Initial Microhardness Research Articles

Сравнительный анализ изменения структуры и свойств сплавов системы Al–Si, подвергнутых электровзрывному легированию

The paper presents the comparative analysis of the structure and mechanical properties (microhardness) of the surface layers of the hypoeutectic Al–11Si alloy and hypereutectic Al–20Si alloy exposed to electroexplosive alloying (treatment mode: aluminum foil mass is 58.9 mg; Y2O3 powder mass is 88.3 mg; the discharge voltage is 2.6 kV). During the research, the authors identified that the Al–11Si alloy initial structure mainly consists of the Al solid solution grains. Eutectic grains are located along the grain boundaries and at the joints of aluminum grain boundaries. In the Al–11Si alloy, the aluminum grain size varies from 25 μm to 100 μm, and the Al–Si eutectic grain size varies within 10–30 μm. The hypereutectic composition Al–20Si alloy in the initial state is characterized by the presence of primary silicon inclusions predominantly of a plate-like shape. The sizes of these inclusions reach 120 μm. After electroexplosive alloying, in the Al–11Si alloy, the author identified the formation of a multilayer structure consisting of a highly-porous coating irregular in thickness, a liquid-phase alloying layer, and a heat-affected layer. The modified layer thickness for the Al–11Si alloy varies in the range of 33–60 μm, and for the Al–20Si alloy, the modified layer thickness varies within 20–100 μm. The microhardness value of the initial hypoeutectic Al–11Si alloy was 64 HV 0.05, for the hypereutectic Al–20Si alloy – 71 HV 0.05. It can be noted that the microhardness of the Al–11Si alloy surface layer exceeds the initial material microhardness more than 2.5 times. In the Al–20Si alloy, the surface layer microhardness exceeds the one of the initial material more than twice. With the increase of the distance from the modification surface, the microhardness decreases and reaches the initial alloy value at the depth of ≈90 μm.

Surface integrity evolution of a Ni-based single crystal superalloy by laser shock peening

The single crystal superalloy SRR99 experimental samples were single point treated by laser shock peening (LSP) with laser pulse energy of 5–7 J. The surface morphology, micro-hardness, surface residual stress and surface microstructure of samples prior and after LSP were determined by corresponding characterization instrument. From the surface morphology, a circular pit was formed in surface, which due to the severe plastic deformation induced by LSP, and the diameter & maximum relative height of circular pit were increase with laser pulse energy. From the micro-hardness and residual stress test results of samples, these were increased after LSP treatment. In detail, the initial microhardness and residual stress were 398 HV and -498 MPa, with laser pulse energy of 5 J, the microhardness and residual stress were increased to 455 HV and -843 MPa, when the laser pulse energy was increased to 7 J, the microhardness and residual stress were increased to 512 HV and -942 MPa. In addition, the surface roughness of samples was increased too, which reflect the severe plastic deformation. By observing the microscopic morphology of the bottom of the pit, it is found that there are convex structure and crater shape defect structures on the bottom surface, and the formation of these structures may affect the surface roughness of the shock area. Although LSP caused certain degree of twist deformation of the shape of the γ' phase, the original strengthening method characteristics of the matrix phase and strengthening phase was not destroyed, which still maintained the creep strength and thermal fatigue properties of superalloy. The experiment show that LSP can cause significant work hardening effect on the surface of superalloy, and the generated high residual compressive stress can effectively delay the initiation and propagation of cracks. Therefore, LSP technology can effectively improve the fatigue life of single crystal blade components.

Efficacy of fluoride varnishes with different compositions on white spot lesions remineralization

Objective: To evaluate the efficacy of different fluoride varnishes on white spot lesions (WSL) remineralization. Material and Methods: Polished bovine enamel specimens were obtained (n = 60) and had their initial surface Knoop microhardness (SMH) determined. WSL were created and the SMH was measured again. Then, specimens were allocated into six groups: C – Control (without varnish); BF – Bifluorid 12 (6% NaF + 6% CaF2); DP – Duraphat (5% NaF); PF – Profluorid (5% NaF); FP - Fluor Protector (0.2% NaF + 0.9% difluorsilane); CW - Clinpro White Varnish (5% NaF + 5% TCP). After varnishes application, specimens were immersed in artificial saliva for 24 h. Then, pH-cycling was performed for 8 days and SMH was measured. Data were analyzed by one-way ANOVA and Tukey’s test. Results: Non-significant differences were observed among the groups at baseline (p = 0.187) and after WSL formation (p = 0.999). After treatments, significant differences were observed among the groups (p = 0.001). Mean % of alteration (SD) and results of Tukey test were: C- 92.40 (12.10)a; PF- 88.66 (10.66)a; FP- 85.90 (14.49)ab; BF- 67.85 (17.86)bc; CW- 66.60 (18.48)c; DP- 58.62 (8.69)c. Conclusion:. Bifluorid 12, Clinpro White Varnish, and Duraphat showed higher efficacy than artificial saliva in promoting the remineralization of WSL, nevertheless, none of the treatments were able to recover sound enamel baseline microhardness. Keywords Dental caries; Fluoride; Fluoride varnishes.

Comparing Enamel Microhardness in Decidous Teeth With Primary Carious Lesions After Applying Three Fluoride Containing Materials in Vitro

Background and Aim: For decades, using fluoride has been introduced to prevent the development and progression of primary carious lesions. Increased surface microhardness of primary caries is among the essential factors in preventing lesion progression and cavity formation. The present study aimed to compare the microhardness changes of primary caries treated with 3 products, containing fluoride (varnish, toothpaste, & mouthwash) in dental teeth. Methods & Materials: In this study, 45 extracted human deciduous molars were used. Using a diamond-winning disc, enamel blocks with a dimension of 1 x 4 x 4 mm were prepared from the buccal surface of the teeth, i.e., healthy and without structural defects; they were mounted in acrylic self-adhesive. Initial microhardness test (Vicker’s test) with a force of 300 gr and Dwell time for 15 seconds was applied on samples. Next, artificial caries with the standard solution were created in all samples and the microhardness of samples was recorded at this stage. The study samples were randomly divided into 3 groups of 15, treated with fluoride varnish, mouthwash, and toothpaste. Then, the microhardness of samples was re-measured. The mean surface microhardness was compared between the study groups by Independent Samples t-test and Bonferroni test. All analyses were performed using SPSS at the significance level of P<0.05. Ethical Considerations: This study was approved by the Ethics Committee of the Arak University of Medical Science (Code: IR.ARAKMU.REC.1397.264). Results: Increase in surface microhardness of primary caries in fluoride varnish group was statistically significant; in GC MI paste plus toothpaste and Oral B mouthwash was non-significant. The research samples treated by fluoride varnish had a higher surface microhardness, compared to toothpaste and mouthwash. Conclusion: According to the present research results, fluoride varnish was superior to fluoride mouthwash and toothpaste in improving the microhardness of primary dental caries.

In Vitro Evaluation of the Stabilization Time of Chemical Bonds During Setting Reaction and Microhardness of Preheated Glass-Ionomer Cements.

To evaluate the effect of preheating glass-ionomer cement (GIC) restorative materials on stabilization time (ST) of their metal carboxylate bonds and on microhardness. Two conventional high-viscosity GICs, Ketac Universal (3M ESPE) and Equia Forte (GC), were evaluated. The thermographic camera was used to measure the temperature inside the glass-ionomer cement capsules before and after heating. The preheating of capsules was performed at 54°C for 30 seconds in a commercial device. Characterization of ST in the GICs was determined by Fourier Transform Infrared (FTIR) spectroscopy. For this, 10 samples of each material were prepared, five in the non-preheated group (control) and five with preheating. FTIR spectra were obtained 10 minutes after mixing (control group) or after heating and then every 10 minutes for 120 minutes. For the microhardness test, 20 cylindrical specimens (3 mm height x 6 mm diameter) were prepared for each material (10 preheated, 10 control). The microhardness was determined at three time intervals: 10 minutes after mixing, after the ST as detected through the FTIR part of the study, and after one week. Knoop microhardness was assessed using a diamond indenter with a 25 g load and 15 seconds dwell time. Ketac Universal showed an increase in temperatures of 15.7°C for powder and 3.6°C for liquid, while Equia Forte showed 16.4°C for powder and 8.5°C for liquid. FTIR spectra indicated that preheating reduced the ST for Equia Forte but increased it for Ketac Universal. Preheating increased the initial microhardness (T1) of Equia Forte. With maturation over one week, it was observed that preheating significantly improved the microhardness of both materials compared with the control specimens. Preheating influenced the ST and the microhardness of Ketac Universal and Equia Forte. The ST and microhardness of Ketac Universal increased after seven days, whereas Equia Forte showed a reduced ST and increased microhardness from the outset.

Effect of ozone and 10% sodium ascorbate on human dentin microhardness

: Several strategies have been tried out for the control and antimicrobial treatment of carious lesions such as the direct application of ozone. However, the the oxidation process after the use of ozone facilitates the permanence of residual oxygen, which can negatively influence the use of adhesive systems. The application of 10% sodium ascorbate on the dentin surface can neutralize the effect of oxygen. However, the influence of these substances on the coronary dentin microhardness must be studied. Objective: This study aimed to evaluate the microhardness of human dentin after the application of gaseous ozone and sodium ascorbate. Material and methods: Nineteen third molars were sectioned in order to separate the occlusal surface from the roots leaving a 4 mm thick specimen which was further divided into its mesial and distal parts. The mesial parts were allocated to Group A which was subdivided into two groups: control group, in which the initial microhardness was measured, and an ozone group, in which the application of gaseous ozone was performed for 40 seconds followed by the measurement of the final microhardness. The distal parts were allocated to Group B, subdivided into two groups, a control group in which the initialmicrohardness was measured and an ozone + sodium ascorbate group in which the application of gaseous ozone was performed for 40 seconds and a solution of 10% sodium ascorbate for 10 minutes followed by measurement of the final microhardness. Results: The results showed that there was a statistically significant increase in dentin microhardness (p>0.05) in Group A (control and ozone) and in Group B (control and ozone + sodium ascorbate). However,there was no statistically significant increase in microhardness (p>0.05) between ozone in group A and ozone + sodium ascorbate in group B. Conclusion: The application of gaseous ozone increased the microhardness of human dentin and the application of sodium ascobate had no influence on the microhardness that has already been modified by gaseous ozone.

Changes in surface properties of PI/WO2 сoatings after vacuum ultraviolet irradiation

This paper presents the results of a study on the effects of deep vacuum and vacuum ultraviolet (VUV) irradiation on polymer сoatings based on thermoplastic polyimide (PI) and tungsten oxide (WO2). Samples from pure PI (without filling) and polymer сoatings with 65 wt% WO2 (PI/WO2) were studied. The VUV irradiation occurred at 125 °C for 24 h, with no more than 10−5 Pa pressure. The VUV radiation intensity was 0.5 W/m2, and the wavelength was 90–115 nm. The total mass loss after VUV treatment for PI was 1.29 wt%, and for PI/WO2 сoating it was 0.63 wt%. The changes in the structure of PI and PI/WO2, established by IR spectroscopy, lead to loosening of the structure of the materials’ surface layers. A decrease in surface microhardness was measured after 24 VUV treatments for PI (12.17 %) and for PI/WO2 сoating (3.68 %), compared to the initial microhardness. It was found that VUV treatment of PI/WO2 сoating lead to an increase in surface roughness, while smoothing (decrease in roughness) of the surface was observed for pure PI.

Comparative Study of the Effect of Flavonoids and the Whey Extract on Enamel Microhardness: An In Vitro Study

Background: Preventing caries or stopping primary caries lesions is one of the most important goals of oral health care. The aim of this study was to compare the effect of flavonoids and the whey extract on tooth enamel by measuring the microhardness of enamel following its demineralization. Methods: In general, 42 samples of healthy enamel were prepared in this experimental-laboratory study. After measuring the initial microhardness using Vickers hardness tester )Buehler, Lake Bluff, IL, USA(, the samples were immersed in the demineralization solution for 4 days and re-tested for microhardness. Then, the samples were randomly divided into three groups of 14 and treated, including the grape seed extract w/v8%, the whey extract, and the artificial saliva. The samples were in contact with the treatment material for 8 days in an incubator at 37°C and then their microhardness was evaluated again. Results: The analysis of covariance showed that there was a significant difference in the amount of microhardness changes between the study groups (P < 0.001) so that microhardness changes were the highest in the grape seed extract group while they decreased in the control group. However, the post hoc test showed no statistically significant difference between the whey extract and grape seed extract groups (P = 1.000). Finally, the control group had a statistically significant difference from the whey extract and grape seed extract groups. Conclusions: Both grape seed extract and whey extract increased remineralization and the microhardness of tooth enamel compared to the control group. Thus, these two substances can be considered as natural and effective substances in the non-invasive treatment of carious lesions.

Effect of bleaching agents on mechanical properties of bulk fill resin and conventional composites

This study evaluated the effect of tooth whitening on resin composites (RC) on roughness, microhardness and flexural strength. There were three RC: one Bulk Fill type resin (Filtek Bulk Fill) and two conventional, Filtek Z350 (Z350) and Z250 (Z250). Twenty-four bar-shaped specimens were made for each RC. First, the initial roughness and microhardness were evaluated; thus, the RC were subdivided into 3 other groups, according to treatments: control group (C), this did not receive bleaching treatment; home bleaching with 10% carbamide peroxide (10%CP) (Opalescence PF), 8h/14 days; home-office bleaching with 40% hydrogen peroxide (40%HP) (Opalescence Boost PF) 3 ´ 15 minutes for 3 days at 48 hour intervals. After treatments, roughness and microhardness were again evaluated and then the samples submitted to the three-point flexural test. Data were tabulated, normality assessed, then submitted to ANOVA followed Tukey’s test (p <0.05). The results showed that the bleaching change the roughness of RC, but 10%CP had a significant increase. The gel concentration does not influence microhardness and flexural strength. After bleaching, Z350 has a lower elastic modulus. Based in the results obtained, could be concluded that the different bleachings did not promote significant changes on the RC studied.

Properties of the Surface Layer after High-Energy Treatment by Powder Particles

Experiments on the high-energy surface treatment of a substrate made of St.3 structural steel by the flow of particles of tungsten, nickel, and titanium nitride particles are performed. The collision pressure of the particles accelerated by the explosion energy on a steel target is evaluated using the momentum conservation equation and linear equation of the impact adiabat of the particle material. It is established that the collision pressure is, GPa, 62 for the tungsten particle, 48 for the nickel particle, and 41 for the titanium nitride particle. The particle heating temperature with the collision with the surface of a steel target is calculated allowing for conservation conditions of the mass and momentum on the shock-wave front. The maximal particle heating temperature in their collision place with the substrate surface (at a particle velocity of 2000 m/s) is, K, 1103 for the tungsten particles, 755 for the nickel particles, and 589 for the titanium nitride particles. It is shown that hardness of a steel target increases after its high-energy treatment by the particle flow. Maximal hardening of the surface layer of a steel target when compared with initial microhardness increases 32–55% and is observed at a depth of 2–4 mm from the treatment surface. Then it decreases to the microhardness of the initial material (170 HV) at a distance of 15–20 mm from the treated surface.

The effect of rapid high-intensity light-curing on micromechanical properties of bulk-fill and conventional resin composites

Rapid high-intensity light-curing of dental resin composites is attractive from a clinical standpoint due to the prospect of time-savings. This study compared the effect of high-intensity (3 s with 3,440 mW/cm2) and conventional (10 s with 1,340 mW/cm2) light-curing on micromechanical properties of conventional and bulk-fill resin composites, including two composites specifically designed for high-intensity curing. Composite specimens were prepared in clinically realistic layer thicknesses. Microhardness (MH) was measured on the top and bottom surfaces of composite specimens 24 h after light-curing (initial MH), and after subsequent immersion for 24 h in absolute ethanol (ethanol MH). Bottom/top ratio for initial MH was calculated as a measure of depth-dependent curing effectiveness, whereas ethanol/initial MH ratio was calculated as a measure of crosslinking density. High-intensity light-curing showed a complex material-dependent effect on micromechanical properties. Most of the sculptable composites showed no effect of the curing protocol on initial MH, whereas flowable composites showed 11–48% lower initial MH for high-intensity curing. Ethanol/initial MH ratios were improved by high-intensity curing in flowable composites (up to 30%) but diminished in sculptable composites (up to 15%). Due to its mixed effect on MH and crosslinking density in flowable composites, high-intensity curing should be used with caution in clinical work.

Effects of violet radiation and nonthermal atmospheric plasma on the mineral contents of enamel during in-office dental bleaching.

This in vitro study assessed the effects of in-office bleaching with gels (35% hydrogen peroxide [HP] or 37% cabamide peroxide [CP]) and two activation sources (violet radiation [LED] or nonthermal atmospheric plasma [NTAP]) on the mineral content of bovine enamel. Dental blocks (n = 90) were assessed for initial microhardness before random distribution into nine groups: LED, LED + HP, LED + CP, NTAP, NTAP + HP, NTAP + CP, HP, CP and control (without treatment). Specimens were subjected to bleaching (2 clinical sessions, 7 days apart) using LED [20x/session, 1-min/each, 30 s apart] or NTAP [1x/session, 10 min]. μRaman determined contents of phosphate (PO43) and carbonate (CO32). Micro-energy dispersive X-ray fluorescence (μEDXRF) and spectrophotometry of enamel microbiopsy evaluated the calcium to phosphorous ratios (Ca/P). Two-way ANOVA and Tukey tests analyzed μRAMAN and μEDXRF results. Spectrophotometry results were analyzed using Kruskal-Wallis and Dunn tests. Pearson correlation tested μEDXRF and spectrophotometry results (α = 5%). NTAP and NTAP + HP exhibited greater PO43- content than LED, LED + HP and control (p < 0.05). No statistical differences were detected between CO32- among groups. While μEDXRF evaluation demonstrated that NTAP and LED did not alter Ca/P ratio of enamel (p > 0.05), spectrophotometry showed that Ca/P reduced for LED + HP (p < 0.05). No correlation was found between μEDXRF and enamel microbiopsy spectrophotometry (p > 0.05). Activation sources did not adversely impact enamel's phosphate and carbonate concentrations after specimens' exposure to bleaching gels (either HP or CP). Visible light radiation emitted by a LED source was shown to adversely impact specimens' Ca/P ratios when treated with HP-containing bleaching gels.

Rheological Properties and Microstructure of PH1 Stainless Steel Produced by Selective Laser Melting

The present study is focused on rheological properties of PH1 stainless steel, produced by selective laser melting (SLM), at temperatures of hot deformation, with the aim to investigate the dependence of strain resistance on temperature and strain degree. The tests of cylindrical specimens, made of PH1 stainless steel, were carried out using a cam plastometer in temperature range 700 – 1200 °C at a strain rate ξ equal to 1 s-1 up to strain degree e equal to 0.8 – 1.2. The paper presents the results of investigation of initial microstructure, microhardness measurement and flow curves of PH1 steel, produced by SLM method. The flow curves of PH1 steel produced by SLM can be used in the development of new methods of manufacturing the metallic parts by additive technologies with the use of deformation post-processing.

Low Temperature Nanoindentation: Development and Applications.

Nanoindentation technique at low temperatures have developed from initial micro-hardness driving method at a single temperature to modern depth-sensing indentation (DSI) method with variable temperatures over the last three decades. The technique and implementation of representative cooling systems adopted on the indentation apparatuses are discussed in detail here, with particular emphasis on pros and cons of combination with indentation technique. To obtain accurate nanoindentation curves and calculated results of material properties, several influence factors have been carefully considered and eliminated, including thermal drift and temperature induced influence on indenter and specimen. Finally, we further show some applications on typical materials and discuss the perspectives related to low temperature nanoindentation technique.

Properties of the surface layer after high-energy treatment by powder particles

Experiments were conducted on high-energy surface treatment of a structural steel substrate with a flow of tungsten, nickel, and titanium nitride powder particles. The impact pressure of the steel target and particles accelerated by explosion energy was estimated using the momentum conservation equation and the linear equation of the particle material shock adiabat. It was found that the impact pressure of the target and particles is 62 GPa for a tungsten particle, 48 GPa for a nickel particle, and 41 GPa for a titanium nitride particle. The heating temperature of particles during their collision with the steel target surface was calculated taking into account the conditions of mass and momentum conservation at the shock wave front. The maximum heating temperature of particles at the point of their collision with the substrate surface (at a particle velocity of 2000 m/s) is 1103 K for tungsten particles, 755 K for nickel particles, and 589 K for titanium nitride particles. It was shown that the steel target strength increases when it is subjected to high-energy treatment with a flow of particles. The maximum hardening of the steel target surface layer increases by 32–55 % compared to initial microhardness and is observed at a depth of 2–4 mm from the treatment surface. Then it decreases to the value of starting material microhardness (170 HV) at a distance of 15–20 mm from the treated surface.

The effect of laser-activated bleaching with 810 nm and 980 nm diode lasers on enamel micro-hardness; an in vitro study

The aim of this study was to assess the micro-hardness of treated enamel with 810 nm and 980 nm diode lasers and to compare it with a conventional bleaching process.A sample of 45 caries-free human premolar teeth were selected. The enamel surfaces were completely polished. The crown portion of each tooth was then sectioned with a diamond disk, at dimensions of 3 × 3 × 3 mm. These sections were embedded in acrylic resin. The initial micro-hardness was determined by Vickers hardness apparatus at a vertical load of 200 g for 15 s. The samples were then randomly assigned to three groups of 15 samples.– Study group 1 (SG1): bleaching with Heydent JW gel and an 810 nm diode.– Study group 2 (SG2): bleaching with Heydent JW gel and a 980 nm diode.– Control group (CG): bleaching with Opalescense Boost.After bleaching, the Vickers micro-hardness was again evaluated. An analysis of covariance (ANCOVA) was used to compare the micro-hardness between the groups after bleaching, considering the initial micro-hardness as a covariate. A paired samples t-test was also used to compare micro-hardness before and after bleaching in each group and between groups.There was a significant difference in micro-hardness after bleaching with a laser and without a laser. After bleaching, the Vickers micro-hardness in the CG was significantly higher than in SG1 and SG2. There was no significant difference between SG1 and SG2 after bleaching (p value > 0.05).According to this study, laser irradiation with 810 nm and 980 nm diode lasers during tooth bleaching could cause a significant decrease in enamel micro-hardness.

A Comparative Evaluation of Two Commonly Used GP Solvents on Different Epoxy Resin-based Sealers: An In Vitro Study.

ABSTRACTAimThis study evaluates epoxy resin-based sealers after their final set, immersed in Endosolve-R or xylene for 1–2 minutes, for its easy removal mechanically after softening.Materials and methodsSixty Teflon molds were grouped with 20 samples in each of the three commercially available sealers, i.e., AH 26, AH Plus, and Adseal. The sealers were put in the specific molds after their manipulation as per the instructions given in the literature by the manufacturer. They were allowed to harden for 2 weeks at 37°C in 100% humidity. Two subgroups, A-Xylene and B-Endosolv-R, of 10 samples each, were formed from 20 set specimens based on solvents to which they were immersed for 1 and 2 minutes, respectively. The data obtained was subjected to the Mauchly's test one-way ANOVA and two-way ANOVA for analysis.ResultsIt was proved that for all the sealers immersed in solvents, there was a significant reduction in the mean Vickers hardness as the time increases. There was a significant difference in the initial hardness between the mentioned sealers with AH plus showing the highest followed by AH 26 and Adseal showing the lowest. AH Plus and Adseal sealers were softened by xylene after 2 minutes of their initial microhardness (p < 0.001); least effect was seen on AH 26. After 2 minutes, Endosolv-R softened initial microhardness of all the three sealers (p < 0.001).ConclusionIt was concluded that Endosolv-R was more effective in softening the epoxy-based resin sealer than xylene, after 2 minutes of exposure.How to cite this articleTyagi S, Choudhary E, Choudhary A, et al. A Comparative Evaluation of Two Commonly Used GP Solvents on Different Epoxy Resin-based Sealers: An In Vitro Study. Int J Clin Pediatr Dent 2020;13(1):35–37.

Can innovative methods of polymerization improve the physical-mechanical behavior of acrylic resins?

Acrylic-based resin is the material of choice for the fabrication of definitive and provisional prostheses. In order to achieve clinical success, it is important to know the most suitable polymerization process for this material. The aim of this study was to evaluate the influence of different polymerization methods on several physical and mechanical properties, before and after thermocycling, of a heat-activated acrylic resin (HAAR). In addition, the degree of conversion (DC) was evaluated for all polymerization methods. Ninety HAAR samples were divided into three groups: conventional polymerization (CP), dry-heat polymerization (DHP), and digital pneumatic polymerization (DPP). Color, microhardness (n = 10), and flexural strength tests (n = 20) were performed, before and after 2000 cycles of thermocycling. The analysis of the DC was performed by using Fourier transform infrared spectroscopy (n = 4). Color alteration and DC data were submitted to one-way analysis of variance (ANOVA). Microhardness and flexural strength data were submitted to two-way repeated measures ANOVA. All results were submitted to the Tukey test (α = .05). The color alteration was statistically lower in the DHP group. The DPP group exhibited higher initial microhardness with a statistically significant difference from other the groups. There was no statistical difference between the groups in regards to flexural strength. The CP and DPP groups had higher DC results. The proposed polymerization methods had divergent results for the different properties analyzed. However, these results were similar to those of conventional polymerization, which is a viable and adequate alternative.

Experimental composites containing quaternary ammonium methacrylates reduce demineralization at enamel-restoration margins after cariogenic challenge

ObjectiveThis study evaluated the influence of experimental composites containing quaternary ammonium monomers (QAM) at different concentrations and alkyl chains on demineralization at enamel-composite margins after cariogenic challenge. MethodsStandardized 4×4mm cavities were cut into 35 bovine enamel blocks, which were randomly divided into seven groups (n=5) and restored with the following experimental composites and commercial materials: (G12.5) – 5% dimethylaminododecyl methacrylate (DMADDM) with a 12-carbon alkyl chain (G12.10) – 10% DMADDM, (G16.5) – 5% dimethylaminohexadecyl methacrylate (DMAHDM) with a 16-carbon alkyl chain (G16.10) – 10% DMAHDM, (CG) – control group (without QAM), (GZ250) – commercial composite (Filtek Z250®), and (GIC) – glass ionomer cement (Maxxion R®). After restorative procedures, initial microhardness was measured and experimental composites were subjected to Streptococcus mutans biofilm formation for 48h. After cariogenic challenge, the samples were washed and microhardness was reassessed. A 3D non-contact profilometer was used to determine surface roughness and enamel demineralization was assessed by micro-CT. Microhardness results were analyzed by the Kruskal–Wallis and Mann-Whitney tests and micro-CT results were analyzed by Tukey’s HSD test (95% confidence interval). ResultsNone of the materials could prevent mineral loss at the enamel-restoration margins. The addition of 10% DMAHDM yielded the lowest, albeit statistically significant, mineral loss (p<0.05). 3D non-contact profilometry showed enamel surface roughness modification after biofilm exposure. The CG had the highest roughness values. Micro-CT analysis revealed mineral loss, except for GIC. SignificanceThe addition of 10% QAM with a 16-carbon chain in experimental composites reduced mineral loss at the enamel-restoration margins after cariogenic challenge.

Vickers Micro-Hardness of New Restorative CAD/CAM Dental Materials: Evaluation and Comparison after Exposure to Acidic Drink.

CAD/CAM (computer-aided design/computer-aided manufacturing) for indirect restorative materials has been recently introduced in dentistry. The purpose of this study was to evaluate the change of the surface micro-hardness of different restorative CAD/CAM materials after exposure to a carbonated acidic drink (Coca-Cola, Coca-Cola Company, Milan, Italy). One hundred and eighty specimens of identical size (2 mm thickness) were obtained by sectioning each tested CAD/CAM block of four materials: a hybrid ceramic (CERASMART™, GC Corporation, Tokyo, Japan), a resin nano ceramic (Lava™ Ultimate, 3M, Monrovia, CA, USA), a nanohybrid composite (Grandio blocs, VOCO GmbH, Cuxhaven, Germany), and a zirconia-reinforced lithium silicate glass ceramic (VITA SUPRINITY® PC; VITA Zahnfabrik, Bad Sackingen, Germany). Forty-five specimens of each material were tested. Micro-hardness was measured at baseline, after 7 days and after 28 days. The data were analyzed. The micro-hardness of each material varied significantly after immersion in Coca-Cola. The nanohybrid composite had a high initial micro-hardness and the greatest percentage loss after acid exposure. The hybrid ceramic and the resin nano ceramic had similar percentage losses of micro-hardness values even if the second material had higher initial values. The zirconia-reinforced lithium silicate glass ceramic had the highest baseline values and the lowest percentage loss of micro-hardness. The different CAD/CAM materials presented different micro-hardness values before and after acid exposure.