Achieving property enhancements in dental resin composites via reduced concentrations of camphorquinone within a ternary initiator system.

OBJECTIVES: The study aimed to assess the impact of diphenyliodonium hexafluorophosphate (DPI) on the physicochemical properties of experimental resin composites (ECRs) featuring reduced concentrations of camphorquinone (CQ)/amine. METHODS: Five concentrations of CQ (0.125, 0.25, 0.5, 0.75, and 1 mol%) with dimethylaminoethyl amine benzoate (EDAB) in a 1:2 mol% ratio (CQ:EDAB) were incorporated into a 50:50 mass% monomer blend of bisphenol glycidyl methacrylate (BisGMA) and triethyleneglycol dimethacrylate (TEGDMA). An additional 5 groups with the same CQ:EDAB concentrations had 0.5 mol% DPI added. Each resin group contained 60 wt% of 0.7 µm barium-alumino-silicate glass. Light transmission (n = 3), real-time degree of polymerization (n = 3), temperature change during polymerization (n = 5), polymerization shrinkage strain (n = 3), flexural strength, and modulus (n = 12), as well as water sorption and solubility (n = 5), were evaluated. Data were analyzed using two-way ANOVA and Tukey's post-hoc test (α = 0.05). RESULTS: Light transmission was reduced in groups containing 0.125 and 0.25 mol% of CQ without DPI. DPI increased temperature, degree and rate of polymerization, despite the reduction in CQ/amine concentration. Additionally, there was an increase in polymerization shrinkage strain, flexural strength and modulus, and a reduction in water sorption and solubility in ECRs with DPI, even with lower concentrations of CQ/EDAB. SIGNIFICANCE: DPI improved the assessed properties of composites across various concentrations of CQ/EDAB, showing the benefit of reducing the quantity of CQ used without compromising the properties and curing of the resin composites.

Influence of different concentrations of an iodonium salt on properties of amine-free resins.

OBJECTIVES: to evaluate the effect of different concentrations of an iodonium salt on the degree of conversion, polymerisation rate, flexural strength and modulus of an amine-free photopolymerizable resin system. METHODS: Two series of UDMA/TEGDMA resin mixtures (1:1 mass ratio) containing 0, 0.5, 1.0 or 2.0 mol% of bis(4-methyl phenyl)iodonium hexafluorophosphate(BPI): and 1 mol% camphorquinone (CQ) were evaluated. One of the series contained 2 mol% of the amine (2-(dimethylamino)ethyl methacrylate-DMAEMA), while the other series had only CQ and BPI as photoinitiators. Polymerisation kinetics and degree of conversion (DC) were evaluated by Fourier transform near-infrared spectroscopy (n = 3). Flexural strength (FS) and modulus (E) were evaluated by a three-point bending method (n = 12). Data were analysed by two-way ANOVA and Tukey's test. RESULTS: The system containing CQ + DMAEMA + BPI provided the highest DC and FS. Amine-free resins had similar E regardless of the presence of BPI. The resins containing CQ+DMAEMA with 1 and 2 mol% of BPI presented higher E compared with others. SIGNIFICANCE: Amine-containing resins reached statistically higher DC, rate of polymerisation and FS than amine-free systems. The use of higher BPI concentrations did not improve the properties of amine-free resins.

Bis(4-methyl phenyl)iodonium as an alternative component to diphenyliodonium in camphorquinone-based ternary initiating systems.

OBJECTIVE: To evaluate the influence of different co-initiators (diphenyliodonium hexafluorophosphate - DPI - and bis(4-methyl phenyl)iodonium hexafluorophosphate - BPI) on chemical and mechanical properties of resins. METHODS: Nine experimental resins (50% Bis-GMA and 50% TEGDMA, w/w) with 60 wt% filler particles were formulated. The initiating system used was camphorquinone (CQ-1 mol%) and ethyl dimethylaminobenzoate (EDAB-2 mol%). Experimental groups were established according to DPI and BPI quantities (0.25, 0.5, 0.75, and 1 mol%). The control group was a resin containing only CQ-EDAB. Light transmission through the resin during polymerisation was analysed with a UV-vis spectrophotometer. Real-time polymerisation of the systems was evaluated using an FTIR spectrometer. Real-time polymerisation shrinkage strain was evaluated, and the flexural strength and modulus of materials were obtained by 3-point bending. Experimental groups were statistically analysed by Analysis of Variance and Tukey's test (α = 0.05). Dunnett's test was applied to compare experimental groups with control. RESULTS: Light transmission rapidly increased initially for resins containing DPI or BPI. After 30 s cure, the irradiance on the lower surface of resin specimens was similar for all groups. After 10 s of light irradiation, groups containing DPI and BPI had higher conversion than the control. However, conversion after 120 s post-irradiation was similar for all groups. The rate of polymerisation, shrinkage strain, and the maximum strain rate were higher for groups containing DPI/BPI. The use of iodonium salts increased the flexural strength and flexural moduli of resins. SIGNIFICANCE: DPI and BPI increased resin reactivity similarly. Increased rate of polymerization influenced light transmission through the resin in the first seconds of polymerisation and increased resin shrinkage and rate of shrinkage, as well as flexural strength and moduli.

Increased rates of photopolymerisation by ternary type II photoinitiator systems in dental resins.

To evaluate the effects of Type I and Type II photoinitiator systems on curing efficiency, degree of conversion (DC) and chemico-physical properties of resin based materials. A comonomer base containing 50%wt 2.2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane (bis-GMA) and 50%wt triethyleneglycol dimethacrylate (TEGDMA) was formulated with either 0.5 or 1mol% of Type II camphoroquinone (CQ), Type I monoacylphosphine oxide (MAPO) or bis-acylphosphine oxide (BAPO) photoinitiators. The Type II system was either a binary (1: 2 CQ:amine) or ternary system (1: 2 CQ:amine + 0.5 mol% DPI). Degree and rate of polymerization was measured by Fourier Transform Infrared Spectroscopy (FTIR). Knoop micro-hardness prior to and following ethanol immersion was assessed. Flexural strength and modulus was measured under three-point bend test. Water sorption and solubility was also evaluated. The photoinitiator absorption spectra and the total absorbed energy per unit volume (Eabs) for 0.5mol% photoinitiator in each material was calculated. Despite the reduced total absorbed energy per unit volume for CQ based systems, ternary Type II system significantly improved curing efficiency (P < 0.05) compared to both Type I photoinitiators and degree of conversion compared to MAPO only, whilst exhibiting comparable mechanical and physical properties compared to both Type I based materials at equivalent molar concentrations of photoinitiator (P > 0.05). Ternary Type II systems is an efficient alternative to improve the polymerization of resin materials, promoting similar or even better properties than Type I initiators. DPI can increase the reactivity of CQ systems and promote polymerization rates superior than Type I photoinitiators.

Influence of light-curing unit on the network structure and mechanical properties of model resin cements containing diphenyliodonium compared with a commercial reference.

OBJECTIVE: To evaluate the effects of dyphenyliodonium hexafluorophosphate (DPI) on crosslink density (CLD), flexural strength (FS), and flexural modulus (FM) of a light-cured experimental resin cement compared with a commercial dual-cured cement. MATERIALS AND METHODS: Bis-GMA combined with TEGDMA (50-50%) was used as resin matrix. Silanated barium-aluminum-silica glass was used as inorganic filler. Camphorquinone (CQ) - 1 mol%, 2-(dimethylamino)ethyl methacrylate (DMAEMA) - 2 mol%, and two concentrations of DPI (0 or 0.5 mol%) were used as the photoinitiator system. Two light-curing units (LCUs) were used (a single-peak (Radii-Cal) and a polywave (Bluephase)). The CLD was indirectly assessed in a softening test by Knoop hardness indentation; FS and FM were measured by means of a three-point bending test. RESULTS: DPI positively influenced Knoop hardness when compared with experimental resin without DPI. The flexural strength of experimental cements was lower than that found with Variolink II. The crosslinking density (obtained by reduction of Knoop hardness) of cement with 0.5% DPI was similar to that of dual - cured Variolink II. CONCLUSIONS: DPI showed an improvement in some of the properties tested but was inferior to the commercial dual-cured resin cement. The LCUs had no influence on the flexural strength of the resin cements.

Effect of diphenyliodonium hexafluorphosphate on resin cements containing different concentrations of ethyl 4-(dimethylamino)benzoate and 2-(dimethylamino)ethyl methacrylate as co-initiators.

OBJECTIVE: The present study evaluated the influence of diphenyliodonium hexafluorphosphate (DPI) combined with two different amines [ethyl 4-(dimethylamino)benzoate (EDAB) and 2-(dimethylamino)ethyl methacrylate (DMAEMA)] on the properties of model resin cements. METHODS: A comonomer base containing a 1:1 mass ratio of 2.2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane (bis-GMA) and triethyleneglycol dimethacrylate (TEGDMA) was obtained, after which 1mol% of camphorquinone and 0.1mol% of hydroxyl butyl toluene were added to the comonomer blend. Concentrations of co-initiators varied at 0, 0.5 or 1mol% for DPI and in 1 or 2mol% for amines (DMAEMA or EDAB). Silanated Ba-Al-Si glass (60wt%) was added as filler. The combination of each amine and DPI concentration resulted in 12 formulations, which had the following properties analyzed: degree of conversion (DC), water sorption (Wsp) and solubility (Wsl), flexural strength (FS) and flexural modulus (Ef). Data for DC, FS and Ef were analyzed by two-way ANOVA and Tukey's test (α=0.05) and Wsp and Wsl by Kruskal-Wallis and Dunn tests (α=0.05). RESULTS: EDAB promoted a higher DC than did DMAEMA; however, DPI increased DC for all materials with DMAEMA. The physical properties of resin formulations containing EDAB were significantly better than those of groups with DMAEMA; however, DPI had a positive influence on the chemical and physical properties of the model resin cement containing DMAEMA, especially with higher concentrations of amine. SIGNIFICANCE: EDAB proved to be more reactive than DMAEMA, being less influenced by DPI. Resins containing a 1:2 CQ/amine ratio had better properties than those with 1:1.

The effect of surface treatment and bonding procedures on the bond strength of silorane composite repairs.

OBJECTIVE: The aim of this study was to evaluate the effect of surface treatments and adhesive protocols on the microtensile bond strength of a low-shrinkage composite repair. MATERIALS AND METHODS: Ninety-six blocks of composite resin Filtek LS were prepared using a half-hourglass-shaped silicone matrix. The specimens were storage for 24 h in distilled water and were randomly divided into the experimental (6) and negative control (2) groups (n = 12) according to the surface treatment (diamond bur and aluminum oxide sandblasting) and adhesive protocol (none; Filtek LS adhesive; phosphoric acid + Filtek LS adhesive; and phosphoric acid + silane + Filtek LS adhesive). After the adhesive procedure, the specimens were fixed in an hourglass-shaped silicone matrix and the other half of the specimen was restored. Hourglass shaped specimens (n = 12) were used as positive control (cohesive strength of the resin). The microtensile bonding test was performed at a crosshead speed of 0.5 mm/min. The data were analyzed using ANOVA, Tukey's and Dunnett's tests (α = 0.05). RESULTS: The bond strength values were similar for all experimental groups, except the groups without adhesive application. None of the experimental groups presented results similar to the positive control group. CONCLUSIONS: The repair of silorane restorations is viable; nevertheless, the different bonding procedures tested were incapable to produce bond strengths similar to the cohesive strength of the material.

Mechanical properties and degree of conversion of etch-and-rinse and self-etch adhesive systems cured by a quartz tungsten halogen lamp and a light-emitting diode.

The aim of the present study was to evaluate the degree of conversion (DC), elastic modulus (E), and flexural strength (FS) of five adhesive systems (only the bonding component of both Scotchbond MP-SBMP and Clearfil Protect Bond-CP; Single Bond 2-SB2; One-up Bond F Plus-OUP; and P90 System Adhesive: primer-P90P and bond-P90B) cured with a quartz tungsten halogen (QTH) lamp and a light-emitting diode (LED). Two groups per adhesive were formed (n=5), according to the light source (quartz tungsten halogen-QTH: Demetron LC; and light-emitting diode-LED: UltraLume 5). Bar-shaped specimens were evaluated using three-point bending. The DC was obtained by Fourier transform infrared spectroscopy (FTIR). SB2 and P90P exhibited better DC values for QTH curing. However, SB2 and P90P presented the worst results overall. The light source was statistically significant for all adhesives, except for P90B and OUP. Non-solvated adhesives presented the best E and FS values. It could be concluded that the DC and E values can be influenced by the light source; however, this interference is material dependent.

Photoelastic evaluation of the effect of composite formulation on polymerization shrinkage stress

We compared polymerization stress in two commercial composites and three experimental composites made using camphorquinone (CQ) and/or phenylpropanedione (PPD) as photoinitiators. The internal surfaces of photoelastic resin discs with cylindrical cavities were roughened and treated with adhesive. Composites were divided into five groups: two commercial composites (Filtek Silorane and Filtek Z250) and three experimental composites with CQ/amine, CQ/PPD/amine, and PPD/amine. Composites were photopolymerized inside cavities, and subjected to photoelastic analysis immediately and at 24 hours and 7 days later using a plane polariscope. Stress created by Silorane (3.08 ± 0.09 MPa) was similar to that of Z250 (3.19 ± 0.13 MPa) immediately after photopolymerization (p > 0.05). After 24 hours and 7 days, Z250 (3.53 ± 0.15 and 3.69 ± 0.10 MPa, respectively) showed higher stress than Silorane (3.19 ± 0.10 and 3.16 ± 0.10 MPa, respectively). Qualitative analysis immediately after photopolymerization showed composite/CQ promoted higher stress than PPD, but stress levels at other evaluated times were statistically similar, varying between 3.45 ± 0.11 MPa and 3.92 ± 0.13 MPa. At 24 hours and 7 days, Silorane created the lowest stress. All photoinitiators created comparable tensions during polymerization.

Photoelastic evaluation of the effect of composite formulation on polymerization shrinkage stress.

We compared polymerization stress in two commercial composites and three experimental composites made using camphorquinone (CQ) and/or phenylpropanedione (PPD) as photoinitiators. The internal surfaces of photoelastic resin discs with cylindrical cavities were roughened and treated with adhesive. Composites were divided into five groups: two commercial composites (Filtek Silorane and Filtek Z250) and three experimental composites with CQ/amine, CQ/PPD/amine, and PPD/amine. Composites were photopolymerized inside cavities, and subjected to photoelastic analysis immediately and at 24 hours and 7 days later using a plane polariscope. Stress created by Silorane (3.08 ± 0.09 MPa) was similar to that of Z250 (3.19 ± 0.13 MPa) immediately after photopolymerization (p > 0.05). After 24 hours and 7 days, Z250 (3.53 ± 0.15 and 3.69 ± 0.10 MPa, respectively) showed higher stress than Silorane (3.19 ± 0.10 and 3.16 ± 0.10 MPa, respectively). Qualitative analysis immediately after photopolymerization showed composite/CQ promoted higher stress than PPD, but stress levels at other evaluated times were statistically similar, varying between 3.45 ± 0.11 MPa and 3.92 ± 0.13 MPa. At 24 hours and 7 days, Silorane created the lowest stress. All photoinitiators created comparable tensions during polymerization.

Influence of sterilization method on the bond strength of caries-affected dentin.

This study evaluated the effect of sterilization method on the bond strength of caries-affected dentin before artificial caries development and after restoration. Twelve bovine incisors were sectioned perpendicularly to their long axes at 7 mm from the amelodentinal junction. They were painted with acid-resistant nail varnish, except on an exposed coronal dentin area. Four groups were formed (n = 3) in accordance with the sterilization method used, before artificial caries development and after complete restoration: NE - no sterilization (control group); G - gamma-rays before and after; A - steam autoclave before and after; AG - steam autoclave before and gamma-rays after. For artificial caries development, dentin sections were immersed in BHI broth with S. mutans. After the soft carious tissue was removed, dentin was restored with Scotchbond Multi-Purpose and Filtek Z250. Next, the samples were sterilized in accordance with the methods described above and microtensile testing was performed. The data were analyzed by the Mann-Whitney test (p < 0.05). The G (22.7 MPa) and AG groups (16.3 MPa) were not statistically different from the NE group (17.5 MPa). Nevertheless, there were statistical differences between groups A (6.3 MPa) and NE, A and G, A and AG, G and AG. The bond strength of caries-affected dentin was not influenced by gamma-ray sterilization irrespective of whether the sterilization was performed before or after restoration.

Influence of sterilization method on the bond strength of caries-affected dentin

This study evaluated the effect of sterilization method on the bond strength of caries-affected dentin before artificial caries development and after restoration. Twelve bovine incisors were sectioned perpendicularly to their long axes at 7 mm from the amelodentinal junction. They were painted with acid-resistant nail varnish, except on an exposed coronal dentin area. Four groups were formed (n = 3) in accordance with the sterilization method used, before artificial caries development and after complete restoration: NE - no sterilization (control group); G - gamma-rays before and after; A - steam autoclave before and after; AG - steam autoclave before and gamma-rays after. For artificial caries development, dentin sections were immersed in BHI broth with S. mutans. After the soft carious tissue was removed, dentin was restored with Scotchbond Multi-Purpose and Filtek Z250. Next, the samples were sterilized in accordance with the methods described above and microtensile testing was performed. The data were analyzed by the Mann-Whitney test (p < 0.05). The G (22.7 MPa) and AG groups (16.3 MPa) were not statistically different from the NE group (17.5 MPa). Nevertheless, there were statistical differences between groups A (6.3 MPa) and NE, A and G, A and AG, G and AG. The bond strength of caries-affected dentin was not influenced by gamma-ray sterilization irrespective of whether the sterilization was performed before or after restoration.