Increase In Microhardness Research Articles

Effect of Al-Si and Al-Mg filler wires on microstructure and mechanical properties of bead-on-plate weld on AA6061-T6 using CMT welding

In recent times, cold metal transfer (CMT) welding has become a popular choice to weld large structures of aluminium and its alloys as it provides good quality weld beads with lesser heat input. The welded joint of AA6061-T6 achieved through CMT welding provides the desired characteristics and better mechanical performance than other fusion welding methods. In the present work, bead-on-plate experimentation has been performed on an AA6061-T6 plate with two different filler wires ER4043 and ER5356 using two combinations of welding speed and current, keeping the gas flow rate constant throughout the experiment in CMT welding. Optical micrograph and X-ray diffraction analysis have been studied from which it has been observed that bead welded with ER5356 exhibits more fine equiaxed grain structure in the fusion zone and columnar-dendritic fragmentation in HAZ than beads welded with ER4043 due to the presence of higher amount of Mg2Si. X-ray diffraction reveals the presence of different phases with silicon found exclusively in specimens welded with ER4043. Porosity, dilution, microhardness and tensile strength have been examined over the weld bead and a comparison has been done between the filler wires at the same welding parameters. Porosity levels have notably elevated, measuring 53.69% and 55.71% higher in specimens welded with ER4043 filler than ER5356. Similarly, the dilution level is 33.33% and 17.51% higher in specimens welded with ER4043 filler than ER5356. Conversely, specimens welded with ER5356 filler exhibited a 4.02% and 20.37% increase in microhardness and a 3.42% and 8.82% improvement in tensile strength as compared to ER4043.

A Comparative Evaluation of Surface Properties of Cention N and TiO2-Enriched Cention N After Brushing Simulation and Erosive Challenge: An In Vitro Study.

Background This study aimed to evaluate and compare the abrasive and erosive wear resistance of Cention N and titanium dioxide (TiO2) nanoparticle-enriched Cention N after three years of brushing simulation. Methodology A total of 48 freshly extracted mandibular molars were mounted in acrylic blocks and divided into two groups of 24 molars based on the type of restorative material used to restore them. Cavities of a standardized size were prepared. Group A was restored with Cention N, and group B was restored with 5% TiO2-enriched Cention N. Each group was further divided into three subgroups of eight. Subgroup 1was the control subgroup. Subgroup 2 was the abrasive subgroup, subjected to the abrasive challenge in a brushing stimulator with 30,000 cycles to 10,000 cycles in the linear X-axis and Y-axis each and another 10,000 cycles divided into 5,000 cycles clockwise and 5,000 cycles anticlockwise. The total number of brushing cycles was equal to three years of brushing with a duration of eight to nine hours. Subgroup 3 was the erosive and abrasive subgroup, subjected to an erosive pH cycle consisting of exposure to Coca‑Cola for five minutes thrice a day for seven days, and then subjected to brushing simulation as above. After the surface treatment, specimens were subjected to the Vickers microhardness test using a diamond indenter and the surface roughness test using an optical profilometer. The resulting values were subjected to statistical analysis. Results There was a significant decreasein mean surface roughness in group B, where TiO2 nanoparticles were added after erosive challenge and brushing simulation, than in group A. There was an increase in mean microhardness in group B which was not significant. Conclusions With the addition of 5% TiO2 to Cention N, there was a significant reduction in surface roughness. The surface microhardness of Cention N containing 5% TiO2 increased non-significantly compared to the control group.

Модификация диффузионных бор- и алюминийсодержащих слоев электронно-пучковой обработкой

The article presents testing results of electron beam processing (EBP) modes applied on the diffusion layers based on boron and aluminum produced on the surface of steel 20. An ion current feedback loop in the accelerating gap in a modernized plasma electron source allows increasing the beam generation control and the electrical strength of the accelerating gap. This ensures sample surface processing at a specified temperature. In order to ensure the EBP process stability, it is proposed to preheat the surface to a temperature range of 400-700℃ by pulses with a controlled current. Further modification of the diffusion layers is conducted on the surface at a temperature of around 1900℃. Ensuring this temperature range demands the discharge current within the range of 20 - 150A during a single pulse with a duration of 950 μs. The total number of pulses is three and the interval between them is 3 seconds. These processing modes lead to a structural transformation of the diffusion layer to a depth of more than 150 μm and to a significant microhardness increase. The approved EBP modes can be recommended as a promising alternate approach of the combined modification technologies of diffusion layers based on boron and aluminum.

Research of the Process of Electrochemical Deposition of Chromium in the Presence of a Composite Compound Based on Detonation Diamond-Containing Carbon

The purpose of the study is to develop a method for obtaining high-quality electrochemical chromium coating using a new type of diamond-containing additive that has significant advantages over traditionally used detonation nanodiamonds (DNA) in the form of aqueous suspensions. Detonation diamond-containing carbon (DDC) obtained by detonation of charges from tetryl was used as an additive. DDC contains 63,0 wt. % DNA and 4.4 wt. % non-combustible impurities. We used standard chromium electrolyte: CrO3 - 250 g/l, H2SO4 – 2,5 g/l, DNA – from 0,2 to 5 g/l, traditional methodologies and algorithm of experimentation. The scope of the study is limited to the creation and application of a specific, easy to handle and prepare formulation with DDC. DDC can be added to the standard chromium electrolyte directly or in the form of freshly prepared aqueous suspension, it is environmentally safe. The originality of the work lies in the application of a cheap diamond-containing product obtained directly after the explosion of an individual explosive (tetryl) and providing stability of DDC suspensions. An increase in microhardness of wear-resistant chrome coating by 1,5 times (up to 11 GPa) and hard chrome coating by 1,7 times (up to 13,3 GPa) was achieved. The wear resistance of the obtained coatings increased by 1,9 times. Concentration (per pure detonation nanodiamond (DNA)) from 0,63 to 3,15 g/l in the electrolyte (very low).

High strain rate induced shear banding within additively manufactured AISI 316L

The effects of post-processing via cold/hot rotary swaging, combined with high strain rate deformation, on formation of shear bands and deformation induced martensite within AISI 316L steel prepared by Selective Laser Melting are investigated. The as-built sample exhibited randomly oriented grains and residual porosity, which was reduced/eliminated by rotary swaging and subsequent high strain rate deformation. Hand in hand with significant changes in grain morphology after swaging (grain elongation and refinement, especially under cold conditions) and high strain rate processing (formation of shear bands and deformation induced martensite), the combined deformation imparted substantial hardening and resulted in microhardness increase by more than 20 %, primarily due to the occurring martensitic transformation. The structure changes were observed especially for the cold processed sample, due to aggravated plastic flow and hindered movement of generated partial dislocations.

Microstructure and corrosive-wear resistance of surfacing layers for underwater wet welding

Underwater wet welding (UWW) is a widely employed method for underwater welding. In this study, Ts306 electrodes were utilized for surfacing on Q235 base material by UWW, and the microstructure and corrosive-wear resistance of the surfacing layers were studied. The results demonstrate that the UWW presents thicker surfacing layer compared with that welded in air, due to the compressive effect of the water on the arc. Meanwhile, the microstructure of the UWW surfacing layer is closely related to the welding current. When the current reached 120 A, the structure of the surfacing layer was mainly pearlite and ferrite. The microstructures of grain boundary ferrite (GBF), acicular ferrite (AF), ferrite with second phase arrangement (FSP), and proeutectoid ferrite (PF) began to exhibit as the current increased to 135 A. When the welding current reached 150 A, the proportion of AF content experienced an increase. The microstructure of the surfacing layer can be refined, leading to an obvious increase in microhardness and corrosive-wear resistance. The substantial increase in the microhardness of the surface layer by 32% and the significant enhancement in corrosive-wear resistance by 60% were observed. Furthermore, the transition of corrosive-wear mechanisms from fatigue wear, corrosion wear, and oxidation wear to abrasive wear, oxidation wear, and adhesive wear was noted.

Influence of machining process of MoS2/B4C/Az31 Mg alloy composite and its tribological characteristics

The automotive, biomedical, and aerospace industries are among those with a rising need for lightweight materials with enhanced mechanical and tribological qualities. Composites based on magnesium alloys have attracted interest because of their excellent strength-to-weight ratio and promise to improve component performance. Magnesium (Mg) alloy-based composites find applications in sports and leisure equipment, aerospace, biomedical implants, and more. The research outlined here serves a critical need in the field of materials science and engineering, particularly regarding the development of advanced magnesium (Mg) alloy-based composites. In this study, we have created a new aluminum composite using the AZ31 alloy mixed with 5% boron carbide (B4C) and 5% molybdenum disulfide (MoS2) as reinforcement through a powder metallurgical technique. The magnesium alloy contains 3% aluminum and 1% zinc. Our research aims to understand the mechanical and tribological behaviors and the impact of Electrical Discharge Machining (EDM) process parameters on AZ31 magnesium alloy. We need to modify these properties for various applications. Many industrial researchers have studied the machinability of magnesium alloys using EDM. We conducted wear tests on AZ31 alloy reinforced with both B4C and MoS2 in altered quantities using a pin-on-disc setup. The outcome displays that the wear resistance of these composites is considerably better matched to other magnesium matrix composites (MMCs). We also measured various densities of the hybrid composite, including apparent density, green density, and sintered density, which were found to be 0.839, 1.495, and 1.504 g/cm3, respectively—better than other composites. In addition, the hybrid composite exhibited a substantial increase in micro hardness, reaching 22.012 HV, indicating improved wear resistance of the material. Comparatively, low density, minimum wear profile, and maximum hardness were recorded for the sample of AZ31 + 5%MoS2 + 5%B4C. The influence of EDM parameters was discussed.

In vitro evaluation of the effect of addition of biomaterials to carbamide peroxide on the bleaching efficacy and microhardness of enamel.

Teeth bleaching, although considered safe and conservative, cause microscopic changes in the tooth structure. The aim of this study is to evaluate the bleaching efficacy of carbamide peroxide (CP) bleaching gel when modified with the incorporation of bioactive glass (BG) and hydroxyapatite (HA) and its effect on enamel microhardness. Forty-five maxillary incisors were decoronated, artificially stained and mounted in acrylic. The samples were divided into three groups of 15 each and subjected to the following bleaching protocol for 8 h/day at 37°C for 2 weeks: Group 1 - 16% CP, Group 2 - CP modified with BG, and Group 3 - CP modified with hydroxyapatite (HA). Spectrophotometric color assessment using CIE L*a*b* system and Vickers microhardness were assessed before and after bleaching. Data were analyzed using Student's paired t-test and one-way ANOVA followed by Tukey's post hoc analysis. There was a significant change in color (L*a*b*) in all the three groups when compared to the baseline values. However, no significant difference in the total color change (ΔE) was observed between the three groups. Enamel microhardness reduced significantly in the CP group, whereas it increased in the BG and HA group after bleaching. Scanning electron microscopy images of BG and HA groups showed crystalline deposits suggesting mineral deposition. Addition of biomaterials can be a beneficial alternative to bleaching with CP alone, considering the increase in microhardness without hindering the bleaching action.

Evaluation of the Remineralization Capacity of Water-based Silver Fluoride

Silver diamine fluoride, which can arrest dental caries, is alkaline and may cause mild soft tissue irritation. Water-based silver fluoride has a neutral pH, which is closer to the physiological range, and is biocompatible for use in the oral environment. This study aimed to evaluate the effect of water-based silver fluoride on remineralizing early enamel lesions by comparing it with other fluoride agents through microhardness and quantitative light-induced fluorescence measurements. An in vitro study with intact bovine incisors was performed. Artificial enamel lesions were induced and subjected to microhardness and quantitative light-induced fluorescence testing. Specimens were randomly divided into 4 groups for treatment. The specimens in group I were treated with water-based silver fluoride and potassium iodide, group II with silver diamine fluoride and potassium iodide, group III with sodium fluoride varnish, and group IV with distilled water. After 8 days of pH cycling, the specimens were subjected to microhardness and quantitative light-induced fluorescence testing. Water-based silver fluoride and silver diamine fluoride showed the greatest increases in microhardness and quantitative light-induced fluorescence, with no significant differences between the two. Sodium fluoride varnish also exhibited a significant increase in microhardness and quantitative light-induced fluorescence, but the differences were smaller than those for water-based silver fluoride and silver diamine fluoride. Water-based silver fluoride is considered useful in a clinical setting for remineralizing enamel lesions, with the advantages of no risk of tissue burn and improved taste and smell.

Efficacy of Three Remineralizing Agents on Erosion of Root Dentin by Cola Drink: An In Vitro Study

Abstract Objective The aim of the study was to investigate the effects of silver diamine fluoride (38% SDF), sodium fluoride (NaF) varnish, and casein phosphopeptide-amorphous calcium phosphate fluoride (CPP-ACPF) on cola-eroded root dentin microhardness and mineral alteration in vitro. Materials and Methods Forty human root dentin slabs were exposed to alternating 10 cycles of cola drink and artificial saliva, repeated 3 times at 6-hour intervals. Specimens were randomly assigned to four groups: control (deionized water), 38% SDF, NaF varnish, and CPP-ACPF. All specimens underwent the second erosion process. Microhardness was measured at baseline (KHN0), pretreatment (KHN1), and posttreatment (KHN2). The mean difference of microhardness (ΔKHN2-1) was analyzed using one-way analysis of variance (ANOVA) and Tukey's post hoc tests (α = 0.05). The chemical composition and surface morphology were assessed using energy dispersive spectroscopy (EDS) and scanning electron microscope (SEM). Results All experimental groups exhibited dentinal tubule occlusion. Both 38% SDF and NaF varnish demonstrated a statistically significant increase in microhardness compared to CPP-ACPF. However, CPP-ACPF was comparable to the control group. EDS analysis showed an increase in weight percentage of fluorine in all groups. Furthermore, silver and chlorine were detected in the 38% SDF group. Conclusion All treatments enhanced eroded root dentin microhardness, with 38% SDF and NaF varnish demonstrating superior acid resistance and preventing morphological changes induced by cola re-immersion.

Enhancement of hardness and wear strength of pure Cu and Cu–TiO2 composites via a friction stir process while maintaining electrical resistivity

Abstract The study aims to enhance the hardness and wear of copper and Cu–TiO2-based composites while maintaining high electrical conductivity through friction stir processing (FSP). It assesses the impact of TiO2 volume fractions and groove widths (GWs) on the wear, hardness, resistivity, and microstructure of FSPed Cu and FSPed Cu–TiO2 surface composite. The samples obtained from the stir zone showed an increase in microhardness of the Cu–TiO2 surface composite due to particle refinement, uniform distribution, and efficient sticking of TiO2 with Cu. Furthermore, the wear rate increased with decreasing TiO2 volume fractions in the composite. The worn surface microstructural analysis indicated a transition from harsh to gentle wear with increasing TiO2 volume fractions and GWs. The average grain size reduced significantly in reinforced stir zones compared to pure Cu, and particle size decreased further with increasing groove size. Hardness increased by 25 and 50% compared to unprocessed Cu, but only a negligible increase in electrical resistivity (2.3% Ωm) after FSP.

Surface integrity and fatigue behavior of AISI 4340 steel after hybrid laser-ultrasonic assisted ball burnishing process

The final surface modification processes enhance the fatigue strength, wear resistance, and corrosion resistance of the workpiece by improving the surface quality, enhancing the microhardness, generating compressive residual stresses on the surface, and creating favorable changes in the microstructure. In this regard, using processes with different mechanisms is regarded as an optimal method to increase the efficiency of the final surface modification processes. This research seeks to experimentally investigate the hybrid laser-ultrasonic assisted ball burnishing (LUAB) process and its effect on the surface integrity and fatigue strength of 4340 alloy steel. The effect of the process on the sample’s microstructure was evaluated by the images obtained from the optical microscope and SEM. Further, the parameters of mean surface roughness and microhardness, as well as the results of the uniaxial tensile test and fatigue test of the workpiece were evaluated. In the case of using appropriate parameters in the process, the results indicated a 93.38% reduction in mean surface roughness and an increase of surface microhardness by 3.4 times compared to the initial sample. Additionally, the investigation of microstructure revealed the accessibility of homogeneous and refinement martensitic structures without surface melting. The results of uniaxial tensile and fatigue tests indicated a 6.29% increase in tensile strength and a 20.71% increase in the endurance limit of the treated sample (LUAB) compared to the initial sample. Finally, the results also showed a change in the fracture mode in the uniaxial tensile test and a reduction in the final fracture area in the fatigue test.

Mechanically tailored surface of titanium based alloy (Ti6Al4V) by laser surface treatment

In this study, laser surface treatment (LST) of Ti6Al4V carried out by melting within a narrow regime of optimum process parameters for the formation of a surface with improved wear and tribo-corrosion resistance is presented. The effect of applied power and shrouding gas on the microstructure, phase, surface hardness, residual stress, dry wear (against tungsten carbide, WC) and tribocorrosion resistance (against ZrO2 in Hank's solution) is established. LST in argon atmosphere leads to the formation of a composite structure consisting of acicular α’ martensite and α. LST in nitrogen atmosphere causes the formation of titanium nitride (TiN and Ti2N) dispersed in α matrix. Due to LST, there is an increase in surface microhardness both under argon (435–630 VHN) and nitrogen atmosphere (839–1327 VHN) when compared to untreated Ti6Al4V (278 VHN). There is a marginal decrease in wear rate (against WC ball) due to laser surface melting (5.17–5.81 × 10−3 mm3/Nm) under argon and a substantial decrease in wear rate when melting was conducted under nitrogen atmosphere (1.91–4.94 × 10−3 mm3/Nm) as compared to Ti6Al4V (5.93 × 10−3 mm3/Nm). The mechanism of wear is established. On the other hand, the tribo-corrosion rate is found to decrease for laser surface melting (3.5–4.8 × 10−3 mm3/Nm) and nitriding (1.3–3.2 × 10−3 mm3/Nm) as compared to Ti6Al4V (5.7 × 10−3 mm3/Nm). Bioactivity in terms of calcium phosphate deposition followed by dipping in Hank's solution was found to increase due to both melting and nitriding, though nitriding offered a marginally higher bioactivity than only melting.

Effect of Al2O3 on Microstructure and Corrosion Characteristics of Al/Al2O3 Composite Coatings Prepared by Cold Spraying

Cold spraying was used to prepare Al/Al2O3 composite coatings. The Al2O3 content was controlled to increase the mechanical property and corrosion resistance of the composite coating. The inclusion of Al2O3 particles results in considerable plastic deformation of Al particles and grain size refinement in the coating. Additionally, the coating’s surface roughness decreased from 24.63 μm to 9.02 μm, and the porosity decreased from 6.34% to 2.07%. The increase in microhardness of the composite coatings was attributed to the combined effect of residual compressive stress, second phase strengthening of Al2O3, and plastic hardening of Al particles. The electrochemical test results indicate that the mass fractions of Al2O3 significantly affected the corrosion resistance of the Al/Al2O3 composite coating. Compared to the Al coating, the composite coating exhibited improved corrosion resistance, with a reduction in corrosion current density from 1.09 × 10−3 A/cm2 to 2.67 × 10−6 A/cm2 and an increase in corrosion potential from −1.57 V to −1.14 V. However, when the alumina particle content exceeded 17.7%, it led to more Al2O3 particle breakage, increasing the weak bonding interfaces in the composite coating, and consequently reducing its corrosion resistance.

Study on the effect of magnetic needle grinding process on the service properties of medical Mg-1.6Ca-2.0Zn alloy

Magnesium alloy, valued for its superior mechanical properties and biocompatibility in biomaterials, faces limitations such as rapid corrosion, poor wear resistance, and unfavorable cell adhesion. To address these challenges and enhance medical magnesium alloy development, this study investigates a magnetic needle grinding process on magnesium alloy. Mg-1.6Ca-2.0Zn alloy, prepared through powder metallurgy and T6 aging treatment, undergoes milling, and magnetic grinding using various needle sizes. The impact is assessed through Vickers hardness, residual stresses, surface roughness, friction and wear tests, electrochemical assessments, and contact angle tests. Results indicate a 22.59% microhardness increase, 30.43 MPa residual compressive stress, increased surface roughness, improved wear and corrosion resistance, and improved hydrophilia after magnetic needle grinding. This research provides a theoretical foundation for advancing medical magnesium alloy industrially.

A comparative study of the activation energy and shielding properties of some binary and ternary echo-friendly alloys reinforced by Bi substitutes Zn particles for radiation protection

The thermal and mechanical stability besides environmentally friendly of some low-melting binary systems dopant with third element such as Bi started to gain much attention. This study provides the synthesized, effects of rapid solidification processing (RSP) and Bi doping on the microstructural, mechanical performance and gamma radiation shielding of various lead-free binary and ternary alloys have compositions Sn-(50-x)Zn-xBi (where x = 0, 10, 20, 30 and 40 wt.%) using high cooling rate. Microstructure modifications, elastic and plastic behavior were investigated. As well as the gamma-ray shielding performance of all as-prepared melt-spun process alloys was examined experimentally using FH 40G dose rate measuring unit. Phy-X/PSD software was used to compute the μ m values across a large energy range of 0.015 MeV–15 MeV. To clearly understand the gamma radiation shielding capability of the melt-spun process alloys, different shielding parameters includes linear attenuation coefficients, LAC, mass attenuation coefficient, MAC, mean free path, MFP, half value layer (HVL) and tenth value layer (TVL) were calculated and compared to other commonly shielding materials. X-ray diffraction (XRD) analysis confirms the presence of different phases such as β-Sn, Bi, Zn as well as two IMCs Sn0.95Bi0.05 and Sn0.85Zn0.15. The morphology features of the samples using scanning electron microscopy (SEM) revealed that Bi particles dopant the matrix led to refine the microstructures as well as forming a uniform and homogeneous distribution of IMCs. It is also, reported that the increase of Bi dopant led to enhancing the Bi segregation in the matrix in addition to decreasing the crystallite size which reinforces the mechanical strength and radiation shielding properties. The elastic modulus and Vickers microhardness increase with increasing Bi additions to about 35% and 27%, respectively. The results showed that correlation between activation energy and shielding properties of as-prepared alloys. The mass and linear attenuation coefficient for all prepared samples increases as Bi increases from 10 to 40 wt.%. On the other hand, low activation energies indicate easier formation and growth of IMCs. The results also show that the Sn-10Zn-40Bi alloy has the highest mechanical and shielding attenuation properties. It may be attributed to promoting the brittleness of Bi, refinement of crystallite size, extended the solid solubility and microstructure features accompanying Bi content using rapid cooling. As a result, Sn-10Zn-40Bi alloy may be recommended as a preferable alloy for radiation shielding performance to be used for medical, industrial and nuclear waste storage fields. In the current work, an attempt has been made not only to summarize the various investigations made so far on visualizing the feasibility of alloys as radiation shielding material; but also, to provide a comparative study for further consideration to be used in other fields.

Grain refinement and anisotropy improvement of arc-directed energy deposited Ti–6Al–4V with oscillating laser

Ti–6Al–4V parts fabricated by wire plus arc additive manufacturing (WAAM) usually exhibit columnar grain shapes and serious anisotropy in mechanical properties. This study aims to solve these issues by proposing a laser-assisted WAAM technique in which a vertically oscillating laser beam acts on the molten pool in WAAM. The influences of oscillation laser power on the microstructure and mechanical properties of Ti–6Al–4V parts built in WAAM are revealed and discussed. The oscillation laser can refine prior-β grains in WAAM. As the laser power increases, the depths of laser fusion lines in deposited layers increase, the size of prior-β grains decreases first and then increases, and both the microhardness and ultimate tensile strength (UTS) increase first and then decrease. At a laser power of 1600 W, the columnar prior-β grains are completely transformed into equiaxed shapes. The UTS values in the vertical and horizontal directions reach 1322 and 1309 MPa, respectively, respectively 30.5% and 15.7% higher than those of the WAAM sample. Meanwhile, the indices of plane anisotropy of UTS and elongation decrease by 90.6% and 76.4%, respectively.

In vitro remineralization of adjacent interproximal enamel carious lesions in primary molars using a bioactive bulk-fill composite

BackgroundSurface remineralization is recommended for the management of active non-cavitated interproximal carious lesions in primary teeth. According to the American Academy of Pediatric Dentistry, a recently recognized category of materials called bioactive restorative materials can be used for remineralization. This study aimed to evaluate the release of fluoride (F), calcium (Ca) and phosphate (P) ions from Predicta® Bioactive Bulk-fill composite compared with EQUIA Forte® and Filtek™ Z350 and to determine the remineralization effect of these 3 restorative materials on adjacent initial interproximal enamel carious lesions.MethodsThe release of F, Ca and P ions from 3 groups ((n = 10/group) (Group 1- Predicta®, Group 2- EQUIA Forte® and Group 3- Filtek™ Z350)) was determined at 1st, 4th, 7th and 14th days. After creating artificial carious lesions, human enamel samples were randomly assigned into 3 groups (n = 13/group) which were placed in contact with occluso-proximal restorative materials and exposed to a 14-day pH cycling period. Surface microhardness was determined using a Knoop microhardness assay at baseline, after artificial carious lesions formation and after pH cycling. The difference in the percentage of surface microhardness recovery (%SMHR) among groups was compared. Mineral deposition was analyzed with energy-dispersive x-ray spectroscopy (EDS) and the enamel surface morphology was evaluated with scanning electron microscopy (SEM). Kruskal-Wallis’s test with Dunn’s post hoc test and one-way ANOVA with Tukey’s post hoc test were used for data analysis.ResultsEQUIA Forte® released the highest cumulative amount of F and P ions, followed by Predicta® and Filtek™ Z350. Predicta® released higher amount of Ca ions than EQUIA Forte® and Filtek™ Z350. Predicta® demonstrated the highest %SMHR, followed by EQUIA Forte® and Filtek™ Z350. There was a significant difference in the %SMHR between Predicta® and Filtek™ Z350 (p < 0.05). However, EQUIA Forte® demonstrated the highest fluoride content, followed by Predicta® and Filtek™ Z350. The SEM images of EQUIA Forte® and Predicta® revealed the greater mineral deposition.ConclusionPredicta® demonstrated a marked increase in surface microhardness and fluoride content of adjacent initial interproximal enamel carious lesions in primary molars compared with Filtek™ Z350. Predicta® is an alternative restorative material to remineralize adjacent initial interproximal enamel carious lesions in primary molars, especially in high-risk caries patients.

Effect of ECAP and volume ultrasonic treatment on the corrosion resistance of magnesium

Magnesium and its alloys are promising materials for manufacturing bioresorbable implants. Various combinations of thermo-mechanical processing are used to improve the mechanical properties and corrosion resistance of magnesium alloys, forming the necessary structural state, which, in turn, requires determining the influence of various structural factors (grains, grain boundaries, dislocations, second-phase particles, etc.) on the complex properties of 'strength - corrosion resistance'. In this study, an experiment was conducted to determine the influence of structural changes in pure magnesium on mechanical properties and corrosion resistance in a physiological environment after deformation using equal channel angular pressing (ECAP) and post-deformation ultrasonic treatment. It was found that ECAP and subsequent ultrasonic treatment lead to a twofold increase in the yield strength of magnesium from 30 to 60 MPa. The increase in microhardness after ECAP is 50 MPa, while ultrasonic treatment results in an increase in microhardness by 230 MPa. After deformation, corrosion resistance changes significantly: ECAP reduces the corrosion rate compared to the initial state of magnesium by approximately 7 times, to values of 7 mm/year. Subsequent volume ultrasonic treatment does not lead to significant changes in the corrosion rate, which in this case was 10 mm/year.

Evaluation of Remineralizing Capacity of Tricalcium Phosphate, Nano-Hydroxyapatite and Ozone Remineralizing Agents on the Artificial Carious Lesion.

Dental caries is a dynamic process. By using therapeutic agents, early, noncavitated lesions and caries limited to the enamel can be stopped or even remineralized. For the remineralization of the initial carious lesion, many nonfluoridated remineralizing agents were investigated. An observational study to assess the remineralizing efficacy of tricalcium phosphate (TCP), nano-hydroxyapatite (nHAp) and ozone remineralizing agents on the artificial carious lesion. In this observational research, the artificial carious lesion was produced on extracted 40 premolar teeth. Later, remineralizing agents (Group A: nHAp, Group B: TCP, Group C: Ozone remineralizing agents, Group D: Control group (Deionized water) were used to remineralize demineralized teeth. Utilizing the Vickers Hardness Number, the level of demineralization and remineralization was assessed. Later these readings were statistically assessed using the Tukey's HSD (honestly significant difference) and ANOVA tests in SPSS version 21.0. The P value was set at 0.05 or less. After demineralization, there was a decrease in enamel microhardness values, with 32% in Group A, 26% in Group B, 22% in Group C, and 21% in Group D, respectively. From the baseline to demineralization, there was a statistically significant decrease in microhardness across all groups. After remineralization, Groups A, B, and C experienced an increase in microhardness while Group D experienced no changes. This showed that Group A had the highest remineralization percentage, followed by Group B and Group C. nHAp and TCP had the greater remineralizing ability, which can be used to manage initial carious lesions.