Evaluation of biofilm accumulation on and deactivation force of orthodontic NiTi archwires before and after exposure to the oral medium: in vitro study

OBJECTIVE: The aim of this in vitro study was to evaluate biofilm accumulation on and deactivation force of orthodontic Nickel-Titanium (NiTi) archwires, before and after exposure to the oral medium. METHODOLOGY: Four commercial brands of orthodontic NiTi 0.016" archwires were examined before and after exposure to the oral medium for 4 weeks. Six archwire segments 30 mm long, of each manufacturer were tested in a device with four self-ligating brackets, channel 0.022", adapted to a universal test machine to evaluate the deactivation force between 0.5 and 3 mm of deflection. The presence of biofilm on the archwire surfaces was evaluated by Scanning Electron Microscopy, before and after exposure to the oral medium. The Wilcoxon and pondered Kappa tests were applied to the biofilm scores, 3-way ANOVA for repeated measures (Bonferroni post-test) and linear regression between biofilm and deactivation force. RESULTS: exposure to the oral medium promoted moderate to severe presence of debris on the archwire surfaces and caused a reduction in deactivation force for the Ormco and GAC brands, however, maintaining them with adequate force levels. The MORELLI and ORTHOMETRIC archwires underwent no significant reduction in deactivation force; moreover, these maintained elevated levels of force after exposure to the oral medium. The Spearman test indicated low correlation between biofilm accumulation and deflection force for the Morelli (R2=0.132 and p=0.683) and Orthometric (R2=0.308 and p=0.330) brands. On the other hand, the GAC (R=0.767 and p=0.004) and ORMCO (R=0.725 and p=0.008) brands presented statistically significant correlation between these variables. CONCLUSION Exposure to the oral medium for a period of one month may cause significant change in the dissipation of Forces of orthodontic NiTi archwires, resulting from biofilm accumulation.