Hypodontia

Hypodontia means that there are fewer than the normal complement of teeth in the dentition. It may be an isolated single tooth missing with no known etiology or it could be associated with a syndrome due to an event occurring before tooth germ formation.

The incidence of hypodontia is <1% in the primary dentition incidence and is approximately 2.5-3.5% in the secondary dentition.

The secondary teeth most frequently missing are the

third molars

second premolars

maxillary lateral incisors

The image above is an example of an abnormality of numbers (congenitally missing permanent maxillary left lateral incisor) and an abnormality of shape. The permanent maxillary right lateral incisor is a peg lateral incisor (courtesy of Drs. Steve Ahing and John Perry, University of Manitoba)

This is an example of a retained primary molar (primary mandibular right second molar) and a single congenitally missing tooth (permanent mandibular right second premolar).

The image on the left is another example of an abnormality of numbers (congenitally missing permanent maxillary right lateral incisor) and an abnormality of shape. The permanent maxillary left lateral incisor is a peg lateral incisor (courtesy of Drs. Steve Ahing and John Perry, University of Manitoba).

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The panoramic radiograph above illustrates a case of a congenitally missing permanent maxillary right lateral incisor. The permanent mandibular right third molar had been previously extracted (courtesy of Dr. BM Cleghorn, Dalhousie University).

The bitewing radiograph on the left is of the patient's posterior right and illustrates the posterior teeth in quadrants 1 and 4. The primary maxillary right second molar is retained and the permanent maxillary right second premolar is congenitally missing (courtesy of Dr. BM Cleghorn, Dalhousie University).

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The panoramic radiograph above illustrates a congenitally missing permanent maxillary right lateral incisor (arrow labeled 1.). The arrow labeled 2. is an example of an abnormality in shape as the permanent maxillary left lateral incisor is a peg lateral (courtesy of Dr. BM Cleghorn, Dalhousie University).

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This panoramic radiograph is suggestive of a patient with ectodermal dysplasia. The clinical findings were inconclusive and confirmation of the diagnosis is awaiting genetic testing. Congenitally missing teeth include the permanent maxillary right second premolar, permanent mandibular left first and second premolars and the permanent mandibular right second premolar. Ankylosed primary teeth are present as well as an anomalous permanent maxillary left first premolar. The full case report labeled Case RT is included later in this unit (courtesy of Dr. BM Cleghorn, Dalhousie University).

The periapical radiograph on the left illustrates a single congenitally missing tooth. The arrow points to the congenitally missing permanent mandibular left second premolar. Above the arrow is the retained primary mandibular left second molar with partially resorbed roots (courtesy of Drs. Steve Ahing and John Perry, University of Manitoba).

The illustration on the left is an example of induced anodontia. True anodontia is rare. This patient has been rendered edentulous as a result of caries or periodontal disease (courtesy of Drs. Steve Ahing and John Perry, University of Manitoba).

The patient on the left only has four permanent canines remaining. Each of these teeth has been restored with full crowns. This condition is described as partial anodontia (courtesy of Drs. Steve Ahing and John Perry, University of Manitoba).

Oligodontia

Oligodontia is considered a subset of hypodontia and is due to an event that occurs before tooth germ formation. 6 or more teeth are missing. Oligodontia is usually associated with a syndrome.

This panoramic radiograph is an example of oligodontia (6 missing teeth). Also present is a peg lateral incisor.

1. congenitally missing permanent maxillary right second premolar.

2. congenitally missing permanent maxillary right lateral incisor.

3. peg lateral incisor.

4. congenitally missing permanent maxillary left first premolar.

5. congenitally missing permanent maxillary left second premolar.

6. congenitally missing permanent mandibular left second premolar.

7. congenitally missing permanent mandibular left first premolar.

8. congenitally missing permanent mandibular right second premolar.

(courtesy of Dr. BM Cleghorn, Dalhousie University)

The image on the left is an example of ectodermal dysplasia. The only teeth present are anomalous permanent mandibular canines. Ectodermal dysplasia is comprised of a group of inherited conditions that affects ectodermal structures (such as skin, teeth, hair, salivary and sweat glands). This condition can result in multiple missing teeth (hypodontia or oligodontia). This is an example of oligodontia. More than six teeth are missing and the remaining ones are abnormally formed. Therefore, in addition, this is also an example of an abnormality of shape (courtesy of Drs. Steve Ahing and John Perry, University of Manitoba).

Hyperdontia

The panoramic radiograph above is an example of a patient with cleidocranial dysplasia. This is an autosomal dominant genetic disorder that affects the face, the skull and the clavicles. The ossification of the clavicles, cranium and other long bones is defective. The clavicular defects can result in the patient being able to touch their shoulders. The intraoral features include multiple unerupted supernumerary teeth and delayed eruption of the permanent teeth (courtesy of Dr. BM Cleghorn, Dalhousie University).

The occlusal view of the mandibular arch pictured on the left illustrates a slightly crowded arch. Close examination reveals a supernumerary mandibular central incisor. This is not a common anomaly and illustrates the importance of careful identification and charting in dentistry (courtesy of Dr. BM Cleghorn, Dalhousie University).

The periapical radiograph of the 4th quadrant to the left illustrates a supernumerary mandibular right premolar.

1. permanent mandibular right second premolar.

2. supernumerary mandibular right second premolar.

3. permanent mandibular right first premolar.

(courtesy of Dr. BM Cleghorn, Dalhousie University)

Many mesiodens remain unerupted. This is an example of a fully erupted mesiodens lingual to the permanent maxillary left central incisor (courtesy of Drs. Steve Ahing and John Perry, University of Manitoba).

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