Effects of Coffee Temperature and Immersion Duration on the Physicochemical and Mechanical Properties of Orthodontic Elastomeric Chains

Objective: This study aimed to evaluate the effects of coffee temperature and immersion duration on the percentage weight change, force degradation, mechanical properties (300% modulus, and strain at break), and surface morphology of orthodontic elastomeric chains. We also aimed to examine the relationship between weight change and force degradation. Materials and Methods: Latex-free closed-type elastomeric chains were stretched to generate a force of 300 gf and assigned to four groups: control (artificial saliva, 37 °C) and three coffee-immersion groups (cold, 4 °C; room temperature, 25 °C; hot, 65 °C). Coffee groups were immersed for 15 min/day and stored in artificial saliva at 37 °C between immersion cycles. Weight change, force degradation, 300% modulus, strain at break, and surface morphology (scanning electron microscopy [SEM]) were evaluated on days 1, 3, 7, 14, and 21 (N = 10/group/time point). Two-way ANOVA with Tukey’s HSD post hoc test was used to analyze the effects of temperature and duration, and Pearson’s correlation was used to assess the relationship between weight change and force degradation. Results: Weight change was significantly affected by immersion temperature and duration (both p < 0.001), with the hot group showing significantly greater overall weight change than the control group (1.61% vs. 0.87%). Immersion temperature and duration significantly affected 300% modulus and strain at break, with significant temperature-duration interactions (p < 0.001). The hot group showed a consistently higher modulus and lower strain at break than the control group throughout the 21-day period, accompanied by progressively increasing surface irregularity on SEM. Force degradation was significantly greater in the hot group than in all other groups at every time point (p < 0.001) and increased continuously over 21 days, whereas the control, cold-, and room-temperature groups plateaued after days 7–14. Weight change was significantly and positively correlated with force degradation overall (r = 0.332, p < 0.001) and within each temperature group (r = 0.388–0.633), with the strongest correlation observed in the hot group. Conclusions: Coffee temperature and immersion duration significantly affected the physicochemical and mechanical properties of orthodontic elastomeric chains with hot-coffee exposure producing the greatest weight change, mechanical stiffening, surface roughening, and force degradation. Weight change was positively associated with force degradation, which suggests a link between physicochemical alteration and mechanical force loss, particularly under hot-temperature exposure.