The Twin Block is a two-piece removable appliance that utilizes acrylic blocks formed in conjunction to position the mandible forward and improve forward growth of the lower jaw. The upper and lower pieces of the removable orthodontic appliances fit similarly like retainers but with posterior bite blocks that interlock at 70° angle to advance the mandible and help correct a Class II malocclusion. They achieve rapid functional correction of malocclusion by the transmission of favourable occlusal forces to occlusal inclined planes that cover the posterior teeth. The Twin Block appliance may be designed with a variety of components such as springs and clasps.