The effect of pH on the mechanical properties of beta titanium orthodontic arch wires

This study sought to compare mechanical properties of beta titanium orthodontic wires to stainless steel and NiTi archwires under different pH conditions and for different time intervals.

Twenty samples of 5 different orthodontic arch wires were submerged in buffer solutions with pH 4.0, 5.5, and 7.0 for 6 and 18 weeks. Tensile and flexural strength tests were performed. 2-factor ANOVA was performed for the pH/time combinations and the 5 different arch wires. Wald-based tests were performed to determine if the change rate of the wires differed significantly from the others.

Two beta titanium wires at pH 4.0 exhibited significantly lower flexural strength at 6 weeks (T1) but difference diminished at 18 weeks (T2). pH value did not impact the flexural strength of NiTi and SS wires. There was no trend in the flexural strength of any wires in any pH solution from T0-T1 but there was significant decrease in strength for all wires from T0-T2. There was no trend in the change in tensile strength of the beta titanium wires and NiTi wires across any pH or time interval. There was a significant increase in the tensile strength of stainless-steel wires over all pH environments and time points.

There was a significant decrease in flexural strength of all wires over time and beta titanium archwires decreases significantly more than NiTi and SS wires. There is no significant change in tensile strength of beta titanium and NiTi wires over time. Tensile strength of stainless-steel wires increased significantly over time.