A wide range of materials are used in routine and cosmetic dentistry, including metals and their alloys, polymers, ceramics and composites. Dental applications of metals and alloys include fillings, prosthetic devices (crowns, bridges and removable prostheses), dental implants and orthodontic appliances.
Nickel is found in many alloys used in dental treatment to provide improved physical and chemical properties, such as strength and durability, as well as to reduce the cost of using precious alloys such as gold. The amount of nickel in any dental alloy can vary from a few per cent to over 60%. Nickel alloys are recognised for their ability to withstand the harsh oral environment and have a long-standing history of successful use in dentistry.
Nickel dental alloys are used in the construction of long-term restorations designed to remain in clinical service for many years, including crowns, fixed bridges and removable partial dentures. They are also used for shorter-term applications, such as in orthodontic appliances to move and straighten teeth.
Nickel is a common allergen and the use of nickel-containing materials in dentistry has sometimes been reported as a source of adverse reactions. This advisory note aims to provide reassurance and advice about the safe use of nickel as part of an alloy in dental materials.
The amount of nickel in dental alloys is not indicative of the amount of nickel that might be released when the material is in the mouth and in contact with surfaces or with saliva: different alloys have different levels of corrosion resistance and hence different levels of nickel release. For example, studies in the dental literature show that the amount of nickel released from nickel-chromium dental alloys is strongly influenced by the content of chromium and beryllium in the alloy. A chromium content of below 15% leads to increased metal ion release in all alloy components, including nickel, since the chromium share is not sufficient to passivate the entire surface. The addition of beryllium in the alloy – even minor amounts – also leads to increased ion release1. Nickel-chromium dental alloys that are beryllium-free and contain a minimum chromium content of 20% prove to be adequately resistant to corrosion, even under extreme experimental conditions. These high quality dental alloys release very low levels of nickel ions: up to 15 μg per dental crown per day2, which is well below the normal range of 100 – 600 μg of nickel ingested daily through food3. Controls on the use of dental alloys should therefore be based on an assessment of the level of total metal ion release (including nickel), and not on nickel content.
Recommendations For dental practitioners: • Ascertain whether the patient has a history of nickel allergy, and if so, avoid using nickel-containing alloys.
• Select high quality dental alloys. For the case of nickelchromium alloys, select those that are beryllium-free
and contain over 20% chromium.
• Ensure that dental technicians who are responsible forpreparing dental alloys receive proper materials handling training. Improper melting, casting or heat treatment of an alloy can affect the quality and corrosion resistance of a dental restoration.
For dental patients:
• If you have an allergy to nickel, discuss this with your dentist before a material is chosen for restoration,
surgical or orthodontic dental work.