Application of 17-7 Precipitation-hardenable Stainless Steel in Dentistry.

Several alloys described as stainless steel which resist tarnish and corrosion in the mouth are being used for a variety of dental appliances and instruments. Probably the greatest application of stainless steel is for orthodontic arch wires and bands, while a more limited use is for temporary space maintainers and crown forms. Root-canal files and reamers designed for endodontic operations also are being fabricated from stainless steel. For each of these applications there are advantages to having an alloy which will respond to hardening heat treatments. Stainless steels generally can be classed as ferritic, martensitic, or austenitic. Although the properties and physical metallurgy of these stainless steels is quite well known, the use of precipitation-hardenable stainless steels has developed since 1946.'' 2 Since this time, austenitic, martensitic, and semiaustenitic stainless steels have been developed which are subject to precipitation hardening. Of these three types of precipitationhardenable stainless steels the semiaustenitic type is capable of producing the higheststrength materials. The treatment of the semiaustenitic stainless steel consists of three separate parts:3'(1) a solution treatment at 1,9500 F., (2) transformation of the austenite to martensite, and (3) the precipitation of hardening phases within the martensite. The initial solution treatment results in the solution of