Retention vs. Stability: A Comparative Study of Thermoplastic Materials for Oral Appliance Therapy

Background and aim Retention and stability are important mechanical factors influencing the effectiveness of oral appliance therapy for obstructive sleep apnea (OSA). Retention refers to the force required to maintain the appliance in place, whereas stability reflects the ability to preserve retentive force during repeated use. Although thermoplastic materials are widely used for oral appliances, differences in their initial retention and long-term stability remain unclear. This study aimed to compare retentive force and stability over repeated removal cycles between two thermoplastic materials, Duran and New Duran, using standardized maxillary and mandibular models. We hypothesized that Duran would exhibit higher initial retentive force, whereas New Duran would demonstrate greater stability over repeated use. Methods Two types of thermoplastic materials were evaluated using standardized dental models. Retentive force was measured during 100 consecutive removal cycles. Each experiment was repeated three times. A linear mixed-effects model was used to analyze the effects of material type, removal cycle, and their interaction. Initial retentive force was compared using Welch's t-test. Results In the maxillary model, Duran showed higher initial retentive force than New Duran, although the difference was not statistically significant (1.457 ± 0.117 N vs. 1.040 ± 0.251 N, p = 0.085). In contrast, in the mandibular model, Duran demonstrated significantly higher initial retention (1.683 ± 0.132 N vs. 0.857 ± 0.107 N, p = 0.0013). Over repeated removal cycles, Duran exhibited a gradual decrease in retention, whereas New Duran showed relatively stable retentive force. A significant interaction between material type and removal cycle was observed, indicating different degradation patterns between materials. Conclusions Duran provides a higher initial retentive force, particularly in the mandibular model, whereas New Duran demonstrates superior stability over repeated use. These findings suggest that material selection should be tailored according to anatomical conditions and clinical priorities.