Lower Degree Of Conversion Research Articles

Degree of conversion of 3D printing resins used for splints and orthodontic appliances under different postpolymerization conditions.

To measure the degree of conversion (DC) of different 3D printing resins used for splints or orthodontic appliances under different postpolymerization conditions. Five 3D-printed photopolymer resins were studied. Each resin was analyzed in liquid form (n = 15), and then cylindrical specimens (n = 135) were additively manufactured and postcured with Form Cure (Formlabs) at different times (10, 60, and 90min) and temperatures (20°C, 60°C, and 80°C). The DC of each specimen was measured with Fourier transform infrared spectroscopy (FTIR). The data were statistically analyzed using a 3-way ANOVA followed by Tukey's post hoc test. The time and temperature of postpolymerization significantly influenced the DC of each resin: when time and/or temperature increased, the DC increased. For all resins tested, the lowest DC was obtained with a postcuring protocol at 10min and 20°C, and the highest DC was obtained at 90min and 80°C. However, at 80°C, the samples showed a yellowish color. With the Form Cure device, the time and temperature of postcuring could have an impact on the DC of the 3D printing resins studied. The DC of the 3D printing resins could be optimized by adjusting the postpolymerization protocol. Regardless of the resin used, when using the Form Cure device, postcuring at 60min and 60°C would be the minimal time and temperature conditions for achieving proper polymerization. Beyond that, it would be preferable to increase the postcuring time to boost the DC.

Synthesis of amphiphilic molecular brushes by solution radical copolymerization of oligoethylene glycol and oligopropylene glycol methacrylates

The regularities of radical copolymerization of methoxyoligo(ethylene glycol)methacrylate (MOEGM) with an ethoxylation degree of 11 and methoxyoligo(propylene glycol)methacrylate (MOPGM) with a propoxylation degree of 6 or 10 in toluene solutions were determined. The copolymers formed at low degrees of conversion are enriched with ethoxylated ether units in both pairs of monomers. The relative activities of the comonomers determined by the Fineman-Ross methods are in the range of 1.36–1.88 (MOEGM) and 0.56–0.92 (MOPGM). It has been established that the activity of MOPGM decreases with an increase in the length of the oligopropylene glycol chain.

Influence of bioactive particles and onium salt on the physicochemical properties of experimental infiltrants.

This study evaluated physicochemical properties of experimental infiltrants after addition of hydroxyapatite nanoparticles (HAp) or 58S bioactive glass (BAG) and diphenyliodonium hexafluorophosphate (DPI). The resin matrix was composed of TEGDMA/Bis-EMA (3:1), 0.5 mol% CQ, and 1 mol% EDAB. The blends received or not 0.5 mol% DPI and 10% wt BAG or HAp. Icon was used as commercial control. The groups were characterized by XRD, FT-IR spectrometry, and SEM before and after simulated body fluid (SBF) immersion for up to 7 days. Polymerization kinetics (n =3 ), water sorption and solubility (n=10), and viscosity (n = 3) were surveyed. For polymerization kinetics, the samples were polymerized for 5 min and the data were obtained from 40 s and 5 min. Statistical analysis was made using ANOVA and Tukey's test (a = 0.05). After 7 days of SBF immersion, XRD and FT-IR showed that the HAp crystalline phase was present only in the HAp groups. A lower degree of conversion (DC) and polymerization rate were observed for the Icon and BAG groups, whereas HAp showed higher values. For the BAG group, DPI increased polymerization rate and DC in 40 s. After 5 min, all groups presented DC above 80%. In groups with particles, the HAp groups exhibited higher viscosity, whereas DPI groups showed a decrease in viscosity. Icon had the highest water sorption. To conclude, BAG neither improved the physicochemical properties studied, nor did it show bioactive properties. The addition of DPI reduced viscosity caused by particle addition and also attenuated the DC decrease caused by BAG addition. The addition of bioactive particles to infiltrants should be seen with caution because they increase viscosity and may not bring major clinical improvements that justify their use. DPI might be indicated only if any component is added to the infiltrant to act as a compensation mechanism.

Effect of thickness on the degree of conversion, monomer elution, depth of cure and cytotoxicity of bulk-fill composites

Today, bulk-fill composites are used as a single layer with a thickness of up to 4-5 mm. However, is proper polymerization achieved with this increased thickness? This study was designed to investigate the effect of thickness on the degree of conversion (DC) (n = 6), the elution of monomers (n = 6), depth of cure (DoC) (n = 10) and cytotoxicity (n = 6) of the bulk-fill composites SDR Flow Plus (SDR), SonicFill2 SingleFill (SF) and ACTIVA Bioactive Restorative (ACT) in comparison to the conventional G-aenial Posterior (GC). Two-way analysis of variance (ANOVA) was used to assess the interaction between materials and surfaces, and one-way ANOVA and Tukey tests were used to compare the degree of conversion, monomer elution and cytotoxicity values (P < 0.05). The highest DC was found at the top surface of SDR, while the lowest DC was found at SF. The V2 mm/V0 mm DoC ratios of the composites except ACTs were appropriate according to the threshold. None of the composites were cytotoxic on day 1. In bulk-fill composites, DC decreased and monomer elution increased with increasing depth. The V4 mm/V0 mm ratios of all bulk-fill groups were not appropriate. Additionally, only ACTs had a cell viability of <70% on day 7.

Thermogravimetric analysis and kinetic modeling of the co-pyrolysis of a bituminous coal and poplar wood

The co-pyrolysis of coal and biomass has proven to be a promising route to produce liquid and gaseous fuels as well as specific value-added chemicals while contributing to mitigating CO2 emissions. The interactions between the co-processed feedstocks, however, need to be elucidated to support the development of such a thermochemical conversion process. In this context, the present work covers the kinetic analysis of the co-pyrolysis of a bituminous coal with poplar wood. In this research, biomass was blended with coal at two different mass ratios (10% (mass) and 20% (mass)). Thermogravimetric analyses were carried out with pure and blended samples at four heating rates (5, 10, 15 and 30 °C·min−1). A direct comparison of experimental and theoretical results (based on a simple additivity rule) failed to yield a clear-cut conclusion regarding the existence of synergistic effects. Kinetic analyses have therefore been achieved using two model-free methods (the Ozawa–Flynn–Wall and Kissinger–Akahira–Sunose models) to estimate the rate constant parameters related to the pyrolysis process. A significant decrease of the activation energy has thus been observed when adding wood to coal (activation energies associated with the blend containing 20% (mass) of biomass being even lower than those estimated for pure wood at low conversion degrees). This trend was attributed to the possible presence of synergies whose related mechanisms are discussed. The rate constant parameters derived by means of the two tested models were finally used to simulate the evolution of the conversion degree of each sample as a function of the temperature, thus leading to a satisfying agreement between measured and simulated data.

Raman Spectroscopy as Spectral Tool for Assessing the Degree of Conversion after Curing of Two Resin-Based Materials Used in Restorative Dentistry.

(1) Background: The treatment of dental cavities and restoration of tooth shape requires specialized materials with specific clinical properties, including being easy to model, light-cured, having a natural color, reduced shrinkage, a hardness similar to hydroxyapatite, and no leakage. The dimensional stability of resin composite materials is affected by polymerization shrinkage, degree of conversion (number of π carbon bonds converted into σ ones), thermal contraction and expansion, and interactions with an aqueous environment. (2) Methods: The materials used in our investigation were two composite resins with similar polymer matrices, but different filler (micro/nano filler). To evaluate the properties of samples, we employed the pycnometer technique (pycnometer from Paul Marienfeld Gmbh, Lauda-Königshofen, Germany), RAMAN spectroscopy technique (MiniRam Equipment from B&W Tek Inc., Plainsboro Township, NJ, USA; 785 nm laser source), SEM and EDX (FEI Inspect S.). (3) Results: The size of the filler plays an important role in the polymerization: for the pycnometric results, the larger particle filler (Sample 1) seems to undergo a rapid polymerization during the 45 s curing, while the nanoparticle filer (Sample 2) needs additional curing time to fully polymerize. This is related to a much larger porosity, as proved by SEM images. The lower degree of conversion, as obtained by Raman spectroscopy, in the same geometry means that the same volume is probed for both samples, but Sample 1 is more porous, which means less amount of polymer is probed for Sample 1. (4) Conclusions: For the two composites, we obtained a degree of conversion of 59% for Sample 1 and 93% for Sample 2, after 45 s of curing.

The Effect of Different Light-curing Units and Tip Distances on the Polymerization Efficiency of Bulk-fill Materials.

In an average class II posterior preparation, the curing light tip is placed at a distance from the restoration surface that far exceeds the 1-mm manufacturer's recommendation. This distance can have potentially detrimental effects on the curing efficiency of the light-curing unit as well as the properties of the resin-based composite restoration, especially at the bottom of the cavity preparation. The purpose of this study was to evaluate the effects of various types of light-curing units (LCUs) and the different curing distances on the degree of conversion (DC) and the surface hardness of bulk-fill composite materials. A total of 390 specimens of three resin-based composites (RBCs) were fabricated. Two bulk-fill RBCs, including Filtek Bulk Fill Posterior (3M ESPE GmbH, Seefeld, Germany) and Tetric N-Ceram Bulk Fill (Ivoclar Vivadent AG, Schaan, Liechtenstein), as well as a Filtek Z350 XT nano-filled composite (3M ESPE GmbH, Seefeld, Germany), were utilized. In this study, the Vickers microhardness number (VMN) and the DC were evaluated at 2 and 4 mm thicknesses. Polymerization for 20 seconds was performed using two high-power light-curing units, namely the polywave Bluephase G2 light-emitting diode (LED) LCU (Ivoclar Vivadent AG, Schaan, Liechtenstein) and the monowave Elipar Deep Cure S LED LCU (3M Oral Care, St Paul, MN, USA) at 0, 2, and 4 mm distance between the curing tip and the RBC surface. The results were analyzed using the two-way analysis of variance method. Scheffe's post-hoc multiple comparison tests were used to determine significant differences between the materials, the LCU, and the tip distances. The highest DC (70.17) was shown by Filtek Bulk Fill Posterior at a distance of 0 mm, whereas the lowest DC (45.99) was measured for the conventional Filtek Z350 XT at a 4 mm distance. Moreover, higher VMNs were shown by Filtek Bulk Fill and Filtek Z350 composites at 0 mm distance than by the Tetric N-Ceram Bulk Fill composite material when cured with a Bluephase G2 LCU. For all materials, a significant decrease in the DC and mean VMN values was observed at a 4 mm distance in comparison with 0 and 2 mm distances. The DC and VMN values among the studied bulk fill materials were more significantly affected by the material composition and curing protocols. The increased distance from the light tip has a detrimental effect on the mechanical properties of composite resin materials. Significant differences were observed in the curing efficiency of the two LCUs investigated.

Effect of replacing UDMA by a new tetramethacrylate monomer on the properties of dental resin composite

AbstractThe aim of this study is to synthesize the tetramethacrylate monomer (TIMA) and evaluate its effect as a substituent for UDMA in the formulation of photopolymerizable dental resin composites (DRC). 1H NMR, 13C NMR and FTIR spectroscopies corroborate the chemical structure of the TIMA monomer. The experimental composite resin is a mixture of TIMA/TEGDMA monomers and silanized inorganic filler while, the control resin is a mixture of UDMA/TEGDMA and filler. The double‐bond conversion, polymerization kinetics, volumetric shrinkage, aqueous sorption, solubility, mechanical properties, and cell viability are studied. The flexural strength of the composite resin formulated with TIMA monomer does not show statistical differences compared to the control (p &gt; 0.05). However, formulations with the TIMA monomer presented higher elastic modulus (2425.37 MPa) and lower degree of conversion 38.5%, (p &lt; 0.05). The differences in the water sorption, water solubility and volumetric shrinkage are not statistically significant between the groups (p &gt; 0.05). Finally, the cell viability test show that the experimental resin formulated with TIMA monomer exhibited a cellular viability close to 100%. Due to its characteristics, TIMA monomer could be considered an alternative to UDMA in the composite resins with applications in dentistry.

Influence of ceramic veneer on the transdentinal cytotoxicity, degree of conversion and bond strength of light-cured resin cements to dentin

ObjectivesTo investigate the transdentinal cytotoxicity (TC), degree of conversion (DC), and micro shear bond strength (μSBS) to dentin of light-cured resin cements (LCRCs) photoactivated directly or through a ceramic veneer( ± CV). Materials and methodsThe TC was assessed using human dentin discs adapted into artificial pulp chambers. Odontoblast-like cells were seeded on the pulp surface of the discs, then three LCRCs( ± CV) were applied on their etched and hybridized occlusal surface (n = 8/group). The adhesive systems of each LCRCs and sterile phosphate-buffered saline were used as positive and negative controls, respectively. After 24 h, the viability and morphology of cells adhered on discs were assessed. The extracts (culture medium + components of the materials diffused through the discs) were applied on the MDPC-23 to evaluate their viability, adhesion/spreading (A/S), alkaline phosphatase activity (ALP), and mineralized nodule formation (MN). LCRCs( ± CV) specimens were evaluated concerning the DC and μSBS to dentin. Data were analyzed by one-, two-, or three-way ANOVA/Dunnett, Sidak, and Games-Howell tests (α = 5%). ResultsAll LCRCs( ± CV) reduced cell viability, A/S, ALP, MN, and DC. Except for μSBS, the intensity of reduction was dependent on the LCRC used. LCRCs+CV resulted in lower DC and μSBS but did not increase the TC. SignificanceBesides the presence of CV between the light source and LCRCs reduces the degree of conversion and bond strength to dentin, these materials cause variable level of transdentinal toxicity to pulp cells. Thus, the composition and curing protocols of LCRCs should be revisited and reinforced to prevent mechanical and biological drawbacks.

Influence of Concentration Levels of β-Tricalcium Phosphate on the Physical Properties of a Dental Adhesive.

Our study assessed the influence of integrating 5% and 10% tricalcium phosphate (β-TCP-Ca3(PO4)2.) nanoparticles into a dental adhesive on the adhesive’s bonding. To evaluate the filler nanoparticles, scanning electron microscopy (SEM), Energy Dispersive X-Ray (EDX) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and micro-Raman spectroscopy techniques were used. Shear Bond strength (SBS) testing, degree of conversion (DC) analysis, investigation of the adhesive–dentin interface, and biofilm experiments were conducted. The SEM micrographs revealed non-uniform agglomerates, while the EDX demonstrated the existence of oxygen ‘O’ (24.2%), phosphorus ‘P’ (17.4%) and calcium ‘Ca’ (60.1%) in the β-TCP nanoparticles. The FTIR and micro-Raman spectra indicated characteristic bands for β-TCP containing materials. The 10 wt.% β-TCP adhesive presented the highest SBS values (NTC-10 wt.% β-TCP: 33.55 ± 3.73 MPa, TC-10 wt.% β-TCP: 30.50 ± 3.25 MPa), followed by the 5 wt.% β-TCP adhesive (NTC-5 wt.% β-TCP: 32.37 ± 3.10 MPa, TC-5 wt.% β-TCP: 27.75 ± 3.15 MPa). Most of the detected failures after bond strength testing were adhesive in nature. The β-TCP adhesives demonstrated suitable dentin interaction by forming a hybrid layer (with few or no gaps) and resin tags. The β-TCP adhesives (10 wt.%) revealed lower DC values compared to control. The incorporation of 5 and 10 wt.% concentrations of β-TCP particles resulted in an increase in SBS values. A linear decline in DC values was witnessed when the nanoparticle concentration was increased. Further research focusing on exploring the influence of higher filler concentrations on adhesive’s properties is recommended.

Water Sorption, Water Solubility, and Rheological Properties of Resin-Based Dental Composites Incorporating Immobilizable Eugenol-Derivative Monomer.

The present study aimed to evaluate the properties of new dental formulations incorporating a new polymerizable-derivative of eugenol (EgGMA). The experimental composites were prepared (by weight) with 35% resin-based matrix (1:1, bisphenol A-glycidyl methacrylate/triethylene glycol dimethacrylate) and 65% reinforcing materials (4:3, hydroxyapatite/zirconium oxide). A portion of 0.0, 2.5, and 5.0% of the resins with respect to the total composite was replaced by EgGMA monomer to obtain TBEg0, TBEg2.5, and TBEg5, respectively. The complex viscosity (at 25 and 37 °C), degree of conversion (DC), and water sorption (WSP) and water solubility (WSL) (3 cycles of sorption-desorption process) were investigated. Data were statistically analyzed using one-way and Tukey post-hoc tests. The results revealed a viscosity reduction with shear-thinning behavior as the EgGMA amount and temperature increased. The average complex viscosities at a lower frequency (ω = 1.0 rad/s) and at 25 °C were 234.7 ± 13.4, 86.4 ± 16.5, and 57.3 ± 17.1 (kPa·s) for TBEg0, TBEg2.5, and TBEg5, respectively. The inclusion of EgGMA led to a lower DC and WSP but higher WSL, compared to those of the reference (TBEg0). However, no significant differences between TBEg2.5 and control were detected (p > 0.05). Therefore, the incorporation of EgGMA in a low quantity, e.g., up to 8.45 mol% of resins, within the matrix may enhance the composite’s performance, including handling and solubility properties without any apparent effect on DC and water sorption, making it a promising monomeric biomaterial for various applications including restorative dentistry.

Polymer characteristics and mechanical properties of bulk-fill, giomer, fiber-reinforced and low-shrinkage composites

Introduction/Objective. The objective was to determine the degree of conversion (DC), cross-link density, percentage of leachable monomers, flexural strength (FS), and hardness (HV) of nanohybrid, nanofilled bulk-fill, giomer, fiber-reinforced, and low-shrinkage composites. Methods. Standardized specimens (n = 5/group) of Tetric EvoCeram Bulk Fill, Filtek Bulk Fill, Beautifil, EverX posterior, Kalore, Filtek Z250 (microhybrid control), and Tetric EvoCeram (nanohybrid control) were subjected to micro-Raman spectroscopy, three-point bending, and HV. Cross-linking density and leachable monomers were ascertained based on the ratio of HV and DC before and after immersion in absolute ethanol. Results. DC was in the range 50.4?70.5%, the highest for Filtek Bulk and the lowest for Kalore. The highest %DC change was in Beautifil (10.3%) and the lowest in Filtek Bulk (1.4%) and Z250 (1.28%). FS ranged between 78.9 MPa (TEC) and 126.7 MPa (Filtek Bulk). HV ranged between 58.6 (Kalore) and 113.9 (Z250) and significantly decreased post-immersion (19?55%). HV48h inversely correlated to HV% loss (r = -0.761), whilst DC positively correlated with FS (r = 0.893). Conclusion. Filtek Bulk, EverX, and Z250 showed the highest DC. The lowest DC and mechanical properties were observed for Kalore. The greatest cross-link density was shown by Filtek Bulk. There were up to 10% of leachable monomers. DC and FS positively correlated.

Influence of curing modes on conversion and shrinkage of dual-cure resin-cements

ObjectiveTo explore the effect of curing modes of dual-cure resin cements on their degree of conversion (DC) and polymerization shrinkage (PS) over specific post-activation periods. MethodsFive self-adhesive (PANAVIA SA, RelyX Universal Resin, RelyX Unicem 2, Bifix SE, and SpeedCEM Plus) and three conventional (PANAVIA V5, Nexus Third Generation, and RelyX Ultimate Universal) dual-cure resin cements were studied. Four specimens (n = 4) were made per curing mode (light/self-cure) to measure either DC or PS. FTIR was utilized to measure real-time DC (%) over 24 h. The Bonded Disk method was used to measure shrinkage at 23 °C over 1 h. The data were analyzed using one-way ANOVA, Tukey post-hoc tests and independent/ paired sample t-tests (a = 0.05). ResultsAfter 1 h post-activation, the DC of light-cured (LC) specimens ranged between 66.6% and 77.4%, whereas for self-cured (SC) specimens DC ranged between 44.4% and 73.2%. After 24 h, the DC of LC specimens ranged between 74.8% and 82.4% and between 62.7% and 81.7% for SC specimens. After 24 h, the DC of three cements (BSE, PV5, and RXU) were comparable between their curing modes (p > 0.05), whereas five cements (CEM, NX3, PSA, RXU2, RXL) had significantly lower DC for SC compared to LC specimens (p < 0.05).After 1 h post-activation, shrinkage ranged between 5.9% and 8.5% for LC and between 4.9% and 8.3% for SC specimens. Most cements were not significantly different between curing modes. However, light-cured PAS, RXL and RXU2 had significantly higher shrinkage (p < 0.05). After 1 h post-activation, a strong positive correlation existed between conversion and shrinkage (LC: r2 = 0.95 and SC: r2 = 0.93). SignificanceWhenever light access is possible, light-curing of resin-cements remains beneficial to the overall efficacy of their conversion and thus all factors that depend on that. Conversion and shrinkage behavior are intrinsically important factors in clinical selection of resin-cement products.

Influence of Application of Dimethyl Sulfoxide on the Bonding Properties to Eroded Dentin.

To evaluate the effect of dimethyl sulfoxide (DMSO) on the microtensile bond strength (µTBS), nanoleakage (NL), and degree of conversion (DC) of universal adhesives on eroded dentin. One hundred thirty-four extracted (134) human third molars were selected for the study. After the dentin surface was exposed, 128 teeth were randomly assigned to 16 experimental groups as follows: dentin surfaces (sound dentin and eroded dentin), application of DMSO (without or with the application of DMSO), and adhesive strategies (etch-and-rinse [ER] and self-etch [SE]). The universal adhesive systems iBond Universal (IBU) and Scotchbond Universal (SBU) were applied and the teeth were restored using a resin composite. After 24 h in distilled water at 37°C, the samples were sectioned and evaluated for μTBS. Selected sticks from each tooth were used for evaluating NL and DC. The remaining six teeth were used to measure the thickness of the collagen layer of the artificially eroded dentin using scanning electron microscopy. Data on μTBS, NL, and DC (%) were analyzed using three-way ANOVA and Tukey's test (α = 0.05). Significantly lower μTBS (p = 0.0001) and DC (p = 0.01) were observed for eroded dentin than for sound dentin. However, a significant increase in the μTBS (p = 0.0007) and DC (p = 0.001) was observed for both substrates when DMSO was applied. Moreover, the application of DMSO decreased the concentration of silver nitrate at the bottom of the hybrid layer for both sound and eroded dentin (p = 0.002). Eroded dentin showed enlarged tubules with the presence of a collapsed collagen fibril layer approximately 5.0 ± 2.0 mm of thickness. The bonding performance of both tested universal adhesives improved on both sound and eroded dentin with DMSO pretreatment.

Evaluating the Bonding Performance of a Novel Dual-curing Composite Cement to Zirconia.

To investigate the bond strength and durability of a novel dual-curing composite cement to zirconia under different curing conditions. Zirconia plates of different thickness (0.5, 1, and 2 mm) were bonded with either a novel dual-curing composite cement (Panavia V5, PV5, Kuraray Noritake) or a traditional one (RelyX Ultimate, RUL, 3M Oral Care; Multilink Automix, MLA, Ivoclar Vivadent), in light-, self-, or dual-curing mode. Bonded specimens were subjected to shear bond strength (SBS) tests after 24 h of water storage or after artificially aging by 20,000 thermal cycles plus 150 days of water storage. The degree of conversion (DC) of the composite cements under different curing conditions was measured by Fourier transform infrared (FTIR) spectroscopy. The irradiance and translucency of the zirconia plates of different thickness were also investigated. The irradiance and translucency of zirconia decreased significantly with increasing thickness (p = 0.00). Both before and after aging, SBS of PV5 in self-curing mode was significantly higher than that of RUL (p = 0.07 before aging and 0.02 after aging) and MLA (p = 0.00 both before and after aging). However, for the three composite cements, light- and dual curing yielding the same SBSs for a constant Y-TZP thickness (p > 0.05). The FTIR analysis showed that, for all three dual-curing composite cements examined in this study, the mean DC values obtained in dual-curing mode were lower than those achieved in light-curing mode (p = 0.00 for PV5, RUL, and MLA). For RUL and MLA, lower mean DC values were obtained in self-curing than dual-curing mode (p = 0.00 for both RUL and MLA), while the DC values of PV5 showed no significant difference between self-curing and dual-curing mode (p = 0.33). When the photoactivation time is 60 s and the thickness of the zirconia restoration is less than 2 mm, it is safe to use the two traditional dual-curing composite cements RUL and MLA and PV5 for bonding zirconia. However, when the light exposure time is insufficient, PV5 provides improved bond strength and durability to zirconia.

Pre-Heating Effect on Monomer Elution and Degree of Conversion of Contemporary and Thermoviscous Bulk-Fill Resin-Based Dental Composites

Detection of unreacted monomers from pre-heated resin-based dental composites (RBC) is not a well-investigated topic so far. The objectives were to determine the temperature changes during the application and polymerization, the degree of conversion (DC) and unreacted monomer elution of room temperature (RT), and pre-heated thermoviscous [VisCalor Bulk(VCB)] and high-viscosity full-body contemporary [Filtek One Bulk(FOB)] bulk-fill RBCs. The RBCs’ temperatures during the sample preparation were recorded with a K-type thermocouple. The DC at the top and bottom was measured with micro-Raman spectroscopy and the amounts of eluted BisGMA, UDMA, DDMA, and TEGDMA were assessed with High-Performance Liquid Chromatography. The temperatures of the pre-heated RBCs decreased rapidly during the manipulation phase. The temperature rise during photopolymerization reflects the bottom DCs. The differences in DC% between the top and the bottom were significant. RT VCB had a lower DC% compared to FOB. Pre-heating did not influence the DC, except on the bottom surface of FOB where a significant decrease was measured. Pre-heating significantly decreased the elution of BisGMA, UDMA, DDMA in the case of FOB, meanwhile, it had no effect on monomer release from VCB, except TEGDMA, which elution was decreased. In comparison, RBC composition had a stronger influence on DC and monomer elution, than pre-cure temperature.

Effects of shades of a multilayered zirconia on light transmission, monomer conversion, and bond strength of resin cement.

To evaluate the influence of shades of a multilayered zirconia on light transmission, resin cement degree of conversion, and shear bond strength of resin cement. The light transmission through opaque (OPQ) and translucent (TNS) regions of Katana UTML zirconia (Kuraray Noritake Dental) were evaluated for using a spectroradiometer (n=5). Degree of conversion of dual-cure resin cement (Panavia V5, Kuraray Noritake Dental) was measured after light-activation through OPQ or TNS regions and direct exposure. Composition of the zirconia was analyzed with energy dispersive x-ray spectroscopy (EDS). Shear bond strength (SBS) was evaluated on the OPQ and TNS regions after 24 h and 1 year from specimen preparation (n=15). The OPQ region produced higher irradiance loss (95.1%) than TNS one (92.9%), and lower degree of conversion (52.4%) than TNS (71.2%) at 24 h post-light activation. EDS analysis did not show differences on the microstructure of the OPQ and TNS regions. There were no significant differences on the SBS between zirconia regions. For both zirconia regions, a significant reduction on the SBS occurred after aging, being 31.7% for OPQ and 38% for TNS. Both OPQ and TNS regions affected the light transmission through the multilayered zirconia. The OPQ region yielded the highest light attenuation and the lowest degree of conversion of resin cement. Different regions of the zirconia did not influence the SBS. Clinical significance Although opaque and translucent regions of the multilayered zirconia reduced the light transmission from LED curing unit and the degree of conversion of resin cement, the regions did not affect the resin cement adhesion.

Evaluation of the Polymerization Properties of Bulk-Fill Composite Resins

Introduction: The aim was to evaluate the polymerization properties of bulk-fill composite resins in terms of the degree of conversion (%DC), Vickers hardness (HV). SonicFill (SF, Kerr, CA, USA), Tetric Evo Ceram Bulk-Fill (TECBF, Ivoclar Vivadent Schaan, Lichtenstein), and X-trafil (XTF, Voco GmbH, Cuxhaven, Germany) were investigated. Methods: The samples prepared from composites (n = 10) were polymerized via three different curing modes (standard mode: 20 s, high-power mode: 12 s, extra power mode: 6 s) using a polywave LED. %DC was determined by FTIR-ATR-spectroscopy. HV was measured at the top and bottom of the specimens. Data were analyzed by two way ANOVA, and Bonferroni’s post-hoc respectively (α=0.05). Results: Except TECBF (%41.10 ± 3.1) in three different curing modes, all materials showed no significant inferior %DC. In all curing modes, the highest hardness ratio was found in XTF (0.84 ± 0.03 GPa), and the lowest hardness ratio was found in the TECBF (0.78 ± 0.02GPa). In the cases where the extra power mode of the Valo Led was applied, the lowest degree of conversion and hardness were also measured. Conclusion: It has been observed that the examined properties of some tested materials change with the curing time and power of the light and however, the results are dependent on the material.Extra power mode of the Valo Led negatively affected high viscosity bulk-fill composites in terms of their polymerization properties

Time-dependent degree of conversion, Martens parameters, and flexural strength of different dual-polymerizing resin composite luting materials

ObjectiveTo investigate the degree of conversion (DC), Martens hardness (HM), elastic indentation modulus (EIT), and biaxial flexural strength (BFS) of six dual-polymerizing resin composite luting materials initially and after 2 and 7 days of aging.Materials and methodsSpecimens fabricated from Bifix QM (BIF; VOCO), Calibra Ceram (CAL; Dentsply Sirona), DuoCem (DUO; Coltène/Whaledent), G-CEM LinkForce (GCE; GC Europe), PANAVIA V5 (PAN; Kuraray Europe), and Variolink Esthetic DC (VAR; Ivoclar Vivadent) (n = 12 per material) were light-polymerized through 1 mm thick discs (Celtra Duo, Dentsply Sirona). DC, HM, and EIT were recorded directly after fabrication, and after 2 and 7 days of aging. As a final test, BFS was measured. Univariate ANOVAs, Kruskal–Wallis, Mann–Whitney U, Friedman, and Wilcoxon tests, and Weibull modulus were computed (p < 0.05).ResultsWhile CAL presented low DC, HM, EIT, and BFS values, DUO and BIF showed high results. Highest Weibull moduli were observed for VAR and DUO. DC and Martens parameters increased between the initial measurement and 2 days of aging, while aging for 7 days provided no further improvement.ConclusionsThe choice of dual-polymerizing resin composite luting material plays an important role regarding chemical and mechanical properties, especially with patients sensitive to toxicological issues. DUO may be recommended for bonding fixed dental prostheses, as it demonstrated significantly highest and reliable results regarding DC, HM, and BFS. As DC and HM showed an increase in the first 48 h, it may be assumed that the polymerization reaction is not completed directly after initial polymerization, which is of practical importance to dentists and patients.Clinical relevanceThe chemical and mechanical properties of dual-polymerizing resin composite luting materials influence the overall stability and long-term performance of the restoration.

Degree of conversion and cohesive strength of conventional dual resin and self-adhesive cements by using of different forms of activation

The aim of this study was to evaluate the degree of conversion (DC) and cohesive strength (CS) of two conventional resin cements and a self-adhesive resin cement using different forms of activation. Two conventional dual resin cements (Variolink II and RelyX ARC) and a self-adhesive resin cement were polymerized in three different ways of activation, namely Chemically Activated (CA), Light Activated with Interposition of a resin disc (LI) and Light-Activated (L). The DC was evaluated using Fourier Transformed Infrared Spectroscopy - FTIR (Spectrum 100). In the CS test, the samples were tested until fracture in a universal testing machine (Instron 4411). The mean values obtained in the DC and CS tests were evaluated using two-way analysis of variance (ANOVA) (cement and activation) and Tukey test (p≤0.05). Irrespective of the activation mode, RelyX ARC showed the highest DC values, RelyX U200, the lowest values, and Variolink II intermediate values. Group L always had higher for DC and CS values than group CA. Among the resin cements, irrespective of the activation mode, there were no differences in CS values. The chemical activation mode of dual resin cements led to lower DC and CS values. RelyX ARC cement had the highest DC values and RelyX U200 cement the lowest values, however, in relation to CS, there were no differences.