Effects of different stretching extents, morphologies, and brands on initial force and force decay of orthodontic elastomeric chains: An in vitro study

Elastomeric chains are of clinical importance to orthodontics. Therefore, their behavior should be assessed under different conditions. Some of their critical aspects remain unstudied (including effects of different elongations and chain forms on their force properties). Therefore, we aimed to assess these factors.

This in vitro study was performed on 540 observations: first, 90 chains (10 specimens per subgroup of three brands [American Orthodontics, Ortho Technology (OT), and G&H], each from three chain types [closed, short, and long]) were stretched for three extents (40%, 60%, and 100%) and their forces were measured using a universal testing machine. Afterward, 270 new chains of the same brands/types were stretched for the same extents by installing them onto pairs of pins with different interpin distances. Plates holding pins/chains were incubated in artificial saliva at 37°C for 4 weeks. Afterward, their forces were measured and analyzed using partial correlation coefficient, three‑way analysis of variance (ANOVA), Tukey, Student’s t, and Mann–Whitney tests (α = 0.001).

Forces degraded significantly from an overall mean of 3.97 ± 0.97 N to 1.29 ± 0.39 N after 4 weeks (all P = 0.000, t‑test/Mann–Whitney). ANOVA showed highly significant differences among brands, types, and elongations, in terms of “initial force, force decay, and residual force” (all P = 0.000). Almost all post hoc pairwise comparisons were significant (Tukey P = 0.000). There was a strong positive correlation between elongation extent and force loss (r = 0.846, P = 0.000).

OT might be the most preferable brand. Closed chains might usually show better results, especially in OT chains. Instead of using chains half of the size of the space (to elongate for 100%), longer chains should be used to stretch for lesser extents.