Lower Flexural Modulus Research Articles

Physicochemical characterization of experimental resin-based materials containing calcium orthophosphates or calcium silicate

ObjectiveTo evaluate experimental dimethacrylate-based materials containing calcium orthophosphates or calcium silicate particles in terms of their optical, mechanical and Ca2+ release behaviour. MethodsDicalcium phosphate dihydrate (DCPD), hydroxyapatite (HAp), beta-tricalcium phosphate (β-TCP) or calcium silicate (CaSi) particles were added to a photocurable BisGMA/TEGDMA resin (1:1 in mols) at a 30 vol% fraction. Materials containing silanized or non-silanized barium glass particles were used as controls. Degree of conversion (DC) at the top and base of 2-mm thick specimens was determined by ATR-FTIR spectroscopy (n = 5). Translucency parameter (TP) and transmittance (%T) were determined using a spectrophotometer (n = 3). Biaxial flexural strength (BFS) and flexural modulus (FM) were determined by biaxial flexural testing after 24 h storage in water (n = 10). Ca2+ release in water was determined during 28 days by inductively coupled plasma optical emission spectrometry (n = 3). Statistical analysis was performed using ANOVA/Tukey test (DC: two-way; TP, %T; BFS and FM: one-way; Ca2+ release: repeated measures two-way, α = 5 %). Results: CaSi and β-TCP particles drastically reduced DC at 2 mm, TP and %T (p < 0.001). Compared to both controls, all Ca2+-releasing materials presented lower BFS (p < 0.001) and only the material with DCPD showed significantly lower FM (p < 0.05). The material containing CaSi presented the highest Ca2+ release, while among materials formulated with calcium orthophosphates the use of DCPD resulted in the highest release (p < 0.001). SignificanceCaSi particles allowed the highest Ca2+ release. Notwithstanding, the use of DCPD resulted in a material with the best compromise between optical behaviour, DC, strength and Ca2+ release.

Effect of different weft-knitted structures on the mechanical performance of bio-based flexible composites

This work investigates composites from renewable resources that exhibit high flexibility. The effect of three different weft-knitted structures on the tensile properties, flexural properties, tear resistance and puncture impact properties is analyzed in combination with two different flexible matrix materials. Furthermore, the potential of the knitted structures in flexible composites is compared to a woven fabric and comprehensively discussed. The tear resistance and the total absorbed energy in puncture impact tests were unaffected by the matrix material. Among the knitted structures, the highest tensile strength, tear resistance and impact properties were achieved with the interlock structure, whereas the double jersey with tuck stitch structure resulted in the lowest flexural modulus. However, a much higher tensile strength was achieved with the woven fabric, at the expense of a higher flexural modulus. Overall, knitted structures proved promising to be used in bio-based flexible composites for applications requiring high flexibility without the need for high tensile strength.

Mechanical properties of interply and intraply hybrid laminates based on jute-glass/epoxy composites

Currently, hybridization of natural-synthetic fibers within a polymeric matrix has received wide attention owing to its promising properties. This study investigated the mechanical properties of interply and intraply hybrid jute (J)-glass (G) fiber/epoxy composites. The mechanical properties (i.e., tensile, flexural, and impact) of the pure jute, pure glass, and their hybrid composites were evaluated. The prepared composite samples consisted of five plies of woven fabrics. Interply hybrid composites comprised three layering sequences: G3JG, GJGJG, and 2GJ2G. Intraply hybrid composites of similar co-woven plies were fabricated by either the alternative replacement of a single glass yarn with a single jute yarn (G1J1) or two jute yarns (G1J2). The results showed that increasing the glass fraction in the interply hybrid composites improved their tensile properties. The two intraply hybrid composites provided almost similar tensile moduli, while the tensile strength of the G1J1 samples was approximately 41% higher than that of the G1J2 counterparts. The maximum flexural properties were provided by 2GJ2G composites, followed by GJGJG, and they were interestingly higher than those of pure glass composites. The G1J1 intraply hybrid composites offered a higher flexural strength and a lower flexural modulus than those provided by the pure glass composites. Compared to the pure glass composites, the impact strengths of the 2GJ2G and GJGJG samples decreased by 4% and 16%, respectively. In summary, the GJGJG hybrid composites exhibited the highest specific tensile, flexural, and impact properties compared to the other hybrid composites.

Highly Efficient and Flexible Perovskite Nanocrystal Light-Emitting Diodes on Disposable Paper Substrates.

Perovskite nanocrystals have been widely applied in the field of light-emitting diodes (LEDs) due to their excellent optoelectronic properties. However, there is generally a serious degradation of device efficiency when transferring the device from rigid to flexible substrates due to the high roughness, poor wettability, and low endurance temperature of flexible substrates. Herein, a highly flexible perovskite light-emitting diode (PeLED) by utilizing label paper as substrates and poly(methyl methacrylate) (PMMA) as the modified layer was reported. Compared with the reference device based on commonly used polyethylene terephthalate (PET) substrates, the label paper/PMMA-based devices did not show the degraded device performance when transferring from rigid to flexible substrates. This is mainly because of low roughness and good wettability of PMMA-modified label paper, which significantly improve the film-forming ability of the bottom electrode and functional layer. Furthermore, the flexibility of both devices was explored by a three-point bending flexural test, indicating that the label paper-based device has better bending stability than the polyethylene terephthalate-based one due to the lower flexural modulus for label paper. As a result, the label paper-based flexible PeLEDs exhibited the highest external quantum efficiency (EQE) of 14.3% among perovskite nanocrystal-based flexible LEDs and preeminent flexibility with 29% luminance degradation after bending for 1000 cycles at a small radius of 1.5 mm. This extension of the substrate to paper will widen the opportunity of PeLEDs in extremely flexible and inexpensive applications.

Design and 3D printing of novel titanium spine rods with lower flexural modulus and stiffness profile with optimised imaging compatibility.

To manufacture and test 3D printed novel design titanium spine rods with lower flexural modulus and stiffness compared to standard solid titanium rods for use in metastatic spine tumour surgery (MSTS) and osteoporosis. Novel design titanium spine rods were designed and 3D printed. Three-point bending test was performed to assess mechanical performance of rods, while a French bender was used to assess intraoperative rod contourability. Furthermore, 3D printed spine rods were tested for CT & MR imaging compatibility using phantom setup. Different spine rod designs generated includes shell, voronoi, gyroid, diamond, weaire-phelan, kelvin, and star. Tests showed 3D printed rods had lower flexural modulus with reduction ranging from 2 to 25% versus standard rod. Shell rods exhibited highest reduction in flexural modulus of 25% (~ 77.4GPa) and star rod exhibited lowest reduction in flexural modulus of 2% (100.8GPa). 3D printed rod showed reduction in stiffness ranging from 40 to 59%. Shell rod displayed highest reduction in stiffness of 59% (179.9N/mm) and gyroid had least reduction in stiffness of 40% (~ 259.2N/mm). Rod bending test showed that except gyroid, other rod designs demonstrated lesser bending difficulty versus standard rod. All 3D printed rods demonstrated improved CT/MR imaging compatibility with reduced artefacts versus standard rod. By utilising novel design approach, we successfully generated a spine rod design portfolio with lower flexural modulus/stiffness profile and better CT/MR imaging compatibility for potential use in MSTS/other conditions such as osteoporosis. Thus, exploration of new rod designs in surgical application could enhance treatment outcome and improve quality of life for patients.

Load-bearing composite fracture-fixation devices with tailored fibre placement for toy-breed dogs

Fibre reinforced composites are attractive materials for hard tissue reconstructions, due to the high strength and low flexural modulus. However, lack of contourability in the operation theatre inhibits their clinical applications.The study presents a novel in situ contourable composite implant system for load-bearing conditions. The implant system consists of a thin bioresorbable shell with several cavities, much like bubble-wrap. The central cavity contains a semi-flexible glass fibre preform prepared using Tailored Fibre Placement method. The preform is either pre-impregnated with a light curable resin, or the resin is injected into the cavity during the surgical procedure, followed by light curing. The semi-flexible glass fibre preforms were also examined as separate devices, “miniplates”. Two types of miniplates were scrutinized, a simplified pilot design and a spatially refined, “optimized” design. The optimized miniplates were implemented as biostable and bioresorbable versions.The feasibility of the in situ contourable composite implant system was demonstrated. The potential of Tailored Fibre Placement for the semi-flexible glass fibre preforms and miniplates was confirmed in a series of biomechanical tests. However, structural optimization is required. Antebrachial fractures in toy-breeds of dogs are exemplar veterinary applications of the devices; further applications in veterinary and human patients are foreseen.

Design and 3D printing of novel titanium spine rods with lower flexural modulus & stiffness profile with optimised imaging compatibility

Design and 3D printing of novel titanium spine rods with lower flexural modulus & stiffness profile with optimised imaging compatibility

Anisotropicity and flexibility in trilayered microfibrous substrates promote heart valve leaflet tissue engineering

Heart valve leaflet substrates with native trilayer and anisotropic structures are crucial for successful heart valve tissue engineering. In this study, we used the electrospinning technique to produce trilayer microfibrous leaflet substrates using two biocompatible and biodegradable polymers—poly (L-lactic acid) (PLLA) and polycaprolactone (PCL), separately. Different polymer concentrations for each layer were applied to bring a high degree of mechanical and structural anisotropy to the substrates. PCL leaflet substrates exhibited lower unidirectional tensile properties than PLLA leaflet substrates. However, the PLLA substrates exhibited a lower flexural modulus than the PCL substrates. These substrates were seeded with porcine valvular interstitial cells (PVICs) and cultured for one month in static conditions. Both substrates exhibited cellular adhesion and proliferation, resulting in the production of tissue-engineered constructs. The PLLA tissue-engineered constructs had more cellular growth than the PCL tissue-engineered constructs. The PLLA substrates showed higher hydrophilicity, lower crystallinity, and more significant anisotropy than PCL substrates, which may have enhanced their interactions with PVICs. Analysis of gene expression showed higher α-smooth muscle actin and collagen type 1 expression in PLLA tissue-engineered constructs than in PCL tissue-engineered constructs. The differences in anisotropic and flexural properties may have accounted for the different cellular behaviors in these two individual polymer substrates.

PEEK polymer in orthodontics: a scoping review.

The aim of this scoping review was to evaluate the application of polyether-ether-ketone (PEEK) in orthodontics. Search strategies were executed for electronic databases through PubMed, Scopus, Web of Science, Lilacs, Opengrey, Embase, Cochrane Library and records identified through hand or electronic search. The keywords used were: "PEEK" OR "Polyether-ether-ketone" AND "orthodontics". The period selected of article publication was from January 2015 to June 2021. Due to excellent physical, mechanical, aesthetic properties and biocompatibility, its low plaque affinity and flexural modulus close to enamel and dentin, PEEK can be used also in orthodontics. However, more clinical research should be done to find out all the advantages and disadvantages of this material.

Facile fabrication of lightweight carbon fiber/phenolic ablator with improved flexibility via natural rubber modification

The rigidity and low strain-to-failure of the phenolic impregnated carbon ablator seriously restrict the application of this state-of-the-art thermal protection material. In this study, to improve the flexibility of carbon fiber/phenolic ablator (CFPA), natural rubber (NR) was deposited homogeneously onto the surface of the carbon fibers through impregnation. Thus, a “bridge” was built between the carbon fiber reinforcement and the phenolic resin aerogel matrix, allowing the interface better connection and better deformation ability. Experimental results indicate that, compared with the unmodified, modified CFPA has lower flexural modulus and higher fracture strain, 6.3 MPa and 39.6% at the optimal NR latex mass fraction respectively, while maintains low density, good thermal insulation properties, and excellent ablation properties. The facile fabrication via natural rubber modification of CFPA improved its flexibility and could broaden the application scenarios of lightweight carbon/phenolic composite.

Mechanical and dynamic responses of unidirectional/woven carbon fiber reinforced thermoset and thermoplastic composites after low velocity impact

It is highly important to determine how mechanical and dynamic properties of composite materials will change after impact loads considering the coupled effects of composite design parameters. For these reasons, three-point bending and vibration tests have been carried out for the carbon fiber reinforced thermoset and thermoplastic composites with various stacking sequences before and after low velocity impact, and it is expected that these results achieved from the current study will be beneficial for applications where high damping and impact resistance are demanded together. In this context, vibration tests were carried out under free-free boundary conditions, and their natural frequencies, flexural moduli and structural damping were obtained. Furthermore, three-point tests were conducted in the elastic region with 1 mm/min crosshead speed using a universal test machine, and thus flexural moduli of the composite specimens were obtained. The results were validated by comparing the flexural moduli obtained from the both vibration and three-point bending tests, found to be reliable and comparable. As a result of the current study, it was concluded that woven fabric reinforced composite specimens exhibited 50% higher specific damping capacity (SDC) but 70% lower flexural modulus than unidirectional specimens thanks to biaxially fiber alignment. On the other hand, specific damping capacities of the thermoset and thermoplastic composites with different stacking sequences have been examined, and it was observed that thermoset specimens exhibited unexpectedly 192% higher SDC compared to the thermoplastics. This was interpreted as even though thermoplastics are normally expected to exhibit more damping than thermosets, stacking sequence being more effective on damping responses. Apart from that, although there were slight changes in material properties due to degradation in structural integrity after 2 m/s and 3 m/s low-velocity impacts, it was not found to be significantly effective due to the limited damage areas.

Low-velocity impact and residual flexural properties of intraply hybrid laminates reinforced with glass and flexible fibers

In this study, Low-velocity impact and residual flexural properties of intraply hybrid epoxy composites reinforced with E-glass, aramid, high tenacity polyester (HTPES), and ultra-high molecular weight polyethylene (UHMWPE) fibers were investigated. Flexural properties of the samples were measured before and after applying a 5 J impact by performing the three-point bending test. The Charpy impact test was also performed on the samples to measure their impact resistance. Based on the results, the pure glass fiber composite had 85–112% higher flexural strength and 55–127% higher flexural energy than hybrid samples, but 18% and 27–34% lower flexural modulus than hybrid glass/aramid and glass/UHMWPE composites, respectively. However, hybrid samples were considerably less affected by the impact loads. The loss in flexural strength and flexural energy after the impact for hybrid samples were 2–20% and 2.5–34% and for pure glass sample 63% and 71%, respectively. Scanning electron micrographs of the fractured surface of samples after the Charpy impact showed that the flexible fibers can contribute to the impact strength of the composite with such mechanisms as elongation, pull-out, and folding.

Evaluation of a photo-initiated copper(I)-catalyzed azide-alkyne cycloaddition polymer network with improved water stability and high mechanical performance as an ester-free dental restorative

ObjectiveThe objective is to develop and characterize an ester-free ether-based photo-CuAAC resin with high mechanical performance, low polymerization-induced stress compared with common BisGMA/TEGDMA (70/30) resins, and improved water stability in comparison to previously developed urethane-based photo-CuAAC resins. MethodsTriphenyl-ethane-centered ether-linked tri-azide monomers were synthesized and co-photopolymerized with ether-linked tri-alkyne monomers under visible light irradiation using a copper(II) pre-catalyst and CQ/EDAB as the initiator. The ether-based CuAAC formulation was investigated for thermo-mechanical properties, polymerization kinetics and shrinkage stress, and flexural properties with respect to a conventional BisGMA/TEGDMA (70/30) dental resin. In addition, both the ether-based CuAAC resin and the urethane-based CuAAC resin were examined for their water stability using the BisGMA/TEGDMA (70/30) resin as a control. ResultsThe ether-based CuAAC network (AK/AZ-1) exhibited a slightly lower glass-transition temperature compared with the BisGMA/TEGDMA network (108 °C vs 128 °C), but because of its much sharper glass transition, the AK/AZ-1 CuAAC-network maintained storage modulus higher than 1 GPa up to 100 °C. In addition, the ether-based AK/AZ-1 network exhibited reduced shrinkage stress (0.56 MPa vs 1.0 MPa) and much higher flexural toughness (7.6 MJ/m3vs 1.6 MJ/m3) while showing slightly lower flexural modulus and slightly higher flexural strength compared with the BisGMA/TEGDMA network. Moreover, the ether-based AK/AZ-1 CuAAC network displayed comparable water stability in comparison to the BisGMA/TEGDMA network with slightly higher water sorption (46 μg/mm3vs 38 μg/mm3) and much lower water solubility (2.3 μg/mm3vs 4.4 μg/mm3). SignificanceEmploying the ether-based hydrophobic CuAAC formulation significantly improved the water stability of the CuAAC network compared with previously developed urethane-based CuAAC networks. Furthermore, compared with the conventionally used BisGMA/TEGDMA formulation, the reduced shrinkage stress, comparable flexural strength/flexural modulus, and the superior flexural toughness of the ether-based CuAAC network make it a promising ester-free alternative to the currently widely-used methacrylate-based dental restoratives.

Incorporation of Copper-Doped Mesoporous Bioactive Glass Nanospheres in Experimental Dental Composites: Chemical and Mechanical Characterization.

Experimental dental resin composites incorporating copper-doped mesoporous bioactive glass nanospheres (Cu-MBGN) were designed to impart antibacterial and remineralizing properties. The study evaluated the influence of Cu-MBGN on the mechanical properties and photopolymerization of resin composites. Cu-MBGN were synthesized using a microemulsion-assisted sol–gel method. Increasing amounts of Cu-MBGN (0, 1, 5, and 10 wt %) were added to the organic polymer matrix with inert glass micro- and nanofillers while maintaining a constant resin/filler ratio. Six tests were performed: X-ray diffraction, scanning electron microscopy, flexural strength (FS), flexural modulus (FM), Vickers microhardness (MH), and degree of conversion (DC). FS and MH of Cu-MBGN composites with silica fillers showed no deterioration with aging, with statistically similar results at 1 and 28 days. FM was not influenced by the addition of Cu-MBGN but was reduced for all tested materials after 28 days. The specimens with 1 and 5% Cu-MBGN had the highest FS, FM, MH, and DC values at 28 days, while controls with 45S5 bioactive glass had the lowest FM, FS, and MH. DC was high for all materials (83.7–93.0%). Cu-MBGN composites with silica have a potential for clinical implementation due to high DC and good mechanical properties with adequate resistance to aging.

Microstructure and properties of zirconia-alumina composites fabricated via powder injection molding

This study aimed to fabricate zirconia-alumina composites via powder injection molding and investigated the effects of alumina addition on microstructure as well as physical properties of the composites. Zirconia-alumina composites were prepared using polyethylene glycol (PEG) and polyvinyl butyral (PVB) as binders. The powder loading was fixed at 38 vol%, and PEG: PVB binder weight ratio was fixed at 80:20. Alumina content within ceramic component was varied at 0, 10, 20, 30, 40 and 50 vol% to observe the effect of alumina on the composite structures and properties. The injection molding was done at 190℃ followed by water debinding of PEG at 40℃. Thermal debinding of PVB at 450℃ was performed prior to sintering at 1450℃. From the density measurement via Archimedes’ method, the relative density of sintered samples was found to be highest at 10 vol% alumina and gradually lower at higher alumina content. The condition with highest density yielded the highest flexural modulus and flexural strength. XRD indicated that tetragonal zirconia phase coexisted with alumina when alumina was added. Above 20 vol% alumina, monoclinic zirconia was also detected. The increased porosity in samples with high alumina content, as confirmed in SEM morphological observation, correlated with lower flexural strength and lower flexural modulus. The results illustrated the feasibility of powder injection molding in the production of zirconia-alumina composites and the optimum condition in this study was 10 vol% alumina.

THE DEVELOPMENT OF FLEXIBLE DENTURE MATERIALS AND CONCEPT: A NARRATIVE REVIEW

Introduction: Flexible denture is an alternative treatment modality for removable partial denture (RPD) that aid the retention by ensuring seal around the entire border of the denture. It is also referred as hypoallergenic denture especially for those who are allergic towards conventional acrylic denture which is the poly-methylmethacrylate monomer (PMMA) and metal (cobalt chromium). The flexible material exhibits lower flexural modulus than conventional type of baseplate material denture that makes it nearly unbreakable. Nowadays, there are a handful of different flexible materials in the dental market for the general dental practitioners to choose but somehow the studies on the properties of these different types of flexible materials are sparse. Objectives: The present study is to study the development of the flexible materials, the different type of flexible materials and their physical properties. Methods: From the limited article journals available, the authors have summarized the history, development and constituents of different type of flexible materials used in fabricating denture. Besides that, the authors also discussed about the indications, contraindications, advantages and disadvantages of the materials in denture constructions based on all the published researches available on this topic using published materials available in the dental library, University of Malaya and the databases (Science Direct, PubMed). Conclusion: Each flexible material has its pros and cons. Therefore, careful selection of material and understanding of the flexible dentures’ indications and contraindications are utmost importance to make sure the best treatment outcome. Hence, patients’ best interest and quality of life can be upheld.

Effect of different lignocellulosic fibre based needle punched nonwovens on mechanical properties of bio-reinforced composite

Bio-reinforced composites have been prepared using polyester resin matrix and cross-laid needle-punched nonwoven fabrics of different lignocellulosic natural fibres (Jute, flax, sunhemp, kenaf, ramie, sisal, coir and pineapple) as well as jute-polypropylene and jute-acrylic blend reinforcement. The composite properties, such as tensile strength, flexural strength and impact strength, have been evaluated. The findings show that the tensile strength and stiffness are very high in case of sisal (211 MPa and 21 GPa) and flax (304 MPa and 30 GPa), which is almost comparable with e-glass. Properties of sunnhemp, coir, pineapple, and kenaf are found superior to ramie, jute and jute blend. The impact strength of pineapple composite (751 kJ/m 2 ) is found very high. The mechanical properties of woven fabric composite are much lower than nonwoven fabric. Cross- direction of composite from nonwoven shows superior mechanical properties as compared to that of the machine direction. Synthetic fibre shows low stiffness (1 GPa) and flexural modulus (1.2 GPa) but very high impact strength (655 kJ/m 2 ). Hence, most of the lingo-cellulosic fibres are suitable for composite reinforcement, especially where the high performance of glass-reinforced plastic is not essential.

Dual modified nanosilica particles as reinforcing fillers for dental adhesives: Synthesis, characterization, and properties

A facile procedure has been devised to develop a novel dentin bonding system containing poly (acrylic acid)-grafted-silanized fumed silica particles as reinforcing filler, with high stability of nanoparticle dispersion and enhanced bond strength and mechanical properties. In the first step, the silanization of fumed silica nanoparticles was performed in the following conditions: (i) ethanol-water solution with a pH of 5 and (ii) cyclohexane with a pH of 9 using trimethoxysilylpropyl methacrylate (γ–MPS) as a reactive silane coupling agent. FTIR and TGA analyses confirmed the presence of silane in the resultant structure and enhanced dispersion stability of modified particles was proved by a separation analyzer and also zeta potential analyses. In the second step, free radical polymerization of acrylic acid monomers in the presence of silanized nanoparticles was carried out and poly (acrylic acid) -grafted- silanized fumed silica were acquired. The flexural strength and fracture toughness of the adhesive containing 0.2 wt.% of the dual modified filler reached maximum of 70.4 MPa and 1.34 MPa m1/2, respectively, showing average improvements of 74% and 179%, respectively, in comparison with the adhesive without filler. Flexural modulus values did not significantly change with increasing the filler content except the adhesive containing 5 wt.% having the lowest flexural modulus. The highest microtensile bond strength was also observed at 0.2 wt.% filler content showing the average improvements of 197% as compared with the neat adhesive. Energy dispersive X-ray (EDX) mapping confirmed a homogenous and uniform distribution of the fillers in the adhesive matrix containing 0.2 wt.% and 0.5 wt.% of filler while incorporation of 5 wt.% led to large particle aggregates. SEM images of the fracture surface of the adhesive with different filler contents subjected to fracture toughness test showed rougher surface and longer crack path by increasing filler concentration. The adhesive containing 0.2 wt.% of filler perfectly penetrated into the dentin tubules proved by the SEM micrographs in microtensile bond strength test.

Development and characterisation of dental composites containing anisotropic fluorapatite bundles and rods

ObjectivesTo develop dental composites incorporating fluorapatite (FA) crystals as a secondary filler and to characterise degree of conversion, key mechanical properties and fluoride release. MethodsFA rod-like crystals and bundles were hydrothermally synthesised and characterised by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), X-ray diffraction (XRD) and 19F MAS-NMR. Composites were formulated containing BisGMA/TEGDMA/BisEMA and barium-aluminium-silicate glass (0FA). FA crystals were incorporated at 10 (10FA), 20 (20FA), 30 (30FA) and 40wt% (40FA) maintaining a filler content of 80wt% (63–67vol%). Degree of conversion (DC), flexural strength (FS), flexural modulus (FM), fracture toughness (K1C), Vickers hardness (HV) and 2-body wear were measured. Fluoride release was measured in neutral and acidic buffers. ResultsXRD and 19F MAS-NMR confirmed that only FA was formed, whilst SEM revealed the presence of single rods and bundles of nano-rods. DC ranged between 56–60% (p>0.05). FA composites showed lower FM and lower FS (p<0.05), but comparable wear resistance and HV (p>0.05) to 0FA. 30FA and 40FA showed similar K1C to 0FA (p>0.05), with SEM showing evidence of toughening mechanisms, whereas 10FA and 20FA showed lower K1C (p<0.05). FA containing composites released fluoride that was proportional to the amount of FA incorporated (p<0.05) but only under acidic conditions. SignificanceThe addition of FA to the experimental composites reduced strength and stiffness but not the DC, hardness or wear rate. 30FA and 40FA had a higher K1C compared to other FA groups. Fluoride release occurred under an accelerated acidic regime, suggesting potential as a bioactive ‘smart’ composite.

Outcomes of ultra-fast (3 s) photo-cure in a RAFT-modified resin-composite

ObjectiveThis study evaluates critical material properties resulting from ultra-fast (3 s) photo-polymerization at high radiant emittance of a pre-production, novel bulk-fill resin-based composite (RBC) modified for reversible addition-fragmentation chain transfer (RAFT) polymerization. MethodsThe output characteristics of the associated light curing unit (LCU) were measured on a laboratory-grade spectrometer. Real-time Fourier Transform Infrared Spectroscopy (FTIR) and mechanical investigations (depth-sensing indentation with a linear and spatial distribution of the measured properties, and three-point bend tests) were performed using, as reference material, an established bulk-fill RBC of comparable chemical composition. Micro-mechanical properties were mapped to quantify material tolerance to sub-optimal curing conditions (exposure distance of 5 mm and an angulation of the LCU of 20° and 30°) vs. ideal curing conditions (exposure distance of 0 mm and no angulation), with 3 s polymerization. Weibull statistics, one- and multiple-way analysis of variance (ANOVA) and the Tukey honestly significant difference (HSD) post hoc-test (α = 0.05) were used for data comparison. ResultsThe change in cure mechanism to RAFT polymerisation gave slightly faster initial polymerisation kinetics, but DC measured 300 s post irradiation was similar, irrespective of material, curing depth or polymerisation condition. Slightly better polymerisation, in layers thicker than 4-mm, was identified in the RAFT polymerised RBC. However, slightly lower flexural modulus and hardness, up to 1.5-mm subsurface, were related to the ca. one wt.% lower inorganic filler content. SignificanceRAFT polymerisation induced comparable properties to a RBC cured via free radical polymerisation of comparable chemical composition. The RAFT polymerised RBC with high irradiance for 3 s was equivalent to 10 s of moderate irradiance. However, the clinical tolerance for 3 s irradiance should be limited to an exposure distance of 5-mm and angulation of the LCU should be avoided. If this is not possible, an additional 3 s polymerisation is recommended.