Surface Microhardness Test Research Articles

Comparative Evaluation of Root Caries Remineralization Effect of Plain Milk, 5 ppm of Fluoridated Milk, and 5 ppm of Sodium Fluoride in Deionized Water Using Surface Microhardness Test: An In Vitro Study.

ABSTRACTBackground:There is an increase in longevity of teeth retained in elderly population, leading to increased risk of root caries. Therefore, new and affordable preventive strategies are in need to reduce this problem. Hence, the aim and objective of the study was to assess and compare the root caries remineralization effect of plain milk, 5ppm of fluoridated milk, and 5ppm of NaF in deionized water.Materials and Methods:The study was an in vitro experimental design. Sixty root samples were divided into five groups (sound root, demineralized root treated in deionized water, plain milk, 5-ppm fluoridated milk, and 5-ppm fluoridated deionized water) of 12 samples each after baseline surface microhardness analysis and standardization was carried out in the study. All groups except the sound root were subjected to demineralization procedure for 4 days at 37°C. The demineralized four groups were treated to test solutions and subjected to pH cycling for 14 days. This was followed with assessment of postintervention surface microhardness. Student’s paired t test was used for comparing surface within groups. One-way analysis of variance test and post hoc Tukey’s test were conducted for between groups’ comparison.Results:There was a significant difference between groups (P < 0.05). The results of post hoc showed that significant difference was found between the group sound root and demineralized treated with 5-ppm fluoridated milk and 5-ppm fluoridated deionized water with an effect size of 2.15 and 2.87, with CI (–26.8 to –8.1) and (–36 to –17.3), respectively. There was a significant difference in all the groups when compared within the group (P < 0.05).Conclusion:Plain milk, 5-ppm fluoridated milk, and 5-ppm fluoridated deionized water showed remineralizing potential against demineralized in vitro root caries samples. 5-ppm fluoridated deionized water and 5-ppm fluoridated milk have a better effect compared to plain milk.

Effects of lemon essential oil and limonene on the progress of early caries: An in vitro study

ObjectiveThe purpose of this study was to investigate the effects of Lemon essential oil (LEO) and Limonene (LIM) in the progress of early caries. DesignLEO and LIM were selected as experimental medicine, while sodium fluoride (NaF) and deionized water (DW) were positive and blank controls, respectively. Bovine incisors were used to establish enamel and dentin early caries models by demineralization method in vitro. Then specimens were subjected to pH cycling. Calcium and phosphate release of demineralizing solution were measured by an automatic biochemical analyzer; Surface microhardness tester and energy dispersive X-ray spectrometer were used to detect the surface microhardness recovery and calcium- phosphate ratio on tooth surface; Degraded collagen matrix by collagenase was investigated by assaying hydroxyproline. ResultsCalcium release of dentin demineralizing solution of LEO group was lower than DW group’s and higher than NaF group’s. Both of LEO and LIM groups, the surface microhardness recovery were significantly lower than those of NaF group, which were similar to DW group. Dentin surface calcium- phosphate ratio of LEO and LIM groups were lower than those of NaF group and higher than those of DW group. Hydroxyproline concentration in the remineralizing solution of LEO and LIM groups were lower than DW groups’ and higher than NaF groups’. ConclusionsLEO and LIM have influence on the progress of dentin early caries, which can stabilize its structure by inhibiting collagen degradation. Meanwhile, these medicines may provide a new drug choice for the prevention and treatment of early root caries.

Remineralization effectiveness of the PAMAM dendrimer with different terminal groups on artificial initial enamel caries in vitro

ObjectiveDisruption of the demineralization–remineralization balance could trigger the development of dental caries, making it challenging for enamel to “self-heal”. Thus, extrinsic assistance is needed to restore enamel lesions and stop undermining progression. The aim of this study was to investigate enamel remineralization in a simulated oral environment via poly (amino amine) (PAMAM) dendrimers quantitatively. MethodsBovine enamel specimens were shaken in demineralization solution (pH 4.5, 37°C, 50rpm/min) for 72h to create initial enamel carious lesions. The subsurface-demineralized specimens were then divided into four groups: enamel treated with PAMAM-NH2, enamel treated with PAMAM−COOH, enamel treated with PAMAM−OH, and enamel treated with deionized water. The treated specimens underwent subsequent 12-day pH cycling. Enamel blocks were analyzed by transverse microradiography (TMR), surface microhardness testing and scanning electron microscopy (SEM) before and after demineralization and pH cycling. ResultsGroups treated with PAMAM dendrimers showed lower lesion depth and less mineral loss, attained more vertical-section surface microhardness recovery, and adsorbed more mineral deposits (p<0.05). The enamel lesion remineralization values of PAMAM-NH2, PAMAM-COOH, and PAMAM-OH groups were 76.42±3.32%, 60.07±5.92% and 54.52±7.81%, respectively. SignificanceIn conclusion, PAMAM with different terminal groups could induce enamel remineralization, among which PAMAM-NH2 showed the most prominent competence, followed by PAMAM-COOH and PAMAM-OH, in that order.

Properties and Corrosion Resistance of AISI H13 Hot-Work Tool Steel with Borided B4C Powders

In this study, the surface of AISI H13 steel was borided with powder blends of B4C and NaBF4 using the powder-pack method at 800, 900 and 1000 °C for 2, 4 and 6 h. The structural and mechanical characteristics of the boride layers formed on the surface were characterized using scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry, 2D surface profilometry, microhardness and electrochemical corrosion (3.5 wt% NaCl) tests. The boride layer exhibited a single phase structure (Fe2B) in samples coated at 800 °C and a dual-phase structure (FeB + Fe2B) at higher boriding temperatures (900 and 1000 °C). The boride layers were compact and crack-free in all boriding conditions. Depending on boriding parameters, the thickness, hardness and average surface roughness (Ra) of the coatings were found to range between 5.81 and 102.46 µm, 1635–1915 HV and 0.315–0.650 µm, respectively. The borided AISI H13 steel displayed up to 33.5 times and 2.4 times higher corrosion resistance than untreated AISI H13 steel and martensitic AISI 431 steel, respectively. This suggests potential use of borided AISI H13 steel in the steam turbines and marine applications as an alternative to the more costly martensitic and duplex stainless steel grades. The corrosion resistance depended on the phase structure (single- or dual-layer), density, thickness and surface roughness of the boride coatings.

Assessment of enamel remineralising capability of three different remineralising agents using vicker’s surface microhardness test.

Assessment of enamel remineralising capability of three different remineralising agents using vicker’s surface microhardness test.

Three-dimensional printing of zirconia: characterization of early stage material properties

Objective: The aim of this study was to evaluate the mechanical properties of 3D printed zirconia (ZrO2). Materials and Methods: The test specimens were produced with a 3D printer that uses lithography-based ceramic manufacturing (LCM) technique with two different parameters in horizontal and vertical printing orientations. Altogether four groups of nine specimens were printed and examined. Mechanical characterization was performed using 3-point bending test (ISO 10477) and surface microhardness (Vickers) test. Grain structure, porosity and printing layer morphology were examined with optical and scanning electron microscopy (SEM). Additionally fractography analysis was done to investigate and evaluate features of fracture initiation site. Numeric results were statistically analyzed with ANOVA (a = 0.05). Results: The average flexural strength reached for printed zirconia was 499 MPa (+/−75 MPa) for specimens printed in horizontal orientation and 575 MPa (+/−69 MPa) for specimens printed in vertical orientation. Optical microscopy and SEM analysis revealed that fractures initiated between the printing layers or from a local porosity. Printing layer thickness varied from under 13 μm to over 20 μm. Conclusions: The study revealed that 3D printed zirconia has challenges in regards to layer integration. Based on this study, 3D printed zirconia still suffers from low mechanical strength, which together with long carbon-debinding time, does not make 3D printed zirconia a potential material for dental appliances at this stage. Further research is needed to create more suitable zirconia precursor slurries and to optimize printing parameters and sintering conditions to be able to 3D print zirconia with higher mechanical properties.

Tribological behavior of borided surface on CoCrMo cast alloy

CoCrMo alloys are used in a wide range of applications because of their acceptable fatigue strength and corrosion resistance. However, CoCrMo-based components exhibit a deleterious effect of wear. For this reason, surface modification through ceramic coatings has become in a useful alternative to improve mechanical resistance. The main aim of the present study was to investigate the tribological behavior of a system of diffusional boride layers formed on the substrate of CoCrMo alloy. For this purpose, different boron diffusion heat treatment parameters were performed: 1223, 1248 and 1273 K by 6, 8 and 10 h, respectively. Surfaces were characterized using scanning electron microscopy (SEM), surface roughness measurement, micro-hardness testing, and X-ray diffraction. The tribological response was studied by means of ball on disc tribometer under dry-sliding conditions tracking their friction coefficient, mass loss, wear rate and surface damage by stereoscopy and SEM. Boride coating at 1223 K by 6 h showed the better wear resistance, increased it 6 times relative to the wear resistance obtained for the CoCr alloy untreated sample.

Comparative evaluation of compressive strength and surface microhardness of EQUIA Forte, resin-modified glass-ionomer cement with conventional glass-ionomer cement.

The study aimed to evaluate and compare the compressive strength and surface microhardness of EQUIA Forte, light cure, and conventional glass-ionomer cement (GIC). Fifty-four pellets of G-Coat (GC) Gold Label 2, GC Gold Label light-cured universal restorative material, and EQUIA Forte GIC were prepared of dimensions (6 × 4) mm and were divided into three groups (18) each and were stored at 37°C for 1 h and then immersed in 20 ml of deionized water, artificial saliva, and lactic acid six each, respectively, over 30 days. Samples were subjected to surface microhardness and compressive strength test on the 1st day, 7th day, and 30th day. Results were subjected to ANOVA and Bonferroni post hoc test. Comparing the compressive strength of EQUIA Forte from day 1 to 30 when placed in artificial saliva, there was a significant increase on day 30 (P = 0.007); compared to other groups. The surface microhardness of EQUIA Forte from day 1 to 30 when placed in artificial saliva nonsignificantly decreased comparing to other groups. Surface microhardness and compressive strength of EQUIA Forte were significantly high in comparison to the other groups.

Setting Time and Surface Microhardness of Mineral Trioxide Aggregate and 1% and 5% Fluoride-Doped Mineral Trioxide Aggregate Mixed with Water and Gel-like Polymer.

Mineral trioxide aggregate (MTA) is extensively used in endodontics. However, it has limitations such as long setting time, low compressive strength and poor handling properties. Our study aimed to compare the setting time and surface microhardness of MTA and fluoride-doped MTA (FMTA) using gel-like polymer (GLP) or distilled water (DW) as liquid. An MTA-like cement was prepared by mixing Portland cement, bismuth oxide and gypsum (75%, 20% and 5%, respectively). FMTA (1% and 5%) was made by substituting 1% and 5% of MTA powder with fluoride. GLP, composed of methyl cellulose (MC) and propylene glycol (PG), was used as the hydrating liquid and compared with distilled water. Six experimental groups (n=10) were examined for each test. The samples were subjected to Vickers surface microhardness test after 4 and 28 days. Setting time was measured using ANSI/ADA standards. Data was analyzed using two-way and repeated measured ANOVA and the Tukey HSD tests. The MTA-like cement hydrated with GLP showed a significantly reduced setting time (P<0.05); 1% FMTA, mixed with GLP, had the shortest initial and final setting times. The microhardness values of all samples increased at different rates during 28 days (P<0.00001). The microhardness significantly decreased by addition of fluoride to MTA (P<0.001). The results of the present in vitro study suggested that using GLP as the hydrating liquid enhances the setting time with no adverse effect on the surface microhardness. However, adding fluoride can negatively affect the microhardness of MTA.

Effects of femtosecond laser shock peening in distilled water on the surface characterizations of NiTi shape memory alloy

NiTi shape memory alloy was processed by femtosecond laser shock peening (FLSP) without protective coating in distilled water to modify its surface characterizations. The surface topography, microhardness, microstructure and scratch testing were studied before and after FLSP treatment. The experimental results show that FLSP with different laser scanning speeds and passes can change the surface roughness and microhardness due to laser ablation and high pressure of shock wave. The average microhardness value of the specimens FLSPed in distilled water increased. Grain refinement was observed in the surface layer of FLSPed NiTi alloy. The scratch testing revealed that FLSP process can decrease the frictional force and coefficient of friction, and it also demonstrated that the FLSP technique is beneficial to enhance the surface wear property of NiTi alloy.

Effect of Heavy Metals Contamination from Cigarette Smoke on Sound and Caries-Like Enamel.

In this study, we sought to evaluate the influence of cigarette smoke and pH cycling on the chemical composition and surface/cross-sectional enamel microhardness. A total of 40 dental blocks obtained from bovine incisors were divided into four groups (n=10): no treatment (control); exposure to cigarette smoke (CS); exposure to pH cycling (PC); and exposure to cigarette smoke and pH cycling (CS-PC). The samples were analyzed by synchrotron radiation micro X-ray fluorescence, bench mode X-ray fluorescence, as well as surface microhardness (SMH) and cross-sectional microhardness (CSMH) testing. The SMH results were submitted to analysis of variance (ANOVA) and Tukey's test. The CSMH results were evaluated using split-plot ANOVA and Tukey's test. A high amount of Cd and Pb and traces of Ni and As were observed in enamel and dentin after exposure to cigarette smoke (CS and CS-PC). The SMH and CSMH of CS were statistically higher when compared with the control. The PC and CS-PC showed lower SMH and CSMH. We conclude that exposure to cigarette smoke promoted heavy metal deposition in enamel/dentin. In addition, it increased the enamel microhardness but did not promote a protective effect on the in vitro development of caries. The clinical significance of this work is that there is significant bioaccumulation of heavy metals from cigarette smoke on the surface and in the enamel and dentin.

Performance evaluation of high-speed incremental sheet forming technology for AA5754 H22 aluminum and DC04 steel sheets

Incremental sheet forming (ISF) has received tremendous attraction in industrial, academia and research segments due to its inherent advantages. To deploy ISF technology in the manufacturing sector, various aspects have to be addressed such as geometrical accuracy, non-homogenous thickness distribution, and process slowness. In this study, extensive experimental work was performed to satisfy the industrial requirements. The influence of forming parameters (step depth, forming wall angle and feed rate) was investigated to access the ISF feasibility at higher speeds when forming the AA5754-H22 aluminum alloy and DC04 steel. The surface roughness, thickness distribution, and microhardness tests were carried out for the samples, which were successfully formed at the higher levels of process parameters. These experimental results were obtained at different locations on the sheet after forming. The analysis has revealed that the possible reduction in the execution time is up to 84% faster for AA5754 H22 aluminum alloy and 74% in case of DC04 steel. In this way, the current study not only provides the necessary framework for the future development of ISF but also commercialization of this technology.

Investigation on Surface Integrity of Rapidly Solidified Aluminum RSA 905 by Magnetic Field-Assisted Finishing.

RSA 905, a rapidly solidified aluminum alloy, has been widely utilized in optical, automotive, and aerospace industries owing to its superior mechanical properties such as hardness and strength compared to conventional aluminum alloys. However, the surface finishing of RSA 905 to achieve submicron surface roughness is quite challenging and was rarely addressed. This paper presents an experimental and analytical study on magnetic field-assisted finishing (MFAF) of RSA 905 through a systematic investigation on surface integrity in relation to the MFAF process parameters. The effect of abrasive and polishing speed conditions on material removal and surface roughness was quantitatively investigated. The surface and subsurface quality were evaluated by optical microscope and scanning electron microscope (SEM) observations, residual stress measurement, surface microhardness and tribology test. The results show that relatively high material removal and low surface roughness were obtained under conditions using the SiC abrasive with a grit size of 12 µm at polishing speed of 400 rpm or using the Al2O3 abrasive with a grit size of 5 µm at polishing speed of 800 rpm. Heat melt layer caused by wire electrical discharge machining (EDM) during the sample preparation was removed by MFAF without inducing new subsurface damage. The MFAF process also helps release the surface residual stress and improve the tribological performance although the surface microhardness was slightly reduced.

The effect of drinking yogurt on the microhardness of posterior composites resin

Background :This study was conducted to evaluate the effect of yogurt on thesurface microhardness of two types of composite resins; (Filtek™ P90 Low ShrinkPosterior Restorative, 3M ESPE,USA), and (Filtek™ Z350 Posterior Restorative, 3MESPE,USA).Forty samples of composite were prepared by using cylindrical mold (2mm inhight and 8mm in diameter )..All specimens were stored in plastic container thatcontain distilled water and incubated 37cº for 24 hours before they were tested. twentysamples of each type of composite were divided into two groups (10) for each ,baseline measurements for surface microhardness test was taken for all compositesamples using the micromet microhardness tester (Vichers hardness tester) with al00g load was applied for 15 seconds in which three indentations were made for eachsample and converted into Vickers Hardness Number (VHN ) .After baselinemeasurement 10 samples of each type of composite were alternately immersedmanually by holding the specimen by a pair of tweezers from its sides, , in drinkingyogurt (Activia ,KSA) and artificial saliva for 10 cycles 5 seconds each at roomtemperature (25cº). This was repeated three times a day (8am,4pm,12am) at 8hoursintervals for one week. the other 10 samples for each type of composite wereimmersed in artificial saliva only. The total soaking time in both drinking yogurt andsaliva was 100 seconds. After the soaking sequence was completed the specimen wasrinsed with distilled water and subjected to surface microhardness test (Vichershardness tester).Descriptive statistics(mean values and standard deviations with the minimum andmaximum values and Statistical analysis of data by using student t - test for all groupswas carried out between the means of each type of composites ,the results showed asignificant reduction in VHN values (at P&lt;0.05)of Filtek™ Z350 PosteriorRestorative composites after immersion in artificial saliva, while the (Filtek™ Z350Posterior Restorative, 3M ESPE) composite showed a highly significant reduction inVHN values (at P&lt;0.01)after immersion in drinking yogurt. Filtek™ P90 Low ShrinkPosterior Restorative composites showed a non significant reduction in VHN values(at P&gt;0.05) after immersion in artificial saliva and after immersion in drinking yogurt.Filtek™ P90 Low Shrink Posterior Restorative composites have highest VHNvalue than Filtek™ Z350 Posterior Restorative composites, and surface microhardnessresults showed that drinking yogurt highly significantly effect on the Filtek™ Z350Posterior Restorative composites while it has non significant effect on the Filtek™P90 Low Shrink Posterior Restorative composite

Influence of cryogenic treatment prior to laser peening on mechanical properties and microstructural characteristics of TC6 titanium alloy

In this study, the mechanical properties and microstructural characteristics of TC6 titanium alloy subjected to Cryogenic Treatment (CT) prior to Laser Peening (LP) were experimentally investigated by means of x-ray diffraction (XRD) technology, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) observations. Surface micro-hardness and tensile tests were also carried out. Experimental results showed that in comparison to single CT or LP process, CT prior to LP can induce finer grain size and higher dislocation density. Meanwhile, CT prior to LP can provide better mechanical properties. The surface micro-hardness and tensile strength of the specimen subjected to LP after CT with 18 h achieved an increase with 28.11% and 28.71%, respectively, while its elongation only reduced by the extent of 4.19% compared with untreated sample. Meanwhile, in comparison to the process of single CT or LP, LP after CT with 18 h provided the maximum amplitude compressive residual stress and Full Width at Half Maximum (FWHM) values, the values reached to −633 MPa and 2.47°, respectively. Additionally, based on the experimental results, the microscopic strengthening mechanism of CT prior to LP on the mechanical properties of TC6 titanium alloy was analyzed in detail.

EFFECT OF DIFFERENT POLISHING SYSTEMS ON PROPERTIES OF CONTEMPORARY COMPOSITE RESINS

Objectives: This study aimed to evaluate the effects of different polishing systems on the surface roughness and surface micro-hardness of three types of composites. Materials and Methods: One hundred and eighty samples were prepared in disc-shaped stainless steel molds with a uniform size of 6 mm in diameter and 4 mm in thickness. The samples were divided according to the materials used into three groups of 60 samples for each material, and each group was then subdivided into subgroups according to the polishing instruments with 20 samples in each subgroup: Group I (control group) (Mylar’s strip) with no finishing and polishing. Group II, polishing with Spiral polishing wheels and Group III, polishing with Sof-lex Pop-on discs. Each subgroup was divided into two groups according to measurements of surface roughness and microhardness (n=10). Restorative materials were handled according to the manufacturers’ instructions. The molds were placed on flat glass plates covered with Mylar’s strips and then were filled with restorative materials. The materials were covered with Mylar’s strips, and a glass slide was pressed against the mold to adapt the materials completely to the inner portions of the molds. The excess material was removed, and the samples were photo-activated for 40 sec at the top surface using high intensity Elipar TM LED light curing unit, all samples were light cured following the manufacturers’ instructions. The specimens’ surfaces in groups II and III were finished with an ultrafine diamond finishing. After finishing the group II specimens were polished using Spiral polishing wheel. Group III specimens were polished using Sof-Lex Pop-on discs, strictly following the manufacturer’s instructions. All of the groups were stored in saline for 24 hr. All of the specimens were equally subdivided for both the surface roughness and micro-hardness test. The data were analyzed using one-way ANOVA at a significance level of 0.05 for both the surface roughness and microhardness tests, followed by Tukey,s post hoc test, using SAS software. Results: Comparing between the three polishing techniques, the Mylar’s strips (control group) exhibited significantly lower roughness values (smoothest surface) than the polishing systems (p <0.0001). Nanocomposite had the lowest surface roughness comparing to other materials. Comparing between the three materials, the greatest microhardness mean value was recorded with Sonic bulkfill, using Mylar’s strips or Spiral wheel or Solfex disc polishing techniques(p <0.0001). Conclusions: The control group had the lowest surface roughness and microhardness values compared to the polishing groups. No significant difference on surface roughness between Spiral wheel disc values and Soflex disc. The lowest surface roughness material was Nano-composite in each of the used techniques and Sonic bulkfill had the highest mic-ohardness than bulkfill and nanocomposite

Effect of fluoride varnish with added casein phosphopeptide-amorphous calcium phosphate on the acid resistance of the primary enamel.

BackgroundThis study aimed to investigate the effects of a fluoride varnish with added Casein Phosphopeptide-Amorphous Calcium Phosphate (CPP-ACP) treatments on acid resistance of primary teeth enamel.MethodsEnamel specimens obtained from 40 primary incisors (for surface microhardness testing) and 40 primary molars (for demineralization depth measurement) were randomly divided into four groups (n = 10 incisors and 10 molars) each according to surface treatment: no treatment (control), MI varnish (1–8 % sodium fluoride and 1–5 % CPP-ACP), Clinpro White (1–5 % sodium fluoride and <5 % modified tricalcium phosphate), Duraphat (<5 % sodium fluoride). Specimens were stored for 24 h in a moist environment. After varnish residues were removed, specimens were subjected to pH cycling. The effects of fluoride varnishes were evaluated according to surface microhardness, lesion depth and structural changes. Results were analyzed by ANOVA and Tukey’s tests.ResultsThe lowest changes in surface microhardness and lesion depth occurred in MI varnish group, followed by the Clinpro White, Duraphat and no treatment (control) group (for percentage of loss surface microhardness −20.80, −34.60, −57.80 and −73.40; for lesion depth values 23.60 μm ± 3.36, 29.85 μm ± 3.27, 40.37 μm ± 3.41 and 54.56 μm ± 4.16, respectively). Statistically significant differences in both surface microhardness and lesion depth were observed among all groups (P < 0.05).ConclusionsWithin the limitations of this in vitro study, fluoride varnish containing CPP-ACP was more effective in increasing the acid resistance of primary enamel than other fluoride varnishes. However, further clinical research is needed to confirm these in vitro results.

Surface Properties and Color Stability of Resin-Infiltrated Enamel Lesions.

To examine the surface topographies, microhardness, and color stability of resin-infiltrated enamel lesions before and after aging challenges in vitro using three-dimensional laser scanning profilometry, surface microhardness testing, spectrophotometry, and scanning electron microscopy. Forty human third molars were embedded in epoxy resin, and each tooth was prepared to have two white spot lesions and one sound enamel area. One white spot lesion received resin infiltration and the other was untreated. Ten specimens were subjected to thermocycling for 10,000 cycles, 10 specimens were immersed in coffee solutions, and 10 specimens were placed in water storage. Surface area roughness (Sa), Vickers microhardness (VHN), and CIE L*a*b* color values were measured on sound enamel, resin-infiltrated lesions, and untreated lesions before and after aging. The surface morphology of resin-infiltrated lesions was observed after aging under scanning electron microscopy and compared with 10 specimens that were not subjected to aging challenge. Resin infiltration increased the surface microhardness of the enamel lesions from 89.3 to 212.0 VHN. The surface microhardness of resin-infiltrated enamel lesions was not significantly affected by aging. The surface roughness of resin-infiltrated lesions (0.32-0.37 μm) was greater than that of sound enamel (0.05-0.06 μm) and untreated lesions (0.12-0.13 μm). Thermocycling and water storage further increased surface roughness of resin-infiltrated surfaces. Resin-infiltrated enamel lesions showed greater discoloration than sound enamel surfaces. Surface microfissures and microcracks were observed on resin-infiltrated enamel lesions after thermocycling. Surface hardness of enamel lesions increased significantly after resin infiltration and remained stable following thermocycling. Surface roughness and color stability of resin-infiltrated enamel lesions were less than ideal and might further deteriorate after aging in the oral environment.

Experimental Study of Laser Welding Process and Properties of 2205 Duplex Stainless Sheet Steels

2205 duplex (austenitic-ferritic) stainless steel has a good weldability and an excellent corrosion resistance. The good weldability is achieved when in close to 50-50 ferrite-austenite ratio. In this study, the welding process and properties were investigated by pulsed Nd:YAG laser welding. Tensile test, surface microhardness test, surface topography and microstructures of 2205 duplex stainless steel welds were performed under different welding speeds, input currents, pulse widths, frequencies and defocus distance. The relationship among them was revealed and the optimal welding parameters were obtained. The results showed in the condition of I = 160 A, T = 5 ms, f = 25 Hz, V = 500 mm/min and Z =-1 mm, the amount of ferrite and austenite in welds was roughly same, overlap rate of solder joints was above 78% and the weldability was good.

Changes in surface characteristics of two different resin composites after 1 year water storage: An SEM and AFM study.

To evaluate changes in surface characteristics of two different resin composites after 1 year of water storage using a profilometer, Vickers hardness, scanning electron microscopy (SEM), and atomic force microscopy (AFM). A total of 46 composite disk specimens (10 mm in diameter and 2 mm thick) were fabricated using Clearfil Majesty Esthetic and Clearfil Majesty Posterior (Kuraray Medical Co, Tokyo, Japan). Ten specimens from each composite were used for surface roughness and microhardness tests (n = 10). For each composite, scanning electron microscope (SEM, n = 2) and atomic force microscope (AFM, n = 1) images were obtained after 24 h and 1 year of water storage. The data were analyzed using two-way analysis of variance and a post-hoc Bonferroni test. Microhardness values of Clearfil Majesty Esthetic decreased significantly (78.15-63.74, p = 0.015) and surface roughness values did not change after 1 year of water storage (0.36-0.39, p = 0.464). Clearfil Majesty Posterior microhardness values were quite stable (138.74-137.25, p = 0.784), and surface roughness values increased significantly (0.39-0.48, p = 0.028) over 1 year. One year of water storage caused microhardness values for Clearfil Majesty Esthetic to decrease and the surface roughness of Clearfil Majesty Posterior increased. AFM and SEM images demonstrated surface detoration of the materials after 1 year and ensured similar results with the quantitative test methods. SCANNING 38:694-700, 2016. © 2016 Wiley Periodicals, Inc.