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Designation of dental alloys

 

Terms such as “non-precious”, “semi-precious” and “precious” are frequently used in advertising material and communication with dental laboratories. Such terms should be avoided because they are vague and undefined (Figure 1). Rather, the composition of the alloy should be stated, using at least the two most abundant elements in order.

The current ISO standard for fixed and removable restorations (ISO 22674:2006) classifies alloys according to physical properties, ranging from Type 0 being soft metals to Type 5 which are high-strength and high-stiffness alloys for partial removable dentures and parts with thin sections. Many but not all of the alloys are designed for ceramic veneering (1).

Knowledge about the composition of alloys for prosthetic use is important in the selection of products. Some patients are hypersensitive to specific metals, which highlights the need for detailed compositional information (2-5). Particularly, the “cross reaction” between nickel and palladium has been discussed (6). In general, the patient’s anamnesis regarding potential contact allergies should be scrutinized in order to avoid use of alloys that might pose a risk for hypersensitivity reactions.

The ISO standard for alloys no longer requires a classification based on composition. The manufacturer should, however, declare the amount of each element that exceeds 1% by weight. Hazardous elements, i.e. beryllium, cadmium and nickel, have to be declared when exceeding 0.1% for nickel and 0.02% for the other two elements.

Figure 1. The boxes represent recommended terminology for designating dental alloys. The figure shows that the terms “non-precious”, “semi-precious” and “precious” are too unspecific to merit further use. These terms should be replaced by the chemical composition. For example, a “precious” high-palladium alloy should be termed “palladium–gold alloy”.

Author
Nils R. Gjerdet, PhD, Professor
References
1. Roberts HW, Berzins DW, Moore BK, Charlton DG. Metal–ceramic alloys in dentistry: a review. J Prosthod. 2009; 18: 188–94.
2. Zhou J, Paul A, Bennani V, Thomson WM, Firth NA. New Zealand dental practitioners’ experience of patient allergies to dental alloys used for prosthodontics. N Z Dent J. 2010; 106: 55–60.
3. Raap U, Stiesch M, Reh H, Kapp A, Werfel T. Investigation of contact allergy to dental metals in 206 patients. Contact Dermatitis. 2009; 60: 339–43.
4. Garner LA. Contact dermatitis to metals. Dermatol Ther. 2004; 17: 321–7.
5. Garhammer P, Schmalz G, Hiller KA, Reitinger T, Stolz W. Patients with local adverse effects from dental alloys: frequency, complaints, symptoms, allergy. Clin Oral Investig. 2001; 5: 240–9.
6. Faurschou A, Menne T, Johansen JD, Thyssen JP. Metal allergen of the 21st century – a review on exposure, epidemiology and clinical manifestations of palladium allergy. Contact Dermatitis. 2011; 64: 185–95.