Unilateral crossbite involves one side of the arch. The most common cause of unilateral crossbite is a narrow maxillary dental arch. This can happen due to habits such as digit sucking, prolonged use of pacifier or upper airway obstruction. Due to the discrepancy between the maxillary and mandibular arch, neuromuscular guidance of the mandible causes mandible to shift towards the side of the crossbite. This is also known as Functional mandibular shift. This shift can become structural if left untreated for a long time during growth, leading to skeletal asymmetries. Unilateral crossbites can present with following features in a child

- Lower midline deviation to the crossbite side

- Class 2 Subdivision relationships

- Temporomandibular disorders

Talon Cusp will show physical signs of the irregular dental formation of the teeth and cause other symptoms of the disease that could possibly lead to dental problems in the future depending on severity of the deformity. Most commonly, the extra cusp is located on the lingual surface, giving a three-pronged appearance which has been described as an eagle talon. Rarely however the extra cusp may be situated on the facial surface, or there may be extra cusps on both lingual and facial surfaces. There may be a deep groove between the talon cusp and the rest of the tooth. The extra cusp typically contains pulp tissue. When viewing talon cusp from the occlusal, the projection will appear "x-shaped" as well as appears conical and mimicking the shape of an "eagle's talon".

Symptoms of talon cusp include:

- Interference with occlusion or bite

- Irritation of soft tissues and tongue

- Accidental cusp fracture

- Susceptible to dental caries

1-increased localised pressure.

2- focal growth retardation and stimulation.

Bjork defined posterior crossbite as a malocclusion where the buccal cusps of canine, premolar and molar of upper teeth occlude lingually to the buccal cusps of canine, premolar and molar of lower teeth. Posterior crossbite is often correlated to a narrow maxilla and upper dental arch. A posterior crossbite can be unilateral, bilateral, single-tooth or entire segment crossbite. Posterior crossbite has been reported to occur between 7–23% of the population. The most common type of posterior crossbite to occur is the unilateral crossbite which occurs in 80% to 97% of the posterior crossbite cases. Posterior crossbites also occur most commonly in primary and mixed dentition. This type of crossbite usually presents with a "functional shift of the mandible towards the side of the crossbite". Posterior crossbite can occur due to either skeletal, dental or functional abnormalities. One of the common reasons for development of posterior crossbite is the size difference between maxilla and mandible, where maxilla is smaller than mandible. Posterior crossbite can result due to

- Upper Airway Obstruction where people with "adenoid faces" who have trouble breathing through their nose. They have an open bite malocclusion and present with development of posterior crossbite.

- Prolong digit or suckling habits which can lead to constriction of maxilla posteriorly

- Prolong pacifier use (beyond age 4)

This anomaly is large enough to be seen with the naked eye. One can see the projection on the incisal edge of a tooth looking into the mouth of the affected person. The structure is described to be "T'shaped" or "X-shaped" however will differ depending on its shape, size, structure, location and site of origin. X-rays and radiographs can also show evidence of the abnormality. The digital images would show a tooth with talon cusp as if it were "double teeth".

When looking at a radiograph some features to look for would be location, edge, shape and number. The location would be on an anterior tooth, the edge would be clear and well defined and can be seen even by the naked eye, and the shape would appear "talon-like" over the top portion or crown of the affected tooth. There could potentially be one, two or multiple protrusions depending on the type of cusp.

Talon cusp can fall under three categories: Type I, Type II and Type III. They are created based on the cusp formation shape and length of extension.

- Type I - Talon: The additional cusp or talon projects from the palatal surface of a primary or permanent anterior (front) tooth that extends at least half of the distance from the cemento enamel junction to the incisal edge.

- Type II - Semi Talon: The semi talon cusp measures about 1mm or more in length but extends less than half of the distance seen in Type I Talon.

- Type III - Trace Talon: The projection originates from the cingulum (also known as the "cervical third") of the root and is enlarged or prominent in any form (conical, or tubercle-like)

Since many cases of Talon cusp go unreported, it is hard to draw linkage maps but it is safe to assume that dental formation is influenced by genetic factors. Talon cusp is also seen in association with conditions such as Rubinstein-Taybi syndrome, Mohr syndrome, Ellis–van Creveld syndrome, Incontinentia pigmenti achromians, Berardinelli-Seip syndrome, and Sturge–Weber syndrome.

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.

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.

Dens invaginatus, also known as dens in dente ("tooth within a tooth") is a condition found in teeth where the outer surface folds inward. There are coronal and radicular forms, with the coronal form being more common.

Dens invaginatus is a malformation of teeth most likely resulting from an infolding of the dental papilla during tooth development or invagination of all layers of the enamel organ in dental papillae. Affected teeth show a deep infolding of enamel and dentine starting from the foramen coecum or even the tip of the cusps and which may extend deep into the root. Teeth most affected are maxillary lateral incisors and bilateral occurrence is not uncommon. The malformation shows a broad spectrum of morphologic variations and frequently results in early pulp necrosis. Root canal therapy may present severe problems because of the complex anatomy of the teeth. Cause, prevalence, classification, and therapeutic considerations including root canal therapy, apical surgery and prevention of pulpal involvement are reviewed.

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.

Loss of attachment:

- By far the most common cause is periodontal disease (gum disease). This is painless, slowly progressing loss of bony support around teeth. It is made worse by smoking and the treatment is by improving the oral hygiene above and below the gumline.

- Dental abscesses can cause resorption of bone and consequent loss of attachment. Depending on the type of abscess, this loss of attachment may be restored once the abscess is treated, or it may be permanent.

- Many other conditions can cause permanent or temporary loss of attachment and increased tooth mobility. Examples include: Langerhans cell histiocytosis.

Increased forces on the tooth:

- Bruxism (abnormal clenching and grinding of teeth) can aggravate attachment loss and tooth mobility if periodontal disease is already present. The tooth mobility is typically reversible and the tooth returns to normal level of mobility once the bruxism is controlled.

- Dental trauma. Luxations, and root fractures of teeth can cause sudden mobility after a blow. Dental trauma may be isolated or associated with other facial trauma.

- Increased biting force on one tooth can cause temporary increased mobility until corrected. A common scenario is a new filling or crown which is a fraction of a millimeter too prominent in the bite, which after a few days causes periodontal pain in that tooth and/or the opposing tooth.

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.

All the teeth are normal size but appear smaller relative to enlarged jaws. Relative generalized microdontia may be the result of inheritance of a large jaw from one parent, and normal sized teeth from the other.

Clinically, there is a number of physiological results that serve as evidence of occlusal trauma:,

- Tooth mobility

- Fremitus

- Tooth migration

- Pain

- Thermal sensitivity

- Pain on chewing or percussion

- Wear facets

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.

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.

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.

The reported symptoms are very variable, and frequently have been present for many months before the condition is diagnosed. Reported symptoms may include some of the following:

- Sharp pain when biting on a certain tooth, which may get worse if the applied biting force is increased. Sometimes the pain on biting occurs when the food being chewed is soft with harder elements, e.g. seeded bread.

- "Rebound pain" i.e. sharp, fleeting pain occurring when the biting force is released from the tooth, which may occur when eating fibrous foods.

- Pain when grinding the teeth backward and forward and side to side.

- Sharp pain when drinking cold beverages or eating cold foods, lack of pain with heat stimuli.

- Pain when eating or drinking sugary substances.

- Sometimes the pain is well localized, and the individual is able to determine the exact tooth from which the symptoms are originating, but not always.

If the crack propagates into the pulp, irreversible pulpitis, pulpal necrosis and periapical periodontitis may develop, with the respective associated symptoms.

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.

Microscopically, there will be a number of features that accompany occlusal trauma:

- Hemorrhage

- Necrosis

- Widening of the periodontal ligament, or PDL (also serves as a very common radiographic feature)

- Bone resorption

- Cementum loss and tears

It was concluded that widening of the periodontal ligament was a "functional adaptation to changes in functional requirements".

Taurodontism is a condition found in the molar teeth of humans whereby the body of the tooth and pulp chamber is enlarged vertically at the expense of the roots. As a result, the floor of the pulp and the furcation of the tooth is moved apically down the root. The underlying mechanism

of taurodontism is the failure or late invagination of Hertwig's epithelial root sheath, which is responsible for root formation and shaping causing an apical shift of the root furcation.

The constriction at the amelocemental junction is usually reduced or absent. Taurodontism is most commonly found in permanent dentition although the term is traditionally applied to molar teeth.

In some cases taurodontism seems to follow an autosomal dominant type of inheritance.

Taurodontism is found in association with amelogenesis imperfecta, ectodermal dysplasia and tricho-dento-osseous syndrome.

The term means "bull like" teeth derived from similarity of these teeth to those of ungulate or cud-chewing animals.

According to Shaw these can be classified as hypotaurodont, hypertaurodont and mesotaurodont.

According to Mangion taurodontism may be:

- A (mentally retarded) character

- A primitive pattern

- Mendelian recessive character

- Atavistic feature

- A mutation

It has also been reported in Klinefelter's syndrome, XXYY and Down's syndrome .

The teeth involved are invariably molars, sometimes single and at the other times multiple teeth may be involved. The teeth themselves may look normal and do not have any particular anatomical character on clinical examination.

On a dental radiograph, the involved tooth looks rectangular in shape without apical taper. The pulp chamber is extremely large and the furcations may be only a few millimeters long at times.

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

If Turner's hypoplasia is found on a canine or a premolar, the most likely cause is an infection that was present when the primary (baby) tooth was still in the mouth. Most likely, the primary tooth was heavily decayed and an area of inflamed tissues around the root of the tooth (called a periapical inflammation), affecting the development of the permanent tooth. The tooth most likely affected by this cause is the canine tooth. The appearance of the abnormality will depend on the severity and longevity of the infection.

If Turner's hypoplasia is found in the front (anterior) area of the mouth, the most likely cause is a traumatic injury to a primary tooth. The traumatized tooth, which is usually a maxillary central incisor, is pushed into the developing tooth underneath it and consequently affects the formation of enamel. Because of the location of the permanent tooth's developing tooth bud in relation to the primary tooth, the most likely affected area on the permanent tooth is the facial surface (the side closer to the lips or cheek). White or yellow discoloration may accompany Turner's hypoplasia. Enamel hypoplasia may also be present.

Turner's hypoplasia usually affects the tooth enamel if the trauma occurs prior to the third year of life. Injuries occurring after this time are less likely to cause enamel defects since the enamel is already calcified.

The same type of injury is also associated with the dilaceration of a tooth.

Most commonly the individual complains of food getting lodged beneath the gums and a soreness that is usually confused with throat infections. In slightly milder forms a swelling is visible and mouth opening becomes difficult in severe cases. Pain is invariably present.

All teeth, although the same size, grow in larger than normal. This is seen in cases of growth hormone excess called pituitary gigantism. It is the rarest of the types.

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