In situ comparison of thermoplastic and thermoset orthodontic elastomeric chains after 30 days of intraoral exposure

Objectives: To compare viscoelastic behavior of thermoplastic and thermoset elastomeric chains after 30 days of intraoral exposure and to evaluate influence of color on mechanical performance and color stability. Materials and Methods: Twenty patients in the retention phase wore Hawley retainers containing four elastomeric chain segments: gray thermoplastic, transparent thermoplastic, gray thermoset, and transparent thermoset (n = 20 per group). Chains were stretched to a standardized distance of 20 mm and worn intraorally for 30 days. Dimensional deformation, tensile force at 20 mm and at 2 × and 3 × stretching, rupture force, and color change were assessed at baseline and after intraoral exposure. Data were analyzed using factorial analysis of variance with Tukey's post hoc test and paired t-tests (α = .05). Results: Thermoplastic elastomeric chains exhibited significantly greater permanent deformation than thermoset chains (P < .0001). Although thermoplastics generated higher initial tensile forces, they showed greater force degradation after intraoral exposure, whereas thermoset elastomers maintained higher residual forces at the tested activation distance of 20 mm. Thermoplastic chains exhibited higher rupture forces but greater reductions from baseline, while thermoset elastomers demonstrated superior elastic recovery. Transparent elastomers showed greater color change (ΔE) than gray elastomers; however, all ΔE values remained within clinically acceptable limits. Conclusions: After 30 days of intraoral exposure, thermoset elastomeric chains demonstrated superior mechanical stability and force retention compared with thermoplastic chains. Although transparent elastomers were more susceptible to discoloration, esthetic changes remained clinically acceptable. These findings reflect elastomeric behavior under controlled intraoral conditions.