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

Area of Science:

• Biomaterials Science
• Orthodontics
• Polymer Science

Background:

• Clear orthodontic appliances are preferred for aesthetics and comfort.
• Novel materials are needed to improve the performance of clear aligners.

Purpose of the Study:

• To investigate a new shape memory polyurethane (SMP) composite material, polydl-lactide and hydroxyapatite (PDLLA/HA), for orthodontic applications.
• To evaluate the mechanical performance and shape recovery forces of the PDLLA/HA composite under simulated oral conditions.

Main Methods:

• Finite element (FE) analysis was employed to model the composite's mechanical behavior using viscoelasticity and phase transition theories.
• Experimental characterization included determining glass transition temperature (Tg), tensile properties, and creep behavior.
• A customized UMAT subroutine in Abaqus simulated the shape memory effect, and orthodontic forces were measured using aligners fabricated from the composite.

Main Results:

• The glass transition temperature (Tg) of the SMP samples decreased progressively upon water immersion, reaching 35°C after 15 days.
• Orthodontic forces generated by aligners displacing teeth 0.1, 0.2, and 0.3 mm facially were approximately 0.16, 0.17, and 0.35 N, respectively.
• These experimental forces showed 85.3% agreement with FE simulation results.

Conclusions:

• The PDLLA/HA composite demonstrates suitable and stable shape recovery forces for orthodontic treatment under simulated oral conditions.
• FE analysis can predict orthodontic forces from clear aligners, aiding in optimizing treatment plans for various malocclusions.