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The bond between methacrylic polymer adhesives and dental restoratives is not perfect and may fail either in the short or in the long term. This study aims to evaluate the effects of particle incorporation in a self-etch model adhesive on mechanical and physical properties that are relevant during application and service. Filled adhesives containing 5, 10, 15 or 25 wt% glass fillers were compared to their unfilled counterpart in terms of water sorption and solubility; viscosity and dynamic viscosity during polymerization were recorded using rheological measurements and compared to FTIR analysis of the real-time degree of cure. Elastic modulus and ultimate tensile strength measurements were performed in uniaxial tension; the energy to fracture was used to calculate the fracture toughness of the adhesives. Finally, the experimental adhesives were applied on dentin substrate to test the bond strength using the microtensile test. Results showed that the incorporation of 5–10 wt% nanofiller to self-etching dental adhesives is efficient in accelerating the polymerization reaction and increasing the degree of cure without compromising the film viscosity for good wettability or water sorption and solubility. Fillers increased the elastic modulus, tensile strength and fracture toughness to a plateau between 5 and 15 wt% filler concentration, and despite the tendency to form agglomerations, active crack pinning/deflection toughening mechanisms have been observed. The bond strength between resin composite and dentin was also improved when adhesives with up to 10 wt% fillers were used, with no additional improvements with further packing. The use of fillers to reinforce dental adhesives may therefore be of great practical benefit by improving curing and mechanical properties.
The characterization of oxygen diffusion zone in titanium and the effect of this zone on macroscopic properties are still of high interest for a base to predict and to enhance life time of titanium and titanium alloy components. The aim of this study was to contribute to the understanding of the impact of oxygen on fatigue properties of oxygen diffusion hardened Ti and Ti alloys. Oxygen diffusion hardening implies two process steps, first the oxidation of the surface and secondly the diffusion of oxygen into metal matrix. Due to the one-step treatment used in this study the oxidation step could take place easily avoiding scaling and grain boundary diffusion. In spite of this precaution, the fatigue properties in the present study were found to be decreased after the performed oxygen diffusion hardening. The reason for the reduction of mechanical properties were claimed to be oxide clusters on the surface acting as crack initiation sites. Comparison and discussion with literature revealed varying partially contradictory fatigue results. Therefore precise analysis of the fatigue failure is necessary as a base for further development of the oxygen diffusion hardening.
A proposal for the classification of dental alloys according to their resistance to corrosion
(2007)
Objectives
The purpose of this study was to establish a method to compare and classify dental alloys in relation to their resistance to corrosion.
Methods
Alloy samples and pure metal samples were prepared and tested in chemical and electrochemical corrosion according to ISO 10271. For electrochemical test, the rest potential versus time and a potentiodynamic scan were recorded. After chemical corrosion test, the ions released were analyzed by ICP (induced coupled plasma) spectroscopy.
Results
High gold alloys had a similar polarization curve than gold. The same effect was observed for Pd–base alloys, their curves were similar to the one of palladium. The ions released during chemical corrosion were non-precious metallic ions. Thereby Ni–Cr alloys were found to release the most ions. Au–Pt alloys showed the highest release of ions compared with other precious alloys but low compared with Ni–Cr. Electrochemical corrosion was more aggressive than chemical corrosion and every type of elements was etched, the higher the precious metal content, the higher the resistance to corrosion of the alloy.
Discussion
Using the recorded data, a classification system for electrochemical corrosion was developed and discussed to judge the results. Hereby were gold and zinc used as reference materials. The applied classification system defines five classes and it is proposed that alloys of class V are not acceptable. For chemical corrosion resistance, three classes were distinguished according to the quantity of metallic ions released and it is proposed that class III (100–1000 μg/cm2 week) is not acceptable. Palladium and Pd–base alloys showed a higher electrochemical and chemical corrosion resistance than gold.
This review comprehensively covers research carried out in the field of degradable coatings on Mg and Mg alloys for biomedical applications. Several coating methods are discussed, which can be divided, based on the specific processing techniques used, into conversion and deposition coatings. The literature review revealed that in most cases coatings increase the corrosion resistance of Mg and Mg alloys. The critical factors determining coating performance, such as corrosion rate, surface chemistry, adhesion and coating morphology, are identified and discussed. The analysis of the literature showed that many studies have focused on calcium phosphate coatings produced either using conversion or deposition methods which were developed for orthopaedic applications. However, the control of phases and the formation of cracks still appear unsatisfactory. More research and development is needed in the case of biodegradable organic based coatings to generate reproducible and relevant data. In addition to biocompatibility, the mechanical properties of the coatings are also relevant, and the development of appropriate methods to study the corrosion process in detail and in the long term remains an important area of research.
Electrophoretic chitosan deposits on stainless steel AISI 316 L were produced and characterized. The coating quality (thickness, defectiveness, corrosion protection ability) was seen to depend on the electric field used for EPD. Corrosion studies in concentrated simulated body fluid (SBF5) demonstrated that the surface characteristics of AISI 316 L can be positively influenced by the chitosan coating.
We investigate the mechanical and microstructural properties of a diamond-like carbon coating (DLC) which is deposited by plasma enhanced chemical vapor deposition (PECVD) onto an alumina/aluminosilicate glass composite used for biomedical applications. Ball-on-ring tests yield a fracture strength that is essentially influenced by the surface topology/roughness. The surface topology of the coating is investigated by atomic force microscopy (AFM). Tribology tests and nanoindentation represent the wear resistance and hardness; these are properties that are mainly influenced by the microstructural properties of the DLC coating. This microstructure is investigated by transmission electron microscopy (TEM) and analyzed by parallel electron energy loss spectroscopy (PEELS). For the general applicability of the coated composite, the interfacial adhesion of the DLC coating on the comparably rough substrate (roughness amplitudes and wavelengths are in the micrometer range) is important. Therefore, we focus on TEM investigations that show the interface to be free of gaps and pores that we, together with a characteristic microstructure adjacent to the interface, relate to the excellent adhesion. The interlayer consists of a high density of SiC grains, part of them directly bound to the substrate, and part of them bound to other SiC grains. This interlayer is followed by an essentially different region of the coating as concerns the microstructure; this region consists of nanocrystalline diamond particles embedded in an amorphous carbon matrix. It is this heterogeneous microstructure to which we attribute (i) the good adhesion based upon the interface stabilizing SiC grains, and (ii) the high hardness and wear resistance based upon the diamond nanocrystals in the coating.
We investigate the mechanical and microstructural properties of a diamond-like carbon coating (DLC) which is deposited by plasma enhanced chemical vapor deposition (PECVD) onto an alumina/aluminosilicate glass composite used for biomedical applications. Ball-on-ring tests yield a fracture strength that is essentially influenced by the surface topology/roughness. The surface topology of the coating is investigated by atomic force microscopy (AFM). Tribology tests and nanoindentation represent the wear resistance and hardness; these are properties that are mainly influenced by the microstructural properties of the DLC coating. This microstructure is investigated by transmission electron microscopy (TEM) and analyzed by parallel electron energy loss spectroscopy (PEELS). For the general applicability of the coated composite, the interfacial adhesion of the DLC coating on the comparably rough substrate (roughness amplitudes and wavelengths are in the micrometer range) is important. Therefore, we focus on TEM investigations that show the interface to be free of gaps and pores that we, together with a characteristic microstructure adjacent to the interface, relate to the excellent adhesion. The interlayer consists of a high density of SiC grains, part of them directly bound to the substrate, and part of them bound to other SiC grains. This interlayer is followed by an essentially different region of the coating as concerns the microstructure; this region consists of nanocrystalline diamond particles embedded in an amorphous carbon matrix. It is this heterogeneous microstructure to which we attribute (i) the good adhesion based upon the interface stabilizing SiC grains, and (ii) the high hardness and wear resistance based upon the diamond nanocrystals in the coating.
The morphology and microstructure of an Al2O3 glass composite (trade name In-Ceram, Vita Zahnfabrik) were studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composite was produced by infiltration of a lanthanum-based glass throughout a porous Al2O3 body. This alumina body was formed by three classes of particles differing in size and shape: faceted particles typically ≤4 μm in diameter, platelets of average diameter 8 μm, 1.5 μm thickness, and small spheres 0.4 μm in diameter. The outstanding strength properties of the composite (600 MPa, ball-on-ring test) are a result of the high wetting capability of the glass phase on the Al2O3 surface. In addition, plastic strain relaxation in the faceted particles by dislocation formation compensates partially for residual stresses and impedes crack formation at the glass/Al2O3 interface.
A lot of dental alloys are available on the market. Among these alloys, there are the conventional alloys, the so called casting alloys used without ceramics, the bonding alloys used with high fusing ceramics and the universal alloys used without or with low fusing ceramics. It is im portant to know the physical and mechanical properties of these materials but also their biocompatibility and their resistance to corrosion. Dental alloys are generally placed in the mouth for many years, they must not induce adverse biological reactions such as gingival swelling and erythema, mucosal pain and lichenoid reactions. Although these troubles are often caused not by the materials itself (1, 2), they can be induced by the metallic ions released during their corrosion. In order to decrease the risks to the health, it is necessary to study the corrosion of the dental alloys. Currently, the ISO 10271 Standard (3), describes 3 different corrosion tests: a static immersion test (chemical corrosion), an electrochemic al test and a tarnish test. However, there are no indications yet about the possible interpretation of test results. In this paper, we propose a method to compare and classify the dental alloys in relation to their chemical and electrochemical corrosion results. METHODS: The material tested are pure metals such as gold, palladium, silver, copper and zinc as well as dental alloys which are commercially sold (see Table 1). 54 different materials have been tested. A minimum of four samples of each material were tested by electrochemic al corrosio n and a minimum of three in chemical test. The samples were cast and prepared as indicated by the manufacturer and by the ISO 10271. For the electrochemical test, the samples are in the form of disks 11 mm in diameter. They are tested with a potentiostat/galvanostat Voltalab Model 21. For the chemical test, the samples are rectangular with the dimensions 35X10X1.7 mm. The solution used and the operating conditions are described in the ISO 10271. The concentration of metallic ions released is measured by Induced Coupled Plasma
In Vitro Analysis of Human Cartilage Infiltrated by Hydrogels and Hydrogel-Encapsulated Chondrocytes
(2023)
Osteoarthritis (OA) is a degenerative joint disease causing loss of articular cartilage and structural damage in all joint tissues. Given the limited regenerative capacity of articular cartilage, methods to support the native structural properties of articular cartilage are highly anticipated. The aim of this study was to infiltrate zwitterionic monomer solutions into human OA-cartilage explants to replace lost proteoglycans. The study included polymerization and deposition of methacryloyloxyethyl-phosphorylcholine- and a novel sulfobetaine-methacrylate-based monomer solution within ex vivo human OA-cartilage explants and the encapsulation of isolated chondrocytes within hydrogels and the corresponding effects on chondrocyte viability. The results demonstrated that zwitterionic cartilage–hydrogel networks are formed by infiltration. In general, cytotoxic effects of the monomer solutions were observed, as was a time-dependent infiltration behavior into the tissue accompanied by increasing cell death and penetration depth. The successful deposition of zwitterionic hydrogels within OA cartilage identifies the infiltration method as a potential future therapeutic option for the repair/replacement of OA-cartilage extracellular suprastructure. Due to the toxic effects of the monomer solutions, the focus should be on sealing the OA-cartilage surface, instead of complete infiltration. An alternative treatment option for focal cartilage defects could be the usage of monomer solutions, especially the novel generated sulfobetaine-methacrylate-based monomer solution, as bionic for cell-based 3D bioprintable hydrogels.