Do dual-cure bulk-fill resin composites reduce gaps and improve depth of cure

This in vitro study aimed to evaluate the gaps length and depth of cure of dual-cure bulk-fill resin composites inserted in box-shaped preparations. Box-shaped preparations (4 mm deep) were made in fifteen human third-molars and divided into three groups according to the resin composites (n=5): Dual-cure bulk-fill BulkEZ (BEZ); Dual-cure bulk-fill HyperFIL (HF); and Tetric Evoceram Bulk-fill (TETRIC), as control. Gaps length (%) was evaluated in tooth-restoration interface with micro-computed tomography (µCT). The restorations were sectioned, and the degree of conversion (DC) and Knoop microhardness were evaluated at five depths (0.3, 1, 2, 3, and 4 mm). Microhardness data were statistically evaluated using absolute values (KHN) and relative values (microhardness percentages in relation to top). Gaps length (%) increased in the following order: BEZ=TETRIC<HF. The microhardness percentages in relation to top significantly decreased from 2 mm for TETRIC and 3 mm for HF. BEZ had constant microhardness and DC at all depths, while HF and TETRIC presented a significant decrease on DC at 4 mm. Dual-cure bulk-fill composites did not reduce gaps compared to light-cure bulk-fill, but they can improve depth of cure of bulk-filled restorations.

Influence of different types of light curing units and photoinitiators in microhardness and color of composite resins after immersion in wine

Objective: the aim of this study to evaluate the microhardness and color change (ΔE) of composite resins, light cured with different LEDs, submitted to staining drink. Materials and Methods: Two composite resins with lucerin-TPO (Tetric N-Ceram/ Vit-l-escence) and camphorquinone (Filtek Z350) were select. Specimens (n=120) were prepared. Then were photopolymerized with LED of singlewave or polywave. Microhardness and color evaluations were performed before and after chalanges. Data were evaluated by two-way ANOVA, Tukey's test (p≤0,05). Results: No statistically significant difference between the two generations of LEDs was found for microhardness data. Regarding the ΔE, statistical difference between the two LEDs was observed for Tetric N- Ceram and Filtek Z350. Conclusion: Compostion of composites appears to have more influence on analyses than the type of LEDs.

Secondary Caries in situ Models: A Systematic Review

In situ caries research serves as a bridge between clinical research and laboratory studies. In this kind of research, volunteers wear a removable intraoral splint or prosthesis containing research samples. Many different in situ models exist to investigate secondary caries. This systematic review compared currently existing secondary caries models and their lesion progression per day values. Materials and Methods: Three databases (Medline, Embase, and Cochrane) were searched for relevant literature. Bias risk was assessed and model parameters and caries-related outcomes were extracted by 2 independent researchers. Where possible, caries-related outcomes were normalized by estimating lesion progression per day by dividing lesion depth extracted from microradiographic or microhardness data by the number of days the study lasted. Results: The literature search identified 335 articles. After eliminating duplicates and selection, 31 articles were included. The models differed greatly on factors such as sample location, presence of fluoride in the model, and analysis methods. Three main groups could be identified by sample placement; 68% of models placed samples palatally in the upper jaw, and the lower jaw model could be divided into the buccal (26%) and approximal (6%) areas. Average lesion progression in enamel next to composite was 4.3 ± 2.8 µm (range1.1–8.8 µm/day). Discussion: Studies conducted with palatal models showed caries progression rates 2–5 times higher than the estimated clinical progression rates. Lesion progression per day could be a useful tool for future comparison of models and establishing a standardized model.

Polymerization Shrinkage Stress Kinetics and Related Properties of Bulk-fill Resin Composites

SUMMARY The present study assessed the polymerization shrinkage stress kinetics of five low-shrinkage light-cured bulk-fill resin composites: Surefil SDR flow (SF, Dentsply), Tetric EvoCeram Bulkfil (TE, Ivoclar Vivadent), Venus Bulk Fill (VB, Heraeus Kulzer), x-tra fil (XF, Voco), and experimental bulk fill (FB, 3M ESPE). Filtek Z250 (FZ, 3M ESPE) was used as a control. Real-time shrinkage stress of investigated composites was measured using a tensometer; maximum shrinkage stress, stress rate (Rmax), and time to reach maximum stress rate (tmax) were recorded. Flexural strength and modulus were measured using a standard procedure, and curing efficiency of 4-mm long specimens was determined using bottom/top percentage Knoop microhardness. Data were analyzed using one-way analysis of variance and Bonferroni multiple range tests at a significance level of α=0.05. Results of shrinkage stress, Rmax, and tmax of all bulk-fill materials were significantly lower (p&lt;0.05) than those of the control except for XF. All tested bulk-fill materials were able to achieve acceptable curing efficiency (≥80% bottom/top percentage) at 4-mm depth. In conclusion, this study reports a significant reduction in polymerization shrinkage stress while maintaining comparable curing efficiency at 4 mm for some bulk-fill composites and supports their potential use in posterior clinical situations.

Estimation of Hydrogen Diffusivity in Austenitic Stainless Steels by Microhardness Gradient Technique

The present study developed a subsurface microhardness gradient technique to estimate hydrogen diffusivity of stainless steels, as per the similarity between concentration distribution and hardness gradient. Cathodic charging were performed on 304 stainless steels for 24 h in a 0.5 mol/L H2SO4 solution using a current density of 100 mA/cm2, with 0.25g/L Na2S as the hydrogen recombination poison. Microhardness in the cross-sectional region had an increase than the uncharged materials due to the hardening mechanism as found by martensite transformation. Hydrogen diffusivity was estimated using the microhardness data and the diffusion equation. The estimated diffusivity of hydrogen at 306 K in 304 stainless steels is 3.28×10-13 m2/s, which has good agreements with the one measured by time-lag electrochemical method in a previous research.

PMMA-Y2O3 (Eu3+) nanocomposites: Optical and mechanical properties

The results of a study related to the processing and characterization of PMMA-Y2O3 (Eu3+) nanocomposites are presented herein. The nanocomposite samples were prepared using a laboratory mixing molder with different contents of Eu-ion doped Y2O3 nanophosphor powder. The influence of particle content on the optical and dynamic mechanical properties of the nanocomposites was investigated. The intensity of the luminescence emission spectra increased as the nanophosphor content in the composite increased. The results of dynamic mechanical analysis revealed that the storage modulus, loss modulus and glass transition temperature (Tg) of the polymer composites increased with increasing content of the nanophosphor powder. The microhardness data also confirmed that the hardness number increased with nanoparticles concentration in the PMMA nanocomposites. The obtained results revealed a relatively linear relationship between Tg and the Vickers hardness.

Nanocrystallization and Dissolution of Immiscible Powder Alloys Using High Pressure Torsion

Precompacts out of immiscible systems CuCr (75/25 wt%) and WCu (80/20 wt%), respectively, were made by pressing mixed powders and sintering. By applying different strains and hydrostatic pressures of HPT at room temperature, disc-shaped samples with a diameter of 8 mm were produced. They were investigated by Light Microscopy, Scanning-Electron Microscopy using Back-Scattered Electrons, and X-ray Line Profile Analysis. In addition, Vickers microhardness data were collected. Both systems showed the highest microhardness at a shear strain of about γ = 170. The density (for the case of Cu25Cr) of the consolidated material could be increased to the theoretical value. Microhardness and grain sizes were studied individually for each of the phases, too.