Orthodontic wires

The property most frequently cited in connection with the use of Ti dental or medical appHances is titanium s unique biocompatibiHty. This helps practitioners avoid occasional allergic reactions that occur with nickel or chromium alloys, and removes concerns about the toxic or carcinogenic potential of appHances that contain nickel, chromium, or beryUium. Wrought alloys of titanium are used for orthodontic wires because of their unique elastic... 

Today, stainless steels find their primary use in wrought form for temporary appHcations such as orthodontic wires, brackets, and temporary crowns. The temporary crowns are obtained in preformed sizes/shapes and then are trimmed by the dentist with shears to fit over prepared teeth that are awaiting the fabrication of permanent cast crowns. 

Uses. Dental solders and fluxes are used to join orthodontic wires, fasten attachments to partial dentures, repair castings units, and join crown and bridge units either before or after the appHcation of porcelain. They may also be used to repair fixed and removable dental appHances. 

Strobel et al. (101) reported a unique approach to delivery of anticancer agents from lactide/glycolide polymers. The concept is based on the combination of misonidazole or adriamycin-releasing devices with radiation therapy or hyperthermia. Prototype devices consisted of orthodontic wire or sutures dip-coated with drug and polymeric excipient. The device was designed to be inserted through a catheter directly into a brain tumor. In vitro release studies showed the expected first-order release kinetics on the monolithic devices. 

Shape-memory alloys (e.g. Cu-Zn-Al, Fe-Ni-Al, Ti-Ni alloys) are already in use in biomedical applications such as cardiovascular stents, guidewires and orthodontic wires. The shape-memory effect of these materials is based on a martensitic phase transformation. Shape memory alloys, such as nickel-titanium, are used to provide increased protection against sources of (extreme) heat. A shape-memory alloy possesses different properties below and above the temperature at which it is activated. Below this temperature, the shape of the alloy is easily deformed due to its flexible structure. At the activation temperature, the alloy can be changed by applying a force, but the structure resists this deformation and returns back to its initial shape. The activation temperature is a function of the ratio of nickel to titanium in the alloy. In contrast with Ni-Ti, copper-zinc alloys are capable of a two-way activation, and therefore a reversible variation of the shape is possible, which is a necessary condition for protection purposes in textiles used to resist changeable weather conditions. 

Gjerdet NR, Kallus T, Hensten-Pettersen A. 1987. Tissue reactions to implanted orthodontic wires in rabbits. Acta Odontol Scand 45 163-169. 

Many people are familiar with traditional orthodonture, the process by which steel wires are used to straighten teeth. An orthodontist installs the steel wires, which guide the growth of teeth in some particular, desired directions. The problem with this very popular technique is that stainless steel does not stretch and adjust very well, and a patient may have to visit an orthodontist quite frequently to have adjustments made in the tensions of the wires. The use of SMA materials for orthodontic wires reduces this problem. Such wires exert the force of tension needed to direct the growth of teeth, but they do so with more elasticity and, therefore, less discomfort to patients. Patients must still visit their orthodontist for adjustments, but at much less frequent intervals. 

Rigid-rod compositions consisting of polyphenylene derivatives were used by Goldberg [2] as advanced thermoplastics in preparing orthodontic wire. 

Nickel-titanium alloys, based upon the equi-atomic intermetallic compoimd NiTi, have very low values of elastic modulus (approximately 35 GPa), compared to stainless-steel alloys (approximately 160-180 GPa) [4]. As a consequence, nickel-titanium alloys have considerable clinical importance for endodontic instruments, permitting negotiation of curved root canals with much greater facility than traditional stainless-steel instruments [5], and for orthodontic wires that have a much more favourable light-force delivery for tooth movement than traditional stainless-steel orthodontic wires [6,7],... 

R-phase, which serves as an intermediate phase to facilitate the transformation between martensite and austenite. Formation of the R-phase is reported to arise from the presence of dislocations and precipitates [11]. A substantial dislocation density is expected in the vwought nickel-titanium endodontic instruments and orthodontic wires, which are subjected to extensive mechanical deformation during manufacturing processes [12], Microstructural precipitates are a consequence of the inevitable deviation of the nickel-titanium alloy composition from the equi-atomic NiTi composition [13,14],... 

The structural transformation between austenite and martensite occurs when the mechanical stress attains a certain level, or with an appropriate temperature change, A reversible twinning process takes place at the atomic level, which can result in superelastic behaviour and shape memory [8], The properties of the nickel-titanium endodontic instruments and orthodontic wires depend critically upon the nature and proportions of the NiTi phases in their microstructures, as discussed in the following sections. While X-ray diffraction has been used to study the phases in nickel-titanium endodontic instruments [15,16] and orthodontic wires [7,17,18], this analytical technique is limited to a near-surface region less than 50 pm in depth for metallic materials [19], and study of the phase transformations with temperature is not generally convenient. In contrast, DSC can provide information about the phases present in bulk nickel-titanium endodontic instruments and orthodontic wires with facility, and the effect of temperature changes on the NiTi phase transformations is easily studied. 

The AH values in Table 1 lie within the range of 1.7 to 19.2 J/g reported for nickel-titanium orthodontic wires [7]. From DSC results for shape memory orthodontic wires [7,25], these nickel-titanium rotary instruments might possess shape memory at room temperature (and in the oral environment) if manufacturers used the appropriate processing steps [26], However, future... 

Since our pioneering study on as-received [22] nickel-titanium endodontic instruments, other DSC studies have confirmed that as-received instruments are in the superelastic condition, which persists after numerous sterilization cycles [28,29]. As would be expected, mechanical properties of these instruments are related to the phase transformation behaviour of the nickel-titanium alloy [30]. Accordingly, suitable elevated-temperature heat treatment may favourably alter the mechanical properties of these instruments [31,32], as was previously found for nickel-titanium orthodontic wires [21,33]. 

Orthodontics is concerned with tooth movement to optimal positions, using metallic archwires ligated to brackets bonded to enamel or dental restorations by adhesive resins, as well as using suitable other metallic appliances, to provide appropriate forces and bending moments in vivo. The force generated by a bent orthodontic wire is proportional to its elastic modulus, and relatively light and continuous forces are considered to be optimum. There is considerable interest in nickel-titanium orthodontic wires, which have the lowest elastic modulus of the major wire alloys [7]. 

The nickel-titanium orthodontic wire (Nitinol, 3M Unitek, Monrovia, CA, USA) that was first marketed [6] had a heavily cold-worked stable martensite structure [25], but superelastic wires [21] were subsequently introduced and followed [34] by wires having shape memory in the oral environment [7]. For the most efficient treatment, the archwire that is bent by the clinician for treating malpositioned teeth should return completely to the initial undeformed state during the process of tooth movement. Complete recovery will not occur for superelastic wires if there is permanent deformation [33], whereas full recovery will take place for nickel-titanium wires with in vivo shape memory. 

Broadj low-temperature exothermic peaks appear on the nonreversing heat flow curves in Figures 7 and 8, indicating transformation within martensite to another structure (M ). Low-temperature peaks had previously been reported from DSC [10] and electrical resistivity measurements [38] of engineering and NiTi orthodontic alloys, respectively. However, our group was unable to confirm these peaks on DSC plots for five representative orthodontic wires[25]. 

Orthodontics Wires, palatal arches, distractors, endodontic files Nickel-titanium (Ni-Ti) Titanium- molybdenum Teeth anchorage Root canal treatments... 

Industrial applications of shape memory polymers are e.g. as foams in the building industry and in sportswear. Further potential applications include selfrepairing structural components. More recently, especially potential biomedical applications are discussed as, e.g., intravenous cannula, self-adjusting orthodontic wires and selectively pliable tools for small scale surgical procedures. 

Alloy metal needles are made by electrolytically sharpening orthodontic wire (Rocky Mountain Orthodontics, Denver, CO) with a wire polishing unit (Dental Corporation of America, Hagerstown, MD). 

Many materials used in dentistry contain nickel, such as orthodontic wires, dental prostheses and dental casting alloys. In most instances this does not seem to cause adverse effects in nickel-sensitive individuals (Hensten-Pettersen 1989). The possibility of induction of tolerance in non-sensitised individuals by oral nickel exposure, as in orthodontic treatment, has been proposed (van Hoogstraten et al. 1991,1992). The clinical significance of this possibility is, however, not known. 

The large strains at nearly constant stresses can be used in many applications in which great displacement must be set up at constant forces, e. g. minimal surgery instruments, orthodontic wires and glass frames. 

Shape memory alloys (e.g. CuZnAl-, FeNiAl-, TiNi-alloys) are already being used in biomedicine as cardiovascular stents, guidewires and orthodontic wires. The shape memory effect of these materials is based on a martensitic phase transformation. 

Katz, A., Redlich, M., Rt oport, L., Wagner, H. D. and Tame, R., Self-lubricating coatings containing fijllerme-like WS2 nanoparticles for orthodontic wires and other possible medical applications. Tribology Letters, 21 (2), 2006,135-139. 

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