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Titanium Applications in Dentistry

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Titanium Applications in Dentistry ASSOCIATION I REPORT Background. The ADA Council on Sci­ entific Affairs outlines the status oftita­ nium and titanium alloys used in dentistry and provides its recommendations con­ cerning their use in clinical practice. Conclusions. Titanium and titanium Titanium applications alloys, based on their physical and chemical properties, appear to be especially suitable in dentistry for dental implants and prostheses. For the construction ofendosseous implant devices, titanium and its alloys have become well­ ADA COUNCIL ON SCIENTIFIC AFFAIRS accepted and can be considered the mate­ rials ofchoice. Clinical Implications. For crown and he use oftitanium and titanium alloys for bridge prostheses, dentists can consider medical and dental applications has increased titanium and its alloys as viable options to dramatically in recent years. Historically, more traditional noble and base metal titanium has been used extensively in alloys, but careful selection ofprocessing aerospace, aeronautical and marine applica­ methods and laboratory skill are necessary tionsTbecause ofits high strength and rigidity, its low to ensure success. density and corresponding low weight, its ability to withstand high temperatures and its resistance to corrosion. 1 Over the past three decades, the development of when chemically pure, is similar to that new processing methods-such as lost-wax casting, of many dental alloys. Titanium also computer-aided machining and electric discharge can be alloyed with other metals, such __________________________________ machining-has expanded titanium's as aluminum, vanadium or iron, to useful range of applications in biomed­ modify its mechanical properties. Both titanium ical devices. 2 Today, titanium and tita­ ASTM International (the American and titanium nium alloys are used for the fabrication Society for Testing and Materials) rec­ alloys appear ofprosthetic joints, surgical splints, ognizes four grades of commercially to be especially stents and fasteners, dental implants, pure titanium, or Ti, and three titanium dental crowns and partial denture alloys (Ti-6Al-4V, Ti-6Al-4V Extra Low suitable for tv o dental implants frameworks. This report outlines the Interstitial [low components] and Ti-Al­ o current status of titanium and titanium Nb).5 Titanium is a highly reactive 'D and prostheses. alloys used in dentistry and presents metal that readily passivates to form a the Council's recommendations con­ protective oxide layer, which accounts cerning their use in clinical practice. for its high corrosion resistance. The low density oftitanium provides for PHYSICAL AND CHEMICAL PROPERTIES high-strength, lightweight prostheses. Titanium, in the form ofthe oxide rutile, is abundant in Additionally, dental porcelain can be the earth's crust. Titanium ore can be refined to metallic fused and bonded to titanium to pro­ titanium using a method called the Kroll process.3 In its duce an esthetic, lifelike restoration. metallic form at ambient temperature, titanium has a Titanium's highly reactive nature hexagonal, close-packed crystal lattice (ex phase), which provides both advantages and disadvan­ transforms into a body-centered cubic form (B phase) at tages for its use. Titanium must be 883 C (with a melting point of 1,680 C).4 melted in a vacuum or under inert gas Many of titanium's physical and mechanical proper­ to prevent oxidation and the incorpora­ ties make it desirable as a material for implants and tion of oxygen that can lead to embrit­ prostheses. The strength and rigidity oftitanium are tlement of the cast meta1. 6 Contamina­ comparable to those of other noble or high noble alloys tion with even low concentrations of commonly used in dentistryy and titanium's ductility, atmospheric oxygen can lead to signifi- JADA, Vol. 134, March 2003 347 Copyright ©2003 American Dental Association. All rights reserved. ASSOCIATION REPORT cant loss of ductility. The molten alloy also can using laser welding or electric spot welding. react readily with refractory investment mate­ rials, requiring careful selection of compatible DENTAL USES materials, removal of the surface-reacted layer of Titanium has been used in cast dental prostheses metal or both. since the 1970s.4 Equipment is available to cast This same reactivity is responsible for many of titanium into single-and multiple-unit-crown­ titanium's favorable properties. The metal oxi­ and-bridge frameworks, implant-supported struc­ dizes almost instantaneously in air to form a tures and partial or full denture bases. Methods tenacious and stable oxide layer approximately have been developed for fusing dental porcelain 10 nanometers thick. 1.6 This oxide layer provides to titanium for crowns and bridges, but the a highly biocompatible surface and a corrosion choice of dental porcelain is limited by two resistance similar to that of noble metals. In critical factors: the porcelain fusion temperature addition, the oxide layer allows for bonding of must be below 800 C to avoid the ex to Bphase fused porcelains, adhesive polymers or, in the transition, and the coefficient of thermal expan­ case of endosseous implants, plasma-sprayed or sion of the porcelain must match that of the surface-nucleated apatite coatings. metal.2.4 High fusing temperatures ------------------------------------------------- also can lead to excessive oxide for- CASTING Equipment is mation, and a recent study9 showed Dental castings are made via pres­ available to cast that porcelain fired under inert sure-vacuum or centrifugal casting titanium into single­ atmosphere resulted in improved methods.7 The metal is melted bonding. Furthermore, it is difficult and multiple. unit­ using an electric plasma arc or to maintain consistency in tita­ inductive heating in a melting crown-and-bridge nium dental castings because of chamber filled with inert gas or frameworks. their inherently poor castability, held in a vacuum. The molten implant-supported and few laboratories are able to metal then is transferred to the strudures and partial provide this service. Though tita­ refractory mold via centrifugal or or full denture bases. nium is economical, biocompatible pressure-vacuum filling. ................................................. and readily available, the technolo- Castings of titanium commonly gies necessary for casting, are used to fabricate crowns, bridge machining, welding and veneering frameworks and full or partial denture frame­ this metal are relatively new and more expensive works. Several commercial machines for casting than those used for conventional dental metals. titanium are available, but their cost is consider­ For these reasons, the use of titanium for dental ably higher than that for standard dental casting castings has not become a prevalent laboratory tv o equipment. I Materials with low reactivity are and clinical practice. o used to prevent surface reaction with the molten 'D metal, and materials with high setting expansion IMPLANTS are used to compensate for the high casting For more than 25 years, titanium has been used shrinkage of titanium. for both endosseous and subperiosteal implants. lO Endosseous implants have taken the form of MACHINING rods, posts and blades made of either pure tita­ Dental implants generally are machined from nium or titanium alloys. The passivating oxide billet stock of pure metal or alloy. Dental crowns on the implant surface permits close apposition and bridge frameworks also can be machined of physiological fluids, proteins, and hard and from solid metal stock via computer-aided soft tissues to the metal surface. This process, machining. Abrasive machining of titanium, whereby living tissue and an implant become however, is slow and inefficient, which greatly structurally and functionally connected, is called limits this approach. Another method for fabri­ osseointegration.ll Titanium also has been used cating dental appliances is electric discharge successfully as a biocompatible implant material, machining, which uses a fabricated graphite die and continual improvements in both device (often reproduced from the dental working die) to design and clinical implantation techniques have erode the metal to final shape via spark erosion.8 led to well-accepted and predictable procedures. Multiple dental prostheses also can be connected In 1996, the ADA's Council on Scientific 348 JADA, Vol. 134, March 2003 Copyright ©2003 American Dental Association. All rights reserved. ASSOCIATION REPORT Affairs updated its position regarding the use of whom the risks and benefits have been carefully endosseous implants as a treatment modality for weighed and thoroughly discussed. For crown and full or partially edentulous patients. 12 In this bridge prostheses, dentists can consider titanium 1996 update, the Council stated that ADA­ and its alloys as viable options to more traditional Accepted endosseous implants, including those noble and base metal alloys, but careful selection made of pure titanium or titanium alloys, can be ofprocessing methods and laboratory skill are nec­ used only to treat carefully selected patients with essary to ensure success. To date, however, there whom the relative merits ofbenefit and risk have are few clinical data available that compare the been fully discussed. Before the 1996 update, the long-term success oftitanium restorations with Council had not recommended endosseous those made from more traditional metals. • implants for routine clinical practiceY Neverthe­ less, the Council's report indicated that many fac­ The ADA Council
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