Microhardness Research Articles

Dentin Microhardness and Sealer Bond Strength to Root Dentin are Affected by Using Bioactive Glasses as Intracanal Medication.

This study investigated the human dentin microhardness (MH) and the MTA Fillapex® (Fillapex) and AH Plus®(AH) bond strength (BS) to dentin after using calcium hydroxide (Ca(OH)2) and bioactive glasses (45S5 and an experimental niobium phosphate bioactive glass (NbG)) as intracanal medications. For the MH test dentin slices were filled with medications and were submitted to Knoop MH (KHN) test (at day-0 (baseline data/without medication) and at day-15 (after using medication)). For the BS test, after medications had remained for 15 days in the roots, dentin slices were obtained and filled with the sealers. Seven days later, sealer BS to dentin was measured by push-out test (MPa). Data were statistically analyzed. Failure mode was visually assessed. The use of NbG, 45S5 for 15 days, increased the dentin MH and reduced the BS between AH sealer and dentin, but did not interfere with the Fillapex BS.

Experimental Investigation and Optimization of Process Parameters in Laser welding of NiTinol Shape Memory Alloys

Abstract In this work, an attempt was made to conduct bead on plate welding of NiTinol Shape memory alloy utilizing Yb: YAG laser welding process and identify the optimized parameters using Deng’s Similarity based approach integrated with Entropy Weight Method. Bead on Plate welding was carried out based on L9 Taguchi array with laser power, focal position, shielding gas blown distance and welding speed as input parameters. Bead width (BW), depth of penetration (DOP), microhardness (MH), and corrosion current density were measured as output parameters. Entropy weight method was first utilized to determine the weights that had to be given to output parameter, and Deng’s similarity based approach was used to find the optimized welding parameter combinations. The metallurgical characterization of the optimized weld was discussed with the aid of microstructure. Entropy weight Method results suggested to give more importance to microhardness. Deng’s Similarity approach identified that the 7th experimental (welding speed = 2400 mm/min, shielding gas blown distance = 8mm, focal position= 0.5 mm, power = 900 W) run as the optimized parameter combination for getting the weld with full penetration, lesser bead width, higher microhardness and corrosion resistance

An experimental study on joining of AISI 304 SS to Cu by Nd-YAG laser welding process

In this current study, a challenging dissimilar metal combination AISI 304 stainless steel and copper is welded by pulsed wave Nd-YAG laser welding process without use of any filler material, followed by its mechanical as well as metallurgical investigation. Macroscopic as well as microscopic examination of the weld surface and weld bead has been carried out to observe the weld penetration depth and metallurgical behavior inside the weld zone. Weld pool geometry confirms about attainment of full penetration depth in pulsed wave Nd-YAG laser and also describes that the penetration depth is directly proportional pulse energy as (penetration depth7 J = 69%) < (penetration depth14 J = 82%) < (penetration depth21 J = 100%). The formed copper micro-channels suggest that the copper solidifies last and flows inside the weld zone matrix during the solidification. The average width of the heat affected zone (HAZ) and partially melting zone (PMZ) have been found to be 23.0 µm and 6.0 µm on the stainless steel (SS) side respectively. The microhardness (MH) study shows that (MHCopper = 75 HV0.1) < (MHWeld zone = 90–200 HV0.1) < (MHSS = 210 HV0.1).

Performance analysis of tool electrode prepared through laser sintering process during electrical discharge machining of titanium

Nowadays, additive manufacturing (AM)-based rapid prototyping (RP) is used as a convenient route for making tool electrodes required in electrical discharge machining (EDM). AM enables direct fabrication of complex shaped EDM electrode in comparatively less time in contrast to subtractive machining processes. In this study, an EDM electrode is prepared directly by selective laser sintering (SLS) process using metal matrix composite of aluminium (Al), silicon (Si) and magnesium (Mg). To study the performance of the prepared RP tool electrode in electrical discharge machining, titanium is used as workpiece material and EDM-30 oil as dielectric medium during machining. The performance of the prepared tool electrode is compared with conventional copper and graphite tool electrodes. Experiments have been conducted changing EDM process parameters viz. open circuit voltage (V), peak current (Ip), duty cycle (τ) and pulse duration (Ton) along with three tool electrodes such as RP, graphite and copper tool electrodes. The performance measures considered during the experimental study are material removal rate (MRR), tool wear rate (TWR), average surface roughness (Ra), white layer thickness (WLT), surface crack density (SCD) and micro-hardness (MH) on white layer. SEM and EDX of the machined surface reveal that tool material is generally eroded and deposited on the machined surface with formation of metal carbides. However, tool erosion is more pronounced in case of RP tool electrode. XRD analysis reveals the formation of titanium carbides on the machined surface resulting in increase in the micro-hardness of white layer. Discharge current and tool type are found to be significant parameters influencing the performance measures considered in the study. The surface produced when machined with RP tool electrode exhibits superior surface characteristics while graphite tool electrode produces better MRR and TWR.

Microstructure study on electro discharge deposited magnesium alloy with semi sintered and sintered electrode

In this research, electro discharge deposited ZE41A magnesium alloy with semi sintered and sintered electrode are studied. Parameters used in this study were compaction load, current and pulse on time and coating responses were material deposition rate (MDR), micro hardness (MH). For the electrical discharge coating (EDC), electrodes were prepared using tungsten carbide and copper powder by powder metallurgy method. It was observed that the MDR and MH increased when increased current and pulse on time in low compaction load for semi sintered and sintered electrode. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were analysed in the deposited surface to study the microstructure and presence of electrode materials respectively. Comparative microstructure study on electrical discharge coating of ZE41A magnesium alloy with powder metallurgy semi sintered and sintered electrode was carried. Among two conditioned electrode, semi sintered electrode has the higher material deposition rate and micro hardness. Further increased the sintering temperature the deposition is formed with the large cracks and craters.

Influence of different irrigation protocols on microhardness and flexural strength values of young and aged crown dentin.

To investigate the effect of different irrigation protocols on microhardness (MH) and flexural strength (FS) values of young and aged crown dentin. In addition to ageing, root canal irrigation might also affect the mechanical properties of coronal dentin walls. One hundred and twenty dentin bars (2mm×2mm×8mm) were obtained from the crowns of extracted, non-caries, human molars of young and older patients (n=60 bars; average patient ages: 16.7 and 65.4, respectively). Subgroups were formed as follows: 2.5%NaOCl(sodium hypochlorite)+5%EDTA(ethylenediaminetetraacetic acid), 2.5%NaOCl+15%EDTA, 2.5%NaOCl, 5%EDTA, 15%EDTA and Saline. NaOCl and saline were used for 20minutes and EDTA solutions for 1minute. MH values of each sample were measured before and after the irrigation protocols. The same samples were also submitted for FS analysis. The data were statistically analysed. Young samples had lower MH values at pre- and post-treatment compared to aged samples (P<.05). A significant decrease was observed in MH values of aged samples exposed to 2.5%NaOCl and both NaOCl+EDTA combinations (P<.05). FS values of the young saline-treated group were statistically higher than aged ones (P<.05). Both NaOCl+EDTA combinations caused a significant decrease in FS values of young samples compared to saline (P<.05). Ageing has a significant effect on the MH and FS values of crown dentin samples. 5% EDTA solutions revealed similar results to 15%EDTA regarding MH and FS values of crown dentin in both age groups. The NaOCl+EDTA combination had a prominent effect than EDTA alone, on MH values of young-, and FS values of aged dentin samples.

Grey Relational Analysis of EDM of Ti6Al4V using TiC/Cu Composite Tool Electrode Made with Nano and Micron Sized Particles

This paper covers the use of Taguchi based grey relational analysis in EDM process. The analysis is used to determine an optimum combination of process parameters, which involves individual and simultaneous improvement of surface roughness (SR) and the micro hardness (MH) of Ti6Al4V alloy in electric discharge machining (EDM). The tool used in the machining process is TiC/Cu powder metallurgy (P/M) electrode. Taguchi’s L18 mixed orthogonal array is used to plan experimentations which includes the machine tool and electrode parameters as the study parameters. The analysis of variance (ANOVA) for grey relational grade showed that particle size EDM electrode was the most dominant factor (64.13%) followed by peak current (7.41%) in influencing surface quality of ED Med Ti6Al4V alloy. Whereas, peak current is the most influential parameter while evaluating the individual responses of SR and MH. Finally, the optimum combination of process parameters was validated by confirmation experiments that considerably improved the multiple quality characteristics simultaneously.

Influence of Energy and Soft Drinks on the Surface and Mechanical Properties of Nanofilled Composite Resin

Aim: To evaluate the effect of energy drinks (Redbull and Bison) and soft drinks (CocaCola and 7 Up) on the surface roughness (SR) and microhardness (MH) of Filtek Z350 nanofilled composite resin. Materials and methods: A total of 60 disk-shaped specimens were prepared from Filtek Z350 XT restorative material and randomly allocated to 5 groups (n=12). The specimens were stored in petri dish containing Redbull (Group 1); Bison (Group 2); Coca-Cola (Group 3); 7 Up (Group 4) and distilled water (Group 5/Control). The SR and hardness of the composite specimens were determined after 24 hours (n=6) and 28 d (n=6) of storage in energy and soft drinks. SR (in Ra) was measured using a non-contact optical profilometer and MH (VHN) was tested using hardness tester equipped with a Vickers diamond indenter. The data obtained was analyzed using SPSS v.20 statistical analysis software. The data was analyzed using Wilcoxon sign rank test. A P < 0.05 was considered as statistically significant. Result: Group Redbull showed maximum SR at 28 days (0.30 0.11) followed by Bison at 28 days (0.21 0.09). MH test results showed specimens in distilled water with increased MH at 24 hours (114 9.4). The least MH was seen in Redbull (85 12.3) at 28 days. Conclusion: The energy drinks have a substantially damaging effect on SR and MH compared to soft drinks and distilled water; and these effects are increased with duration of exposure.

Surface morphology evaluation of hardened HSLA steel using cryogenic-treated brass wire in WEDM process

Surface morphology of a high strength low alloy steel is analyzed on wire electric discharge machining (WEDM) process with a cold-treated (CT) brass wire. Cold treatment process is carried out at − 70 °C for 24 h to refine the microstructure of brass wire for smooth discharge energy during machining process. Fractional factorial design is used to measure the response of recast layer thickness (RLT), wire material infusion (WMI), and micro-hardness (MH) of hardened HSLA steel. CT brass wire, servo voltage (SV), pulse on time (Ton), pulse off time (Toff), wire tension (Tw), and flushing pressure (Fp) of deionized water are selected as input process parameters. Analysis of variance (ANOVA) is performed to test the adequacy and significance of the developed mathematical models. Ton is observed as the most effective input process parameter followed by Toff and CT brass wire. Low-energy parameters with CT brass wire exhibits results with reduced RLT and WMI on machined surface as compared to NCT brass wire. CT brass wire is less wear off with respect to NCT brass wire while machining workpiece at same input process parameters.

Morphochemical characterization, microhardness, water sorption, and solubility of regular viscosity bulk fill and traditional composite resins.

To evaluate the morphology of filler particles, chemical composition, microhardness (MH), water sorption (WSp), and solubility (WSl) of a regular viscosity bulk fill and traditional composite resins. Eighty samples (Ø:5 mm; height: 4 mm) were prepared according to the factors "composite" (Aura/SDI, FiltekZ250 XT/3M, Aura Bulk Fill/SDI, and Filtek Bulk Fill/3M) and "filling technique" (incremental and bulk) (n = 10). Vickers MH was measured on the top and bottom surfaces of each samples, and then WSp and WSl were obtained by means of mass gain and loss. Morphology of filler particles and chemical characteristics of composites were evaluated by scanning electron microscopy (SEM) and energy dispersity spectroscopy (EDS) in additional samples (n = 1/group). Data were analyzed using two- and three-way ANOVA and Tukey's tests (p < .05). No significant difference was found for WSp among the groups. Comparing composites in the incremental technique, Aura bulk fill composite showed lower WSI than the other materials and in the bulk fill technique, Filtek Bulk Fill showed the lowest value. Filtek Bulk Fill showed higher MH than the other composites on the bottom surface when samples were produced by bulk filling. The composites presented good physical properties, but the bulk fill ones showed better results for the bottom microhardness and solubility, although chemical elements and morphology were similar in general.

Development of numerical model for predicting the characteristics of Ni–SiC nano composite coatings on AISI 1022 substrate

The strength of nano coatings predominantly depends on the selection of optimum combination of input parameters. This problem can be solved by developing an empirical relationship between input parameters to predict microhardness (MH), average surface roughness (Ra), specific wear rate (Ws) and co-efficient of friction (CoF) of the pulse electroplated coating by response surface methodology (RSM). In this paper an attempt has been made to optimize the electroplating process parameters of Ni–SiC nano coating using Grey-RSMapproach. This experiment highlights the use of RSM by designing the three factor three level central composite design. The Ni–SiC nano coating was deposited on AISI 1022 low carbon steel substrates under pulse current electroplating technique using nickel watts bath by varying input parameters such as frequency (Hz), duty cycle (%) and current density (A/Cm2). The optimum electroplating parameter was obtained through grey relational analysis (GRA). The prediction of optimum nano composite coating parameter is found at frequency 10 Hz (F1), duty cycle 10% (D1) and current density 0.2 A Cm−2 (C2), then confirmation experiment is performed to verify the optimum process parameter condition. The influences of those optimized coating parameters over the microstructure, morphology, coating thickness, EDAX, x-ray diffraction and wear rate of Ni-nano SiC composite coatings were also investigated.

Improving microhardness and wear resistance of 316L by TiO2 powder mixed electro-discharge treatment

Electro Discharge Treatment (EDT) has been carried in this study for the surface modification of 316 L stainless steel. The process is carried out in TiO2 powder mixed dielectric medium and assessed in terms of change in microhardness (MH) and wear resistance (WR). The presence of Titania particles, changed structural phases, of the treated specimens, was examined by scanning microscopy (SEM), x-ray diffraction (XRD) respectively. Nano-indentation test revealed the maximum value of microhardness attained (942.90 HV, average) for the specimen machined at the higher discharge current of 28 A in the presence of TiO2. The surface thus produced was 233% more superior in terms of microhardness value compared to bare metal, due to the formation of carbides, silicides and several intermetallic compounds on the treated surface. Furthermore, surface with maximum microhardness also witnessed the dominating wear resistance characteristic with a protective efficiency of 80% compared to the substrate.

An integrated multifunctional hybrid cement (pRMGIC) for dental applications

ObjectiveGlass-ionomer and resin-modified glass-ionomer cements are versatile materials with the ability to form a direct bond with tooth tissues. The aim of this study was to formulate a novel class of dental bio-interactive restorative material (pRMGIC) based on resin-modified glass-ionomer cements via the inclusion of an organophosphorus monomer, ethylene glycol methacrylate phosphate, with a potential to improve the mechanical properties and also function as a reparative restorative material. MethodspRMGIC was formulated with modification of the resin phase by forming mixes of ethylene glycol methacrylate phosphate (EGMP; 0–40%wt) and 2-hydroxyethyl methacrylate monomer into the liquid phase of a RMGIC (Fuji II LC, GC Corp.). The physical properties of the cements were determined including setting characteristics, compressive strength and modulus (CS &CM), microhardness (MH) and biaxial flexural strength (BFS). Fluid uptake and fluoride release were assessed up to 60 days storage. Adhesion to sound dentine was measured using micro-tensile bond strength and surface integrity was analysed using SEM coupled with EDX. Statistical analysis was performed using ANOVA and Bonferroni post-hoc tests. ResultsThe pRMGIC cements exhibited an increase in working time with increasing EGMP concentration however were within the limits of standard clinical requirements. Although the compressive strength of pRMGIC cements were comparable to control cements in the early stages of maturation, the higher EGMP-containing cements (EGMP30 and 40) exhibited significantly greater values (p < 0.05) after 4 weeks storage (141.0 ± 9 and 140.4 ± 8 MPa, respectively), in comparison to EGMP0 (128.8 ± 7 MPa). A dramatic two fold increase in biaxial flexural strength (p < 0.001) was observed for the pRMGIC’s. Furthermore, the ability to decalcify tooth apatite resulted in enhanced interfacial adhesion due to chelation with calcium ions of tooth apatite. The inclusion of EGMP encouraged formation of reinforcing complexes within the RMGIC, thus improving physical properties, decreasing solubility and lower fluoride release. A dense microstructure was observed with increasing EGMP content. SignificanceA novel universal bio-interactive adhesive repair material will enable clinicians to offer more effective repair of the tooth-restoration complex, thus future treatments will benefit both patient and a severely constrained healthcare budget.

Biological, mechanical and adhesive properties of universal adhesives containing zinc and copper nanoparticles

ObjectivesTo evaluate the effect of addition of zinc oxide and copper nanoparticles (ZnO/CuNp) into universal adhesives, on antimicrobial activity (AMA), cytotoxicity (CTX), water sorption (WS) and solubility (SO), microhardness (MH) and in vitro degree of conversion (DC), as well as resin-dentin microtensile bond strength (μTBS), nanoleakage (NL) and in situ DC. MethodsZnO/CuNp (0% [control]; 5/0.1 and 5/0.2 wt%) were added in Prime&Bond Active (PBA) and Ambar Universal (AMB). The AMA was evaluated against Streptococcus mutans. For CTX, Saos-2 cell-line was used. For WS and SO, specimens were tested for 28d. For MH, specimens were tested after 24 h and 28d and for in vitro DC, specimens were evaluated after 24 h. After, the adhesives were applied to flat dentine surfaces, composite resin build-ups, specimens were sectioned to obtain resin–dentine sticks. It was evaluated in μTBS, NL and in situ DC after 24 h of water storage. ANOVA and Tukey’s test were applied (α = 0.05). ResultsThe addition of 5/0.2 ZnO/CuNp increase AMA and WS, but decrease the SO when compared to control (p < 0.05). The CTX and μTBS were maintaining with adhesive-containing ZnO/CuNp (p > 0.05). MH, in vitro DC and in situ DC was significant increase (AMB) or maintaining (PBA) with ZnO/CuNp addition. However, significantly lower NL was observed for ZnO/CuNp groups (p < 0.05). ConclusionsThe addition of ZnO/CuNp in the tested concentrations in universal adhesive systems may be an alternative to provide antimicrobial activity and improves the integrity of the hybrid layer, without jeopardizing biological, adhesives and mechanical properties. SignificanceThis is the first study that demonstrates that the addition of zinc oxide and copper nanoparticles in concentrations up to 5/0.2 wt% in two universal adhesive systems is a feasible approach and may be an alternative to adhesive interfaces with antimicrobial properties and less defects in the resin-dentin interface.

Surface alloying of D2 steel using EDM with WC/Co P/M electrodes made of Nano and Micron sized particles

The present study is an experimental work carried for surface alloying/modification of D2 alloy steel using WC/Co powder metallurgy (P/M) electrode made of nano, micron and mixture of nano and micron sized particles. Both, machine tool and electrode parameters were selected for study and experiments were planned as per Taguchi’s L18 mixed orthogonal array. Optimal combination of parameters was obtained using Taguchi’s method and analysis of variance (ANOVA) was performed to evaluate influence of parameters on surface roughness (SR) and micro-hardness (MH). The parameters Peak current (IP), pulse on time (TON) and particle size (PS) were found to be most influential on both SR and MH. In EDM, surface modification is performed by deliberate transfer of tool elements onto the work surface. In the present investigation, EDS analysis reveals the migration of tungsten (W) and cobalt (Co) electrode particles, deposition of carbon particles and diffusion of oxygen particles onto the work surface. High reactive surface area of nano particles made greater surface alloying than other tool electrodes and has shown its influence positively on both SR and MH. Low thermal conductivity of nano particle electrodes (NP) makes improved surface alloying than other tool electrodes. Because of the particle size is reduced to nano level its dimension is smaller than the spark gap dimension hence, reduced arcing and improved process stability was obtained, which eventually improved the surface roughness of the component. At optimum MH, higher values of TON and IP gives the sufficient time and temperature for formation of following carbides and oxides viz., Fe3C, Cr23C6 , Cr2Fe14C, Fe2W2C, W3O and Cr3O were responsible for increased hardness of the work surface. The range of roughness values obtained in the present investigation is 1.65-5.82 μm. The highest hardness of 981 HV was obtained without much sacrificing the surface finish.

Multi-objective particle swarm optimization of EDM parameters to deposit HA-coating on biodegradable Mg-alloy

The present research work is aimed to discuss a novel method of depositing hydroxyapatite coats, with interconnected pores, on the surface of bio-degradable MgZnMn alloy by using hydxroxyapatite (HA) powder mixed electric discharge machining (HAM-EDM) process. The parameters of HAM-EDM process has been optimized using multi-objective particle swarm optimization (MO-PSO) technique to determine the optimal levels of concentration of hydroxyapatite powder (CHA), peak-current (Ip), pulse-on (Ton), and pulse-off (Toff). The surface roughness (SR), thickness of recast layer (RLT), and micro-hardness (MH) were chosen as output response characteristics. The experiments were performed according to L27 orthogonal array and an empirical model has been developed to interpret the co-relation amongst input and output parameters. A number of optimal solutions (∼100) were obtained by MO-PSO technique, where all responses were optimized. Among them, best optimal condition is to deposit biomimetic HA-containing layer with low SR (0.70 μm), low RLT (11.85 μm) and high MH (246 HV) was CHA = 5.28 g/l, Ip = 3.48 A, Ton = 40.33 μs, and Toff = 109.29 μs? Further, the specimens produced were characterized, morphologically and topologically, and revealed the existence of hydroxyapatite (HA) layer with interconnected pores of 5–10 μm size. The EDS spectrum showed that presence of Ca, P, and O on the modified surface, which conferred the deposition of HA-layer on the surface. The XRD pattern investigations of modified surface confirmed the formation of various biocompatible phases, which enhanced the mechanical properties, corrosion and osseintegration characteristics.

Surface Modification of Ti6Al4V Alloy Using EDMed Electrode Made with Nano- and Micron-Sized TiC/Cu Powder Particles

The present study is an experimental work carried on for surface modification of Ti6Al4V alloy using TiC/Cu powder metallurgy (P/M) electrode. Both, machine and tool parameters were selected for study, and these experiments were planned as per Taguchi’s L18 mixed orthogonal array. Optimal combination of parameters was obtained using Taguchi’s method, and analysis of variance was performed to evaluate the influence of parameters on surface roughness (SR) and micro-hardness (MH). Peak current, particle size and pulse on time were found to be the most significant accordingly on both SR and MH. High reactive surface area of nanoparticles made greater surface alloying than the other tool electrodes and has shown its influence positively on both SR and MH. The EDS analysis reveals the migration of Ti and Cu elements, deposition of carbon and diffusion of oxygen particles on the surface. The XRD spectrum confirms the presence of carbides (TiC, $$\hbox {Ti}_{2}\mathrm{C}$$ , $$\hbox {Fe}_{5}\mathrm{C}_{2}$$ and $$\hbox {Fe}_{3}\mathrm{C}$$ ) and oxides (TiO and $$\hbox {Ti}_{3}\mathrm{O}$$ ) at different machining conditions which indicates the influence of TON and IP on discharge energies and in turn on the properties of machined surface. The carbides, generated on the machined surface, increased the hardness as high as 912 HV, without much sacrifice of the roughness of the machined surface. The range of roughness values obtained in the present investigation is 1.88–4.449 $$\upmu \hbox {m}$$ .

The Influence Of Sand Casting Mold Solidfication Pressure Variations To The Quality Of Al-Si Alloy Casting Product

The purpose of this study is to find The influence of the sand cast solidification pressure variations to the quality of an alloy Al-Si casting product. An experimental method was used in the study and the analysis of the data used descriptive analysis to explain the charts. The stages of researched process is preparation material and equipment; making the design and manufacture of a pattern; manufacture of the sand mold by 35, 40, 45, 50, and 55 kg/cm 2 pressure variation; casting process; observation of defect; measurement of the level roughness; microstructure examination; assay composition; and last test is hardness micro vickers test. The research results show that variations pressure 35 kg/cm 2 does not occur defect the needle at al. A defect of the needle that occur most frequently upon variations of the pressure of the 55 kg/cm 2 is as much as 0.62 % . Air cavities formed to variation pressure solidification 35 kg/cm 2 of 0.77 % to the least, while in variation 55 kg/cm 2 happened the number of defect air cavities the most namely 3.96 % . The mold fall defect largest namely 1.95 % happened to variation pressure 35 kg/cm 2 . Defect of sand inclusion the least of 0.06 % happened to variation pressure 55 kg/cm 2 . Defect of fins formed due to variation pressure solidification sand mold experienced the number of been fluctuating, recorded high in early then decline and to high back in highest variation. The pressure variation 35 kg/cm 2 it has value roughness flattened 3.17 and products castings the most rough happened to sand mold solidification variation pressure 55 kg/cm 2 , with on average of 5.44. the degree of hardness highest of 141.8 VHN happened to variation pressure 35 kg/cm 2 and lowest of 124.8 VHN happened to variation 55 kg/cm 2 . Concluded that the solidification of pressure variations sand mold 45 kg / cm 2 produce castings products with the most optimal average in terms of the measurement of the defective; variation pressure solidification sand mold of sand casting 35 kg / cm 2 produce a smooth surface, and the higher pressure make surface castings becomes rougher; solidification of pressure variations and coarse sand mold 35 kg / cm 2 produce micro structure with smooth grains and becomes more violent along with increasing pressure; pressure variation 35 kg / cm 2 produce a hardest surface, the higher of the pressure variation it becoming violence number progressively lower. Keywords : Pressure variations, sand casting, quality

Influence of Time Intervals between Bleaching Procedures on Enamel Microhardness and Surface Roughness.

Background:Dental bleaching has been increasingly sought out to improve dental aesthetics, but it may cause changes in dental enamel.Objective: To assess the influence of different time intervals on bleaching gel applications with regard to the Microhardness (MH) and Surface Roughness (SR) on dental enamel.Material and Methods:Forty bovine incisors were randomly divided into two groups (G1 and G2) and both were bleached with 35% Hydrogen Peroxide (HP35) (n=20; G1: seven-day interval and G2: two-day interval). The MH and SR tests were performed before bleaching (T0) and after the first (T1), second (T2), and third (T3) bleaching gel applications. The specimens were stored in artificial saliva between each application (37°C). The data were analyzed using the student’s t-test (p ≤ 0.05) for dependent samples.Results:The reduced time interval (two days) led to a significant reduction in MH, while MH was not affected during the seven-day interval. The SR results increased regardless of the bleaching gel application time interval.Conclusion:The decreased time interval of two days between bleaching gel applications caused changes in MH but did not influence the SR of dental enamel.

Influence of polymerization time on properties of dual-curing cements in combination with high translucency monolithic zirconia

PurposeThe aim of this in vitro study was to assess conversion degree (DC), micro-hardness (MH) and bond strength of two dual-curing resin cements employed under translucent monolithic zirconia irradiated with different time protocols. Methods84 square shaped samples of 1mm thickness were prepared from high translucency zirconia blocks and divided into two groups (n=24) according to the cement employed: (1) Rely-X Ultimate; (2) Panavia SA. Each group was further divided into 3 subgroups (n=8) according to the irradiation time: (a) no light; (b) 20s; (c) 120s. Light curing was performed 60s after the sample was placed on the diamond support of a FT-IR spectrophotometer with a high power multiLED lamp. Final DC% were calculated after 10min. After 24h, Vickers Test on the cement layer was performed. The same protocol was used to lute composite cylinders in order to evaluate microshear bond-strength test. ANOVA and Bonferroni tests were performed to find differences between MH and bond-strength to zirconia, while for DC% the Scheirer–Ray–Hare two-way test was used. ResultsThe two cements reached higher DC% in subgroup (b) and (c). As concern MH, statistics showed an increase in curing time was able to improve MH significantly. Bond-strength was not affected by irradiation time only for Panavia SA. ConclusionsThe first null hypothesis has to be rejected since DC% and MH of the dual-cements tested were influenced by the curing time. The second null hypothesis is partially rejected since the bond strength was influenced by the curing time only for Rely-X Ultimate.