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 person experiencing caries may not be aware of the disease. The earliest sign of a new carious lesion is the appearance of a chalky white spot on the surface of the tooth, indicating an area of demineralization of enamel. This is referred to as a white spot lesion, an incipient carious lesion or a "microcavity". As the lesion continues to demineralize, it can turn brown but will eventually turn into a cavitation ("cavity"). Before the cavity forms, the process is reversible, but once a cavity forms, the lost tooth structure cannot be regenerated.

A lesion that appears dark brown and shiny suggests dental caries were once present but the demineralization process has stopped, leaving a stain. Active decay is lighter in color and dull in appearance.

As the enamel and dentin are destroyed, the cavity becomes more noticeable. The affected areas of the tooth change color and become soft to the touch. Once the decay passes through enamel, the dentinal tubules, which have passages to the nerve of the tooth, become exposed, resulting in pain that can be transient, temporarily worsening with exposure to heat, cold, or sweet foods and drinks. A tooth weakened by extensive internal decay can sometimes suddenly fracture under normal chewing forces. When the decay has progressed enough to allow the bacteria to overwhelm the pulp tissue in the center of the tooth, a toothache can result and the pain will become more constant. Death of the pulp tissue and infection are common consequences. The tooth will no longer be sensitive to hot or cold, but can be very tender to pressure.

Dental caries can also cause bad breath and foul tastes. In highly progressed cases, an infection can spread from the tooth to the surrounding soft tissues. Complications such as cavernous sinus thrombosis and Ludwig angina can be life-threatening.

Attrition occurs as a result of opposing tooth surfaces contacting. The contact can affect cuspal, incisal and proximal surface areas.

Indications of attrition can include:

- Loss of tooth anatomy: This results in loss of tooth characteristics including rounding or sharpening of incisal edges, loss of cusps and fracturing of teeth. Enamel of molar teeth may appear thin and flat. When in occlusion the teeth may appear the same height which is particularly apparent for anterior teeth.

- Sensitivity or pain: Attrition may be entirely asymptomatic, or there may be dentin hypersensitivity secondary to loss of the enamel layer, or tenderness of the periodontal ligament caused by occlusal trauma.

- Tooth discolouration: A yellow appearance of the tooth surface may be due to the enamel being worn away, exposing the darker yellower dentin layer underneath.

- Altered occlusion due to decreasing vertical height, or occlusal vertical dimension.

- Compromised periodontal support can result in tooth mobility and drifting of teeth

- Loss in posterior occlusal stability

- Mechanical failure of restorations

Early childhood caries (ECC), also known as "baby bottle caries," "baby bottle tooth decay" or "bottle rot," is a pattern of decay found in young children with their deciduous (baby) teeth. The teeth most likely affected are the maxillary anterior teeth, but all teeth can be affected. The name for this type of caries comes from the fact that the decay usually is a result of allowing children to fall asleep with sweetened liquids in their bottles or feeding children sweetened liquids multiple times during the day.

Another pattern of decay is "rampant caries", which signifies advanced or severe decay on multiple surfaces of many teeth. Rampant caries may be seen in individuals with xerostomia, poor oral hygiene, stimulant use (due to drug-induced dry mouth), and/or large sugar intake. If rampant caries is a result of previous radiation to the head and neck, it may be described as radiation-induced caries. Problems can also be caused by the self-destruction of roots and whole tooth resorption when new teeth erupt or later from unknown causes.

Children at 6–12 months are at increased risk of developing dental caries. For other kids aged 12–18 months, dental caries develop on primary teeth and approximately twice yearly for permanent 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.

Clinical signs of TRs are often minimal since the discomfort can be minor. However, some authors have described discomfort while chewing, anorexia, dehydration, weight loss, and tooth fracture. The lower third premolar is the most commonly affected tooth.

Dental fluorosis (also termed mottled enamel) is an extremely common disorder, characterized by hypomineralization of tooth enamel caused by ingestion of excessive fluoride during enamel formation.

It appears as a range of visual changes in enamel causing degrees of intrinsic tooth discoloration, and, in some cases, physical damage to the teeth. The severity of the condition is dependent on the dose, duration, and age of the individual during the exposure. The "very mild" (and most common) form of fluorosis, is characterized by small, opaque, "paper" white areas scattered irregularly over the tooth, covering less than 25% of the tooth surface. In the "mild" form of the disease, these mottled patches can involve up to half of the surface area of the teeth. When fluorosis is moderate, all of the surfaces of the teeth are mottled and teeth may be ground down and brown stains frequently "disfigure" the teeth. Severe fluorosis is characterized by brown discoloration and discrete or confluent pitting; brown stains are widespread and teeth often present a corroded-looking appearance.

People with fluorosis are relatively resistant to dental caries (tooth decay caused by bacteria), although they may be of cosmetic concern. In moderate to severe fluorosis, teeth are physically damaged.

The two main classification systems are described below. Others include the tooth surface fluorosis index (Horowitz et al. 1984), which combines Deans index and the TF index; and the fluorosis risk index (Pendrys 1990), which is intended to define the time at which fluoride exposure occurs, and relates fluorosis risk with tooth development stage.

Opacities due to MIH can be quite visible especially on anterior teeth which could present as a problem aesthetically. Patients frequently claim aesthetic discomfort when anterior teeth are involved. The discoloured appearance of the anterior teeth could also have negative effects on a child’s psychological development and self-esteem.

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.

Dental attrition is a type of tooth wear caused by tooth-to-tooth contact, resulting in loss of tooth tissue, usually starting at the incisal or occlusal surfaces. Tooth wear is a physiological process and is commonly seen as a normal part of aging. Advanced and excessive wear and tooth surface loss can be defined as pathological in nature, requiring intervention by a dental practitioner. The pathological wear of the tooth surface can be caused by bruxism, which is clenching and grinding of the teeth. If the attrition is severe, the enamel can be completely worn away leaving underlying dentin exposed, resulting in an increased risk of dental caries and dentin hypersensitivity. It is best to identify pathological attrition at an early stage to prevent unnecessary loss of tooth structure as enamel does not regenerate.

Abrasion is a pathological, non-carious tooth loss that most commonly affects the premolars and canines. Abrasion frequently presents at the cemento-enamel junction and can be caused by many contributing factors, all with the ability to affect the tooth surface in varying degrees.

Sources of abrasion may arise from oral hygiene habits such as toothbrushes, toothpicks, floss, and dental appliance or may arise from other habits such as nail biting, chewing tobacco or another object. Abrasion can also occur from the type of dentifrice being utilized as some have more abrasive qualities such as whitening toothpastes.

The appearance may vary depending on the aetiology of abrasion, however most commonly presents in a V-shaped caused by excessive lateral pressure whilst tooth-brushing. The surface is shiny rather than carious, and sometimes the ridge is deep enough to see the pulp chamber within the tooth itself.

In order for successful treatment of abrasion to occur, the aetiology first needs to be identified and ceased, e.g. overzealous brushing. Once this has occurred subsequent treatment may involve the changes in oral hygiene or toothpaste, application of fluoride to reduce sensitivity or the placement of a restoration to aid in reducing the progression of further tooth loss.

Tooth wear (also termed non-carious tooth substance loss) refers to loss of tooth substance by means other than dental caries or dental trauma. Tooth wear is a very common condition that occurs in approximately 97% of the population. This is a normal physiological process occurring throughout life, but accelerated tooth wear can become a problem.

Tooth wear is majorly the result of three processes; attrition, abrasion and erosion. These forms of tooth wear can further lead to a condition known as abfraction, where by tooth tissue is 'fractured' due to stress lesions caused by extrinsic forces on the enamel. Tooth wear is a complex, multi-factorial problem and there is difficulty identifying a single causative factor. However, tooth wear is often a combination of the above processes. Many clinicians therefore make diagnoses such as "tooth wear with a major element of attrition", or "tooth wear with a major element of erosion" to reflect this. This makes the diagnosis and management difficult. Therefore, it is important to distinguish between these various types of tooth wear, provide an insight into diagnosis, risk factors, and causative factors, in order to implement appropriate interventions.

Multiple indices have been developed in order to assess and record the degree of tooth wear, the earliest was that by Paul Broca. In 1984, Smith and Knight developed the tooth wear index (TWI) where four visible surfaces (buccal, cervical, lingual, occlusal-incisal) of all teeth present are scored for wear, regardless of the cause.

Early Childhood Caries (ECC), formerly known as nursing bottle caries, baby bottle tooth decay, night bottle mouth and night bottle caries, is a disease that affects teeth in children aged between birth and 71 months. ECC is characterized by the presence of 1 or more decayed (noncavitated or cavitated lesions), missing (due to caries), or filled tooth surfaces in any primary tooth. ECC has been shown to be a very common, transmissible bacterial infection, usually passed from the primary caregiver to the child. The main bacteria responsible for dental caries is Streptococcus mutans (S. Mutans) and Lactobacillus. There is also evidence that supports that those who are in lower socioeconomic populations are at greater risk of developing ECC.

Early childhood caries (ECC) is a multi-factorial disease, referring to various risk factors that inter-relate to increase risk of developing the disease. These risk factors include but not limited to, cariogenic bacteria, diet practices and socioeconomic factors. Normally after 6 months, deciduous teeth begin to erupt means, they are susceptible to tooth decay or dental caries. In some unfortunate cases, infants and young children have experienced severe tooth decay called ECC. This can result in the child experiencing severe pain, extensive dental restorations or extractions. The good news is that ECC is preventable, however, still remains a large burden particularly towards health care expenditure.

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.

Feline Tooth Resorption (TR) is a syndrome in cats characterized by resorption of the tooth by odontoclasts, cells similar to osteoclasts. TR has also been called "feline odontoclastic resorption lesion" (FORL), neck lesion, cervical neck lesion, cervical line erosion, feline subgingival resorptive lesion, feline caries, or feline cavity. It is one of the most common diseases of domestic cats, affecting up to two-thirds. TRs have been seen more recently in the history of feline medicine due to the advancing ages of cats, but 800-year-old cat skeletons have shown evidence of this disease. Purebred cats, especially Siamese and Persians, may be more susceptible.

TRs clinically appear as erosions of the surface of the tooth at the gingival border. They are often covered with calculus or gingival tissue. It is a progressive disease, usually starting with loss of cementum and dentin and leading to penetration of the pulp cavity. Resorption continues up the dentinal tubules into the tooth crown. The enamel is also resorbed or undermined to the point of tooth fracture. Resorbed cementum and dentin is replaced with bone-like tissue.

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

Tooth discoloration (also termed tooth staining) is abnormal tooth color, hue or translucency. External discoloration is accumulation of stains on the tooth surface. Internal discoloration is due to absorption of pigment particles into tooth structure. Sometimes there are several different co-existent factors responsible for discoloration.

Internal resorption may sometimes follow dental trauma (although in other cases it appears unrelated). This is where the dentin is resorbed and replaced instead by hyperplastic, vascular pulp tissue. As this process starts to approach the external surface of the tooth, a pink hue of this replacement pulp tissue may become visible through the remaining overlying tooth substance. This appearance is sometimes termed "pink tooth of Mummery".

Dental plaque is a biofilm or mass of bacteria that grows on surfaces within the mouth. It is a sticky colorless deposit at first, but when it forms tartar, it is often brown or pale yellow. It is commonly found between the teeth, on the front of teeth, behind teeth, on chewing surfaces, along the gumline, or below the gumline cervical margins. Dental plaque is also known as microbial plaque, oral biofilm, dental biofilm, dental plaque biofilm or bacterial plaque biofilm.

Progression and build-up of dental plaque can give rise to tooth decay – the localised destruction of the tissues of the tooth by acid produced from the bacterial degradation of fermentable sugar – and periodontal problems such as gingivitis and periodontitis; hence it is important to disrupt the mass of bacteria and remove it. Plaque control and removal can be achieved with correct daily or twice-daily tooth brushing and use of interdental aids such as dental floss and interdental brushes.

Oral hygiene is important as dental biofilms may become acidic causing demineralization of the teeth (also known as dental caries) or harden into dental calculus (also known as tartar). Calculus cannot be removed through tooth brushing or with interdental aids, but only through professional cleaning.

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.

When an individual's mouth is at rest, the teeth in the opposing jaws are nearly touching; there is what is referred to as a "freeway space" of roughly 2–3 mm. However, this distance is partially maintained as a result of the teeth limiting any further closure past the point of maximum intercuspation. When there are no teeth present in the mouth, the natural vertical dimension of occlusion is lost and the mouth has a tendency to overclose. This causes the cheeks to exhibit a "sunken-in" appearance and wrinkle lines to form at the commissures. Additionally, the anterior teeth, when present, serve to properly support the lips and provide for certain aesthetic features, such as an acute nasiolabial angle.

Loss of muscle tone and skin elasticity due to old age, when most individuals begin to experience edentulism, tend to further exacerbate this condition.

The tongue, which consists of a very dynamic group of muscles, tends to fill the space it is allowed, and in the absence of teeth, will broaden out. This makes it initially difficult to fabricate both complete dentures and removable partial dentures for patients exhibiting complete and partial edentulism, respectively; however, once the space is "taken back" by the prosthetic teeth, the tongue will return to a narrower body.

Attrition is loss of tooth substance caused by physical tooth-to-tooth contact. The word attrition is derived from the Latin verb "attritium", which refers to the action of rubbing against something. Attrition mostly causes wear of the incisal and occlusal surfaces of the teeth. Attrition has been associated with masticatory force and parafunctional activity such as bruxism. A degree of attrition is normal, especially in elderly individuals.