Supernumerary teeth can be classified by shape and by position. The shapes include the following:

- Supplemental (where the tooth has a normal shape for the teeth in that series);

- Tuberculate (also called "barrel shaped");

- Conical (also called "peg shaped");

- Compound odontoma (multiple small tooth-like forms);

- Complex odontoma (a disorganized mass of dental tissue)

When classified by position, a supernumerary tooth may be referred to as a "mesiodens", a "paramolar", or a "distomolar".

The most common supernumerary tooth is a mesiodens, which is a malformed, peg-like tooth that occurs between the maxillary central incisors.

Fourth and fifth molars that form behind the third molars are another kind of supernumerary teeth.

This type of failure of eruption takes place when the affected tooth is ankylosed to the bone around it. This is different than primary failure of eruption where the affected tooth/teeth were not ankylosed. In mechanical failure of eruption, affected tooth has partial or complete loss of PDL in a panoramic radiograph and teeth distal to affected tooth do not have this condition. On a percussion test, a tooth with mechanical failure of eruption will have a dull metallic sound.

The lesions that appear in teeth affected with MIH can present as opacities that vary from white to yellow-brown. They are usually asymmetrical in appearance, with a sharp demarcation that distinguishes between normal and affected enamel. The lesions usually do not involve the cervical third of affected teeth.

Males tend to have larger teeth than females, and tooth size also varies according race. Abnormal tooth size is defined by some as when the dimensions are more than 2 standard deviations from the average. Microdontia is when the teeth are abnormally small, and macrodontia is when the teeth are abnormally large.

All the teeth are smaller than the normal size. True generalized microdontia is very rare, and occurs in pituitary dwarfism. Due to decreased levels of growth hormone the teeth fail to develop to a normal size.

The phenomenon of gemination arises when two teeth develop from one tooth bud and, as a result, the patient has an extra tooth, in contrast to fusion, where the patient would appear to be missing one tooth.

Fused teeth arise through union of two normally separated tooth germs, and depending upon the stage of development of the teeth at the time of union, it may be either complete or incomplete. On some occasions, two independent pulp chambers and root canals can be seen. However, fusion can also be the union of a normal tooth bud to a supernumerary tooth germ. In these cases, the number of teeth is also normal and differentiation from gemination may be very difficult, if not impossible. In geminated teeth, division is usually incomplete and results in a large tooth crown that has a single root and a single canal. It is an asymptomatic condition.

The prevalence of germination or fusion is 2.5% in primary dentition, and 0.1 - 0.2% in permanent dentition. It is more frequently observed in primary than permanent dentition; anterior than posterior teeth; unilaterally than bilaterally. It commonly occurs in the primary upper incisors.

Most often natal teeth are mandibular central incisors. They have little root structure and are attached to the end of the gum by soft tissue and are often mobile.

There have been many syndromes which have been identified to be related to failure of eruption of teeth. These syndromes are Cleidocranial dyspalsia, Osteoporosis, Rutherford syndrome, GAPO syndrome and Osteoglophonic dysplasia.

The presence of a supernumerary tooth, particularly when seen in young children, is associated with a disturbance of the maxillary incisor region. This commonly results in the impaction of the incisors during the mixed dentition stage. The study debating this also considered many other factors such as: the patient’s age, number, morphology, growth orientation and position of the supernumerary tooth. Therefore, the presence of a supernumerary tooth when found must be appropriately approached with the correct treatment plan incorporating the likelihood of incisal crowding.

Impacted wisdom teeth without a communication to the mouth, that have no pathology associated with the tooth and have not caused tooth resorption on the blocking tooth rarely have symptoms. In fact, only 12% of impacted wisdom teeth are associated with pathology.

When wisdom teeth communicate with the mouth, the most common symptom is localized pain, swelling and bleeding of the tissue overlying the tooth. This tissue is called the operculum and the disorder called pericoronitis which means inflammation around the crown of the tooth. Low grade chronic periodontitis commonly occurs on either the wisdom tooth or the second molar, causing less obvious symptoms such as bad breath and bleeding from the gums. The teeth can also remain asymptomatic (pain free), even with disease. As the teeth near the mouth during normal development, people sometimes report mild pressure of other symptoms similar to teething.

The term asymptomatic means that the person has no symptoms. The term asymptomatic should not be equated with absence of disease. Most diseases have no symptoms early in the disease process. A pain free or asymptomatic tooth can still be infected for many years before pain symptoms develop.

A single tooth is larger than the rest. This is unusual and could be the result of fusion and germination that cause enlarged crowns.

Most commonly used classification system with respect to treatment planning. Depending on the angulation the tooth might be classified as:

- Mesioangular

- Horizontal

- Vertical

- Distoangular

- Palatal

- Buccal

- Lingual

Classifications enable the oral surgeon to determine the difficulty in removal of the impacted tooth. The primary factor determining the difficulty is accessibility, which is determined by adjacent teeth or other structures that impair access or delivery pathway. The majority of classification schemes are based on analysis on a radiograph. The most frequently considered factors are discussed below.

The distribution of disease in those affected with MIH can vary greatly. It can be common for the enamel of one molar to be affected while the enamel of the contralateral molar is clinically unaffected, or with minor defects only.

Males tend to have larger teeth than females, and tooth size also varies according to race. Abnormal tooth size is defined by some as when the dimensions are more than 2 standard deviations from the average. Macrodontia is when the teeth are abnormally large, and microdontia is when they are abnormally small.

Other kinds of malocclusions can be due to tooth size or horizontal, vertical, or transverse skeletal discrepancies, including skeletal asymmetries. Long faces may lead to "open bite malocclusion", while short faces can be coupled to a "Deep bite malocclusion". However, there are many other more common causes for open bites (such as tongue thrusting and thumb sucking), and likewise for deep bites. Upper or lower jaw can be overgrown or undergrown, leading to Class II or Class III malocclusions that may need corrective jaw surgery or orthognathic surgery as a part of overall treatment, which can be seen in about 5% of the general population.

In dentistry, hypodontia is the condition at which the patient has missing teeth as a result of the failure of those teeth to develop (also called tooth agenesis). Hypodontia describes a situation where the patient is missing up to five permanent teeth, excluding the 3rd molars. Missing third molars occur in 9–30% of studied populations. In primary dentition the maxilla is more affected, with the condition usually involving the maxillary lateral incisor.

The condition of missing over five (six or more) permanent teeth, excluding 3rd molars or wisdom teeth, has been called oligodontia. The condition for missing all teeth, either primary and/or permanent), is called anodontia. A similar condition is hyperdontia, in which there are more than the usual number of teeth, more commonly called supernumerary teeth.

Many other terms to describe a reduction in number of teeth appear in the literature: aplasia of teeth, congenitally missing teeth, absence of teeth, agenesis of teeth and lack of teeth.

All teeth are classified as either developing, erupted (into the mouth), embedded (failure to erupt despite lack of blockage from another tooth) or impacted. An impacted tooth is one that fails to erupt due to blockage from another tooth.

Wisdom teeth develop between the ages of 14 and 25, with 50% of root formation completed by age 16 and 95% of all teeth erupted by the age of 25. However, tooth movement can continue beyond the age of 25.

Impacted wisdom teeth are classified by the direction and depth of impaction, the amount of available space for tooth eruption. and the amount of soft tissue or bone (or both) that covers them. The classification structure helps clinicians estimate the risks for impaction, infections and complications associated with wisdom teeth removal. Wisdom teeth are also classified by the presence (or absence) of symptoms and disease.

One review found that 11% of teeth will have evidence of disease and are symptomatic, 0.6% will be symptomatic but have no disease, 51% will be asymptomatic but have disease present and 37% will be asymptomatic and have no disease.

Impacted wisdom teeth are often described by the direction of their impaction (forward tilting, or mesioangular being the most common), the depth of impaction and the age of the patient as well as other factors such as pre-existing infection or the presence of pathology. Of these predictors, age correlates best with extraction difficulty and complications during wisdom teeth removal rather than the orientation of the impaction.

Another classification system often taught in U.S. dental schools is known as "Pell and Gregory Classification". This system includes a horizontal and vertical component to classify the location of third molars (predominately applicable to mandibular third molars): the third molar's relationship to the occlusal plane being the vertical or "x-component" and to the anterior border of the ramus being the horizontal or "y-component". Vertically, Class A impaction is one in which the occlusal surface of the impacted tooth is level or nearly level with the occlusal plane and the cervical line of the adjacent second molar.

Tooth gemination is a dental phenomenon that appears to be two teeth developed from one. There is one main crown with a cleft in it that, within the incisal third of the crown, looks like two teeth, though it is not two teeth. The number of the teeth in the arch will be normal.

Oral habits and pressure on teeth or the maxilla and mandible are causes of malocclusion.

In the active skeletal growth, mouthbreathing, finger sucking, thumb sucking, pacifier sucking, onychophagia (nail biting), dermatophagia, pen biting, pencil biting, abnormal posture, deglutition disorders and other habits greatly influence the development of the face and dental arches.

Pacifier sucking habits are also correlated with otitis media.

Dental caries, periapical inflammation and tooth loss in the deciduous teeth alter the correct permanent teeth eruptions.

1-increased localised pressure.

2- focal growth retardation and stimulation.

For people, the relevance and functionality of teeth can be easily taken for granted, but a closer examination of their considerable significance will demonstrate how they are actually very important. Among other things, teeth serve to:

- support the lips and cheeks, providing for a fuller, more aesthetically pleasing appearance

- maintain an individual's vertical dimension of occlusion

- along with the tongue and lips, allow for the proper pronunciation of various sounds

- preserve and maintain the height of the alveolar ridge

- cut, grind, and otherwise chew food

Type II would mostly cause discolouration to the primary teeth. Affected teeth usually appear as brownish-blue, brown or yellow. Translucent “opalescence” is often one of the characteristics to describe teeth with DD-2. In some cases teeth might show slightly amber coloured but in most of the cases permanent teeth are unaffected and appear normal regardless of colour, shape and size. Dental X-rays is the key to diagnose dentine dysplasia, especially on permanent teeth. Abnormalities of the pulp chamber is the main characteristic to make a definitive diagnosis.

In the primary teeth, coronal dentin dysplasia may appear similar to Dentinogenesis Imperfecta type II (DG-II) but if abnormalities features appear to be more pronounced in the permanent teeth, then consider changing the diagnosis to DGI-II instead of DD-2.

Regional odontodysplasia or odontogenesis imperfecta is an uncommon developmental abnormality of teeth, usually localized to a certain area of the mouth. The condition is nonhereditary. There is no predilection for race, but females are more likely to get regional odontodysplasia. The enamel, dentin, and pulp of teeth are affected, to the extent that the affected teeth do not develop properly. These teeth are very brittle. On radiographs the teeth appear more radiolucent than normal, so they are often described as "ghost teeth". Most cases are considered , but some cases are associated with syndromes, growth abnormalities, neural disorders, and vascular malformations.

Permanent teeth usually show effects of regional odontodysplasia if the deciduous tooth was affected. Many of these teeth do not erupt, and those that do have an increased risk of caries and periapical inflammation.

Hair abnormalities are very prominent in majority of the cases of TDO. Kinky/curly hair that is unusually dry and easily sheds is present at birth. In 80% of cases, the hair has a more relaxed appearance by adolescence. The presence of this hair texture type is a defining characteristic between a diagnosis of TDO verses amelogenesis imperfecta with hypomaturation. Additionally, in TDO the nails are usually abnormally thin, brittle, and split frequently. Cranial deficiencies are marked by the presence of having a long skull relative to its width, or protrusive foreheads due to increased thickness of the cranial bones and premature closing of the associated sutures in the skull. The long bones in the body (arms, legs) are also abnormally long and tend to fracture very easily. Osteosclerosis, commonly seen in TDO cases is characterized by an increase in bone density, affecting the skull and the mastoid process located behind the jawbone on the skull, as well as a shortened ramus seen in people with TDO. There are no known pathological problems associated with hair and bone changes in people with this disease. Changes in the long bones tend to appear later in development, but changes in the teeth appear once the teeth being to form, called primary dentition. The hair and bone abnormalities are evaluated radiographically during initial diagnosis, and visually during the course of the disease. Radiographic exams may be repeated if there is suspect of fracture.