Comparison of Single-Layer and Triple-Layer TPU MaxFlex Aligners After Intraoral Use

Clear aligner therapy (CAT) has become an increasingly popular alternative to fixed orthodontic appliances due to its aesthetic advantages, improved patient comfort, and ease of oral hygiene maintenance. Thermoplastic materials, particularly thermoplastic polyurethane (TPU), are widely used in the fabrication of aligners due to their favorable mechanical and elastic properties.

Recent advancements in aligner materials have led to the development of multilayer TPU systems designed to enhance flexibility, force delivery, and clinical performance. Triple-layer TPU aligners typically consist of a soft inner layer for patient comfort, a rigid intermediate layer for structural strength, and a flexible outer layer to improve adaptability and fit. In contrast, single-layer TPU aligners are composed of a homogeneous material and are generally more cost-effective.

Despite these developments, limited evidence exists regarding the comparative behavior of single-layer and multilayer TPU materials following intraoral exposure. The oral environment, characterized by temperature fluctuations, moisture, masticatory forces, and enzymatic activity, may contribute to material degradation, potentially affecting aligner performance.

This randomized controlled trial is designed to evaluate the effects of intraoral aging on the mechanical properties and surface morphology of single-layer and triple-layer TPU aligners (MaxFlex). Participants will be randomly assigned to receive one type of aligner material and will be instructed to wear the aligners for a standardized duration of 10 days (minimum 22 hours per day).

Aligners will be collected at baseline (prior to intraoral use) and after the 10-day wear period. Following retrieval, samples will undergo standardized cleaning procedures before laboratory analysis.

Mechanical testing will be performed using dynamic mechanical analysis to assess tensile properties, stress relaxation behavior, and creep characteristics. Surface morphology will be evaluated using scanning electron microscopy to identify features such as roughness, cracks, and voids. Additionally, Fourier transform infrared spectroscopy will be used to detect potential chemical changes in the material composition.

The primary objective of this study is to compare the mechanical performance of single-layer and triple-layer TPU aligners before and after intraoral use. Secondary outcomes include evaluation of surface morphology and chemical structure changes associated with intraoral aging.

The findings of this study are expected to provide insight into the durability and clinical performance of different aligner materials, which may help guide material selection and improve orthodontic treatment outcomes.

Inclusion criteria

Patients aged 18-30 years Fully erupted permanent dentition Good periodontal health Patients undergoing orthodontic treatment with clear aligners Mild crowding or spacing requiring labiolingual tooth movement Willingness to wear aligners for at least 22 hours per day Provision of informed consent

Exclusion criteria

Use of aligners from manufacturers other than study-specific TPU aligners Damaged or fractured aligners Poor compliance (wear time less than 22 hours/day) Presence of parafunctional habits (e.g., bruxism) Hypodontia or partially erupted dentition Cases involving bonded attachments on maxillary incisors Cases requiring rotational movement of maxillary incisors Patients with systemic or oral conditions affecting saliva composition or the oral environment