Reduction In Microhardness Research Articles

Effects of 35% Versus 10% Carbamide Peroxide At-Home Bleaching Agents with or without MI Paste Plus on Enamel Properties

This study compared the effects of 35% with 10% carbamide peroxide (CP) home used bleaching agents on enamel color change, microhardness, and surface changes in association with MI paste plus (CPP -ACPF). Forty buccal and lingual enamel samples from twenty human third molars were prepared and divided into four groups (n=10). The groups were bleached for two weeks according to different bleaching regimens as follow; G1 bleached with 10%CP, G2 bleached with 35%CP, G3 bleached with a mixture of 10%CP and MI paste plus, and G4 bleached with a mixture of 35%CP and MI paste plus. Color change was recorded with a colorimeter before and after bleaching and total color differences (ΔE*) was calculated. Vickers microhardness test was recorded for all the samples before and after treatment. One sample from each group was evaluated for surface changes by scan electron microscopy (SEM). The data were analyzed with repeated measure of variance and student's t-test at p<0.05. No significant difference in ΔE* was recorded among the four groups (p>0.05). Significant reduction in enamel microhardness was only recorded for G2 (p=0.003). SEM for G3 and G4 showed obvious mineral deposition. Similar teeth color whitening can be resulted after two weeks of bleaching with both 10%CP and 35%CP when used as recommended by the manufacturer with and without the addition of MI paste plus. Using 35%CP decreased enamel microhardness significantly, whereas MI paste plus when mixed with both bleaching agents could compensate for the microhardness reduction.

Influence of Coca-cola on Surface Roughness and Microhardness of Flexible Denture Base Material

Two potential problems commonly associated with flexible denture base material are surface roughness and the reduction of microhardness due to many reasons, rough surface can cause bacterial collection and the patient feels discomfort, and the possibility of the denture scratched when the surface hardness is reduced. The aim of this study was to evaluate the influence of Coca-cola on the surface quality of the flexible denture base material represented by the surface roughness and microhardness. A total of (10) samples were prepared for this study with the dimension of ( 40mm, 10mm, 3mm) length, width, and height respectively from thermo-plastic flexible resin (X-flexible capsules, color; K2 , size; L\China) by the conventional methods following the manufacturer instructions. The samples were immersed in Coca-cola drink for 12 days at room temperature. This period represents the average of one year of the beverage consumption, the drink has been changing daily.The samples were marked randomly and kept in special containers, and each sample has two rectangular surfaces used for the tests. One side is used for microhardness test and the other side used for the surface roughness test. The first tests were done before immersing the samples in coca-cola as control group. And after immersing the second tests were done as experimental group. In this study the data was analyzed using Independent samples (T- test). And results showed that there is no statistically significant difference in the surface roughness of the samples before and after immersing in Coca-cola (P-value > 0,05), while the microhardness test showed statistically a significant difference (P-value < 0,05) before and after immersing in Coca-cola. The surface roughness of flexible thermoplastic resin is not affected by coca-cola drink. While the levels of mirohardness showed decreasing after immersion in coca-cola drink. Therefore, the flexible thermoplastic material could be damaged if it is subjected to extra consumption of Coca-cola drink by the patient and this leads to lessen the amount of hardness by the time that could affect the efficiency of the prostheses, also could affect the mechanical bonding between artificial teeth and flexible denture base.

Comparative Assessment of the Effect of EDTA, Lactic acid and Citric acid on Root Dentin Microhardness

Aim: To determine the effect of ethylenediaminetetraacetic acid (EDTA), lactic acid and citric acid on root dentin microhardness. Materials and Methods: In this in vitro study, twenty freshly extracted anterior teeth were transversely sectioned at the level of cementoenamel junction. The middle third of each root is then horizontally sectioned into slices that are 4 mm thick to obtain a total of 20 dentin discs. Based on the chelating agent used, the samples were randomly divided into four groups- saline (control group), 17% EDTA, 20% lactic acid and 10% citric acid. Vicker’s indenter was used to test the microhardness of the dentin before and after treatment with the chelating agents for two minutes. Data was obtained and statistically evaluated using a one-way analysis of variance (ANOVA), paired – t test and Tukey’s post hoc test. Results: The microhardness values varied significantly among the groups. Citric acid and and lactic acid were less effective at reducing dentin microhardness. EDTA led to a higher reduction in microhardness. Conclusion: All the chelating solutions reduced the microhardness. Lactic acid showed less alteration in the hardness of root dentin than EDTA.

Evaluation of the feasibility and machining performance of internal cooling grinding Inconel 718 superalloy

Inconel 718 superalloy generates a large amount of grinding heat in the grinding process, posing challenges in its effective control through cooling techniques. Proposing a phyllotaxy arrangement internal cooling grinding wheel (ICGW) for grinding processing and using water-based ILs-MWCNTs/MoS2 composite nanofluid as a coolant can improve this situation. The thermal physical properties and contact angles of composite nanofluids at variable temperatures were measured to investigate the heat transfer capability and lubrication of coolant in the grinding area and compare them with conventional coolant. The CFD and CFX methods were used to optimize the abrasive cluster and to study the effects of the flow ability of the two coolants in the grinding area and the heat transfer properties, respectively, and grinding experiments were conducted. The simulation results showed that the coolant had better flow properties when phyllotaxy coefficient k is 1.186 and abrasive cluster diameters d is 1.5. The composite nanofluid obtained a lower surface temperature of the abrasive cluster than the conventional coolant. The thermal conductivity of the composite nanofluid exhibited a significant enhancement of 37.3 % and a substantial decrease of 45.9 % in viscosity at elevated temperatures, as demonstrated by the characterization experiments, in contrast to the conventional coolant. The machining experiments revealed a decrease in the grinding temperature by approximately 11.2 % to 25.6 %. The surface roughness value improved by 15.7 %–22.3 %, and the maximum reduction of workpiece surface microhardness increased by about 7.2 %. The workpiece surface exhibited superior quality compared to the conventional coolant.

Effect of whitening toothpastes on the surface roughness and microhardness of human teeth—an in vitro study

ObjectiveTo determine the effect of whitening toothpastes on the surface roughness and microhardness of human teeth.MethodologySurface roughness was estimated using the Talysurf instrument, and microhardness was estimated using the Vickers hardness tester before and after the application of whitening toothpastes on mounted extracted human teeth.ResultsIn the activated charcoal group, there was a reduction in the surface roughness from 1.21 at baseline to 1.09 at 1 month and a further reduction to 1.02 at 3 months, which was found to be statistically significant. However, no statistically significant difference in surface roughness was found in the other toothpaste groups. With respect to microhardness, all 4 whitening toothpastes showed a statistically significant reduction in microhardness after 3 months of brushing. However, the reduction was significantly higher in group 2 and in group 4 compared to the others.ConclusionThis study showed that whitening toothpaste containing activated charcoal significantly reduced the surface roughness, whereas toothpastes with blue covarine and toothpastes containing activated charcoal significantly reduced the microhardness of the tooth.Clinical relevanceThis study emphasizes the need for healthcare professionals to be aware of the potential disadvantages of whitening toothpastes and make evidence-based decisions when recommending the product to patients.

Experimental Investigation on Microstructure Alteration and Surface Morphology While Grinding 20Cr2Ni4A Gears with Different Grinding Allowance Allocation.

Transmission gear is a key component of vehicles and its surface integrity affects the safety of the transmission system as well as the entire mechanical system. The design and optimization of allowances in form grinding are important for improving dimensional accuracy and machining efficiency during the manufacturing of heavy-duty gears. This work aims to investigate the effects of grinding allowance allocation on surface morphology, grinding temperature, microstructure, surface roughness, and microhardness fluctuation during the form grinding of 20Cr2Ni4A gears. Results indicated that grinding temperature was primarily influenced by rough grinding involving significant grinding depths exceeding 0.02 mm. The ground surface exhibited slight work hardening, while thermal softening led to a reduction in microhardness of around 40 HV. Ground surface roughness Ra varied from 0.930 μm to 1.636 μm, with an allowance allocation of the last two passes exerting the most significant influence. Analysis of surface and subsurface microstructures indicated that a removal thickness of 0.02 mm during fine grinding was insufficient to eliminate the roughness obtained from rough grinding. Evident ridges, gullies, and surface defects such as material extraction, adhesion, and plastic deformation were also observed. The proposed grinding strategy was validated in practical manufacturing with good surface quality and geometrical accuracy.

Comparative Evaluation of Microhardness, Smear Layer Removal Efficacy and Depth of Penetration Using Punica granatum, Emblica officinalis and Sodium Hypochlorite As Endodontic Irrigants: An In Vitro Study.

Introduction Root canal morphology tends to be complicated by natureand dealing with this intricacy can be challenging because it makes it difficult to completely disinfect the root canal space.The success of root canal therapy is also determined by the biomechanical preparation of the canal with the application of instruments and irrigating solutions.Due to the fact that the root dentin surface continues to interact with the irrigating solution during preparation, it's critical to evaluate the mechanical characteristics and smear layer removal. Though sodium hypochlorite (NaOCl) is the most commonly used irrigant due to its tissue-dissolving abilities, it has certain drawbacks which include the inability to remove the smear layer and also affects the mechanical properties of root dentin. To overcome these limitations, a variety of herbal substitutes likePunica granatumand Emblica officinaliswhich possess anti-bacterial and anti-fungal properties can be used as endodontic irrigants.Several studies on the anti-bacterial properties of natural irrigants of pomegranateand amla were reported. However, the mechanical properties and smear layer removal of Punica granatum and Emblica officinalis have not been explored in the field of endodontics. Aim The main aim of this in vitro study is to compare and evaluate microhardness, smear layer removal efficacy and depth of penetration of herbal and conventional irrigants. Materials and methods Thirty-six palatal roots of maxillary molars were decoronated and instrumented up to F3. These roots were sectioned longitudinally and divided into three test groups: Group 1: 12.5% Punica granatum;Group 2: 6.25% Emblica officinalis; control: Group 3: 2.5% NaOCl. All specimens were irrigated with 5ml of each irrigant for 5 minutes. Microhardness of root dentin was measured using a Vickers diamond intender, smear layer removal using a scanning electron microscope (SEM) and depth of penetration using a stereomicroscope. The data was analyzed using one-way ANOVAand the inter-group comparison using Tukey's post hoc test. Results Statistical analysis was done using one-way analysis of variance (ANOVA) and Tukey's post hoc test using SPSSsoftware version 17.0 (SPSS Inc., Chicago ). The highest microhardness was seen in Group 1(cervical: 53.8375±1.35956, middle: 53.9875±1.01761, apical: 53.6875± 1.63133)while Group 2(cervical: 43.2750±1.73596, middle: 43.3125±1.17648, apical: 43.8000± ​​​​​​​1.32665) and Group 3 (cervical: 42.7250±​​​​​​​2.93391, middle: 41.9625±​​​​​​​1.66985, apical: 42.0250±​​​​​​​2.21085) showed significant reduction in root dentin hardness. Regardingsmear layer removalGroup 1 (1.3750±​​​​​​​0.51755), and Group 2 (1.2500±​​​​​​​0.46291) reveals greater smear removal in the middle third of the root dentin compared with Group 3 (2.3750±​​​​​​​0.51755), which showed the least smear layer removal. A greater depth of penetration was seen in Group 1 (0.5488± 0.05222) and Group 2 (0.5263±​​​​​​​0.05181)than in Group 3 (0.3087±​​​​​​​0.05743). Conclusion The present study reveals that the least reduction of microhardness was seen in Punica granatum followed by Emblica officinalis and NaOCl. The smear layer removal efficacy and depth of penetration were greater in Punica granatum and Emblica officinalis than in NaOCl. It was concluded that as these herbal irrigants are biocompatible agents, they can be considered for future use in root canal treatment.

Maintenance of enamel properties after bleaching with high-concentrated hydrogen-peroxide gel containing calcium polyphosphate sub-microparticles.

To assessed the physical and chemical properties of human-enamel after treatment with an experimental bleaching gel containing 35%-hydrogen peroxide (HP) and calcium polyphosphate sub-microparticles (CaPP). Enamel/dentin specimens (4 × 4 × 3mm) were obtained (n = 120) and allocated to different groups: control (saliva only); experimental (HP35%); commercial (whiteness-HP-Maxx); CaPP0.5% (HP35% + CaPP0.5wt%); CaPP1.5% (HP35% + CaPP1.5wt%). Three sessions were performed. The specimens' color was assessed using a spectrophotometer and the color (ΔE/ΔE00) and bleaching index (ΔWID) determined. The surface roughness and microhardness were assessed with a roughness tester and Knoop indenter. Raman spectroscopy was performed to obtain the ratios between the areas under the 431, 580, and 1070cm-1 and the 960cm-1 bands (430:960, 580:960, 1070:960). Kruskal-Wallis and Dunn compared the color, Ra, and SMH data. The Raman data was analyzed with Kruskal-Wallis and Dunn (α = 5%). The ΔE, ΔE00, and ΔWID were similar among the bleached groups (p > 0.05). The roughness was not different between the groups (p > 0.05). After the 3rd session, CaPP0.5% had higher microhardness than the experimental (p < 0.05). The 1070:960 was higher in the experimental than in the CaPP1.5% and control (p < 0.05). In human enamel, CaPP did not alter the bleaching effectiveness or roughness, and additionally, CaPP-containing gels increased the microhardness and preserved the mineral content when compared to the experimental without CaPP. Experimental bleaching gels containing calcium polyphosphate sub-microparticles as a mineral source reduce the mineral content alteration and superficial microhardness reduction, known potential side effects of the in-office bleaching treatments.

In Vitro Evaluation of the Effects of Different Beverages on the Surface Microhardness of a Single-Shade Universal Composite.

The aim of this in vitro study was to analyze the influence of various beverages on the surface microhardness of a single-shade composite resin. Seventy-five Omnichroma composite discs were fabricated and divided into five subgroups according to the beverages. The groups were Group A: tea; Group B: coffee; Group C: beer; Group D: whisky; and Group E: artificial saliva. The samples were immersed in their respective beverages for 15 minutes per day for 15 days. The Vickers microhardness values were taken before and after the immersion of the composite disc samples in their respective beverages. A one-way analysis of variance (ANOVA) test was conducted using IBM SPSS Statistics software version 23 (IBM Corp., Armonk, New York, USA), with a statistical significance level of 5%. It was observed that there was a reduction in the surface microhardness of the composite resin after immersion in most of the solutions. An increase in the mean percentage change of surface microhardness was observed in the beer group (29%; mean difference = 16.52±12.05), followed by the coffee group (27.2%; mean difference = 15.51±9.28). The least mean percentage change in microhardness was noted in group E, artificial saliva (8.5%; mean difference = 4.81±3.04). The surface microhardness of composite resin can be influenced by the type of beverages used for immersion and the duration of immersion.However, it is important to note that the interaction between composite resin and various beverages is influenced by a complex interplay of multiple variables.

Effects of Acidic Beverages on Surface Microhardness of a New Ion-Releasing Restorative Material with Surface Sealant

Objective: Many factors in the mouth affect the clinical lifetime of materials. Acids, enzymes, acidic properties of food and beverages formed in the plaque could change the physicochemical properties of restorative materials. The aim of the study is to examine the effect of acidic beverages on the microhardness of alkasites, and conventional glass ionomers, with changes in surface coating applications. Materials and Methods: Forty specimens in eight mm diameter and two mm thick discs were made with each Cention N and Ionofil U. Half of the specimens were covered with surface sealant. In each of the four subgroups: cola, orange juice, sparkling mineral water and distilled water, 10 discs were stored for 5 minutes, three times a day for a week. Microhardness measurements were made after they were kept in an acidic environment. Results: Acidic beverages significantly reduce the microhardness of restorative materials. The highest microhardness value was observed in the Cention N group with surface sealant. The lowest microhardness value was observed in the Ionofil restorative material group without sealant. Conclusion: The acidic agents tested (cola, orange juice, and sparkling mineral water) have an effect on the reduction of surface microhardness of restorative materials. For clinical decision-making, Cention N is the most suitable material for restorations in patients who are at high risk for erosive conditions.

Ultra-precision cutting characteristics of binderless tungsten carbide by in-heat-process laser-assisted diamond machining

The study systematically investigates the ductile-brittle transition behavior, material removal mechanism, and end-face turning performance of binderless tungsten carbide using in-process-heat laser-assisted diamond machining. Both numerical simulation analysis and experimental cutting experiments were conducted. To ensure that the laser loading condition and energy distribution were consistent with the ray-tracing simulation and spatial power density distribution measurement, a practical thermal simulation model was created with a semicircular Gaussian distribution. This model was then used to study the temperature distribution, and the material's thermal transient response to laser radiation was also analyzed in detail. The high-temperature nanoindentation revealed increased ductile machinability due to plastic deformation, microhardness reduction, and Young's modulus decrease at elevated temperatures, providing fundamental support for the ductile-brittle transition behavior. The ductile-brittle transition depth increased by 247.20% compared to conventional groove cutting without laser assistance. The cutting forces during groove cutting decreased gradually with increasing laser power, but excess laser power may cause fluctuations in cutting forces due to surface high-temperature oxidation and potential thermal expansion. The ductile-brittle transition dynamic behavior analysis, based on the discrete wavelet transform algorithm, showed good consistency with the conventional groove profile analysis. The friction coefficient between the tool rake face and chip decreased with increasing laser power, which facilitated improving the tool life. The statistical analysis of end-face turning experiments based on the Taguchi method indicated that laser power was the most significant factor affecting surface quality. The verification turning experiments validated the determined optimal parametric combination. Ultra-high-quality spherical lenses were obtained in ductile cutting mode with slightly less tool wear, a more homogeneous finish (less than 3 nm in Sa), and more outstanding form accuracy (133 nm in PV) compared to conventional turning without laser assistance.

Evaluation of Physical-Chemical Properties of Contemporary CAD/CAM Materials with Chromatic Transition "Multicolor".

The use of materials for computer-aided design/computer-aided manufacturing (CAD/CAM) has been rapidly increasing in daily practice. However, one of the main issues regarding modern CAD/CAM materials is their aging in the oral environment, which may lead to significant changes in their overall properties. The aim of this study was to compare the flexural strength, water sorption, cross-link density (softening ratio%), surface roughness, and SEM analysis of three modern CAD/CAM "multicolor" composites. Grandio (Grandio disc multicolor-VOCO GmbH, Cuxhaven, Germany), Shofu (Shofu Block HC-Shofu Inc., Kyoto, Japan), and Vita (Vita Enamic multiColor-Vita Zahnfabrik, Bad Sackingen, Germany) were tested in this study. They were prepared in stick-shaped specimens and submitted to different tests after several aging protocols, such as thermocycling and mechanical cycle loading challenge. Further disc-shaped specimens were also created and tested for water sorption, cross-link density, surface roughness, and SEM ultramorphology, before and after storage in an ethanol-based solution. For flexural strength and ultimate tensile strength, Grandio showed the greatest values both at baseline and after aging (p < 0.05). Grandio and Vita Enamic presented the highest modulus of elasticity and the lowest water sorption (p < 0.05). A significant reduction (p < 0.05) in microhardness after ethanol storage (softening ratio%) was observed especially in Shofu. Grandio had the lowest roughness parameters compared to the other tested CAD/CAM materials, while ethanol storage significantly increased the Ra and RSm values in Shofu (p < 0.05). Despite the comparable modulus of elasticity of Vita and Grandio, this latter showed greater flexural strength and ultimate tensile strength both at baseline and after aging. Hence, Grandio and Vita Enamic may be employed for the anterior teeth and for those restorations requiring load-bearing capacity. Conversely, aging seems to affect several properties of Shofu, so its use for permanent restorations should be well-pondered based on the clinical situation.

Water-Induced Changes in Experimental Resin Composites Functionalized with Conventional (45S5) and Customized Bioactive Glass

The aim of the study was to evaluate microhardness, mass changes during 1-year water immersion, water sorption/solubility, and calcium phosphate precipitation of experimental composites functionalized with 5–40 wt% of two types of bioactive glass (BG): 45S5 or a customized low-sodium fluoride-containing formulation. Vickers microhardness was evaluated after simulated aging (water storage and thermocycling), water sorption and solubility were tested according to ISO 4049, and calcium phosphate precipitation was studied by scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy. For the composites containing BG 45S5, a significant reduction in microhardness was observed with increasing BG amount. In contrast, 5 wt% of the customized BG resulted in statistically similar microhardness to the control material, while higher BG amounts (20 and 40 wt%) resulted in a significant improvement in microhardness. Water sorption was more pronounced for composites containing BG 45S5, increasing 7-fold compared to the control material, while the corresponding increase for the customized BG was only 2-fold. Solubility increased with higher amounts of BG, with an abrupt increase at 20 and 40 wt% of BG 45S5. Calcium phosphate was precipitated by all composites with BG amounts of 10 wt% or more. The improved properties of the composites functionalized with the customized BG indicate better mechanical, chemical, and dimensional stability without compromising the potential for calcium phosphate precipitation.

The Effect of Exposure to Dried Fruits on the Surface Micro-Hardness of Dental Enamel

Background: This study investigated the effect of exposure of enamel surfaces to dried fruit suspension including dates, raisins, and dried apricot on their micro-hardness changes.&#x0D; Methods: In this in vitro study, fifty enamel sections of bovine incisor teeth were mounted inside the acrylic resin so that the enamel surface would not be exposed to the acrylic. After surface polishing, the initial micro-hardness was measured by a Vickers hardness-testing machine. The samples were randomly placed into five different solutions including apricot, raisin and date suspension, citric acid (positive control) or sorbitol (negative control), 5 times a day, each time for 5 minutes, and then in artificial saliva for 60 minutes. This process was repeated for 20 days. Eventually, the final micro-hardness of the samples was measured. Micro-hardness changes between groups were compared through ANOVA and TUKEY test using SPSS 23 software with a significance level of P&lt;0.05.&#x0D; Results: After exposure, the micro-hardness of the teeth was significantly reduced in all three suspensions prepared from dried fruit (P&lt;0.05). Apricot and date had the highest and lowest effects on reducing the micro-hardness of teeth, respectively. Sorbitol solution did not have a significant effect on changing the micro-hardness of teeth (P=0.13).&#x0D; Conclusion: The suspension of studied fruits (apricot, raisin, date) causes a significant reduction in micro-hardness of the dental enamel surface, indicating the negative effect of frequent consumption of dried fruits over long periods of time on dental health.

Effect of non-vital tooth bleaching photoactivated with blue or violet LED on color and microhardness

BackgroundTo evaluate the efficacy of dental bleaching protocols using 35% hydrogen peroxide photoactivated with violet LED on color and microhardness of endodontically treated teeth. MethodsForty specimens were selected and randomized into 4 groups (n = 10): C - Control, HP - 35% hydrogen peroxide, HP + BL - 35% hydrogen peroxide + blue LED, HP + VL - 35% hydrogen peroxide + violet LED. Three bleaching sessions were performed for each group. Color analysis was performed 7 days after each bleaching session. Two-way repeated measure ANOVA and Bonferroni test were used to evaluate the effect of different bleaching protocols and evaluation times on the dependent variables (∆E and ∆L). Dentin microhardness was measured 24 h after the third bleaching session. Data were evaluated by ANOVA and Tukey's test at a significance level of 5%. ResultsDifferences on ∆E and ∆L were verified after the first and second bleaching sessions (p < 0.05) and showed stability after the third one, for all the groups. No differences were observed among HP, HP + BL, and HP + VL groups, regardless of the evaluation time (p > 0.05). HP and C showed the greatest and smallest reduction in dentin microhardness (p < 0.05), respectively. No difference between HP + BL and HP + VL protocols (P > 0.05) was observed. ConclusionsHigh concentration hydrogen peroxide (35%) photoactivated with violet LED bleached endodontically treated teeth effectively. However, the same protocol negatively affected the dentin microhardness, but not in the same level of 35% HP solely used.

Does periodontal ligament removal using natural proteolytic enzymes alter the surface structure and microhardness of cementum of avulsed tooth? An in vitro analysis

Introduction: Surface treatment of avulsed tooth must be directed towards the debridement of necrotic periodontal fibers while having no effect on the cementum microhardness. The role of proteolytic enzymes on the periodontal ligament (PDL) surface and hardness of cementum has not been investigated in the literature. Aim: The present study aimed to evaluate the effect of 5.25% sodium hypochlorite (NaOCl), 10% bromelain, 10% papain and 10% panzyme on root surface topography and microhardness of avulsed teeth. Materials and Methods: Forty healthy premolars were freshly extracted and randomly allocated into five treatment groups based on the surface agent employed; Group 1: 50 ml saline, Group 2:20 ml of 5.25% NaOCl, Group 3: 20 ml of 10% bromelain enzyme, Group 4: 20 ml of 10% papain enzyme, and Group 5: 20 ml of 10% mixed panzyme enzyme. The specimens were then subjected to confocal laser scanning microscopy and scanning electron microscopic examination. Supplemental set of freshly extracted forty premolars were decoronated longitudinally and one-half from each specimen was submitted for Vickers microhardness testing before and after application of the above-mentioned agents. Statistical Analysis: Intragroup comparison of mean percentage hardness reduction was assessed using paired t-test. Results: Treatment with NaOCl led to complete removal of PDL fibers with the presence of cracks and crazes on the root surface along with a significant reduction in microhardness. Bromelain and papain revealed regular and even distribution, while few PDL fibers were evident with papain. Panzyme revealed a shiny surface with minute cracks and a significant reduction in microhardness. Conclusion: Ten percentage bromelain for 10 min was effective in the removal of necrotic PDL fibers and preserved the cementum integrity better.

Preventive effect of combined Er, Cr: YSGG and fluoride gel on acid resistance of the permanent tooth enamel: An in vitro study.

Increasing the resistance of enamel to acids may prevent dental erosion and diminish microhardness alterations in the enamel. This study aimed to evaluate the preventive effect of erbium, chromium: yttrium, scandium, gallium, and garnet laser combined with 1.23% acidulated phosphate fluoride gel on enamel resistance to demineralization. Thirty-four human maxillary first premolars were randomly assigned to three groups. Group I (control group), group II were treated with fluoride gel for 4-minutes and group III received ten seconds of laser treatment; then fluoride has applied. Each sample was immersed in a soft drink for 2 minutes, then washed and kept in deionized water. Four consecutive cycles were carried out at 6 hours intervals. The effects were studied utilizing the Vickers microhardness test and scanning electron microscopy. Data analyses were performed by Levene test and General Linear Model Repeated Measure Factorial ANOVA with Bonferonni post hoc test, the accepted level of significance was 0.05. Microhardness was increased statistically in groups II and III after treatment, with the highest value for group III. After demineralization, the control group had the lowest microhardness score, followed by group II and group III, which showed the least reduction in microhardness with a statistical significance (p<0.05). There was a correlation between the morphological alterations in enamel surfaces and the increased enamel resistance. Both fluoride and the combined laser fluoride treatment had an advantage in protecting the enamel and increasing enamel resistance to acids, with a more significant benefit for the combined laser fluoride group. Key words:Prevention, Er, Cr: YSGG, enamel demineralization, fluoride, microhardness.

Farklı İrrigasyon Solüsyonlarının Fiber Postların Kök Kanal Dentinine Bağlanma Mukavemeti ve Dentin Mikrosertliği Üzerindeki Etkisi: Metadolojik Çalışma

Objective: This study aimed to compare the effect of sodium hypochlorite (NaOCl), chlorhexidine (CHX), ethylene daimine tetra acetic acid (EDTA) and etidronic acid (HEBP) solutions and their combinations on a push-out bond strength of fiber posts to root canal dentin and on root dentin microhardness. Material and Methods: Sixty human maxillary central incisors were sectioned below the cementoenamel junction, the roots were endodontically treated and were divided into 6 groups (n=10) according to the final irrigation protocol: (1) Distilled water, (2) CHX, (3) HEBP-NaOCl combination, (4) HEBP, (5) 2.5 % NaOCl, (6) 17% EDTA. The fiber posts were then cemented with self-etching resin cement. Bonded specimens were cut (1-mm-thick), the first slice of the coronal 3rd was used for dentin microhardness analysis, and other slices were used for the push-out bond strength test. The data were statistically analyzed by using Shapiro-Wilk, Oneway ANOVA, and the Games-Howell test. Results: The lowest microhardness was observed in HEBP-NaOCl and NaOCl (p<0.05). CHX, HEBP, and EDTA resulted in less reduction in microhardness as compared to other groups (p<0.05). HEBP-NaOCl and NaOCl showed significantly higher mean bond strength to root dentin in the cervical thirds than in other groups (p<0.05). Conclusion: With regard to the push-out bond strength of the fiber post to dentin, NaOCl and HEBP-NaOCl increased bond strength compared to other groups. NaOCl and HEBP-NaOCl have lower microhardness of dentin. Compared to HEBP, EDTA increases microhardness and does not make a significant difference in push-out bond strength. Therefore, it is recommended to use HEBP alone.

Application of a high-speed infrared thermographic camera to the study of HAZ softening in S960 welded joints

Hot strip rolling of low-carbon advanced high-strength (AHS) sheet steels is difficult because their products require specific chemical compositions to achieve excellent mechanical properties. The formation of a heat-affected zone (HAZ) during welding is therefore a challenge in terms of maintaining high strength values. This fact complicates the formation of the softening area when the hardness in the HAZ rapidly decreases. According to the continuous cooling transformation diagram (CCT), the chemical composition of the base metal is directly related to the fine-grained martensitic microstructure arising from very high cooling rates and microalloying up to 0.2 wt% by Nb, V, and Ti. The gas metal arc welding (GMAW) was used to perform the study, what presents a challenge for thin sheets because of very narrow HAZ formation, suscepible to HAZ softening phenomenon. The width of the HAZ was about 6 mm and determined by applying an infrared thermographic camera to measure the real-time temperature development. The significant reduction in microhardness, known as the softening phenomenon, occurred in the intercritical heat-affected zone or at the boundary between intercritical and subcritical HAZ, according to real-time diagnostics of the temperature development and the microhardness results. The amount of heat produced during welding plays an important role in this context and is directly connected to the heat input of the welding process. The softening area can be reduced and its impact on the mechanical properties can be lowered by appropriately modifying the welding conditions, e.g., optimising the heat input. The purpose of this paper is to point out the change in temperature during the welding process.

Evaluation of Effect of Natural Extract Sodium Gluconate on Smear Layer and Dentine Decalcification Compared with EDTA - An In-vitro Study.

Mechanical instrumentation of the root canal system generates a smear layer on the canal walls which are removed most commonly with the help of chelators such as ethylenediaminetetraacetic acid (EDTA) but can potentially cause severe dentinal erosion. Considerable research has been conducted to find an al- ternative to EDTA which removes the smear layer without causing dentinal erosion. The current study aimed at evaluating the ability of sodium gluconate compared with that of 17% EDTA in smear layer removal along with its effect on dentine decalcification when used as a final irrigant. Twenty single-rooted mandibular premolars were collected and prepared based on the pre-set criteria. Following preparation, the specimens were exposed to the test solutions as a final irrigant. Then the specimens were subjected to (Scanning electron microscope) SEM analysis at 1000x for evaluating the smear layer and 5000x for evaluating the dentinal erosion, and a Vickers microhardness tester was used for evaluat- ing the reduction in dentine microhardness post-treatment. The values obtained were analysed using SPSS software for a statistically significant difference with Mann-Whitney U test for evaluating of smear layer remov- al and dentinal erosion and using one-way (Analysis of variance) ANOVA test for microhardness evaluation. The smear layer removal capability of sodium gluconate was as effective as EDTA on the contrary so- dium gluconate did not cause any dentinal erosion compared to EDTA with a statistically significant difference (p=0.002 in middle third and p=0.001 in apical third of the canal). Microhardness reduction caused by sodium gluconate was less compared to EDTA, however, no statistically significant difference (p=0.113) was noted. Sodium gluconate, therefore, can produce a balance between smear layer removal and dentinal decalcification and can be considered a potential alternative to EDTA. (EEJ-2023-01-017).