Composite Discs Research Articles

Inertio-elastic instability of functionally graded nanotube-reinforced composite disks

Rotational elastic instability of annular members is an important phenomenon which may lead to the destruction of structures. The instability analysis of rotating disks made of carbon nanotube reinforced composite (FG-CNTRC) has been presented. This study is the first to investigate the rotational instability of FG-CNTRC disks, providing new insights into the design of high-stability rotating structures. The rotating disk mounted to rigid shaft has variable-thickness and the function of CNT distribution along the radial coordinate may be uniform or functionally graded. The refined rule of mixture approach is used to obtain the material properties of composite where efficiency parameters are considered. The actual centrifugal force with radial displacement is taken into account and the burst velocities at which instability observed are obtained. The theory used in the analysis is plane elasticity and the governing differential equations of the problem have variable-coefficients where the analytical solution may not be available. Complementary Functions Method, which is a powerful numerical solution scheme, is implemented into the analysis and high accuracy with few collocation points are achieved using non-dimensional parameters. The influences of CNT distribution pattern, volume fraction of CNTs and variations of thickness profiles on the burst velocities of disk are examined. It is revealed that CNT addition to the isotropic polymer has a stabilizing effect on the rotating disk by increasing the burst velocity and the most effective parameter is the CNT distribution pattern. Considering all distribution patterns, the FG-V pattern yields the most stable disk design. Validation of the results is done using analytical solution which is only available for uniformly distributed CNTRC with the hyperbolic thickness profile.

Fracture Characteristics and Tensile Strength Prediction of Rock–Concrete Composite Discs Under Radial Compression

To investigate the fracture mechanism of rock–concrete (R–C) systems with an interface crack, Brazilian splitting tests were conducted, with a focus on understanding the influence of the interface crack angle on failure patterns, energy evolution, and RA/AF characteristics. The study addresses a critical issue in rock–concrete structures, particularly how crack propagation differs with varying crack angles, which has direct implications for structural integrity. The experimental results show that the failure paths in R–C disc specimens are highly dependent on the interface crack angle. For crack angles of 0°, 15°, 30°, and 45°, cracks initiate from the tips of the interface crack and propagate toward the loading ends. However, for angles of 60°, 75°, and 90°, crack initiation shifts away from the interface crack tips. The AE parameters RA (rise time/amplitude) and AF (average frequency) were used to characterize different failure patterns, while energy evolution analysis revealed that the highest percentage of energy consumption occurs at a crack angle of 45°, indicating intense microcrack activity. Moreover, a novel tensile strength prediction model, incorporating macro–micro damage interactions caused by both microcracks and macrocracks, was developed to explain the failure mechanisms in R–C specimens under radial compression. The model was validated through experimental results, demonstrating its potential for predicting failure behavior in R–C systems. This study offers insights into the fracture mechanics of R–C structures, advancing the understanding of their failure mechanisms and providing a reliable model for tensile strength prediction.

Effects of Various Solutions on Color Stability and Surface Hardness of Nanohybrid Dental Composite Under Simulated Oral Conditions.

This study evaluated effects of various solutions on color stability and surface hardness of a nanohybrid dental composite in simulated oral environments. Sixty-four composite disks were fabricated and randomly allocated into eight groups (n = 8 per group): Artificial saliva (AS), Biotene (B), passion fruit juice (PFJ), orange juice (OJ), Sprite (S), Coca-Cola (CO), apple cider vinegar (ACV), and cranberry juice (CJ). Specimens were immersed in respective solutions at 37°C for 28 days. Surface microhardness was assessed using Vickers microhardness test, and color alterations were quantified using SpectroShade Micro spectrophotometer. Measurements were taken 24 hours after initial polymerization and after 28-day immersion period. Statistical analysis was performed using mixed model ANOVA. After 28 days, specimens exhibited significant changes in microhardness and color. Polished surfaces showed microhardness decreases of 21.9-35.5%, with ACV and CJ causing largest reductions. Non-polished surfaces unexpectedly showed increased microhardness (11.2-17.4%). Color changes were more pronounced on polished surfaces, with CO and CJ causing maximum alterations. Statistical analysis revealed significant interactions between surface treatment, staining media, and immersion time (p < 0.05). All experimental groups demonstrated significant changes, highlighting composite materials' susceptibility to environmental factors. Even well-polymerized and polished surfaces underwent alterations, emphasizing necessity for periodic follow-up and maintenance polishing in esthetic restorations. The present research emphasizes significance of oral environmental factors on composite restoration longevity and esthetics, advocating for patient education on dietary impacts and tailored maintenance strategies to preserve restoration quality. How to cite this article: Shetty P, Jayakumar HDN, Pulickal TJ, et al. Effects of Various Solutions on Color Stability and Surface Hardness of Nanohybrid Dental Composite Under Simulated Oral Conditions. J Contemp Dent Pract 2024;25(7):669-676.

Effect of Multivitamins on the Color Stability of Dental Materials Used in Pediatric Dentistry: An In Vitro Study

The longevity and acceptance of aesthetic dental materials are directly proportional to color stability. The aim of this study was to analyze the relationship between the use of multivitamins and the color stability of dental restorative materials. A total of 45 discs of nanohybrid composite, 45 of Reinforced Glass Ionomer (RGI), and 45 of Giomer were prepared. Subsequently, the samples were randomly divided into three solution groups (n = 15): Group 1—Sambucol Pediatric Syrup, Group 2—Hidropolivital Baby Drops, and Group 3—artificial saliva, which is preparation for patients with xerostomia. For 28 days, the specimens were immersed in 10 mL of each multivitamin for two minutes every 24 h. Color measurements were repeated on days 7, 14, 21, and 28. Statistical analysis was performed using the Jamovi software version 2.2.5, employing the Shapiro–Wilk test for normality and the Kruskal–Wallis test for non-parametric data. When comparing materials, statistically significant differences (p &lt; 0.001) were observed between RGI and Giomer, and RGI and composite, but not between Giomer and composite (p = 0.716). The highest change was observed in RGI–Hidropolivital ΔE00 = 3.27 (2.38–4.59) and the least in composite–Sambucol ΔE00 = 0.72 (0.30–1.18). In conclusion, the exposure time and the multivitamin influence the color change of restorative materials.

In Vitro Testing of Protective Eye Wear in Blocking Blue Light from Dental Light Curing Unit

Aim: To evaluate the ef?cacy of wearing protective eyewear in preventing harmful Dental light-curing units (LCUs). Background: Dental light-curing units generate blue light, capable of inducing soft-tissue burns and ocular harm like retinal damage. The intensity of blue light emitted by dental Light Curing Units is substantially higher, thereby potentially constituting a significant "blue light hazard." Material and Methods: To study the effect of protective glasses, reverse methodology was followed as the effect of blue light on the eye is difficult to measure; Circular composite disc samples were grouped into two, one of which was polymerized directly while the other had protective glass in between, Fourier transform infrared spectroscopy (FTIR) analysis was done and the degree of conversion was calculated. Results: Data obtained were analysed using One Way ANOVA. The mean values for "Degree of Conversion" in Group I (Without Protective Glass) is 1.334 +512 and for Group II (with protective glass) is -2.623 + 1.544 .One Way ANOVA revealed statistically significant difference between Group I and Group II (p=0.000) Conclusion: Within the limitations of this in vitro study, it can be concluded that the protective glasses are successful in filtering the harmful blue light emitted by LCU and should be used in day-to-day practice to improve the amount of light they deliver to the restoration from the LCU and prevent any harm to the ocular tissues. Clinical implications: Blue light filtering glasses in a dental operatory provide optimum protection, and the operator can safely watch and improve the amount of light delivered to the restoration from the LCU.

Enhancing the Sr uptake on resorcinol–formaldehyde polycondensates by modifying the structure and shape

AbstractResorcinol–formaldehyde polycondensates—the well-established Cs-selective agents, along with their crown ether (18-crown-6) composite discs, were synthesized, characterized (FT-IR, SEM–EDS, surface area, porosity) and applied for strontium uptake from aqueous solutions. Effects of crown ether amounts, Sr in feed, pH, equilibration time, temperature, competing ions, on the sorption, along with re-usability of synthesized sorbents, were evaluated. The fate of Sr was followed by EDXRF spectrometry on both solution and solid phases. Solution pH (3–12) and temperature (upto 100 °C) had negligible impact on the holding capacities. Sorption capacity was enhanced by ~ 33% upon modification, and followed pseudo-second order kinetics.

Aero-thermodynamic responses of a novel FGM sector disks using mathematical modeling and deep neural networks

Composite sector disks have extensive applications in aerospace industries, particularly when exposed to challenging conditions such as supersonic airflow and thermal environments. These applications leverage the superior properties of composite materials, including high strength-to-weight ratios, enhanced durability, and excellent thermal resistance, to meet the stringent requirements of aerospace operations. Multi-directional functionally graded (MD-FG) materials due to high-temperature resistance and other amazing properties in each direction have gotten plenty of attention recently. So, in this research, a thermoelasticity solution has been presented to study fundamental frequency traits of an MD-FG sector disk in supersonic airflow via both mathematics simulation and deep neural networks technique. For obtaining exact displacement fields, along with defining the changes of transverse shear strains along the system's thickness, the refined zigzag hypothesis is utilized. For obtaining the temperature-dependent equations, heat conduction relation and thermal boundary conditions of the MD-FG structure are presented. A coupled quasi-3D new refined theory (Q3D-NRT) and generalized differential quadrature method (GDQM) are presented for obtaining and solving the partial differential equations in the time-displacement domain. After obtaining the mathematics results, appropriate datasets are made for testing, training, and validation of the deep neural networks technique. Finally, the results have shown that aerodynamic pressure, temperature changes, Mach number, free stream speed, and air yaw angle have a major role in the stability/instability analyses of the thermally affected MD-FG sector disk in supersonic airflow. As an amazing outcome, increasing the sector angle, FG indexes, and temperature change lead to the reduction of the critical Mach number, and aerodynamic pressure associated with the flutter phenomenon.

In Vitro Effects of Sof-Lex, Eve, and Astropol Polishing Systems on Composite Resin Surface Roughness after Aging.

Objectives: Surface roughness is one of the important properties of composite restorations. Different polishing systems are used to provide an appropriate composite restoration surface. The aim of this study was to evaluate the effects of Sof-Lex, Eve, and Astropol polishing systems on composite resin surface roughness after aging. Materials and Methods: In this in vitro study, 36 composite discs (8×2mm) were fabricated. The specimens were randomly divided into three groups (N=12) for polishing with (I) Sof-Lex (3M ESPE), (II) Eve (Ernst Vetter GmbH), and (III) Astropol (Ivoclar/Vivadent) polishing systems. The specimens were then subjected to thermocycling. Surface roughness of the specimens was measured before and after polishing, and after thermocycling by a contact profilometer. Repeated Measures ANOVA was used to analyze the data (α=0.05). Results: Although Astropol showed slightly higher surface roughness in comparison to Sof-Lex and Eve, the level of surface roughness before and after polishing and after aging was not significantly different among the three polishing systems (P=0.704). Conclusion: Within the limitations of this in vitro study, Sof-Lex, Eve, and Astropol showed similar acceptable results with regard to composite resin surface roughness.

Structure and tribological behavior of a polyetherimide/polytetrafluoroethylene matrix filled with negative thermal expansion zirconium tungstate particles

Thermal expansion mismatch stresses may be a reason for premature failure of sealing and bearing components made of polymer composites that are rubbed against metallic surfaces at elevated temperatures. It is of particular importance for polymer matrix composites loaded with anti-friction inclusions of polytetrafluoroethylene (PTFE) that possesses high coefficient of thermal expansion. In this regard, a study was undertaken to elucidate the effect of the thermal mismatch on wear and friction of amorphous polyetherimide (PEI) matrix loaded with either polytetrafluoroethylene (PTFE) particles (i) or PTFE particles covered with negative thermal expansion zirconium tungstate (ZT) α-ZrW2O8 (ii) at temperatures 23 °C, 120 °C and 180 °C. The ball-on-disk testing scheme was used according to standard with AISI 52100 steel balls rubbed against a polymer composite disks at normal force P = 5 N and sliding velocity V = 0.3 m/s. The PEI/PTFE/ZT composite demonstrated a tendency for wear rate (WR) reduction in sliding at 120 °C and 180 °C as compared to corresponding WR enhancement on the PEI/PTFE. The rationale is provided that the ZT additive effectively reduced thermal expansion of the PTFE in the PEI matrix and thus improved wear resistance of the composite. New thermal expansion-controlled wear and friction instability mechanism has been proposed and discussed.

High-resolution Elemental Abundance Measurements of Cool JWST Planet Hosts Using AutoSpecFit: An Application to the Sub-Neptune K2-18b’s Host M Dwarf

We present an in-depth, high-resolution spectroscopic analysis of the M dwarf K2-18, which hosts a sub-Neptune exoplanet in its habitable zone. We show our technique to accurately normalize the observed spectrum, which is crucial for a proper spectral fitting. We also introduce a new automatic, line-by-line, model-fitting code, AutoSpecFit, which performs an iterative χ 2 minimization process to measure individual elemental abundances of cool dwarfs. We apply this code to the star K2-18, and measure the abundance of 10 elements: C, O, Na, Mg, Al, K, Ca, Sc, Ti, and Fe. We find these abundances to be moderately supersolar, except for Fe, with a slightly subsolar abundance. The accuracy of the inferred abundances is limited by the systematic errors due to uncertain stellar parameters. We also derive the abundance ratios associated with several planet-building elements such as Al/Mg, Ca/Mg, Fe/Mg, and (a solar-like) C/O = 0.568 ± 0.026, which can be used to constrain the chemical composition and the formation location of the exoplanet. On the other hand, the planet K2-18 b has attracted considerable interest, given the JWST measurements of its atmospheric composition. Early JWST studies reveal an unusual chemistry for the atmosphere of this planet, which is unlikely to be driven by formation in a disk of unusual composition. The comparison between the chemical abundances of K2-18 b from future JWST analyses and those of the host star can provide fundamental insights into the formation of this planetary system.

In Vitro Kinetic and Thermodynamic Staining Study of Three Energy Drinks on the Restorative Charisma Composite

Abstract Aim: The research utilized charisma composite resin, a dental restorative material known for its esthetic properties, with the chemical formula 2,2-bis[p(2-hydroxy-3-methacryloxy propoxyphenyl)] propane. The primary objective of the study was to examine the overall color change (ΔE*ab) of the charisma resin after it was subjected to three distinct energy drink solutions: Monster Energy Ultra-Sunrise, Wild Tiger, and Red Bull. Further we examined the effects of temperature and time on the staining interaction and overall color difference ΔE*ab on the surface of charisma restorative resin generated by three energy drink. Materials and Methods: A microfilled Charisma Classic composite resin was used in presented comparative study selected. The prepared 144 composite disk samples (subdivided n=48) with random allocation method were used for the three energy drinks to determine the effect of temperature and time over the course of 90 days. A metallic circulator mold was prepared. Every set of 48 specimens in the energy drink was heated in a water bath for 1, 7, 30, 60, and 90 days at four different temperatures This investigation spanned various time intervals, ranging from 1 to 90 days, and encompassed four temperature levels between 283 and 310 K. One-way ANOVA was used to evaluate the mean data for color change between the energy drinks, and Tukey’s post hoc test was used for multiple comparisons, with a significance level of P &lt; 0.05. Results: The study revealed that the rate of staining was most pronounced in the case of Wild Tiger, while it was comparatively lower for Monster Energy Ultra-Sunrise. These findings were established through an examination of the kinetic and thermodynamic behavior of surface color changes in micro-hybrid composites treated with the three energy drink solutions. Conclusions: The observed patterns aligned with the pseudo second-order model. It was observed that the Red Bull drink displayed a negative activation energy, resulting in a slower color change rate with increase in temperature. In contrast, endothermic, spontaneous, and regular staining activity was demonstrated throughout time by Monster Energy Ultra-Sunrise and Wild Tiger.

High-field complex parameters characterization of PMN-PT single crystal/epoxy 1–3 composites (φ = 0.4) under a high AC electric field with a varied intensity

It is essential to characterize the high-field properties of piezoelectric composites for their applications in ultrasonic transducers. This study involved the development of an experimental characterization system of piezoelectric impedance spectra and mechanical quality factors under high-field conditions to analyze the properties of PMN-PT piezoelectric single-crystal composites. The impedance spectra and mechanical quality factors of a [001]c-poled 0.69PMN-0.31PT single crystal/epoxy 1–3 composite disk with filling ratio φ = 0.4 under thickness resonance mode were tested at different driving voltages ranging from 1 to 120 Vpp to explore the influence of AC electric field on the material properties. By utilizing a theoretical approach, an evaluation was conducted on the variations in the material properties such as stiffness, permittivity, piezoelectric coefficient, and electromechanical coupling factor, along with respective loss factors. Our results suggest that as the AC electric field increases, the elastic modulus c33D and the mechanical quality factor Qm decrease, while the piezoelectric strain coefficient d33 and the electromechanical coupling factor kt increase. However, the dielectric coefficient ε33X does not show an obvious change in this field range. Furthermore, the elastic loss factor tanϕ, the dielectric loss factor tanδ33′, the piezoelectric loss factor tanθ33′, and the electromechanical coupling loss factor tanχt all increase, indicating that the loss of the piezoelectric composite becomes more evident as the AC electric field grows.

Prediction of wear of short glass fiber reinforced polyamide 66 composite sprocket

The wear of a polymer composite sprocket primarily depends on contact pressure and sliding velocity that vary significantly during service. The sliding distance and contact pressure at the sprocket/roller interface were estimated for a pristine polymer composite sprocket engaged with a standard and a 3% extended steel chain by employing the explicit finite element method. A set of experiments was executed to find the friction and wear coefficients of sprocket material using polyamide 66 composite pins and standard steel disc at sliding speeds of 1, 2, and 3 m/s and normal loads of 10, 20, 30, and 40 N. The wear depth is estimated after getting friction and wear coefficients experimentally, and contact pressure and sliding distance numerically. Archard wear model was executed using the UMESHMOTION subroutine with the Arbitrary Lagrangian-Eulerian technique in ABAQUS. The peak contact pressure on the sprocket is increased approximately by 1.5 times as the chain elongates from 0% to 3%. A pristine sprocket engaging a 3% extended chain after one lakh cycles experienced an approximate wear depth of 90 µm.

Calcium Sulfate Disks for Sustained-Release of Amoxicillin and Moxifloxacin for the Treatment of Osteomyelitis.

The purpose of this in vitro study was to develop calcium sulfate (CS)-based disks infused with an antimicrobial drug, which can be used as a post-surgical treatment modality for osteomyelitis. CS powder was embedded with 10% antibiotic, amoxicillin (AMX) or moxifloxacin (MFX), to form composite disks 11 mm in diameter that were tested for their degradation and antibiotic release profiles. For the disk degradation study portion, the single drug-loaded disks were placed in individual meshes, subsequently submerged in phosphate-buffered saline (PBS), and incubated at 37 °C. The disks were weighed once every seven days and analyzed via Fourier-transform infrared spectroscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and scanning electron microscopy. During the antibiotic release analysis, composite disks were placed in PBS solution, which was changed every 3 days, and analyzed for antibiotic activity and efficacy. The antibacterial effects of these sustained-release composites were tested by agar diffusion assay using Streptococcus mutans (S. mutans) UA 159 as an indicator strain. The degradation data showed significant increases in the degradation of all disks with the addition of antibiotics. Following PBS incubation, there were significant increases in the amount of phosphate and decreases in the amount of sulfate. The agar diffusion assay demonstrated that the released concentrations of the respective antibiotics from the disks were significantly higher than the minimum inhibitory concentration exhibited against S. mutans over a 2-3-week period. In conclusion, CS-antibiotic composite disks can potentially serve as a resorbable, osteoconductive, and antibacterial therapy in the treatment of bone defects and osteomyelitis.

Experimental and numerical analysis of Brazilian splitting mechanical properties and failure mechanism for composite discs

The properties of structural planes and the strength of rock matrix significantly influence the splitting characteristics of composite rock masses. To investigate the effects of structural plane and differences in matrix strength on the mechanical behavior and failure characteristics of composite jointed rock bodies, composite jointed disc specimens with varying structural plane roughness and matrix combinations were prepared. These specimens were then subjected to Brazilian split tests under different loading angles ranging from 0° to 90°. Results indicate that the failure mode of the specimens is determined by the angle of the structural plane. As the structural plane angle increases, the failure mode transitions from structural plane failure to combination failure and finally back to structural plane failure. Increased roughness of the structural plane reduces the extent of structural plane failure, while matrix strength has no significant impact on the failure mode. The failure load of the specimens increases with increasing structural plane angle, roughness, and matrix strength. The influence of structural plane roughness and matrix strength on the mechanical properties of the specimens grows with increasing structural plane angle. Increases in structural plane roughness and matrix strength significantly enhance the strain energy and dissipated energy of the disc model. Finally, an analysis of the stress state on the structural planes is combined with an exploration of the failure mechanisms of the specimens.

Research on the Brazilian splitting characteristics and failure mechanism of jointed composite disks

The stress state of composite rock joints has a significant impact on the overall stability of the rock mass. Studying the composite mechanism disk specimens with different matrix strengths and inclination angles under Brazilian splitting state is of great significance for improving the safety of surrounding rock. This research conducted Brazilian tests on different types of jointed composite disk specimens at different inclination angles and explored the effects of inclination angle and material strength on the mechanical properties and deformation characteristics of specimens. Clarified the failure mechanism of joint specimen. The experimental results indicate that the disk specimens under different inclination angles exhibit three typical failure modes. As the inclination angle increases, failure mode changes from Disk matrix failure (DM failure) to Disk matrix and structural failure (DMS failure), and ultimately to Disk structural failure (DS failure). Failure load, input energy, and strain energy of the specimen continue to decrease as the inclination angle increases and the matrix strength decreases. The decrease in matrix material significantly weakens the strength of the specimen, but this effect continues to decrease with the increase of inclination angle. DIC results show that as the inclination angle increases, the position of cracks exists from the loading end to the joint surface. Through theoretical analysis, it is found that as the inclination angle increases, the stress state at the center of the specimens changes from compression-shear state to shear state, and finally to tension state, corresponding to three failure modes: DM failure, DMS failure, and DS failure, respectively.

The effect of adding chitosan nanoparticles on different properties of the adhesive and high-filled composite resin

PurposeTo evaluate the effect of adding nano-chitosan on different properties of the adhesive and high-filled flowable composite resin (viewing the graphical abstract is suggested). BackgroundIncorporating chitosan might improve the quality of adhesive and high-filled composite resin used in the deep margin elevation (DME) and other restorative methods. Materials and methodsTwo groups of composite disks (without chitosan, with 1 % chitosan) were created to evaluate antimicrobial effects, degree of conversion (DC), solubility and water sorption. Antimicrobial activity was evaluated through biofilm inhibition and disk agar diffusion tests while DC was analyzed using FTIR. For the microshear bond strength test (μSBS), extracted maxillary molars were sectioned 1 mm under the CEJ, undergoing immediate dentin sealing and DME in four groups: control, pretreatment chitosan application, adhesive+1 % chitosan, and composite+1 % chitosan. The forces and the modes of failure were recorded. ResultsAdding chitosan nanoparticles increased the antimicrobial activity, significantly (p < 0.05). The μSBS and DC did not differ significantly between the groups (p > 0.05), and the failures were mostly found in the adhesive mode. The solubility and water sorption increased significantly (p < 0.05), remaining in a clinically acceptable range though. ConclusionAdding chitosan could be a potential option to increase the antibacterial effect in the high-filled composite resin without any negative affect on μSBS or DC, and clinically unacceptable effect on solubility and water sorption. (The graphical abstract has been provided). Clinical significanceAdding chitosan nanoparticles to high-filled flowable composite resin, increases the success rate of related restorative technique by adding the antimicrobial effect without any significant negative influence on other biomechanical properties.

Calculation of elastic tensile behavior of CF/PA6 composite material disc

In this paper, the characteristic behavior of the disc consisting of thermoplastic composite CF/PA6 material was considered. Analysis was made by taking into account the usage areas of the materials and referring to certain temperatures between 30 ℃ and 150 ℃ temperatures. Composite materials are lightweight, they show high strength. For these reasons, they are preferred in technology, especially in the aircraft and aerospace industry. With this study, the radial and tangential stresses determined within a certain temperature The temperatures were determined and compared with previous studies in the literature. According to the results obtained, it is believed that the thermoplastic composites CF/PA6 disc design can be used in engineering.

Evaluation of Surface Roughness and Microhardness of Bulk-fill and Nanohybrid Composite after Exposure to Different Beverages at Various Time Intervals - An In vitro Study.

The aim of the study was to compare the surface roughness and microhardness of bulk-fill composite and nanohybrid composite resin after exposure to three different beverages at different time intervals. In this study, 60 composite discs each for bulk fill and nanohybrid, of dimensions 10 mm × 2 mm were made. Both composites were randomly divided into four subgroups, i.e., 15 samples each for artificial saliva, tea, coffee, and soft drinks which were further subdivided into five samples for three time intervals. Composite resin discs were immersed in beverages for 4 min in 24 h for 7, 15, and 30 days. All samples were evaluated for surface roughness and microhardness before and after immersion. Both the composites showed a significant increase in surface roughness in all the beverages with maximum change in surface roughness observed in nanohybrid composite resin immersed in soft drinks. Furthermore, the microhardness of both the composites was decreased significantly in all beverages with maximum change in microhardness observed in nanohybrid composite resin immersed in soft drinks. Bulk-fill composite resin has better resistance to surface roughness and higher microhardness as compared to nanohybrid. Furthermore, acidic beverages highly affect the physical properties of both composite resins for longer periods.

Assessment of Effect of Flowable Composite on the Shear Bond Strength of Sapphire Bracket Bonded to Composite Restoration: An in Vitro Study

Introduction: We aimed to assess the effect of flowable composite on shear bond strength (SBS) of sapphire bracket bonded to composite restoration. Methods: Forty composite discs (3M Filtek Z250) were allocated into four groups: control group (C) conventional primer (Transbond XT) with conventional composite (Transbond XT adhesive paste) was used, group (F1): conventional bonding agent, group (F2): universal bonding agent (Scotchbond) and group (F3): all surface bonding agent (Assure plus) were used with bulk fill flowable composite (3M Filtek), then sapphire brackets were bonded to the composite discs. After bonding, the specimens were thermocycled for 5000 cycles, SBS was measured, and the adhesive remnant index (ARI) was determined. Results: One-way analysis of variance and the post-hoc Tukey’s test demonstrated significant differences between conventional and flowable composite. Kruskal–Wallis test found that there was no significant difference in ARI between the study groups. Conclusion: Flowable composite groups had significantly lower SBS than the control group.