Glass Filler Particles Research Articles

Modifying dental composites to formulate novel methacrylate-based bone cements with improved polymerisation kinetics, and mechanical properties

ObjectivesThe aim was to develop bone composites with similar working times, faster polymerisation and higher final conversion in comparison to Cortoss™. Additionally, low shrinkage/heat generation and improved short and longer-term mechanical properties are desirable. MethodsFour urethane dimethacrylate based composites were prepared using tri-ethylene-glycol dimethacrylate (TEGDMA) or polypropylene dimethacrylate (PPGDMA) diluent and 0 or 20 wt% fibres in the glass filler particles. FTIR was used to determine reaction kinetics, final degrees of conversions, and polymerisation shrinkage/heat generation at 37 °C. Biaxial flexural strength, Young’s modulus and compressive strength were evaluated after 1 or 30 days in water. ResultsExperimental materials all had similar inhibition times to Cortoss™ (140 s) but subsequent maximum polymerisation rate was more than doubled. Average experimental composite final conversion (76%) was higher than that of Cortoss™ (58%) but with less heat generation and shrinkage. Replacement of TEGDMA by PPGDMA gave higher polymerisation rates and conversions while reducing shrinkage. Early and aged flexural strengths of Cortoss™ were 93 and 45 MPa respectively. Corresponding compressive strengths were 164 and 99 MPa. Early and lagged experimental composite flexural strengths were 164–186 and 240–274 MPa whilst compressive strengths were 240–274 MPa and 226–261 MPa. Young’s modulus for Cortoss™ was 3.3 and 2.2 GPa at 1 day and 1 month. Experimental material values were 3.4–4.8 and 3.0–4.1 GPa, respectively. PPGDMA and fibres marginally reduced strength but caused greater reduction in modulus. Fibres also made the composites quasi-ductile instead of brittle. SignificanceThe improved setting and higher strengths of the experimental materials compared to Cortoss™, could reduce monomer leakage from the injection site and material fracture, respectively. Lowering modulus may reduce stress shielding whilst quasi-ductile properties may improve fracture tolerance. The modified dental composites could therefore be a promising approach for future bone cements.

Thermal shock behavior and high-temperature oxidation performance of PDC-based environmental barrier coatings on AISI 441 stainless steel

The present work aimed to investigate the influence of different testing conditions on high-temperature oxidation performance of selected polymer-derived ceramic (PDC) environmental barrier coatings on AISI 441 stainless steel substrates. For this purpose, two types of double-layer PDC-based glass-ceramic coatings containing passive and glass fillers were fabricated using a combination of dip coating and spray coating processes. To evaluate the performance of the coatings in harsh environments simulating real applications, thermal cyclic tests in dry air, long-term static oxidation tests in humidified air, and thermal shock tests were performed. YAG, monoclinic ZrO2, cubic ZrO2, and a newly formed BaAl2Si2O8 phase were identified from XRD patterns of the tested PDC coatings. The SiO2 reflections, detected in the coatings after pyrolysis, were absent after both oxidation and thermal shock resistance tests. The SEM examination indicated that the performance of the studied PDC coatings was mainly affected by the microstructural modifications induced by differential sintering of the glass filler particles, leading to an expansion of existing pores, which represented preferential failure sites in the coating. In contrast, the existence of internal porosity relieved the residual stresses and reduced the driving force for crack extension, resulting in an increased thermal shock resistance. A combined scratch test based on the acoustic emission signal record along with the SEM observation of the resulting scratch tracks were also carried out. The most significant damage event in both tested PDC coatings was partial decohesion and surface chipping, which, however, did not translate into a critical adhesive failure. These findings confirm that the developed PDC coatings can be used for the protection of stainless steel in oxidizing environments up to 900 °C.

Optimized regression model for microhardness of experimental dental composite resins with nano-hydroxyapatite filler particles

ABSTRACT Background: Bioactive materials produce a biological reaction such as stimulation of pulpal cells for dentinal repair and induction of the formation of hydroxyapatite. Aim: The study was conducted to evaluate the microhardness of experimental dental composite resins (EDCR) containing nano-hydroxyapatite, zirconia, and glass filler particles. Materials and Methods: The EDCR was prepared with varying concentrations of barium aluminum fluoride glass (5–20 nm), zirconia (4–11 nm), and hydroxyapatite (20–80 nm) filler particles added to the organic matrix. The L9 orthogonal array was used to prepare a sample size of 27 samples. Disc-shaped specimens of 10 mm diameter and 4 mm thickness were prepared using the American Society for Testing and Materials E384 standard for testing the microhardness. The Taguchi’s method of optimization was used to obtain a composite with optimum microhardness. A regression model was developed. Results: EDCR with 23.7% of zirconia, 27.5% of nano-hydroxyapatite, and 20% of glass filler particles gave the optimum microhardness of 222.67 HV. The confirmatory experimental test of EDCR gave a microhardness of 225 HV. The model developed with regression equation for the microhardness was 60–123 Z + 114 H + 17.8 G + 2.48 ZH − 0.02 HG + 0.97 Z2 − 3.40 H2. The difference between the R 2 (99.9) and adjusted R 2 values (99.4) is <0.5, this shows that the model is acceptable. Conclusion: The EDCR developed after using Taguchi’s method of optimization had microhardness superior to that of the commercially available composite resins.

Effect of Nanohydroxyapatite, Zirconia and Glass Filler Particles on the Wear and Microhardness of Experimental Dental Composite Resin.

To study the influence of nanoparticles of hydroxyapatite, zirconia, and glass on the wear and the microhardness of the organic matrix of experimental dental composite resin. The dental composite resin matrix was fabricated from bisphenol A-glycidyl methacrylate (Bis-GMA) (40 wt%), triethylene glycol dimethacrylate (TEGDMA) (36 wt%), and camphorquinone (0.4 wt%). Nanohydroxyapatite, glass, and zirconia fillers were silane treated. Nano-hydroxyapatite, glass, and zirconia were incorporated at three different concentrations. The polymerization of the dental composite resin was done using a light curing unit. Experimental dental composite resins were evaluated for wear and microhardness. The data were analyzed by one-way analysis of variance (ANOVA) test. The experimental dental composite resin composed of 32% of nanohydroxyapatite, 27% of zirconia, and 19% of glass as filler showed the minimum amount of wear. The Vickers hardness (VHN) number was observed to be minimum for the experimental dental composite resin composed of 24.1% of nanohydroxyapatite, 22% of zirconia, and 14.5% of glass. The inclusion of 32% nanohydroxyapatite, 27% of zirconia, and 19% of glass as filler into the experimental dental composite resin decreased the wear and increased the hardness. Mirajkar CK, Winnier J, Hambire U. Effect of Nanohydroxyapatite, Zirconia and Glass Filler Particles on the Wear and Microhardness of Experimental Dental Composite Resin. Int J Clin Pediatr Dent 2023;16(S-1):S81-S84.

Comparative evaluation of dental resin composites based on micron- and submicron-sized monomodal glass filler particles

ObjectivesA model resin composite containing a novel monomodal inorganic filler system based on submicron-sized Ba–Si–Al glass particles (NanoFine NF180; Schott) was formulated and compared with an experimental composite containing micron-sized particles (UltraFine UF1.0; Schott). MethodsThe filler particles were characterized using X-ray microanalysis and granulometry, while the composites were characterized in terms of filler–resin morphology, radiopacity, degree of CC conversion, hardness, flexural strength/modulus, work-of-fracture, surface roughness and gloss (before and after simulated toothbrushing abrasion), and bulk compressive creep. The composites were formulated from the same photoactivated dimethacrylate co-monomer, incorporating mass fractions of 75% micron- and 78% submicron-sized particles. Quantitative data were analyzed at a significance level of p<0.05. ResultsBoth filler systems exhibited a narrow grain size range (175±30 and 1000±200nm), with differences restricted to the size and specific area of the particles. The composites were similar in radiopacity, flexural strength, work-of-fracture, and creep. The submicron composite was harder but had lower flexural modulus and CC conversion. No significant differences in roughness were observed before brushing, although the submicron composite had higher gloss. Brushing increased roughness and decreased gloss on both materials, but the submicron composite retained higher gloss after brushing. SignificanceThe monomodal submicron glass filler system demonstrated potential for use in restorative dental composites, particularly due to improved esthetic properties.

Color stability, conversion, water sorption and solubility of dental composites formulated with different photoinitiator systems

ObjectivesThe aim of this study was to formulate materials with high color stability and reduced degradation by using photoinitiator systems derived from phosphine oxides alternative to the traditional camphorquinone (CQ)/amine system. MethodsMaterials were formulated with the monomers BisGMA and TEGDMA as organic matrix. The photoinitiators tested were CQ+amine (EDMAB), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO), BAPO+EDMAB, diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide (TPO) and TPO+EDMAB. A 60% mass of silanated glass filler particles was added. Degree of CC conversion was evaluated by Fourier-transformed infrared spectroscopy 10min after photopolymerization. The color properties were evaluated by a digital spectrophotometer, applying the CIELab parameters, either before photoactivation, immediately after photoactivation, 24h after dry storage, and one month after water immersion. Water sorption and solubility were assessed by mass gain or loss after storage in water for 30 days. Data were analyzed using ANOVA and Tukey's test (5%). ResultsDegree of conversion did not differ statistically among all the tested formulations. Regarding color, only groups with TPO presented satisfactory color stability after one month of water storage (ΔE<3.3). Water sorption and water stability did not differ among the groups. ConclusionsDegree of conversion, water sorption and water solubility did not differ among all the tested groups. The TPO-based groups were the only materials with satisfactory color stability after one month of water storage. Clinical significanceThe use of a photoinitiator system containing TPO might improve the color stability of resin composites compared with the traditional CQ/amine system while attaining similar physico-chemical properties for the composite.

Characterisation of novel precursor-derived ceramic coatings with glass filler particles on steel substrates

Ceramic coatings based on polysilazanes guarantee optimum surface adhesion on metals. For some applications they are either too thin or too porous. These shortcomings are corrected with filler particles. Our research focuses on a coating that protects steel from corrosion and abrasive wear at high temperatures. A non-porous, scratch resistant 100μm thick coating was synthesised. The properties of polysilazane-derived coatings possessing a borosilicate–bariumsilicate glass filler particle mixture are presented in this article. These coatings were analysed using helium-ion microscopy, scanning electron microscopy with energy dispersive X-ray analysis, abrasion resistance and thermal diffusivity tests. The coatings thickness, adhesion and abrasion resistance make them ideal candidates for corrosion and abrasion protection at elevated temperatures, where a chemically and mechanically stable coating is required.

Microhardness and chemical analysis of high-viscous glass-ionomer cement after 10 years of clinical service as ART restorations

ObjectivesThe aim of this study was to evaluate the Knoop microhardness (KHN) and chemical composition of high-viscous glass-ionomer cement (HVGIC) after 10 years of clinical service. MethodsSix HVGIC samples were cut from 10-year ART restorations. The sections were embedded in acrylic moulds with their longitudinal profile exposed. KHN was determined by performing three sequences of five indentations at 10, 30, 50, 70 and 90μm of HVGIC outer surface. For the control group (n=6), HVGIC specimens were stored in distilled water for 24 months. Hardness measurements were taken at days 7, 30, 60, 120, 180, 360, and 720. For chemical analysis using SEM-EDX, 10-year and control specimens were dehydrated and coated with carbon. Data were analysed using T-test and ANOVA/Tukey's test (p<0.05). ResultsA significant KHN increase was observed in the control group up to the 180-day period. From this point the values stabilized and no more significant differences were found between the 10-year and the control KHN values. No statistical differences were observed amongst the KHN from inner distances compared to the outer surface of the 10-year HVGIC specimens. In one 10-year specimen, SEM-images identified the transformation of HVGIC in an altered layer with no glass filler particles detectable, and raised Ca, K and P contents. ConclusionsKHN values of ten-year HVGIC specimens were similar to the control group values at 180-day storage period. Except for one 10-year specimen in that an altered layer could be seen, chemical composition was similar amongst the depths evaluated.

Characterisation of surface organisation and morphology of some new experimental dental resin-based composites

The aim of this work was to investigate the morphology and to determine the roughness of a series of three new experimental resin-based composite materials containing different inorganic fillers using the AFM technique. Dental composites with photochemical initiation of polymerisation were prepared using the same resin consisting of synthesised aromatic dimethacrylic oligomers mixture containing Bis-GMA monomer – 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy) phenyl]-propane and the corresponding Bis-GMA dimer and triethyleneglicol dimethacrylate. The inorganic fillers used in the composites were: From the point of view of the surface uniformity, we can conclude that the smoothest surface results from the composite based on synthesised hydroxyapatite, followed by the composite based on commercial hydroxyapatite, the highest roughness being observed for the composite based on glass filler particles. All three composite materials present compact structures of undermicronic particles uniformly assembled.

Resistance of nanofill and nanohybrid resin composites to toothbrush abrasion with calcium carbonate slurry

The aim of this study was to investigate the wear of four nanofilled resin composites using simulated toothbrushing for 50,000 cycles with calcium carbonate slurry. The depth of abrasion and roughness (Ra) were measured after each 10,000 brushing cycle. The surface texture of the worn samples was examined by SEM.The wear depths of the nanofill Filtek Supreme XT (FIL), the nanohybrides Grandio (GRA), Tetric EvoCeram (TET), and Venus Diamond (VED) increased linearly with numbers of brushing cycles or approximately 80, 12, 600, and 60 mum, respectively after 50,000 strokes. Surface roughness showed virtually no change between 10,000 and 50,000 brushing cycles; the ranking order was TET < FIL < GRA < VED. FIL showed rather uniform abrasion with nanoclusters protruding from the surface. TET was very smoothly abraded without signs of debonding of the prepolymerized particles, whereas GRA and VED showed pronounced wear of the matrix polymer surrounding larger glass filler particles.

Organic overlayer model of a dental composite analyzed by laser desorption postionization mass spectrometry and photoemission

Some dental composites consist of a polymerizable resin matrix bound to glass filler particles by silane coupling agents. The resin in these composites includes bisphenol A diglycidyl methacrylate (Bis-GMA) as well as other organic components. Silane coupling agents such as 3-(trimethoxysilyl) propyl methacrylate (MPS) have been used to improve the mechanical properties of the dental composites by forming a covalent bond between the glass filler particles and the resin. These resin-glass composites undergo material property changes during exposure to the oral environment, but degradation studies of the commercial composites are severely limited by their chemical complexity. A simplified model of the dental composite has been developed, which captures the essential chemical characteristics of the filler particle-silane-resin interface. This model system consists of the resin matrix compound Bis-GMA covalently bound via a methacryloyl overlayer to amorphous silicon oxide (SiO2) surface via a siloxane bond. Scanning electron microscopy shows the porous characteristic and elemental composition of the SiO2 film, which approximately mimics that of the glass filler particles used in dental composites. LDPI MS and XPS verify the chemistry and morphology of the Bis-GMA-methacryloyl overlayer. Preliminary results demonstrate that LDPI MS will be able to follow the chemical processes resulting from aging Bis-GMA-methacryloyl overlayers aged in water, artificial saliva, or other aging solutions.

Susceptibility of a Polycaprolactone-Based Root Canal Filling Material to Degradation. II. Gravimetric Evaluation of Enzymatic Hydrolysis

Polycaprolactone is susceptible to enzymatic biodegradation via ester bond cleavage. This study examined the susceptibility of Resilon, a polycaprolactone-based root filling material to enzymatic hydrolysis. Resilon, gutta-percha, and polycaprolactone disks, prepared by compression molding, were incubated in phosphate-buffered saline, lipase PS or cholesterol esterase at 37°C for 96 h. They were retrieved at different time intervals for gravimetric analysis and scanning electron microscopy. The materials exhibited slight weight gains when incubated in phosphate-buffered saline that can be attributed to water sorption. Gutta-percha showed similar weight gains in the two enzymes. Conversely, Resilon and polycaprolactone exhibited extensive surface thinning and weight losses after incubation in lipase PS and cholesterol esterase. Glass filler particles in Resilon were exposed following surface dissolution of the polymer matrix, creating rough surface topography. Biodegradation of Resilon by bacterial and salivary enzymes warrants further investigation of their activities using cultures of endodontically relevant microbes and human saliva extracts.

A study of localized curing of glass-filled composites using microhardness measurements

Extent of cure of hybrid composite systems is examined by conducting hardness measurements at different stages of the photopolymerization reaction and obtaining kinetic parameters that matched the experimental data. The materials are commercial dental composites based on bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane resins with different photoinitiator concentrations as well as filler particle sizes and combinations. Samples (five per group) were made using nylon molds (2.5 × 5 mm) of the tested composites. The samples were light cured with a constant-power light source for durations up to 20 s. After curing, all samples underwent Vicker's hardness testing of top and bottom surfaces. While there are significant differences in the polymerization behavior between the top and bottom locations for the tested composites, the corresponding growth exponent n, a kinetic parameter in the kinetic theory, is very close in all cases. For the tested materials the coefficient factor k is much lower for the bottom surfaces compared with the top surfaces. This reduction in the value of k is more severe for the material with a higher concentration of the photoinitiator as well as a higher percentage of glass filler particles in the wavelength range affecting the photopolymerization. It is argued that a relationship between k and the irradiation intensity can be used to quantify the decay of irradiated light with its penetration into the composites. The comparisons can be used to draw preliminary conclusions on the parameters controlling the effective depth of cure in a hybrid composite. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 426–431, 2005

Fracture toughness of aged dental composites in combined mode I and mode II loading.

Resin-based laboratory dental composites for prosthetic restorations have been developed in the past years as a cost-effective alternative to conventional porcelain-fused-to-metal or full ceramic restorations. The fracture toughness at different stress states (K(Ic), K(IIc), and mixed-modes K(I), K(II) ) was assessed for three laboratory dental composite resins used for prosthetic restorations that were aged up to 12 months in a food simulating fluid (10% ethanol) at 37 degrees C. The materials were mainly di- methacrylate based resins reinforced with submicron glass filler particles. The Brazilian disk test was used on precracked chevron-notched specimens, and different stress states were obtained by angulating the precracked chevron notch relative to the diametral compressive loading direction. The stress intensity factors were calculated using Atkinson et al.'s relation. For all three materials, mode I fracture toughness values ranged between 0.48-0.64 MPa. m(0.5) and mode II values ranged between 0.93-1.2 MPa. m(0.5). Overall, aging time and storage media had little effect on toughness. Considering the inherently low toughness of these restorative materials, their use should be limited to low stress masticatory areas.

Effects of daily topical fluoride gels on resin composite degradation and wear

Objectives. This in vitro study compares the effects of professional and consumer-applied topical fluorides on the weight, wear resistance and surface appearance of a resin composite containing barium boroaluminosilicate glass filler particles. Methods. Prior to wear studies with a pin and disc apparatus, specimens were immersed for 6 min 10 times in water, three consumer-applied topical fluorides (1.1% NaF, 0.4% SnF 2, or 0.5% APF gel) or a professionally applied topical fluoride (1.23% APF gel). Specimens were weighed before and after each immersion. Following wear studies, the specimen surfaces were visually evaluated using scanning electron microscopy. Weight changes were analyzed for significant differences using one-way ANOVA and Duncan's multiple range test (p = 0.01). Values of wear parameters were ranked and tested for significance using one-way ANOVA with least squares mean contrast (p = 0.05). Results. Significant differences were found in the weight loss of specimens treated with different fluoride agents: 1.23% APF = 0.5% APF > 0.4% SnF 2 1.1% NaF = water (p ⪯ 0.0001). Significant differences in initia wear depth (S.) occurred in the following samples: 1.23%APF > 1.1% NaF = 0.5% APF (p = 0.04).Scanning electron micrographs showed variable wear tracks on the specimen surfaces. The specimen surfaces outside the wear track were smooth for those treated with water or with NaF; the surfaces outside the wear track of specimens treated with APF showed extensive loss of filler particles. Significance. Topical APF agents caused extensive loss of filler from the resin composite specimens whereas 1.1% NaF caused the least damage. Although significant differences in surface wear resistance were detected, clinical studies are needed to determine the effect of topical fluorides on the properties of this resin composite.