Orthodontics

Medicine. The polymethacrylates have been used for many years in the manufacture of dentures, teeth, denture bases, and filling materials (116,117) (see Dental materials). In the orthodontics market, methacrylates have found acceptance as sealants, or pit and fissure resin sealants which are painted over teeth and act as a barrier to tooth decay. The dimensional behavior of curing bone-cement masses has been reported (118), as has the characterization of the microstmcture of a cold-cured acryUc resin (119). Polymethacrylates are used to prepare both soft and hard contact lenses (120,121). Hydrogels based on 2-hydroxyethyl methacrylate are used in soft contact lenses and other biomedical appHcations (122,123) (see Contactlenses). 

Zinc Phosphate Cements. Zinc phosphate cements are the oldest of the aqueous-based cements (see Table 1) and are stiU used in a wide range of appHcations eg, cavity bases, temporary restoratives, and for the fixation of inlays, crowns, fixed partial dentures (bridges), posts, facings, and orthodontic bands. 

Sticky waxes are used as thermoplastic cements. The broken pieces of a plaster impression are reassembled and held in position with sticky wax. Broken denture bases may be held in proper alignment for repair. Orthodontic apphances may be assembled with a sticky wax prior to investing and soldering. Plaster splints may be sealed to stone models in the production of porcelain or resin facings. Thus, sticky wax is useflil in almost any operation where it is desired to position and hold several small pieces in a temporary relationship. 

GoldJilloys, Wrought Type. Two types of wrought gold alloys were formerly recognized by the ADA specification no. 7 for the fabrication of orthodontic and prosthetic dental appHances, ie, type I, high-precious-metal alloys, and type II, low-precious-metal alloys (gold color). Alloys of this type are seldom used in the United States they have been replaced by stainless steels and nickel—titanium alloys. 

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. 

Chicago Ivoclar North America, Amherst, N.Y. J. M. Ney,, Monrovia, Calif. and Masel Orthodontics, Bristol, Pa. 

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. 

Mizrahi, E. Smith, D. C. (1969a). Direct cementation of orthodontic brackets... 

It is superior to the zinc phosphate cement for bonding orthodontic bands to teeth (Clark, Phillips Norman, 1977). It has greater durability and there is less decalcification in adjacent tooth enamel. This latter beneficial effect must arise from the release of fluoride which is absorbed by the enamel, so protecting it in a clinical situation where caries-produdng debris and plaque accumulate. 

Cameron, J. C., Charbeneau, G. T. Craig, R. G. (1963). Some properties of dental cements of specific importance in the cementation of orthodontic bands. Angle Orthodontics, 33, 233-45. 

Kendzior, G. M., Leinfelder, K. F. Hershey, H. G. (1976). The effect of cold temperature mixing on the properties of a zinc phosphate cement. Angle Orthodontics, 46, 345-50. 

Savignac, J. R., Fairhurst, C. W. Ryge, G. (1965). Strength, solubility and disintegration of zinc phosphate cement with clinically determined powder/liquid ratio. Angle Orthodontics, 35, 126-30. 

Skibell, R. B. Shannon, I. L. (1973). Addition of stannous fluoride to orthodontic cement. International Journal of Orthodontics, 11, 131-5. 

Ware, A. L. (1971). Properties of cements for orthodontic bonding. Australian Orthodontics Journal, 2, 254-61. 

Wisth, P. J. (1972). The ability of zinc phosphate and hydrophosphate cements to seal space bands. Angle Orthodontics, 42, 395-8. 

Williams, J. D., Swartz, M. L. Phillips, R. W. (1965). Retention of orthodontic bands as influenced by the cementing media. Angle Orthodontics, 4, 276-85. 

Orthoarsenic acid, 3 264—265 Orthoboric acid, 4 242t, 249—255 Orthoclase, hardness in various scales, l 3t Orthocortex, in wool fibers, 11 173 Orthodontics, superelastic and pseudoelastic SMA devices in, 22 350-351 Orthoesters, 10 498 Orthoferrites, 11 56t, 57 Orthogonal matrices, 6 27 ort/io-hydrogen, 13 759, 760—761 Orthokinetic flocculation, 11 631 22 56 Orthokinetic flocculator, 22 59 Orthomyxoviruses, 3 136—137... 

Titanium alloys generally show a combination of strength and biocompatibility which makes them suitable for medical devices (prosthesis, surgical instruments). The high strength Ti-6Al-7Nb alloy has several orthodontic applications. Only a limited number of alloys have the necessary combinations of properties needed for successful use in the human body. Titanium and its alloys, stainless steels and cobalt-chromium alloys are the workhorse alloys in the medical device industry. 

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