Biodegradation of Orthodontic Appliances: An Atomic Absorption Spectrophotometric Assessment

Abstract

Background: Orthodontic appliances are routinely exposed to the oral environment for extended periods, raising concerns about metal ion release and potential systemic effects.

Objectives: This in vitro study aimed to compare the degradation of nickel and chromium from standard orthodontic appliances containing either stainless steel or nickel-titanium archwires in artificial saliva, and to assess whether released metal concentrations remain within biological limits.

Materials and Methods: Ten identical sets of orthodontic appliances simulating complete maxillary fixed appliances were used. Five sets were ligated with 0.016 × 0.016-inch stainless steel archwires and five with nickel-titanium archwires of identical dimensions. Each appliance was immersed in 100ml of artificial saliva (pH 6.75) and maintained at 37°C for 28 days. Metal ion release was measured at days 1, 7, 14, 21, and 28 using atomic absorption spectrophotometry.

Results: Nickel release peaked on day 7 for both archwire types (0.358 ± 0.013 ppm for stainless steel; 0.372 ± 0.013 ppm for nickel-titanium), while chromium release peaked on day 14 (0.156 ± 0.013 ppm for stainless steel; 0.152 ± 0.008 ppm for nickel-titanium). Total nickel release over 28 days was 1.266 ppm for stainless steel and 1.326 ppm for nickel-titanium appliances. Total chromium release was 0.526 ppm for stainless steel and 0.536 ppm for nickel-titanium. No statistically significant differences were observed between archwire types (p > 0.05).

Conclusion: Both stainless steel and nickel-titanium orthodontic appliances release nickel and chromium ions in artificial saliva, with release patterns showing temporal variation. The amounts released remain within established biological safety limits, though individual patient susceptibility should be considered.