Mean Vickers Hardness Research Articles

Effect of Aging on Hardness of Glass Ionomer, Resin-Modified Glass Ionomer, Giomer and Compomer Dental Restorative Materials

Objective: To assess deionized water's aging effect on the hardness of four direct tooth colored dental filling materials i.e., Glass Ionomer Cement, Resin Modified Glass Ionomer, Giomer and Compomer.Study Design: An in vitro experimental study performed in triplicates.Place and Duration of Study: The study was carried out at PG Laboratory, Department of Science of Dental Materials, Army Medical College, Rawalpindi, Pakistan from February 2023 to August 2023.Methods: Three disc-shaped samples (n=3) of 10 mm diameter and 1 mm thickness of each restorative material were prepared using stainless steel molds per manufacturer's instructions. These disc-shaped samples were then suspended in a 15 mL conical centrifuge tube containing 10 mL deionized water, followed by incubation in a Forced Convection Laboratory Oven at 37 C where these were allowed to age over a period of 1-2 years. Vickers Hardness of each sample was then checked at two-time intervals, i.e., after 24 h setting and after 2.5 years of ageing through the Micro Vickers Hardness Tester calibrated at 1Kgf (9.80 N) with dwell time of 10 seconds and light intensity 10. Results: After one day (24 h) aging in deionized water, maximum mean Vickers hardness number (VHN) was exhibited by Compomer (539.83±58.08 VHN) and least by GIC (175.75±24.47 VHN). After aging the sample for 912 days, maximum mean VHN was observed for GIC (420.67±99.66 VHN) and least by Compomer (354.33±9.22 VHN). Conclusion: RMGIC sustains its hardness on aging, hardness of GIC increases while that of Giomer and Compomer decreases upon aging.
 How to cite this: Gul H, Nayyer M, Junaid Y, Pasha M, Ejaz T, Liaqat U, Hassan SH. Effect of Aging on Hardness of Glass Ionomer, ResinModified Glass Ionomer, Giomer and Compomer Dental Restorative Materials. Life and Science. 2023; 4(4): 438-444. doi: http://doi.org/10.37185/LnS.1.1.437

Evaluation of Surface Properties of Two Remineralizing Agents after Modification by Chitosan Nano Particles: An In vitro Study.

Calcium phosphate-based systems have been introduced as promising bio-mimetic materials due to their close resemblance to the enamel. Chitosan and its derivatives have been an emerging biomaterial due to their additional antibacterial effect and promising re-mineralizing ability. The aim of this study is to evaluate the effect of chitosan nanoparticles on the remineralization of the demineralized enamel surface after being added to nano-hydroxyapatite and nano-calcium phosphate materials. This was in vitro study. Twenty specimens of extracted permanent molars were collected, and then immersed in demineralizing solution, then distributed into four groups according to the remineralizing material. Group 1: Treated with Nano-beta-tricalcium phosphate (Nβ-TCP) gel, Group 2: Treated with Nβ-TCP with chitosan gel, Group 3: Treated with Nanohydroxyapatite (NHA) gel, and Group 4: Treated with NHA with chitosan gel. The surface hardness of the teeth was measured at baseline, after demineralization, and after remineralization. The structural changes in each group were analyzed using the scanning electron microscopy. Shapiro-Wilk's test, one-way ANOVA followed by Tukey's post hoc test was used. In all groups, there was a significant difference in mean Vickers hardness number (VHN) at different intervals, with the highest value found after treatment (301.64-395.65) VHN, followed by the baseline (236.97-276.15) VHN, while the lowest value was detected after demineralization (121.23-124.39) VHN. It was also indicated that baseline treatment, the Hardness percentage change (%) of the nano NHA + Chitosan group showed the highest significant value (55.10%), while the Nβ-TCP group exhibited the lowest significant value (9.56%). It can be concluded that NHA and NΒ-TCP modified by chitosan NPs as remineralizing agents of enamel surface hold promising results.

Dramatic improvement of the strength of laser welded joints of Nb521 to GH3128 by adding pure copper as an interlayer

Weld cracks and low weld strength of Nb521 to GH3128 dissimilar metal welded joint are key factors influencing their weldability. To obtain favorable crack-free laser welded joints, this research adopted copper as an interlayer to research the microstructure and properties of laser direct welded and laser offset welded joints of Nb521 to GH3128 superalloy. Compared to previous research results, the tensile strength of laser direct welded joints is enhanced by 2.5 folds. There is a melting reaction layer at the position where the center welded joints are adjacent to the Nb521 base metal, and Ni3Nb and Laves phases are present in the layer. The copper solid solution is located in the center of fusion zone, and Ni3Nb-Laves hard particles are found. The phases near the side of GH3128 superalloy base metal are Ni solid solution, Cu solid solution, Ni3Nb/Cr2Nb hard particles and high melting point alloy mixture. Macrosegregation at the laser offset welding fusion zone is more serious. The phases near the Nb521 base metal are Nb solid solution, Cu solid solution, Ni3Nb and Cu/Cr eutectic structure. At the center of the fusion zone, Cu solid solution, Ni3Nb and Cu/Cr eutectic structure are observed. The phases near GH3128 base metal are Ni solid solution, Cr2Nb phase and Cu solid solution. Mean Vickers hardness values of the direct welded fusion zone is 271.7 ± 129.8 HV, which reduces mismatching of hardness of the joints to a certain degree. As there are Laves phase and Ni3Nb brittle phase in the melting reaction layer adjacent to Nb521 base metal, the microhardness value is up to 589.1 HV. The average microhardness of the offset welded fusion zone is 449.1 ± 217.4 HV, which is higher than the hardness of Nb521 and GH3128 base metals, due to increasing number of brittle phases in the joints. Strength values of the direct welded and offset welded joints are 418.7 ± 49.8 MPa and 364.3 ± 24.5 MPa respectively, which are separately 86.0% and 74.8% of Nb521 base metal. Fractures are all found to occur at the fusion zone on the side of Nb521. The direct welded joints exhibit mixed fracture characteristics with dimples and cleavage facets on the fracture, while the offset welded joints are characterized by brittle fracture.

A molecular dynamics simulation on corrosion, wear, and mechanical properties of laminated Al/TiC composites

In this study, first, a molecular dynamics simulation (MD) is done to simulate the AA1050/ TiC composites to find mechanical, corrosion, and wear features. Further, fabrication of AA1050/ TiC composites via powder metallurgy and accumulative roll bonding (ARB) is done. Further, mechanical, corrosion, microstructural and wear properties vs Nano TiC Wt.% is examined to verify the simulation results. An excellent particle distribution has been achieved after the 4th cycle. Moreover, density and electrical properties such as electrical resistivity and conductivity vs the Nano TiC composites is considered. Based on both the simulation and empirical results, by increasing the Nano TiC Wt.%., wear and corrosion resistance, density, hardness and strength were enhanced and the elongation, bonding strength and electrical conductivity of samples decreased. Finally, bonding and corrosion of these composite samples’ vs the TiC Wt.% is examined. Composite specimen made by 10 Wt.% of TiC has the elongation value of 1.95 and for monolithic specimen is 4.7 registering 2.41 times reducing. Mean Vickers hardness of specimens enhances from 28 to 62 for monolithic and 10% TiC specimens registering 121% enhancement, individually.

Effects of repetitive firings on mechanical, optical, and phase formation changes of ceramic materials

Statement of problemStudies are sparse on how rapid heating and cooling negatively affect optical properties, including color and transparency, and mechanical properties, including hardness and durability, that affect esthetics and shorten the clinical usage period of the ceramics. PurposeThe purpose of this in vitro study was to determine the effects of repeated firing on the color difference, mechanical properties, and phase formation of different ceramic materials. Material and methodsA total of 160 disks (12×1.35 mm) were produced from 4 different ceramic materials: lithium disilicate glass-ceramic, zirconia-reinforced lithium silicate ceramic, zirconia core, and monolithic zirconia. Specimens from all groups were divided into 4 groups (n=10) with a different number of veneer porcelain firings (1 to 4) by simple randomization. After the firings, color measurement, X-ray diffraction analysis, environmental scanning electron micrograph analysis, surface roughness evaluation, Vickers hardness evaluation, and biaxial flexural strength tests were performed. Data were analyzed with analysis of variance (2-way ANOVA) (α=.05). ResultsRepeated firing did not affect the flexural strength of the specimens in any of the groups (P>.05), while the color, surface roughness, and surface hardness were significantly affected (P<.05). The specimens fired 4 times showed the highest mean Vickers hardness and ΔE00 values but the lowest mean surface roughness values. Zirconia core specimens showed the highest mean ΔE00 and flexural strength values, and lithium disilicate glass-ceramic specimens had the highest mean Vickers hardness values. ConclusionsThe increase in the number of firings affected the color, mechanical properties, and phase formation of the specimens; this change differed according to the ceramic tested.

An In-depth Analysis of the Effects of Preheating Three Different Composite Resin Systems at Two Different Temperatures on Their Microhardness

Abstract Background: Composite restorations often have inferior physical properties compared to natural enamel and dentin, leading to early failure. Preheating the traditional composite before its placement and curing seems to enhance all its physical characteristics magically. The objective of the current research was to assess the impact of preheating on the surface microhardness of commonly used composite resin materials, specifically FILTEK P60, FILTEK Z250XT, and Tetric-N-Ceram Bulk fill. Materials and Methods: The resin composite tubes were either left at the ambient room temperature (24°C ± 1°C) or preheated in a commercial preheating device to 50°C and 60°C for 40 min. By inserting uncured preheated composite resin into class II Mseio-Occluso-Distal (MOD) cavities with specifications of 2 ± 0.3 mm axial height, 2 ± 0.3 mm pulpal depth, parallel proximal walls with a 3 ± 0.3 mm buccolingual width, 1.5 ± 0.3 mm gingival width, and an occlusal isthmus width equal to one-third of the intercuspal distance from composite resin tubes, a total of 99 class II MOD cavities on premolars were established. Each specimen’s Vicker’s hardness number (VHN) was determined. The gathered information was examined utilizing a two-way ANOVA and Tukey’s post hoc test with a significance threshold of 0.05. Results: When preheated to the temperatures of 50°C and 60°C, a remarkable rise in the mean Vickers hardness numbers (VHNs) of all the resin composites compared to those maintained at the room temperature (P &lt; 0.05) was seen. The mean VHNs at the room temperature for FILTEK P60, FILTEK Z250XT, and Tetric-N-Ceram were 47.27 ± 9.08, 59.63 ± 1.56, and 75.69 ± 0.80, respectively, with a significant variation between all of them (P &lt; 0.05). The mean VHNs were, respectively, 108.45 ± 2.42, 103.45 ± 1.29, and 113.00 ± 4.35 at 50°C, with a significant variation between them all. At 60°C, the mean VHNs were, respectively, 121.09 ± 1.30, 128.00 ± 0.89, and 135.00 ± 2.04, with a significant variation between all of them (P &lt; 0.05). Conclusion: The surface microhardness of all investigated composite resins was greatly increased by preheating, with Tetric N-Ceram Bulk Fill showing the greatest value at a preheating temperature of 60°C.

Assessment of the relative efficacy of fluoridated toothpaste with and without eggshell-derived calcium oxide in the prevention of primary tooth enamel demineralization

Background: During the cariogenic challenges, the anticaries action of fluoride is limited by the bioavailability of calcium and phosphate in saliva. This mandates the use of additional extrinsic sources of calcium and phosphate to enhance the anticaries potential of fluoride. Aim: This study aimed to assess and compare the efficacy of fluoridated toothpaste with and without eggshell-derived calcium oxide in the prevention of primary tooth enamel demineralization. Materials and Methods: Sixty samples were obtained from 15 extracted primary second molars and allocated to one of four groups: Group A for baseline Vickers hardness testing, Group B was subjected to demineralization only, Group C was treated with fluoridated toothpaste solution, and Group D was treated with fluoridated toothpaste and chicken eggshell powder solution. Surface microhardness and the amount of calcium that was leached into the demineralizing solutions of groups B, C, and D were statistically assessed after 7 days of pH cycling. Results: The mean Vickers hardness values of groups A, B, C, and D were 402.68, 366.28, 392.79, and 395.27, respectively. The mean calcium concentration released into demineralizing solution of groups B, C, and D were 35.52, 29.12, and 27.12, respectively. No statistically significant difference was found between the fluoridated toothpaste with and without eggshell powder. Conclusion: Both fluoridated toothpaste with and without eggshell-derived calcium oxide were equally effective in the prevention of primary tooth enamel demineralization.

Effects of postpolymerization conditions on the physical properties, cytotoxicity, and dimensional accuracy of a 3D printed dental restorative material

Statement of problemAlthough the introduction of high-speed 3-dimensional (3D) printing technology has significantly reduced printing time, the time required for postpolymerization is a speed-determining step because of the long wait time. How postpolymerization conditions affect material properties is unclear. PurposeThe purpose of this in vitro study was to assess the physical properties, accuracy, and biosafety of a 3D printed dental restorative material according to postpolymerization conditions. Material and methodsSpecimens were prepared by 3D printing with a digital light processing 3D printer with 1 interim dental material (C&B MFH). All printed specimens underwent a postpolymerization process with 5 different postpolymerization devices and were designated as groups D1 (D102H), FO (Form Cure), LC (LC-3DPrintBox), ME (Medusa), and MP (MP100). The light intensity and temperature of each device were measured, and the Vickers hardness, flexural strength and modulus, degree of conversion (DC), cytotoxicity, and polymerization shrinkage were analyzed. Statistical analyses were conducted with 1-way analysis of variance, the Tukey post hoc test, and regression testing (α=.05). Scanning electron microscopy was used to assess the fracture surface characteristics of the specimens. ResultsLight intensity was strongest with the ME device, and the temperature inside the device during postpolymerization showed the highest increase with the LC device and the lowest increase with the D1 device. The LC group specimens showed the highest mean Vickers hardness, and the MP group showed the lowest. The flexural strength was ≥100 MPa in all groups, with a flexural modulus ranging from 1.17 to 1.5 GPa. The DC results were similar to the physical properties test results. The D1, FO, LC, and ME groups all showed ≥70% cell viability, indicating no toxicity. The FO group showed the highest shrinkage rate of 0.52%. ConclusionsWhen the light intensity was strong, the surface was sufficiently hard, and toxic substances were not eluted even after a short postpolymerization time, suggesting that light intensity modulation and time management can be used to improve the postpolymerization process.

Evaluation of wear behavior of dental restorative materials against zirconia in vitro

ObjectivesTo evaluate two-body wear (2BW) and three-body wear (3BW) of different CAD/CAM and direct restorative materials against zirconia using a dual-axis chewing simulator and an ACTA wear machine. Methods3 CAD-CAM resin-based composite or polymer infiltrated ceramic network blocs, 1 lithium disilicate CAD-CAM ceramic (LS2), 3 direct resin composites, amalgam and bovine enamel were tested. For 2BW, 8 flat specimens per material were produced, grinded, polished, stored wet (37 °C, 28d) and tested (49 N, 37 °C, 1,200,000 cycles) against zirconia. For 3BW, specimens (n = 10) were stored accordingly, and tested against a zirconia antagonist wheel (3Y-TZP, d = 20 mm, h = 6 mm; 200,000 cycles, F = 15 N, f = 1 Hz, 15% slip) in millet seed suspension. Wear resistance was analysed in a 3D optical non-contact profilometer, measuring vertical wear depth and volume loss for 2BW and mean wear depth and roughness (Ra) for 3BW. Vickers hardness (15 s, HV2) was measured. Statistical analysis was performed using non-parametric tests (Mann-Whitney-U test, p < 0.05). Results2BW and 3BW have a different impact on material surfaces. Similar wear resistance was observed for direct and indirect resin based materials with analogous filler configurations in both methods. Bovine enamel exhibited the best wear resistance in 2BW, but the least wear resistance in 3BW against zirconia. Regarding 2BW, a direct/indirect composite material pair of the same manufacturer showed the significantly highest mean volume losses (2.72/2.85 mm³), followed by LS2 (1.41 mm³). LS2 presented the best wear resistance in 3BW (mean wear depth 2.85 µm), combined with the highest mean Vickers hardness (598 MPa). No linear correlation was found between Vickers hardness and both wear testing procedures. The zirconia antagonists showed no recordable signs of wear. SignificanceDental restorative materials behave differently in 2BW and 3BW laboratory testing. Vickers hardness testing alone cannot hold for a correlation with wear behavior of materials. Micromorphological investigation of material composition can reveal insights in wear mechanisms related to variations in filler technologies.

Residual stress evolution enhanced martensite phase transition and texture development in cryogenic-tempered WC-Co ultra-coarse grained cemented carbide

The aim of this study is to clarify the effect of residual stress on the microstructure, martensite phase transition of Co binder phase, texture development of WC hard phase and mechanical properties enhancement in cryogenic-tempered WC-6wt.%Co ultra-coarse grained cemented carbides. Sin2(ψ)-2θ method was used to analyze the residual stress, and EBSD was used to reveal the phase transition of Co phase and texture of WC phase. The results showed that the density, grain size and carbon balance of cemented carbide revealed little difference after cryogenic-tempering treatment. The mean compressive residual stress of WC phase increased by 60.84% after cryogenic treatment, while tempering treatment resulted in a significant relaxation of the residual stress by 101.97% and even transformed the compressive residual stress to tensile stress. EBSD analysis showed that the mean ratio of hcp-to-fcc Co increased from 1.75% to 4.22% and 11.61%. It is difficult to distinguish the effect of residual stress increase and the temperature decrease on the martensite transition during the cooling process. However, the occurrence of martensite phase transition during tempering is not temperature-dependent but highly related to the residual stress evolution. After cryogenic-tempering treatment, {0001}<11 2‾ 0> preferred orientation of WC phase was concentrated, which was related to the basal plane slip and grain deflection of WC grains during the evolution of residual stress. Due to the martensite phase transition strengthening of Co and the preferred orientation of WC, the mean Vickers hardness increased from 1068.4 HV30 to 1149.4 HV30. The mean transverse rupture strength firstly decreased from 2747.5 MPa to 2515.3 MPa, and then increased to 2705.0 MPa, which was related to the increase and relief of residual stress during the post treatment. Furthermore, mean fracture toughness showed a slight increase from 22.5 MPa m1/2 to 23.4 MPa m1/2. The simultaneous increase of fracture toughness with hardness can be attributed to the residual stress evolution and martensite phase transition.

Mechanical Analysis of Explanted Telescopic Rods in the Management of Osteogenesis Imperfecta: A Multicenter Study.

Telescopic rods in the management of osteogenesis imperfecta fail frequently. This could be attributed to technical errors, rod design, and rod structure. We aimed to analyze the mechanical properties and tribology of explanted male and female components to identify effects of in vivo telescoping that may relate to observed patterns of successful telescoping or failure. Recruitment took place at 3 of the 4 English centers for osteogenesis imperfecta. Twenty-five rods explanted for growth or failure during revision to a new rod were analyzed in terms of clinical indication and prerevision imaging to identify if there was a technical mode of failure. Laboratory analysis was performed using optical and scanning electrical microscopy, radiograph diffraction analysis, hardness test, bending test, and energy-dispersive x-ray spectroscopy. All implants tested were of high-grade stainless steel. Female components had inferior strength [mean Vickers hardness property (HV0.3) at 0.3 to 313 kg] in comparison to male components (HV0.3 406) due to different techniques of manufacture. Female rods also had a higher wear coefficient (7.89×10-12 m3/N/m3) than the male rods (6.46×10-12 m3/N/m3). Abrasive wear, shear deformation, scratches, and wear debris were identified in all rods. Male and female components displayed corrosion contributing to adhesive wear. Intraoperatively cut rods, particularly the female components, had irregular ends leading to more wear. Current manufacturing techniques result in inferior material strength in female components compared with males, which combined with wear patterns is likely to lead to implant failure. Intraoperative cutting of rods may increase risk of failure due to wear. Considering techniques to improve strength as well as design in new implants may lead to better outcomes. Level IV-cross-sectional study.

Thermal Stability of YSZ Thick Thermal Barrier Coatings Deposited by Suspension and Atmospheric Plasma Spraying

Two types of segmentation-crack structured yttria-stabilized zirconia (YSZ) thick thermal barrier coatings (&gt;500 μm, TTBCs) were deposited onto the stainless steel substrates using atmospheric plasma spraying (APS) and suspension plasma spraying (SPS) process, respectively. In this work, thermal aging behaviors, such as the microstructures, phase compositions, grain growth, and mechanical properties of APS TTBCs and SPS TTBCs, were systematically investigated. Results showed that both as-sprayed TTBCs exhibited a typical segmentation-crack structure in the through-thickness direction. APS coatings mainly comprised of larger columnar crystals, while a large number of smaller equiaxed grains existed in SPS coatings. Both of the coatings underwent tetragonal-monoclinic phase transformation after 155 °C/40 h heat treatment. The poorer phase stability of SPS TTBCs may have a connection with smaller grain size. Thermal-aged APS and SPS coatings exhibited a significant increase in H and E values with the rising of thermal aging temperature, and for the samples that thermal aged at 1550 °C, the H and E values increased sharply during initial stage then decreased after 80 h due to the phase decomposition. The segmented APS coatings had weak bonding between the lamellaes during thermal exposure, which caused the mean Vickers hardness value of APS TTBCs to be much lower than that of SPS TTBCs.

Effect of resin infiltration application on early proximal caries lesions in vitro

Background/purposeResin infiltration (RI) material ICON is used in treating early proximal caries lesions, as it depends on a micro–invasive infiltration technology. This in vitro study aimed to evaluate the effect of ICON resin infiltration (RI) on early proximal caries by comparing surface roughness and hardness before and after treatment with RI using atomic force microscopy (AFM), automated microhardness testing system (AMHTS), and scanning electron microscopy (SEM) in vitro. Materials and methodsTwenty seven premolars extracted for orthodontic reasons were sectioned buccolingually, creating 54 specimens. Each specimen was immersed in demineralizing solution to induce caries. Only teeth with “International Caries Detection and Assessment System” codes 1 and 2 were selected. The specimens were divided randomly into either AFM, AMHTS or SEM groups, which examined demineralized enamel before and after treatment with ICON. ResultsThe mean average surface roughness and root mean square roughness values of demineralized enamel treated with ICON were significantly higher than untreated lesions (P < 0.001). The mean Vickers hardness values for demineralized enamel treated with ICON was significantly higher than untreated lesions (P < 0.001). SEM showed irregular, pitted and rough demineralized enamel surface with destruction of enamel rods and dissolution of enamel crystals. After ICON application, the surface showed complete blockage of enamel rods with RI and irregular, rough uneven topography. ConclusionRI application on proximal incipient caries increased surface roughness and hardness significantly.

Two-body Wear and Hardness of New Generation Artificial Resin Teeth.

The purpose of this study was to evaluate two-body wear and hardness of new generation artificial resin teeth. Ten specimens of four different artificial resin teeth (nanofill composite, nanohybrid composite, microfiller reinforced acrylic and highly modified acrylic) were prepared. Specimens were thermodynamically loaded in a dual-axis chewing simulator (50N, 240,000 cycles, 1.6 Hz, 5/55°C thermocycle). The wear loss was analyzed by using plaster replicas and 3D laser scanner. Vickers hardness was determined before and after thermodynamic loading. Mean Vickers hardness values of highly modified acrylic resin teeth were statistically significantly lower than nanohybrid composite (p⟨0.001), nanofilled composite (p⟨0.001) and microfiller reinforced acrylic resin teeth (p⟨0.001). Mean wear loss of highly modified and microfiller reinforced acrylic resin teeth were statistically significantly lower than nanohybrid composite (p⟨0.001) and nanofilled composite (p⟨0.001) resin teeth. There was a statistically significant difference in wear among the materials. The correlation between hardness and wear was not statistically significant.

In Vitro Re-Hardening of Bleached Enamel Using Mineralizing Pastes: Toward Preventing Bacterial Colonization.

The search for materials able to remineralize human hard tissues is a modern medical challenge. In this study, the protective effect on the enamel microhardness by a paste based on hydroxyapatite and sodium fluoride (Remin Pro) was evaluated after two different enamel bleaching procedures. Forty sound human incisors were randomly assigned to different treatments: bleaching with an in-office agent (Perfect Bleach Office+); bleaching with an at-home agent (Perfect Bleach); bleaching with the in-office agent followed by the prophylaxis paste; bleaching with the at-home agent followed by the prophylaxis paste; no treatment (control). Bleaching was performed at 0, 8, 24 and 32 h, followed by a 3-min re-mineralizing treatment in the subgroups designed to receive it. Specimens underwent a micro-hardness tester and a mean Vickers Hardness number was considered for each specimen. ANOVA exhibited significant differences among groups. Post-hoc Tukey testing showed significant micro-hardness decrease after the application of both the two bleaching agents. The treatment with prophylaxis paste significantly increased the micro-hardness values of bleached enamel.

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.

A Comparison of the Surface Properties of CAD/CAM and Conventional Polymethylmethacrylate (PMMA).

To compare surface properties of 2 brands of pre-polymerized resin blocks for complete dentures (CAD/CAM PMMA) to conventional heat-polymerized PMMA. A total of 45 rectangular specimens (25 × 25 × 3 mm) were fabricated from 3 brands of PMMA (n = 15/group): AvaDent CAD/CAM PMMA, Tizian-Schütz CAD/CAM PMMA, Meliodent conventional PMMA. Specimens were examined for wettability using the sessile drop method, surface roughness using a digital contact profilometer, and microhardness using Vickers hardness number. Statistical analysis was performed using one-way ANOVA and Tukey pairwise multiple comparisons. p-Values of ≤0.05 were considered significant. AvaDent specimens demonstrated the highest mean contact angle (72.87 ± 48°) and the highest mean Vickers hardness number (20.62 ± 0.33). The conventional heat-polymerized specimens showed the highest mean surface roughness (0.22 ± 0.071 μm). Tizian-Schütz specimens showed the lowest mean surface roughness (0.12 ± 0.02 μm). As CAD/CAM PMMA groups exhibited significantly more favorable surface properties in comparison to the conventional heat-polymerized groups, CAD/CAM dentures are expected to be more durable. Different brands of CAD/CAM PMMA may have inherent variations in surface properties.

Effects of an etching solution on the adhesive properties and surface microhardness of zirconia dental ceramics

Statement of problemConventional approaches to adhesive bonding are not applicable to zirconia restorations. Recently, an etching solution, Zeta Etching Solution (ZES), has been introduced for etching the surface of zirconia. The effects of this etching solution on the bond strength and mechanical properties of zirconia are unknown. PurposeThe purpose of this in vitro study was to examine the effects of ZES on the bond strength and surface hardness of zirconia. Material and methodsTwo different types of partially stabilized tetragonal polycrystalline zirconia (TZP), Prettau zirconia (group P) and anterior Prettau (group AP), were evaluated with and without ZES etching. Each group was bonded to a zirconia substrate by using an adhesive resin cement. After 24 hours of storage in distilled water, the bond strength of the zirconia was analyzed. Vickers hardness was determined by using a microhardness tester. Scanning electron microscopy was used to analyze the surface microstructure and determine the mode of failure for each specimen. Results were analyzed and compared using 1-way ANOVA and Student t tests (α=.05). ResultsScanning electron microscopy analysis showed that etching the surface of zirconia with ZES etching solution for 60 minutes changed the morphological characteristics and microstructure of zirconia, making the surface more irregular. The changes were more pronounced for AP specimens. Etching with ZES significantly increased the shear bond strength of zirconia (P<.05) in AP specimens. The bond strength of Prettau (P group) specimens after ZES etching did not increase significantly (P>.05). An adhesive failure mode was observed for P zirconia specimens, whereas zirconia specimens exhibited a cohesive mode of failure. No significant decrease (P>.05) was observed in the mean Vickers hardness numbers. ConclusionsWithin the limitations of this in vitro study, it was concluded that etching in ZES for 30 minutes significantly enhanced the shear bond strength of highly translucent anterior Prettau (AP) zirconia restorations. Moreover, etching with ZES did not adversely affect the surface hardness of the zirconia specimens tested.

Influence of storage temperature on vickers microhardness of resin composite

Introduction: The purpose of this study is to evaluate the effect of three storage temperatures on microhardness of high and low viscosity bulk-fill materials and compare them with conventional resin-based composite materials. Materials and method: Six composite resin-based materials were used in this study (TN, TNB, TNF, FZ250, FB and FBF) samples were subdivided into three groups based on the pre-curing storage temperature (5°C, 23°C and 37°C). Light polymerization for each material was performed based on the manufacturer’s recommendation using Bluephase G2 curing unit (Ivoclar Vivadent, Schaan, Liechtenstein) in a high-intensity mode with an irradiance of 1200 mW/cm2. Vickers hardness values of top and the bottom surfaces of each sample were evaluated using (NOVA 130 series, Vickers and Knoop hardness testing instrument) under a 200 g load with a dwell time of 10 sec. Also three indentations with the random distance of 1 mm were taken from the top and the bottom surfaces of each sample and a mean Vickers hardness (VHN) value were calculated (n=18 top and n=18 bottom). The mean bottom/top ratio was calculated by dividing VHN of the bottom surface by VHN of the top surface. Results: When the tested materials were stored at room temperature (23°C) before testing in the present study, they failed to reach the minimum 80% of the mean bottom to top hardness value ratio except for FZ250 and FBF, where they reached 97.8% and 83.2% respectively. Where in samples that were stored refrigerated at 5°C all the materials have reached the minimum 80% of the mean bottom to top hardness value ratio except for FBF (77.3%) and TB (77.2%). On the other hand, the only material that reached the minimum 80% of the mean bottom to top hardness value ratio when the materials were stored at 37°C was FZ250 (93.5%). Conclusion: Despite the promising results from this preliminary study, regarding improvement of microhardness with refrigerated composite resins, further research has to be conducted. The enhancement of hardness values associated with preheated composites could be beneficial in countries with warm climate such as Saudi Arabia. The association of precooled composite resin and the use of the LED curing units could be recommended to improve resin-based composite hardness. Further research is needed to evaluate the other mechanical properties and whether or not they are influenced by storage temperature.

Microhardness and shear bond-strength of carious dentin after fluorescence-aided or conventionally excavation: (An in-vitro comparison).

BackgroundTo compare the fluorescence-aided and conventionally excavated dentin with microhardness and shear bond strength(SBS) tests.Material and MethodsTwenty-four teeth with dentin caries were bisected through the center of the lesion into two halves. Forty-eight dentin specimens were embedded and mounted in an acrylic resin. All carious tissue was removed and classified as caries free using conventional visual tactile criteria. Then half of the specimens(n=24) were reinspected with fluorescence-aided caries excavation light(FACE) (FaceLight, W&H Dentalwerk, Bürmoos GmbH, Austria). Specimens were subjected to microhardness and shear bond strength testings. The fracture mode analysis was also performed. The data were compared with Student’s t test and Chi-square test.ResultsResidual caries was observed in 2 out of 24 conventionally excavated specimens with FACE inspection(p>0.05). Mean Vickers hardness of the dentin was 61.5±5 in the FACE group and 70.3±3 kg/mm2 in the conventionally excavated group(p>0.05). The mean SBS value of FACE group was 11.42±1.63 MPa and 18.27±1.43 MPa in conventionally excavated group. There was no statistically significant difference between conventional and FACE groups for microhardness and SBS tests(p>0.05). There were also no significant differences on the fracture mode distributions of the groups(p>0.05).ConclusionsFACE method could be considered as a promising technique for removing infected dentin. Key words:FACE, conventional excavation, residual caries detection, shear bond strength, microhardness.