Alterations in the Number of Teeth

There are a number of developmental alterations that may occur which influence the number of teeth that are present. Several different terms are used to describe the absence or presence of teeth.^5,8,9 Anodontia is the proper term for the total lack of tooth development involving the entire dentition.⁵ This is uncommon, particularly in the primary dentition. Several other terms are used to define missing teeth such as hypodontia, one or more missing teeth, and oligodontia, six or more missing teeth excluding the third molars.⁵ In contrast, hyperdontia is the development of more than the usual complement of teeth.⁵ These extra teeth are sometimes referred to as supernumerary teeth.^5,8,9

Hypodontia

While rare in the primary dentition, hypodontia is not uncommon in the permanent dentition. In fact, it is one of the most common developmental abnormalities affecting nearly 20% of individuals with a slight female predominance.⁵ The most frequently missing teeth are the third molars, followed by the second premolars (Figure 20), the maxillary lateral incisors (Figure 22), and mandibular central incisors (Figure 21)^9,10 The maxillary central incisors, the mandibular first molars, and canines are the least likely teeth to be absent.⁵

Figure 20.

Figure 20.

Periapical radiograph of congenitally missing mandibular right premolar tooth #29 with retained primary molar T.

Figure 21.

Figure 21.

Periapical radiograph of congenitally missing mandibular central incisor teeth #24 and #25.

Figure 22

Figure 22

Panoramic radiograph of congenitally missing maxillary lateral incisor teeth #7 and #10.

In instances in which multiple teeth are missing, especially key teeth like maxillary central incisors or the first molars, a hereditary condition known as ectodermal dysplasia should be considered.^9,10 In this entity, the teeth that are present have an abnormal crown shape (Figure 23).⁹ Clinically, dermal adnexal structures like hair, eyebrows and eyelashes are also affected.^5,10

Figure 23.
Cropped panoramic radiograph of child patient with ectodermal dysplasia demonstrating multiple missing key teeth.

Figure 23.
Cropped panoramic radiograph of child patient with ectodermal dysplasia demonstrating multiple missing key teeth.

Image courtesy of Dr. Géza T. Terézhalmy.

Hyperdontia

Extra or supernumerary teeth usually involve a single tooth in the permanent dentition within the maxilla, particularly in the anterior segment.⁵ Other common sites for supernumerary teeth include the maxillary molar area, and the mandibular molar, premolar, canine, and lateral incisor areas.^5,8,9 A supernumerary tooth in the anterior maxilla is a mesiodens (Figure 24A and 24B), while a fourth molar tooth is a distodens or distomolar (Figure 25), and an extra tooth in the premolar area is a peridens (Figure 26).^5,8-10 The term paramolar is used for a posterior extra tooth positioned buccally or lingually to a molar tooth.^9,10 Supernumerary teeth can be of normal size and shape or abnormally shaped and diminished in size. (Figures 25, 27)⁵ The latter type can display various shapes including conical, barrel-like or a petite version of a molar or premolar tooth.⁵ These teeth can be erupted or unerupted.

Figures 24A and 24B.

Figures 24A and 24B.

Periapical radiographs of single inverted (A) and multiple mesiodens (B).

Figure 25.

Figure 25.

Periapical radiograph of a maxillary distomolar.

Figure 26.

Figure 26.

Cropped panoramic radiograph of supernumerary peridens.

Figure 27.

Figure 27.

Cropped panoramic radiograph of supernumerary 4th molar teeth of normal tooth size.

It is possible that supernumerary teeth will present in multiple manners. When multiple extra teeth occur, the most common location is in the mandibular premolar region (Figure 26), but molar and anterior areas also can be involved (Figure 24B, 26, 28).⁵

Figure 28.

Figure 28.

Full mouth radiographic survey of multiple supernumerary teeth. Note the size, shape, and location of the numerous supernumerary teeth present.