Factors affecting on permanent defor-mation of orthodontic arch wires : an in vitro study

Abstract EN

To measure the amount of permanent deformation of different types of orthodontic arch wires and to study the effect of both time interval and simulated oral environment on amount of permanent deformation of different types of nickel titanium and stainless steel orthodontic arch wires.

Materials and Methods : The sample consisted of five types of orthodontic arch wires (extra spring hard stainless steel, spring hard stainless steel, multi strand stainless steel, nitinol nickel titanium and super elastic nickel titanium), 0.016 inch of round section were deflected into orthodontic brackets fitted in acrylic models put in a closely packed glass container and 200 ml artificial saliva added to them and the samples stored in incubator at 37 °C.

At the end of incubation period, the acrylic block take and the wire deactivated and the amount of permanent deformation measured by using Stereo microscope.

The results were subjected to the descriptive statistics and to the ANOVA and Duncan’s Multiple Range Analysis Tests to detect the changes among these groups.

Results The findings of the present study showed that spring hard stainless steel wires at 28 days gave rise to the highest mean values of permanent deformation, while the super elastic wires at 1hr gave rise to the lowest one.

The remaining groups distributed on statistical levels of significant difference (P ≤ 0.05) between the upper and lower levels.

Conclusions : The super elastic nickel titanium wires exhibited better spring back characteristics and less permanent deformation than the stainless steel.

Several wires increased deformation as deflection time increased in simulated oral environment.