Viscoelastic response of the midpalatal suture during maxillary expansion treatment

Objectives - The viscoelastic response of the midpalatal suture during maxillary expansion treatment has been sparsely studied. The aim of our study was to use viscoelastic models to investigate the effect of appliance mechanics on sutural tissue. Materials and Methods - Four creep-strain models were utilized in predicting the midpalatal suture's response to a constant-force application during expansion treatment. The functional forms included a three-term separable, three-term inseparable, two-term inseparable, and single-term arrangement. The functions were then transformed into subsequent stress-relaxation representations to predict suture response as a result of 0.25, 0.20, 0.15, and 0.10 mm displacements. Finally, the single-term creep-strain representation was altered to simulate treatment decaying force during treatment. A force that decays 30 and 10% of an initially applied 0.98 N was considered for decaying functions over a 6-week period, and compared to strain resulting from a constant-force application. Results - This analysis illustrated that the decay in suture strain closely followed decay in force and that the path of decay had minimal impact on overall results. Also, it was found that a single screw activation would likely not cause suture soft tissue failure, even for a 0.25 mm displacement, and that suture stress rapidly decayed within minutes of activation. Conclusion - Results from this study support the notion of maintaining a low-magnitude constant traction on the suture during treatment to avoid soft tissue failure and promote tissue remodeling.