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The purpose of this study was to determine the transformation temperatures for the austenitic, martensitic, and rhombohedral (R) structure phases in representative as-received commercial nitinol (NiTi) orthodontic wire alloys, to reconcile discrepancies among recent publications. Specimens were examined by differential scanning calorimetry (DSC) over a temperature range from approximately -170 degrees C to 100 degrees C, with a scanning rate of 10 degrees C per minute. Two different pathways, with the intermediate R structure either absent or present, were observed for the transformation from martensitic to austenitic NiTi, whereas the reverse transformation from austenitic to martensitic NiTi always included the R structure. The enthalpy (delta H) for the transformation from martensite to austenite ranged from 0.3 to 3.5 calories per gram. The lowest delta H value for the nonsuperelastic Nitinol wire is consistent with a largely work-hardened, stable, martensitic microstructure in this product. The DSC results indicate that the transformation processes are broadly similar in superelastic, body-temperature shape-memory, and nonsuperelastic NiTi wires. Differences in bending properties for the NiTi orthodontic wires at room temperature and 37 degrees C are due to the relative proportions of the metallurgical phases in the microstructures.

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Three series of neat resins, based on methacrylates or dimethacrylates modified with 1‐[3‐(methacryl)propyl]‐3,5,7,9,11,13,15‐heptacyclopentylpentacyclo[9.5.113,­9.15,15.17,13]octasiloxane (Methacryl‐POSS or POSS‐MA), were evaluated. Incorporation of POSS‐MA into the polymeric matrix was accomplished in three ways: (a) resins series I was formulated with one‐pot copolymerization of a bis‐GMA/diluent monomer with POSS‐MA; (b) the copolymer of 2‐hydroxylethyl methacrylate (HEMA) and POSS‐MA, with a weight ratio of 1 : 1, was first made, then the copolymer hydroxyl groups were converted into methacrylate groups to get a macromer; finally the macromer was copolymerized with bis‐GMA/diluents to formulate the second series of neat resins; (c) copolymer of POSS‐MA and t‐butyl methacrylate (t‐BMA) or 2‐ethylhexyl methacrylate (EHMA) were first made, then they were combined with a mixture of bis‐GMA and the corresponding diluent to make the third kind of neat resins. The amount of POSS incorporated into the neat resin matrix was controlled at 5, 10 and 15 wt%. Incorporating only 5 wt% substantially reduced the shrinkage of the prepared neat resins. The percentage of methacrylate‐functionalized POSS monomer in the bis‐GMA/diluent base, was compared to neat resins prepared without the POSS. The mechanical properties of neat resin having POSS were improved for approaches (b) and (c), but remained at the same level as the neat resins without POSS for approach (a). The results show that miscibility between the POSS component and the matrix, especially the diluent, plays a very important role in the improvement of the properties of the formulated thermosets. Copyright © 2001 John Wiley & Sons, Ltd.