The overlay splint is fabricated on the Biostar machine on either arch. It is usually constructed of an exceptionally hard polycarbonate material known as Splint Biocryl. As an option, the overlay can be made of Durasoft material. Durasoft is a dual laminate of hard polycarbonate and soft vinyl laminate material. The appliance is formed so that the soft side contacts the teeth on the arch, the appliance fits onto and the hard side faces the opposing arch.