Mechanical Properties Of Resin Composites Research Articles

Investigation of Mechanical Properties, Shade, and Water Sorption/Solubility of Commercial Composite Resins

Objectives: Assessment of mechanical properties of composite resins is important since they can affect the clinical performance and longevity of restorations. This study aimed to assess and compare different properties of dental composite resins available in the market. Materials and Methods: In this comparative study, samples of four different dental composite resins (Edge COM, Saremco, FGM, and Kulzer) were tested according to ISO 4049:2019 guidelines. Flexural strength (by using a universal testing machine), depth of cure (using the ISO 4049 scrape technique), radiopacity (with aluminum step wedge), water sorption/solubility (by using immersion and drying cycles), and shade (by using Vita Easy Shade) of the samples were assessed. Data were analyzed by one-way ANOVA and Tukey's post-hoc test (alpha=0.05). Results: No significant difference was found in flexural strength among the four groups (P>0.05). The depth of cure of FGM was significantly higher than that of other groups (P<0.05). Solubility and water sorption were the highest in Kulzer, and the lowest in Edge COM (P<0.05). All tested composites met the necessary radiopacity standards for precise radiographic diagnosis; radiopacity was higher in Saremco and FGM groups. None of the composite resins matched the reference A2 shade. Conclusion: Although no significant difference was found in flexural strength of the tested composites, they had differences in other properties. Edge COM exhibited high flexural strength, while Saremco had optimal radiopacity.

Synthesis and challenges of fluorinated divinyl urethane monomers as a strategy for masking hydrolytic sensitive methacrylate groups in resin composites

ObjectiveThe biodegradation of methacrylate (MA)-based dental restoratives has been suggested to contribute to a loss of adhesion and subsequent detachment, or secondary caries, both major causes of restoration failure. Previous studies have demonstrated that intermolecular interactions between resin monomers may affect the hydrolytic-susceptibility of composites. Altering the intermolecular interactions by shielding or masking the hydrolytically-susceptible ester groups found in MA monomers could be an effective strategy to mitigate the biodegradation of resin composites. The objective of this work was to assess whether shielding/masking MAs using fluorinated groups could improve the biostability of experimental composites. MethodsEight fluorinated monomers (FM) were synthesized, characterized (1H NMR), and formulated into experimental resin composites (FC, 65 wt%, microfill). FCs were assessed for interactions with water (water contact angle, water sorption, gel fraction), mechanical properties (both compressive and flexural strength and modulus), cytocompatibility, resistance to biodegradation using simulated human salivary esterase (SHSE) and compared to a control composite (CC) without FM. ResultsIntegration of FMs was found to generally decrease both the physical and mechanical properties under all incubation conditions when compared to the CC. Additionally, all FCs had a negative influence on composite biodegradation following immersion in SHSE when compared to the CC. SignificanceShielding/masking MA-esters inherently inserts molecular spaces between the polymer chains within the resin network, and shielding is likely not possible while also maintaining the necessary cohesive forces that regulate the physical and mechanical properties of resin composites. Novel dental resin development should seek to remove/replace vulnerable ester-containing MAs rather that adopting a shielding/masking approach.

Maximizing dental composite performance: Strength and hardness enhanced by innovative polymer-coated MgO nanoparticles

IntroductionZein-incorporated magnesium oxide nanoparticles (zMgO NPs) can influence the mechanical properties of dental materials. However, the effect of this addition on the mechanical properties of resin composite has yet to be investigated. The objective of this study was to add various concentrations of zMgO NPs to conventional, flowable, and bulk-fill composite and assess the effect on the compressive strength, flexural strength, and microhardness. Methodology150 samples each of conventional composite, flowable composite, and bulk-fill composite (n = 450) were enhanced with concentrations of zMgO NPs at 0 %, 0.3 %, 0.5 %, 1 %, and 2 % (n = 30). 10 samples of each group were randomly allotted to the compressive strength, flexural strength, or hardness test. Characterization of the specimens was performed by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy. Two-way ANOVA test was used to compare between groups, and one-way ANOVA followed by Tukey's test was done at p = 0.05 to determine significance. ResultsCharacterization yielded a uniform distribution of nanoparticles in the matrix and the formation of a new hybrid composite that maintained its properties. Composite of all types enhanced with 0.3 % and 0.5 % zMgO NPs demonstrated a statistically significant increase in compressive strength, flexural strength, and hardness when compared to the control (p < 0.05). The bulk-fill composite with zMgO NPs concentrations of all groups demonstrated a statistically significant increase (p < 0.05) in hardness when compared to the control. ConclusionThe modified composites’ compressive strength, flexural strength, and hardness improved or remained consistent. Clinical significanceAn improved dental resin composite will enhance the quality of care and patient experience. The augmented strength and hardness of resin composite is desirable in prolonging the durability of the restoration.

Preparation of Al-doped mesoporous silica spheres (Al-MSSs) for the improvement of mechanical properties and aging resistance of dental resin composites

ObjectiveThe purpose of this study was to synthesize Al-doped mesoporous silica spheres (Al-MSSs) and evaluate the effect of them as functional fillers on the mechanical properties and aging resistance of dental resin composites. MethodsAl-MSSs were prepared by a two-step method. The effect of Al-MSSs on the performance of the composites was evaluated using neat resin matrix, commercial composites 3M Z350XT and samples containing mesoporous silica spheres (MSSs) and nonporous silica spheres (NSSs) as control. The neat resin matrix consisted of resin monomer (Bisphenol A glycerolate dimethacrylate/triethylene glycol dimethacrylate, 49.5/49.5, wt%) and photoinitiator (camphor quinone/Ethyl-4-dimethylaminobenzoate, 0.2/0.8, wt%). The mechanical properties (flexural strength, flexural modulus, compressive strength and microhardness) of them were evaluated by a universal testing machine and microhardness tester. The mechanical stabilities of the prepared composites in wet environment were evaluated by immersing them in deionized water at 37 °C. In addition, we evaluated the effect of Al-MSSs on other properties of the dental resin composites such as polymerization shrinkage, degree of conversion, curing depth, contact angle, water sorption and solubility according to ISO 4049: 2019. ResultsThe synthesized Al-MSSs possessed good dispersibility with an average particle size of about 505 ± 16 nm. The mechanical properties of resin composites gradually increased with the increase of the loading amounts of inorganic fillers. The reinforcing effect of Al-MSSs was similar to that of MSSs and better than that of the NSSs groups at the same filler loading. After aging in deionized water at 37 °C for 30 days, the mechanical properties of all resin composites decreased. However, the decrease percentage of the composites filled with Al-MSSs was significantly lower than the other groups, indicating that the stability of the dental composites in wet environments was significantly improved by the Al-MSSs fillers. Furthermore, Al-MSSs had no obvious influence on the biocompatibility and other properties of dental resins. SignificanceThe prepared Al-MSSs could effectively improve the mechanical properties and aging resistance without sacrificing other physic-chemical properties of dental resin composites.

In vitro testing methods for the evaluation of the mechanical properties of composite resins

The selection of the right composite resin restorative material for clinical applications can be difficult, due to the wide range of available options. The mechanical properties of these materials have a significant impact on their longevity in the oral environment. Results from laboratory experiments that analyze the effects of compositional modifications can assist clinicians in making a more informed decision about the choice of the most appropriate material. This review examines the testing methods used to evaluate the mechanical properties of composite resin restorative materials.

Effect of Preheating of Resin Composite on Microtensile Bond Strength In Vitro Study

BACKGROUND: Preheating resin composite was one of the latest achievements to improve the mechanical properties of composite. AIM: This study was conducted to assess the effect of preheating of resin composite on microtensile bond strength to dentin. METHODS AND MATERIALS: A total of 32 human molars were selected and divided into two groups according to the type of resin composites either microhybrid (P60) (R1) or nanohybrid (Z250 XT) (R2). The molar teeth were embedded in acrylic resin blocks then the occlusal enamel was removed parallel to cementoenamel junction to expose the dentin. Each group was subdivided into four subgroups according to the number of preheating cycles of resin composite either no heating (C0), one preheating cycle at 68℃ (C1), two preheating cycles at 68℃ (C2), or three preheating cycles at 68℃ (C3). After bonding of resin composite, specimens were cut into beams 1 mm thick and stressed in tension using a universal testing machine (4 teeth per group/12 beams per tooth). STATISTICAL ANALYSIS USED: Two-way ANOVA and Tukey’s post hoc tests were used to test the effect of preheating resin composites for the interaction of different variables. RESULTS: In both variables of the study, the type of resin composite and the number of preheating cycles have a statistically significant effect on the microtensile bond strength to dentin. There was a significant interaction between the variables. CONCLUSION: Pre-heating of Filtek P60 as a packable composite at 68℃ can achieve significantly higher microtensile bond strength compared to Filtek Z250 as a microhybrid composite. Key Messages: Preheating of resin composite enhances the mechanical properties of resin composite. Furthermore, better adaptation is due to easily flow of the material in additional to the improvement of microtensile bond strength of resin composite due to monomer and radical mobility due to complete polymerization during preheating.

Compressive strength of nanohybrid composite resin after the application of glycerin immersed in fermented milk

Background: The prevalence of dental caries in Indonesia in 2018 is 45.3% of the population. Tooth filling is done so that dental caries does not spread further. The restorative material that is commonly used is composite resin. The compressive strength of composite resin is affected by the polymerization process. The surface of the composite resin exposed to air causes the formation of oxygen inhibited layer (OIL). Glycerin acts as a surface coating that can inhibit contact between the composite resin and air so that polymerization can run optimally. Changes in the mechanical properties of composite resins are also influenced by salivary pH and food intake. The acid contained in fermented milk can affect the matrix and filler bonds in composite resins. Further research is needed to determine the compressive strength of nanohybrid composite resins after the application of glycerin in fermented milk immersion. Purpose: To find out whether there is a change in the compressive strength of nanohybrid composite resin after the application of glycerin immersed in fermented milk, also to find out whether the glycerin application and immersion in fermented milk play a role in causing changes of the compressive strength. Methods: Laboratory experimental research with a total sample of 28 which was divided into 4 groups. Composite resin samples were made with a thickness of 3 mm and a diameter of 5 mm, followed by measuring the compressive strength using the Universal Testing Machine. Results: Independent T-Test test showed significantly different results. The compressive strength value of the group with glycerin application was higher than without glycerin application. Meanwhile, the group immersed in fermented milk drinks had lower compressive strength compared to saline immersion. Conclusion: The compressive strength of the nanohybrid composite resin changed after the application of glycerin immersed in fermented milk.

Efecto de la intensidad de las unidades de fotopolimerización sobre la biocompatibilidad y resistencia a la flexión de una resina compuesta

Objective: To determine the effect of the intensity of two light curing units on the biocompatibility, flexural strength and elastic modulus of a composite resin.&nbsp;&nbsp; Methodology: Two groups of Filtek Z250XT (3M ESPE) composite resin were created, each one photopolymerized using different intensities (&lt;400 mW/cm2 for 40s and&gt; 800 mW/cm2 for 20s). Cell viability was analyzed by MTT assay at 24 and 48 hours following the ISO 10993-5 standard. The flexural strength and elastic modulus were analyzed following the ISO 4049 standard. Results: In the group photopolymerized with an intensity &lt;400 mW/cm2, cytotoxicity was statistically higher both at 24 and 48 hours and flexural strength and elastic modulus were statistically lower. Conclusion: A polymerization intensity &lt;400 mW/cm2 increases the levels of cytotoxicity and decreases the mechanical properties of composite resins. The importance of the periodic control of the light curing units is emphasized.

How the Duration and Mode of Photopolymerization Affect the Mechanical Properties of a Dental Composite Resin.

Composite materials are the most common materials in use in modern dentistry. Over the years, the methods of photopolymerization of composite materials have been improved with the use of various devices, such as quartz tungsten halogen lamps (QTHs), light-emitting diode units (LEDs), plasma-arc lamps and argon-ion lasers. This study aimed to compare the mechanical properties of a composite material, depending on the time and mode of photopolymerization. One hundred and forty rectangular specimens (25 × 2 × 2 mm) and forty-two disc-shaped samples (5 mm diameter and 2 mm thickness) were prepared from shade A2 Boston composite resin. Samples were cured using the following seven photopolymerization protocols: four fast-cure modes (full power for 3, 5, 10, and 20 s), two pulse-cure modes (5 and 10 shots of 1 s exposures at full power), and one step-cure mode (soft start with a progressive cycle lasting 9 s). Specimens were subjected to a flexural strength test, Vickers microhardness test, and FTIR spectroscopy test. A 2-factor ANOVA and post-hoc tests were carried out to assess the differences in the flexural strength parameter between the tested groups of samples before and after aging. A mixed-model ANOVA was carried out to assess the differences in the Vickers microhardness parameter between the tested groups of samples before and after aging. The lowest values of flexural strength (p < 0.001) and Vickers microhardness (p < 0.001) were obtained for the 3 s mode for the pre- and post-aging groups. The FTIR mapping tests showed a much more homogeneous chemical structure of the composite after 20 s of continuous irradiation, compared to the sample irradiated for 5 s in the continuous mode. The mode and cure time affects the mechanical properties of the composite resin. Appropriate selection of the cure mode and time ensures better mechanical properties of composite resin. This suggests that the survival of dental restorations within the oral cavity could be extended by using longer photopolymerization durations.

A Narrative Review of Bioactive Glass-Loaded Dental Resin Composites.

This review aims to provide a comprehensive analysis of the characterizations of bioactive glass (BAG)-loaded dental resin-based composite materials. Online databases (Web of Science, PubMed, and Science Direct) were used to collect data published from January 2011 to January 2022. Only BAG-containing resin adhesive and resin restorative composites are discussed in this narrative review. BAG-loaded resin composites exhibit excellent mineralization ability reflecting enhanced ion release, pH elevation, and apatite formation, especially regarding high BAG loading. This aids the anti-demineralization and remineralization of teeth. Furthermore, BAG-loaded resin composites demonstrated in vitro biocompatibility and antibacterial performance. It has been suggested that BAG fillers with small particle sizes and no more than 20 wt% in terms of loading amount should be used to guarantee the appropriate mechanical properties of resin composites. However, most of these studies focused on one or some aspects using different resin systems, BAG types, and BAG amounts. As such, this makes the comparison difficult, and it is essential to find an optimal balance between different properties. BAG-loaded resin composites can be regarded as bioactive materials, which present major benefits in dentistry, especially their capability in the bacterial inhibition, cell biocompatibility, anti-demineralization, and remineralization of teeth.

Preparation of Ca doped wrinkled porous silica (Ca-WPS) for the improvement of apatite formation and mechanical properties of dental resins

The purpose of this work was to fabricate and characterize Ca doped wrinkled porous silica (Ca-WPS), and evaluate their effect on the mineralization and mechanical properties of resin composites as functional fillers. Ca-WPS were prepared by sol-gel method and characterized by scanning electron microscopy, transmission electron microscopy and N2 adsorption–desorption measurements. The mineralization properties of the prepared Ca-WPS particles and the resin composites with different amount of Ca-WPS were evaluated by simulated body fluid (SBF) immersion method. The mechanical properties (flexural strength, flexural modulus, compressive strength and microhardness) of the dental resins containing unimodal Ca-WPS fillers and bimodal Ca-WPS fillers with nonporous silica were evaluated by a universal testing machine. Results showed that after immersing in SBF for 5 d, apatite formed on the surface of Ca-WPS and composites containing Ca-WPS fillers, indicating the excellent mineralization property of the prepared Ca-WPS. The mechanical properties of the dental resins increase with the increase of the proportion of unimodal Ca-WPS fillers. The dental resins with bimodal Ca-WPS fillers showed better mechanical properties than the group with only nonporous fillers at the same filler loading (60 wt%). Among all the samples, the dental composites filled with bimodal fillers (mass ratio of Ca-WPS: nonporous silica = 10:50, total filler loading 60 wt%) exhibited the best mechanical performance. The flexural strength, flexural modulus, compressive strength and microhardness of these samples were 26.96%, 42.75%, 16.04% and 54.1% higher than the composites with solid silica particles alone, respectively. Thus, the prepared Ca-WPS could effectively improve the apatite formation and mechanical properties of resin composites.

Influence of Various Desensitizing Mouthrinses and Simulated Toothbrushing on Surface Roughness and Microhardness of Tetric N-Ceram Bulk-Fill Resin Composite: An In Vitro Study and Scanning Electron Microscope Analysis.

Bulk-filled composite resins are popularly used for posterior restorations due to various advantages. Routine oral hygiene measures like toothbrushing and the use of various mouthrinses can influence the mechanical properties of composite resins. Desensitizing mouthrinses are widely used as well, to manage dentinal hypersensitivity. Studies on the influence of desensitizing mouthrinses on bulk-filled composites are limited. Hence, the objective of the present in vitro study was to evaluate the influence of toothbrushing and various desensitizing mouthrinses on the surface roughness and microhardness of Tetric N-Ceram bulk-fill composite resin. Fifty Tetric N-Ceram bulk-fill composite resin disks were prepared and were randomly divided into five groups (n = 10). Group 1 (Control): no toothbrushing and no mouthrinse; Group 2: toothbrushing only; Group 3: toothbrushing + HiOra-K mouthrinse; Group 4: toothbrushing + Listerine Sensitive mouthrinse; and Group 5: toothbrushing + Shy-OR mouthrinse. The specimens were brushed with a soft bristle brush using a toothpaste slurry and immersed in respective mouthrinse twice daily for 1 month. The mean surface roughness (average roughness) and microhardness (Vickers Pyramid number) values were determined and the data were tabulated. Data were analyzed using one-way analysis of variance, Post-hoc Tukey test, and Pearson correlation test. A p-value less than 0.05 was considered statistically significant. Specimens treated with HiOra-K mouthrinse exhibited maximum surface roughness (p < 0.05) and specimens treated with Listerine Sensitive exhibited the least microhardness (p < 0.05). A weak negative correlation was found between surface roughness and microhardness for groups 1, 2, and 5, while a weak positive correlation was found for groups 3 and 4. It is suggested that desensitizing mouthrinses containing alcohol or essential oils can lead to increased surface roughness and reduction in microhardness of bulk-fill composites, which could have an undesirable effect on their clinical performance.

Effect of LEDs with Different Wavelengths on the Microhardness and Nanohardness of Nanohybrid Composite Resins

The aim of this study is to compare the effectiveness of polymerization of nanohybrid composite resins with different colors and thicknesses, photocured by units of different wavelengths through Knoop microhardness (KHN) and Berkovich nanohardness (DUH). One hundred twenty specimens of Tetric N-Ceram (Ivoclar/Vivadent) were divided into groups (n = 5) according to the experimental test, the color of the composite resin (A2 and Bleach-M/BM), the light source: monowave (Elipar™ FreeLight DeepCure-3M/ESPE), dental products-1200 mW/cm2/15 seconds (FL); or polywave (Bluephase-Ivoclar/Vivadent 1200 mW/cm2/15 and 30 seconds (BP), and thickness (irradiated surface,1, 2, and 3 mm). The specimens were stored dry for 24 hours at 37°C and received five indentations on the top and button surfaces. Analysis of variance (ANOVA), Tukey, and Pearson correlation (p < 0.01%) tests were used. A direct correlation was found between KHN and DUH. The higher values of KHN and DUH were observed with Elipar™ FreeLight DeepCure unit in irradiated surface and 1-mm-thick specimens at A2 color. That Elipar™ FreeLight DeepCure unit showed better effectiveness in curing nanohybrid composite resins, used in this work, in different colors and depths as compared to Bluephase in both experimental tests, and that DUH can substitute KHN test when comparing the effectiveness of polymerization. The evaluation of the mechanical properties of composite resins is essential to verify their possible clinical performance.

Mechanical properties of resin composites containing bioactive glass and experimental nano zinc-silica complex

Aim: Secondary caries is an important problem in dental composite restoration, and nanoparticles are commonly added to the structures of resin composites to improve their antimicrobial properties. The aim of this study is to evaluate the mechanical properties of composite materials containing bioactive glass (BAG) and an experimental nano zinc-silica (NZS) complex.&#x0D; Methodology: An experimental resin composite containing 70 wt% filler was produced and used as a control sample. This experimental resin composite was then modified by adding different amounts of BAG (10%), NZS (10%), and both BAG and NZS (10% + 10%). NZS was synthesized in situ by milling zinc and silica to nanoscale level. Compressive strength and flexural strength were investigated using a universal testing machine. Data were analyzed using one-way ANOVA and the Tukey post-hoc test.&#x0D; Results: There were no statistically significant differences in compressive strength caused by the filler amount, but statistically significant changes were found in flexural strength. Although the addition of antimicrobial agents to resin composites reduces their physical properties, this is not a clinically unacceptable limit.&#x0D; Conclusion: NZS exhibits better mechanical properties than does BAG, but both materials can be used safely in restorative materials.&#x0D; &#x0D; How to cite this article: Tunçdemir MT, Demirel MG. Mechanical properties of resin composites containing bioactive glass and experimental nano zinc-silica complex. Int Dent Res 2021;11(Suppl.1):137-42. https://doi.org/10.5577/intdentres.2021.vol11.suppl1.21&#x0D; &#x0D; Linguistic Revision: The English in this manuscript has been checked by at least two professional editors, both native speakers of English.&#x0D;

The Influence of Popular Beverages on Mechanical Properties of Composite Resins.

Currently, composite resins are used in many restorative procedures. Previous studies showed that drinking beverages may affect the mechanical properties such as microhardness or flexural strength of dental composite resins. The aim of the present study was to investigate the influence of common beverages on the mechanical properties of composite resins. Samples of the materials were prepared according to the ISO 4049:2010 standard and producer’s recommendations. The samples were next conditioned in tested fluids: distilled water, sparkling water, Coca-Cola, Red Bull and orange juice for 7 days. Vickers microhardness and flexural strength testing was performed after 7 days. Performed statistic tests confirmed the significance of microhardness changes of the tested materials in terms of both different conditioning of the samples and different composite materials. The mean flexural strength of composites was highest in distilled water and it was reduced after one week in different beverages. We conclude that all tested beverages influenced on Vickers microhardness of tested composite resins. Flexural strength only in one material was statistically significantly influenced by tested beverages. The results of this study should be taken into consideration by a dentist preparing recommendations for the patients after dental treatment with usage of composite material or after cementing composite based fixed dentures.

Synthesis and characterization of cellulose/hydroxyapatite based dental restorative composites

The aim of this study was an in-situ synthesis of hydroxyapatite (HA) on cellulose fibers to be used as a new reinforcing agent for dental restorations. The microwave irradiation method was used for synthesis and the materials were characterized with analytical techniques. The prepared dental resin composites were mechanically tested by a universal testing machine and electrodynamic fatigue testing system. FTIR, XRD, SEM/EDS analysis confirmed the successful synthesis of HA on cellulose fibers. The Alamar blue biocompatibility assay showed more than 90% cell viability for the prepared cellulose/HA. The mechanical properties of resin composites improved with cellulose content from 30 wt.% to 50 wt.% in the polymer matrix. Substantially, increasing the cellulose/HA content from 40% to 50% improved the mechanical properties. The results suggested that HA could be successfully synthesized on cellulose fibers using microwave irradiation and contributed to improving the mechanical properties of dental resin composites.

Optimisation of Flexural strength in Zirconia nanoclusters of the Bis-GMA & TEGDMA based dental composites

Chewing food is a dynamic and continuous process. tooth is an important component which can not be neglected. Accordingly to WHO(world health organization) report nearly 100% people have decay once in life. Decay can be filled with gold, silver amalgam. Composites have advantages by providing natural colour of tooth, less tooth removal required to fill cavity and natural tooth structure can be maintained. The aim of this work is to present an analysis of the composites and furnish dentists with a basis that can provide criteria for choosing one or another to suit their treatment. The mechanical properties of composite resins are importantly depends upon filler content. Dental composites are using silica, quartz and alumina glass as filler for long time. Zirconia is the latest addition as filler. Chewing of food is a dynamic situation in which many forces are acting in all possible direction, the most important being the flexural force. Our aim is to optimise the flexural strength in Zirconia nanoclusters of the Bis-GMA & TEGDMA based dental composites. The aim of work is to find out best combination of composite material.

Effect of Preheating and Fatiguing on Mechanical Properties of Bulk-fill and Conventional Composite Resin.

Bulk-fill composite resins may have comparable mechanical properties to conventional composite resin. Preheating does not reduce the mechanical properties of composite resins.

Effect of light-curing time on light-cure/post-cure volumetric polymerization shrinkage and regional ultimate tensile strength at different depths of bulk-fill resin composites.

The aim of this study was to investigate volumetric polymerization shrinkage (VS), using swept-source optical coherence tomography (SS-OCT), of bulk-fill composites with different light-curing strategies; immediately after light-irradiation and after 24 h, and to evaluate their regional ultimate tensile strength (UTS) at different curing depths. The immediate VS after photo-polymerization decreased when the curing light-curing time was reduced from 20 to 10 to 5 s. On the other hand, their VS values after 24 h significantly increased due to the post-cure polymerization, resulting in similar VS values at all the light-curing times. Five seconds light-curing decreased the regional UTS of resin composites after the 24 h period compared with the 10 and 20 s light-curing regimes; therefore, the remarkable progress of post-cure polymerization after light-curing for a short time would not lead to an improvement in the mechanical properties of resin composites. The influence of the light-curing time on the curing depth was dependent upon the bulk-fill composite material.

Dispersion Stability and Mechanical Properties of ZrO2/High-temp Composite Resins by Nano- and Micro-particle Ratio for Stereolithography 3D Printing

This study examines the role of the nano- and micro-particle ratio in dispersion stability and mechanical properties of composite resins for SLA(stereolithography) 3D printing technology. VTES(vinyltriethoxysilane)-coated ZrO2 ceramic particles with different nano- and micro-particle ratios are prepared by a hydrolysis and condensation reaction and then dispersed in commercial photopolymer (High-temp) based on interpenetrating networks(IPNs). The coating characteristics of VTES-coated ZrO2 particles are observed by FE-TEM and FT-IR. The rheological properties of VTEScoated ZrO2/High-temp composite solution with different particle ratios are investigated by rheometer, and the dispersion properties of the composite solution are confirmed by relaxation NMR and Turbiscan. The mechanical properties of 3Dprinted objects are measured by a tensile test and nanoindenter. To investigate the aggregation and dispersion properties of VTES-coated ZrO2 ceramic particles with different particle ratios, we observe the cross-sectional images of 3D printed objects using FE-SEM. The 3D printed objects of the composite solution with nano-particles of 80 % demonstrate improved mechanical characteristics.