Prevention of early childhood caries begins before the baby is born; women are advised to maintain a well-balanced diet of high nutritional value, especially during the third trimester and within the infants first year of life. This is since enamel undergoes maturation; if the diet is not sufficient, a common condition that may occur is enamel hypoplasia.

Enamel hypoplasia is a developmental defect of enamel that occurs during tooth development, mainly pre-natally or during early childhood. Teeth affected by enamel hypoplasia are commonly at a higher risk of caries since there is an increased loss of minerals and therefore the tooth surface is able to breakdown more easily than in comparison to a non-hypoplastic tooth. It is therefore suggested to the mother to maintain a healthy diet since evidence suggests malnourishment during the perinatal period increases the risk of hypoplastic teeth in an infant.

The cause of germination is still unknown. However, there are a few possible factors contributing to germination:

- Vitamin deficiency

- Hormonal irregularities

- Infection or inflammation of areas near to the developing tooth bud

- Drug induced

- Genetic predisposition

- Radiotherapy that caused damage to the developing tooth germ

Before root canal treatment or extraction are carried out, the clinician should have thorough knowledge about the root canal morphology to avoid complications.

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

Although the etiology is unclear and it is speculated to be multifactorial. Contributing factors may include the following:

1. children born preterm and those with poor general health or systemic conditions in their first 3 years may develop MIH.

2. environmental changes

3. exposure to dioxine by prolonged breast-feeding could lead to an increase in the risk of MIH

4. respiratory diseases and oxygen shortage of the ameloblasts

5. oxygen shortage combined with low birth weight

Diet plays a key role in the process of dental caries. The type of foods along with the frequency at which they are consumed can determine the risk it puts for also developing carious lesions. With new products being put on supermarket shelves with irresistible prices, this can largely influence what people buy. It is common for infants and young children to frequently consume fermentable carbohydrates, in the form of liquids. The consumption of liquids containing fermentable carbohydrate, include drinks such as: juice, breast milk, formula, soda. These consumables all have the potential to increase the risk of dental caries due to prolonged contact between sugars in the liquid and cariogenic bacteria on the tooth surface.

Recent research has shown that breastfeeding does not increase caries risk up to 12 months of age. Poor feeding practices without appropriate preventive measures can lead to a distinctive pattern of caries in susceptible infants and toddlers commonly known as baby bottle tooth decay or ECC. Frequent and long duration bottle feeding, especially at night, is associated with ECC. This finding can be attributed to the fact that there is less salivary flow at night and hence less capacity for buffering and remineralisation. Each time a child drinks these liquids, acids attack for 20 minutes or longer. A parent's education and health awareness has a major influence on the caries experience of their child - feeding practices, dietary habits and food choices.

The prognosis for impacted wisdom teeth depends on the depth of the impaction. When they lack a communication to the mouth, the main risk is the chance of cyst or neoplasm formation which is relatively uncommon.

Once communicating with the mouth, the onset of disease or symptoms cannot be predicted but the chance of it does increase with age. Less than 2% of wisdom teeth are free of either periodontal disease or caries by age 65. Further, several studies have found that between 30% – 60% of people with previously asymptomatic impacted wisdom teeth will have them extracted due to symptoms or disease, 4–12 years after initial examination.

Extraction of the wisdom teeth removes the disease on the wisdom tooth itself and also appears to improve the periodontal status of the second molar, although this benefit diminishes beyond the age of 25.

Research has shown that there are five million teeth knocked-out each year in the United States.

Up to 25% of school-aged children and military trainees and fighters experience some kind of dental trauma each year. The incidence of dental avulsion in school aged children ranges from 0.5 to 16% of all dental trauma. Many of these teeth are knocked-out during school activities or sporting events such as contact sports, football, basketball, and hockey.It is important for anyone whom is related, working, or witnessing sports that they be educated on this subject matter. Being educated could aid in minimizing injuries that could do further harm to the victim. Being informed and spreading awareness of dental avulsion in the state of knowledge, treatment, and prevention could make an impact.

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.

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.

Few studies have looked at the percentage of the time wisdom teeth are present or the rate of wisdom teeth eruption. The lack of up to five teeth (excluding third molars, i.e. wisdom teeth) is termed hypodontia. Missing third molars occur in 9-30% of studied populations.

One large scale study on a group of young adults in New Zealand showed 95.6% had at least 1 wisdom tooth with an eruption rate of 15% in the maxilla and 20% in the mandible. Another study on 5000 army recruits found 10,767 impacted wisdom teeth. The frequency of impacted lower third molars has been found to be 72% and the frequency of retained impacted wisdom teeth that are free of disease and symptoms is estimated at 11.6% to 29% which drops with age.

The incidence of wisdom tooth removal was estimated to be 4 per 1000 person years in England and Wales prior to the 2000 NICE guidelines.

Reduced salivary flow rate is associated with increased caries since the buffering capability of saliva is not present to counterbalance the acidic environment created by certain foods. As a result, medical conditions that reduce the amount of saliva produced by salivary glands, in particular the submandibular gland and parotid gland, are likely to lead to dry mouth and thus to widespread tooth decay. Examples include Sjögren's syndrome, diabetes mellitus, diabetes insipidus, and sarcoidosis. Medications, such as antihistamines and antidepressants, can also impair salivary flow. Stimulants, most notoriously methylamphetamine, also occlude the flow of saliva to an extreme degree. This is known as meth mouth. Tetrahydrocannabinol (THC), the active chemical substance in cannabis, also causes a nearly complete occlusion of salivation, known in colloquial terms as "cotton mouth". Moreover, 63% of the most commonly prescribed medications in the United States list dry mouth as a known side-effect. Radiation therapy of the head and neck may also damage the cells in salivary glands, somewhat increasing the likelihood of caries formation.

Susceptibility to caries can be related to altered metabolism in the tooth, in particular to fluid flow in the dentin. Experiments on rats have shown that a high-sucrose, cariogenic diet "significantly suppresses the rate of fluid motion" in dentin.

The use of tobacco may also increase the risk for caries formation. Some brands of smokeless tobacco contain high sugar content, increasing susceptibility to caries. Tobacco use is a significant risk factor for periodontal disease, which can cause the gingiva to recede. As the gingiva loses attachment to the teeth due to gingival recession, the root surface becomes more visible in the mouth. If this occurs, root caries is a concern since the cementum covering the roots of teeth is more easily demineralized by acids than enamel. Currently, there is not enough evidence to support a causal relationship between smoking and coronal caries, but evidence does suggest a relationship between smoking and root-surface caries.

Exposure of children to secondhand tobacco smoke is associated with tooth decay.

Intrauterine and neonatal lead exposure promote tooth decay. Besides lead, all atoms with electrical charge and ionic radius similar to bivalent calcium,

such as cadmium, mimic the calcium ion and therefore exposure to them may promote tooth decay.

Poverty is also a significant social determinant for oral health. Dental caries have been linked with lower socio-economic status and can be considered a disease of poverty.

Forms are available for risk assessment for caries when treating dental cases; this system using the evidence-based Caries Management by Risk Assessment (CAMBRA). It is still unknown if the identification of high-risk individuals can lead to more effective long-term patient management that prevents caries initiation and arrests or reverses the progression of lesions.

Saliva also contains iodine and EGF. EGF results effective in cellular proliferation, differentiation and survival. Salivary EGF, which seems also regulated by dietary inorganic iodine, plays an important physiological role in the maintenance of oral (and gastro-oesophageal) tissue integrity, and, on the other hand, iodine is effective in prevention of dental caries and oral health.

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.

Extra teeth, lost teeth, impacted teeth, or abnormally shaped teeth have been cited as causes of malocclusion. A small underdeveloped jaw, caused by lack of masticatory stress during childhood, can cause tooth overcrowding. Ill-fitting dental fillings, crowns, appliances, retainers, or braces as well as misalignment of jaw fractures after a severe injury are other causes. Tumors of the mouth and jaw, thumb sucking, tongue thrusting, pacifier use beyond age 3, and prolonged use of a bottle have also been identified as causes.

In an experiment on two groups of rock hyraxes fed hardened or softened versions of the same foods, the animals fed softer food had significantly narrower and shorter faces and thinner and shorter mandibles than animals fed hard food. Experiments have shown similar results in other animals, including primates, supporting the theory that masticatory stress during childhood affects jaw development. Several studies have shown this effect in humans. Children chewed a hard resinous gum for two hours a day and showed increased facial growth.

During the transition to agriculture, the shape of the human mandible went through a series of changes. The mandible underwent a complex series of shape changes not matched by the teeth, leading to incongruity between dental and mandibular form. These changes in human skulls may have been "driven by the decreasing bite forces required to chew the processed foods eaten once humans switched to growing different types of cereals, milking and herding animals about 10,000 years ago."

It is estimated that tooth loss results in worldwide productivity losses in the size of about US$63 billion yearly.

The aetiology of dental abrasion can be due to a single stimuli or, as in most cases, multi-factorial. The most common cause of dental abrasion, is the combination of mechanical and chemical wear.

Tooth brushing is the most common cause of dental abrasion, which is found to develop along the gingival margin, due to vigorous brushing in this area. The type of toothbrush, the technique used and the force applied when brushing can influence the occurrence and severity of resulting abrasion. Further, brushing for extended periods of time (exceeding 2-3 min) in some cases, when combined with medium/hard bristled toothbrushes can cause abrasive lesions.

Different toothbrush types are more inclined to cause abrasion, such as those with medium or hard bristles. The bristles combined with forceful brushing techniques applied can roughen the tooth surface and cause abrasion as well as aggravating the gums. Repetitive irritation to the gingival margin can eventually cause recession of the gums. When the gums recede, the root surface is exposed which is more susceptible to abrasion.

Comparatively, electric toothbrushes have less abrasive tendencies.

Types of toothpastes can also damage enamel and dentine due to the abrasive properties. Specific ingredients are used in toothpaste to target removal of the bio-film and extrinsic staining however in some cases can contribute to the pastes being abrasive.

Whitening toothpastes are found to be one of the most abrasive types of toothpastes, according to the RDA Scale, detailed below. In-home and clinical whitening have been proven to increase the likelihood of an individual experiencing dental abrasion. It is believed that dental abrasion due to the whitening process is caused by a combination of both mechanical and chemical irritants, for example, using whitening toothpaste and at home bleaching kits together. However, if an individual is regimented in their after-whitening care then they can avoid loss of dentine minerals and in turn abrasion can be avoided. (that contribute to developing abrasion).

Another factor that can contribute to abrasion is alteration of pH levels in the saliva. This can be sugary/ acidic foods and liquids. The reasoning behind this is that an increase in acidity of saliva can induce demineralization and therefore compromising the tooth structure to abrasive factors such as tooth brushing or normal wear from mastication. When the tooth structure is compromised, this is where the mineral content of the saliva can create shallow depressions in the enamel and thus, when brushed can cause irreparable damage on tooth surface. The dental abrasion process can be further stimulated and accelerated through the effects of dental Acid erosion.

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.

Teeth affected with MIH are at an increased risk of acquiring dental caries. This is because the properties of the enamel are altered by increased porosity and decreased hardness. Essentially, the balance between mineralisation and demineralisation shifts to favour demineralisation of enamel, giving the tooth less resilience in structure, thereby making it vulnerable to caries.

The poor structural properties of the enamel in teeth with MIH also increase the likelihood of cavitation of any lesions, thereby causing the lesion to progress at a faster rate. Progression of the carious lesion is also more rapid in teeth with MIH as patients may experience tooth sensitivity while carrying out oral hygiene, causing them to avoid doing so and consequentially accelerating the decay.

Dental caries is an infectious disease caused primarily by "Streptococcus mutans", characterized by acid demineralization of the enamel, which can progress to further breakdown of the more organic, inner dental tissue (dentin). Everybody is susceptible to caries but the probability of development depends on the patient’s individual disease indicators, risk factors and preventive factors. Factors that are considered high-risk for developing carious lesions on the teeth include:

- Low fluoride exposure

- Time, length, and frequency of sugar consumption

- Quality of tooth cleaning

- Fluctuations in salivary flow rates and composition

- Behavior of the individual

- Socioeconomic status of the individual

- Quality and composition of biofilms

Organic acids released from dental plaque lead to demineralization of the adjacent tooth surface, and consequently to dental caries. Saliva is also unable to penetrate the build-up of plaque and thus cannot act to neutralize the acid produced by the bacteria and remineralize the tooth surface.

Crowding of the teeth is treated with orthodontics, often with tooth extraction, clear aligners, or dental braces, followed by growth modification in children or jaw surgery (orthognathic surgery) in adults. Surgery may be required on rare occasions. This may include surgical reshaping to lengthen or shorten the jaw (orthognathic surgery). Wires, plates, or screws may be used to secure the jaw bone, in a manner similar to the surgical stabilization of jaw fractures. Very few people have "perfect" alignment of their teeth. However, most problems are very minor and do not require treatment.

Edentulism affects approximately 158 million people globally as of 2010 (2.3% of the population). It is more common in women at 2.7% compared to the male rate of 1.9%.

A cross-sectional analysis of data from the Survey of Health, Ageing and Retirement in Europe (SHARE) from 14 European countries (Austria, Belgium, Czech Republic, Denmark, Estonia, France, Germany, Italy, Luxembourg, the Netherlands, Slovenia, Spain, Sweden, and Switzerland) and Israel showed substantial variation in the age-standardized mean numbers of natural teeth amongst people aged 50 years and older, ranging from 14.3 teeth (Estonia) to 24.5 teeth (Sweden). The oral health goal of retaining at least 20 teeth at age 80 years was achieved by 25% of the population or less in most countries. A target concerning edentulism (≤15% in population aged 65–74 years) was reached in Sweden, Switzerland, Denmark, France, and Germany. Tooth replacement practices varied especially for a number of up to five missing teeth which were more likely to be replaced in Austria, Germany, Luxembourg, and Switzerland than in Israel, Denmark, Estonia, Spain, and Sweden.

The prevalence of Kennedy Class III partial denture was predominant among younger population of 21-30 year and 31–40 years, whereas in group III between 41 and 50 years Class I was predominant. It can be stated that the need for prosthodontics care is expected to increase with age, and hence, more efforts should be made for improving dental education and motivation among patients.

Edentulism occurs more often in people from the lower end of the socioeconomic scale.

There are certain diseases and disorders affecting teeth that may leave an individual at a greater risk for cavities.

Molar incisor hypomineralization, which seems to be increasingly common. While the cause is unknown it is thought to be a combination of genetic and environmental factors. Possible contributing factors that have been investigated include systemic factors such as high levels of dioxins or polychlorinated biphenyl (PCB) in the mother’s milk, premature birth and oxygen deprivation at birth, and certain disorders during the child’s first 3 years such as such as mumps, diphtheria, scarlet fever, measles, hypoparathyroidism, malnutrition, malabsorption, hypovitaminosis D, chronic respiratory diseases, or undiagnosed and untreated coeliac disease, which usually presents with mild or absent gastrointestinal symptoms.

Amelogenesis imperfecta, which occurs in between 1 in 718 and 1 in 14,000 individuals, is a disease in which the enamel does not fully form or forms in insufficient amounts and can fall off a tooth. In both cases, teeth may be left more vulnerable to decay because the enamel is not able to protect the tooth.

In most people, disorders or diseases affecting teeth are not the primary cause of dental caries. Approximately 96% of tooth enamel is composed of minerals. These minerals, especially hydroxyapatite, will become soluble when exposed to acidic environments. Enamel begins to demineralize at a pH of 5.5. Dentin and cementum are more susceptible to caries than enamel because they have lower mineral content. Thus, when root surfaces of teeth are exposed from gingival recession or periodontal disease, caries can develop more readily. Even in a healthy oral environment, however, the tooth is susceptible to dental caries.

The evidence for linking malocclusion and/or crowding to dental caries is weak; however, the anatomy of teeth may affect the likelihood of caries formation. Where the deep developmental grooves of teeth are more numerous and exaggerated, pit and fissure caries is more likely to develop (see next section). Also, caries is more likely to develop when food is trapped between teeth.

Dental attrition is tooth wear caused by tooth to tooth contact. Well-defined wear facets appear on tooth cusps or ridges. This can be caused by several factors, including parafunctional habits such as bruxism or clenching, developmental defects, hard or rough-textured diet, and absence of posterior teeth support. If the natural teeth oppose or occlude with porcelain restorations, then accelerated attrition of the natural teeth may result. Similarly, when an edge to edge class III incisal relationship is present dental attrition can occur. The underlying cause of attrition may be related to the temporomandibular joint as a disruption or dysfunction of the joint can result in compromised function and complications such as bruxism and clenching of the jaw may arise

The etiology of dental attrition is multifactorial one of the most common causes of attrition is bruxism, one of the major causes being the use of MDMA (ecstasy) and various other related entactogenic drugs. Bruxism is the para-functional movement of the mandible, occurring during the day or night. It can be associated with presence of audible sound when clenching or grinding the teeth. This is usually reported by parents or partners if the grinding occurs during sleep. In some cases, dental erosion is also associated with severe dental attrition. Dental erosion is tooth surface loss caused by extrinsic or intrinsic forms of acid. Extrinsic erosion is due to a highly acidic diet, while intrinsic erosion is caused by regurgitation of gastric acids. Erosion softens the dental hard tissues making them more susceptible to attrition. Thus, if erosion and bruxism both exist, surface loss due to attrition is faster. Severe attrition in young patients is usually associated with erosive factors in their diets. The different physiological processes of tooth wear (abrasion, attrition and erosion) usually occur simultaneously and rarely work individually. Therefore, it is important to understand these tooth wear processes and their interactions to determine causes of tooth surface loss. Demineralization of the tooth surface due to acids can cause occlusal erosion as well as attrition. Wedge-shaped cervical lesions are commonly found in association with occlusal erosion and attrition.

Tooth wear is typically seen in the elderly and can be referred to as a natural aging process. Attrition, abrasion, erosion or a combination of these factors are the main reasons for tooth wear in elderly people who retain their natural teeth. This tooth wear can be pathological or physiological. The number of teeth with incisal or occlusal wear increases with age. Attrition occurs in 1 in 3 adolescents.

In addition to other occlusal factors, independent variables such as male gender, bruxism, and loss of molar occlusal contact, edge-to-edge relation of incisors, unilateral buccolingual cusp-to-cusp relation, and unemployment have been identified in affecting occlusal wear. Similarly, anterior cross-bite, unilateral posterior cross-bite, and anterior crowding have been found to be protective factors for high occlusal wear levels.

Extrinsic discolorations are common and have many different causes. The same range of factors are capable of staining the surface of restorations (e.g., composite fillings, porcelain crowns). Some extrinsic discolorations that are allowed to remain for a long time may become intrinsic.

- Dental plaque: Although usually virtually invisible on the tooth surface, plaque may become stained by chromogenic bacteria such as "Actinomyces" species.

- Calculus: Neglected plaque eventually calcifies, and leads to formation of a hard deposit on the teeth, especially around the gumline. The color of calculus varies, and may be grey, yellow, black or brown.

- Tobacco: Tar in smoke from tobacco products (and also smokeless tobacco products) tends to form a yellow-brown-black stain around the necks of the teeth above the gumline.

- Betel chewing.

- Certain foods and drinks. Foods, such as vegetables, that are rich with carotenoids or xanthonoids can stain teeth. Ingesting colored liquids like sports drinks, cola, coffee, tea and red wine can discolor teeth.

- Certain topical medications.

- Chlorhexidine (antiseptic mouthwash) binds to tannins, meaning that prolonged use in persons who consume coffee, tea or red wine is associated with extrinsic staining (i.e., removable staining) of teeth.

- Cetylpyridinium chloride, which is found in many antimicrobial mouthwashes, can result in staining due to dead bacterial residue.

- Metallic compounds. Exposure to such metallic compounds may be in the form of medication or other environmental exposure. Examples include iron (black stain), iodine (black), copper (green), nickel (green) and cadmium (yellow-brown).

- Antibiotics. Tetracycline and its derivatives are capable of intrinsic discoloration (discussed below). However other antibiotics may form insoluble complexes with calcium, iron and other elements that cause extrinsic staining.