Effect of time and pH on physical-chemical properties of orthodontic brackets and wires.

Objective: To test the hypothesis that treatment time, debris/biofilm, and oral pH have an influence on the physical-chemical properties of orthodontic brackets and arch wires.
Materials and Methods: One hundred twenty metal brackets were evaluated. They were divided into four groups (n  =  30) according to treatment time: group C (control) and groups T12, T24, and T36 (brackets recovered after 12, 24, and 36 months of treatment, respectively). Rectangular stainless-steel arch wires that remained in the oral cavity for 12 to 24 months were also analyzed. Dimensional stability, surface morphology, composition of brackets, resistance to sliding of the bracket-wire set, surface roughness of wires, and oral pH were analyzed. One-way analysis of variance, followed by a Tukey multiple comparisons test, was used for statistical analysis (P < .05).
Results: Carbon and oxygen were shown to be elements that increased expressively and in direct proportion to time, and there was a progressive increase in the coefficient of friction and roughness of wires as a function of time of clinical use after 36 months. Oral pH showed a significant difference between group T36 and its control (P  =  .014).
Conclusions: The hypothesis was partially accepted: treatment time and biofilm and debris accumulation in bracket slots were shown to have more influence on the degradation process and frictional force of these devices than did oral pH.