How We Make Custom Polypropylene Orthoses
At ProLab, we make custom functional polypropylene orthoses using two advanced production methods: vacuum-forming
. The orthoses made by each method are identical in the resulting shape and function. There is a slight variation in application, appearance and advantages. Knowing the difference between vacuum-forming and direct-milling can influence the success of your practice.
Vacuum-Formed Polypropylene Orthoses
Vacuum-formed poly is heated in an oven and vacuumed over a balanced and corrected positive wood mold created from the original negative cast or digital image of the foot. When the poly is heated, almost to the melting point, its physical composition is altered making it more flexible when it cools. To compensate for this additional flexibility, add 1mm when prescribing the poly thickness of the shell to achieve a semirigid device. Otherwise, a semirigid device becomes a flexible device.
Fast Facts for Vacuum-Formed Orthoses
- choice of rearfoot post material: polypropylene or EVA
- advanced accommodations including plantar fascial grooves and sweet spots
- slightly more flexible
- textured surface works well with or without topcover
Milled Polypropylene Orthoses
Producing milled poly orthoses is a more streamlined process than vacuum-forming. The digital image of the foot is balanced and corrected, then sent directly to a computer-programmed mill that carves the orthoses out of a block of polypropylene. This technique, which does not require heating, produces a more rigid device making it possible to fabricate thinner orthoses with the same flexibility as the thicker vacuum-formed devices.
Fast Facts for Milled Orthoses
- can be prescribed as thin as 2mm
- rearfoot post is milled into the device
- less expensive due to lower labor and materials costs
- milling lines on surface work well with or without topcover