bubble_chart Overview

Mandibular retrognathia is a malocclusion deformity characterized by a receding lower jaw, caused by underdevelopment of the mandible, congenital absence of lower front teeth, or dysfunction of the lateral pterygoid muscle.

bubble_chart Diagnosis

1. Mandibular retrusion, maxillary position is basically normal, anterior teeth show deep overbite, upper anterior teeth are significantly inclined, lower anterior teeth bite high on the cingulum or palatal mucosa of the upper anterior teeth, lower lip rests on the lingual surface of the upper anterior teeth, and the posterior occlusion relationship is distal occlusion.

2. Mandibular retrusion, anterior teeth show deep overbite. Upper anterior teeth bite lingually on the labial gingiva of the lower anterior teeth, lower anterior teeth bite on the palatal mucosa, and the posterior occlusion relationship is distal occlusion.

3. Mandibular retrusion, lower dental arch is smaller than the upper dental arch, the lower 1/3 facial height is shortened, and the mandible appears more retruded in the lateral view.

4. In cases of deep overbite of the upper anterior teeth, the upper anterior teeth are exposed outside the mouth, the lateral profile shows retruded mandible and chin, and the upper and lower jaws are extremely disproportionate.

﹝Auxiliary Examination﹞

Particular attention should be paid to the examination of cephalometric X-ray films for this condition.

bubble_chart Treatment Measures

1. Functional Mandibular Retrognathia Therapy: (1) Wear a maxillary removable appliance with a flat bite plate, while minimizing individual tooth interferences and performing lateral pterygoid muscle exercises. When the neutral occlusion habit is largely established, replace the flat bite plate with an inclined bite plate. After posterior teeth regain contact, continue wearing the inclined bite plate for retention.

2. For cases with maxillary arch constriction and mandibular retrognathia, use a removable appliance with a flat bite plate and expansion springs to widen the upper arch. After achieving occlusal balance, switch to an inclined bite plate to guide the mandible forward to its normal position. Alternatively, fixed appliances may be used.

3. For mandibular retrognathia with neutral posterior occlusion, push the lower anterior teeth labially to create space for prosthetic restoration.

4. Severe mandibular retrognathia may require orthognathic surgery combined with genioplasty.

5. For combined mandibular retrognathia and maxillary protrusion (exhibiting severe deep overbite), surgical orthodontics should be the primary treatment, supplemented by orthodontic therapy.

6. Surgical cases should follow preoperative/postoperative antibiotic protocols as prescribed.

Prevention

Mandibular retrognathia is relatively uncommon and often confused with maxillary protrusion. Clinically, it manifests as a short chin, reduced lower facial height (1/3), and a "bird-like" profile, significantly affecting aesthetics and mental health. Etiology includes mandibular hypoplasia, congenital absence of anterior teeth, or lateral pterygoid dysfunction. Treatment varies by age: orthodontics for growing patients versus orthognathic surgery for adults.

Treatment Outcomes

1. Cured: Normal overjet/overbite; SNA, SNB, facial angle, jaw protrusion angle, and ──SN angle all normal; aligned dentition; good masticatory function; harmonious profile.

2. Improved: Normal overjet/overbite; SNB and facial angle near normal; SNA, jaw protrusion angle, and ──SN angle normal; aligned dentition; adequate masticatory function; relatively harmonious profile.

3. Unresolved: No improvement in symptoms, masticatory function, or facial profile. {|111|}

bubble_chart Differentiation

1. The dental model of mandibular retrusion is similar to that of maxillary protrusion, with deep overjet of the anterior teeth often accompanied by deep overbite. The difference is that the maxillary position is normal, while the mandibular chin is retruded.

2. Cephalometric X-ray measurements show that the SNB angle and facial angle are smaller than the normal range. The ANB angle is larger than normal, while the SNA angle is normal.