Dynamic mechanical thermal analysis of composite resins with CQ and PPD as photo-initiators photoactivated by QTH and LED units

Co-initiators of polymerization can modulate the inflammatory cytokine release without major cytotoxic effects in human dental pulp cells

To evaluate the cytotoxicity of co-initiators of polymerization and its influence on cytokine release from human dental pulp cells (hDPCs). Cells were isolated from the dental pulp of sound human third molars. The co-initiators dimethylaminoethyl amine benzoate-(EDAB), 2-(dimethylamino)ethyl methacrylate (DMAEMA); 2-Ethylhexyl 4-(dimethylamino)benzoate (EHA) and bis(4-methyl phenyl)iodonium hexafluorophosphate (BPI) were diluted in dimethylsulfoxide (DMSO) at different concentrations. In this way, experimental groups and one control (without treatment) were obtained. hDPCs (10 × 10⁴ cell per well) were seeded on 96 well plates and incubated at 37°C and 5% CO₂ for 48 h. After this, the cells were exposed to different concentrations of co-initiators cited for 24 h. After this time, the culture medium was removed, and the mitochondrial metabolism was evaluated by MTT assay, cell death by flow cytometry, and cytokine released (IL-1β, IL6, IL-8, IL-10, and TNF-α) was analyzed by MAGPIX assay. The data were analyzed by ANOVA one-way and Tukey's test. EHA, DMAEMA, and EDAB did not reduce the mitochondrial metabolism. BPI presented high toxicity with remarkable reduction (80%) after exposure to 1 mM. The cell death of all test groups was similar to control. After 24 h treatment, the IL-8 was up-regulated by all compounds, while IL-6 was upregulated after exposure to EHA and downregulated after DMAEMA stimulation. BPI, EHA, EDAB, and DMAEMA can trigger an initial inflammatory response, upregulating the IL-8 secretion in hDPCs in a compound-concentration-dependent manner; however, this was not accompanied by major cytotoxic effects at cell death or mitochondrial-metabolism levels.

The Photoinitiators Used in Resin Based Dental Composite-A Review and Future Perspectives

The presented paper concerns current knowledge of commercial and alternative photoinitiator systems used in dentistry. It discusses alternative and commercial photoinitiators and focuses on mechanisms of polymerization process, in vitro measurement methods and factors influencing the degree of conversion and hardness of dental resins. PubMed, Academia.edu, Google Scholar, Elsevier, ResearchGate and Mendeley, analysis from 1985 to 2020 were searched electronically with appropriate keywords. Over 60 articles were chosen based on relevance to this review. Dental light-cured composites are the most common filling used in dentistry, but every photoinitiator system requires proper light-curing system with suitable spectrum of light. Alternation of photoinitiator might cause changing the values of biomechanical properties such as: degree of conversion, hardness, biocompatibility. This review contains comparison of biomechanical properties of dental composites including different photosensitizers among other: camphorquinone, phenanthrenequinone, benzophenone and 1-phenyl-1,2 propanedione, trimethylbenzoyl-diphenylphosphine oxide, benzoyl peroxide. The major aim of this article was to point out alternative photoinitiators which would compensate the disadvantages of camphorquinone such as: yellow staining or poor biocompatibility and also would have mechanical properties as satisfactory as camphorquinone. Research showed there is not an adequate photoinitiator which can be as sufficient as camphorquinone (CQ), but alternative photosensitizers like: benzoyl germanium or novel acylphosphine oxide photoinitiators used synergistically with CQ are able to improve aesthetic properties and degree of conversion of dental resin.

Evaluation of physico-mechanical properties and filler particles characterization of conventional, bulk-fill, and bioactive resin-based composites

OBJECTIVE

This study evaluated physical and mechanical properties and characterized the filler particles of seven composites.

MATERIALS AND METHODS

Filtek Supreme (FS, 3M Oral Care), Forma (FO, Ultradent), Charisma Diamond (CD, Kulzer), Spectra Smart (SS, Dentsply), Filtek Bulk Fill (FB, 3M Oral Care), Tetric N-Ceram Bulk Fill (TB, Ivoclar), and Cention N (Ivoclar) in self- (CNSC) or dual-curing (CNDC) were evaluated. Fillers size, shape, and content were analyzed by scanning electron microscopy (SEM) and X-ray dispersive energy spectroscopy (EDX). Disk-shaped specimens (n = 5) were prepared for sorption (SP) and solubility (SL). Flexural strength and elastic modulus were tested at 24 h and 12 months (n = 10). Degree of conversion (DC%) and maximum rate of polymerization (Rp^max) were evaluated using micro-Raman spectroscopy. SP and SL results were submitted to Kruskal-Wallis one-way ANOVA and Dunn's pairwise test (α = 0.05). Mechanical properties were analyzed by 2-way ANOVA and Tukey's test (α = 0.05). DC% of CNSC and CNDC was compared by independent t-test (α = 0.05). Rp^max results were analyzed by 1-way ANOVA and Tukey's test (α = 0.05).

RESULTS

The composites differed regarding filler size, shape, and content. CD and CNSC showed lower SP than FS. SS had lower SL than CNSC and CNDC. CNDC presented higher DC% than CNSC. CD, TB, and CNDC showed the highest Rp^max. TB, CNSC, and CNDC showed the lowest 24-h flexural strengths. Mechanical properties of CD did not decrease, while FO, TB, and CNSC showed a significant reduction after storage.

CONCLUSIONS

Monomer composition and fillers characteristics greatly influenced the physico-mechanical properties of the tested composites.

Moving Towards a Finer Way of Light-Cured Resin-Based Restorative Dental Materials: Recent Advances in Photoinitiating Systems Based on Iodonium Salts

The photoinduced polymerization of monomers is currently an essential tool in various industries. The photopolymerization process plays an increasingly important role in biomedical applications. It is especially used in the production of dental composites. It also exhibits unique properties, such as a short time of polymerization of composites (up to a few seconds), low energy consumption, and spatial resolution (polymerization only in irradiated areas). This paper describes a short overview of the history and classification of different typical monomers and photoinitiating systems such as bimolecular photoinitiator system containing camphorquinone and aromatic amine, 1-phenyl-1,2-propanedione, phosphine derivatives, germanium derivatives, hexaarylbiimidazole derivatives, silane-based derivatives and thioxanthone derivatives used in the production of dental composites with their limitations and disadvantages. Moreover, this article represents the challenges faced when using the latest inventions in the field of dental materials, with a particular focus on photoinitiating systems based on iodonium salts. The beneficial properties of dental composites cured using initiation systems based on iodonium salts have been demonstrated.

Chemistry of novel and contemporary resin-based dental adhesives

The chemistry of resin-based dental adhesives is critical for its interaction with dental tissues and long-term bonding stability. Changes in dental adhesives composition influences the materials' key physical-chemical properties, such as rate and degree of conversion, water sorption, solubility, flexural strength and modulus, and cohesive strength and improves the biocompatibility to dental tissues. Maintaining a suitable reactivity between photoinitiators and monomers is important for optimal properties of adhesive systems, in order to enable adequate polymerisation and improved chemical, physical and biological properties. The aim of this article is to review the current state-of-the-art of dental adhesives, and their chemical composition and characteristics that influences the polymerisation reaction and subsequent materials properties and performance.

Influence of Photoinitiator on Accelerated Artificial Aging and Bond Strength of Experimental Resin Cements

Abstract The goal of this study was to evaluate in vitro the effect of the photoinitiator phenylpropanedione (PPD), alone or combined with camphorquinone (CQ), on color stability of photoactivated resin cements and their bond strength to ceramics using a micro-shear test. Four resin cements were used: a commercial brand cement (RelyX Veneer®) and 3 experimental cements with different types and concentration of photoinitiators. For color analysis, ceramic discs were cemented on bovine dentin specimens to simulate indirect restorations (n=8) and were exposed to UV for 120 h and tested for color alteration using a reflectance spectrophotometer and the CIEL*a*b* system. Data were analyzed by Anova and Tukey’s test at 5% significance level. The color test results did not present statistically significant difference for the ∆E for all the studied cements, neither for ∆L, ∆a and ∆b. For the bond strength, all the studied cements showed statistically significant differences to each other, with the highest result for the RelyX Veneer® (29.07 MPa) cement, followed by the cement with CQ (21.74 MPa) and CQ+PPD (19.09 MPa) cement; the lowest result was obtained by the cement using only PPD as a photoinitiator (13.99 MPa). So, based on the studied parameters, PPD was not advantageous as photoinitiator of resin cements, because it showed a low value of bond strength to the ceramics and no superior color stability.

Evaluation of phenyl-propanedione on yellowing and chemical-mechanical properties of experimental dental resin-based materials

Objective

To evaluate the influence of phenyl-propanedione on yellowing and chemical-mechanical properties of experimental resin-based materials photoactivated using different light curing units (LCUs).

Material and Methods

Experimental resin-based materials with the same organic matrix (60:40 wt% BisGMA:TEGDMA) were mechanically blended using a centrifugal mixing device. To this blend, different photoinitiator systems were added in equimolar concentrations with aliphatic amine doubled by wt%: 0.4 wt% CQ; 0.38 wt% PPD; or 0.2 wt% CQ and 0.19 wt% PPD. The degree of conversion (DC), flexural strength (FS), Young's modulus (YM), Knoop hardness (KNH), crosslinking density (CLD), and yellowing (Y) were evaluated (n=10). All samples were light cured with the following LCUs: a halogen lamp (XL 2500), a monowave LED (Radii), or a polywave LED (Valo) with 16 J/cm2. The results were analysed by two-way ANOVA and Tukey's test (α=0.05).

Results

No statistical differences were found between the different photoinitiator systems to KNH, CLS, FS, and YM properties (p≥0.05). PPD/CQ association showed the higher DC values compared with CQ and PPD isolated systems when photoactivated by a polywave LED (p≤0.05). Y values were highest for the CQ compared with the PPD systems (p≤0.05).

Conclusion

PPD isolated system promoted similar chemical and mechanical properties and less yellowing compared with the CQ isolated system, regardless of the LCU used.

Evaluation of Eye Protection Filters Used with Broad-Spectrum and Conventional LED Curing Lights

Abstract The high irradiance and the different emission spectra from contemporary light curing units (LCU) may cause ocular damage. This study evaluated the ability of 15 eye protection filters: 2 glasses, 1 paddle design, and 12 dedicated filters to block out harmful light from a monowave (HP-3M ESPE) and a broad-spectrum (Valo, Ultradent) LED LCU. Using the anterior sensor in the MARC-Patient Simulator (BlueLight Analytics) the irradiance that was delivered through different eye protection filters was measured three times. The LCUs delivered a similar irradiance to the top of the filter. The mean values of the light that passed through the filters as percent of the original irradiance were analyzed using two-way ANOVA followed by Tukey test (a= 0.05). The emission spectra from the LCUs and through the filters were also obtained. Two-way ANOVA showed that the interaction between protective filters and LCUs significantly influenced the amount of light transmitted (p< 0.001). Tukey test showed that the amount of light transmitted through the protective filters when using the HP-3M-ESPE was significantly greater compared to when using the Valo, irrespective of the protective filter tested. When using the HP-3M-ESPE, the Glasses filter allowed significantly more light through, followed by XL 3000, ORTUS, Google Professional, Gnatus filters. The Valo filter was the most effective at blocking out the harmful light. Some protective filters were less effective at blocking the lower wavelengths of light (<420 nm). However, even in the worst scenario, the filters were able to block at least 97% of the irradiance.

Effect of diphenyliodonium hexafluorophosphate on the physical and chemical properties of ethanolic solvated resins containing camphorquinone and 1-phenyl-1,2-propanedione sensitizers as initiators

OBJECTIVES

To evaluate the effects of the diphenyliodonium hexafluorophosphate (DPI) on the physical and mechanical properties of solvated dental adhesive resins containing camphorquinone (CQ) and/or 1-phenyl-1,2-propanedione (PPD) as initiators.

METHODS

Model solvated resins containing bisphenol glycidyl methacrylate (BisGMA); triethyleneglycol dimethacrylate (TEGDMA); 1,3-glycerol dimethacrylate (GDMA); 2-hydroxyethyl methacrylate (HEMA); dimethylaminoethyl amine benzoate (EDAB) and ethanol were prepared. The resins were divided in 24 test groups according to the incorporated initiator systems (CQ-0.5 or 1mol%; PPD-0.5 or 1mol%; CQ+PPD-0.5 or 1mol%) as well the presence of DPI (0, 0.5 or 1mol%). Degree of conversion (using Fourier-transformed near infra-red spectroscopy), flexural strength and modulus by three point bending, cohesive strength and water sorption and solubility were measured. Data were statistically analyzed by one and two way ANOVA and Tukey's test (α=0.05).

RESULTS

DPI increased the degree of conversion of all materials tested. Camphorquinone promoted higher degree of conversion than resins containing only PPD or CQ+PPD. Generally, the resins containing PPD+CQ with DPI presented higher flexural strength and modulus, cohesive strength, as well lower water sorption and solubility.

SIGNIFICANCE

The use of PPD combined with CQ can increase the physical properties of the solvated resins. DPI improved the monomer conversion of all experimental materials and can positively modulate most of the physical properties of the solvated resins.

Influence of Photoinitiator and Light-Curing Source on Bond Strength of Experimental Resin Cements to Dentin

Abstract This study evaluated the bond strength (BS) of experimental resin cements formulated with different photoinitiators when activated by two kinds of light-curing units (LCUs) through a ceramic material. Seven resin blends with different camphorquinone (CQ) and/or phenylpropanedione (PPD) concentrations (weight) were prepared: C5: 0.5% CQ; C8: 0.8% CQ; P5: 0.5% PPD; P8: 0.8% PPD; C1P4: 0.1% CQ and 0.4% PPD; C4P1: 0.4% CQ and 0.1% PPD; C4P4: 0.4% CQ and 0.4% PPD. Two LCUs were used: one quartz-tungsten-halogen (QTH - 850 mW/cm²) and one light-emitting diode (LED - 1300 mW/cm²). The microtensile bond strength of each blend was assessed. Data were submitted to two-way ANOVA and Tukey's test (α=0.05). The BS values did not exhibit significant differences for LCUs, regardless of the photoinitiator type. Three cements showed significant differences: P5 and C5 had higher BS with QTH, and C4P1 with LED. For QTH, P5 showed the highest and C1P4 the lowest BS. For the LED, C4P1 showed the highest BS of all the cements. The results indicated that PPD was a viable alternative in the formulation of photocured resin cements, reducing or eliminating CQ that is yellowish without impairing the bond strength. Furthermore, both LED and QTH were effective in curing resin cements that contain PPD or CQ.

Effect of two lasers on the polymerization of composite resins: single vs combination

The selection of a light-curing unit for the curing composite resins is important to achieve best outcomes. The purpose of the present study was to test lasers of 457 and 473 nm alone or in combination under different light conditions with respect to the cure of composite resins. Four different composite resins were light cured using five different laser combinations (530 mW/cm(2) 457 nm only, 530 mW/cm(2) 473 nm only, 177 mW/cm(2) 457 + 177 mW/cm(2) 473 nm, 265 mW/cm(2) 457 + 265 mW/cm(2) 473 nm, and 354 mW/cm(2) 457 + 354 mW/cm(2) 473 nm). Microhardness and polymerization shrinkage were evaluated. A light-emitting diode (LED) unit was used for comparison purposes. On top surfaces, after aging for 24 h, microhardness achieved using the LED unit and the lasers with different conditions ranged 42.4-65.5 and 38.9-67.7 Hv, respectively, and on bottom surfaces, corresponding ranges were 25.2-56.1 and 18.5-55.7 Hv, respectively. Of the conditions used, 354 mW/cm(2) 457 nm + 354 mW/cm(2) 473 nm produced the highest bottom microhardness (33.8-55.6 Hv). On top and bottom surfaces, microhardness by the lowest total light intensity, 354 (177 × 2) mW/cm(2), ranged 39.0-60.5 and 18.5-52.8 Hv, respectively. Generally, 530 mW/cm(2) at 457 nm produced the lowest polymerization shrinkage. However, shrinkage values obtained using all five laser conditions were similar. The study shows the lasers of 457 and 473 nm are useful for curing composite resins alone or in combination at much lower light intensities than the LED unit.