Higher Ra Values Research Articles

Fatigue mechanical properties and Kaiser effect characteristics of the saturated weakly cemented sandstone under different loading rate conditions

Weakly cemented sandstone (WCS) is a unique rock type widely distributed on the surface. Environmental factors such as groundwater and stress variations easily influence its fatigue mechanical properties and fracture characteristics. To design and evaluate the long-term stability of surrounding rock support in tunnel excavation and underground resource mining projects, investigating the fatigue mechanical properties and acoustic emission (AE) response characteristics of saturated WCS under different loading rates is of great practical and theoretical significance. This study employed experimental techniques such as X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and natural water absorption tests to investigate the mineral composition, pore size, and connectivity characteristics of WCS. The multi-level cyclic loading-unloading tests (MCLU) combined with the AE system were conducted on dry and saturated WCS specimens at different loading rates. The results reveal that the deformation modulus of these specimens initially increases and then decreases under cyclic loading conditions. Water significantly influences the fatigue strength and deformation resistance of sandstone. As the loading rate increases, the range of RA values broadens, accompanied by a marked increase in the number of AE signals with high RA values. Saturated sandstone specimens are more prone to developing macroscopic shear fracture surfaces. Water has a more substantial effect on the stress distribution ranges corresponding to the response of the Kaiser effect in WCS than loading rates. The capacity of the Kaiser effect to indicate the extent of rock damage is intricately linked to the progression of internal micro-cracks. When internal damage surpasses the critical value of the Kaiser effect memory damage, the accelerated propagation of shear cracks becomes pivotal in the internal damage of the sandstone. It seems that the presence of water within the interior of the rock may facilitate the dissolution of K-feldspar in WCS, which could result in the formation of kaolinite, which will be further transformed into illite. The hydration expansion of illite may further exacerbate the deterioration effect of the mechanical properties of WCS.

Exploring the impact of cryogenic treatment on detonation spray coated M2 high speed steel

ABSTRACT An Al₂O₃–13% TiO₂ coating was applied to M2 high-speed steel using the d-gun process. The surface properties were compared between uncoated samples, coated samples before cryogenic treatment (CBCT), and coated samples after cryogenic treatment (CACT). The mean particle size was ~17.07 μm, with average coating thicknesses of 212 μm for CBCT and 196 μm for CACT. CACT exhibited 3.19% and 24.65% higher microhardness than CBCT and uncoated samples, respectively. All samples exhibited hydrophilic wettability, with CBCT showing 59.41% and 67.43% higher Ra values, along with 56.03% and 59.70% higher Rz values than CACT and uncoated samples. CBCT also exhibited 32.96% and 98.14% higher porosity than CACT and uncoated samples. CACT showed reduced abrasion loss by 54.05% and 36.25% compared to CBCT and uncoated samples. CBCT has better corrosion resistance of 90.25% and 95.89% than CACT and uncoated samples. The Raman shift revealed increased particle size formation in CACT than other samples.

Effect of Polishing Systems on the Surface Roughness and Color Stability of Aged and Stained Bulk-Fill Resin Composites.

The aim of this study is to investigate how two different polishing techniques affect the color stability, surface roughness, and changes in surface morphology of aged and coffee-stained bulk-fill resin composites. A total of 112 disc-shaped samples were prepared using Omnichroma Flow Bulk (OB), Charisma Bulk Flow One (CB), Estelite Bulk Fill Flow (EB), and Estelite Sigma Quick (control). Samples were divided into two subgroups (n = 16) and aged using thermocycling. A profilometer was used to measure the surface roughness (Ra) and a spectrophotometer was used for color stability (ΔE00). The EB group had the highest Ra values both before aging (disc: 0.23 ± 0.05, twist: 0.42 ± 0.05) and after aging (discs: 0.28 ± 0.04, twist: 0.46 ± 0.05). The OB group had the highest ΔE00 values before and after aging (discs: 3.06 ± 0.54, twist 3.05 ± 0.41) and the highest after coffee-staining (discs: 3.75 ± 0.70, twist: 3.91 ± 0.57). Re-polishing reduced the ΔE00 values in all materials but did not restore all to clinically acceptable levels. According to the results of this study, it can be concluded that the surface roughness and color stability of resin composites are notably influenced by the polishing technique, aging process, and coffee staining. Specimens that were polished using the multi-stage Super-Snap discs consistently exhibited smoother surfaces across all bulk-fill resin composites compared to those polished with the two-stage Diacomp plus Twist.

Prediction of surface roughness using different features in vortex cooled turning process of Ti6Al4V alloy

Despite their superior mechanical properties, titanium alloys cause excessive temperatures in turning operations due to their low thermal conductivity. This situation reduces workpiece quality and shortens tool life. Therefore, it is necessary to determine the type of coolant that will provide the desired product quality at the optimum cost. Surface roughness (Ra) is one of the most important indicators of product quality. The goal of this work is to accurately predict the Ra in various cooling conditions prior to turning the Ti6Al4V alloy. Models built using various machine learning algorithms were used to compare the cutting parameters and features taken from sensor signals. While the lowest Ra values were obtained in dry cutting, the highest Ra values were obtained with vortex CO2. The highest performance success was achieved with the XGBoost algorithm. The model created by enhancing the cutting parameters performed better in predictions than the models created using statistical information taken from the sensor signals. The suggested approach eliminates the need for extra sensors and allows for the low computational cost and high success rate estimation of Ra.

Effect Of Air-Abrasion And Er:Yag Laser On The Bond Strength Between The Metal Housing Of An Overdenture Attachment System And The Hard Relining Material

Objective. This study investigated the effect of air-abrasion and erbium:yttrium-aluminum-garnet (Er:YAG) laser treatments on push-out bond strength (PBS) between hard relining material and metal housing of an overdenture attachment system. Material and Methods. A total of 36 metal housings were randomly divided into 3 subgroups according to surface pretreatments (n=12): Control (no surface treatment; C), air-abrasion (A), and Er:YAG laser (L). Surface roughness (Ra) of specimens was determined using a profilometer. One additional specimen per group was evaluated by scanning electron microscopy (SEM). The hard relining material was bonded to metal housings, and a PBS test was performed using a universal testing machine. Data were statistically analyzed using 1-way analysis of variance (ANOVA), Tukey’s honestly significant difference (HSD), and Tamhane’s T2 tests (α=.05). Results. C and L groups showed the lowest and highest Ra values, respectively. The mean Ra of the A group was statistically different from the mean values of the C and L groups (P<.001). The L group showed higher PBS values than the C group (P<.05), whereas the A group exhibited statistically similar PBS values to both C and L groups (P>.05). Conclusions. Air-abrasion did not significantly increase the bond strength between the metal housing and hard relining material. Er:YAG laser irradiation noticeably improved the PBS but caused surface microcracks.

Effect of the Different Dietary Supplements on the Average Surface Roughness and Color Stability of Direct Restorative Materials Used in Pediatric Dentistry.

Increased surface roughness and discoloration of the direct restorative materials used in pediatric patients affect the longevity of restorations and impair children's oral health. Many factors can alter these properties. One of these factors is the intake of dietary supplements. It is crucial to predict the properties of restorative materials when exposed to dietary supplements to maintain the dental care of children. Thus, this study aimed to investigate the effect of various syrup-formed dietary supplements on the average surface roughness and color stability of current restorative materials used in pediatric dentistry. Seven different restorative materials (conventional glass ionomer [Fuji IX GP], resin-modified glass ionomer, [Fuji II LC], zirconia-reinforced glass ionomer [Zirconomer Improved], polyacid-modified composite resin [Dyract®XTRA], bulk-fill glass hybrid restorative [Equia Forte HT Fill], conventional resin composite [Charisma Smart], and resin composite with reactive glass fillers [Cention N]) were tested. The specimens prepared from each type of restorative material were divided into five subgroups according to dietary supplements (Sambucol Kids, Resverol, Imunol, Umca, and Microfer). These specimens were immersed daily in supplement solution over a period of 28 days. Surface roughness and color difference measurements were performed at baseline and at the 7th and 28th days. The color difference and Ra values showed that there was an interaction among the type of restorative material, type of dietary supplement, and immersion time factors (p < 0.05). Whereas lower Ra values were found in the composite resin group, the highest Ra values were found in the conventional glass ionomer group. All supplements caused increasing color difference values, and Resverol and Umca showed higher discoloration values above the clinically acceptable threshold. The intake of dietary supplement type, the immersion time of the dietary supplement, and the restorative material type affected the surface roughness and color stability of the tested direct restorative materials. All of the experimental groups showed higher Ra values than clinically acceptable surface roughness values (0.2 µm). The color difference values also increased with the immersion time.

Influence of fluoride characteristics on tooth surface protection in an erosive condition: A multifaceted characterization approach.

To evaluate the effect of fluoride consistency and composition to protect enamel and dentin against the dental erosion. Bovine enamel and dentin specimens were treated with artificial saliva, neutral fluoride gel (NFG), acidulated phosphate fluoride gel (AFG), neutral fluoride foam (NFF), and acidulated phosphate fluoride foam. The samples were subjected to cycling. Micro energy-dispersive X-ray fluorescence spectrometry, surface roughness (Ra), contact angle (CA), and scanning electron microscopy (SEM) were performed. Composition, CA and Ra data were analyzed by ANOVA and multiple comparison test (p < 0.05). The dentin protected had a significantly higher mineral content than in the control. Eroded unprotected enamel had higher Ra values than normal surfaces. Fluoride treatments increased the Ra in dentin samples. AFG increased the CA in enamel. Fluoride foams increased CA in dentin with reduced mineral loss. SEM analysis found a deposited layer on enamel treated with AFG and remnants of deposits on dentin treated with NFG and NFF. Regardless of the form of application, fluoride provided protection against erosion, however with different levels. Applying the adequate fluoride form is relevant since the formulations have different effects on both enamel and dentin.

Conjugate free convection in a non-uniform heating walled enclosure filled by ternary hybrid nanofluid under magnetic field

A study was conducted using numerical simulations to analyse the behaviour of heat transfer in a square enclosure filled with a ternary hybrid nanofluid in the occurrence of a magnetic field. The flow in the enclosure is characterised by steady and laminar conjugate-free convection. The enclosure has a vertical border with a finite thickness, while the other three borders are assumed to be very thin. The investigation aims to analyse the impact of several key factors on the average Nusselt number using the finite element method. These parameters include the volume fraction of ternary hybrid type nanoparticles (ranging from 0 to 0.03), Rayleigh number (varying from 103 to 106), solid wall thickness (changing from 0.1 to 0.3), Hartmann number (varying from 0 to 100), and the ratio of thermal conductivities (ranging from 0.1 to 10). A notable enhancement in heat transfer is found by employing a ternary hybrid nanofluid. This enhancement becomes more significant for small Rayleigh numbers, where heat conduction governs the primary means of heat transfer. Also, at low levels of Ra, the development of energy transfer strength becomes insignificant in the existence of a magnetic field. This magnetic field effect is primarily controlled by high values of Ra, which consequently leads to an enhancement in the strength of energy transmission.

Numerical simulation of entropy generation in thermo-magnetic convection in an inverted T-shaped porous enclosure under thermal radiation

PurposeThermo-magnetic convective flow analysis under the impact of thermal radiation for heat and entropy generation phenomena is an active research field for understanding the efficiency of thermodynamic systems in various engineering sectors. This study aims to examine the characteristics of convective heat transport and entropy generation within an inverted T-shaped porous enclosure saturated with a hybrid nanofluid under the influence of thermal radiation and magnetic field.Design/methodology/approachThe mathematical model incorporates the Darcy-Forchheimer-Brinkmann model and considers thermal radiation in the energy balance equation. The complete mathematical model has been numerically simulated through the penalty finite element approach at varying values of flow parameters, such as Rayleigh number (Ra), Hartmann number (Ha), Darcy number (Da), radiation parameter (Rd) and porosity value (e). Furthermore, the graphical results for energy variation have been monitored through the energy-flux vector, whereas the entropy generation along with its individual components, namely, entropy generation due to heat transfer, fluid friction and magnetic field, are also presented. Furthermore, the results of the Bejan number for each component are also discussed in detail. Additionally, the concept of ecological coefficient of performance (ECOP) has also been included to analyse the thermal efficiency of the model.FindingsThe graphical analysis of results indicates that higher values of Ra, Da, e and Rd enhance the convective heat transport and entropy generation phenomena more rapidly. However, increasing Ha values have a detrimental effect due to the increasing impact of magnetic forces. Furthermore, the ECOP result suggests that the rising value of Da, e and Rd at smaller Ra show a maximum thermal efficiency of the mathematical model, which further declines as the Ra increases. Conversely, the thermal efficiency of the model improves with increasing Ha value, showing an opposite trend in ECOP.Practical implicationsSuch complex porous enclosures have practical applications in engineering and science, including areas like solar power collectors, heat exchangers and electronic equipment. Furthermore, the present study of entropy generation would play a vital role in optimizing system performance, improving energy efficiency and promoting sustainable engineering practices during the natural convection process.Originality/valueTo the best of the authors’ knowledge, this study is the first ever attempted detailed investigation of heat transfer and entropy generation phenomena flow parameter ranges in an inverted T-shaped porous enclosure under a uniform magnetic field and thermal radiation.

Research on the correlation between tensile ductility and corrosion behavior of surfacing alloy 625

In this study, the influence of different aging temperatures on the tensile ductility and Intergranular Corrosion (IGC) performance was investigated by using SEM, TEM, U2-net, DL-EPR, and EIS. The U2-net was employed for efficient and accurate identification of the Laves phase in the alloy 625. In parallel, an extensive analysis was conducted to assess the influence of Laves phase precipitation on the tensile ductility of the alloy. Additionally, an investigation into the precipitated phase was undertaken to explore the correlation between tensile ductility and IGC. The research findings indicate that with increasing aging temperature (from 873 K to 993 K), the elongation initially slightly increases, then sharply decreases, and finally slightly increases again. Simultaneously, the sensitivity to Intergranular Corrosion first increases and then slightly decreases. Additionally, the trained U2-Net achieved an average accuracy rate of 99.3% on the validation dataset, demonstrating that deep learning networks can effectively and rapidly identify Laves phases in SEM images. DL-EPR results reveal a certain correlation between high Ra values and low elongation.

PENGARUH PAHAT ENDMILL NORMAL DAN VARIABEL HELIX ANGLE PADA METODE POCKET ZIG-ZAG TERHADAP CHATTER

The manufacturing industry mostly uses CNC Milling machines in processing products that require high precision values. This machine is capable of a wide variety of feeding methods, inclinations, feed speeds, various tool styles, and much more. The purpose of this research is to analyze one method of infeed direction with the Zig-Zag effect by using 2 types of normal and variable tool types combined with variations in spindle speed and DOC to find out which variable is effective and produce a smoother comparison of surface roughness values. The type of material tested was SS 304 because this material has good advantages against corrosion. From the results of research conducted on this material for the use of a variable tool, it has an average roughness value of 0.327 µm and for the results of the roughness test on the use of a normal tool, it has an average roughness value of 0.470 µm. From the results of this research, it can be concluded that the value of the Depth Of Cut (DOC), the roughness value are directly proportional, and the faster the spindle rotation, the frictional force generated also increases. The highest Ra value from the research results occurred in DOC 1.6 mm with a spindle speed of 2750 rpm using a variable tool of 0.361 µm and a roughness value of 0.516 µm on a normal tool. The conclusion of this research is that the variable tool produces a lower Ra value than the normal tool so that the type of material defects caused by chatter vibration can be reduced.

Natural Convection in a Circular Enclosure with Four Cylinders under Magnetic Field: Application to Heat Exchanger

This paper documents the 2D numerical study of magnetohydrodynamic unsteady natural convective heat transfer in a circular enclosure with four heating cylinders in both the horizontal and the vertical mid-plane. The fluid is an incompressible Newtonian fluid. The main transport equations based on the conservation of mass, momentum, and energy are calculated and solved using a finite element numerical solver with the following parameter ranges: dimensionless distance between cylinders S = 0.05–0.29, Rayleigh number Ra=103–106, and Hartmann number for Ha = 0–120. COMSOL Multiphysics, a numerical simulation program, was used to solve the governing equations. It was demonstrated that for lower Ra values, heat transfer through an applied magnetic field is unaffected for a specific S value because the mechanism of transport is diffusion, whereas for larger Ra, there is a complex interaction among magnetic field and physical thermal properties. The features of the heat transfer rate are determined by the interaction. The Nusselt number virtually stays constant as Ha rises at smaller Ra. However, at high Ra, the Nusselt number initially declines with Ha and thereafter essentially stays constant, and at high Ra values, the switch from conduction to convective heat transfer takes place. Additionally, Nu rises slightly with S at increasing Ra.

The Effect of Cutting Speed of Nitrogen Laser Cutting on the Surface Texture of SUS 304 Plate

The focus of today’s machining industry is on how to maintain high productivity and low cost achieved by high tool life during the operation. Laser cutting is considered the right solution because it offers cutting speeds of up to 170000 mm/min through a non-contact process regardless of the workpiece material hardness. The aim of this study is to analyze the effect of cutting speed on the surface texture aspects namely surface roughness, kerf shape, and dross height on the stainless steel 304 plate after laser cutting. The nitrogen laser was utilized with the cutting speed of 400, 1700, and 2000 mm /min and the average roughness (Ra) was then measured using a surface roughness tester. On the other hand, the top, middle, and bottom area of the kerf surface as well as the dross height were analyzed by scanning electron microscopy (SEM). The highest Ra value was resulted at cutting speed of 2000 mm/min with 2.965 ± 0.05 μm while the lowest was at 1400 mm/min with 2.522 ± 0.16 μm. In parallel, the Ra was found to be higher when subjected gradually from the top to bottom zone. The kerf surface also proved that the top zone is dominated by the cutting zone, while the middle and bottom zone are characterized by the transition and deformation zone respectively. The width between kerf lines increased when the higher cutting speed was performed. Additionally, the larger dross height was found at the cutting speed of 1400 mm/min with 32.75 ± 5.21 μm and then degraded gradually at the higher cutting speed. The heat input and laser capability in exposing the material thickness are responsible for determining the corresponding surface texture aspects.

Thermal Analysis of Magneto-Natural Convection Flows within a Partially Thermally Active Rectangular Enclosure

In this study, we numerically investigate heat transfer enhancement in a partially thermally active rectangular enclosure. The enclosure is filled with a ternary hybrid nanofluid (water, Carbon Nanotube, Al2O3, and Graphene). It is subjected to a magnetic field and uniform internal heat generation. The study also investigates the effect of magnetic field strength and direction on the natural convection flow, which arises from density fluctuations caused by partial heating of the left vertical wall. To solve the dimensionless governing equations, the finite element approach is employed. The parameters studied in detail include Rayleigh number (Ra), Hartmann number (Ha), nanoparticle volume fraction (ϕ), and heat generation coefficient (λ). The findings are presented graphically for the range of the parameters as follows: 103≤Ra ≤106, 0≤Ha≤20, 0.01≤ϕ≤0.05, and 0≤λ≤15. It is noted that these parameters have an impact on heat transfer enhancement, flow patterns, and temperature fields. The results show that the average Nusselt number (Nu¯) increases with an increasing value of ϕ. Moreover, it has been noted that Nu¯ decreases as the value of Ha increases, and the impact becomes more obvious at higher Ra values. Finally, the influence of the heat generation coefficient on the heat transfer rate inside an enclosure is examined.

Mechanical and antibacterial properties of an experimental flowable composite containing Nb2O5 and NF_TiO2 nanoparticles.

This study developed an experimental flowable composite incorporated with niobium pentoxide (Nb2O5) combined or not with titanium dioxide co-doped with fluorine and nitrogen (NF_TiO2) and evaluated the mechanical and antibacterial properties. The experimental flowable composite (TEGDMA + BisGMA 1:1 + 60%wt – inorganic filler – borosilicate 0.7 μm) was formulated according to the type and concentration of Nb2O5 and NF_TiO2 (0.5, 1, 1.5 and 2 wt%) or NF_TiO2 + Nb2O5 (0.25, 0.5, 0.75 and 1 wt% - 1:1). The control groups were formed by the experimental composite without the incorporation of Nb2O5 and/or NF_TiO2 (GC-E) and by a commercial flowable composite (GC). The characterization of the surface of the composite and its particles was carried out using scanning electron microscopy (SEM) and energy dispersive x-rays (EDX). Specimens were manufactured and subjected to mechanical tests of flexural strength (FS) (n = 12), flexural modulus (FM) (n = 12), roughness (Ra) (n = 10), microhardness (n = 10), and contact angle (n = 10); and, to evaluate the antibacterial activity, they were submitted to tests of biofilm formation against S. mutans (CFU/mL) (n = 5), biofilm biomass by dry weight (n = 5) and confocal laser microscopy (%LIVE/DEAD) (n = 5). Data were submitted to one-way ANOVA and Tukey's post-hoc and, those that were not homoscedastic, but with normality, were submitted to Welch's ANOVA and Games-Howell's post-hoc. Dunnet's test was used to compare the controls with the other experimental groups (α = 5). The Nb2O5 particles had an average size of 32.4 μm and the nanoparticles (NPs) of NF_TiO2, 10 nm. EDX analysis identified isolated peaks of N, F, Ti, and Nb confirming the presence of these particles in the resin matrix. The 1.5% NF_TiO2 group had a higher FS and FM than the controls (p < 0.05). GC showed higher microhardness between groups (p < 0.05). There was no difference between the experimental groups regarding contact angle and roughness (p > 0.05), except for GC, which had the highest Ra values and the lowest contact angle between groups (p < 0.05). Composites containing 0.5%, 1%, 1.5%, and 2% Nb2O5, 1%, 1.5%, and 2% NF_TiO2 and 2% Nb2O5 + NF_TiO2 showed lower biofilm formation (p < 0.05), lower total biofilm biomass (p < 0.05), and a higher percentage of dead cells (44%, 52%, 52%, 79%, 42% 43%, 62%, 65%, respectively) than GC and GC-E (5% and 1%, respectively). It is concluded that the incorporation of 1.5% NF_TiO2 promoted a greater FS and FM among the experimental composites and that the addition of Nb2O5 particles (0.5%, 1%, 1.5%, and 2%), NF_TiO2 (1%, 1.5% and 2%) and the combination Nb2O5 + NF_TiO2 (2%) showed significant antibacterial effects.

Effects of in vitro erosion on surface texture, microhardness, and color stability of resin composite with S-PRG fillers.

To evaluate the effect of acid erosion on different physical properties of resin composite with S-PRG (surface pre-reacted glass) fillers, by conducting simulations of intrinsic and extrinsic sources. Cylindrical samples (Ø6 vs. 2 mm) of a conventional nanohybrid resin composite (Forma, Ultradent) and of a nanohybrid resin composite with S-PRG filler (Beautifil II, Shofu) were exposed to erosive cycling (5 days), based on (n=12) remineralizing solution (control); 0.3% citric acid (pH=2.6); or 0.01 M hydrochloric acid (pH=2). Roughness (Ra), microhardness (KHN), and color (CIEL*a*b*, CIEDE2000, and Vita scale (SGU)) factors were analyzed at the initial and final time points, and the general color changes (ΔEab, ΔE00, ΔSGU) were calculated. Final images were obtained using scanning electron microscopy (SEM). The data were evaluated by generalized models, Mann-Whitney, Wilcoxon, Kruskal-Wallis, and Dunn tests (α=0.05). Regarding KHN, there was no difference between the groups or the time periods (p = 0.74). As for Ra, there was a significant increase in the Ra of both composites after cycling with hydrochloric acid, but only the resin composite with S-PRG filler showed a change in Ra after cycling with citric acid (p = 0.003). After cycling with citric and hydrochloric acid, the highest Ra values were found for the resin composite with S-PRG filler (p < 0.0001), corroborating the result of images (SEM) indicating loss of filler and porosities in this material. The resin composite with S-PRG filler showed higher ΔEab and ΔE00, in addition to more negative ΔSGU values and lower L* values after exposure to both acids, compared to the control (p < 0.05). The acidic conditions altered the roughness and color stability of the materials tested, pointing out that the resin composite containing S-PRG filler showed greater degradation of its physical properties than the conventional resin composite. Bioactive materials are relevant, considering that their properties interact with dental hard tissues; however, the S-PRG-based resin composite showed greater degradation under acidic conditions than the conventional resin composite.

The effect of different parameters on the wear, surface properties, and shear bond strength of monolithic zirconia CAD/CAM restorative materials

To investigate the effects of preparation order and sandblasting procedures (different particle sizes and sandblasting times) on the wear, surface properties, and shear bond strength of zirconia material. A total of 130 test specimens were fabricated from Katana-Zirconia (n = 10). 70 test samples were sintered. Control, pre-sintered, and sintered groups were formed. The initial weights of the samples were measured. Sandblasting treatments were performed from a distance of 10-mm at 2-bar pressure for 10, 15, and 20-s with 29-µm and 50-µm Al2O3. The weight measurement was repeated. Subsequently, pre-sintered groups were sintered. Samples were scanned using a Nanovea-PS50. Ra, Rz, and Sa values ​​were recorded. Then, samples were embedded in acrylic. Composite bars were fabricated using a Teflon mold and bonded to the samples with G-CEM Link-Force. The shear bond strength test was performed. The data were analyzed using the Shapiro-Wilk test and two-way analysis ANOVA (p < 0.05). The highest Ra values were 1.198 ± 0.105 (Group-6) for PSZ and 0.267 ± 0.015 (Group-6) for SZ. Sa data demonstrated the highest values of 4.628 ± 1.541 (Group-6) for PSZ. The highest SBS values were 15.35 ± 2.75 (Group-4) for PSZ and 12.76 ± 2.39 (Group-1) for SZ. PSZ showed higher wear amount, Ra, Rz, Sa, and SBS in Groups 4 and 5 (p < 0.05). Pre-sintered and sintered zirconia showed different dependencies on sandblasting parameters regarding weight loss, Ra, Rz, Sa, and SBS. Sandblasting zirconia materials with 50-µm Al2O3 for 10 or 15-s before sintering may have beneficial effects on surface roughness and SBS.

Effect of coffee thermocycling on the surface roughness and stainability of nanographene-reinforced polymethyl methacrylate used for fixed definitive prostheses

Statement of problemA nanographene-reinforced polymethyl methacrylate (PMMA) has been introduced for definitive prostheses. However, knowledge on the surface roughness and stainability of this material is lacking. PurposeThe purpose of this in vitro study was to compare the surface roughness and stainability of nanographene-reinforced PMMA with those of a prepolymerized PMMA and a reinforced composite resin after coffee thermocycling. Material and methodsDisk-shaped specimens (Ø10×1.5-mm) were prepared from 3 different A1-shade millable resins (prepolymerized PMMA [M-PM; PMMA]; nanographene-reinforced PMMA [G-CAM; G-PMMA]; reinforced composite resin [Brilliant Crios; RCR]). Surface roughness (Ra) values were measured before and after conventional polishing by using a noncontact profilometer. Initial color coordinates were measured over a gray background with a spectrophotometer after polishing. Specimens were then thermocycled in coffee for 5000 cycles. Measurements were repeated after coffee thermocycling, and color differences (ΔE00) were calculated. Ra values among different time intervals were analyzed by using either the Friedman and Dunn tests (RCR) or repeated measures analysis of variance (ANOVA) and Bonferroni corrected paired samples t tests (PMMA and G-PMMA), while Ra values within a time interval were analyzed by using either the Kruskal-Wallis and Dunn tests (before polishing) or 1-way ANOVA and Tukey HSD (after polishing) or Tamhane T2 tests (after coffee thermocycling). ΔE00 values were analyzed by using 1-way ANOVA and Tukey HSD tests, while color coordinates of the specimens after polishing and after coffee thermocycling were compared by using paired samples t tests (α=.05). ResultsAll materials had their highest Ra values before polishing (P≤.011), while differences after polishing and after coffee thermocycling values were nonsignificant (P≥.140). PMMA had higher Ra than RCR before polishing (P=.002), and RCR had higher values than G-PMMA after polishing and after coffee thermocycling (P≤.023). RCR had the highest ΔE00 (P<.001). Polishing increased the b∗ values of PMMA, and coffee thermocycling increased the a∗ values of G-PMMA and all values of RCR (P≤.012). ConclusionsThe tested materials had similar and acceptable surface roughness after polishing. The surface roughness of materials was not affected by coffee thermocycling. Considering the reported color thresholds, all materials had acceptable color change, but the computer-aided design and computer-aided manufacturing composite resin had perceptible color change after coffee thermocycling.

Antibiofilm Activity of 3D-Printed Nanocomposite Resin: Impact of ZrO2 Nanoparticles.

Poly(methyl methacrylate) (PMMA) is a commonly used material, as it is biocompatible and relatively cheap. However, its mechanical properties and weak antibiofilm activity are major concerns. With the development of new technology, 3D-printed resins are emerging as replacements for PMMA. Few studies have investigated the antibiofilm activity of 3D-printed resins. Therefore, this study aimed to investigate the antibiofilm activity and surface roughness of a 3D-printed denture base resin modified with different concentrations of zirconium dioxide nanoparticles (ZrO2 NPs). A total of 60 resin disc specimens (15 × 2 mm) were fabricated and divided into six groups (n = 10). The groups comprised a heat-polymerized resin (PMMA) group, an unmodified 3D-printed resin (NextDent) group, and four 3D-printed resin groups that were modified with ZrO2 NPs at various concentrations (0.5 wt%, 1 wt%, 3 wt%, and 5 wt%). All specimens were polished using a conventional method and then placed in a thermocycler machine for 5000 cycles. Surface roughness (Ra, µm) was measured using a non-contact profilometer. The adhesion of Candida albicans (C. albicans) was measured using a fungal adhesion assay that consisted of a colony forming unit assay and a cell proliferation assay. The data were analyzed using Shapiro-Wilk and Kruskal-Wallis tests. A Mann-Whitney U test was used for pairwise comparison, and p-values of less than 0.05 were considered statistically significant. The lowest Ra value (0.88 ± 0.087 µm) was recorded for the PMMA group. In comparison to the PMMA group, the 3% ZrO2 NPs 3D-printed group showed a significant increase in Ra (p < 0.025). For the 3D-printed resins, significant differences were found between the groups with 0% vs. 3% ZrO2 NPs and 3% vs. 5% ZrO2 NPs (p < 0.025). The highest Ra value (0.96 ± 0.06 µm) was recorded for the 3% ZrO2 NPs group, and the lowest Ra values (0.91 ± 0.03 µm) were recorded for the 0.5% and 5% ZrO2 NPs groups. In terms of antifungal activity, the cell proliferation assay showed a significant decrease in the C. albicans count for the 0.5% ZrO2 NPs group when compared with PMMA and all other groups of 3D-printed resins. The group with the lowest concentration of ZrO2 NPs (0.5%) showed the lowest level of C. albicans adhesion of all the tested groups and showed the lowest Candida count (0.29 ± 0.03). The addition of ZrO2 NPs in low concentrations did not affect the surface roughness of the 3D-printed resins. These 3D-printed resins with low concentrations of nanocomposites could be used as possible materials for the prevention and treatment of denture stomatitis, due to their antibiofilm activities.

In Vitro Comparison of Surface Roughness, Flexural, and Microtensile Strength of Various Glass-Ionomer-Based Materials and a New Alkasite Restorative Material.

This study aims to evaluate the physical properties of Cention N and various glass-ionomer-based materials in vitro. The groups were obtained as follows: Group 1 (LC-Cent): light-cured Cention N; Group 2 (SC-Cent): self-cured Cention N; Group 3 (COMP): composite (3M Universal Restorative 200); Group 4 (DYRA): compomer (Dyract XP); Group 5 (LINER): Glass Liner; Group 6 (FUJI): FujiII LC Capsule; and Group 7 (NOVA): Nova Glass LC. For the microtensile bond strength (μTBS) test, 21 extracted human molar teeth were used. The enamel of the teeth was removed, and flat dentin surfaces were obtained. Materials were applied up to 3 mm, and sticks were obtained from the teeth. Additionally, specimens were prepared, and their flexural strength and surface roughness (Ra) were evaluated. Herein, data were recorded using SPSS 22.0, and the flexural strength, μTBS, and Ra were statistically analyzed. According to the surface roughness tests, the highest Ra values were observed in Group 6 (FUJI) (0.33 ± 0.1), whereas the lowest Ra values were observed in Group 2 (SC-Cent) (0.17 ± 0.04) (p < 0.05). The flexural strengths of the materials were compared, and the highest value was obtained in Group 2 (SC-Cent) (86.32 ± 15.37), whereas the lowest value was obtained in Group 5 (LINER) (41.75 ± 10.05) (p < 0.05). When the μTBS of materials to teeth was evaluated, the highest μTBS was observed in Group 3 (COMP) (16.50 ± 7.73) and Group 4 (DYRA) (16.36 ± 4.64), whereas the lowest μTBS was found in Group 7 (NOVA) (9.88 ± 1.87) (p < 0.05). According to the μTBS results of materials-to-materials bonding, both Group 2 (SC-Cent) and Group 1 (LC-Cent) made the best bonding with Group 3 (COMP) (p < 0.05). It can be concluded that self-cured Cention N had the highest flexural strength and lowest surface roughness of the seven materials tested. Although the bond strength was statistically lower than conventional composites and compomers, it was similar to resin-modified glass ionomer cements. Additionally, the best material-to-material bonding was found between self-cured Cention N and conventional composites.