1.What are the two types of anterior-posterior underdevelopment of the mandible? 1.Low (mandibular plane) angle deformity; 2.High (mandibular plane) angle deformity, both of which have unique facial appearance and occlusal performance, but both types are characterized by short jaw. 2.What are the characteristics of anterior-posterior underdevelopment of the mandible? The clinical features of mandibular hypogonadism include a small jaw, short facial height, lower lip ectropion and deepening of the chin-labial fold. The mandibular angle and occlusal muscles are usually well developed and their morphology is good, but the maxilla is vertically underdeveloped. The occlusion shows a marked increase in the curvature of the Spee curve of the upper and lower dental arches. The mandibular anterior teeth may bite into the palatal mucosa and have severe deep overjet. Imaging-wise, the height of the mandibular ascending branch is generally near normal, while its cephalometric (correlated with the mandibular ascending branch) angular measurements and linear measurements are usually small. High angle mandibular deformities are usually characterized by normal or excessive facial height, short chin with recession, shallow chin-labial folds, and strong chin muscles. The mandibular ascending branch is usually short, the condyle is small, and the mandibular angle is blunt and underdeveloped. The occlusion is characterized by an anteriorly inclined and narrowed maxillary dentition and a contracted and narrowed mandibular arch, which exhibits a Class II cuspid and molar relationship. This type of malocclusion may also present with open jaw, meaning that there may also be the following conditions: rheumatoid temporomandibular arthritis, TMJ ankylosis, and condylar resorption. If a high-angle malocclusion type has anterior-posterior underdevelopment of the lower jaw with concomitant vertical overdevelopment of the upper jaw, it will exhibit all the characteristics of vertical overdevelopment of the upper jaw and the symptoms associated with underdevelopment of the lower jaw will be aggravated. 3.How to treat mandibular hypoplasia? For isolated mandibular hypoplasia, the treatment approach is usually based on anterior mandibular migration. Bilateral mandibular ascending sagittal split osteotomy (BSSRO) and solid internal fixation are the most common surgical methods to achieve anterior migration of the mandible. When the anterior migration distance is greater than 25px, an inverted “L” sagittal osteotomy of the ascending mandible with bone grafting and strong internal fixation between the osteotomized segments is recommended. In general, the smaller the anterior migration distance, the better the stability of the mandible after anterior migration. Chinplasty (including surgery with allograft material graft and osteotomy for anterior migration) can be performed at the same time as BSSRO or separately for correction of severe chin hypoplasia. Similarly, subapical mandibular osteotomy is also useful for improving the morphology of the mandibular arch. 4.What are the characteristics of mandibular protrusion? Premaxillary mandibular deformity alone is a relatively rare clinical condition, and premaxillary is often accompanied by maxillary hypoplasia. When both problems are present, the cosmetic manifestation of mandibular protrusion appears more pronounced. Overbite in the vertical direction and instability of the median relationship – median bite may coexist and aggravate the symptomatic manifestation of mandibular protrusion. In these patients, the chin and lower lip are significantly more anteriorly positioned in relation to the upper lip, forming the main facial feature. The mandibular body and mandibular angle are well defined, and the mandibular angle is usually obtuse. The occlusal relationship usually shows a Class III relationship, because thanks to the occlusal compensation of the teeth, its occlusal deformity is often less severe than the bony deformity. This occlusal compensation is often manifested by the lip-tilted spread of the maxillary anterior teeth and the upright inversion of the mandibular anterior teeth. 5.How to treat mandibular protrusion deformity? The correction process of mandibular protrusion deformity often takes the form of sagittal splitting osteotomy with internal fixation (mandibular ascending branch). Some surgeons also advocate vertical osteotomy of the ascending branch through the mouth, especially when there is a large distance of posterior movement and when there is a need for asymmetric recession on both sides. However, this procedure has been found to be clinically problematic in terms of uncontrolled movement of the proximal middle bone segment and recurrent postoperative occlusal changes. However, regardless of the procedure performed, adequate preoperative orthodontics needs to be ensured to remove occlusal substitution and, more importantly, to ensure that mandibular development has been completed. 6. What are the clinical and imaging features of condylar hypertrophy? Condylar hypertrophy (hemilateral mandibular elongation) is a typical acquired, progressive asymmetrical jaw deformity. Its clinical features include facial asymmetry (affecting the lower third of the face), deviation of the mandible to the healthy side, and secondary compensatory overgrowth of the maxilla vertically on the affected side; the patient’s mandibular midline is deviated to the healthy side, accompanied by an asymmetric occlusal relationship between the cuspids and molars on both sides, and a lateral retrusion. On the affected side, the cuspid and molar relationship usually shows a Class III sympathetic relationship. Sometimes it is also accompanied by symptoms of mandibular protrusion or maxillary hypoplasia. The imaging features of condylar hypertrophy include elongation of the condylar neck on the affected side, but the morphology of the condylar head is not necessarily accompanied by abnormalities, depending on the growth rate (of the condylar head) at the time of disease onset. Cephalometric lateral views usually show asymmetry of the mandibular ascending branches and mandibular angles on both sides, with varying degrees of dental substitution. Similarly, posterior anterior cephalometric films usually demonstrate mandibular deviation with varying degrees of dental compensation and enlargement of the mandibular ascending branches and condyles on the affected side. 7. What is the treatment for mandibular condylar hypertrophy? An important component of treatment for condylar hypertrophy is to confirm the condition of the condylar growth before implementing interventions, which can be accomplished by taking a detailed history of the patient’s jaw deviation. Significant recent facial changes may suggest active condylar growth, whereas a longer history of mandibular deviation with no significant long-term change in asymmetry may indicate inactive condylar growth. Isotope bone scan studies may be useful in determining the degree of active condylar growth, although there is also the possibility of false positives. Once the growth status of the condyle is determined, the planning and timing of treatment can be decided. If the condylar growth is active, condylectomy can be performed immediately or postponed until condylar growth has ceased. When the condylectomy is completed, reconstruction of the mandibular ascending branch is performed. Correction of facial deviation and malocclusion by osteotomy of the upper and lower jaws, with or without condylectomy, is usually part of the treatment of condylar hypertrophy. 8.What is hemilateral mandibular hypertrophy? Hemilateral mandibular hypertrophy, like condylar hypertrophy, causes asymmetrical facial deviation, but in contrast, hemimandibular hypertrophy usually occurs and develops earlier, in some cases starting in childhood. In this case, there may be secondary changes in the upper jaw, with the occlusal plane tilted downward on the affected side. Due to the varying degrees of occlusal compensation, patients may experience occlusal malocclusion and a deviation of the mandibular midline (which may or may not occur). The healthy lateral mesial component is often shorter, so it is often difficult to define the condition exactly. The main distinguishing feature of this type of disease is the enlargement of all the tissue on the affected side, both bone and soft tissue. The imaging feature of hemimaxillary hypertrophy is the overall enlargement of all parts of the affected mandible, including the condyle, the ascending mandible, the mandibular body, and possibly even the teeth. Hemilateral mandibular enlargement may stop at the midline of the face, but it may also cross the midline and gradually diminish, stopping abruptly at the lower edge of the mandible. The inferior alveolar neurovascular bundle often appears displaced closer to the lower mandibular margin. 9. What is the treatment for mandibular hemimandibular hypertrophy? Just as in the treatment of condylar hypertrophy, a detailed history of abnormal growth of their mandible should be taken, and an isotope bone scan can help determine the degree of active bone growth and serve as an important basis for treatment plan selection. Surgical treatment options include a combined maxillary and mandibular osteotomy to lengthen the shorter side of the face and shorten the longer side of the face, as well as a partial osteotomy of the lower mandibular margin on the affected side, and a healthy side bone graft to make the lower mandibular margin more symmetrical bilaterally. If the condyle is actively growing, condylectomy and mandibular ascending reconstruction can also be performed. 10.What are the clinical features of vertical maxillary hypoplasia (VME)? Vertical maxillary hypoplasia is characterized by open lips, excessive gingival exposure when smiling, and incomplete closure of the upper and lower lips. Open front teeth are common, especially when there is a step in the maxillary occlusal plane. Patients often present with a long facial shape and a chin that is rotated toward the lower back. This is especially noticeable when the patient has a short upper lip or a receding maxilla. Patients with maxillary vertical hypertelorism may have both Class I, II, and III sympathetic relationships. 11.What is the treatment for maxillary vertical hypoplasia? Vertical maxillary hypoplasia can be treated early in development (8-12 years old) by orthodontic intervention through the use of cephalic high traction or an open bionater occlusal appliance to limit vertical maxillary development. If the intervention is effective, this type of treatment can correct bony developmental deformities while the growth of soft and other facial tissues is limited accordingly. In adults, the maxilla can usually only be reset by maxillary LeFort I osteotomy. 12. Are there any other special factors that need to be considered during the treatment of vertical maxillary hypoplasia? Yes. Because the vertical growth of the maxilla is the longest lasting of all directions of maxillary growth, it may continue to grow longer than one would expect. If significant vertical maxillary growth is also present, it may lead to recurrence after corrective surgery. Therefore, surgical correction of such deformities is recommended to be postponed until jaw growth has slowed or ceased. However, if the maxillary vertical overgrowth is very severe, then early surgical intervention should still be performed, as this will benefit the patient’s psychological well-being. 13. What is the etiology of posterior maxillary vertical hypoplasia: When the contralateral mandibular posterior teeth are extracted, the maxillary posterior teeth elongate resulting in Posterior maxillary vertical hypoplasia may also be due to overall vertical hypoplasia of the maxilla, often accompanied by anterior open bite. 14. What are the clinical and imaging features of posterior maxillary vertical hypoplasia? The maxillary occlusal plane often appears to be significantly stepped. If the posterior maxillary hypoplasia is caused by excessive eruption of the posterior teeth, it is often accompanied by a lack of intermaxillary distance, which can make restorative treatment difficult. Facial changes in these patients may not be obvious because the maxillary elongated teeth will stop continuing to erupt when they contact the mandibular alveolar ridge. When posterior vertical overgrowth of the maxilla occurs during the edentulous phase, it can cause the mandible to rotate posteriorly and inferiorly, which can result in a secondary increase in facial height and incomplete closure of the upper lip. The labiodental relationship of the maxillary teeth may still appear normal, but excessive gingival exposure of the posterior region is seen when the mouth is widely opened. Imaging features include an excessive distance from the palatal plane to the cusps of the first molars. In some patients with edentulous dentition, an overly enlarged maxillary sinus is seen. 15.How to treat posterior maxillary vertical hypoplasia? Treatment of vertical overgrowth of the posterior maxillary component consists of segmental osteotomy of the jaw (making osteotomy lines between the teeth) and fixation of the posterior maxillary component by elevation. If there is not enough space between the teeth, orthodontic assistance is required to move the teeth or remove the blocking teeth to avoid damage to the adjacent teeth. In patients with partial edentulism, the occlusion of the anterior region should not be altered when the posterior maxillary osteotomy is performed. In patients with dentition, the posterior maxillary osteotomy may improve the open bite after fixation, thus reducing the facial height, improving the upper lip closure, improving the mandibular inclination, and improving the chin protrusion.