Validation of a human saliva model for the determination of leachable monomers and other chemicals from dental materials

This study aimed to prove the validity of a mixture of chemicals, including salts, small organic molecules, mucin, and α-amylase, as saliva surrogate ("artificial saliva") for assessing leakage of methacrylate monomers and other constituents from dental materials. To achieve this, we developed and validated a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of 2-hydroxyethyl methacrylate (HEMA), triethylene glycol dimethacrylate (TEGDMA), diurethane dimethacrylate (UDMA), bisphenol A glycerolate dimethacrylate (BisGMA), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), bisphenol A (BPA), and five homologues of ethoxylated bisphenol A dimethacrylate (BisEMA EO2-6) in unstimulated and artificial saliva, and compared their concentrations in the two saliva media following either spiking with a mixture of the compounds or incubation of test specimens of printed biomaterials. Test specimens were immersed in unstimulated/artificial saliva, incubated at 37 °C for 24 h, and saliva aliquots were extracted with methanol and subsequently analyzed by LC-MS/MS. The method was validated with regard to matrix effects, linearity, selectivity, lower limits of quantification (LLOQ), precision, bias and combined measurement uncertainty (u'). The performance characteristics of the method were comparable for unstimulated and artificial saliva samples. The combined u' for individual chemicals at a concentration of 10 × LLOQ were within the range of 5.3-14 % for unstimulated saliva and 6.9-16 % for artificial saliva, except for the BisEMA homologues. Combined u' for the latter were 27-74 % in unstimulated saliva, and 27-79 % in artificial saliva. There was no detectable release of BPA from the test specimens, and the TPO concentrations were mainly below the LLOQ. TEGDMA and UDMA were detected in the highest quantities, and at comparable concentrations in the unstimulated and artificial saliva. For all BisEMA homologues, the release was higher in unstimulated saliva than in artificial saliva. The study showed that the artificial saliva model can be a suitable replacement for native saliva, but might underestimate leakage of more lipophilic methacrylates.

Thermal and biological properties of novel sodium carboxymethylcellulose-PPFMA nanocomposites containing biosynthesized Ag-ZnO hybrid filler

The aim of this study was to produce new nanocomposites with antimicrobial, antioxidant and anticancer properties that can be used in biomedical research based on carboxymethyl cellulose (NaCMC) biopolymer. First, poly(2-oxo-2-(pentafluorophenoxy)ethyl-2-methylprop-2-enoate) (PPFMA) was synthesized and characterized by FTIR and NMR techniques. It was then blended with NaCMC by in situ/hydrothermal method to produce a semi-synthetic functional material. Changes in the FTIR data of the blend and the single Tg value from DSC confirmed the compatibility of the blend. To enhance the thermal and biological properties of the NaCMC-PPFMA blend, biosynthesized Ag-ZnONPs were hydrothermally incorporated into the blend at different weight ratios. The prepared materials were characterized by SEM, EDX, TEM, XRD and FTIR. The thermal stability of the materials was determined by thermogravimetric analysis (TGA), and glass transition temperatures (Tg) was determined by differential scanning calorimeter (DSC). The oxidant, antioxidant, antimicrobial, and cytotoxic properties of PPFMA, Ag-ZnONPs, PPFMA-NaCMC blend, and nanocomposites were investigated in detail. The total oxidant state (TOS) value of the NaCMC-PPFMA blend, which was 0.72 μmol equivalent H2O2/L, increased to 7.2-10.4 μmol equivalent H2O2/L with the addition of Ag-ZnONPs. Ag-ZnONPs decreased total antioxidant state (TAS) levels of the nanocomposites while increasing their oxidant activity. Therefore, an increase in the antimicrobial activity of the nanocomposites was observed. Adding Ag-ZnONPs to the NaCMC-PPFMA blend increased the thermal stability by 22 °C and the Tg value by 9 °C. Finally, the potential of Ag-ZnONPs containing nanocomposites in wound healing therapies was examined. The findings suggest that nanocomposites prepared by incorporating Ag-ZnONPs into the semi-synthetic NaCMC-PPFMA blend can be a source of bio-safe raw materials and can be used as potential wound healers.

Bone Cement Waste in Total Knee Arthroplasty: A Preliminary Study of Scope and Cost

Background

Medical waste is both costly and detrimental to the environment, and operating room waste represents a substantial portion of this. To the authors' knowledge, bone cement waste in total knee arthroplasty (TKA) has not previously been studied. The vast majority of TKA are cemented, and the volume of TKA is forecast to increase. Given this, we studied the waste resulting from the routine use of 2 40-gram bags of polymethyl methacrylate (PMMA) powder during cementing in primary TKA.

Methods

We first studied the yield of commercially available plain and gentamicin medium-viscosity bone cement powder and calculated the cost/gram of product. We then collected the PMMA remaining after primary TKA to determine the average amount of waste, its cost, and possible correlations with patient and implant metrics that could improve efficiency and reduce waste of PMMA.

Results

Overall, PMMA waste averaged 59% per TKA, at a median cost of $129 per case. Cost of waste was greater when gentamicin cement was used, as its cost was 2.5X that of plain cement. Implant sizes and surface area ranges were identified that could reliably allow the use of a single 40-gram package of powder, potentially reducing PMMA waste.

Conclusions

While it is acknowledged that zero-waste cementing is not practical, any reduction in waste that does not compromise either the flow of surgery or the adequacy of fixation would be beneficial. Reevaluation of PMMA techniques could reduce waste, resulting in both cost savings and improved sustainability in arthroplasty.

Preparation of nanocomposite based on chitosan-PDCOEMA containing biosynthesized ZnO: Biological and thermal characterization

In this study, poly(2-(3,5-dichloroanilino)-2-oxoethyl 2-methylprop-2-enoate) (PDCOEMA), a new synthetic polymer based on methacrylate, was synthesized and characterized. The blend of PDCOEMA with chitosan (CS) was prepared by the hydrothermal method and the DSC technique confirmed its formation. It was observed that PDCOEMA increased the thermal stability and glass transition temperature (Tg) of CS. The Tg value of the PDCOEMA-CS blend was increased at about 7 °C with the highest ZnO NPs contribution rate. PDCOEMA-CS/ZnO nanocomposites were prepared by adding ZnO NPs produced by biosynthesis at different weight ratios to the PDCOEMA-CS blend by hydrothermal method. When the thermal stability of nanocomposites determined by TGA was examined, it was observed that it increased significantly compared to CS. While the initial decomposition temperature of CS was 270 °C, this value increased to 293 °C after blending with DCOEMA, and to 317 °C with the addition of 7 % ZnO NPs. Antimicrobial, anticancer, cytotoxic, antioxidant, and wound healing properties of PDCOEMA, CS, PDCOEMA-CS blend, and nanocomposites were determined. According to the obtained results, it was observed that nanocomposites containing 5 % and 7 % ZnO NPs showed good anticancer activity against A549 cells at a dose of 10 μg/mL. The results show that the produced nanocomposites can contribute to developing CS-based materials.

New dimethacrylate monomers based on phenolphthalein and resveratrol for the application of dental materials

Potential estrogenic effects and changes in fertility are some of the health problems associated with bisphenol A (BPA) derivatives used to produce some polymers, including dental materials that contain Bis-GMA. Those issues drove this study proposing the synthesis of methacrylate resveratrol and phenolphthalein monomers that, combined with diluent monomers, generate copolymers. Their key characteristics were determined and analyzed on the chemical structure-property perspective considering monomer planarity and flexibility based on molecular dynamic simulations.

METHODS

Methacrylate resveratrol ((E)-5-(4-(methacryloyloxy)styryl)-1,3-phenylenebis(2-methylacrylate)), EMPM) and methacrylate phenolphthalein ((3-oxo-1,3-dihydroisobenzofuran-1,1-diyl)bis(4,1-phenylene)bis(2-methylacrylate)), DIFPM) were synthesized through the reaction of precursors with methacryloyl chloride. After monomers purification and spectroscopic characterization (FTIR and NMR), the following copolymers were produced: DIFPM/TEGDMA and Bis-GMA/TEGDMA, EMPM/HEMA and Bis-GMA/HEMA. Microhardness, degree of conversion, water sorption and contact angle data were statistically analyzed through one-way ANOVA and Tukey's test (p ≤ 0.05).

RESULTS

The DIFPM molecular structure's reduced flexibility proved to be an important factor to inhibit TEGDMA cyclization. In turn, the EMPM molecule's high planarity modified the spatial organization of the HEMA copolymer, altering the water diffusion and, therefore, the water sorption when compared to Bis-GMA copolymers.

CONCLUSION

The scientific findings contribute to better understand the effect of monomer chemical structures, molecular geometry, and planarity on some physicochemical properties of copolymers. Knowledge that can contribute to the design of new monomers to replace Bis-GMA.

Sulfur-Free Radical RAFT Polymerization of Methacrylates in Homogeneous Solution: Design of exo-Olefin Chain-Transfer Agents (R-CH2 C(=CH2 )Z)

In this work, the development of exo-olefin compounds (R-CH₂ C(=CH₂ )Z) as chain-transfer agents for the sulfur-free reversible addition-fragmentation chain transfer (RAFT) radical polymerization of methacrylates in homogeneous solution is described. A series of exo-olefin compounds with a methyl methacrylate (MMA) dimer structure as the R group and a substituted α-methylstyrene unit as the -CH₂ C(=CH₂ )Z (Z: Ph-Y) group were synthesized and used for the radical polymerization of MMA in toluene and PhC(CF₃ )₂ OH. These compounds underwent transfer of the CH₂ C(=CH₂ )Z group via addition-fragmentation of the propagating methacryloyl radical. More electron-donating (Y) substituents, such as methoxy and dimethylamino groups, produced polymers with narrower molecular weight distributions. A continuous monomer addition method further improved molecular weight control and enabled the synthesis of colorless, sulfur-free, multiblock copolymers of methacrylates in homogeneous solutions.

The antimicrobial, physical, and chemical properties of a riboflavin-loaded dental resin intended for antimicrobial photodynamic therapy

BACKGROUND

Dental caries remain a significant global health challenge. Unfortunately, current dental materials lack sufficient antimicrobial power to address the pathogenic species involved in this disease. In this study the potential to load a dental resin blend (RB) with riboflavin (B2) for use in an antimicrobial photodynamic therapy (aPDT) approach was investigated.

METHODS

B2 was added to our experimental RB (0.1 - 10 wt%). Upon investigating the degree of conversion and specimen integrity of the RB as a function of B2 concentration, it was determined that loading should be restricted to 0.1, 1.0, and 1.5 wt%. Subsequent investigation included water sorption (WS) and solubility (SL), as well as shear bond strength (SBS) and flexural strength (FS) of the specimens after 24 h and 28-day water storage. Lastly, the antimicrobial response of Streptococcus mutans (S. mutans) biofilm following 6 h growth and 60 s of blue LED light (1.3 J/cm²) in an aPDT-based approach was measured.

RESULTS AND CONCLUSIONS

Adding up to 1.5 wt% B2 had minimal impact on the FS or SBS of the RB. However, aging for 28-days notably increased the FS by as much as 50% for the 1.5 wt% B2-loaded RB. In addition, adding 1.5 wt% B2 resulted in a significant reduction in WS/SL of the RB. Lastly, while adding B2 did not change the antimicrobial response, this was an initial study under these conditions and future investigation will seek to optimize light parameters to produce a more agonistic response. Overall, a riboflavin-loaded dental resin shows significant promise for utilization in restorative dentistry with aPDT.

Synthesis of Moringa oleifera coated silver-containing nanocomposites of a new methacrylate polymer having pendant fluoroarylketone by hydrothermal technique and investigation of thermal, optical, dielectric and biological properties

Firstly, silver nanoparticles were synthesized by green synthesis method from Moringa oleifera extract. Nanocomposites containing newly synthesized methacrylate polymer, poly 2-(4-fluorophenyl)-2-oxoethyl-2-methylprop-2-enoate (PFPAMA) and Ag nanoparticles from M. oleifera in different mass ratios (1, 3, and 5 wt%) were synthesized using the hydrothermal method. The morphological and structural properties of the materials have been examined by SEM, FTIR, UV, TGA, and XRD techniques. The activation energies (E_a) related to thermal decomposition of the nanocomposites were estimated by the Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose methods by using non-isothermal TGA experiments. The thermal stability, glass transition temperature (T_g), and the thermal decomposition activation energy (E_a) values of nanocomposites were increased by increasing the Ag nanoparticles amount on the composite. The dielectric constant (ε'), the dielectric loss factor (ε″) and ac conductivity of neat PFPAMA and nanocomposites were also measured for the frequency range of 100 Hz to 2 kHz at 25 °C. It was seen that the frequency dependence of the dielectric constant and dielectric loss factor decreased with increasing frequency. The biological activities of nanocomposites against gram-positive (Staphylococcus aureus), gram-negative (Escherichia coli) bacteria and Candida krusei yeast were also tested. The antibacterial effect increased against both bacterial species as the amount of Ag nanoparticles from M. oleifera in the nanocomposites increased. In addition, the wound healing properties of nanocomposites were investigated by the scratch wound test.

Fabrication of monolithic capillary columns with inner diameter 50-530 μm employing a mixture of pentaerythritol tetraacrylate and polyhedral oligomeric silsesquioxane-methacrylate as crosslinkers

Highly crosslinked monolithic capillary columns with inner diameters in the range of 50-530 μm were prepared by radical polymerization of pentaerythritol tetraacrylate, polyhedral oligomeric silsesquioxane-methacrylate, and n-octadecyl methacrylate in the presence of methanol, dodecyl alcohol, and polyethyleneglycol lauryl ether. Columns were evaluated by inverse size-exclusion chromatography employing a set of polystyrene standards of narrow molecular-size distribution and by scanning electron microscopy. Chromatographic performance under reversed-phase conditions was also evaluated. The combination of two effective crosslinkers as pentaerythritol tetraacrylate and polyhedral oligomeric silsesquioxane-methacrylate in the polymerization mixture allows for the preparation of robust and efficient monolithic capillary columns within a fairly wide range of internal diameters. This article is protected by copyright. All rights reserved.

Case series of coronary artery aneurysms after Everolimus eluting stent implantation and comparison with Sirolimus eluting stents

Background

Coronary artery aneurysms after drug eluting stents are rare. We present a case series of type II coronary aneurysms after implantation of Everolimus eluting stents including patients developing giant aneurysms with a toxic course.

Case presentation

Over a span of 3.5 years at our center 2572 patients were implanted Everolimus eluting stents out of which 4 patients developed coronary type II aneurysms an incidence of 0.00156 whereas 5838 patients were implanted Sirolimus eluting 2nd generation stents out of which 2 patients developed similar aneurysms with an incidence of 0.00034. The slight increase in incidence in Everolimus stents does not reach statistical significance (p = 0.054) and is limited by single centre non randomized study. We also propose a hypothesis that the slight increase in the incidence maybe due to allergy to Methacrylate present in Everolimus eluting Xience stent’s primer which is absent in other Sirolimus eluting stents used at our center but that needs to be further investigated. We also found some patients who developed giant aneurysms including Left main aneurysms. In our series operative repair of these patients had better outcomes than covered stent deployment but larger trials maybe needed to confirm the same.

Conclusions

Coronary artery aneurysms after stent implantation are rare but occasionally giant aneurysms are formed with a toxic course. The incidence and morphology of aneurysms after Everolimus and Sirolimus eluting stent deployment do not differ much.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12872-022-02503-1.

Composite repair: On the fatigue strength of universal adhesives

OBJECTIVES

To determine whether the composition of universal adhesives and the use of silane coupling agents could affect the fatigue strength of composite repair.

METHODS

Composite samples were aged in water at 37 °C for 90 days and bonded to fresh composite to produce twin-bonded bar-shaped composite specimens (2 × 2 × 12 mm). Five universal adhesives, a multistep composite repair system and a hydrophobic solvent-free resin associated to a separate silane coupling agent application were used for bonding. Composite samples were tested under 4-pointflexure initially at quasi-static loading (n = 12) followed by cyclic loading (n = 25). The stress-life fatigue behavior was evaluated following the staircase method at 4 Hz. The unfractured side of cyclic loaded beams were evaluated under SEM to determine crack initiation sites. Fatigue data was analyzed by ANOVA and Tukey test and Wilcoxon Rank Sum Test (α = 0.05).

RESULTS

Bonding protocols were unable to restore the cohesive strength of the nanofilled composite (p < 0.05). Fatigue testing was more discriminative to reveal discrepancies in composite repair than conventional quasi-static loading. While the composition of universal adhesives affected composite repair potential, the highest endurance limits occurred for the separate silane coupling agent application. Crack propagation sites were mostly located on the aged composite surface.

SIGNIFICANCE

Although a trend for simplification invariably overruns current adhesive dentistry, composite repair using solely universal adhesives may result in inferior repair potential. The additonal use of silane coupling agents remains as an important procedure in composite repairs.

Fast and selective synthesis of mono-substituted sucrose methacrylate ester monomer

Sucrose methacrylate (SM) is a key monomer for synthesizing biocompatible polymers with a carbohydrate core. However, controlled SM synthesis is challenging due to the possible formation of regio-isomers. This study describes SM synthesis that involves ultrasound irradiation of a homogeneous basic medium. The selectivity for mono-substituted SM was 86% within 30 min of reaction. The newly developed methodology is faster and more selective than that of mono-substituted SM synthesis already described in the literature.

Novel methacrylate copolymers functionalized with fluoroarylamide; copolymerization kinetics, thermal stability and antimicrobial properties

In the first step of this study, 2-oxo-2-[(2,4,6-trifluorophenyl)amino]ethyl-2-methylprop-2-enoate(OTFAMA) monomer was synthesized and characterized. Then, a series copolymers were obtained by free-radical copolymerization method of OTFAMA and glycidyl methacrylate (GMA), which is a commercial monomer at 65 °C in 1,4-dioxane solvent. Structural characterizations of synthesized monomer and copolymers were carried out using FTIR, ¹H-¹³C-NMR instruments. The composition of the copolymers was estimated by elemental analysis. The reactivity ratios (r₁ and r₂) were obtained from the various linear graphical methods. The values of r₁ (OTFAMA) = 0.33 and r₂ (GMA) = 0.45 were found from the same graphical methods. The thermal behaviors of all the polymers have been investigated using the differential scanning calorimetry (DSC) and the thermogravimetric analysis (TGA). A kinetic study of the thermal decompostion of copolymers was investigated using thermogravimetric analyzer with non-isothermal methods selected for analyzing solid-state kinetics data. The average activation energy values were calculated via Kissinger and Ozawa models in a period of α = 0.10-0.80. Photo stability of the copolymers was investigated. Also, the biological activity of the copolymers against different bacterial and fungal species has been investigated.

Effect of side-group methylation on the performance of methacrylamides and methacrylates for dentin hybridization

The stability of the bond between polymeric adhesives to mineralized substrates is crucial in many biomedical applications. The objective of this study was to determine the effect of methyl substitution at the α- and β-carbons on the kinetics of polymerization, monomer hydrolytic stability, and long-term bond strength to dentin for methacrylamide- and methacrylate-based crosslinked networks for dental adhesive applications.

METHODS

Secondary methacrylamides (α-CH3 substituted=1-methyl HEMAM, β-CH3 substituted=2-methyl HEMAM, and unsubstituted=HEMAM) and OH-terminated methacrylates (α- and β-CH3 mixture=1-methyl HEMA and 2-methyl HEMA, and unsubstituted=HEMA) were copolymerized with urethane dimethacrylate. The kinetics of photopolymerization were followed in real-time using near-IR spectroscopy. Monomer hydrolysis kinetics were followed by NMR spectroscopy in water at pH 1 over 30 days. Solvated adhesives (40 vol% ethanol) were used to bond composite to dentin and microtensile bond strength (μTBS) measured after 24h and 6 months storage in water at 37°C.

RESULTS

The rate of polymerization increased in the following order: OH-terminated methacrylates≥methacrylamides>NH2-terminated methacrylates, with minimal effect of the substitution. Final conversion ranged between 79% for 1-methyl AEMA and 94% for HEMA. 1-methyl-HEMAM showed the highest and most stable μTBS, while HEMA showed a 37% reduction after six months All groups showed measurable degradation after up to 4 days in pH 1, with the methacrylamides showing less degradation than the methacrylates. Additionally, transesterification products were observed in the methacrylamide groups.

SIGNIFICANCE

Amide monomers were significantly more stable to hydrolysis than the analogous methacrylates. The addition of a α- or β-CH3 groups increased the rate of hydrolysis, with the magnitude of the effect tracking with the expected base-catalyzed hydrolysis of esters or amides, but opposite in influence. The α-CH3 substituted secondary methacrylamide, 1-methyl HEMAM, showed the most stable adhesive interface. A side reaction was observed with transesterification of the monomers studied under ambient conditions, which was not expected under the relatively mild conditions used here, which warrants further investigation.

Effect of post-rinsing time on the mechanical strength and cytotoxicity of a 3D printed orthodontic splint material

OBJECTIVE

Since the post-rinsing time is inconsistently recommended, this study aims to investigate the effect of post-rinsing time on the flexural strength and cytotoxicity of an stereolithographically (SLA) printed orthodontic splint material.

METHODS

SLA-printed specimens were ultrasonically rinsed with isopropanol (IPA) for 5 min, 12 min, 20 min, 30 min, 1 h, and 12 h, respectively. Surface characterization was conducted by scanning electron microscopy and roughness measurements. Flexural strength was evaluated using a three-point bending test. Cytotoxicity was determined by direct contact test and extract test. For both tests, cell viability (live/dead staining) and cell metabolic activity (CCK-8 assay) were evaluated. Additionally, water sorption and water solubility were tested to analyze the mass loss from immersion.

RESULTS

No apparent surface alterations could be detected on the samples post-rinsed for less than 1 h. In contrast, when the post-rinsing time was prolonged to 12 h, surface fissures could be observed. Flexural strength linearly decreased with increasing post-rinsing time. All post-processed specimens did not show an obvious cytotoxic effect.

SIGNIFICANCE

The removal of cytotoxic methacrylate monomers by post-rinsing with IPA could be achieved in 5 min. Extending post-rinsing time could not improve the cytocompatibility of the SLA-printed orthodontic splint material, and may result in a decrease in flexural strength.

Dual-functional alginate crosslinker: Independent control of crosslinking density and cell adhesive properties of hydrogels via separate conjugation pathways

Alginate is an abundant natural polysaccharide widely utilized in various biomedical applications. Alginate also possesses numerous hydroxyl and carboxylate functional groups that allow chemical modifications to introduce different functionalities. However, it is difficult to apply various chemical reactions to alginate due to limited solubility in organic solvents. Herein, functional moieties for radical polymerization and cell adhesion were separately conjugated to hydroxyl and carboxylate groups of alginate, respectively, in order to independently control the crosslinking density and cell adhesive properties of hydrogels. Sodium counterions of alginate are first substituted with tetrabutylammonium ions to facilitate the dissolution in an organic solvent, followed by in situ conjugations of (1) cell adhesion molecules (CAM) via carbodiimide-mediated amide formation and (2) methacrylate via ring-opening nucleophilic reaction. The resulting CAM-linked methacrylic alginate was able to not only crosslink different monomers to form hydrogels with varying mechanical properties, but also induce stable cell adhesion to the hydrogels.

Synthesis of di- and triacrylamides with tertiary amine cores and their evaluation as monomers in dental adhesive interfaces

PURPOSE/AIM

In an attempt to increase the service life of dental adhesive interfaces, more hydrolytically and enzymatically-stable methacrylate alternatives, such as methacrylamides, have been proposed. The aim of this study was to investigate polymerization behavior, as well as mechanical and biological properties of experimental adhesives containing multi-functional acrylamides.

MATERIALS AND METHODS

Multi-functional acrylamides (N,N-Bis[(3-methylaminoacryl)propyl]methylamine - BMAAPMA, Tris[(2-methylaminoacryl)ethyl]amine - TMAAEA, N,N'-bis(acrylamido) 1,4-diazepane - BAADA, N,N-Diethyl-1,3-bis(acrylamido)propane - DEBAAP) or HEMA (2-Hydroxyethyl methacrylate - control) were added at 40 wt% to UDMA. 0.2 wt% DMPA and 0.4 wt% DPI-PF6 were used as initiators. Polymerization kinetics was followed in real-time in near-IR during photoactivation (320-500 nm, at 630 mW/cm²). Water sorption/solubility and flexural strength/modulus were measured according to ISO 4049. ¹H NMR was used to assess monomer degradation kinetics. MTT assay was used to assess cytotoxicity against OD-21 and DPSC cells. Biofilm formation and adhesion were assessed by Luciferase Assay and Impingement technique, respectively. Solvated adhesives (40 vol% ethanol) were used to test interfacial adhesion strength. The results were analyzed by ANOVA/Tukey's test (α = 0.05).

RESULTS

In general, the pure methacrylate mixture had higher rate of polymerization (Rp_max), degree of conversion (DC) at Rp_max, and final DC than the acrylamides. Flexural properties after water storage decreased between 11 and 65%, more markedly for acrylamides. Interfacial bond strength was greater and more stable long-term for the newly synthesized acrylamide formulations (less than 4% reduction at 6 months) compared to the methacrylate experimental control (42% reduction at 6 months). HEMA degraded by almost 90%, while the acrylamides showed no degradation in acidic conditions. Cytotoxicity and biofilm formation, in general, were similar for all groups.

CONCLUSIONS

Despite demonstrating high water sorption, the acrylamide-containing materials had similar mechanical and biological properties and enhanced interfacial bond strength stability compared to the methacrylate control.

Methacrylamide-methacrylate hybrid monomers for dental applications

OBJECTIVES

The susceptibility of methacrylates to hydrolytic and enzymatic degradation may be a contributing factor limiting the clinical lifespan of resin composite restorations. The elimination of labile ester bonds is a potential advantage of methacrylamides, which have been shown to produce more stable restorative interfaces. The rationale of this study is to design hydrolytically and enzymatically stable adhesive monomers, with the added benefit of being able to form crosslinked networks. The objective of this study was to synthesize difunctional, hybrid methacrylate-methacrylamide monomers, and evaluate them as potential monomers for dental adhesives.

MATERIALS AND METHODS

HEMA, TEGDMA (controls) or secondary methacrylamides (HEMAM - commercially available, 2EM and 2dMM - newly synthesized) either bearing a hydroxyl group or a methacrylate functionality (Hybrids-Hy), were added at 40mass% to bisGMA. The photoinitiator system consisted of 2-dimethoxyphenyl acetophenone (DMPA) and diphenyl iodonium hexafluorophosphate (DPI-PF6) at 0.2 and 0.4mass%, respectively. Polymerization kinetics were followed in real-time by near-IR spectroscopy during light activation at 630mW/cm² for 300s. Water sorption and solubility (WS, SL) were measured according to ISO 4049. Storage modulus in shear (G') for 300s was obtained by oscillatory rheometry. For the microtensile bond strength (μTBS), fully formulated adhesives containing 40vol% ethanol were used to restore caries-free human third molars. Bonded specimens with 1mm² cross-sectional area were tested after 48h and 6 months storage in water at 37°C. Single bond (SB) was tested as a commercial control. Data were analysed with one-way ANOVA and Tukey's test and Student's t-test (α=0.05).

RESULTS

In general, hybrid versions showed lower polymerization rate and degree of conversion, whereas the methacrylate controls, HEMA and TEGDMA, showed the highest values. The hybrid versions showed lower values of WS and SL than their monofunctional versions. HEMAM Hy showed the highest values of G' and TEGDMA, 2EM, and 2dMM-Hy the lowest. The μTBS values between 48h and 6 months were statistically reduced only for the HEMA and both 2dMM materials. The formulation containing the monofunctional methacrylamide (HEMAM) showed only 9% reduction in μTBS after 6 months of aging, while the other groups showed a decrease ranging between 18% and 33%.

CONCLUSION

Overall, hybrid monomers showed lower reactivity than their analogous monofunctional versions, but had markedly lower water sorption. Shear storage modulus was affected differently by the addition of the second functionality. HEMAM-containing systems were able to maintain stable long-term dentin bond strength, which demonstrates that bonding stability is a result of the complex interplay among the factors studied.

CLINICAL SIGNIFICANCE

The novel monomers showed here are potential alternatives to the current methacrylate adhesives, with selected formulations presenting greater bond stability.

In vitro effects of dental monomer exposure - Dependence on the cell culture model

Methacrylate monomers are major components of resin-based biomaterials. The polymerization of these materials is never complete, and methacrylates leaking from cured materials cause exposure of patients. Only some selected methacrylates have thoroughly been tested for possible interaction with living cells. In the current study, we compared the effects of 2-hydroxyethyl-methacrylate (HEMA; a carefully studied methacrylate) and hydroxypropyl-methacrylate (HPMA; a scarcely investigated methacrylate). Five cell lines differing in both source and cell type were used. The cells were exposed to methacrylates (1-8 mM). Cell viability, cell death, glutathione levels, reactive oxygen species (ROS), and cell growth pattern were measured. Both methacrylates reduced cell viability, and glutathione depletion was observed in all cell lines. The cell death pattern varied among the cell lines. The ROS levels and cell growth pattern also differed between the cell lines after exposure to methacrylate monomers. No difference between HEMA and HPMA exposures were observed in any of the cell lines. The variation between cell lines shows that the measured methacrylate toxicity depends heavily on the test system chosen. Further, the conformity between HEMA and HPMA effects suggests that the two methacrylates similarly affect living cells.

Effects of S. mutans gene-modification and antibacterial monomer dimethylaminohexadecyl methacrylate on biofilm growth and acid production

OBJECTIVES

Antibacterial quaternary ammonium monomers (QAMs) are used in resins. The rnc gene in Streptococcus mutans (S. mutans) plays a key role in resisting antibiotics. The objectives of this study were to investigate for the first time: (1) the effects of rnc deletion on S. mutans biofilms and acid production; (2) the combined effects of rnc deletion with dimethylaminohexadecyl methacrylate (DMAHDM) on biofilm-inhibition efficacy.

METHODS

Parent S. mutans strain UA159 (ATCC 700610) and the rnc-deleted S. mutans were used. Bacterial growth, minimum inhibitory concentration (MIC), and minimal bactericidal concentration (MBC) were measured to analyze the bacterial susceptibility of the parent and rnc-deleted S. mutans against DMAHDM, with the gold-standard chlorhexidine (CHX) as control. Biofilm biomass, polysaccharide and lactic acid production were measured.

RESULTS

The drug-susceptibility of the rnc-deleted S. mutans to DMAHDM or CHX was 2-fold higher than parent S. mutans. The drug-susceptibility did not increase after 10 passages (p < 0.05). Deleting the rnc gene increased the biofilm susceptibility to DMAHDM or CHX by 2-fold. The rnc-deletion in S. mutans reduced biofilm biomass, polysaccharide and lactic acid production, even at no drugs. DMAHDM was nearly 40 % more potent than the gold-standard CHX. The combination of rnc deletion+DMAHDM treatment achieved the greatest reduction in biofilm biomass, polysaccharide synthesis, and lactic acid production.

SIGNIFICANCE

Gene modification by deleting the rnc in S. mutans reduced the biofilm growth and acid production, and the rnc deletion+DMAHDM method showed the greatest biofilm-inhibition efficacy, for the first time. The dual strategy of antibacterial monomer+bacterial gene modification shows great potential to control biofilms and inhibit caries.

Phenotyping Occupational Asthma Caused by Acrylates in a Multicenter Cohort Study

BACKGROUND

While acrylates are well-known skin sensitizers, they are not classified as respiratory sensitizers although several cases of acrylate-induced occupational asthma (OA) have been reported.

OBJECTIVE

To evaluate the characteristics of acrylate-induced OA in a large series of cases and compare those with OA induced by other low-molecular-weight (LMW) agents.

METHODS

Jobs and exposures, clinical and functional characteristics, and markers of airway inflammation were analyzed in an international, multicenter, retrospective cohort of subjects with OA ascertained by a positive inhalation challenge to acrylates (n = 55) or other LMW agents (n = 418) including isocyanates (n = 125).

RESULTS

Acrylate-containing glues were the most prevalent products, and industrial manufacturing, dental work, and beauty care were typical occupations causing OA. Work-related rhinitis was more common in acrylate-than in isocyanate-induced asthma (P < .001). The increase in postchallenge fractional exhaled nitric oxide was significantly greater in acrylate-induced OA (26.0; 8.2 to 38.0 parts per billion [ppb]) than in OA induced by other LMW agents (3.0; -1.0 to 10.0 ppb; P < .001) or isocyanates (5.0; 2.0 to 16.0 ppb; P = .010). Multivariable models confirmed that OA induced by acrylates was significantly and independently associated with a postchallenge increase in fractional exhaled nitric oxide (≥17.5 ppb).

CONCLUSIONS

Acrylate-induced OA shows specific characteristics, concomitant work-related rhinitis, and exposure-related increases in fractional exhaled nitric oxide, suggesting that acrylates may induce asthma through different immunologic mechanisms compared with mechanisms through which other LMW agents may induce asthma. Our findings reinforce the need for a reevaluation of the hazard classification of acrylates, and further investigation of the pathophysiological mechanisms underlying their respiratory sensitizing potential.

Entrapment of chitosan, pectin or κ-carrageenan within methacrylate based hydrogels: Effect on swelling and mechanical properties

Composite hydrogels were obtained by the entrapment of chitosan, pectin or κ-carrageenan within methacrylate-based hydrogels to improve their swelling and the mechanical properties. The results indicated that the water uptake (WU) of κ-carrageenan and chitosan hydrogels were until 3.5 and 2.2 times higher than the WU of the synthetic hydrogel, respectively. The surface morphologies of the hydrogels showed that the pectin and κ-carrageenan favors the formation of larger and more defined pores. The mechanical properties indicated that the pectin increased slightly the mechanical properties and the κ-carrageenan improves the mechanical properties of the synthetic hydrogel reaching up 400 N of compression load. Therefore, the entrapment of κ-carrageenan within synthetic hydrogels improved both the swelling and the mechanical properties. The biocompatibility of the hydrogels was evaluated with in vitro cytotoxicity assays and the results indicated that they could be considered as candidates for biomedical use.

Physical properties and cytotoxicity of antimicrobial dental resin adhesives containing dimethacrylate oligomers of Ciprofloxacin and Metronidazole

OBJECTIVE

Antimicrobial oligomers synthesized from ciprofloxacin (CF) and metronidazole (MN) were investigated for their potential use in dental adhesives.

METHODS

Susceptibility of the cariogenic bacterium Streptococcus mutans UA159 to CF, MN, and CF/MN combination was evaluated. Hydrolytic stability and drug release from the oligomers was studied in buffer and simulated human salivary esterase conditions. Cytotoxicity of films with 15wt% drug oligomers co-polymerized with commercial monomers were assessed using human gingival fibroblasts (HGFs). In-house adhesives were prepared and characterized for viscosity. Polymerized films were analysed for gel content and water swelling. Interfacial fracture toughness (K_IC) of composites bonded to dentin by either a 2 or 3-step etch-and-rinse approach using the in-house formulated adhesives was measured.

RESULTS

The respective minimum inhibitory concentration for CF and MN against S. mutans was 0.7 and 2400μg/mL, with the combination having an additive effect (0.35μg/mL CF with 1200μg/mL MN). Antibiotics were released upon hydrolysis of the oligomers. Films containing the drug oligomers were not cytotoxic against HGFs. Replacing 2-hydroxyethyl methacrylate with the drug oligomers increased the viscosity of the experimental adhesives, reduced gel content, and decreased swelling of films in water. Antimicrobial adhesives demonstrated bonding to dentin with interfacial K_IC values comparable to the in-house control in the 2-step application, and with slightly lower K_IC values in the 3-step approach.

SIGNIFICANCE

The antimicrobial oligomers can be incorporated into dental adhesive systems using formulations that show comparable fracture toughness to commercial materials, and may provide a means to deliver local antimicrobial drug release at the marginal interface.

Effects of hydrophilic monomers on sorptive properties of divinylbenzene-based reversed phase sorbents

Solid phase extraction (SPE) has been extensively used as a pretreatment method. In SPE methods, commercially available reversed phase type sorbents, which consist of macroporus styrene-divinylbenzene or copolymers including divinylbenzene (DVB) and hydrophilic monomers, have been applied to a variety of samples. The later sorbents are called hydrophilic lipophilic balanced (HLB) type sorbents. Hydrophilic monomers in hydrophilic lipophilic balanced type sorbents contribute to the increase in retention of polar compounds, because hydrophilic monomers improve the wettability and increase the interaction with polar compounds as analytes. In this study, three different methacrylate monomers (ethylene glycol dimethacrylate (EGDMA), glycerol dimethacrylate (GDMA) and trimethylolpropane trimethacrylate (TMPTMA)), which are expected to improve the retention of polar compounds, were chosen, and DVB-based copolymetric sorbents including the three monomers were newly synthesized. Among them, the sorbents including GDMA or TMPTMA gave higher recoveries to polar compounds such as uridine and adenine than that including EGDMA. The optimization studies of hydrophilic lipophilic balance, inert diluent and the purity of DVB improved the sorptive abilities of the sorbents. The developed sorbents have higher recoveries for variety of polar compounds (cytosine, uracil, cytidine, uridine, 2'-deoxycytidine, 2'-deoxyguanosine, adenine, thymidine, adenosine and 2'-deoxyadenosine) than commercially available hydrophilic lipophilic balanced type sorbents, while the recoveries for theophylline were comparable between the proposed sorbents and the commercial sorbents.

Development of a Porcine Model of Coronary Stenosis Using Fully Percutaneous Techniques Suitable For Performing Cardiac Computed Tomography, CT-Perfusion Imaging and Fractional Flow Reserve

BACKGROUND

The aim of this study was to develop and describe percutaneous coronary angiographic techniques to create a porcine model of acute coronary stenosis with methacrylate plugs that can by assessed using fractional flow reserve (FFR), invasive coronary angiography and coronary computed tomographic (CT) perfusion imaging without introducing artefacts associated with surgical models.

METHODS

Following animal care and institutional approval and using percutaneous coronary catheterisation techniques within an animal laboratory we introduced precision drilled methacrylate plugs into one of the three main coronary arteries of 10 experimental female pigs. Coronary pressure wire measurements were performed across the experimental stenosis for the calculation of FFR. Invasive coronary angiograms were obtained in stenosed arteries. Animals were transported to a dual source CT scanner (Siemens Healthcare, Forcheim, Germany) and CT perfusion imaging was performed.

RESULTS

Ten (10) pigs were investigated with seven data sets obtained. Three (3) pigs expired prior to CT imaging secondary to pneumothorax, high grade coronary stenosis with induced cardiac arrhythmia and iatrogenic air embolism. Graded coronary stenosis was produced in six pigs in the LAD (2), LCX (2) and RCA (2) territories and one animal served as a control. Fractional flow reserve ranged from 0.21 to 0.91. Myocardial blood flow derived from dynamic CT perfusion imaging ranged from 3.5 to 136.7ml/100ml of tissue/minute. No artefacts from the deployment of the methacrylate plug, nor the plug itself, were identified.

CONCLUSIONS

Fully percutaneous preparation of a pig model of acute coronary stenosis is feasible and provides subjects for imaging that are free of surgically induced artefact. This technique is substantially less expensive than surgically induced coronary stenosis and can be performed using standard catheterisation techniques with mobile imaging equipment. The technique is extendable to produce multivessel acute coronary stenosis and can be used for multimodality imaging.

Reducing the effect of polymerization shrinkage of temporary fixed dental prostheses by using different materials and fabrication techniques

OBJECTIVE

The aim of this laboratory study was to evaluate the horizontal and vertical effects of the polymerization shrinkage of three-unit temporary fixed dental prostheses (FDPs) on the position of the prepared teeth. In addition, the reduction of these effects by using different fabrication techniques was evaluated.

METHODS

A total of 192 temporary FDPs were fabricated using one methacrylate (MA) and two dimethacrylate (DMA) materials. Each material group (n=64) was divided into two groups according to the fabrication methods (M1: curing on the prepared teeth, M2: curing in a silicone mold). Each fabrication group was divided into four subgroups (n=8) according to the relining method used (B: no relining, S: spacer foil 300μm, DG: grinding-out with 500μm cutting depth, and FG: free grinding). The experimental apparatus consisted of two abutment teeth lowered at right angles into a silicone mold. One prepared tooth was embedded in silicone to simulate the periodontium and permit slight horizontal tooth movement. The dimensional changes were recorded with an optical microscope. The test images were superimposed and measured using image analysis software.

RESULTS

The statistical analysis showed that there were significantly higher horizontal changes for the MA than the DMA resins in M1, while there was none in M2. Regarding the vertical changes, there were significant differences between the baseline group and all relining and fabrication groups in all materials.

SIGNIFICANCE

Relining of directly fabricated temporary FDPs significantly reduces the effect of polymerization shrinkage and thus secures the position of the prepared teeth.

Preparation and characterization of Bis-GMA free dental resin system with synthesized dimethacrylate monomer TDDMMA derived from tricyclo[5.2.1.0(2,6)]-decanedimethanol

As a substitute for 2,2-bis[4-(2-hydroxy-3- methacryloxypropoxy)phenyl] propane (Bis-GMA) in dental materials, a new dimethacrylate monomer TDDMMA without bisphenol-A structure was synthesized through the reaction between tricyclo[5.2.1.0(2,6)]- decanedimethanol and 2-isocyanatoethyl methacrylate. The TDDMMA was mixed with triethylene glycol dimethacrylate (TEGDMA) to prepare Bis-GMA free dental resin. Physicochemical properties, such as double bond conversion (DC), polymerization shrinkage (VS), water sorption (WS) and solubility (SL), flexural strength (FS) and modulus (FM) and fracture energy of TDDMMA/TEGDMA resin system were investigated. Bis-GMA/TEGDMA resin system was used as a control. The results showed that, compared with Bis-GMA/TEGDMA resin system, TDDMMA/TEGDMA resin system had comparable VS and several advantages like higher DC, lower SL and better mechanical properties after water immersion.

Comparison of the uptake of methacrylate-based nanoparticles in static and dynamic in vitro systems as well as in vivo

Polymer-based nanoparticles are promising drug delivery systems allowing the development of new drug and treatment strategies with reduced side effects. However, it remains a challenge to screen for new and effective nanoparticle-based systems in vitro. Important factors influencing the behavior of nanoparticles in vivo cannot be simulated in screening assays in vitro, which still represent the main tools in academic research and pharmaceutical industry. These systems have serious drawbacks in the development of nanoparticle-based drug delivery systems, since they do not consider the highly complex processes influencing nanoparticle clearance, distribution, and uptake in vivo. In particular, the transfer of in vitro nanoparticle performance to in vivo models often fails, demonstrating the urgent need for novel in vitro tools that can imitate aspects of the in vivo situation more accurate. Dynamic cell culture, where cells are cultured and incubated in the presence of shear stress has the potential to bridge this gap by mimicking key-features of organs and vessels. Our approach implements and compares a chip-based dynamic cell culture model to the common static cell culture and mouse model to assess its capability to predict the in vivo success more accurately, by using a well-defined poly((methyl methacrylate)-co-(methacrylic acid)) and poly((methyl methacrylate)-co-(2-dimethylamino ethylmethacrylate)) based nanoparticle library. After characterization in static and dynamic in vitro cell culture we were able to show that physiological conditions such as cell-cell communication of co-cultured endothelial cells and macrophages as well as mechanotransductive signaling through shear stress significantly alter cellular nanoparticle uptake. In addition, it could be demonstrated by using dynamic cell cultures that the in vivo situation is simulated more accurately and thereby can be applied as a novel system to investigate the performance of nanoparticle systems in vivo more reliable.

Severe Onychodystrophy due to Allergic Contact Dermatitis from Acrylic Nails

Acrylic nails, including sculptured nails and the new ultraviolet-curable gel polish lacquers, have been associated with allergic contact dermatitis (ACD). We report 2 cases of ACD to acrylic nails with severe onychodystrophy and psoriasiform changes including onycholysis and subungual hyperkeratosis. In both cases, the patients did not realize the association between the use of acrylate-based manicures and nail changes. One patient had been previously misdiagnosed and treated unsuccessfully for nail psoriasis. The informed clinician should elicit a history of acrylic manicure in patients with these nail changes, especially in cases of suspected nail psoriasis refractory to treatment. Patch testing is a useful tool in confirming diagnosis.

Silorane, ormocer, methacrylate and compomer long-term staining susceptibility using ΔE and ΔE 00 colour-difference formulas

The aim of this study was to evaluate the staining susceptibility of a silorane (Filtek Silorane), an ormocer (Ceram X Duo), a methacrylate (Tetric EvoCeram) and a compomer (Dyract) exposed on the long term to various staining agents by using ΔE and ΔE 00 colour-difference formulas. Thirty-six disc-shaped specimens were made of each of the four chemically different materials, randomly divided in six groups (n = 6) and immersed in five staining solutions (red wine, juice, coke, tea and coffee) or stored dry (control) in an incubator at 37 °C for 99 days. Spectrophotometric measurements by means of a spectrophotometer (Spectroshade Handy Dental, MHT) were repeated over a white (L* = 92.6, a* = -1.2, b* = 2.9) and black (L* = 1.6, a* = 1.2, b* = -1.0) background made of plasticized paper, in order to determine the colour changes according to ΔE, ΔE 00 and translucency formulas. Statistical analysis was performed by means of factorial Anova, Fisher's LSD test (post hoc) and a Spearman rank correlation between ΔE and ΔE 00. When analysed over a white background, mean ΔE 00 values were highly significantly different and varied from 0.8 (Ceram X Duo/air) to 20.9 (Ceram X Duo/red wine). When analysed over a black background, mean ΔE 00 values were highly significantly different and varied from 1.0 (Ceram X Duo and Tetric/air) to 25.2 (Ceram X Duo/red wine). Differences in translucency varied from 0.3 (Ceram X Duo/air) to 21.1 (Ceram X Duo/juice). The correlation between ΔE and ΔE 00 over a white background was 0.9928, while over a black background, it was 0.9886.

Polymerization kinetics and polymerization stress in resin composites after accelerated aging as a function of the expiration date

OBJECTIVES

To determine the effect of material condition (new, aged, and expired) on the polymerization kinetics and polymerization stress of different classifications of dental composites.

MATERIALS AND METHODS

Specimens were obtained according to the following factors: Composites: (3M ESPE) Filtek P60, Filtek Z250, Filtek Z350XT, and Filtek Silorane; and Material conditions: new, aged, and expired. The syringe composites underwent an accelerated aging protocol (Arrhenius model) representing approximately 9 months of aging. Infrared (IR) spectra were obtained kinetically and were analyzed for: maximum conversion rate (%/s), time into exposure when maximum rate occurred (s), conversion at maximum rate (%), and total conversion (%) at 90 s by comparison of absorption IR peak ratios before and after polymerization. Polymerization was evaluated at the bottom surface of 2.0 mm-thick specimens. Polymerization stress was determined in a tensilometer, inserting the composite between acrylic rods fixed to clamps in a universal test machine and dividing the maximum load recorded by the rods cross-sectional area. Polymerization stress (MPa) was calculated at 300 s. Data were statistically analyzed by two-way ANOVA and Tukey's post hoc test (α=0.05).

RESULTS

The majority of the polymerization kinetic parameters were not influenced by the material condition. Silorane composite presented significantly lower conversion rate and lower conversion at the maximum rate when expired (p<0.05). The nanofilled composite (Filtek Z350XT) presented a significantly higher total conversion when aged and expired compared to the new one (p>0.05). In all conditions, Filtek Z350XT and Filtek Silorane presented significantly lower conversion rates (p < 0.05). Filtek Silorane also exhibited the lowest stress, irrespective of the material condition (p<0.05). The polymerization stress was not influenced by the material condition (p>0.05).

CONCLUSIONS

Most of the kinetic parameters are not influenced by the material condition. Filtek P60 and Filtek Z250 are more stable as both composites present similar polymerization kinetic results, irrespective of the material condition. Silorane composite presents lower stress values among the tested materials in all conditions. Aging does not affect stress development in restorative composites.

Synthesis of antibacterial methacrylate monomer derived from thiazole and its application in dental resin

A non-quaternary ammonium antibacterial methacrylate monomer MEMT derived from thiazole was synthesized and applied into UDMA/TEGDMA dental resin with a series of mass fraction (10 wt%, 20 wt%, and 30 wt%). Double bond conversion, polymerization shrinkage, water sorption, solubility, flexural strength and modulus, and antibacterial activity of MEMT containing resin formulations were investigated with UDMA/TEGDMA as control resin. The results showed that MEMT containing dental resin had higher double bond conversion than control resin. Compared with control polymer, all MEMT containing polymer had comparable or lower polymerization shrinkage, water sorption and solubility, except for the polymer with 30 wt% of MEMT which had higher water sorption and solubility than control polymer. The MEMT had no influence on flexural strength and modulus before water immersion, but all MEMT containing polymers had lower flexural strength and modulus than control polymer after water immersion. The MEMT could endow dental polymer with obvious antibacterial activity by immobilizing MEMT into the polymeric network.

Gelatin methacrylate microspheres for controlled growth factor release

Gelatin has been commonly used as a delivery vehicle for various biomolecules for tissue engineering and regenerative medicine applications due to its simple fabrication methods, inherent electrostatic binding properties, and proteolytic degradability. Compared to traditional chemical cross-linking methods, such as the use of glutaraldehyde (GA), methacrylate modification of gelatin offers an alternative method to better control the extent of hydrogel cross-linking. Here we examined the physical properties and growth factor delivery of gelatin methacrylate (GMA) microparticles (MPs) formulated with a wide range of different cross-linking densities (15-90%). Less methacrylated MPs had decreased elastic moduli and larger mesh sizes compared to GA MPs, with increasing methacrylation correlating to greater moduli and smaller mesh sizes. As expected, an inverse correlation between microparticle cross-linking density and degradation was observed, with the lowest cross-linked GMA MPs degrading at the fastest rate, comparable to GA MPs. Interestingly, GMA MPs at lower cross-linking densities could be loaded with up to a 10-fold higher relative amount of growth factor than conventional GA cross-linked MPs, despite the GA MPs having an order of magnitude greater gelatin content. Moreover, a reduced GMA cross-linking density resulted in more complete release of bone morphogenic protein 4 and basic fibroblast growth factor and accelerated release rate with collagenase treatment. These studies demonstrate that GMA MPs provide a more flexible platform for growth factor delivery by enhancing the relative binding capacity and permitting proteolytic degradation tunability, thereby offering a more potent controlled release system for growth factor delivery.

Investigation of resins suitable for the preparation of biological sample for 3-D electron microscopy

In the last two decades, the third-dimension has become a focus of attention in electron microscopy to better understand the interactions within subcellular compartments. Initially, transmission electron tomography (TEM tomography) was introduced to image the cell volume in semi-thin sections (∼ 500 nm). With the introduction of the focused ion beam scanning electron microscope, a new tool, FIB-SEM tomography, became available to image much larger volumes. During TEM tomography and FIB-SEM tomography, the resin section is exposed to a high electron/ion dose such that the stability of the resin embedded biological sample becomes an important issue. The shrinkage of a resin section in each dimension, especially in depth, is a well-known phenomenon. To ensure the dimensional integrity of the final volume of the cell, it is important to assess the properties of the different resins and determine the formulation which has the best stability in the electron/ion beam. Here, eight different resin formulations were examined. The effects of radiation damage were evaluated after different times of TEM irradiation. To get additional information on mass-loss and the physical properties of the resins (stiffness and adhesion), the topography of the irradiated areas was analysed with atomic force microscopy (AFM). Further, the behaviour of the resins was analysed after ion milling of the surface of the sample with different ion currents. In conclusion, two resin formulations, Hard Plus and the mixture of Durcupan/Epon, emerged that were considerably less affected and reasonably stable in the electron/ion beam and thus suitable for the 3-D investigation of biological samples.

Resin composite characterizations following a simplified protocol of accelerated aging as a function of the expiration date

This study evaluated the mechanical, thermal, and morphological characteristics of different classifications of dental composites as a function of the material condition (new, aged and expired). Specimens were obtained according to these factors: Composites: Filtek P60, Filtek Z250, Filtek Z350XT, and Filtek Silorane; and Material conditions: new, aged, and expired. The syringe composites underwent an accelerated aging protocol (Arrhenius model). The flexural strength (FS) and flexural modulus (E) were obtained. The thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were also performed and the glass transition temperature (Tg) and the weight loss calculated. Topographic analysis of the composites was performed under SEM. The material conditions influenced the mechanical properties of the composites. The silorane composite exhibited a characteristic thermal behavior different from that of the methacrylates. In general, the Tg increased after the accelerated aging protocol and decreased for expired ones, compared to the new composites. A significant increase in FS of Filtek Z350XT after aging was accompanied by an increase in the Tg. The filler packings were in accordance with the manufacture׳s information. The topographic aspects of the composites were modified as a function of the material condition. The mechanical properties of the composites following a simplified protocol of accelerated aging varied as a function of the expiration date. The silorane composite presented a characteristic thermal behavior. Although the dental manufacturers may not be able to control variables as storage temperature and transportation conditions, these effects on the composite clinical performance can be minimized if properly considered.

Effects of 15% carbamide peroxide and 40% hydrogen peroxide on the microhardness and color change of composite resins

OBJECTIVE

The aim of this study was to determine the effects of 40% hydrogen peroxide and 15% carbamide peroxide on microhardness and color change of a silorane-based composite resin in comparison with two methacrylate-based composites.

MATERIALS AND METHODS

Fifty-four disc-shaped specimens (A3 shade) were fabricated of Filtek P90 (P90), Filtek Z350XT Enamel (Z350) and Filtek Z250 (Z250) (3MESPE) (n=18). The samples of each composite were randomly divided into three subgroups of 6. The control subgroups were immersed in distilled water; the test groups were exposed to Opalescence Boost (OB) once; and Opalescence PF (OP) (Ultradent) for two weeks. Vickers microhardness testing and a spectrophotometric analysis of the color of samples were performed before and after each intervention.

RESULTS

The baseline microhardness of P90 was significantly lower than that of the other two composites (P=0.001), but no difference was found between Z250 and Z350 in this respect (P=0.293). Bleaching treatments significantly decreased the microhardness of Z250 and Z350 (P< 0.001), but no change was observed in P90 test and control subgroups (P> 0.05). No significant difference was detected between the two types of bleaching (P>0.05). After bleaching with OB, ΔE value was measured to be 3.12(1.97), 3.31(1.84) and 3.7(2.11) for P90, Z250 and Z350, respectively. These values were 5.98(2.42), 4.66(2.85) and 4.90(2.78) after bleaching with OP with no significant difference.

CONCLUSION

Bleaching decreased the microhardness of methacrylate-based but not silorane-based composites. Although no significant differences were found in ΔE of composites, ΔE of all groups did not remain in the clinically acceptable range after bleaching except for P90 after bleaching with 40% H2O2 (ΔE < 3.3).

Synthesis, characterization and non-isothermal decomposition kinetic of a new galactochloralose based polymer

A glycopolymer, poly(3-O-methacroyl-5,6-O-isopropylidene-1,2-O-(S)-trichloroethylidene-α-d-galactofuranose) (PMIPTEG) was synthesized from the sugar-carrying methacrylate monomer, 3-O-methacroyl-5,6-O-isopropylidene-1,2-O-(S)-trichloroethylidene-α-d-galactofuranose (MIPTEG) via conventional free radical polymerization with AIBN in 1,4-dioxane. The structures of glycomonomer and their polymers were confirmed by UV-vis, FT-IR, (1)H NMR, (13)C NMR, GPC, TG/DTG-DTA, DSC, and SEM techniques. SEM images showed that PMIPTEG had a straight-chain length structure. On the other hand, the thermal decomposition kinetics of polymer were investigated by means of thermogravimetric analysis in dynamic nitrogen atmosphere at different heating rates. The apparent activation energies for thermal decomposition of the PMIPTEG were calculated using the Kissinger, Kim-Park, Tang, Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) and Friedman methods and were found to be 100.15, 104.40, 102.0, 102.2, 103.2 and 99.6 kJ/mol, respectively. The most likely process mechanism related to the thermal decomposition stage of PMIPTEG was determined to be a Dn deceleration type in terms of master plots results.