Computer-Aided Design and Manufacturing Cutting and Drilling Guides with Prebent Titanium Plates Improve Surgical Accuracy of Skeletal Class III Malocclusion

Sir: We read with great interest the article by Li et al.1 on the treatment effect of the computer-aided design and manufacturing cutting and drilling guides with prebent titanium plates for the correction of skeletal class III malocclusion. We congratulate the authors on their comprehensive analysis and remarkable outcomes. However, we have concerns about the application of the prebent titanium plates. First, perhaps patients with adequate maxillary cortical bone thickness and density would benefit more from this new procedure. In the authors’ methodology, the titanium plates were fixed directly according to computer-aided design and manufacturing guides in surgery; in clinical practice, several relocations of the plates in the maxilla might be necessary. Individual variations in maxillary cortical bone thickness and density are determinative factors when choosing plate fixation sites. Adequate thickness is essential to the stability2; nevertheless, the torque generated by screws increases as the cortical thickness mounts up, potentially causing maxillary and screw fracture.3 In addition, adults always present higher values in cortical bone density than adolescents.2 In Le Fort I osteotomy, although apertura piriformis and zygomaticomaxillary processes have been recognized as standard fixation points, the variations as described could still lead to intraoperative complications. Cortical bone fracture during drilling, and the predrilled diameter or direction’s unsuitability for the actual screw insertion, is not rare, especially among novices. In our experience, relocation of the titanium plates is necessary under these circumstances to guarantee stability. In cases where the plates are bent preoperatively, we are worried about the repeated shaping of the plates leading to microfractures and rupture of the material. When confronted with this unexpected occurrence, new titanium plates are often needed, placing a financial burden on patients. Therefore, the new procedure might be advantageous to patients with sufficient maxillary cortical thickness and density, and it would be extremely enlightening to read how to manage unfavorable sequelae. Second, the unevenness of the maxilla could hinder the titanium plates from fitting to its surface perfectly. The maxillary cortical bone is rather thin in the incisor and tuberosity regions; however, its thickness rises sharply to reach a peak in the canine region.3 Such unevenness could interfere with the new surgical method because the plates’ positions had been planned during virtual surgery, posing a challenge to bend the titanium plates manually, especially the L-shaped ones. With the subsequent decreased contact areas between the bone and metal and screw loosening, we are concerned that the osseointegration may be affected in the healing process, resulting in deficiency in stability. Thus, we suppose that the location of virtual plate models should be individualized for the convenience of further bending and fixation. The authors have published extensively on the application of computer-aided design and manufacturing cutting and drilling guides with prebent titanium plates in various orthognathic operations. In this prospective study, they reported an impressive improvement in the surgical accuracy of class III malocclusion correction. We look forward to reading their future articles on this topic. DISCLOSURE Neither of the authors has a financial interest in any of the products or devices mentioned in this communication. Han Zeng, M.D.Xiaolei Jin, M.D.16th DepartmentPlastic Surgery HospitalChinese Academy of Medical SciencesPeking Union Medical CollegeBeijing, People’s Republic of China