This new modification of the Twin Block Appliance has been developed to facilitate controlled gradual advancement of the mandibular position during the treatment of Class II Division I malocclusions. The system features the incorporation of stainless steel screws with conical heads into the blocks of the upper appliance, to provide the inclined plane effect. Advancement is carried out at the chairside, by the addition of acetal spacers between the screw heads and the upper blocks. Currently, advancement of Twin Block Appliances requires the time consuming addition of cold curing acrylic at the chairside, or alternative laboratory modification, whereby the patient can be without the appliance for some time.
The Screw Advancement System provides simple, quick, accurate and safe chairside progressive advancement, as well as improving the clinical flexibility of the appliance, and enhancing patient acceptance in cases where mandibular protrusion is limited initially. Laboratory Construction Procedure, Initially, the screw thread housings, which incorporate 12mm advancement screws, are positioned on the cast model through a wax dam, and aligned relative to the occlusal plane and midline, using the alignment rods.
Sold in a kit which includes: 2 alignment rods, 20 x 12mm advancement screws and housings and 1 advancement screwdriver.