Strength of the material before it begins to permanently deform.

Higher yield stress ensures the aligner holds its shape longer, maintaining consistent force throughout wear.

High yield stress is ideal — It means better durability and force retention during the treatment cycle.

How much the material can stretch before it deforms

This impacts how well the aligner adapts to the teeth and comfort during wear.

Moderate to high yield strain is ideal

A measure of stiffness when the aligner is pulled or stretched

Stiffer materials transmit more force but need to be comfortable.

Moderate to high values are preferred — for effective force with comfort.

Stiffness during bending — important when the aligner is under bite pressure.

Prevents deformation during chewing or clenching.

High flexural modulus is ideal — ensures better shape retention and force consistency.

Resistance to tearing when stress is applied at an angle (e.g., during insertion/removal).

Helps reduce aligner breakage and improves confidence in daily use.

High tear strength is ideal — increases aligner life and patient ease-of-use.

Loss of force after being in a wet, warm environment (like the mouth).

The lower the decay, the better the aligner holds effective force during wear.

Low decay is ideal — ensures sustained force between changes.

The initial force the aligner applies when first worn.

Needs to be high enough to move teeth, but not so high that it causes pain or trauma.

Moderate force is ideal — effective but gentle.