Differences In Microhardness Values Research Articles

Effects of polishing or glazing on surface roughness and microhardness after milling CAD-CAM ceramic materials

Objective: This study aimed to evaluate the surface roughness and microhardness of CAD-CAM ceramic blocks after different surface finishing protocols. Materials and methods: Three ceramics were evaluated: lithium disilicate, leucite-reinforced feldspathic and zirconia-reinforced lithium silicate. Ninety specimens were obtained and distributed into 3 groups (n=10): polishing (specimens were polished with an abrasive rubber kit); conventional glaze (according to the manufacturer's recommendations); and, extended glaze (the specimens were kept for 15 minutes at maximum firing temperature and the furnace was kept closed until reaching 200ºC). In all specimens, a drill was used to simulate the milling machine and thus obtain the initial roughness. Surface roughness was evaluated before and after the finishing protocols, while Vickers microhardness was performed only after the finishing protocols. Roughness data were analyzed to repeated measures two-way ANOVA and Bonferroni post-hoc test and ANOVA with Welch correction and Games-Howell test were used to analyze microhardness data (α = 0.05). Results: Both conventional and extended glazes showed greater smoothness for lithium disilicate and zirconia-reinforced lithium silicate ceramics, while for Empress, extended firing of the glaze provided greater surface smoothness. Regarding microhardness, there was no statistically significant difference among the protocols for the same material. The conventional glaze group made from lithium disilicate did not show a significant difference in microhardness values in relation to the other groups. Conclusion: The application of glaze improves the surface smoothness of the ceramics after milling procedure. There is no change in microhardness with different surface finishing protocols.

Assessment of bulk-fill of resins microhardness longitudinal

Aim: This study aimed to assess the polymerization effectiveness of bulk-fill composite resins in longitudinal microhardness. Methods: Blocks of bulk-fill composite resin with thicknesses of 6 mm were analyzed with Vickers microhardness. The resin blocks were divided into two groups (n=6): resin AURA and OPUS. The microhardness test was performed before (base and top) and after (longitudinal microhardness) sectioning the blocks at distances of 2 mm, 4 mm, and 6 mm from the top of the block. The mean microhardness values were tabulated and subjected to ANOVA followed by Tukey’s test (p<0.05). Results: The OPUS bulk-fill resin samples presented microhardness means of 55.9 kgf/mm2, 53.7 kgf/mm2, and 49.3 kgf/mm2, the AURA bulk-fill resin samples presented microhardness means of 57,02 kgf/mm2, 55,86 kgf/mm2 e 51,77 kgf/mm2 for the distances of 2 mm, 4 mm, and 6 mm, respectively. Tukey’s statistical test showed a significant difference in microhardness values at different distances of 2 mm, 4 mm, and 6 mm (p<0.001) for each resin. Although there was a statistically significant difference within and between the groups assessed, all samples showed polymerization effectiveness when comparing the top and base of the block. Conclusion: Polymerization was effective in different thicknesses (2 mm, 4 mm, and 6 mm) in both resins studied. The microhardness ratio was adequate when comparing the base and top.

Characterization of microstructure, mechanical and corrosion response in AISI 304L and Ti-stabilized 439 stainless steels weld joints

The gas tungsten arc welding (GTAW) was employed to weld dissimilar materials of 304L austenitic stainless steel (ASS) and Ti-stabilized 439 ferritic stainless steel (FSS). Dissimilar joints were produced using 309L ASS filler electrode with low and high heat inputs (HIs). Austenite and ferrite phases were observed in the weld zone (WZ) of both weldments with varying volumetric fractions. The results showed that the ferrite fraction in WZ decreased with increase in HI from 37.2 % (low HI) to 32.39 % (high HI). Formation of ferrite stringers was observed in the unmixed zone of ASS side, whereas chromium-rich carbides were observed in heat affected zone (HAZ) of FSS side. Higher fraction of carbides was observed for the high HI weldment. Mechanical properties of the low HI weldment were superior to high HI weldment due to higher ferrite fraction. Significant differences in microhardness values were observed for the WZ and HAZ between the two HIs weldments. The electrochemical behaviour of the both the weldments were analysed through the various techniques. The results showed that intergranular corrosion resistance was lower for low HI-WZ than high HI-WZ region, however, opposite trend was observed for impedance and pitting resistance.

Effect of Heated Sodium Hypochlorite Irrigant on Structural Changes and Microhardness of Radicular Dentin: An In Vitro Study.

This study is aimed to evaluate the combined effect of sodium hypochlorite at varied concentrations and temperatures on radicular dentin microhardness along with its surface structural changes using an FTIR spectrometer. Mandibular premolars were cleaned and shaped up to F3 Protaper gold rotary files, after which they were subjected to five experimental conditions - group I - neutral saline as negative control, group II - 3% NaOCl solution, group III - 5% NaOCl solution, group IV - 3% intracanal-heated NaOCl solution, and group V - 5% intracanal-heated NaOCl solution. Following this, the microhardness of radicular dentin at 100 µm and 300 µm from the canal lumen and Fourier-transform infrared (FTIR) spectroscopic analysis were performed. The results showed that intracanal-heated sodium hypochlorite group reduced root dentin microhardness at 300 µm than its nonheated counterpart. No difference in microhardness values was observed between 3% intracanal-heated and room-temperature sodium hypochlorite groups at 100 µm. Reduction in amide/phosphate ratio was noted in all the groups treated with sodium hypochlorite irrespective of temperature and concentration. Thus, considering that the level of alteration in physical and structural changes of root dentin with or without heating is insignificant, intracanal-heated low-concentration sodium hypochlorite solutions could be used as an alternative to high-concentration sodium hypochlorite. Intracanal-heated low-concentration sodium hypochlorite enables the clinicians to achieve maximum disinfection while keeping the structural and physical properties of the dentin similar to room-temperature sodium hypochlorite.

Laser Application in Remineralisation of Enamel after Interproximal Reduction: An In-vitro Scanning Electron Microscopic Study

Introduction: Interproximal Reduction (IPR) or reproximation of enamel is of prime importance in orthodontics for correcting arch length-tooth size discrepancies. Despite its widespread application, IPR has been associated with adverse effects on the enamel surface. Aim: The aim of this study was to investigate whether laser application, when combined with fluoride application, enhances the remineralisation potential of enamel. Materials and Methods: This in-vitro study was conducted at Saveetha Institute of Medical and Technical Sciences (SIMATS), Chennai, Tamil Nadu, India, from December 2021 to July 2022. It involved 54 extracted teeth, divided into three groups of 18 samples each. Reproximation of 0.25 mm was performed on the proximal enamel surface of each tooth. Group 1 served as the control, group 2 was subjected to Fluor Protector, and group 3 received low-level laser therapy (Er,Cr:YSGG) after Fluor Protector application. Fluor Protector (Ivoclar Vivadent) was applied for seven days. Following the seven-day fluoride administration, a laser treatment using 0.75 W of power and 8.5 J/cm2 of energy was applied for 20 seconds. Microhardness testing was conducted on the samples using a Vickers Hardness Tester. All specimens underwent surface topographic analysis with Scanning Electron Microscopy (SEM) and were evaluated for mineral content (% weight) using SEM-Energy Dispersive X-Ray analysis (EDX). Paired t-tests were performed to compare the pre- and post-microhardness values, while one-way Analysis Of Variance (ANOVA) test and Tukey’s Post-hoc test were used to compare the microhardness values between the groups. Results: The mean microhardness values recorded for group 1, group 2, and group 3 were 209.4±18.4 N/mm2 , 215.16±21.0 N/ mm2 , and 233±18.05 N/mm2 , respectively. ANOVA test revealed a significant difference in microhardness values between group 1 and group 2 (p-value=0.004), as well as between group 1 and group 3 (p-value=0.001). The microhardness value was highest for group 3, followed by group 2 post-intervention. SEM analysis showed that laser-treated enamel surfaces were smoother, with well-coalesced enamel rods. The porous structure of enamel was lost due to fluoride deposition in group 2 and group 3, resulting in a smooth surface. Conclusion: The combined application of fluoride and laser therapy demonstrated synergistic effects in remineralising the slenderised enamel. This simple, non-invasive technique may benefit patients undergoing IPR procedures by reducing the occurrence of dental caries.

The Effect of Dentifrice on Micro-Hardness, Surface Gloss, and Micro-Roughness of Nano Filled Conventional and Bulk-Fill Polymer Composite-A Micro Indentation and Profilometric Study.

The aim of the present study was to evaluate the effect of brushing with two whitening dentifrices (Colgate Optic White (COW) and Colgate Optic White Charcoal (COC)) on surface gloss, micro-roughness, and micro-hardness of nanostructured hybrid conventional (Z350) and bulk-fill (Tetric N Ceram bulk-fill) polymer composite. In total, 96 disk samples using two nano-hybrid composite polymers (Z350 and Tetric N Ceram Bulk-fill) were prepared. All specimens were exposed to two different dentifrices (COW and COC), resulting in four main subgroups in the study. Specimens were assessed for surface gloss, micro-roughness (Ra), and micro-hardness using standardized methodology. Means and standard deviations of properties compared using paired t-test, one-way and two-way ANOVA, and post hoc test. The presence of dentifrices did not show any significant difference in micro-hardness values of Z350 (p > 0.05), whereas micro-hardness of bulk-fill composite significantly reduced on dentifrices exposure (p ≤ 0.05). Bulk-fill polymer composite showed significant reduction in gloss after dentifrice exposure (p < 0.05), however, Z350 showed no significant loss of gloss due to dentifrices (p > 0.05). A significant increase in Ra was observed for both resin materials after exposure to dentifrices (COC and COW). Conventional resin composite (Z350) showed comparable surface hardness and gloss before and after dentifrice exposure, however, micro-roughness increased significantly due to dentifrice exposure. Bulk-fill resin (Tetric N Ceram) showed significant loss of micro-hardness and gloss and increase in micro-roughness on dentifrice exposure. Conventional nano-hybrid composite polymer showed better durability in resisting loss of surface properties compared to bulk-fill resin polymer in the present experiment.

STUDY OF THE POSSIBILITY OF USING NICKEL-BASED INTERMEDIATE LAYERS WHEN WELDING TITANIUM ORTHOALUMINIDE WITH A NICKEL ALLOY

Titanium aluminides have a low density and maintain high strength at elevated temperatures, which makes them prom-ising for the manufacture of aircraft engine elements. In the presented work, the problem of welding in the solid phase ortho-rhombic titanium aluminide based on the intermetallic compound Ti2AlNb and heat-resistant alloy ЭИ437Бon a nickel base is considered. A review of the state of the problem of welding heat-resistant alloy ЭИ437Бbased on nickel and titanium or-thoaluminide Ti2AlNb was carried out. It was established that the main problem in welding Ti2AlNb alloy with nickel alloy is a strong tendency to the formation of brittle phases in the joint zone, which negatively affect the mechanical properties. A promising method of joining this group of alloys is diffusion welding in a vacuum.The purpose of the work is to study the influence of multilayer and gradient foil on the formation of the zone of titanium orthoaluminide joints with a nickel-based alloy during vacuum diffusion welding.In the work, multilayer and gradient foil based on Al-Ni and Ni-Tisystems were used according to the original structure. The foils were obtained by electron beam evaporation and condensation in a vacuum. The deposition process consists in the layer-by-layer condensation of elements on a horizontal substrate.The work presents the method of conducting experiments, welding modes, chemical composition of materials and foil.The work shows for the first time that during the direct welding of titanium orthoaluminide with the ЭИ437Бalloy, as a result of the strong tendency ofthe materials to form brittle phases at the joint, a significant increase in microhardness is observed in the joint zone up to 2...4 times compared to the base material (up to 11.94 GPa). It was established that the useof layered foil (Ni/Ti, Al/Ni) as intermediate layers allows to significantly reduce the difference in microhardness values in the joint. At the same time, the microhardness in the central part of the joint zone reaches 6.69...8.79 GPa, which is close to the microhardness values of Ti2AlNb.The presented materials can be used as a basis for the development of welding technologies in the solid phase of heter-ogeneous titanium orthoaluminide materials with nickel-based alloys.

Comparative Evaluation of Efficacy of Bioactive Glass, Tricalcium Phosphate, and Ozone Remineralizing Agents on Artificial Carious Lesion.

Objectives:Evaluation of efficacy of bioactive glass (BAG), tricalcium phosphate, and ozone remineralizing agents on artificial carious lesion.Materials and Methods:Freshly extracted 48 human premolar teeth were included for this in vitro study. Remineralization of demineralized teeth was done with respective remineralizing agents (Group A – calcium sodium phosphosilicate [BAG], Group B – tricalcium phosphate [Clinpro Tooth Crème], Group C – ozone remineralizing agents, and control group: Group D – deionized water) three times a day for 12 days for 4 min. The degree of demineralization and remineralization was evaluated with Vickers hardness number.Results:There was a decrease in microhardness from baseline to demineralization in all the groups. The difference in microhardness values from demineralization to remineralization in all the three test groups was found to be statistically highly significant.Conclusion:BAG and Tricalcium phosphate had higher remineralizing capacity, which can be used clinically to treat early carious lesions.

Interface Quality Indices of Al–10Si–Mg Aluminum Alloy and Cr18–Ni10–Ti Stainless-Steel Bimetal Fabricated via Selective Laser Melting

Bimetallic materials are important in many industries (aerospace, medicine, etc.) since they allow the creation of constructions that combine specific functional properties, for example, low density (aluminum alloy) and high corrosion resistance (stainless steel), due to layering fabrication of the bimetallic joint. On the other hand, the difference in thermophysical properties of the dissimilar material layers leads to residual stresses, which cause deformation and destruction of such a bimetallic joint produced via the methods of surfacing or additive technologies. This article discusses the methods based on the gray relational analysis and generalized desirability function for the quality assessment of Al–10Si–Mg aluminum alloy and Cr18–Ni10–Ti stainless-steel bimetal fabricated via selective laser melting (SLM). There are four main parameters (quality indices) of the quality generalized assessment, which determine the degree of Al penetration into the steel substrate and Fe into the deposited layer, the difference in microhardness values on both sides of the interface boundary, and the resistance to mechanical destruction of the bimetallic joint. According to the results obtained, the best set of quality indices corresponds to the SLM technological modes with an energy density of 105 and 147 J/mm3. The greatest functionality of the bimetals is determined by the quality index associated with its strength. Therefore, methods of gray relational analysis and desirability function make it possible to form a generalized assessment for the bimetallic joint quality and, consequently, to select the best technological mode.

Evaluation of root dentin microhardness prepared with hand and two rotary file systems with 2.5% sodium hypochlorite irrigation solution - an in vitro study

Background: Success in endodontic therapy depends on effective chemomechanical preparation of the root canal, but their compromising effects on root dentin microhardness should be taken into consideration. AIM: To evaluate the effect on microhardness of root dentin prepared with hand stainless steel K-Files, ProTaper and K3 NiTi Rotary file systems with 2.5% Sodium Hypochlorite as common irrigating solution. Materials and Methods : Fifty human mandibular single-rooted premolar teeth selected. Access opening was done and working length was determined. All the specimens were then randomly divided into five groups with 10 specimens in each group. Group I- Neither instrumented nor irrigated. Group II- 2.5% NaOCl irrigation Group III- Stainless steel K-files using 2.5% NaOCl Group IV- ProTaper rotary files using 2.5% NaOCl solution. Group V - K3 rotary files using 2.5% NaOCl solution. The specimens were prepared for microhardness testing at a distance of 500 mm and 1000 mm from the lumen of each sample using vickers microhardness test. Results: 1) Significant difference in microhardness values were seen at 500 mm and 1000 mm (P from the lumen in all groups. 2) Statistically significant differences were seen among all the groups except between Group IV & V. Conclusion: Instrumentation with NiTi Rotary files affected dentin microhardness significantly to a lesser extent when compared to Stainless Steel K files using 2.5% NaOCl irrigating solution. Keywords: Microhardness, Sodium hypochlorite, Nickel Titanium Rotary files.,

On the flow and work hardening behavior of tungsten heavy alloy 92W-5.5Ni-2.5Fe

Present work describes flow and work hardening behavior of Tungsten Heavy Alloy 92W-5.5Ni-2.5Fe (wt%) in heat treated and swaged conditions. The morphology of W-grains in heat treated and swaged materials is equiaxed and elongated in longitudinal direction with same volume fraction, respectively. The swaged material depicts different contiguity values along transverse and longitudinal directions. The strength and elongation values in heat treated condition are smaller and larger than those of the swaged material. The difference in σYS and σUTS values is very small in swaged material. The true stress-true plastic strain curve of the alloy on log-log scale exhibits two slopes in heat treated condition and follows Ludwigson constitutive equation. This can be attributed to the differences in micro hardness values of W-grains and matrix phase. In contrast, the true stress-true plastic strain curve of the swaged alloy on log-log scale displays only single slope and follows Swift equation due to the presence of pre-strain in the material. Both the materials exhibit three typical stages (I, II and III) of work hardening and linear part of stage III follows KME model. The fracture surface of heat treated material consists of W-cleavage, W-W decohesion and matrix rupture in considerable proportions. In contrast, the swaged material displays the presence of mainly W-cleavage. The fraction of W-matrix failure is significantly small and more or less same in both the materials.

Influence of ultrasonic excitation on microhardness of glass ionomer cement.

Numerous researchers have attempted to improve the mechanical properties of glass ionomer cement since 1972. In this study, ultrasonic curing treatment was introduced during the mixing of glass ionomer cement (GC Fuji IX) to facilitate intimate mixing, compaction and adaptation of residual glass particle which consequently improves densification of the material. To assess the influence of ultrasonic treatment on the microhardness of glass ionomer cement (GC Fuji IX) and compare it with the conventionally cured method. A total of 40 specimens (2 × 2 mm) were fabricated and equally divided into two groups: Group I (conventional curing method) and Group II (ultrasonically cured). For Group II, an ultrasonic scaler was used which provides energy to ensure proper mixing of material without leaving any air bubbles or unmixed particles. Vicker's hardness test was employed to generate the average microhardness values by making three indentations at different points on each specimen. Statistical Package for Social Sciences (SPSS) Version 17 was used, employing independent samples T test to compare the difference in microhardness values between two curing groups. The average surface hardness value for conventional cured GIC was 62.21 ± 13.61 while ultrasonically cured GIC exhibited a higher mean microhardness value of 66.37 ± 12.83. Additionally, the average microhardness values produced by the two groups showed statistically significant differences (p value < 0.035). Ultrasonic excitation treatment leads to intimate mixing and accelerated hardening of glass ionomer cement thereby enhancing its microhardness and reducing early weakness.

Evaluation of the effect of two commercially available non-alcoholic mouth rinses on the microhardness of composite material - An invitro study

Background; Composites have been widely used for anterior as well as posterior restorations due to increased aesthetic demands. Composite restorations placed in patients oral cavity is subjected to masticatory load, pH changes and chemical effect due to mouthwashes, beverages, food etc and the detrimental effects associated with these challenges on the microhardness of composite has to be determined. The study was conducted to evaluate the effect of two commercially available non-alcoholic mouth rinses on the microhardness of micro-hybrid and nanohybrid composite resins. Materials and methods: Forty disc-shaped composite specimens were made from each type of composite materials and were divided into 5 groups with 8 samples each, Group 1= Microhybrid+Chlorhex, Group2=Microhybrid + Hexidine, Group3= Nanohybrid + Chlorhex, Group4= Nanohybrid+ Hexidine, Group 5= Nanohybrid and Micro hybrid + artificial saliva(Control).The samples were immersed in mouthrinses for 24 hrs and microhardness was subsequently measured using a Vicker’s microhardness tester. Results: There was no significant difference in microhardness values of tested composite resins in either mouth rinses when compared to composites immersed in artificial saliva. Conclusion: Non-alcoholic mouth rinses do not affect the microhardness of micro-hybrid and nanohybrid composites.

Evaluation of the effect of two commercially available non-alcoholic mouth rinses on the microhardness of composite material - An invitro study

Composites have been widely used for anterior as well as posterior restorations due to increased aesthetic demands. Composite restorations placed in patients oral cavity is subjected to masticatory load, pH changes and chemical effect due to mouthwashes, beverages, food etc and the detrimental effects associated with these challenges on the microhardness of composite has to be determined. The study was conducted to evaluate the effect of two commercially available non-alcoholic mouth rinses on the microhardness of micro-hybrid and nanohybrid composite resins. Forty disc-shaped composite specimens were made from each type of composite materials and were divided into 5 groups with 8 samples each, Group 1= Microhybrid+Chlorhex, Group2=Microhybrid + Hexidine, Group3= Nanohybrid + Chlorhex, Group4= Nanohybrid+ Hexidine, Group 5= Nanohybrid and Micro hybrid + artificial saliva(Control).The samples were immersed in mouthrinses for 24 hrs and microhardness was subsequently measured using a Vicker’s microhardness tester. There was no significant difference in microhardness values of tested composite resins in either mouth rinses when compared to composites immersed in artificial saliva. Non-alcoholic mouth rinses do not affect the microhardness of micro-hybrid and nanohybrid composites.

Effect of Indigenously Developed Nano-Hydroxyapatite Crystals from Chicken Egg Shell on the Surface Hardness of Bleached Human Enamel: An In Vitro Study.

Objective:The objective was to evaluate the effect of nano-hydroxyapatite (nHA) derived from chicken eggshell on bleached human enamel in comparison with commercial casein phophopeptide-amorphous calcium phosphate (CPP-ACP) paste using Vickers microhardness test.Materials and Methods:nHA powder was prepared from chicken eggshell using combustion method. nHA slurry was prepared by mixing 1.8 g of nHA powder with 0.3 ml of distilled water. Forty intact maxillary anterior teeth were collected and decoronated, and the crowns were embedded in acrylic mold with the labial enamel surfaces exposed. Baseline microhardness evaluation was done (T0). The specimens were randomly divided into the following four groups (n = 10) based on the surface treatment of enamel: Group 1: no bleaching treatment; Group 2: bleaching with 30% hydrogen peroxide (HP) solution; Group 3: bleaching followed by the application of CPP-ACP; and Group 4: bleaching followed by the application of nHA. The specimens were stored in artificial saliva at 37°C for 2 weeks, after which they were subjected to Vickers microhardness test (T14). One-way ANOVA and Tukey's post hoc multiple comparison tests were used for statistical analysis (P < 0.05).Results:Bleaching with HP significantly decreased the enamel microhardness. CPP-ACP and nHA derived from chicken eggshell increased the enamel microhardness significantly. There was no significant difference in microhardness values among the CPP-ACP and nHA groups.Conclusion:Nano-hydroxyapatite sourced from chicken eggshell was as effective as CPP-ACP in remineralizing and restoring the lost microhardness of bleached enamel.

Surface Hardening Low Alloy Structural Steel By Laser Welding

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Influence of application of hybrid MQL-CCA method of applying coolant during hob cutter sharpening on cutting blade surface condition

Abrasive machining processes are aimed at the complete removal of the coolant which is designed mainly to cool and lubricate the machining zone. This results from economic reasons, which require a decrease in the general production costs, as well as environmental reasons and the necessity to adjust production processes to ever-stricter environmental protection regulations. Complete coolant elimination is difficult to achieve in grinding processes. The heat and high temperature that appear in the area of contact between the tool and the workpiece cause an unacceptable deterioration of the quality of the machined surfaces. The research presented here concerns the determination of the influence of the application of the MQL-CCA hybrid method that decreases the amount of the coolant applied during sharpening of the hob cutters on the condition of the cutting blades' surface layer. The MQL-CCA method consists of the simultaneous introduction into the grinding area of both a minimal amount of the lubricating agent using the minimum quantity lubrication (MQL) method and the coolant in the form of compressed cooled air (CCA). For comparison, the tests were also carried out by applying the coolant with the flood method (WET) and with MQL, as well as by providing CCA. The research results show that (in the described range of changes in grinding parameters) solely applying the MQL-CCA method does not cause considerable changes in surface layer microhardness as compared to “wet” processing. The differences in microhardness values (on the Vickers' scale – HV) obtained closest to the grinding surface are 3–5 units. At the same time, for both of the applied grinding depths (0.01 and 0.03 mm) changes in microhardness were observed up to approximately 40 μm from the cutter dressing surface. In the case of the MQL and CCA methods being applied separately, the drop in microhardness was observed up to approximately 60–70 μm from the grinding surface, while microhardness at a depth of 10 μm was smaller by approximately 70–100HV for each grinding depth. Moreover, the surface roughness obtained when using the MQL-CCA method is comparable to that obtained during grinding with the flood method. For a grinding depth of 0.01 mm, the difference in the Rz parameter values is 4.6%, while for a grinding depth of 0.03 mm it was only 2.5%. In the case of applying the MQL method, the obtained surface roughness with a grinding depth 0.01 mm is approximately 30% larger in relation to WET and approximately 47% larger for a grinding depth of 0.03 mm. As far as the CCA method is concerned, the roughness is approximately 135% greater as compared to WET for both grinding depths. The SEM images for the MQL-CCA and WET method did not reveal any typical defects in the form of feather edges or chips on the edges of the ground surfaces. Simultaneously, burrs occurred on edges that were ground using minimal lubrication with the MQL method or by applying cooled compressed air (CCA). The research results indicate that it is possible to considerably limit the traditional cooling coolant flow rate by applying the hybrid MQL-CCA method without considerable deterioration of the quality of the surface layer of the ground surfaces. Therefore, grinding cutting hobs using the hybrid MQL-CCA method in the described range of grinding conditions may be an alternative to using the conventional flood method (WET).

Safety of nonthermal atmospheric pressure plasma for tooth bleaching evaluated in terms of microhardness and mineral content

The purpose of this study was to evaluate the influence of bleaching with nonthermal atmospheric pressure plasma and 15% hydrogen peroxide (HP) or 15% carbamide peroxide (CP). Sixty human enamel and dentin slabs were randomly assigned to six groups as follows: Group 1 was a control group and did not receive any treatment; Group 2 was exposed only to plasma, as a negative control; Group 3 was treated with 15% HP; Group 4 was treated with 15% HP plus plasma; Group 5 was treated with 15% CP alone; and Group 6 was treated with 15% CP plus plasma during 30 min bleaching treatments. A microhardness measurement was conducted according to a microhardness tester. The amount of calcium (Ca), phosphorus (P), chloride (Cl), sodium (Na), magnesium (Mg), and zinc (Zn) in the enamel and dentin was quantified with an electron probe microanalyzer (EPMA). The data were analyzed by using the Student’s t test and one-way analysis of variance (ANOVA), complemented by Tukey’s test. The statistical analysis did not show any significant differences in microhardness values and six mineral contents in all groups (p > 0.05). Therefore, we believe that the application of nonthermal atmospheric pressure plasma is a safe energy source for tooth bleaching.

Impact of hydrogen peroxide activated by lighting-emitting diode/laser system on enamel color and microhardness: An in situ design.

Background:Hydrogen peroxide (HP) at lower concentration can provide less alteration on enamel surface and when combined with laser therapy, could decrease tooth sensitivity. This in situ study evaluated the influence of 15% and 35% HP gel activated by lighting-emitting diode (LED)/laser light for in-office tooth bleaching.Materials and Methods:Forty-four bovine enamel slabs were polished and subjected to surface microhardness (load of 25 g for 5 s). The specimens were placed in intraoral palatal devices of 11 volunteers (n = 11). Sample was randomly distributed into four groups according to the bleaching protocol: 15% HP, 15% HP activated by LED/laser, 35% HP, and 35% HP activated by LED/laser. The experimental phase comprised 15 days and bleaching protocols were performed on the 2nd and 9th days. Surface microhardness (KHN) and color changes were measured and data were analyzed by ANOVA (α = 0.05).Results:There were no significant differences in microhardness values neither in color alteration of enamel treated with 15% HP and 35% HP activated or not by LED/laser system (P > 0.05).Conclusions:Both concentrations of HP (15 or 35%), regardless of activated by an LED/laser light, did not affect the surface microhardness and had the same effectiveness in enamel bleaching.

Evaluation of the flexural strength and microhardness of provisional crown and bridge materials fabricated by different methods.

Purpose:The purpose of this study was to evaluate and compare the flexural strength and microhardness of provisional restorative materials fabricated utilizing rapid prototyping (RP), Computer Assisted Designing and Computer Assisted Milling (CAD-CAM) and conventional method.Materials and Methods:Twenty specimens of dimensions 25 mm × 2 mm × 2 mm (ADA-ANSI specification #27) were fabricated each using: (1) Three dimensional (3D) printed light-cured micro-hybrid filled composite by RP resin group, (2) a milled polymethyl methacrylate (CH) using CAD-CAM (CC resin group), and (3) a conventionally fabricated heat activated polymerized CH resin group. Flexural strength and microhardness were measured and values obtained were evaluated.Results:The measured mean flexural strength values (MegaPascals) were 79.54 (RP resin group), 104.20 (CC resin group), and 95.58 (CH resin group). The measured mean microhardness values (Knoop hardness number) were 32.77 (RP resin group), 25.33 (CC resin group), and 27.36 (CH resin group). The analysis of variance (ANOVA) test shows that there is statistically significant difference in the flexural strength values of the three groups (P < 0.05). According to the pairwise comparison of Tukey's honest significant difference (HSD) test, flexural strength values of CC resin group and CH resin group were higher and statistically significant than those of the RP resin group (P < 0.05). However, there was no significant difference between flexural strength values of CC resin and CH resin group (P = 0.64). The difference in microhardness values of the three groups was statistically significant according to ANOVA as well as the intergroup comparison done using the Tukey's HSD (post hoc) test (P < 0.05).Conclusions:CC-based CH had the highest flexural strength whereas RP-based 3D printed and light cured micro-hybrid filled composite had the highest microhardness.