What Is Mandibular Prognathism?

The mandibular protrusion (prognathism or mandibular protrusion), when the teeth are occluded normally, the upper anterior teeth always cover the lower anterior teeth. If the opposite occurs, that is, the lower anterior teeth carry the upper anterior teeth, this is what people call "ground bag", which is medically called the mandibular anterior process and anterior deformity.

Mandibular protrusion

Overview of mandibular protrusion

Causes of the disease:

Bad oral habits

Poor breastfeeding posture, such as improper feeding from a bottle, the jaw needs to be sucked forward hard, which can cause anterior teeth recombination.

Bad habit of biting upper lip or mandibular extension can lead to anterior teeth recombination and mandibular protrusion.

2. Local disorders during tooth replacement

Retaining or premature loss of deciduous teeth can cause individual anterior teeth or most anterior teeth.

Premature deciduous molars are lost early, and the anterior teeth of Shangheng are moved backward, which can form anterior teeth recombination.

(3) Insufficient wear of the deciduous canine, which is higher than the plane of the occlusal arch. In order to avoid the possible early contact of the upper and lower jaw deciduous teeth, the lower jaw will move forward or laterally, with anterior or anterior cross-reflection Pseudomandibular protrusion.

Congenital absence of the maxillary permanent incisors, such as the common absence of maxillary lateral incisors, can cause underdevelopment of the anterior maxilla and form anterior teeth.

3. Disease

Chronic inflammation of the palatine tonsil or lingual tonsil stimulates mandibular extension, which over time can cause anterior teeth to merge with mandibular protrusion.

Patients with palatal cleft lip and palate often suffer from underdevelopment of the upper jaw, which is likely to cause anterior teeth resection and mesial misalignment, and the lower jaw is relatively protruded.

(3) In patients with rickets, calcium and phosphorus metabolism disorders and abnormal dynamics of the facial and maxillary muscles can often lead to more severe mandibular protrusions or anterior teeth opening and closing deformities.

Endocrine disorders, such as hyperfunction of the anterior pituitary gland, can cause deformities of the mandibular protrusion.

4. Hereditary anterior teeth with mandibular anterior penetrating process, with obvious family background, and abnormal mandibular and facial deformities are significant.

Clinical manifestations of mandibular protrusion

1. Dermatogenic: Mostly due to local obstacles during tooth eruption or replacement, often manifested as simple anterior tooth recombination. The anti-coverage is smaller and the molar relationship is neutral or near neutral. The shape and size of the lower jaw were basically normal, the relationship between the upper and lower jaw bones was not abnormal, the crotch was not protruded, and the face was basically normal. The lower jaw can retreat to the front-to-edge relationship. X-ray head shadow measurement showed no morphological abnormalities in bones, easy correction and good prognosis.

2. Bone-derived: mostly due to genetic and disease factors, in addition to anterior teeth recombination often shows a large anti-coverage. Molars are mesial and misaligned with jaw deformities. It can be manifested as blunt mandibular angle, long mandibular body, short mandibular branch or underdevelopment of the upper jaw. The crotch is prominently protuberant, and the lower jaw often cannot retreat by itself. The face is mostly concave, sometimes accompanied by jaw deformity. Its orthodontic treatment is difficult, and the effect of orthodontic treatment is not necessarily good. Divided into 3 types according to mechanism:

Anterior maxillary is underdeveloped and mandible is normal.

The maxillary development is normal, and the mandible is overdeveloped.

(3) Underdevelopment of the upper jaw is accompanied by overdevelopment of the lower jaw.

3. Functionality: The mandibular function is caused by excessive forward extension of the mandible due to poor breastfeeding posture, etc., but the mandibular protrusion and anterior teeth are recombined, but the shape and size of the mandible are basically normal. Relationship, some people call it pseudomandibular protrusion. If it is not corrected early, it may develop into a true mandibular protrusion.

4. Complications: It can cause psychological and mental disorders for patients. If it affects chewing function, it can cause indigestion and gastrointestinal diseases.

Medical examination of mandibular protrusion

X-ray head shadow measurement.

1. The increase of SNB angle and face angle indicates that the mandibular angle is increased relative to the anterior process of the skull base. The above measurements were normal for those with odontogenic anterior teeth.

2. Mandibular anterior process with maxillary retraction, the SNB angle decreases S-Ptm, Ptm-6 decreases. The above measurements were normal in those without maxillary retraction.

3. The ANB angle and AB plane angle increase, and the AO-BO value decreases, indicating that the relationship between the upper and lower jaw is obviously not adjusted. The above measurements of those with anterior tooth anterior teeth recombination are basically normal.

4. Increasing the facial protrusion angle (G-Sn-Pg '), decreasing the H angle (H line -N'P'g) and increasing the Z angle (FH-H line) indicate that the lateral protrusion of the soft tissue is reduced. The upper lip protrusion (Ls-SnPg ') is reduced or normal. Lower lip protrusion (Li-SnPg ') increased. Maxillary process distance (Sn-G) decreased or normal, and mandibular process distance (Pg'-G) line increased.

Diagnosis of mandibular protrusion

There are malformations of the jaw, long mandible body, sometimes short mandibular branches, blunt mandibular angles, prominent sacral protuberances, underdeveloped or normal anterior maxillae, most of them are concave. Most of the upper anterior teeth are located on the lingual side of the lower anterior teeth, often showing reverse coverage and repeated occlusion, which deepen with age, and the molars are mesial and occlusal. The lower jaw cannot retreat by itself. May be accompanied by crowded dentition or occlusion. X-ray head shadow measurement showed that the SNA angle was smaller than normal, and the SNB and SND angles were larger than the normal range; or the SNB angle was larger than normal and the SNA angle was normal. The jaw convexity is negative and the face angle is greater than normal.

Mandibular protrusion process principle

1. Headgear and traction loop correction device. Suitable for patients with early skeletal anterior teeth and mandibular protrusion. Can be used in the late stage of the deciduous teeth, the replacement period or the initial period of permanent teeth. It can be used in conjunction with intraoral appliances, such as cushioned reed appliances.

2. Forward traction correction device. It is suitable for the combination of early skeletal anterior teeth combined with underdevelopment of the upper jaw and mandibular protrusion. It can be used in the replacement period or the permanent period.

3. Functional orthotics, such as activator or Frankel III. It is suitable for early skeletal anterior teeth and functional anterior teeth. It can be used in the replacement period, especially in the late period.

4. Class III traction correction device. It is mainly used to adjust the relationship between the near-middle jaw. It is often used in early anterior skeletal anterior teeth. It can be used in the late stage of the tooth replacement or the early stage of the permanent tooth. The intraoral correction device can be a removable maxillary plane or a occlusal appliance, or a fixed appliance, or a combination of both.

5. Removable maxillary occlusal reed corrector can be used for any correction of anterior teeth retraction, can be used alone, or combined with other orthopedic devices such as lap pockets and orthotics such as holders. Specific devices and applications.

6. Fixed orthosis, including edgewise square wire orthosis and Begg orthosis, can be used to correct anterior teeth resection, often used in the replacement period or permanent period. When using a Begg appliance, a type III pull-in should be performed instead of a type II traction. The traction force is about 80g.

7. Adult anterior teeth correction, if it is tooth-derived anterior teeth or mild bony anterior teeth, you can use the above-mentioned correction device with non-orthopedic force for correction. If the anterior teeth are combined with obvious skeletal deformities, a combination of orthodontics and surgical orthodontics is required.

8. Cure standard: Through intermaxillary traction or surgical treatment, normal anterior occlusion and normal occlusion of posterior teeth can be achieved. Facial appearance is normal. X-ray head shadow measurements are all within the normal range.

9. Criteria for improvement: The appearance of the face has improved, the anterior occlusion has been lifted, the dentition is aligned, and the X-ray head shadow measurement value is close to normal.

Mandibular protrusion

1. During breastfeeding, correct the poor breastfeeding posture and avoid excessive forward extension of the baby's jaw.

2. To maintain the space of premature loss of deciduous teeth, it is particularly important to try to maintain the space of premature loss of upper molars. Removal of lingering teeth, especially early lingering lower molars.

3. Those who are caused by chronic inflammation of the tonsil should treat the tonsil disease in time.

4. Anterior teeth recombination caused by insufficient wear of the deciduous canine can reduce the lower jaw by adjusting excessive interference.

5. Those who are caused by bad oral habits should get rid of bad habits early. ^[1]