Females are affected more than males, and the condition occurs in permanent (adult) teeth more than deciduous (baby teeth or milk teeth).

The cause of isolated missing teeth remains unclear, but the condition is believed to be associated with genetic or environmental factors during dental development. Missing teeth have been reported in association with increased maternal age, low birth weight, multiple births and rubella virus infection during embryonic life.

There is a possible correlation between tooth agenesis and innervation. A relationship was also postulated between abnormalities of the brainstem and the presence of agenesis.

Hypodontia is often familial, and can also be associated with genetic disorders such as ectodermal dysplasia or Down syndrome. Hypodontia can also be seen in people with cleft lip and palate.

Among the possible causes are mentioned genetic, hormonal, environmental and infectious.

Cause due to hormonal defects: idiopathic hypoparathyroidism and pseudohypoparathyroidism. Exists the possibility that this defect depends on a moniliasis (candidiasis, "candida endocrinopathy syndrome").

Environmental causes involving exposure to PCBs (ex.dioxin), radiation, anticancer chemotherapeutic agents, allergy and toxic epidermal necrolysis after drug.

Infectious causes of hypodontia: rubella, candida.

The Journal of the American Dental Association published preliminary data suggesting a statistical association between hypodontia of the permanent teeth and epithelial ovarian cancer (EOC). The study shows that women with EOC are 8.1 times more likely to have hypodontia than are women without EOC. The suggestion therefore is that hypodontia can serve as a "marker" for potential risk of EOC in women.

Also the increased frequency of hypodontia in twins and low birth weight in twins with hypodontia suggests that environmental factors during perinatal are responsible hypodontia.

There are many potential factors involved.

- Congenital hypopituitarism

- Ectodermal dysplasia

- Down syndrome

- Ionizing radiation to the jaws during tooth development (odontogenesis)

- Chemotherapy during tooth development

- Marshall syndrome

- Rieger syndrome

- Focal dermal hypoplasia

- Silver-Russell syndrome

- Williams syndrome

- Gorlin-Chaudhry-Moss syndrome

- Coffin–Siris syndrome

- Salamon syndrome

- Cleft lip and palate

Others include trichorhinopharyngeal, odontotrichomelic, neuroectodermal and dermo-odontodysplasia syndromes.

The cause of talon cusp is unknown. The anomaly can occur due to genetic and environmental factors but the onset can be spontaneous. Prevention is difficult because the occurrence happens during the development of teeth.

Talon cusp affects men and women equally, however the majority of reported cases are of the male gender. Individuals of Asian, Arabic, Native American and Inuit descent are affected more commonly. Talon cusp is also highly observed in patients with orofacial digital II syndrome and Rubinstein Taybi syndrome. Other anomalies that occur with talon cusp can include peg laterals, supernumerary teeth, dens envaginatus, agenesis and impaction. A person belonging to one of these particular demographics or one who has any of these deformities or syndromes may have a higher risk of having a talon cusp.

Genetic causes also involve the genes MSX1 and PAX9.

Genetic associations for selective tooth agenesis ("STHAG") include:

Future studies will look further into the relationship of talon cusp and Rubinstein-Taybi syndrome and other oral-facial-digital syndromes. A former study showed a direct correlation in which 45 affected patients with Rubinstein-Taybi syndrome, 92% of these patients had talon cusp. Other researchers are attempting to trace talon cusp to ancestors and comparing dentition to modern humans. Another study done in 2007 examined the dentition of 301 Native American Indian skeletons for the presence or absence of talon cusp. The results showed five skeletons (2 percent) in the population had the trait.

In 2011, only 21 cases of talon cusp have been reported and are in literature. It appears that as of 2014 and 2015, additional research continues in hopes of finding the cause and mechanism of talon cusp. With the majority of cases of talon cusp being unreported, it remains difficult to conduct tests, come up with conclusions, conduct surgery and perform research with small numbers.

There is still some discussion on whether FND is sporadic or genetic. The majority of FND cases are sporadic. Yet, some studies describe families with multiple members with FND. Gene mutations are likely to play an important role in the cause. Unfortunately, the genetic cause for most types of FND remains undetermined.

The median alveolar cyst is a rare cyst, occurring in the bony alveolus between the maxillary central incisors. It is distinguished from a periapical cyst by the fact that adjacent teeth are vital.

OAFNS is a combination of FND and oculo-auriculo-vertebral spectrum (OAVS).

The diagnosis of OAVS is based on the following facial characteristics: microtia (underdeveloped external ear), preauricular tags, facial asymmetry, mandibular hypoplasia and epibulbar lipodermoids (benign tumor of the eye which consists of adipose and fibrous tissue).

There still remains discussion about the classification and the minimal amount of characteristics. When someone presents with FND and the characteristics of OAVS, the diagnosis OAFNS may be made.

As the incidence of OAFNS is unknown, there are probably a lot of children with mild phenotypes that aren’t being diagnosed as being OAFNS.

The cause of OAFNS is unknown, but there are some theories about the genesis. Autosomal recessive inheritance is suggested because of a case with two affected siblings and a case with consanguineous parents. However, another study shows that it is more plausible that OAFNS is sporadic.

It is known that maternal diabetes plays a role in developing malformations of craniofacial structures and in OAVS. Therefore, it is suggested as a cause of OAFNS. Folate deficiency is also suggested as possible mechanism.

Low-dose CT protocols should be considered in diagnosing children with OAFNS.

Because MLIA can be detected from partial skeletal remains, it is useful in the field of anthropology. Anthropologically-interesting human remains often have relatively well preserved skeletons, but no soft tissues or intact DNA. This makes it hard to determine relationships between the deceased individuals. MLIA is sometimes related to inbreeding, so the presence of MLIA in many members of a large collection of remains can indicate that the population that lived there was relatively inbred. This technique has been used to study a group of Neolithic farmers.

Maxillary lateral incisor agenesis (MLIA) is lack of development (agenesis) of one or both of the maxillary lateral incisor teeth. In normal human dentition, this would be the second tooth on either side from the center of the top row of teeth. The condition is bilateral if the incisor is absent on both sides or unilateral if only one is smissing. It appears to have a genetic component.

A median mandibular cyst is a type of cyst that occurs in the midline of the mandible, thought to be created by proliferation and cystic degeneration of resting epithelial tissue that is left trapped within the substance of the bone during embryologic fusion of the two halves of the mandible, along the plane of fusion later termed the symphysis menti. A ture median mandibular cyst would therefore be classified as a non-odontogenic, fissural cyst. The existence of this lesion as a unique clinical entity is controversial, and some reported cases may have represented misdiagnosed odontogenic cysts, which are by far the most common type of intrabony cyst occurring in the jaws. It has also been suggested that the mandible develops as a bilobed proliferation of mesenchyme connected with a central isthmus. Therefore, it is unlikely that epithelial tissue would become trapped as there is no ectoderm separating the lobes in the first instance.

Because the cause of facial clefts still is unclear, it is difficult to say what may prevent children being born with facial clefts. It seems that folic acid contributes to lowering the risk of a child being born with a facial cleft.

The globulomaxillary cyst is a cyst that appears between a maxillary lateral incisor and the adjacent canine. It exhibits as an "inverted pear-shaped radiolucency" on radiographs, or X-ray films.

The globulomaxillary cyst often causes the roots of adjacent teeth to diverge.

This cyst should not be confused with a nasopalatine cyst.

The developmental origin has been disputed. Today, most literature agree based on overwhelming evidence that the cyst is predominantly of tooth origin (odontogenic), demonstrating findings consistent with periapical cysts, odontogenic keratocysts or lateral periodontal cysts.

Mutations in the cathepsin C gene (CTSC), located at human chromosome 11q14.1-q14.3, are the cause of PLS. The disorder is inherited in an autosomal recessive manner. This means the defective gene responsible for the disorder is located on an autosome (chromosome 11 is an autosome), and two copies of the defective gene (one inherited from each parent) are required in order to be born with the disorder. The parents of an individual with an autosomal recessive disorder both carry one copy of the defective gene, but usually do not experience any signs or symptoms of the disorder.

Papillon–Lefèvre syndrome (PLS), also known as palmoplantar keratoderma with periodontitis, is an autosomal recessive genetic disorder caused by a deficiency in cathepsin C.

It can be caused by any of the following:

- Nutritional factors.

- Some diseases (such as undiagnosed and untreated celiac disease, chicken pox, congenital syphilis).

- Hypocalcemia.

- Fluoride ingestion (dental fluorosis).

- Birth injury.

- Preterm birth.

- Infection.

- Trauma from a deciduous tooth.

Turner's hypoplasia is an abnormality found in teeth. Its appearance is variable, though usually is manifested as a portion of missing or diminished enamel on permanent teeth. Unlike other abnormalities which affect a vast number of teeth, Turner's hypoplasia usually affects only one tooth in the mouth and, it is referred to as a Turner's tooth.

There is no known cure for this syndrome. Patients usually need ophthalmic surgery and may also need dental surgery

Genetic counseling and screening of the mother's relatives is recommended.

One dental textbook defines it as: “Dollicofacial, there is excess of lower facial height usually associated with lower occlusal and mandibular plane angles.” This is often associated “with vertical maxillary excess and mandibular hypoplasia.” Luc P. M. Tourne, a Fellow in the Department of TMJ and Craniofacial Pain at the University of Minnesota School of Dentistry, noted: "There is a clinically recognizable facial morphology, the long face syndrome, which has been incompletely described in the literature," However, her study of 31 adults with this syndrome, which included "analysis of esthetics, skeletal morphology, and occlusion" confirmed "this basic dentofacial deformity" has associations " with excessive vertical growth of the maxilla." She reported that closed bite and dental open are two pf the syndrome's variants.

The treatment for young patients troubled by long face syndrome is to halt and control descent of the lower jaw and to prevent the eruption of posterior teeth. In severe cases of deformity, a mixture of orthodontics and orthognathic surgery may be the only effective solution. The long term (more than 6 years) effectiveness of surgical treatments for long face syndrome has been subject to study.

"In the American literature, the terms long-face syndrome and short-face syndrome are often used." To be sure, there are reported "long and the short face anomalies" and open bite cases. However, in the opinion of Hugo Obwegeser, there is no medical justification for naming theme as a "syndrome" the signs and symptoms do not meet the definitional threshold.

There is controversy concerning the use of the descriptor "long-face syndrome." While increased anterior "total and lower face height" in many ages, combined with vertical maxillary excess in adults has been observed, the causes are controversial. Specifically, there is disagreement about possible potential environmental influences on genetic components.

Anecdotally, it was said to be a genetic condition, which could only be corrected with “massive amounts” of debilitating, frequent and long dental and facial reconstructive surgery.

For children, there is a concern that mouth breathing can contribute to the development of long face syndrome. A recent study finds that it is a growing problem which should be treated as "It won't just go away." In addition to mouth breathing, it may be associated with sleep apnea.

Because of Long face syndrome's sometime association with pediatric obstructive sleep apnea (OSA) and allergic reactions, it is essential that treating physicians differentiate the conditions and the treatments; treating one may not cure the other. Multilevel coblation surgery is sometimes used to correct moderate to severe OSA, and Long Face Syndrome can be a rare factor in considering surgery.

Schmitt Gillenwater Kelly syndrome is a rare autosomal dominant congenital disorder consisting of radial hypoplasia, triphalangeal thumbs, hypospadias, and maxillary diastema.

OAF is a complication of oroantral communication. Other complications may arise if left untreated. For example:

- Candidal infection

- Chronic maxillary sinus infection of bacterial origin

- Osteomyelitis

- Rhinosinusitis

- Sinus pathology

Therefore, OAF should be dealt with first, before treating the complications.

Literature states that very few crossbites tend to self-correct which often justify the treatment approach of correcting these bites as early as possible. Only 0–9% of crossbites self-correct. Lindner et al. reported that in a 50% of crossbites were corrected in 76 four year old children.

Another abnormal condition is hypodontia, in which there are fewer than the usual number of teeth.

Hyperdontia is seen in a number of disorders, including Gardner's syndrome and cleidocranial dysostosis, where multiple supernumerary teeth are seen that are usually impacted.

There is evidence of hereditary factors along with some evidence of environmental factors leading to this condition. While a single excess tooth is relatively common, multiple hyperdontia is rare in people with no other associated diseases or syndromes. Many supernumerary teeth never erupt, but they may delay eruption of nearby teeth or cause other dental or orthodontic problems. Molar-type extra teeth are the rarest form. Dental X-rays are often used to diagnose hyperdontia.

It is suggested that supernumerary teeth develop from a third tooth bud arising from the dental lamina near the regular tooth bud or possibly from splitting the regular tooth bud itself. Supernumerary teeth in deciduous (baby) teeth are less common than in permanent teeth.