Scanning Electron Microscopy Evaluation of Dental Root Resorption Associated With Granuloma.

The inflammatory resorption of dental root apex (i.e., the process of removal of cementum and/or dentine through the activity of resorbing cells) may show different configurations and damage the apical root structure. As knowing the morphology of resorption areas of human teeth is essential for the success of endodontic treatments, we investigated the apical resorption by scanning electron microscopy, focusing on roots with granulomas. A total of 30 teeth (with penetrating carious lesions and chronic periapical lesions) were examined, the apical third of the roots were removed and analyzed to estimate periforaminal and foraminal resorption, shape and morphology of foramen resorption, centering of the periforaminal resorption area, and diameters of each apical foramen. Periforaminal resorption was present in all samples, whereas foraminal resorption was present in 92% of cases (mainly funnel shaped). Lacunae were observed in the foraminal resorption area with an average diameter of 35±14 µm. The major and minor diameters of the foramina in teeth with resorption were 443 and 313 µm, respectively (higher than in healthy teeth). This result indicates an expansion of the apical diameters caused by the pathology, which could encourage a different clinical instrumentation for these teeth.

The interaction of bacteria with engineered nanostructured polymeric materials: a review.

Bacterial infections are a leading cause of morbidity and mortality worldwide. In spite of great advances in biomaterials research and development, a significant proportion of medical devices undergo bacterial colonization and become the target of an implant-related infection. We present a review of the two major classes of antibacterial nanostructured materials: polymeric nanocomposites and surface-engineered materials. The paper describes antibacterial effects due to the induced material properties, along with the principles of bacterial adhesion and the biofilm formation process. Methods for antimicrobial modifications of polymers using a nanocomposite approach as well as surface modification procedures are surveyed and discussed, followed by a concise examination of techniques used in estimating bacteria/material interactions. Finally, we present an outline of future sceneries and perspectives on antibacterial applications of nanostructured materials to resist or counteract implant infections.

Enhancing osteoconduction of PLLA-based nanocomposite scaffolds for bone regeneration using different biomimetic signals to MSCs.

In bone engineering, the adhesion, proliferation and differentiation of mesenchymal stromal cells rely on signaling from chemico-physical structure of the substrate, therefore prompting the design of mimetic "extracellular matrix"-like scaffolds. In this study, three-dimensional porous poly-L-lactic acid (PLLA)-based scaffolds have been mixed with different components, including single walled carbon nanotubes (CNT), micro-hydroxyapatite particles (HA), and BMP2, and treated with plasma (PT), to obtain four different nanocomposites: PLLA + CNT, PLLA + CNTHA, PLLA + CNT + HA + BMP2 and PLLA + CNT + HA + PT. Adult bone marrow mesenchymal stromal cells (MSCs) were derived from the femur of orthopaedic patients, seeded on the scaffolds and cultured under osteogenic induction up to differentiation and mineralization. The release of specific metabolites and temporal gene expression profiles of marrow-derived osteoprogenitors were analyzed at definite time points, relevant to in vitro culture as well as in vivo differentiation. As a result, the role of the different biomimetic components added to the PLLA matrix was deciphered, with BMP2-added scaffolds showing the highest biomimetic activity on cells differentiating to mature osteoblasts. The modification of a polymeric scaffold with reinforcing components which also work as biomimetic cues for cells can effectively direct osteoprogenitor cells differentiation, so as to shorten the time required for mineralization.

Thermomechanical, antioxidant and moisture behaviour of PVA films in presence of citric acid esterified cellulose nanocrystals.

In the present work, poly(vinyl alcohol) (PVA) active packaging films containing different amounts (1, 3, 5, 10 and 15% wt.) of unmodified cellulose nanocrystals (CNC) and citric acid modified cellulose nanocrystals (mCNC) were prepared by solvent casting and their effect on thermal, mechanical and wettability behaviour of the resulted films was investigated. Results showed that both CNC and mCNC improved the thermal stability of the neat PVA matrix, but different mechanical properties and water wettability were found. Thermal stability of the materials was enhanced, by measuring shift of onset and peak temperatures that moved, respectively, from 251.5 to 298.1 °C and from 283.4 to 374.2 °C, in the case of PVA/15CNC and PVA/15mCNC films. The presence of mCNC contribute to increase the crystallinity up to 52% for PVA/10mCNC film, while it was limited to 39% for PVA/10CNC. Interestingly, PVA/mCNC composite films showed a clear UV shielding effect, while no UV resistance behaviour was detected for PVA/CNC films. Overall migration tests revealed that the migration value was well below the legislative limits (60 mg kg-1) for food contact materials, PVA/mCNC composite films have higher radical scavenging activity than PVA/CNC films and moisture content of PVA films containing mCNC was reduced at high RH. In conclusion, PVA/mCNC films could be considered as high-performance active food packaging materials.

Poly(lactic acid)/lignin films with enhanced toughness and anti-oxidation performance for active food packaging.

In this study, grafting of star-like lignin microparticles (LMP) onto PLA (LMP-g-PLA) was successfully realized by ring open polymerization of l-lactide, initiating from the hydroxyl groups on LMP surface. After that, various amount of LMP-g-PLA were melt blended with neat PLA and ethylene-vinyl acetate-glycidyl methacrylate (NPG) to prepare different PLA composites films, by exploiting the interfacial reactions between epoxy groups of NPG and carboxyl and hydroxyl groups of both LMP-g-PLA and PLA. Mechanical test results show that the addition of LMP-g-PLA made a significant contribution to the toughness of PLA/NPG blend, as the elongation at break increased up to 236% in PLA/NPG/1LMP sample. Although the addition of NPG and LMP-g-PLA hindered the crystallization capacity of PLA, good dispersion of LMP-g-PLA and compatibility between LMP and PLA acted as longer tortuous paths, consequently reducing the water vapor transmission rate. Meanwhile, the UV-Vis spectroscopy results showed that PLA/NPG/LMP films have excellent UV resistance behaviour without sacrificing too much the transparency. Results from overall migration tests and testing of anti-oxidant behaviour demonstrated that PLA films blended with NPG and lignin can be used as competitive materials in active food packaging industry.

Stimuli responsive hydrogels prepared by frontal polymerization.

Frontal polymerization was used as an alternative method for the easy and fast preparation of polymer hydrogels prepared from N-isopropylacrylamide (NIPAAm) and N-vinylcaprolactam (VCL), the latter being less toxic and less expensive than NIPAAm. All samples were characterized in terms of their swelling behavior, and their thermal properties were investigated by DSC. It was found that VCL influences both pore size and shape distribution. Moreover, also the swelling ratio of the materials is dependent on the monomer ratio. Eventually, by a comparison with analogous samples prepared by the classical polymerization technique, it was found that the two methods give rise to hydrogels characterized by very diverse swelling capability; furthermore, swelling reversibility was also found to be different when temperature is allowed to cyclically vary between values that are below and above the lower critical solution temperature. In particular, samples prepared by frontal polymerization are characterized by lower swelling ratio and larger swelling recovery capability.

Surfactant effects on morphology-properties relationships of silver-poly(styrene-b-isoprene-b-styrene) block copolymer nanocomposites.

Good dispersion of silver nanoparticles in poly(styrene-b-isoprene-b-styrene) block copolymer matrix has been achieved by adding dodecanethiol as surfactant to lower the high surface energy of metal nanoparticles. First, the influence of surfactant in the cylindrical nanostructure of neat block copolymer matrix has been analyzed. Taking into account the high solubility between dodecanethiol and the PS block of the SIS block copolymer, when silver nanoparticles and surfactant have been added to the block copolymer matrix its morphology changes from cylindrical to lamellar nanostructure. For the nanocomposite without surfactant, the block copolymer matrix loses its capability to self-assemble in lamellar nanostructure and in this case, agglomeration of silver nanoparticles occurs. Rheological, mechanical and morphological analysis were carried out in order to study the optimal content of surfactant necessary to obtain well-dispersed nanoparticles without worsen the final properties of the nanocomposite. The best silver/dodecanethiol w/w ratio appears to be 1, as confirmed by UV-Vis analysis. Moreover, semi-empirical models, such as Guth and Gold, and Halpin-Tsai, have been used in order to both predict and verify experimental tensile modulus of the obtained nanocomposites. The Guth and Gold equation, applicable to elastomers filled with spherical nanoparticles, provides a result closer to the experimental values than Halpin-Tsai model.

Combined effect of cellulose nanocrystals, carvacrol and oligomeric lactic acid in PLA_PHB polymeric films.

Biodegradable multicomponent films based on poly(lactic acid) (PLA) and poly(3-hydroxybutyrate) (PHB) plasticized with oligomeric lactic acid (OLA), reinforced with synthetized cellulose nanocrystals (CNC) and modified by a natural additive with antimicrobial activity (carvacrol) were formulated and processed by extrusion. Morphological, mechanical, thermal, migration and barrier properties were tested to determine the effect of different components in comparison with neat poly(lactic acid). Results showed the positive effect of CNC in the five components based films, with the increase of the Young's modulus of the PLA_PHB_10Carv_15OLA, associated with an increase in the elongation at break (from 150% to 410%), by showing an OTR reduction of 67%. Disintegrability in compost conditions and enzymatic degradation were tested to evaluate the post-use of these films. All formulations disintegrated in less than 17 days, while proteinase K preferentially degraded the amorphous regions, and crystallinity degree of the nanocomposite films increased as a consequence of enzyme action.

Effect of fibre posts, bone losses and fibre content on the biomechanical behaviour of endodontically treated teeth: 3D-finite element analysis.

The aim of this work was to evaluate the stress distribution inside endodontically treated teeth restored with different posts (glass fibre, carbon fibre and steel posts) under different loading conditions by using a 3D-finite element analysis. The effect of masticatory and impact forces on teeth with different degrees of bone loss was analysed. The model consists of: dentine, post, cement, gutta-percha, core and crown. Four simulations were conducted with two static forces (170N horizontal and 100N oblique) and two sections constrained: 1mm (alveolar bone position in a normal periodontium) and 6mm (middle of root) below the crown. Von Mises and the principal stresses were evaluated and analysed with a 3-way ANOVA and Tukey test (α=0.05) and the effect of fibre percentage analysed. Significant differences were found among the stress values for all conditions (p<0.05). Impact load was always responsible for the most critical situation especially when the bone loss was more evident. The system with steel posts showed the highest principal stresses at the post-cement interface with horizontal load and top constraints (compressive stress of 121MPa and tensile stress of 115MPa). The use of glass posts provides a more homogeneous behaviour of the system with lower stresses. Higher fibre percentages gave higher stress in the posts. Moreover, larger bone losses are responsible for important increase in stress. Thus, this work demonstrated that periodontal disease has an important role in the success of tooth restoration after endodontic therapy, influencing the choice of post material and depth.

PLLA-grafted cellulose nanocrystals: Role of the CNC content and grafting on the PLA bionanocomposite film properties.

Cellulose nanocrystals (CNC), extracted from microcrystalline cellulose by acid hydrolysis, were grafted by ring opening polymerization of L-Lactide initiated from the hydroxyl groups available at their surface and two different CNC:L-lactide ratios (20:80 and 5:95) were obtained. The resulting CNC-g-PLLA nanohybrids were incorporated in poly(lactic acid) (PLA) matrix by an optimized extrusion process at two different content (1 wt.% and 3 wt.%) and obtained bionanocomposite films were characterized by thermal, mechanical, optical and morphological properties. Thermal analysis showed CNC grafted with the higher ratio of lactide play a significant role as a nucleating agent. Moreover, they contribute to a significant increase in the crystallization rate of PLA, and the best efficiency was revealed with 3 wt.% of CNC-g-PLLA. This effect was confirmed by the increased in Young's modulus, suggesting the CNC graft ratio and content contribute significantly to the good dispersion in the matrix, positively affecting the final bionanocomposite properties.

Mechanical effect of static loading on endodontically treated teeth restored with fiber-reinforced posts.

The aim of this study was to investigate the mechanical behavior of a dental system built up with fiber-reinforced composite (FRC) endodontic posts with different types of fibers and two cements (the first one used with a primer, the second one without it). Six FRC posts were used. Each system was characterized in terms of structural efficiency under external applied loads similar to masticatory forces. An oblique force was applied and stiffness and maximum load data were obtained. The same test was used for the dentine. The systems were analyzed by scanning electron microscope (SEM) to investigate the surface of the post and inner surface of root canal after failure. The mechanical tests showed that load values in dental systems depend on the post material and used cement. The highest load (281 ± 59 N) was observed for the conical glass fiber posts in the cement without primer. There was a 50 and 85% increase in the maximum load for two of the conical posts with glass fibers and a 229% increase for the carbon fiber posts in the cement without primer as compared with the cement with primer. Moreover, almost all the studied systems showed fracture resistances higher than the typical masticatory loads. The microscopic analysis underlined the good adhesion of the second cement at the interfaces between dentine and post. The mechanical tests confirmed that the strength of the dental systems subjected to masticatory loads was strictly related to the bond at the interface post/cement and cement/dentine.

Biodegradable composite scaffolds: a strategy to modulate stem cell behaviour.

The application of new biomaterial technologies offers the potential to direct the stem cell fate, targeting the delivery of cells and reducing immune rejection, thereby supporting the development of regenerative medicine. Cells respond to their surrounding structure and with nanostructures exhibit unique proliferative and differentiation properties. This review presents the relevance, the promising perspectives and challenges of current biodegradable composite scaffolds in terms of material properties, processing technology and surface modification, focusing on significant recent patents in these fields. It has been reported how biodegradable porous composite scaffolds can be engineered with initial properties that reproduce the anisotropy, viscoelasticity, tension-compression non-linearity of different tissues by introducing specific nanostructures. Moreover the modulation of electrical, morphological, surface and topographic scaffold properties enables specific stem cell response. Recent advances in nanotechnology have allowed to engineer novel biomaterials with these complexity levels. Understanding the specific biological response triggered by various aspects of the fibrous environment is important in guiding the design and engineering of novel substrates that mimic the native cell matrix interactions in vivo.

Compressive and flexural behaviour of fibre reinforced endodontic posts.

OBJECTIVES: The aim of this study was to investigate the mechanical properties of five types of fibre-reinforced composite (FRC) posts and compare them with traditional metal post. METHODS: Five FRC posts and a metallic post having different geometry and type of fibre (glass, carbon or quartz fibre) were loaded to failure in compression and bending. The transverse sections of FRC posts were observed using SEM to evaluate the fracture mode and the percentage of fibres (compared with burn-off test). Densities and voids content were also evaluated. RESULTS: Mechanical results were subjected to a one-way ANOVA and Tukey test (p<0.05). In compression, quartz fibre posts exhibited the greater maximum load and ultimate strength, carbon fibre posts showed a poor compressive behaviour. All posts had similar compressive moduli. Carbon posts showed the highest flexural properties (p<0.0001) while glass posts the greater maximum load. The fracture load values correlated to the diameters of posts showed a parabolic behaviour. The flexural strengths of all posts were four and seven times higher than dentine. The elastic moduli of almost all posts were similar to dentine. The compressive strengths were lower than flexural strengths. The fibre diameters ranged from 5.2 to 26 µm, the volume percentage of fibres was about 64%. The content of voids of some posts lower their mechanical behaviour. CONCLUSIONS: Compressive properties of FRC posts were lower than in bending. The flexural properties of FRC posts were higher than the metal post and similar to dentine. The mechanical behaviour is influenced by voids.

Effects of carbon nanotubes (CNTs) on the processing and in-vitro degradation of poly(DL-lactide-co-glycolide)/CNT films.

Nanocomposite films based on single wall carbon nanotubes (SWNTs) and poly(DL-lactide-co-glycolide) copolymer (50:50 PLGA) were processed and analyzed. The purpose of this study was to investigate the effect of different functionalization systems on the physical stability and morphology of PLGA films. Both covalent and non covalent functionalization of carbon nanotubes were considered in order to control the interactions between PLGA and SWNTs and to understand the role of the filler in the biodegradation properties. Using a solvent casting process, different PLGA/SWNT nanocomposites were prepared and incubated using organic solution under physiological conditions. In-vitro degradation studies were conducted by measurements of weight loss, infrared spectroscopy, glass transition temperature and SEM observations as a function of the incubation time, over a 9-week period. All PLGA films were degraded by hydrolitical degradation. However, a different degradation mechanism was observed in the case of functionalized SWNTs with respect to pristine material. It has been observed that system composition and SWNT functionalization may play a crucial role on the autocatalytic effect of the degradation process. These studies suggest that the degradation kinetics of the films can be engineered by varying carbon nanotube (CNT) content and functionalization. The combination of biodegradable polymers and CNTs opens a new perspective in the self-assembly of nanomaterials and nanodevices.