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.

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.

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

Mulberry molars are a dental condition usually associated with congenital syphilis, characterized by multiple rounded rudimentary enamel cusps on the permanent first molars. Mulberry molars are physically defective permanent molars. The deformity is caused by congenital syphilis. This type of abnormality is characterized by dwarfed molars with cusps covered with globular enamel growths. These teeth are functional but can be cosmetically fixed with crowns, bridges, or implants.

Just above the gum line, the mulberry molar looks normal. A deformity becomes apparent towards the cusp or top grinding surface of the tooth. Here, the size of the mulberry molar is diminished in all aspects, creating a stumpy version of a conventional molar. The cause of the molar atrophy is thought to be enamel hypoplasia, or a deficiency in tooth enamel. The underlying dentin and pulp of the tooth is normal, but the enamel covering or molar sheath is thin and deformed, creating a smaller version of a typical tooth.

The grinding surface of a mulberry molar is also corrupted. Normally, the grinding surface of a molar has a pit and is surrounded by a circular ridge at the top of the tooth, which is used for grinding. The cusp deformity of the mulberry molar is characterized by an extremely shallow or completely absent pit. Instead, the pit area is filled with globular structures bunched together all along the top surface of the cusp. This type of deformity is also thought to be caused by enamel hypoplasia. Mulberry molars are typically functional and do not need treatment. If the deformity is severe or the person is bothered by the teeth, there are several options. The teeth can be covered with a permanent cast crown, stainless steel crown, or the molars can be removed and an implant or bridge can be put in place of the mulberry molar.

A mulberry molar is caused by congenital syphilis, which is passed from the mother to the child in the uterus through the placenta. Since this particular symptom of congenital syphilis manifests later in childhood with the eruption of the permanent molars, it is a late stage marker for the disease. Hutchinson’s teeth, marked by dwarfed teeth and deformed cusps that are spaced abnormally far apart, are another dental deformity caused by congenital syphilis. Mulberry molars and Hutchinson’s teeth will often occur together. Pregnant women with syphilis should tell their doctors about the condition and be treated for it during pregnancy, otherwise the baby should be screened for the disease after birth and treated with penicillin if necessary.

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.

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.

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.

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.

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.

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.

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.

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.

1-increased localised pressure.

2- focal growth retardation and stimulation.

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.

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.

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.

In persons of European ancestry, the most common missing teeth are the wisdom teeth (25–35%), the permanent upper lateral incisors (2%), the lower second premolars (3%), or the upper second premolar, with a higher prevalence in females than in males. The prevalence of missing primary teeth is found at 0.1–0.9%, with a 1:1 male to female ratio. Excluding the third molars, missing permanent dentition accounts for 3.5–6.5%. Similar trends of missing teeth can be seen in approximately 3–10% of orthodontic patients.

30-50% of people with missing primary teeth will have missing permanent teeth, as well.

Pericoronitis is an infection of the soft tissue that covers the crown of an impacted tooth and is usually caused by the normal oral microbiota. For most people there exists a balance between the host defenses and the oral micriobiota but if the host defenses are compromised like during minor illness such as influenza or an upper respiratory tract infection, pericoronitis results. Another common cause is entrapment of food beneath the gum flap (also called an operculum). Pericoronitis can present as a mild infection or severe infection. In its mildest form it is just a localized tissue swelling and soreness whereas in severe forms the swelling is slightly larger even sometimes creating trismus (difficulty opening the mouth).

Occasionally, an impacted tooth causes sufficient pressure on the roots of adjacent teeth causing it to resorb.

An impacted tooth occupies space that is usually filled with bone. This weakens that area of bone and renders the jaw more susceptible to fracture.

When impacted teeth are retained completely within the alveolar process, the associated follicular sac is also retained along with it. Though in most persons the dental follicle maintains its original size sometimes it may undergo cystic degeneration and become a dentigerous cyst or a keratocyst.

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.

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.

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.

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.

There are two main types: compound and complex.

- A "compound" odontoma still has the three separate dental tissues (enamel, dentin and cementum), but may present a lobulated appearance where there is no definitive demarcation of separate tissues between the individual "toothlets" (or denticles). It usually appears in the anterior maxilla.

- The "complex" type is unrecognizable as dental tissues, usually presenting as a radioopaque area with varying densities. It usually appears in the posterior maxilla or in the mandible.

In addition to the above forms, the dilated odontoma is an infrequent developmental alteration that appears in any area of the dental arches and can affect deciduous, permanent and supernumerary teeth. Dens invaginatus is a developmental anomaly resulting from invagination of a portion of crown forming within the enamel organ during odontogenesis. The most extreme form of dens invaginatus is known as dilated odontoma.

Dental open bite occurs in patients where the anterior teeth fail to touch. However, this is not accompanied by the skeletal tendency of having an open bite. Thus this type of open bite may happen in patients who have horizontal or hypodivergent growth pattern. These patients have normal jaw growth and do not have the long face syndrome. The anterior open bite in these patients may be caused by Macroglossia, Tongue thrusting habit or digit sucking habits. Some of the characteristics of a dental open bite include:

- Normal lower anterior facial height

- Horizontal/Hypodivergent growth pattern

- Occlusal plane diverges after the premolar contact

- Under-eruption of the anterior incisors

- Over-eruption of the posterior incisors

- Proclined upper and lower incisors

- No vertical maxillary excess or gummy smile

- Presence of habits such as thumb sucking, tongue thrusting

- Spacing between anterior incisors due to their proclination

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