerable efforts are being made around the world to reduce or eliminate these undesirable properties. The use of fluoride-releasing monomer systems, some of which are under investigation, has been suggested to mitigate the negative effects of marginal gaps formed in consequence of polymerization shrinkage. The very crux of the problem has also been approached with the synthesis of potentially low-shrinking/non-shrinking resin composites involving ring opening or cyclopolymerizable monomers. By the use of additives with a supposed chain transfer agent function, monomer systems have been formulated that improve the degree of conversion of methacrylate double bonds and mechanical properties. Many promising monomer systems have been devised, the implementation of which may be expected to improve the longevity of resin composite fillings and expand the indications for resin composites.

Effect of propanal and diacetyl on quantity of remaining double bonds of chemically cured BisGMA/TEGDMA resins

The aim of the present study was to determine the effect of propanal and diacetyl addition on the quantity of remaining double bonds of chemically cured dental resins. Propanal (propionaldehyde) or diacetyl (2,3-butanedione) was added to monomer mixtures, which were then made chemically curable. The monomer mixtures were varied with respect to content of propanal or diacetyl. Addition of propanal or diacetyl to chemically curable resins resulted in a decrease in the quantity of remaining double bonds from 19.6% to 1.9% and from 19.6% to 11.4%, respectively. A negative correlation of statistical significance was found between content of propanal and quantity of remaining double bonds, while the relationship between content of diacetyl and quantity of remaining double bonds was found not to be linear. Propanal was equally effective in reducing the quantity of remaining double bonds in chemically cured and in the light cured resins studied previously. As regards diacetyl, a more pronounced effect on quantity of remaining double bonds was noted for light cured resins as compared with chemically cured resins. The most likely common reaction mechanism of propanal and diacetyl seemed to be that of chain transfer reactions. Furthermore, analysis of the data indicated a possible additional photoinitiating function of diacetyl.

In vitro wear, hardness, and conversion of diacetyl-containing and propanal-containing resin materials

OBJECTIVES

This study was conducted to determine the effect of diacetyl or propanal activities: 1) on the in vitro wear of 22 experimental resin composites; and 2) on the Wallace indentation hardness of the unfilled resins. The objective was to examine the correlation between wear, hardness, and quantity of remaining double bonds (determined previously).

METHODS

Diacetyl or propanal agents were added in varying concentrations to monomer mixtures. The resins were made light-curing and those used for measurement of wear were loaded with filter. The results were analyzed by ANOVA and Newman-Keuls' multiple range tests.

RESULTS

In the composite systems, adding diacetyl or propanal resulted in decreased in vitro wear. The quantity of remaining double bonds in the dental polymers with these additives was also reduced. Their effect on Wallace indentation depth was less clear-cut. Low concentrations of additives decreased indentation depth of the unfilled materials, whereas high concentrations increased indentation depth. If it assumed that differences in the polymer have a major influence on the wear when the filter content and particle matrix interface are kept constant, then the hardness data on the unfilled resin can be used to correlate property changes of the polymer in the composite. A three-dimensional regression analysis found that in vitro wear decreased with decreasing Wallace indentation depth and decreasing quantity of remaining double bonds.

SIGNIFICANCE

Addition of diketone or monoaldehyde to resin monomers may provide a means of increasing wear resistance of composites and allow their use in stress-bearing areas.

Current trends in dental composites

The clinical performance of dental composites has been significantly improved over the past decade through modifications in formulation that include: using more stable polymerization promoters for greater color stability; incorporating high concentrations of finely ground fillers to produce adequate strength and excellent wear resistance while retaining translucency; adding radiopacifying agents for improved diagnostics; and utilizing dentin adhesives. However, there are problems which limit the use of composites, especially in posterior teeth. The materials remain very technique-sensitive, due to the extensive contraction which accompanies polymerization and negatively influences marginal sealing. In addition, the materials are generally considered to have inadequate mechanical properties and wear resistance in contact areas to serve as total replacements for amalgams. Current efforts are focusing on several areas, including the development of non- or minimally-shrinking dental composites containing spiro-orthocarbonates as additives to dimethacrylates or epoxy-base resins, and the production of alternative filler materials for ideal wear resistance and esthetics. This paper reviews the composition and characteristics of current dental composites, as well as recent areas of study.

Factors affecting the adherence energy of experimental resin cements bonded to a nickel-chromium alloy

Reliable adherence of resin-based cements is of prime importance for the longevity of cemented restorations. The present study investigated whether a relationship exists between adherence energy to a metal substrate and the degree of cross-linking and wetting characteristics of resin-based luting agents. The adherence energies between a sand-blasted metal surface and a series of experimental resin cements were measured by means of the wedge test. The degree of cross-linking was calculated from the monomer composition of the resin cements. The measured wetting characteristics were work of adhesion and surface tension, and their dispersive and polar components. Adherence energy varied between 22 and 81 J/m2 and was influenced by the nature of the resin cements: Those with a low degree of cross-linking resulted in high adherence values. Furthermore, resin cements whose monomers were relatively polar gave rise to high adherence values. Although other metals may not behave in exactly the same way, these results may help in the formulation of new, more retentive resin cements.

Quantity of remaining double bonds of diacetyl-containing resins

The present study determined the effect of diacetyl addition on the quantity of remaining double bonds of dental resins. Diacetyl was added to monomer mixtures, which were then made light-curing. The monomer mixtures were varied with respect to monomer composition and content of diacetyl. The quantity of remaining double bonds was determined by means of transmission infrared spectra of the resins recorded before and after wet or dry storage for one wk. Addition of diacetyl resulted in a decrease in the quantity of remaining double bonds by as much as 78% as compared with the mixtures without diacetyl. Negative correlations of statistical significance were found between content of diacetyl and quantity of remaining double bonds in BISGMA: TEGDMA-based as well as in UEDMA: HEMA-based resins for both modes of storage. Significant negative correlations were found between quantity of remaining double bonds and the previously determined mechanical properties.

Annual review of selected dental literature: report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

The annual review of selected dental literature this year cites 384 published papers and reports. This year's review contains more editorial comment than reviews of years passed. New data on the biological responses to materials is emphasized in several sections. Observations on new compounds able to prevent plaque formation are presented. Clinically relevant advances in knowledge concerning the etching of different tooth structures are reported along with the effect of etching procedures on the dental pulp. Evaluation of periodontal diseases in all age groups is a topic. Limitations of current diagnostic techniques in periodontal disease, temporomandibular disorders, and implant therapy are included. There are new views on the use of dental amalgam. The future use of dental mercury is predicted. Interest in new ceramic systems is indicated as the demand for esthetics continues. Clinical information is emphasized over scientific information throughout this year's review.

Influence of aldehydes on selected mechanical properties of resin composites

The present study investigated whether propanol, a monofunctional aldehyde, was able to improve the mechanical properties of dental polymers. The underlying hypothesis was that a cross-linking reaction is possible between various functional groups of different polymers. Propanol was added to monomer mixtures, which were then made light-curing and loaded with filler. The monomer mixtures were varied with respect to monomer composition and content of aldehyde. Four mechanical properties of the experimental resin composites were determined. Addition of propanol gave rise to significant improvements in mechanical properties, which may be indicative of a cross-linking ability of monofunctional aldehydes. With the exception of modulus of elasticity, the mechanical properties of resin composites based on UEDMA/HEMA were superior to those of BISGMA/TEGDMA-based materials, even though the improvements in flexural strength and modulus of resilience were most pronounced for the BISGMA/TEGDMA-based resin composites.