Multilayer Polymer Sheets

What is this patent about?

’091 is related to the field of orthodontics, specifically the design and materials used in removable dental aligners. Traditional aligners, like braces, apply force to teeth to gradually shift them. Newer aligner systems use a series of preformed appliances designed using computer modeling to incrementally reposition teeth. There is a need for aligner materials with improved durability and elastic properties to reduce the number of aligners needed and avoid mid-course corrections.

The underlying idea behind ’091 is to create a multilayer aligner with improved mechanical properties by combining a hard polymer layer between two soft polymer layers. This configuration aims to enhance the aligner's ability to maintain consistent force over time, resist deformation, and withstand wear and tear from insertion, removal, and teeth grinding. The combination of materials is designed to provide both the necessary stiffness for tooth movement and the flexibility for patient comfort and appliance durability.

The claims of ’091 focus on a multilayer sheet incorporated into an orthodontic appliance, where the sheet comprises a first layer of a single co-polyester polymer with specific mechanical properties (high flexural modulus, tensile strength, and elongation), a second layer of a single thermoplastic polyurethane elastomer polymer with its own set of properties (high tensile strength, elongation, and hardness), and a third layer. The key is the specific combination of these materials to achieve a balance of strength and flexibility.

The aligner is fabricated by thermoforming this multilayer sheet over a model of the patient's teeth in a target position. The co-polyester layer provides the necessary stiffness to apply force to the teeth, while the thermoplastic polyurethane elastomer layers offer flexibility and comfort for the patient. This construction allows the aligner to maintain its shape and force over a longer period, reducing the need for frequent aligner changes or mid-course corrections.

Prior aligners often suffered from stress relaxation and deformation, leading to reduced effectiveness over time. The ’091 invention addresses this by using a specific combination of materials that exhibit improved stress relaxation properties and long-term unloading characteristics. Tests show that aligners made with this multilayer sheet maintain their shape and apply force more consistently compared to existing materials, ultimately leading to more efficient and predictable tooth movement.