Biodegradation of orthodontic metallic brackets and associated implications for friction

This study aimed to assess the effect of clinical exposure on the surface morphology, dimensions, and frictional behavior of metallic orthodontic brackets.

Ninety-five brackets, of 3 commercial brands, were retrieved from patients who had finished orthodontic treatment. As-received brackets, matched by type and brand, were used for comparisons. Surface morphology and precipitated material were analyzed by optical and scanning electron microscopy and x-ray microanalysis. Bracket dimensions were measured with a measuring microscope. Resistance to sliding on a stainless steel wire was assessed.

Retrieved brackets showed surface alterations from corrosion, wear, and plastic deformation, especially in the external slot edges. Film deposition over the alloy surface was observed to a variable extent. The main elements in the film were carbon, oxygen, calcium, and phosphorus. The as-received brackets showed differences (P <0.05) in the slot sizes among brands, and 1 brand showed a 3% increase in the retrieved brackets' slots. The frictional behavior differed among brands. Retrieved brackets of 2 brands showed 10% to 20% increases in resistance to sliding.

Metallic brackets undergo significant degradation during orthodontic treatment, possibly with increased friction. At present, it is difficult to predict the impact of these changes on the clinical performance of orthodontic components.