Disc-shaped Specimens Research Articles

Insights Into the Effects and Implications of Acidic Beverages on Resin Composite Materials in Dental Restorations: An InVitro Study.

Dental composite resins are commonly used due to their excellent physical and mechanical properties. However, exposure to beverages like Coca-Cola, Apple juice, and Black coffee can negatively impact these materials. This study examined the effects of these drinks on the surface microhardness and surface roughness of Nanohybrid, Giomer, and Dual-Cure Bulk-fill resin composites. Seventy-two disc-shaped resin composite specimens were prepared and divided into four groups (n = 18) based on immersion liquid: Group 1 (Coca-Cola), Group 2 (Apple juice), Group 3 (Black coffee), and Group 4 (Distilled water). The composites were further categorized into NeoSpectra (Subgroup 1), Beautifil II (Subgroup 2), and Predicta (Subgroup 3). Specimens were immersed for 14 days, alternating 18 h in beverages and 6 h in distilled water daily. Microhardness was measured using a Vickers microhardness tester, and surface roughness was analyzed by atomic force microscopy. Data were assessed using one-way ANOVA and Tukey's post hoc test, with significance set at p < 0.05. All groups experienced significant decrease in microhardness and surface roughness. Coca-Cola led to the highest roughness and hardness reduction. Among composites, the Nanohybrid resin (NeoSpectra) showed the least alteration. NeoSpectra ST, a nanohybrid composite, demonstrated superior resistance to acidic beverages compared to Giomer and Bulk-fill composites. The study finds that out of three composite materials, nanohybrid composites are the most acid resistant which provides a suitable material for patients who consume acidic beverages more frequently. In this way, clinicians can use this information to help optimally increase the longevity of their restorations by selecting materials according to oral exposure levels of acids in their patients.

Comparison of Optical Properties in Single-Shade and Multi-Shade Composite Resins

This study aimed to evaluate the differences in optical properties, such as color and translucency, between single-shade composite resins (Omnichroma) and multi-shade composite resins (Filtek Z350XT). Furthermore, the study assessed the influence of the surrounding structure’s shades on the shade matching of Omnichroma. Two types of disc-shaped specimens were prepared: Single specimen (diameter, 8.0 mm; thickness, 1.0 and 2.0 mm), consisting of either Omnichroma or Filtek Z350XT in the A1B, A2B, and A3B shades, and dual specimen (diameter, 8.0 mm; thickness, 2.0 mm), featuring a bottom layer (diameter, 8.0 mm; thickness, 1.0 mm) of Filtek Z350XT in the A1B, A2B, and A3B shades, and a top layer (diameter, 8.0 mm; thickness, 1.0 mm) filled with Omnichroma. Commission Internationale d’Eclairage &lt;i&gt;L&lt;sup&gt;*&lt;/sup&gt;a&lt;sup&gt;*&lt;/sup&gt;b&lt;sup&gt;*&lt;/sup&gt;&lt;/i&gt; color measurements and calculations for color differences (Δ&lt;i&gt;E&lt;sup&gt;*&lt;/sup&gt;&lt;sub&gt;ab&lt;/sub&gt;&lt;/i&gt;) and translucency parameters (TP) of each specimen were performed. Omnichroma exhibited a lighter, more greenish, and blueish color compared to the Filtek Z350XT in A1B, A2B, and A3B shades. With increased thickness, Omnichroma became more yellowish, whereas Filtek Z350XT became less yellowish. Additionally, when Omnichroma was applied over Filtek Z350XT in dual specimens, the yellowness increased further beyond Omnichroma’s original yellowness level. Consequently, Omnichroma achieved clinically acceptable shade matching, especially in the A3 shade, because it aligns well with the original high yellowness of the A3 shade. Additionally, Omnichroma’s superior shade-matching ability was attributed to its higher translucency compared to Filtek Z350XT. Therefore, Omnichroma might be considered useful in pediatric dentistry by simplifying the shade selection process.

Evaluation of Colour Stability of Activa Pronto and Beautifil Flow Plus in Three Different Solutions - An In Vitro Study

Objective: To assess the colour stability of two bioactive restorative materials Activa Pronto (Pulpdent, USA) and Beautifil Flow Plus (Shofu, Japan) when exposed to three commonly consumed beverages: coffee, tea, and Coca-Cola.Materials and Methods: 80 disc-shaped specimens were prepared, 40 samples each of the material and were divided into four groups based on the staining solution, which included: distilled water (control), coffee, tea, and Coca-Cola. The specimens were placed in the respective solution for 30 days. Solutions were replaced daily to avoid contamination. Color measurements were performed before (baseline) and after 30 days using a VITA Easyshade spectrophotometer, and the colour changes (ΔE) were calculated in the CIE Lab* system.Results: For the ΔE values, Activa Pronto showed significantly lower values than Beautifil Flow Plus in both coffee (p=0.001) and Coca-Cola (p=0.000) solutions. In the tea group, no significant difference was observed (p=0.223). Activa Pronto generally had more stable color, especially in acidic and staining solutions like coffee and Coca-Cola solutions.Conclusion: Activa Pronto presented greater color stability than Beautifil Flow Plus; therefore, it is a more suitable material for patients who would take much notice of the aesthetic appearances of their restorations in the long term. The most stained materials by Coca-Cola and coffee meant further investigation into the long-term clinical behaviour of these materials was essential.

Bacterial Adhesion and In Situ Biodegradation of Preheated Resin Composite Used as a Luting Agent for Indirect Restorations.

To evaluate surface roughness and bacterial adhesion after in situ biodegradation of the cementation interface of indirect restorations cemented with preheated resin composite. Resin composite blocks (Z250XT/3M ESPE) were cemented to bovine enamel (7 × 2.5 × 2 mm) using preheated microhybrid resin composites: (1) Filtek Z100 (3M ESPE) (Z100); (2) Gradia Direct X (GC America) (GDX); and (3) Light-cured resin cement RelyX Veneer (3M ESPE) (RXV) (n=21). The resin composites were preheated on a heating device (HotSet, Technolife) at 69°C for 30 minutes. Disk-shaped specimens (7 × 1.5 mm) were made for biodegradation analysis with the luting agents (n=25). The in situ phase consisted of 20 volunteers' using an intraoral palatal device for 7 days. Each device had six cylindrical wells for the blocks and the disk-shaped specimens. Biodegradation was evaluated through surface roughness (Ra), scanning electron microscopy (SEM) micromorphological analysis, and colony-forming unit (CFU) count. The film thickness of the luting agents was also measured under stereomicroscopy. Increased surface roughness was observed after the cariogenic challenge without differences between the luting agents. Higher variation and surface flaws suggestive of particulate detachment were observed for Z100. No differences were observed in CFU counts. All materials underwent surface biodegradation, and the surface roughness of the resin cements was similar to or lower than that of the preheated resin composites. The resin composites' film thickness was thicker than that of the resin cement. Clinicians should be aware of these factors when choosing the use of preheated resin composite since it can lead to reduced longevity of the cementation interface and, therefore, restorations.

Color Stability of Bulk-Fill Flowable Resin Composites After Artificial Aging.

This study aimed to evaluate the color stability of bulk-fill flowable resin composites with 2 difference shades at baseline and after artificial aging. Disk-shaped specimens (Ø10 × 4 mm) were fabricated from three bulk-fill flowable resin resin composites (Filtek Bulk-Fill Flow, Venus Bulk-Fill Flow, and Estelite Bulk-Fill Flow). The specimens in each bulk-fill resin composite group were divided into two subgroups (n = 10 per subgroup) with two different shades, A1 (N = 30) and A3 (N = 30), and were polymerized with light curing (800 mW/cm2/Valo LED Unit, Ultradent) and polished. The color difference between bulk-fill resin composites was evaluated at baseline and after artificial aging using a spectrophotometer (CM-700d, Konica Minolta, Tokyo, Japan) under D65 illumination. Color coordinates were measured with CIEDE2000, and color differences (∆E00) and relative translucency parameter (RTP) values were calculated. Subsequently, the comparison of color changes (∆E00) before and after thermocycling was performed using the t-test for paired samples. The bulk-fill flow resin composites evaluated in the present study were capable of mimicking important optical properties such as light transmission. All the resin composites provided acceptable color stability at baseline and after thermocycling when the color A1 was used. On the other hand, whenever the shade A3 was used, the Venus Bulk-Fill Flow demonstrated the best optical properties. There was no statistically significant difference when comparing baseline and after thermocycling in bulk-fill flowable resin composites (p > 0.05). After thermocycling, A1 bulk-fill flowable resin composites provided acceptable color stability, and all A3 bulk-fill flowable resin composites provided visible color change, except for the Venus Bulk-Fill Flow (∆E00 = 2.35). Estelite Bulk-Fill Flow displayed the best color stability (∆E00 = 2.22) between all the combinations evaluated.

Impact of S-PRG/Giomer and Bulk-fill technologies on the hygroscopic profile of resin composites under erosive condition

ObjectiveThe emergence of new resin composites (RCs) incorporating bioactive ingredients and/or used as bulk-fill materials aims to enhance restorative potential beyond just the mechanical properties. However, this innovation may affect their performance under clinically simulated conditions, such as erosive challenges (EC). This study evaluated the impact of different technologies on the hygroscopic properties of RCs. Materials and Methods: The evaluated materials were: Gold Label – GL (resin-modified glass-ionomer cement – control); Filtek Z350 – FZ (no bioactive control); Filtek One Bulk – FO (bulk-fill); Beautifil II – BII (bioactive/S-PRG); Beautifil Bulk – BB (bioactive/S-PRG + bulk-fill). Disk-shaped specimens (10 mm x1 mm) were prepared and evaluated by: 1) water sorption – WS and solubility – WSB (n = 10); 2) wettability – W (n = 6); 3) surface microhardness – SM (n = 6); 4) qualitative surface analysis by SEM (n = 3). Except for WS and WSB, tests were performed before and after EC. Data were analyzed by two-factor ANOVA and Tukey tests (p < 0.05). Results: Positive WS and negative WSB were observed for all materials. In terms of W, GL>BII>FZ>BB>FO. GL and BB exhibited similar/lower SM. EC hampered SM for all materials. Conclusions: It may be concluded that the composition and proportion of monomers have a greater influence on the hygroscopic profile of resin composites than the incorporation of bioactive components. Clinical significanceWhile renewed technologies have introduced components to enhance the performance and practicality of resin composites, actual clinical longevity depends on challenges such as erosive conditions. Bioactive ingredients seem to be beneficial without impairing the hygroscopic profile, whereas the monomers can interfere.

Impact of Acidic and Alkaline Environments on the Surface Morphology of Biodentine and White Mineral Trioxide Aggregate - An In-vitro Study.

The physical and chemical properties of calcium silicate cement might be affected due to exposure to acidic or alkaline conditions during clinical use. The present study aimed to evaluate the effect of acidic and alkaline environments on the surface morphology of biodentine (BD) and white mineral trioxide aggregate (wMTA). Disc-shaped specimens of BD (n = 30) and wMTA (n = 30) were prepared in a metal mould and wrapped in pieces of gauze. They were divided into three sub-groups according to the storage media: group A, soaked in sterile distilled water at a pH of 7.0; group B, exposed to butyric acid buffered at pH 4.0; and group C, exposed to calcium hydroxide solution buffered at pH 12.0. The specimens were incubated for 7 days at 37°C, followed by examination under scanning electron microscopy at 1000x and 5000x magnification to characterise the microstructural morphology. Definite changes were seen in the microstructure of BD and wMTA on exposure to acidic and alkaline pH. The microstructure of wMTA tends to exhibit reduced cohesion when exposed to an acidic environment, especially when compared to an alkaline pH. Acidic pH exerts a milder influence on the morphological structure of BD when contrasted with its effects on wMTA. Biodentine may emerge as a more prudent choice than wMTA for utilisation in inflamed periapical regions.

Assessment of the Microhardness of Three Different Glass Ionomer Cements After Microhydroxyapatite Incorporation: An In Vitro Study.

Aim The study aimed to evaluate the impact of incorporating microhydroxyapatite on the microhardness of three different types of glass ionomer cement. Methodology A total of 120 disc-shaped specimens (7 mm in diameter and 3 mm in height) were prepared for the study, divided into three groups, each containing four subgroups of 10 samples. The materials tested included Zirconomer, conventional glass ionomer cement (CGIC), and resin-modified glass ionomer cement (RMGIC), with the addition of microhydroxyapatite in varying concentrations of 0, 5, 15, and 25 wt%. All specimens were stored in deionized water at 37ºC for 24 hours before being subjected to the Vickers microhardness test. Statistical analysis was performed using one-way ANOVA and Tukey's post hoc honest significance test (HSD) test, with a significance level set at p<0.05. Results The addition of 5 and 15 wt% microhydroxyapatite to Zirconomer and RMGIC significantly increased microhardness (p<0.001). The highest Vickers hardness number (VHN) was observed in the RMGIC group with 5 wt% of microhydroxyapatite. However, the RMGIC group with 25wt% microhydroxyapatite showed a lower VHN compared to the control group (without hydroxyapatite) (p<0.001). Conclusion The incorporation of 5 and 15 wt% microhydroxyapatite enhanced the microhardness of CGIC, RMGIC, and Zirconomer. However, adding 25 wt% of microhydroxyapatite to RMGIC resulted in a reduction in hardness compared to the control group without microhydroxyapatite.

Factors Influencing Measurement of Dynamic Elastic Modulus from Disk-Shaped Concrete Specimen

The decrease in dynamic elastic modulus is a primary indicator of quantitative damage in concrete. To quantitatively assess depth-by-depth damage within a concrete structure, cylindrical specimens obtained through coring can be cut into disk specimens to measure the dynamic elastic modulus of concrete at each depth. To minimize external damage during coring, it is essential to extract cylinders with the smallest possible diameter. In addition, for higher resolution in depth-based damage assessment, creating disk specimens with the smallest possible thickness is necessary. However, there is no information available in the literature on experimental limitation of smallest possible diameter and thickness for dynamic elastic modulus of disk-shaped specimens. This study evaluated whether the dynamic modulus measured from various sizes of concrete disk specimens provided sufficient reliability compared to reference values obtained from cylinders. Moreover, the study examined how the presence of coarse aggregate and variation in the water–cement ratio significantly influenced the dynamic modulus measurement. In addition, test results from impulse excitation technique (IET) and impact resonance (IR) were compared to find a more reliable test method for dynamic elastic modulus of disk specimen. The experimental findings revealed that as the thickness-to-radius ratio of the disk specimens decreased, measured data variation increased. Mortar specimens without coarse aggregates showed less variability compared to concrete specimens, and the variation in dynamic modulus measured by IR was lower than that measured by IET.

Influence of Polymerization Protocol on Adhesion and Proliferation of Streptococcus mutans on Three Dental Composite Resins.

Background/Objectives: The aim of this in vitro study was to analyze and compare the Streptococcus mutans ability to adhere and form biofilm on the surface of light-cured VS heat-cured dental composite resins; Methods: Three composite resins with different chemical formulations were selected: GrandioSO (GR), Venus Diamond (VD) and Enamel Plus Hri Biofunction (BF). Disk-shaped specimens were manufactured by light-curing the composite resins (light-cured subgroups) and subjecting them to a further heat-curing cycle at 80° for 10 min (heat-cured subgroups). Specimens were analyzed for planktonic CFU count (CFU/mL), sessile CFU count (CFU/mL) and for biomass quantification (OD570nm); Results: The planktonic CFU count was higher in all the light-cured subgroups than in the heat-cured subgroups (light-cured: GR = 7.23 × 106, VD = 2.14 × 107, BF = 4.40 × 107; heat-cured: GR = 4.89 × 106, VD = 4.95 × 106, BF = 2.80 × 107), with a statistically significant increase for BF and VD. Focusing on the sessile CFUs, both GR (light-cured = 7.49 × 106; heat-cured = 3.97 × 106) and VD (light-cured = 2.93 × 107; heat-cured = 6.07 × 106) showed a significantly increased number of colonies in the light-cured subgroups. The OD570nm values recorded for the light-cured BF subgroup (0.4280) were significantly increased compared to the heat-cured BF subgroup (0.1931); Conclusions: A more complete polymerization protocol seems to lead to a potential reduction in the risk of secondary caries.

Surface and bulk viscoelastic stability of solvent-stored bulk-fill resin-based composite

ObjectiveInvestigate the effect of solvent-storage on surface hardness and bulk creep of fast photo-cured bulk-fill resin-based composite (RBC) compared to conventionally irradiated bulk-fill RBCs. MethodsThree bulk-fill RBCs were studied: Tetric® PowerFill (fast photo-cured bulk-fill RBC) (TPF), Tetric EvoCeram® (EVO), and GrandioSO® x-tra (GSOx) (conventional). Disk-shaped specimens of clinically realistic thickness (4 mm) were prepared from each material for: Group A: surface measurements (18 mm diameter) and Group B: 4 mm diameter for bulk compressive creep measurements. Group A disks were light-cured from the upper ‘occlusal’ surface for either 3 s or 20 s according to the manufacturer’s recommendation. Martens hardness (HM) of both top and bottom surfaces of each specimen were measured. Group B: 4 × 4 mm cylindrical specimens were fully cured to measure bulk creep (CB). A 20 MPa static compressive stress was applied for 2 h, followed by 2 h of unloading. Strain deformation was recorded continuously for 4 h. Both Martens and bulk creep studies were performed under the following storage conditions at 37 °C: (i) dry at 24 h post curing (baseline), and (ii) after 7 and 30 d of storage in two different media: distilled water (DW) and 75 % ethanol/water (75 % E/W). ResultsAt baseline, HM for all materials ranged from 587 to 439 N/mm2 (top) and 398 to 342 N/mm2 (bottom). After 30 d of solvent-storage, more pronounced HM changes were observed, with the bottom surface being more affected. Normalised HM for TPF decreased by 44 % after 30 d in 75 % E/W. Maximum creep strain ranged from 1.1 % to 2.1 % at baseline, and after 30 d in 75 % E/W this increased from 1.9 % to 2.9 %. Depending on the material and storage condition, the percentage creep strain recovery after 30 d ranged between 65.2 % and 80 %. Increased filler loading in the bulk-fill RBCs decreased the creep strain magnitude and increased the surface hardness. SignificanceSolvent storage decreased the Martens hardness of both upper and lower surfaces and increased the bulk creep characteristics of bulk-fill RBCs. Nevertheless, there was a similar relative stability in surface hardness and viscoelastic stability of fast-cured PowerFill compared to conventionally irradiated RBCs.

Optical properties of advanced lithium disilicate.

A variety of firing protocols are available for the IPS e.max lithium disilicate (LD) and can be used for new, 'advanced' LD (ALD). However, the impact of firing protocols on the optical properties of ALD is still unknown. The aim of the present study was to evaluate the color difference (ΔE00), the translucency parameter (TP00) and the whiteness index for dentistry (WID) for both LD glass ceramics after the processes of firing/glazing. Fifty disk-shaped specimens, with a diameter of 10 mm and a thickness of 1.2 mm, were fabricated from IPS e.max CAD (LD; Ivoclar) and another 50 from CEREC Tessera™ (ALD; Dentsply Sirona). The specimens from each group were further divided into 5 subgroups (n = 10) according to the firing/glazing protocol applied: crystallization (c); one-step crystallization and glazing (cg); crystallization and refiring (c-r); two-step crystallization and glazing (c-g); or long-firing crystallization (lfc). The ΔE00, TP00 and WID were assessed. The statistical analysis of ΔE00 was performed using the one-way analysis of variance (ANOVA) and Tukey's post hoc test, while TP00 and WID were analyzed with the two-way ANOVA and Tukey's post hoc test at a statistical significance level of 0.05. The cg groups were designated as the reference. The ANOVA showed that the firing procedures had no effect on ΔE00, TP00 and WID in the case of LD. In addition, LD exhibited greater translucency and brightness as compared to ALD. For ALD, all color changes observed in relation to the reference firing protocol were clinically unacceptable. The ALD specimens which underwent 1 standard firing cycle showed higher TP00 and WID values than other ALD groups. The choice of the firing protocol has no impact on the color, TP00 or WID of LD. Additionally, LD presents higher WID values than ALD, irrespective of the firing protocol used. Alternative firing protocols result in clinically unacceptable color variations when compared to the manufacturer-recommended protocol for ALD. Advanced LD is more sensitive to different firing protocols with regard to its optical properties, which makes the workflow less predictable in comparison with LD.

An Advanced Surface Treatment Technique for Coating Three-Dimensional-Printed Polyamide 12 by Hydroxyapatite

Polymer 3D printing has is used in a wide range of applications in the medical field. Polyamide 12 (PA12) is a versatile synthetic polymer that has been used to reconstruct bony defects. Coating its surface with calcium phosphate compounds, such as hydroxyapatite (HA), could enhance its bonding with bone. The aim of this study was to coat 3D-printed polyamide 12 specimens with hydroxyapatite by a simple innovative surface treatment using light-cured resin cement. Polyamide 12 powder was printed by selective laser sintering to produce 80 disc-shaped specimens (15 mm diameter × 1.5 mm thickness). The specimens were divided randomly into two main groups: (1) control group (untreated), where the surface of the specimens was left without any modifications; (2) treated group, where the surface of the specimens was coated with hydroxyapatite by a new method using a light-cured dental cement. The coated specimens were characterised by both Fourier transform infrared spectroscopy (FTIR) and Transmission Electron Microscopy (TEM), (n = 10/test). The control and treated groups were further randomly subdivided into two subgroups according to the immersion in phosphate-buffered saline (PBS). The first subgroup was not immersed in PBS and was left as 3D-printed, while the second subgroup was immersed in PBS for 15 days (n = 10/subgroup). The surfaces of the control and treated specimens were examined using an environmental scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDXA) before and after immersion in PBS. Following the standard American Society for Testing and Materials (ASTM D3359), a cross-cut adhesion test was performed. The results of the FTIR spectroscopy of the coated specimens were confirmed the HA bands. The TEM micrograph revealed agglomerated particles in the coat. The SEM micrographs of the control 3D-printed polyamide 12 specimens illustrated the sintered 3D-printed particles with minimal porosity. Their EDXA revealed the presence of carbon, nitrogen, and oxygen as atomic%: 52.1, 23.8, 24.1 respectively. After immersion in PBS, there were no major changes in the control specimens as detected by SEM and EDXA. The microstructure of the coated specimens showed deposited clusters of calcium and phosphorus on the surface, in addition to carbon, nitrogen, and oxygen, with atomic%: 9.5, 5.9, 7.2, 30.9, and 46.5, respectively. This coat was stable after immersion, as observed by SEM and EDXA. The coat adhesion test demonstrated a stable coat with just a few loose coating flakes (area removed &lt;5%) on the surface of the HA-coated specimens. It could be concluded that the 3D-printed polyamide 12 could be coated with hydroxyapatite using light-cured resin cement.

Comparative Evaluation of Biofilm Formation on Temporization Crown Materials Used in the Rehabilitation of Primary Dentition With Different Polishing Materials: An In Vitro Study.

Introduction Advancements in dental materials have enhanced aesthetic treatments for managing dental caries and injuries in primary dentition. Bis-acryl composite-based temporization materials are now preferred for restoring primary crowns due to their superior properties. However, prolonged exposure to dietary and hygienic factors can lead to discoloration and roughness, making efficient polishing essential to prevent plaque buildup. Objective This study aims to evaluate Streptococcus mutans biofilm formation on temporization material polished with different polishing systems. Methods This study tested bis-acryl methacrylate temporization material. Thirty disk-shaped specimens were prepared and divided into three groups according to the polishing system used (n = 10 per group): Shofu Super Snap mini kit (Shofu, San Marcos, CA), aluminum oxide polishing paste, and propol polishing paste. Each group's specimens were polished according to the manufacturer's instructions. Surface roughness (SR), scanning electron microscopy (SEM) morphological analysis, and Streptococcus mutans biofilm formation were assessed for each group. Results The results showed significant differences in roughness average (Ra) values among the polishing materials, with the Shofu Super Snap mini kit having the highest roughness (Ra = 2.04), followed by propol polishing paste (Ra = 1.30)and aluminum oxide paste (Ra = 0.75). Additionally, polishing methods significantly affected mean colony-forming unit (CFU) levels, with the first group having the highest mean CFU value (0.24), with SEM images showing substantial biofilm formation by Streptococcus mutans. Conclusion Bacterial biofilm formation on the aluminum oxide paste group's surface differed from that on the propol polishing paste and aluminum oxide disc groups. The polishing techniques that we tested significantly influenced surface properties and biofilm formation. These findings suggest that selecting an appropriate polishing system can reduce the risk of gingival inflammation associated with temporization materials.

Role of oxidation in thermal fatigue damage mechanisms and life of X38CrMoV5 (AISI H11) hot work tool steel

Hot work tools steels, which are submitted to severe solicitations in service, are often damaged by thermal fatigue and corrosion. Interrupted Thermal Fatigue experiments were performed on X38CrMoV5 tool steel between 100 and 650 °C, in air and reduced oxygen partial pressure atmospheres after primary or secondary vacuum. A thermal and thermo-mechanical analysis by finite element method was carried out to estimate the strains and stresses undergone by the axisymmetric disc-shaped specimen during thermal cycling. The morphology, structure and phase composition of the oxide layer were analysed using scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. It was shown that the thickness, homogeneity, structure, and compacity of the oxide multilayer formed on the specimen changed depending on test atmosphere. In air, crack initiation and propagation were strongly assisted by oxidation, leading to reduced fatigue life compared to inert atmospheres. Steel softening was highlighted in sub-surface, whatever the test atmosphere.

Enhanced Antimicrobial Properties of Polymeric Denture Materials Modified with Zein-Coated Inorganic Nanoparticles.

Polymeric denture materials can be susceptible to colonization by oral microorganisms. Zein-coated magnesium oxide nanoparticles (zMgO NPs) demonstrate antimicrobial activity. The aim of this study was to investigate the antimicrobial effect and adherence of different oral microorganisms on hybrid polymeric denture materials incorporated with zMgO NPs. Five types of polymeric denture materials were used. A total of 480 disc-shaped specimens were divided by material type (n=96/grp), then subdivided by zMgO NPs concentration: control with no nanoparticles and other groups with zMgO NPs concentrations of 0.3%, 0.5% and 1% by weight. Characterization of the polymeric denture materials incorporating zMgO NPs was done, and the antimicrobial activity of all groups was tested against four types of microorganisms: 1) Streptococcus mutans, 2) Staphylococcus aureus, 3) Enterococcus faecalis and 4) Candida albicans. The samples underwent an adherence test and an agar diffusion test. Experiments were done in triplicates. The characterization of the hybrid samples revealed variation in the molecular composition, as well as a uniform distribution of the zMgO NPs in the polymeric denture materials. All hybrid polymeric denture materials groups induced a statistically significant antimicrobial activity, while the control groups showed the least antimicrobial activity. The agar diffusion test revealed no release of the zMgO NPs from the hybrid samples, indicating the NPs did not seep out of the matrix. The zMgO NPs were effective in reducing the adherence of the tested microorganisms and enhancing the antimicrobial activity of the polymeric denture materials. This antimicrobial effect with the polymeric dentures could aid in resisting microbial issues such as denture stomatitis.

Estimation of temperature-dependent piezoelectric material parameters using ring-shaped specimens

Abstract Simulation-driven design processes of piezoelectric actuators and sensors necessitate precise material parameter knowledge. Historically, the IEEE standard on piezoelectricity is used for this purpose, which proposes an analytical method for material parameter identification based on resonance frequency evaluations. This method requires different impedance measurements on differently shaped and processed samples, which yields inconsistent material parameter sets due to processing effects on material properties. Previous studies show that an inverse procedure using a single disc-shaped specimen with some adaptations can be used to identify a full set of parameters. As high-power actuators often use ring-shaped components, this method needs adaptation for this kind of specimen. Furthermore, the dependence of the material parameters on temperature needs to be considered to characterise the temperature effects and the associated non-linear effects of the specimens. For this purpose, samples with different geometrical dimensions at a range of different temperatures are examined in this study. Material parameters are then estimated using an inverse approach utilising the measurement data in conjunction with a numerical FEM simulation model. The observed temperature dependence of the estimated material parameters is examined and presented in this contribution.

Comparison of the Ability to Mask the Color of Endodontic Filling Materials Using Several Types of Base Materials

In clinical pediatric dentistry, a base material with optical properties, including transparency, that can mask the color of the material used for root canal-filling is preferred. This study aimed to examine the optical properties of various base materials by thickness. The disk-shaped specimens were photopolymerized and fabricated using Ionosit (IN), TheraCal LC (TL), TheraCal PT (PT), and A2 shade of Filtek&lt;sup&gt;TM&lt;/sup&gt; Supreme Flowable Restorative (FZ), Fuji II LC (FL), and Ketac&lt;sup&gt;TM&lt;/sup&gt; Fil (KF) with 1 and 2 mm thickness. The color parameters of these specimens were measured using a spectrophotometer on a black and white background and were measured using the same method on a mold containing Vitapex® and gutta-percha. The translucency parameter (TP) and color difference were calculated for each group. The Kruskal-Wallis and Bonferroni tests were used in the statistical analyses. The TP decreased when the thickness was 2 mm compared with 1 mm. The TP values of TL and PT were the lowest at all thicknesses. The TP values of 2 mm thickness in all molds filled with Vitapex® and gutta-percha were the lowest for TL, PT, KF, and IN. In TL and PT, the color difference before and after the application of the canal-filling material was the smallest, regardless of material thickness. Within the limits of this in vitro study, TL, PT, KF, and IN demonstrated better masking of the color of canal-filling material.

Effects of UV Postcuring Times on the Color Stability, Surface Properties and Conversion of 3D-printed Temporary Resin Composites.

To evaluate the effects of UV postcuring times on color stability (CS), surface properties (wettability [°] and surface roughness [Ra]), and conversion of 3D-printed resins for temporary restorations. Disc-shaped specimens (10.0×3.0 mm) and maxillary central incisors (8.2×10.3 mm) were fabricated using provisional 3D-printed resin (PriZma Bio Prov [PZ] and PrintaX AA TEMP [PX]) in A2 shade and subjected to UV postcure times of 0 (T0), 5 (T1), 10 (T2), and 15 (T3) minutes (n=15). The incisors were used for CS evaluation with a colorimeter. In contrast, discs were used to measure the contact angle using the sessile drop method, surface roughness with an optical profilometer, and degree of conversion with FT-NIR. For CS, Ra, contact angle, and degree of conversion, a two-way ANOVA with Bonferroni post-hoc test (α=0.05) was used. PX resin demonstrated greater color stability than PZ (p=0.001). Long UV postcuring times (10 to 15 minutes) will increase the contact angle (p=0.013) and stabilize the degree of conversion (p=0.01), while 5 to 10 minutes of UV postcuring will provide better surface smoothness (p=0.04) of both resins. Long UV postcuring times (10 to 15 minutes) lead to greater alterations in color, contact angle, and stability of the degree of conversion, while 5 to 10 minutes lead to a smoother surface of the 3D-printed temporary resins.

Relationship between Roughness and Wettability of Nine Types of Implant Surfaces and Potential Interference of Surface Oxygen and Carbon: In Vitro Evaluation.

Aim: To assess the roughness and hydrophilicity of nine types of dental implant surfaces, while also examining the presence of contaminants carbon and oxygen on these surfaces. Furthermore, the study investigated potential correlations between these characteristics across the analyzed surfaces. Materials and Methods: The surfaces analyzed were as follows: MI: machined (turned), Implacil implant; TOI: blasted with titanium oxide, Implacil implant; TOAEI: blasted with titanium oxide and acid-etched, Implacil implant; ZAED: blasted with zirconia and acid-etched, DSP implant; CPD: coated with calcium phosphate, DSP implant; XD: subjected to an experimental treatment (patent pending), DSP implant; DAEHAS: double acid-etched and activated with hydroxyapatite nano-crystals, SIN implant; DAES: double acid-etched, SIN implant; and AMP: untreated surface of the Plenum implant, produced by additive manufacturing. Four and five disc-shaped specimens were used in the hydrophilicity and roughness assessments, respectively. Roughness was evaluated by optical profilometry and scanning electron microscopy; hydrophilicity was determined using the sessile-drop technique; and the chemical analysis was performed using X-ray photoelectron spectroscopy. The Kruskal- Wallis, Mann-Whitney, and Spearman correlation tests were employed to analyze the data (p < 0.10). Results: Significant differences were observed among the analyzed surfaces in terms of both roughness and hydrophilicity (p < 0.001). The surface exhibiting the highest roughness was AMP, whereas the greatest hydrophilicity was exhibited by CPD. Correlations between roughness and hydrophobicity were observed for MI (r = 0.936, p = 0.009), ZAED (r = 0.957, p = 0.004), and DAES (r = 0.964, p = 0.005). The carbon concentration observed on the CPD surface was lower than that observed on the other surfaces, whereas the oxygen concentrations were similar. No correlations were observed between the presence of contaminants and the roughness or hydrophilicity characteristics. Conclusion: Roughness and hydrophilicity values exhibited considerable variation among the tested surfaces. Aside from the CPD surface, comparable concentrations of carbon and oxygen were detected. Although correlations between roughness and hydrophilicity were observed only for the ZAED, DAES, and MI surfaces, these correlations were inadequate to establish a causal relationship between the two surface characteristics.