Article review

Abstract

In the oral environment, orthodontic appliances are exposed to potentially damaging physical and chemical agents that can cause metallic corrosion. Objective: The aim of the study was to compare the metal ions released from new and recycled metal brackets after immersion in artificial saliva under controlled conditions of pH over an extended period of time. Method: Four different types of metal brackets were investigated: DynaLock twin torque brackets (Unitek), metal base brackets (Tomy), standard edgewise brackets (Ormco), and Ricketts brackets (Dentaurum). A total of 320 brackets were tested. The new brackets were used as received from the manufacturers. Recycling was mimicked by applying adhesive to the bracket base, and, once set, the bracket was heated to 350°C for 30 minutes to burn off the adhesive, simulating the heat treatment at commercial recyclers. The brackets were immersed in relevant solutions and incubated at 37°C for 48 weeks. The release of nickel, chromium, iron, copper, cobalt, and manganese ions was analyzed by atomic absorption spectrophotometry. The results were compared by using 1-way analysis of variance (ANOVA). Results: Metal brackets immersed in a pH4 solution release more ions than those immersed in a buffered artificial saliva solution at pH7. The release of metal ions increased with long-term immersion of the brackets; nickel was the most predominant metal ion released. The highest level of copper ion release was found with the Dentaurum brackets after immersion for 48 weeks. Metal brackets used in orthodontic appliances were shown to corrode in an acid or neutral environment after long-term use. Conclusions: Both new and recycled brackets will corrode in the oral environment. To avoid clinical side effects, metal brackets should be made more resistant to corrosion, and, according to the authors, recycled brackets should not be used.