Micrognathia is a dental anomaly of a “skeletal” form, characterized by a decrease in the size of the upper or lower jaw. Patients may complain about unsatisfactory facial aesthetics. Diagnosis includes examination of the patient, a comprehensive orthodontic examination using radiation techniques (telerentgenography, computed tomography, orthopantomography), compilation of a photo protocol, removal of impressions of dentition with subsequent casting of plaster models. Treatment can be conservative (hardware) or surgical (bone-reconstructive orthognathic operations).
ICD 10
K07.0 Main anomalies of jaw sizes
Meaning
Micrognathia (Greek – “small jaw”) refers to skeletal abnormalities of the size of the jaw bones, expressed in the underdevelopment of one or both jaws. Pathology can be diagnosed in adults and children of various age groups and of any gender. The upper micrognathia is one of the most common forms of mesial bite (10.4%), the lower, or microgenia, is distal (36.5% ― in combination with the lower retrognathia, 7.9% – as an independent form). Correction of the anomaly should be started as early as possible, even in childhood, in order to form the correct bite and aesthetically harmonious facial features in the child.
Causes
Skeletal dentoalveolar anomalies, in contrast to dental alveolar ones (defects of individual teeth, the ratio of dentition, the shape and size of dental arches), are the result of an incorrect position of the jaws in the skull or a mismatch of their sizes with average indicators. Micrognathia can be congenital and acquired, according to which its causes are divided into prenatal and postnatal.
Prenatal factors affect the development of the dental system during the prenatal period. These include:
- the effect of teratogens (some drugs, chemicals, radiation);
- incorrect position or compression of the fetus in the womb;
- genetic mutations (Robin syndrome, in which extreme underdevelopment of the mandibular bone is combined with cleft palate).
Postnatal causes are those unfavorable conditions that affect the development of the jaws in childhood and throughout life. They include:
- artificial feeding;
- early removal of baby teeth;
- injuries (long-standing fracture of the mandibular condyle), including generic;
- pathological oral habits (prolonged sucking of the nipple, finger, lip, pencils);
- TMJ diseases (for example, rheumatoid arthritis);
- violation of bone formation due to rickets, dyspepsia, infectious and endocrine diseases.
Pathogenesis
If the fetal head in the womb is tightly pressed against the chest, or the hand is pressed against the face, this leads to compression and underdevelopment of the lower or upper jaw, respectively. Teeth stimulate the growth of jaw bones, so early removal of milk teeth and the absence of permanent teeth can slow down their development. Restriction of growth and asymmetry of the jaws can be observed with torticollis, when excessive unilateral contraction of the cervical muscles occurs.
Micrognathia developed after injury is caused by scars that prevent the normal progress of the upper or more often lower jaw bone, and growth can become asymmetric if there are more scars on one side. With improper sucking, artificial feeding, the period of active extension of the mandibular bone, which induces its growth, is reduced.
Symptoms
Patients may not make any complaints, but some of them are worried about the unsightly appearance. The upper micrognathia is manifested by the flattening of the area of the upper jaw with incisors and canines, and all the upper incisors tilt palatally, and the lower ones are ahead of the upper ones. The reverse incisor ratio is formed. Contact between the incisors is usually preserved, erasure pads are formed on the vestibular surface of the upper incisors.
Depending on the degree of reduction in the size of the upper jaw, a gap is sometimes observed between the upper and lower front teeth. The entire lower dental arch can be located in reverse overlap with the upper one (the lower teeth overlap the upper ones). Patients with micrognathia experience complexes due to a violation of facial aesthetics: the middle part of the face is flattened, the upper lip sinks, forming a significant step with the lower one in profile, sometimes the face is asymmetrical due to a combination of an anomaly with a displacement of the mandibular bone to the side.
A characteristic feature of the face with lower micrognathia is a sloping chin. Most have a decrease in the height of the lower part of the face due to the underdevelopment of the mandibular bone branch, its alveolar process in the lateral sections. The upper teeth overlap the lower ones, but there is a gap between the lower and upper incisors. Patients often complain of dental crowding and anomalies of the position of individual teeth. The lower micrognathia is sometimes combined with a deep bite.
Complications
Micrognathia can lead to a pathological bite (upper ― to mesial, lower ― to distal) and a violation of aesthetics, which is sometimes a powerful traumatic factor, especially if the patient is a teenager. The psyche of teenage children is extremely susceptible to various influences, in particular the trends of fashion and the cult of beauty. Psychological problems associated with a child’s complex and self-rejection can go from adolescence to adulthood, disrupt the process of social adaptation, prevent a person from realizing himself professionally and personally. A negative emotional background forms a state comparable to chronic stress.
Diagnostics
An orthodontist is responsible for determining the presence, nature and type of dental anomalies. He may suspect micrognathia already at the first clinical appointment, but a number of studies will be required to confirm the diagnosis in the future. They help to differentiate micrognathia from retrognathia of the corresponding jaw, as well as from macro- and prognathia of the opposite. Stages of diagnosis:
- Orthodontic consultation. The patient’s complaints are clarified, if necessary, a conversation is held with his parents to clarify the presence of bad habits in the child, dental anomalies in his parents, violations during pregnancy in the mother, etc. An examination of the face and oral cavity is performed. Sometimes diagnostic tests are used (a test with the extension of the mandibular bone forward, etc.).
- Photometry. Photographing of the patient’s dentition, his face in full face, in profile, with a smile and without. The photoprotocol evaluates the symmetry of the face, the location of the midline, and reveals violations. Sometimes computer programs are used that simulate the result of treatment.
- Production and calculation of models. Dental impressions are taken, plaster models are cast, calculations are carried out for treatment planning. Recently, an intraoral scanner has become popular, which allows you to dispense with impressions and plaster models by projecting a 3D image of the dentition onto a computer screen.
- X-ray examination. TRG is performed with subsequent analysis of radiographs. Attention is drawn to the state of bone tissue, teeth, the location of various anatomical formations. In some cases, an X-ray of the hands is examined to determine the growth period.
Treatment
The question of the need for correction of micrognathia is considered based on the wishes of the patient and his physical, psychological well-being. Crucial in choosing tactics (conservative and surgical) is the age of the patient, more precisely, the growth activity.
Conservative therapy
Conservative correction of micrognathia with growth modification is effective if carried out during the period of active development. It is best to start treatment at the peak of growth, which can be approximately determined by the TRG in the lateral projection or radiograph of the hands. There are many orthodontic devices for stimulating the growth of an underdeveloped jaw:
- Face mask. Induces stretching in the area of bone sutures through the zone of the upper first permanent molars, stimulating the development of the upper jaw. The device must be worn for at least 8 hours during the day. The patient can independently remove the facial mask, while the specific time of its use is set by the doctor, based on the individual parameters of the TRG.
- The Frenkel apparatus. Upper micrognathia is considered an indication for treatment with a type III Frenkel function regulator. Under the influence of this removable construction, the pressure of soft tissues (lips and cheeks) on the alveolar process of the upper jaw is eliminated, which promotes bone growth. A properly designed Frenkel apparatus has an irritating effect on the periosteum and stimulates bone growth.
- The Herbst apparatus. The design is located in the oral cavity around the clock without the possibility of self-removal by the patient, pushes the lower jaw forward, causing tension in the cartilage of the condyle processes and stimulating the development of the mandibular bone. The device promotes distal displacement of the upper dentition even after the end of growth, improving the eruption of the lower wisdom teeth.
Surgical treatment
In modern orthodontics, it is used, as a rule, not earlier than 18 years, when correction with the help of growth modification is no longer effective. Orthognathic bone reconstructive surgery is performed − osteotomy of an underdeveloped jaw with its displacement. In children, the classic ways to eliminate lower micrognathia are different methods of bone grafting using autogenic and allogeneic grafts, titanium or ceramic implants. Compression-distraction osteosynthesis is also possible in childhood.
Experimental treatment
A new protocol of orthognathic operations has been developed, which increases the effectiveness of double-jaw surgical interventions in skeletal forms of dental anomalies. It is based on some changes during the operation: the interdigital ligature binding is performed only once, the surgical template is not made, certain reference points are used to place the jaws in a new position.
All this allows you to accurately and simultaneously move the bicuspid complex to the planned position. Thus, high accuracy, stability of the result of the operation, reduction of its traumatism and time of carrying out are achieved.
Prognosis and prevention
In general, micrognathia does not lead to any fatal consequences in the human body, so its prognosis can be considered favorable. However, it is better to start prevention of the anomaly in the prenatal period: it is necessary to avoid exposure to exogenous and endogenous teratogenic factors, especially in the first trimester of pregnancy, when the organs of the maxillofacial region of the fetus are laid. A pregnant woman should refrain from smoking, taking alcohol, and medications.
After the birth of a child, timely treatment of diseases (TMJ pathology, muscle dysfunction, caries) should be carried out. It is necessary to teach the child oral hygiene, to prevent injuries and premature tooth extraction. In case of injury to the mandibular condyle, active conservative therapy should be carried out (to prevent scarring) and early mobilization of the jaw bone.
Literature
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