Etiology of Malocclusions:

 Here is a summary of a very interesting article on malocclusions. https://www.researchgate.net/publication/281574669_Etiologia_das_mas_oclusoes_Causas_hereditarias_e_congenitas_adquiridas_gerais_locais_e_proximais_habitos_bucais

Etiology of Malocclusions:

It is fascinating to consider that living beings are in constant evolution, and humans are no exception. When we think about human evolution, it is evident that jaw atrophy is becoming more pronounced due to lifestyle changes, where it is no longer necessary to chew as rigid foods as in prehistoric times. This promotes a retrognathism of the jaws and also explains why some people are born without third molars. These evolutionary mutations often result in malocclusions, respiratory problems, and, currently, aesthetic concerns.

Due to the direct influence of evolution, hereditary factors are now the primary causes of malocclusions. In most cases, if a family member with malocclusion reproduces, the genetic predisposition to malocclusion is passed on. Even in the combination of parental genes, malocclusion in offspring can be favored. The most frequent anomalies include microdontia and macrodontia, followed by teeth with extra cusps, fused, and geminated teeth. These numerical anomalies are predominantly hereditary but can be associated with syndromes such as ectodermal dysplasia and cleidocranial dysostosis. These anomalies are most likely atavistic (characteristics of a distant ancestor) and genuinely evolutionary in humans.

It is interesting to note that in monozygotic twins, their dental arches are extremely similar, which may not be true for heterozygotic twins. Since monozygotic twins share the same DNA, while heterozygotic twins have a 50% genetic variation, this differentiation is possible.

Another aspect worth evaluating is the mixing of races. In areas with little or no racial mixing, "pure races" have fewer cases of malocclusions, whereas in regions with a high degree of racial mixing, there is a substantial increase in the number of patients with malocclusions.

Analyzing facial shape is often a predisposing factor for malocclusions. There are three types of facial shapes: brachyfacial (width predominates over height), dolichofacial (height predominates over width), and mesofacial, where the width and height are similar.

Skeletal factors can be classified using Angle's classification, which designates patients with a mandible that is more protrusive than the maxilla as Class III, and patients with a maxilla that is much more protrusive than the mandible, with a larger overjet, as Class II of Angle. Clinically, this can be observed and classified by the positioning of the upper and lower first molars in maximum habitual intercuspation.

Considering additional etiological factors for malocclusions, congenital factors can be evaluated, where malformations occur in the developing fetus, resulting in conditions such as cleft lip or palate. These congenital malformations (cleft lip and palate) can be classified into three groups, using the incisive foramen as a reference. Group 1: Pre-foramen clefts, which can be divided into right and left, complete or incomplete, bilateral, and median, all of which can be complete or incomplete. Group 2: Trans-foramen clefts, which can also be divided into unilateral or bilateral, right or left. Patients in group 2 always have malocclusion because the lip and palate are completely split in the middle. Group 3: Post-foramen clefts, where the palate is open only posterior to the incisive foramen. This group can be classified as partial or total, with partial being a cleft only in the soft palate or only in the hard palate, and total extending through both. Finally, Group 4 consists of the rarer clefts, such as transverse, oblique, and lower lip clefts. It is estimated that out of 650 newborns, 1 will have a cleft. There is a higher prevalence in female patients (59%) than in males (41%).

Another congenital factor is skeletal syndromes, such as cleidocranial dysostosis. This condition significantly affects the orofacial structure, including cementum hypoplasia, maxillary hypoplasia, and mandibular protrusion, in addition to a higher prevalence of supernumerary teeth and delayed eruption of permanent teeth.

We also have ectodermal dysplasia, a hereditary and congenital syndrome characterized by reduced activity of ectodermal tissues, resulting in deficiencies in hair, nails, teeth, face, and associated glands such as sweat glands, often causing hyperthermia. In the orofacial region, some characteristics may include agenesis (absence of all or partial teeth), reduced vertical dimension, a reduced middle third of the face, absence of alveolar bone, underdeveloped jaws, and prominent lips, giving a senile appearance to a child.

Continuing with hereditary and congenital syndromes, we have incontinentia pigmenti or Bloch-Sulzberger syndrome, which only affects female patients due to its transmission via the X chromosome. This condition is characterized by ocular anomalies, facial asymmetry, nasal dystrophy, scalp anomalies, and dental disorders such as agenesis and shape anomalies like conoid teeth, microteeth, or even dens invaginatus, along with enamel hypoplasia and fused or geminated teeth.

Lastly, within these syndromes, we have Rieger syndrome, characterized by maxillofacial anomalies such as maxillary dystrophy, mandibular protrusion, agenesis, microteeth, conoid teeth, talon cusps, and enamel hypoplasia.

Moving away from congenital causes, we have acquired postnatal malocclusions, which can be divided into three categories: general, local, and proximal. General causes include traumatic factors, endocrinopathies, systemic diseases, and nutritional factors. Acquired deformities that lead to malocclusion include general factors, local factors, and proximal factors. General factors include trauma, endocrine disease, systemic disease, and malnutrition, which can affect dental development. Local factors include premature loss of primary teeth, prolonged retention, dental abnormalities (such as hypoplasia and the presence of supernumerary teeth), ankylosis, and cysts. Proximal factors are related to harmful oral habits, such as prolonged thumb-sucking or pacifier use, which can lead to open bite and other dental deformities.