Characterization of a new shape memory composite material for orthodontic aligners - a preliminary study.

Objective: Clear orthodontic appliances without metal brackets are highly favored by orthodontic patients due to their aesthetic appearance, easy to clean, and comfort. This pilot study aimed to investigate a new shape memory polyurethane (SMP) composite material for orthodontic applications.

Methods: Finite element (FE) analysis was used to evaluate the mechanical performance of the composite material, which consists of polydl-lactide and hydroxyapatite (PDLLA/HA) model based on viscoelasticity and phase transition theories. Experimental characterization included determination of glass transition temperature (T), tensile properties, and creep behaviors. A customized UMAT subroutine was developed for Abaqus to simulate the thermodynamic process of shape memory effect based on the experimental data. Orthodontic forces generated by aligners fabricated from the composite were evaluated under simulated intraoral conditions.

Results: The results showed a progressive decline in T of the SMP samples following immersion in water, with T values decreasing to 45, 37, and 35 ℃ after 5, 10, and 15 days, respectively. When displacing teeth 0.1, 0.2, and 0.3 mm facially using this aligner, the initial orthodontic forces recorded were approximately 0.16, 0.17, and 0.35 N, respectively, achieving 85.3% agreement with the FE simulation results.

Conclusions: PDLLA/HA composite exhibits an appropriate and stable shape recovery force under simulated oral conditions, indicating its potential suitability for application in orthodontic treatment.

Clinical Relevance: Incorporating FE analysis enables the prediction of orthodontic forces exerted by clear aligners under various malocclusion conditions, thereby optimizing orthodontic treatment plans in clinical practice.