Thank you for the interest shown in our case report and giving us some comments on the rationale of the Twin-block incline.

The appliance that we developed was named the sagittal-guidance Twin-block appliance because of the bite blocks between the upper and lower jaws. However, the mechanism of treatment might be quite different from the classic Twin-block appliance. The fact that we use it as a functional appliance, not just a postural one, could be the most controversial opinion between us. We use a 70° incline on the blocks to maintain the mandible in a forward position even when open in the rest position. Also, we recommend that all patients should wear this appliance 24 hours a day for 12 months. It not only stimulates the forward posturing adaptation of the masticatory system at rest as well as in function, but also stimulates the growth of mandible and the adaptative remodeling of the fossa and condyle. Through 3-dimensional cephalometric superimposition, we found significant length increments in the mandible but did not observe the distraction of the mandibular condyle from the glenoid fossa. In the maxilla, the superior-posterior force on the bonded appliance could result in the distalization of the whole maxillary posterior dentition and a certain degree of inhibition of the maxilla. After removal of the appliance, a 2-3 mm space between the maxillary canines and first premolars was usually observed. The relief of crowding was a common phenomenon, although no treatment was carried out on the maxillary anterior teeth.

We have treated more than 300 Class II Division 1 and Division 2 patients with this appliance, and almost all of them had good treatment outcomes as well as long-term stability. We will publish the 2- and 3-dimensional cephalometric analyses and superimposition results soon.