Corrosion of orthodontic bracket bases Dr. Maijer R. Maijer” and D. C. Smith* Toronto, Ontario, Canada Attention has recently been focused on the development of black and green stains in association with directly bonded stainless steel brackets. Twelve clinical cases cf staining were studied in this investigation. After intraoral photography of the stains, the brackets were removed for examination with the scanning electron microscope. Multiple voids were observed at the Fesin-bracket interface, especially-at the periphery. Considerable deterioration of the alloy base and mesh structure was observed in the void areas. Preliminary analysis of the stains showed that chromium compounds were present The findings suggested that the presence of voids, together with poor oral hygiene, led to crevice corrosion of the Type 304 stainless steel and formation of colored corrosion products which can result in enamel stains. The use of stainless steels of improved corrosion resistance is recommended to overcome this problem. Key words: Bracket bases, bonding, corrosion, enamel stain, stainlesssteel P lacement of orthodontic attachments by welding the attachment onto small stainless steel bases which are directly bonded to the enamel has become commonplace in orthodontic therapy. The earliest ap- plication of this technique was reported in 1969 by Mizrahi and Smith,’ who used stainless steel band ma- terial to which mesh was welded. This bracket base, which was primarily used for the testing of polycar- boxylate cement as a medium for orthodontic bonding, did not gain much attention. In the years that followed, perforated bracket bases and unreinforced mesh bases were promoted strongly. This went hand in hand with the use of the ultraviolet and chemically cured resins used for bonding. An improved version of Mizrahi ‘s bracket base, the sintered foil mesh base, has gained renewed popularity. The foil mesh bases are significantly less plaque reten- tive than bases of the perforated type.* Although these bracket bases were a significant improvement from a hygienic point of view, esthetically, they were still showing a great deal of metal. In an attempt to improve this, the manufacturers resorted to smaller and smaller bracket bases as orth- odontic bonding systems became more reliable. A number of articles have reported on the performance of the various brackets.“-” From the Faculty of Damstry, University of Toronto. This work was supported in part by Ontario Provincial Health Research Grant P. R. 851 *Research Associate, Department of Biomaterials, and Visiting Professor, De- partment of Graduate Orthodontics. **Professor of Biomaterials. OOOZ-9416/82/010043+06$00.60/0 @ 1982 The C. V. Mosby Co. In the past 3 years black and green stains have been observed in association with bracket bases (personal communication in 1979 with A. J. Brennan). In some cases enamel was permanently marked with black or green stain after the bracket and resin had been re- moved. lo A recent unpublished survey” indicated that such stains are not uncommon across North America. This situation obviously warrants a detailed look at what conditions may contribute to their presence and why these stains occur, since they may be associated with the resin or the bracket. MATERIALS AND METHODS In order to evaluate these stains, a clinical study was undertaken. Teeth that had been bonded by a con- ventional acid-etch technique with subsequent place- ment of orthodontic brackets were photographed when a stain appeared. Two months after the stain was noted, the bracket was removed and the enamel polished with a No. 7902 finishing bur* followed by a Shofu cup? as described in an earlier publication. l2 The bracket bases were then prepared for scanning electron microscopy evaluation. A total of twelve brackets were evaluated in this preliminary study. RESULTS A typical clinical situation showed a dark stain on a maxillary canine (Fig. 1). Stain usually accumulated *Beaver Dental Products, Morrisburg, Ontario. ?Shofu Dental Corporation, Menlo Park, Calif. 43