Preliminary Study of New Low-Temperature Hard Abrasion Resistant Fe-P and Fe-P-X (X = C or/and B) Casting Alloys.

This article analyses the as-cast state of practically unknown Fe-P-based cast alloys with or without an addition of carbon and/or boron, cast into a grey cast iron mould. The melting intervals of the alloys were determined by DSC analysis, and the microstructure was characterized by optical and scanning electron microscopy with an EDXS detector. The hardness and microhardness of the alloys were also measured. Their hardness reached values between 52 and 65 HRC depending on chemical composition and microstructure, showing their high abrasion resistance. The high hardness is a consequence of the eutectic and primary intermetallic phases of Fe3P, Fe3C, Fe2B or mixed type. By increasing the concentration of metalloids and combining them, the hardness and brittleness of the alloys were increased. The alloys with predominantly eutectic microstructures were the least brittle. Depending on the chemical composition, the solidus and liquidus temperatures ranged from 954 °C to 1220 °C and were lower than those of the well-known wear-resistant white cast irons.

Case report of a molar-root incisor malformation in a patient with an autoimmune lymphoproliferative syndrome.

BACKGROUND: Molar-root incisor malformation (MRIM) is a novel dental phenotype likely related to a patient's past medical history. This case aimed to confirm MRIM by histological and scanning electron microscopy (SEM) examination for the first time in a patient diagnosed with autoimmune lymphoproliferative syndrome (ALPS) and to propose a possible link between ALPS and MRIM that could be attributable to abnormally proliferated bone marrow. CASE PRESENTATION: A 12.5-year-old boy with an extensive medical history, including diagnosis of ALPS, was examined clinically and radiologically to elucidate the reason for pain primarily originating from the area of the lower left permanent first molar tooth (PFM; tooth 36). Dental examination and radiographic survey revealed abnormal pulp cavity morphology of all four PFMs, and these were extracted, resolving the dental pain in the patient. The extracted PFMs were subjected to light microscopy, SEM evaluation and mineral density and elemental composition analyses. Histology of two PFMs revealed the presence of dentin-, bone- and cartilage-like tissues with abundant blood vessels occupying the majority of the pulp chamber. The root canals were obliterated with mineralized structures resembling pulp stones. Two different, highly mineralized abnormal tissues filling the majority of the pulp chamber revealed by SEM and confirming the diagnosis of MRIM displayed a mineral density and elemental composition similar to those of enamel and dentin, respectively. CONCLUSIONS: It appears likely that in addition to the complex medical history during early childhood in the present case, extensive lymphoid infiltrates that are possible in ALPS patients can be regarded as a cofactor in the development of MRIM by exerting considerable pressure on the developing tooth bud and providing cells capable of differentiating into diverse cell types.

The effect of pH, fluoride and tribocorrosion on the surface properties of dental archwires.

Nickel-titanium and stainless steel are the most commonly used alloys for orthodontic treatments. Even though both are known to be resistant to corrosion, there are circumstances that can lead to undesired situations, like localized types of corrosion attack, wear during sliding of an archwire though brackets and breakdowns due to iatrogenic causes. The aim of this research was to analyse the influence of environmental effects on the corrosion and tribocorrosion properties of NiTi and stainless steel dental alloys. The effects of pH and fluorides on the electrochemical properties were studied using the cyclic potentiodynamic technique. The migration of ions from the alloy into saliva during exposure to saliva with and without the presence of wear was analysed using ICP-MS analyses. Auger spectroscopy was used to study the formation of a passive oxide layer on different dental alloys. It was found that lowering the pH preferentially affects the corrosion susceptibility of NiTi alloys, whereas stainless steel dental archwires are prone to local types of corrosion. The NiTi alloy is not affected by smaller increases of fluoride ions up to 0.024M, while at 0.076M (simulating the use of toothpaste) the properties are affected. A leaching test during wear-assisted corrosion showed that the concentrations of Ni ions released into the saliva exceeded the limit value of 0.5µg/cm2/week. The oxide films on the NiTi and stainless steel alloys after the tribocorrosion experiment were thicker than those exposed to saliva only.

Structural characterization of platinum foil for neural stimulating electrodes.

OBJECTIVE: The objective of this study was to investigate the structural properties of a cold-rolled platinum foil used to manufacture multi-electrode spiral nerve cuffs. METHODS: To attain this objective, 0.03-mm-thick cold-rolled platinum foil strips with 99.99 wt% purity were used. The resistivity measurements were made using a 4-point probe technique in which the strips were subjected to dynamic annealing in an argon atmosphere. The stored energy of platinum was recorded in an argon atmosphere using differential scanning calorimetry (DSC). Finally, the microstructure of the strips was investigated by optical microscopy. RESULTS: In the resistivity measurements, a small change is observed at ~280°C. This change could be explained as the partial recovery elicited by the decrease of dislocation density. Above 500°C, a significant decrease in resistivity was recorded, and the decrease reached a maximum at ~750°C. These results are consistent with the recrystallization trend detected in DSC, namely the DSC measurement detected very weak heat release during recrystallization, which was actually accumulated during the cold-working. This exothermal peak occurred in the temperature range 380-800°C.