Endogenous causes of dentofacial anomalies
The development of the dentofacial system largely depends on internal, nature-driven mechanisms of the organism. Two groups of factors play a key role:
- Genetic. The combination of parental genes determines potential disproportions in the sizes of the jaw bones and the teeth themselves. Congenital pathologies include various dysostoses, cleft lip, alveolar ridge and palate, as well as specific conditions (e.g., Robin sequence or anhidrotic ectodermal dysplasia).
- Endocrine. Hormonal background directly affects tooth eruption timing and facial skeleton growth.
| Gland pathology | Effect on the maxillofacial region |
|---|---|
| Hypothyroidism | Delayed eruption of deciduous and permanent teeth, microgenia |
| Hyperthyroidism | Early eruption, inhibition of sagittal jaw growth |
| Cerebrohypophyseal dwarfism | Delayed eruption, underdevelopment of the entire facial skeleton |
| Adrenal dysfunction | Accelerated growth of jaw bones with spacing (tremas) |
Exogenous developmental factors (prenatal and 1st year of life)
External influences can disrupt bite formation both prenatally and during the child's growth.
Prenatal period Organogenesis can be disrupted due to mechanical influences (amniotic fluid pressure, maternal trauma, abnormal fetal presentation), chemical toxins (smoking, alcoholism, occupational hazards), biological agents (past syphilis, rubella, mumps), radiation, and severe psychological stress in the first trimester of pregnancy.
Postnatal period (first year of life) Proper feeding is critical during this period. Artificial feeding using an overly long and rigid nipple traumatizes the mucosa and disrupts tongue function. A soft nipple with a large opening causes muscle hypotonia and reinforces infant retrognathia, while pressure from the bottleneck deforms the alveolar ridge.
Birth injuries contribute to severe consequences (e.g., forceful extraction of the fetus by the lower jaw damages the growth zones of the condylar process), alongside hematogenous osteomyelitis and rickets. With vitamin D deficiency, the bones of the facial skeleton are poorly mineralized, leading to the formation of a V-shaped or saddle-shaped upper jaw, as well as a deep or open bite (due to the displacement of the mandibular angle).
Exogenous developmental factors (ages 2 to 13)
As the child grows older, the spectrum of factors threatening a normal bite changes.
Ages 2–3: The main enemies become bad habits (thumb, tongue, or pacifier sucking), tonsillar hypertrophy (forming a distal bite and increasing palatal height), and eating exclusively soft food that provides no stimulus for bone growth. Sleeping posture is of immense importance: a hand under the cheek distorts the jaws, a chin pressed against the chest leads to excessive overlapping of the upper teeth by the lower ones, and a tilted-back head inhibits lower jaw growth. A shortened lingual frenulum also hinders lower jaw development.
Ages 3–6: Functional disorders come to the foreground. With incorrect swallowing, the tongue presses against the lips (the "thimble sign" occurs), whereas normally the teeth should be clenched and the tongue should press against the anterior part of the hard palate. The absence of physiological abrasion of deciduous teeth enamel delays the mesial shift of the lower jaw. Unilateral chewing destroys the temporomandibular joint (TMJ).
Ages 7–13: In schoolchildren, dentofacial anomalies are provoked by caries complications, disrupted tooth replacement timing, macroglossia, and poor posture. Interestingly, even playing musical instruments affects the bite: wind instruments lead to an open bite, while the violin leads to a crossbite.
Physiological bite and its stages
Bite (occlusion) is the closure of dental arches in a static and habitual position of the lower jaw. In a normal (physiological) bite, the habitual position of the jaw coincides with the central position, the head of the articular process is located at the base of the articular tubercle slope, and the masticatory muscles contract evenly on both sides.
Bite formation goes through several stages that have their own markers of norm:
- Deciduous bite. The masticatory (distal) surfaces of the second deciduous molars are located strictly in one vertical plane. The anterior teeth of the upper jaw tightly overlap the lower antagonists. There are normally no spaces (tremas) between the anterior teeth.
- Mixed dentition. Characterized by the appearance of a mesial step in the area of the second molars. The incisors are set in a direct occlusion. An obligatory sign of this stage is the presence of physiological tremas and diastemas, which prepare space for larger permanent teeth.
Briefly: answers to topical questions
What are the sequential periods of human bite formation from birth to the end of jaw growth?
The available materials describe only the distinguishing features of deciduous and mixed bites.
- Deciduous bite — the distal surfaces of the second molars are located strictly in one vertical plane, the incisors and canines of the upper jaw overlap the lower ones forming tight contact, with no tremas in the anterior region.
- Mixed dentition — the distal surfaces of the second molars form a mesial step, the incisors of the upper and lower jaw are in direct occlusion, and the presence of physiological tremas and diastemas is characteristic.
What bad habits contribute to the development of dentofacial anomalies in childhood?
The following bad habits lead to the development of dentofacial anomalies in childhood:
- Sucking — fingers, pacifiers, various objects, and the tongue.
- Incorrect sleeping posture — placing a hand under the cheek (causes jaw distortion), pressing the chin to the chest (lower teeth overlap the upper), or throwing the head back (leads to delayed lower jaw development).
Consuming soft food also has a negative impact, leading to jaw underdevelopment and crowding of permanent teeth.
What are the main classifications of dentofacial anomalies in orthodontics?
The following main classifications of dentofacial anomalies are used in orthodontics:
- MSMSU classification of tooth and jaw anomalies — includes anomalies of teeth (shape, hard tissue structure, color, size, such as macrodentia and microdentia), as well as disorders of the mutual arrangement of jaw parts and the position of the jaw bones.
- L.S. Persin's classification — describes bite anomalies in the lateral segment in the sagittal direction.
Additionally, combined anomalies in two and three directions are distinguished.
To memorize the impact of musical instruments on the bite, associate them with the musician's posture: the violin is pressed from the side (jaw shift left/right — crossbite), while wind instruments are blown straight, opening the front teeth with the mouthpiece (open bite).
Class and exam questions
How does improper sleeping posture affect the jaws?
Sleeping with a hand tucked under the cheek causes jaw deformation. If the chin is constantly pressed against the chest, the lower teeth begin to overlap the upper ones, while the head thrown back leads to retarded growth of the mandible.
What is the "thimble sign"?
This is a pathological tension of the tissues around the mouth at the moment of swallowing. It occurs when the tongue assumes an interdental position and forcefully presses against the inner surface of the lips instead of the hard palate.
Why are spaces between teeth necessary in mixed dentition?
Tremas and diastemas during the tooth replacement period are normal. They are necessary to create additional space in the dental arch, as permanent teeth are wider and larger than temporary (deciduous) ones.
What else to study on this topic
- Mechanisms of infant retrognathia development during artificial feeding.
- The connection between hypertrophy of the palatine and pharyngeal tonsils and the formation of a high palate.
- Temporomandibular joint (TMJ) pathology in habitual unilateral chewing.
- Specific jaw deformations in rickets (V-shaped and saddle-shaped forms).
- Symptoms and orthodontic consequences of the Robin sequence.
Master the entire topic in the «Propaedeutics of Dentistry» course
This is a summary. The course covers everything tested in classes and exams.
- Full study guide on "Introduction to Orthodontics" and 868 more subject pages
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 65 video lessons on the subject
Other topics in "Chapter 11. Introduction to Orthodontics"
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.