When patient compliance is a concern, the Twin Block can be delivered as a fixed appliance. The simplest design involves merely bonding the Twin Block Incline components directly to the posterior dentition. The teeth to be bonded must be secure. If the blocks are placed on primary molars, it is important that they are expected to be stable for at least 9 months. This technique is used primarily when only mandibular advancement is needed. It is difficult to adjust the blocks intraorally to accomplish vertical changes. The molars are banded and “C” clasps are placed on the first bicuspids -- making the appliance easy to seat (by eliminating any path-of-insertion problems), while adding the option of increasing retention (by bonding the “C” clasps to the bicuspids). Since the Twin Block portions are not bonded to the occlusal surfaces, appliance removal after treatment is easy. Again, this fixed design is best used to accomplish mandibular advancement when the patient has adequate vertical dimension. Molar bands and occlusal acrylic prohibit vertical eruption to correct deep bites.