mohammad atai

This study compared the efficacy of an experimental resin containing polyhedral oligomeric silsesquioxane (POSS) nanoparticles with methacrylate groups (MA-POSS) versus the Icon resin regarding the masking, color stability, and microhardness of artificially induced white spot lesions (WSLs).  

In this in vitro study, 60 bovine enamel specimens were assigned to two groups for assessment of color (group C) and surface microhardness (group H). white spot lesions were induced on the specimens using demineralizing and remineralizing solutions. Each group was divided into two subgroups for the application of experimental resin and Icon. the color and surface microhardness of specimens were measured, after the induction of WSLs, and after infiltration. Group C samples were immersed in coffee (1 hour/day for one week) and their color was measured again. ANCOVA was used to compare microhardness between the two resin groups. To compare the masking and staining of infiltrated lesions, ΔE, ΔL and L* values after infiltration and staining were compared with the values after the induction of WSLs using independent t-test and repeated measures ANCOVA (α=0.05). 

Microhardness analysis by ANCOVA revealed no significant difference between the groups following resin infiltration (P=0.144). The performance of the two resins after infiltration (P=0.75 for ΔE, P=0.20 for ΔL, P=0.57 for L*) and after staining (P=0.31 for ΔE, P=0.07 for ΔL, P=0.32 for L*) was not significantly different.

The experimental resin was comparable to Icon with the main advantage of easier availability in Iran.

The present study was conducted with the aim of behavioral modeling to reduce human error in the country's air transportation industry. This study, in terms of the purpose of an applied-developmental research, from the point of view of the method and time frame of data collection, is a cross-sectional survey research that was conducted with a mixed approach. The community of participants of the qualitative part includes the managers of the country's air transportation industry, 11 of whom were selected in a targeted manner until reaching theoretical saturation. The statistical population is a small part of the experts and activists of the country's air transportation industry, and the sample size was estimated by Cochran's formula of 366. Quantitative sampling was done by cluster-random method. The data collection tool was a semi-structured interview and researcher-made questionnaire, which was validated by construct validity, convergent validity and divergent validity methods. Using Cronbach's alpha and composite reliability, the reliability of the questionnaire was also checked. The value of convergent validity for all constructs was above 0.5 and Cronbach's alpha and combined reliability were estimated to be above 0.7 for all constructs, so validity and reliability were evaluated as favorable.-..

In general, bioactive glasses (BAGs) can react with tissue minerals and promote remineralization. However, the application of BAG in bonding agents and its impact on bond strength remain uncertain due to insufficient information and limited research in this area.

This study employed a randomized controlled design to assess the effects of composite‑bonding agents with varying BAG contents on shear bond strength and fracture pattern in sound and demineralized teeth, with and without thermocycling. Thus, 80 healthy third molars were randomly divided into two groups: sound teeth and demineralized teeth. Five bonding agents were applied to the prepared dentin surfaces, including four experimental composite‑bonding agents with varying BAG content (0, 0.2, 0.5, and 2 wt%) and the Adper Single Bond commercial bonding as control. The shear bond strength of all samples was measured using a universal tester. The type of failure of each specimen was determined using a stereomicroscope. Kruskal–Wallis nonparametric test was performed on the obtained shear bond strength data followed by Mann–Whitney post hoc test with Bonferroni correction to determine statistical significance. The level of significance was considered P ≤ 0.05 for all tests and was adjusted by Bonferroni correction.

Demineralization significantly decreased shear bond strength in the teeth samples. Adper Single Bond exhibited the highest shear bond strength values. The addition of BAG did not have a significant influence on shear bond strength, regardless of demineralization or thermocycling condition. Adhesive failure was the predominant type of failure in all groups.

The incorporation of BAG filler up to 2 wt% did not result in significant changes in shear bond strength. Experimental adhesive bonding agents with 2 wt% BAG content demonstrated shear bond strengths comparable to the commercial bonding agent in sound nontreated, sound thermocycled, demineralized nontreated, and demineralized thermocycled groups.

Entrepreneurial behaviors play a cardinal role in achieving highly radical innovations and absolute competitive advantages by businesses and nations. Reviewing the literature around entrepreneurial behaviors leading success shows there is not a satisfactory separation between factors and behavioral aspects. Using a grounded theory approach, in this article, twenty Startups and Stablished Entrepreneurs seat in the Academic Science and Technology Park interviewed and data analyzed through three phase coding process. Both reliability and validity measures of data gathering tool were at a satisfactory level and this has been confirmed by experts. Results of the analysis interviews show that entrepreneurial behavior, triggered by predicting factors, can be categorized into four distinct groups. These groups include Informational behaviors, Relational and network-building behaviors, Strategic management behaviors and Executive management behaviors. This study also provides the reader with macro and micro-level environmental factors affecting entrepreneurial behaviors and classified the success criteria divided into both objective and subjective criteria.

Statement of the Problem: 

Using plate and screws as the conventional bone fixation method in maxillofacial fractures leads to many complications as plate exposure, infection or unpleasant feeling on touching. Finding a substitute fixation method has been a far desire for many years.

This study compared the new bone formation using an experimental bone adhesive containing a functional monomer (benzophenone tetracarboxylic di-methacrylate, BTDMA) and the conventional plate and screw in fractured mandibles of rabbit.

This is an experimental animal study. The artificial fractures were induced at the mandibular angles of three male New Zealand rabbits. Screw and plate were used as control and titanium mesh with the resin-based bone adhesive containing 15 wt. % BTDMA monomer were applied as treatment. The mandible radiography were obtained and the density of the fracture line was compared to the control. The newly formed bone was assessed by a microscope.

The results obtained from the MTT cytotoxicity assay showed that 70% of cells were able to grow in the presence of the adhesive. The radiographic density of mesh-adhesive specimens was 119.88±76.29, while conventional plate specimens’ density was 120.38±73.89. The average new bone formation score in the mesh specimens and plate specimens was 3.67±4.62 and 7±4.36, respectively. There was no significant difference between the two groups. The application of bone adhesive containing 15% BTDMA monomer in a group of the rabbits showed lamellar bone formation.

Using bone adhesives containing BTDMA could lead to a new bone formation with high density in the case of adequate bonding to the fractured area.

To improve the limitations, many modifications in the resin‑modified glass ionomer (RMGI) composition have been proposed. In this study, we evaluated the effect of different concentrations of zinc oxide (ZnO) nanoparticles incorporated into RMGI cement on its physical and antimicrobial properties.

In this in vitro study, ZnO nanoparticles with 0–4 wt.% concentrations were incorporated into RMGI. The following tests were carried out: (a) Antibacterial activity against Streptococcus mutans tested by disc diffusion method,(b) mechanical behavior assessment by measuring flexural strength (FS) and flexural modulus (FM),(c) micro‑shear bond strength (µ‑SBS), and (d) fluoride and zinc release. Data were analyzed using the statistical tests of ANOVA, t‑test, and Tukey’s HSD post hoc in SPSS V22. The level of significancy was 0.05.

In the disc diffusion method, specimens with 2 wt.% ZnO nanoparticles showed the highest antimicrobial efficacy (P < 0.05). After 1 month of water storage, no significant difference was observed in FS and FM of the samples (P > 0.05). In 2 wt.% ZnO nanoparticles group, µSBS increased in the first 7 days but decreased by 17% after one month, which showed a significant difference with that of the control group. The fluoride release did no change in the ZnO nanoparticle‑containing group compared with the control group at all time intervals.

Incorporation of 2 wt.% ZnO nanoparticles into the RMGI cement adds antimicrobial activity to the cement without sacrificing FS and fluoride release properties, while decreased µSBS.

Design and synthesis of self-curable solutions containing polyethylene glycol (PEG) and polyhedral oligomeric silsesquioxane (POSS) is a simple and economical method to enhance the physical and mechanical properties of biodegradable PEG.

First POSS nanoparticles were treated with acryloyl chloride (AC) to obtain POSS-AC nano-powder. In another reaction, PEG was copolymerized with fumaryl chloride to prepare polyethylene glycol fumarate (PEGF). POSS-AC was subsequently dispersed in PEGF matrix in 1 and 2% (wt) in the presence and absence of N-vinyl pyrrolidone as a reactive diluent. The obtained slurries were photocured by blue light irradiation using camphorquinone as photoinitiator. The crystal structure, dispersion quality, crosslink ability, mechanical, thermal and thermomechanical characteristics of the prepared nanocomposites as well as crosslinked neat PEGF were studied by XRD, TEM, equilibrium swelling, tensile, TGA and DMTA tests, respectively.

The XRD pattern of nanocomposites did not show any sharp peak related to the aggregation and agglomeration of the nanoparticles. TEM pictures revealed good dispersion of POAA-AC nanoparticles with mean diameter within 10-50 nm range. Furthermore, the presence of POSS-AC and reactive diluent led to an increase in the Tg of cured PEGF (as a blank system) from -16°C to a value in the range of -13 to -3°C, gel content from 45% to 62-84%, storage modulus from 1.6 GPa to 2.2-3.3 GPa, maximum decomposition temperature from 395 °C to 408-432°C, and Young's modulus from 0.46 MPa to 1.2-1.6 MPa. As a result, the nanocomposites designed in this study exhibited good mechanical properties and fast curing which would be considered as potential candidates for tissue engineering and biomedical applications.

In oral and maxillofacial fractures, plates and screws routinely fix fragments until the completion of healing process, which has its own complications in some critical fractures. To overcome this drawbacks bone adhesives are developed for the immobilization of fractured bones.

In this in-vitro study we compared the bond strength obtained by immobilization of the bone fragments using plates and screw and new adhesive containing BTDMA monomer.

In this experimental in-vitro trial, bone fractures were simulated in bovine’s mandibular bone using an electrical saw. The bone fragments were randomly allocated in different groups and were immobilized with either plate and screws and adhesive containing 0, 10, 15% BTDMA. After 24 hours tensile bond strength was calculated using universal testing machine. One-way ANOVA and Tukey post hoe test were used for statistical analysis.

Mean (±standard deviation) of tensile bond strength of bone fixation using adhesive containing 15% (W/W) BTDMA monomer were 176.0 (±18.89) N. These values were 149.1 (±23.88) N for adhesive containing 10% BTDMA; 102 (±17.99) N for the base adhesive and 278.9 (±24.12) N for the screw and plate technique. Significant differences were found regarding bond
strength of bone fixation in 4 groups using bone adhesives or plate technique (P<0.001). The highest bond strength was recorded for the plate group and the least was related to the base adhesive. Significant differences existed between all bone adhesives as declared by paired comparison (p<0.05).

Despite the lower bond strength in adhesive groups in comparison with screw and plate, with regards to possible complications of screw and plate technique, it seems bone adhesives containing BTDMA monomer can be used for bone fragment fixation. However, bond strength is just one of the numerous properties that an adhesive should have and more studies must be done on these kinds of adhesives.

The clinical success of glass ionomer restorations depends on the strength of resin-modified glass ionomer (RMGI) cement bonding to dentin and there is limited information available regarding the bond strength of resin modified glass ionomers containing silica nanoparticles to dental structures. The aim of this study was to compare the microshear bond strength (µSBS) of RMGI with and without silica (SiO2) nanoparticles to dentin of permanent teeth. in this experimental study, the occlusal surfaces of 30 freshly extracted intact third molars were ground to expose the flat dentin and after conditioning with 20% poly acrylic acid, were randomly assigned to two main groups (n=15). The first group was filled with RMGI (Fuji II LC, GC) and the second group was filled with RMGI plus 0.5%wt. silica nanoparticles. Then, each main group was divided into three subgroups, and then stored in an incubator at 37 oC with 100% humidity for 1, 7, and 30 days. The µSBS test was performed using a universal testing machine (1 mm/min). The data were analyzed by t-test, repeated measures ANOVA and Tukey test (p< 0.05). There were no statistically significant differences between the mean µSBS of the groups with and without nanoparticles along the different storage periods (p> 0.05). There was significant difference in µSBS values among the three different storage periods in all the tested materials (p< 0.05). Incorporation of 0.5 %wt. silica nanoparticles did not compromise the µSBS of Fuji II LC RMGI to dentin.

During the last decades, an increasing attention has been paid to pharmaceutical and biomedical applications of queous polymeric solutions which respond in accordance to the changes in their environmental conditions i.e., stimuli by turning into in situ forming hydrogels. Of all the stimuli-responsive hydrogels, temperature-responsive solutions have been widely investigated due to their simplicity, applicability and relatively high frequency of temperature-responsiveness, in situ gelling polymeric (natural or synthetic) systems. In contrast with the conventional hydrogels, in situ forming temperature-responsive hydrogels can form under physiological conditions and preserve their morphological integrity for a definite time course. Using the materials makes it easier to formulate pharmaceutical formulations by mixing polymer and drug, and also improve the dissolution of hydrophobic drugs with low molecular weight. Due to the simplicity of the pharmaceutical formulation by simple solution mixing, biocompatibility and convenient usage these materials can be used in biomedical and pharmaceutical fields for tissue engineering, solubilizing of sparingly soluble drug molecules, controlled delivery of drugs and biomacromolecules, such as proteins and genes. In this review, temperature-responsive hydrogels are studied regarding their classification, applications and thermodynamics. Moreover, temperature-responsiveness mechanisms, polymeric gels, recent advances in surface, hydrogel and molecular design and biomedical application are investigated. Also, this review focuses on recent investigation based on the designs of temperature-responsive micelles and intelligent bioconjugates. Finally, limitations and potentials of applications of the temperature-responsive in situ forming hydrogels have been reported. The reported information in this paper are necessary to design and develop a desirable temperature-responsive hydrogels with different characteristics and applications.

The aim of this study was to assess for the first time the effects of different amounts of ethanol solvent on the microtensile bond strength of composite bonded to dentin using a polyhedral oligomeric silsesquioxane (POSS)‑incorporated adhesive. This experimental study was performed on 120 specimens divided into six groups (in accordance with the ISO TR11405 standard requiring at least 15 specimens per group). Occlusal dentin of thirty human molar teeth was exposed by removing its enamel. Five teeth were assigned to each of six groups and were converted to 20 microtensile rods (with square cross‑sections of 1 mm × 1 mm) per group. The “Prime and Bond NT” (as a common commercial adhesive) was used as the control group. Experimental acrylate‑based bonding agents containing 10 wt% POSS were produced with five concentrations of ethanol as solvent (0, 20, 31, 39, and 46 wt%). After application of adhesives on dentin surface, composite cylinders (height = 6 mm) were bonded to dentin surface. The microtensile bond strength of composite to dentin was measured. The fractured surfaces of specimens were evaluated under a scanning electron microscope to assess the morphology of hybrid layer. Data were analyzed using one‑sample t‑test, one‑way analysis of variance (ANOVA), and Tukey tests (α = 0.05).
the mean bond strength in the groups: “control, ethanol‑free, and 20%, 31%, 39%, and 46% ethanol” was, respectively, 46.5 ± 5.6, 29.4 ± 5.7, 33.6 ± 4.1, 59.0 ± 5.5, 41.9 ± 6.2, and 18.7 ± 4.6 MPa. Overall difference was significant (ANOVA, P Incorporation of 31% ethanol as solvent into a 10 wt% POSS‑incorporated experimental dental adhesive might increase the bond strength of composite to dentin and improve the quality and morphology of the hybrid layer. However, higher concentrations of the solvent might not improve the bond strength or quality of the hybrid layer.

ZnO nanostructures were formed via a hydrothermal reaction mechanism between simple anionic (ammonia orsodium hydroxide) and cationic (zinc acetate dehydrate) precursors without using any organic templates. Effect of the reaction conditions including the initial solution pH, concentration and type of the anionic and cationic precursors, and the reaction time and temperature on the nanostructure particle size and morphology were investigated. The nanostructures formed were analyzed by powder X-ray diffraction, energy dispersive X-ray analysis, and scanning electron microscopy. According to the results, the morphology of the nanostructures is highly pH-dependent. Needle-like nanostructures were formed using ammonia at initial solution pH value around 9 but plate-like nanostructures were formed using NaOH at pH value around 13 regardless of the reaction time or temperature. Varying the precursor concentrations could not be considered as an independent parameter per se due to the consequent changes impress the reaction medium pH which affects morphologies in turn. In general, increasing the reaction time and temperature increased the mean particle size of the nanostructures with no significant change in their morphology. It was found that the nanostructure morphology changes from nanoneedles to star-like ones due to higher addition rate of ammonia.

This study aimed to evaluate the effect of different percentages of ethanol solvent of an experimental methacrylate‑based dentin bonding agent containing polyhedral oligomeric silsesquioxanes (POSS) on the microleakage of resin composite restorations.
In this experimental study, 42 extracted human premolar teeth used and 84 standard Class V cavities were prepared on the buccal and lingual surfaces of the teeth. The teeth were divided into 6 groups of 7. Experimental bonding agents with different percentages of solvent were used in 5 groups and Single Bond® as a control. The teeth were restored with resin composite and subjected to thermal cycling test. Teeth were then immersed in a solution of 2% basic fuchsine dye for 24 h and sectioned buccolingually and scored using stereomicroscope with ×32 magnification. Microleakage data were analyzed using the Kruskal–Wallis, Mann Whitney U, and Wilcoxon tests.
There were significant differences between the microleakage enamel margins (P = 0.036) and dentinal margins (P = 0.008) in all the groups. These significant differences were seen between the control group and groups containing 46 wt% solvent (P = 0.011), 46 wt% and 31 wt% solvent in dentinal (P = 0.027), 31 wt% and 0 wt% in enamel (P = 0.021), also 0 wt% and control in enamel (P = 0.039), and dentinal margins microleakage (P = 0.004). The microleakage in dentinal margins was higher than enamel margins (P The adhesive containing 31 wt% solvent showed the least marginal microleakage, presence of POSS filler may also result in the reduction of microleakage.

Statement of Problem: The degree of conversion depends on the material composition, light source properties, distance from light source, light intensity, curing time, and other factors such as shade and translucency.
In the present study, we evaluated the effects of different light- curing modes and shades of methacrylate and silorane-based resin composites on the degree of conversion of resin composites (DC).
The methacrylate-based (Filtek Z250, 3M, ESPE) and low-shrinkage silorane-based (Filtek P90, 3M, ESPE) resin composites were used in three groups as follows: group 1-Filtek Z250 (shade A3), group 2-Filtek Z250 (shade B2), and group 3-Filtek P90 (shade A3). We used a light-emitting diode (LED) curing unit for photopolymerization. 10 samples were prepared in each group to evaluate the degree of conversion; 5 samples were cured using soft-start curing mode, and the other 5 were cured using standard curing mode. The DC of the resin composites was measured using Fourier Transform Infrared Spectroscopy (FTIR). The data were analyzed using Kruskal Wallis and one- way ANOVA statistical tests.
The degree of conversion of silorane-based resin composite was 70 - 75.8% and that of methacrylate-based resin composites was 60.2 - 68.2% (p = 0.009). The degree of conversion of the composite with brighter colour (B2) was statistically more than the darker composite (A3). Higher degree of conversion was achieved applying the standard curing mode.
The results of the study showed that the colour and type of the resin composite and also the curing mode influence the degree of conversion of resin composites.

This study investigated the reinforcing effect of silica nanoparticles when incorporated into the matrix phase of an experimental dental fiber reinforced composites (FRC) through the evaluation of the flexural properties of the composites.
In this experimental study FRC samples were divided into two main groups (containing two or three bundles) either of them consist of five subgroups incorporating 0, 0.2, 0.5, 2 and 5 wt.% of silica nanoparticles in the matrix resin (n=10 in each subgroup); While a commercial FRC (Angelus, Brazil) was used as control group (n=10). Three point bending test was performed for evaluating the flexural strength and modulus. Thereafter, the microstructure of the fractured samples was evaluated using scanning electron microscopy (SEM). The results were analyzed using one way ANOVA and Tukey's HSD tests.
The results revealed that the silica nanoparticles had a significant positive effect on the flexural strength and modulus of the FRCs (P0.05) in either groups incorporating two or three bundles of fibers.
Incorporating silica nanoparticles into the FRC resin phase resulted in the composites with improved properties.

Nitrile rubber/clay nanocomposites were prepared via in-situ emulsifier-free emulsion polymerization technique in the presence of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and pristine sodium montmorillonite (Na-MMT). The morphology of the nanocomposites was studied using X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM). The XRD results showed exfoliated morphology for the nanocomposites containing up to 3 wt% nanoclay and exfoliated-intercalated morphology for the nanocomposite containing 5 wt% nanoclay. The basal spacing of the nanocomposite، containing 5 wt% nanoclay، was increased to 1. 8 nm، which was 0. 61 nm wider than that obtained using pristine Na-MMT. Compared to neat rubber، the thermogravimetric analysis (TGA) revealed improvements in the thermal stability of all nanocomposite samples، in which the thermal degradation temperature was increased by increasing the clay content. The maximum increase in the thermal stability of the nanocomposites was obtained for the nanocomposite containing 5 wt% nanoclay with exfoliated-intercalated morphology. The tensile testing results showed remarkable improvements in the mechanical strength of the nanocomposites. In comparison with the neat nitrile rubber، the exfoliated nanocomposite، containing 3 wt% nanoclay، showed 302% and 219% increases in tensile modulus and tensile strength، respectively. The reason for improvementin mechanical properties of a nanocomposite، containing 3 wt% of nanoclay with respect to the nanocomposite containing 5 wt% of nanoclay، was related to the better dispersion of nanoclay platelets in the matrix and formation of exfoliated morphology. In addition، elongation-at-break and hardness were increased in the nanocomposites، when compared with the neat nitrile rubber.

The aim of this study was to investigate the mechanical properties (flexural strength، micro-shear bond strength) and remineralizing potential of fissure sealants by adding various concentrations of β-tricalcium phosphate nanoparticles. This in-vitro study consisted of five experimental groups containing prepared nano-fisssure sealants (1-5 wt. % b-TCP nanoparticles) and two control groups containing a prepared and a commercial fissure sealant. Flexural/micro-shear bond strength values were measured using Zwick test machine. Cavities on sixty healthy premolar teeth were filled with the fissure sealants containing 0-5 wt. % of nano b-TCP. The samples were assessed for remineralization under scanning electron microscopy (SEM) and EDAX. Kolmogorov-Smirnov test، One-way ANOVA and Tukey''s Post Hoc analysis/HSD were used to analyze the data. There was no significant difference between the flexural strengths/elastic modulus of the 0-5 wt. % nano β-TCP groups (p>0. 05). The average flexural strength/elastic modulus of the prepared fissure sealant group (0%) was significantly higher than the commercial fissure sealant group (Clinpro) (p<0. 05). There was no significant difference between micro-shear bond strengths of the experimental groups (1-5 wt. %)، and between the commercial and the prepared (0%) fissure sealant groups (p>0. 05). Examining the samples under SEM showed a significant increase in thickness of the intermediate layer with increasing concentrations of β-TCP nanoparticles (p<0. 05). Addition of 1-5 wt. % b-TCP nanoparticles to the fissure sealants significantly increased the remineralization potential without affecting the mechanical properties.

Biocompatible cellulosic polymer hydrogels are used in in-situ forming injectable scaffolds for bone regeneration. The hydrogels، however، generally suffer from their inherent weak mechanical properties. Calcium phosphate particles are used to enhance the mechanical strength and to improve the bone tissue regeneration capability of the scaffolds. In this study، hydroxypropyl methylcellulose (HPMC) was utilized as a polymeric matrix and β-tricalcium phosphate (β-TCP) and hydroxyapatite (HAp) nanoparticles were used to improve the mechanical properties. β-TCP Nanoparticles with plate-like morphology was synthesized through a wet chemical precipitation method. The morphology of the particles was confirmed using scanning electron microscope (SEM). Because the gelation temperature of the HPMC solution was above the temperature of normal human body، different concentrations of sodium sulphate (Na2SO4) were incorporated into the HPMC solutions to examine and adjust the gelation temperature. The cloud point and gelation temperature of the hydrogels were measured using UV/Vis spectroscopy and oscillatory rheometry، respectively. The injectability of the hydrogels، with different inorganic contents، was also measured using a universal testing machine. The results indicated that the cloud point and the gelation temperature of the hydrogels dropped with increase in the sodium sulphate concentration due to Hofmeister effect. The rheology measurements also revealed that β-tricalcium phosphate was more effective than hydroxyapatite in reducing the gelation temperature and enhancement of the modulus and viscosity of the hydrogels. The HPMC hydrogels containing β-tricalcium phosphate and hydroxyapatite nanoparticles were injectable at room temperature. The hydrogels based on HPMC matrix and the calcium phosphate nanoparticles provided promising hydrogels applicable as in-situ forming injectable scaffolds.

Little is known about the interaction of tissue conditioners and modeling plastics.This study evaluates the influence of a variety of commercial tissue conditioners on alteration of viscoelastic properties of modeling plastics. In this in vitro study, the dynamic viscoelastic properties of four commercially available tissue conditioners (TC), Visco-gel (VG), GC Soft-Liner (SL), FITT (FT), and Coe Comfort (CC), relined to modeling plastics with a thickness of 2mm were evaluated after 1 and 7 days of water immersion with the use of storage modulus, loss modulus, and tan delta parameters. Values for these three parameters for each tissue conditioner were statistically analyzed by Kruskal Wallis and Mann Whitney tests with P value sets at<0.05. Complex modulus and loss tangent values of TC were not significantly different among specimens containing 0, 2, 5 and 10 wt.%-SZ, respectively. In FT and TC containing 2 wt.%-SZ, these values were not significantly different between 1 and 28 days in both water- and saliva immersions. The results suggest that relining with modeling plastics does affect TC’s inherent dynamic viscoelastic properties, while the other tissue conditioners investigated may be found to have changed viscoelastic properties as a consequence of vicinity to the modeling plastics.

Hollow microspheres or microballoons are gas-filled spherical particles with diameters between 1 to 1000 micrometers. The wall material may be made from glass, ceramic oxides, polymers or even metals. The typical thickness of the wall is in the range of 1 to 10% of the outer diameter of the sphere. Hollowmicrospheres have low density and high specific surface. They are widely used as toners, immobilization carriers, chromatographic packings, and sound dampening or adsorption materials. Thermally expandable microspheres are hollow balloons that consist of a thermoplastic shell with a liquid blowing agent as the core. These microspheres are expanded by applying temperatures higher than the glass transition temperature of the thermoplastic shell. The particles expand due to the evaporation of the encapsulated solvent which causes an internal pressure. In this study the primary expandable particles were synthesized via suspension polymerization of methacrylate monomers in the presence of pentane as a blowing agent and benzoyl peroxide as a thermal initiator. In the second step, the particles consisting of PMMA shell and pentane core were expanded at elevated temperature to obtain microballoons with a very low density. Morphology of the particles was studied using scanning electron microscopy. The results showed that the process successfully resulted in formation of spherical microballoons. The mean diameter of unexpanded particles was about 30 μm and thickness of the shell was about 2 μm while, their mean diameter after expansion was about 90 μm and the thickness of the shell decreased to 400 nm. The diameter to wall thickness ratio of expanded particles was about 1:200 which provided particles with a very low density of 0.05 g/cm3.

Flexural strength of prosthesis made with dental composite resin materials plays an important role in their survival. The aim of this study was investigating the effect of nanoclay fillers and Poly (methyl methacrylate)-grafted (PMMA-grafted) nanoclay fillers loading on the flexural strength of fiber-reinforced composites (FRCs). Standard FRC bars (2 × 2 × 25 mm) for flexural strength testing were prepared with E-glass fibers and a synthetic resin loaded with different quantities of unmodified nanoclay and PMMA-grafted nanoclay filler particles (0% as control group, 0.2%, 0.5%, 1%, 2%, 5%). Flexural strength and flexural modulus were determined. The data were analyzed using 2-way, 1-way ANOVA and post hoc Tukey’s test (a = 0.05). The fracture surfaces were evaluated by Scanning Electron Microscopy. For groups with the same concentration of nanoparticles, PMMA-grafted filler-loaded group showed significantly higher flexural strength, except for 0.2% wt. For groups that contain PMMA-grafted nanoclay fillers, the 2% wt had the highest flexural strength value with significant difference to other subgroups. 1% wt and 2% wt showed significantly higher values compared to control (P < 0.05). None of the unmodified nanoclay particles loaded group represented statistically higher values of flexural strength compared to control group (P > 0.05). Flexural modulus of 2%, 5% wt PMMA-grafted and 0.5%, 1%, 2%, 5% wt unmodified nanoclay particles-loaded subgroups decreased significantly compared to control group (P < 0.05). PMMA-grafted nanoclay filler loading may enhance the flexural strength of FRCs. Addition of unmodified nanoparticles cannot significantly improve the flexural strength of FRCs. Addition of both unmodified and PMMA-grafted nanoclay particles in some concentrations decreased the flexural modulus.

The surface modulus and hardness of photo-crosslinkable cyanoacrylate bioadhesives containing TMPTMA and POSS as crosslinking agents were studied using nanoindentation technique. Adhesives containing 2-octyl cyanoacrylate (2-OCA) and different percentages of POSS nanostructures and TMPTMA as crosslinking agents were prepared. 1-Phenyl-1,2-propanedione (PPD) was incorporated as photo-initiator into the adhesive in 4 wt%. Mechanical properties of the surface of the adhesives were measured using nanoindentation technique applying a Berkovich tip. The results (three replicates) were analyzed and compared using one-way ANOVA and Tukey test at a significance level of 0.05. The results showed that by incorporation of crosslinking agents, surface modulus and hardness increased and force loss during holding decreased. The incorporation of crosslinking agents into the adhesives enhanced their elastic properties. The surface modulus and hardness increased by increasing crosslinking concentration. The results also indicated that the elastic work increased, and plastic work dropped due to increasing crosslinking density. The samples which had been stored in water for 24 h before the tests, showed reduced elastic properties due to the plasticization effect of water.

Background and aims. The aim of the present study was to evaluate the effect of nanoparticles of zirconia mixed with glass-ionomer on the proliferation of epithelial cells and adhesive molecules (ICAM-1).Materials and methods. Zirconia nanoparticles were mixed with glass-ionomer powder in weight percentages of 0%, 5%, 50%, 70%, and 100%. The powders were then mixed with glass-ionomer liquid in 2:1 weight ratios. The paste was then inserted into a steel ring mold (5 mm in diameter and 0.5 mm in thickness) sandwiched between two glass slides. Glass-ionomer was then cured using a light-curing unit. Seven samples (discs) were prepared for each mixing percentage. Cell cultivation (epithelial) and MTT tests were performed to assess the cytotoxicity of specimens containing different nanozirconia contents. Finally, human ICAM-1 platinum ELISA test was performed for quantitative diagnosis of human ICAM-1 epithelial cells.Results. Statistically significant differences (p < 0.001) were observed in the cytotoxicity of specimens with different nanozirconia contents after 1 and 24 hours and one week. There were no significant differences between the specimens in relation to the ICAM-1 molecules released from epithelial cells.Conclusion. The results revealed that incorporation of zirconia nanoparticles (except for the pure zirconia particles) stimulated the adhesion of epithelial cells to the specimens, making the zirconia-containing glass-ionomers promising biomaterials for dental applications. The highest biocompatibility was obtained for 70 wt% of zirconia after 24 hours.

Polypropylene-clay nanocomposites were prepared in solution and followed by amelt mixing process. The nanocomposites were prepared for 5% (by weight)organoclay with varying amounts of two oxidized polypropylene waxes (OPPWs)as compatibilizer. The clay dispersion was analyzed by X-ray diffraction (XRD),transmission electron microscopy and melt rheology technique. The extent ofintercalation in clay platelets was quantified by XRD analysis based on interactionsbetween OPPW and clay layers. A maximum of ca. 10% increase in clay basalspacing was observed. It was revealed that the degree of clay intercalation in solutiontechnique varies by the polarity of OPPW. In subsequent melt mixing process, the claydispersion was evaluated by XRD which correlated well with the variations of storagemoduli at low frequency region and displayed a pseudo solid-like behaviour. Therheological measurements also showed higher dispersion of clay platelets in PP matrixin the presence of OPPW. The increase in storage moduli especially at low frequencyregion implied that there were stronger interactions between Cloisite® 15A organoclaysand polymer chains when OPPW is present. The TEM images mainly suggested tocom-patibilizing effect of OPPW in clay intercalation. In spite of low mechanicalproperties of OPPW, the DMTA showed the highest modulus of glassy region innanocomposites with maximum OPPW content. These findings agreed well with eachother in co-intercalation effect of OPPW in PP nanocomposites.

Different studies have demonstrated that resin penetration into collagen fibers is influenced and promoted by the presence of a solvent in the bonding agents, but in order to create a reliable bond, it should be removed before curing. This study investigates the effect of adding ethanol as a solvent on the microshear bond strength of a solvent-free dentin bonding agent. After removing the occlusal enamel of 20 caries-free human third molars, midcoronal dentin slices, each about 2 mm thick were prepared then polished by silicon paper. The superficial dentin surfaces were randomly distributed into four groups and treated with James-2 containing different concentrations of ethanol (0, 5, 10, and 20 wt%) in two layers and then light-cured. The micro shear bond strength (µSBS) was tested using a universal testing machine. The data were finally subjected to one-way ANOVA followed by Tukey's post-hoc test. James-2 containing 5 wt% ethanol provided the highest micro-shear bond strength (32.1 ± 6.69 MPa). There were no statistical differences in µSBS values between other groups (25 ± 5.8 MPa, 24.8 ± 4.93 MPa and 21.8 ± 4.51 MPa, respectively). Adding ethanol as a solvent resulted in increased micro shear bond strength to dentin. At higher solvent concentrations no significant change was observed indicating that the solvents may not have been completely removed leading to poor polymerization and porosity reflected as lower bond strengths.