Effect of the addition of functionalized TiO2 nanotubes and nanoparticles on properties of experimental resin composites

ObjectiveTo evaluate the influence of the addition of functionalized and non-functionalized TiO₂ nanostructures on properties of a resin composite.MethodsTiO₂ nanostructures were synthesized and functionalized, using 3-(aminopropyl)triethoxysilane (APTMS) and 3-(trimethoxysilyl)propyl methacrylate (TSMPM). Characterizations were performed with XRD, EDS, TEM, and TGA. Resin composites containing Bis-GMA/TEGDMA, CQ, DABE, and barium-aluminum silicate glass were produced according to TiO₂ nanostructure (nanotube or nanoparticle), concentration (0.3 or 0.9 wt%), and functionalization (APTMS or TSMPM). The resin composite without nanostructures was used as control. The amount of fillers was kept constant at 78.3 wt% for all materials. The degree of conversion (DC - at 0 h and 24 h), maximum polymerization rate (Rp_max), and Knoop microhardness (KHN before and after ethanol softening) were evaluated. Data were analyzed with two-way ANOVA with repeated measures and Tukey's HSD (α = 0.05).ResultsTGA results demonstrated that functionalizations were effective for both nanostructures. For DC, resin composites, time and interaction effect were significant (p < 0.001). Higher DC was found for 0.3-wt%-functionalized-nanotubes at 24 h. For nanoparticles, only 0.9-wt%-non-functionalized and 0.3-wt%-APTMS-functionalized showed DC similar to the control and all other groups showed higher DC (p < 0.05). Rp_max was higher for 0.3-wt%-APTMS-nanotubes, which corresponded to higher DC after 24 h. The lowest Rp_max occurred for 0.9-wt%-TSMPM-nanotubes, which showed smaller DC at 0 h. For KHN, resin composites, ethanol softening and interaction effect were significant (p < 0.001). KHN decreased after ethanol softening all groups, except for 0.3-wt%-TSMPM-nanotubes, 0.9-wt%-TSMPM-nanotubes, and 0.3-wt%-non-functionalized-nanoparticles.ConclusionThe resin with 0.3-wt%-TSMPM-nanotubes showed higher DC after 24 h, while being the most stable material after the ethanol softening.SignificanceThe addition of functionalized TiO₂ nanostructures in resin-based materials may improve the properties of the material.     

Influence of refractive index on optical parameters of experimental resin composites

Abstract

Objective. Color characteristics of the experimental resin composites were determined to know the influence of different refractive index (RI) on optical parameters. Materials and methods. Four experimental light-cured resin composites of the same shade but with different RI were used. The colorimetric values of the specimens were measured against black and white backgrounds using spectrophotometry. The results were converted to CIE L*a*b* color-space values. The chroma (C*ab), color difference (ΔE), translucency parameter (TP) and opacity (OP, opposite property of TP) values were calculated. Surface gloss (GS) of the specimen was also measured. Results. The L* coordinate, a* coordinate and ΔE*ab values increased as the difference in RI increased. The OP and GS values increased and the TP values decreased as the refractive-index difference increased. The L* and C*ab values increased as the value of the RI increased. The TP, OP and GS values were highly correlated with the RI value. The TP value decreased and the OP and GS values increased, as the RI value increased. Conclusions. Refractive index of resin composites is important when thinking about improving the color appearance of esthetic restorations.     

Influence of ketones on selected mechanical properties of resin composites.

The present study investigated a concept for additional cross-linking of dental polymers, by which resistance to wear of resin composites might be increased. Bifunctional ketones were added to monomer mixtures, which were then made light-curing and loaded with filler. The monomer mixtures were varied with respect to type and ratio of monomer and ketone. For measurement of possible effects of the cross-linking agents added, four mechanical properties of the experimental resin composites were determined. Addition of the bifunctional ketone diacetyl resulted in the following increases in mechanical properties: diametral tensile strength, 11%; flexural strength, 29%; modulus of elasticity, 19%; and modulus of resilience, 50%.     

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.     

Influence of carboxylic anhydrides on selected mechanical properties of heat-cured resin composites.

Resin composites are still in need of improved abrasion resistance for them to be ideal restorative materials for use in large occlusal cavities. The present study proposes a concept for additional cross-linking of dental monomers, by which mechanical properties and possibly the resistance to abrasion of the resin composites are increased. Cyclic acid anhydrides were added as cross-linking agents to different monomer mixtures, which were then loaded with filler. The monomer mixtures were varied with respect to type and ratio of monomer and anhydride. For measurement of diametral tensile strength, flexural strength, modulus of elasticity, and modulus of resilience, specimens were initially cured by light and then post-cured for one h at 150 degrees C. Resin composites based on UEDMA and HEMA were found to be superior to BISGMA- and TEGDMA-based composites. Increases in mechanical properties were highest when unsaturated anhydrides were used. An optimal effect of anhydride addition was found in resin composites also containing methacrylamide. Such materials resulted in a 20% increase in the mechanical properties investigated.     

Non-silicate nanoparticles for improved nanohybrid resin composites

ObjectiveZirconia and alumina nanoparticles were coated with a silica-rich layer (ALSI and ZRSI) and used to prepare experimental nanohybrid resin composites, which were characterized and compared to a control commercial resin composite (Filtek Z350 XT).MethodsSilica nanoparticles with sizes compatible to ALSI (Aerosil 150) and ZRSI (Aerosil OX 50) were tested as references. The volume of nanoparticles was equivalent across the composites, which also had consistent content of glass microparticles. CC conversion, viscosity, depth of cure, surface topography, hardness, opacity, radio-opacity, and edge chipping resistance (ReA) were tested after 24 h. Flexural strength (σ_f) and fracture toughness (K_IC) were also tested after 15 K thermal cycles. Data were analyzed using one-way or two-way ANOVA and Tukey’s test (α = 0.05).ResultsALSI and ZRSI yielded resin composites with lower viscosity and more irregular nanoagglomerates compared to nanosilica-based composites. CC conversion and depth of cure were lower for ZRSI composite, which had higher opacity, radio-opacity, and hardness. ReA was higher for ALSI composite. Composites with ALSI and ZRSI showed stable σ_f after aging, whereas the control and Aerosil 150 resin composites showed significant degradation. The commercial and nanosilica-based composites showed up to 42% reduction in K_IC after aging, whereas resin composites with ZRSI and ALSI showed a more stable K_IC.SignificanceALSI and ZRSI generated nanohybrid resin composites with improved and/or more stable physical properties compared with nanosilica-based and commercial composites. This study suggests that changing the composition of nanofillers is a simple method to enhance the performance of nanohybrid composites.     

Influence of various irradiation processes on the mechanical properties and polymerisation kinetics of bulk-fill resin based composites

ObjectivesTo assess the effect of irradiation time and distance of the light tip on the micro-mechanical properties and polymerisation kinetics of two bulk-fill resin-based composites at simulated clinically relevant filling depth.MethodsMicro-mechanical properties (Vickers hardness (HV), depth of cure (DOC) and indentation modulus (E)) and polymerisation kinetics (real-time increase of degree of cure (DC)) of two bulk-fill resin-based composites (Tetric EvoCeram^® Bulk Fill, Ivoclar Vivadent and x-tra base, Voco) were assessed at varying depth (0.1–6 mm in 100 μm steps for E and HV and 0.1, 2, 4 and 6 mm for DC), irradiation time (10, 20 or 40 s, Elipar Freelight2) and distances from the light tip (0 and 7 mm). Curing unit's irradiance was monitored in 1 mm steps at distances up to 10 mm away from the light tip on a laboratory-grade spectrometer.ResultsMultivariate analysis (α = 0.05), Student's t-test and Pearson correlation analysis were considered. The influence of material on the measured mechanical properties was significant (η² = 0.080 for E and 0.256 for HV), while the parameters irradiation time, distance from the light tip and depth emphasise a stronger influence on Tetric EvoCeram^® Bulk Fill. The polymerisation kinetics could be described by an exponential sum function, distinguishing between the gel and the glass phase. The above mentioned parameters strongly influenced the start of polymerisation (gel phase), and were of less importance for the glass phase.ConclusionsBoth materials enable at least 4 mm thick increments to be cured in one step under clinically relevant curing conditions.Clinical significanceThe susceptibility to variation in irradiance was material dependent, thus properties measured under clinically simulated curing conditions might vary to a different extent from those measured under ideal curing conditions.     

Influence of polishing duration on surface roughness of resin composites

There is a need for effective polishing instruments for resin composite restorations with highly polished surfaces. The purpose of this study was to investigate the influence of polishing duration on surface roughness of light-cured resin composites. Four polishing systems, Compomaster (Shofu), Silicone Points C Type (Shofu), Super Snap (Shofu) and Enhance Finishing and Polishing System (Dentsply/Caulk), were used to polish two commercially available resin composites, Clearfil AP-X (Kuraray Medical) and Lite-Fil II A (Shofu). Resin pastes were condensed into molds (10 mm in diameter, 5 mm in depth) and light irradiated for 40 s. Composite surfaces were ground with # 600 SiC paper followed by polishing with an instrument for 30 s, and the surface roughness was measured every 10 s during polishing procedures. The average surface roughnesses (Ra) were determined using a profilometer. Data were analyzed by Tukey HSD test (P = 0.05). After 30 s of polishing, mean Ra values ranged from 0.07 to 0.50 for Clearfil AP-X, and from 0.11 to 0.57 for Lite-Fil II A. Although the time required for polishing was longer, the surface finish produced by multiple-step polishing systems was superior to that obtained with one-step polishing systems.     

Influence of centrifugal force on filler loading of resin composites

This study examined the influence of centrifugal force on the filler loading of composites using a light-polymerizing apparatus combined with a centrifuge. To assess uneven filler particle distribution resulting from specimen rotation, two low-viscosity composites (Palfique Estelite LV and Revolution Formula 2) were placed in test tubes, centrifuged, and subsequently light-polymerized with the apparatus. After each specimen was sliced into four disks (2-mm thickness), the inorganic filler content and Knoop hardness number (KHN) of each disk were determined. The results suggested that filler loading of composites could be increased by application of centrifugal force if the filler and monomer components were properly arranged.     

Influence of color parameters of resin composites on their translucency

OBJECTIVES: To determine the influence of color parameters and the difference in color parameters by the background on the translucency of resin composites. METHODS: Eight light-curing resin composites, a total of 41 shades, were investigated. The color of specimens was measured after polymerization on a reflection spectrophotometer with the SCE geometry over white and black backgrounds. The translucency parameter (TP), contrast ratio (CR) and the difference in color parameters by the background (DeltaL*, Deltaa*, Deltab* and DeltaC*ab: values over the white background minus value over the black background) were calculated. Correlations between TP values, CR values at every 50-nm interval and the color parameters as well as the differences in color parameters by the background were analyzed with regression analysis. RESULTS: Correlations between TP values, and the color parameters and the differences in color parameters were significant except chroma difference (p<0.01). The correlation between TP values and chroma was significant (r= -0.489 and -0.603, p<0.01). The correlation between TP values and DeltaL* was very high (r=0.868). Correlations between the color parameters, the differences in color parameters and CR values were varied by the wavelength. TP values were highly correlated with the CR value at the wavelength of 700 nm. SIGNIFICANCE: More chromatic shades of commercial resin composites were less translucent. Translucency increased as the wavelength increases.     

Influence of polishing instruments on the surface texture of resin composites.

OBJECTIVE: There is a need for an ideal polishing system for resin composite restorations. The purpose of this study was to investigate the influence of polishing instruments on the surface texture of light-cured resin composites. METHODS AND MATERIALS: Four polishing systems-Compomaster (Shofu), Silicone Points C Type (Shofu), Super-Snap (Shofu), and Enhance Finishing and Polishing System (Dentsply/DeTrey)-were used to polish the flat surface of cylindrical blocks made of 3 different resin composites: Beautifil (Shofu), Clearfil AP-X (Kuraray Medical), and Lite-Fil II A (Shofu). The average surface roughness (Ra) and surface gloss (Gs60 degrees) were determined. Scanning electron microscopic observations of the polished specimens were made. The polished samples were immersed in a 0.3% acid rhodamine B solution for 1 week, and change in color was determined. RESULTS: The multiple-step systems, Enhance and Super-Snap, resulted in the best surface finishes. A new single-step point, Compomaster, ranked third in surface finish but was significantly better than the older point system, Silicone Points C. The color-staining experiments showed that there were no significant differences between the Compomaster system and the multiple-step systems, which were all significantly better than the older polishing point. CONCLUSION: The newly introduced 1-step polishing point has the ability to polish resin composites as effectively as multistep polishing systems.     

Influence of light irradiation on the volumetric change of polyacid-modified resin composites

OBJECTIVES: Recently, a new restorative material called a 'compomer', which is classified as a polyacid-modified resin composite, has become available. The volumetric shrinkage of compomers may create marginal gaps that influence the bonding ability and longevity of a restoration. Since compomers have been introduced recently, their volumetric change during curing is not fully understood. The purpose of this study was to evaluate the volumetric change of compomers. METHODS: Three compomers, Compoglass (Vivadent), Dyract (Dentsply), and Ionosit Fil (DMG) were employed. The material was placed into a Teflon mould, 4 mm in diameter and 2 mm height, and extruded into the dilatometer. Then the specimens were light activated and the change in the height of the meniscus of water was recorded using a CCD camera and VRC. RESULTS: The average volumetric shrinkages of the compomers after 160 s were 2.4% for Compoglass, 2.7% for Dyract, and 2.1% for Ionosit-Fil. For all materials tested, there was a tendency of increasing volumetric shrinkage with increased irradiation time. CONCLUSIONS: The results of this study indicate that the volumetric change of compomer is influenced by the duration of light exposure, light intensity, and environmental conditions to which the materials are exposed.     

Influence of photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites

ObjectiveTo establish the relationship between photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites.MethodsModel composites based on BisGMA/TEGDMA (60:40 mol%) were loaded with 40 wt% of 7 nm or 16 nm-sized filler particles. One of the following photoinitiator systems was added: camphorquinone (CQ) associated with an amine (EDMAB), monoacylphosphine oxide (TPO), or bysacylphosphine oxide (BAPO). The optical properties of disk-shaped specimens were measured 24 h after curing and repeated after storage in water for 90 days and coffee for 15 days. A large spectrum LED unit (Bluephase G2, Ivoclar Vivadent) was used for photoactivation. CIE L*a*b* parameters, color difference (ΔE), and translucency parameter (TP) were calculated. Knoop hardness readings were taken at top and bottom composite surfaces. Cure efficiency was determined by bottom/top hardness ratio. Data were statistically analyzed at α = 0.05 significance level.ResultsComposites formulated with 16 nm particles had higher CIE L* than those with 7 nm particles in all storage conditions. BAPO-based composites generally had lower CIE a* than the other composites. The group TPO + 16 nm before storage and all groups with 16 nm-sized particles after storage had lower CIE b* (i.e. lower degree of yellowing) than the other groups. TPO-based materials had higher color stability. The cure efficiency was not significantly affected by photoinitiator system or particle size. CQ + 7 nm had the lowest and BAPO + 16 nm the highest hardness values.SignificanceCombination of photoinitiator system and filler particle size might affect the optical properties of composites, with low influence on cure efficiency.     

Influence of fluorescent whitening agent on the fluorescent emission of resin composites.

OBJECTIVES: The objective of this study was to determine the fluorescent emission of experimental resin composites after addition of a fluorescent whitening agent in varied concentrations. The effects of thermocycling and composition of resin matrix on the fluorescent emission were also determined. METHODS: An experimental light curing resin matrix was made by mixing Bis-GMA, UDMA and TEGDMA in the ratio of 1:1:1 by weight, and silane coated glass filler was added in the ratio of 50 wt.% of resin composite. A fluorescent whitening agent [FWA, 1,4-double-(benzoxazole-group-2-group)naphthalene] was added with the concentration of 0.01-0.1%. To determine the difference by the resin matrix, two resin composites (60 wt.% Bis-GMA or UDMA with 40 wt.% TEGDMA) with the same filler content were made, and the FWA was added. Five specimens of 2mm in thickness were made for each group. Spectral reflectance was measured relative to the illuminant D65 on a reflection spectrophotometer. From the spectral reflectance values, the difference in reflectance (fluorescence spectra) by the inclusion or exclusion of UV component was calculated. After the baseline measurement, thermocycling was performed for 500 and 1000 cycles, and the fluorescent emission was measured again. RESULTS: The concentration of FWA influenced the fluorescent peak heights and areas (p<0.05), but thermocycling up to 1000 cycles did not influence the values. Fluorescence peak wavelength was not changed by the resin matrix, but peak height and area were influenced by the resin matrix (p<0.05). SIGNIFICANCE: FWA added with the concentrations of 0.01 and 0.05% emitted fluorescence, which was higher than those from commercial resin composites.     

Influence of scattering/absorption characteristics on the color of resin composites.

OBJECTIVES: Optical scattering has been studied because of its important effects on the color and translucency of a material. The objective of this study was to determine the influence of the scattering and absorption characteristics including translucency and opalescence on the CIE color coordinates (L(*), a(*), and b(*)) of resin composites. METHODS: Color and spectral distribution of seven resin composites (14 shades, 1mm thick) were measured in the reflectance and the transmittance modes. Optical constants including scattering coefficient (S), absorption coefficient (K) and light reflectivity (RI) were calculated from the spectral reflectance data using Kubelka's equations. The opalescence parameter (OP) was calculated as the difference in yellow-blue (Deltab(*)) and red-green (Deltaa(*)) coordinates between the reflected and transmitted colors. The translucency parameter (TP) was calculated for the translucency evaluation. Simple correlation among each of CIE L(*), a(*) and b(*) values measured using varied protocols with optical parameters (S, K, RI, OP and TP) was determined, and multiple regression analysis was used to determine the significantly influencing variables on the color coordinates (p<0.05). RESULTS: CIE L(*), a(*), and b(*) values were influenced by S, K, RI, TP and OP values. The CIE L(*) value without backing and that in the transmission mode were highly correlated with S. OP and TP values also influenced CIE L(*) value. The CIE b(*) value was correlated with the OP value when different composites with the same shade designation were compared. SIGNIFICANCE: Since the scattering and absorption characteristics influence the color of resin composites, the size and volume fraction of fillers should be controlled for the best color reproduction, considering the refractive indices of filler and resin matrix.     

Influence of filler distribution on the color parameters of experimental resin composites.

OBJECTIVES: Simulating the optical properties of natural tooth would be the final goal for esthetic restorative materials. Filler distribution in resin composites determines the scattering in composite materials, which in turn would influence the color parameters such as lightness, chroma and hue. The objective of this study was to determine the influence of filler size and amount on the color parameters of experimental resin composites. METHOD: Color of 11 experimental resin composites with two different sized fillers (LG: 0.77 microm and SG: 0.50 microm) in 10-70 wt% was measured by a spectrophotometer. Color coordinates (CIE L*, a* and b*), chroma and hue angle were determined. Optical constants including scattering coefficient (S), absorption coefficient (K) and light reflectivity (RI) were calculated. To determine the influence of the amount of filler on the optical parameters, Pearson correlations between the amount of filler (%) and color parameters and optical constants were calculated. Correlations between the optical constants (S, K and RI) and color parameters were calculated (p<0.05). RESULTS: S value increased as the amount of filler increased. RI value generally increased as the amount of filler increased for LG filler group, and increased up to 40% filler for SG filler group. CIE L* value increased as the amount of filler increased in both of LG and SG filler groups. CIE L* value was highly correlated with S and RI values for both filler groups (r=0.961-0.974). CONCLUSION: Lightness was highly correlated with the amount of filler, S and RI values (r=0.932-0.974). But the correlation coefficients between the amount of filler and chroma/hue were moderate (r=0.406-0.827); therefore, pigmentation would be tried to simulate the color of resin composites to those of natural tooth. Optical properties of resin composites could be partly simulated to those of teeth by controlling the filler distribution.