Effects of intraoral aging of arch-wires on frictional forces: An ex vivo study

INTRODUCTION: Archwires act as gears to move teeth with light, continuous forces. However, the intraoral use of orthodontic archwires is liable to surface deposits which alter the mechanical properties of archwires, causing an increase in the friction coefficient. OBJECTIVES: To evaluate the surface changes of the stainless steel archwires after 6 weeks of intraoral use and its influence on frictional resistance during sliding mechanics. MATERIALS AND METHODS: As-received rectangular 0.019” × 0.025” stainless steel orthodontic archwires (control) were compared with the archwires retrieved after the final phase of leveling and alignment stage of orthodontic treatment collected after 6 weeks of intraoral exposure (test samples) from 10 patients undergoing treatment. The control and test samples were used to evaluate surface debris using Scanning Electron Microscopy, surface roughness was assessed using Atomic Force Microscope and frictional forces were measured using Instron Universal Testing Machine in the buccal inter-bracket region that slides through the molar tube for space closure. Unpaired t-test and Pearson correlation tests were used for statistical analysis (P < 0.05 level of significance). RESULTS: Significant increase was observed in the level of debris (P = 0.0001), surface roughness (P = 0.0001), and friction resistance (P = 0.001) of orthodontic archwires after their intraoral exposure. Significant positive correlations (P < 0.05) were also observed between these three variables. CONCLUSION: Stainless steel test archwires showed a significant increase in the degree of debris and surface roughness, increasing the frictional forces between the archwire-bracket interfaces which would considerably reduce the normal orthodontic forces. Thus, continuing the same archwire after levelling and alignment for space closure is not recommended.