Anodontia, Hypodontia
Definition
• Refers to a defect characterized by congenital absence from the dental arch of some teeth (hypodontia) or all of them (anodontia) (Figs. 1.16, 1.17). Severe hypodontia is also termed oligodontia.
• Anodontia and hypodontia may affect both the primary and permanent dentition. Pseudohypodontia is characterized by the absence of teeth from the dental arch due to impaction, delay of eruption, or early exfoliation.
Etiology
• The defect results from dental lamina obstruction or disruption during the early stages of embryogenesis, caused by abnormal activity of local, systemic, and genetic factors. Genetic factors, usually multigenic, have been strongly implicated.
• Hypodontia and anodontia are frequently associated with more than 70 genetic disorders and syndromes, primarily with those characterized by ectodermal involvement, such as the ectodermal dysplasias and the following syndromes: Rieger’s, incontinentia pigmenti, Robinson’s, Seckel’s, orofaciodigital, focal dermal hypoplasia, Hallermann-Streiff, oculoden-todigital, Russell-Silver, chondroectodermal dysplasia, frontometaphyseal dysplasia, craniofacial dysplasia, and others. It is also a frequent finding in patients with cleft lip and cleft palate.
Occurrence in children
• Anodontia: rare.
• Hypodontia of primary teeth: 0.1–0.7%.
• Hypodontia of permanent teeth, excluding third molars: 3.0–7.5%.
• In hypodontia, two or more teeth are involved in 50% of the cases.
• Considerable ethnic variation.
Localization
• Third molars, upper lateral incisors, second premolars.
Clinical features
• Missing teeth, spacing, and occasionally abnormal location in the remaining teeth.
Complications
• Aesthetic and mastication problems.
Treatment
• Orthodontic and prosthetic treatment, implants.
Fig. 1.15 Ectopic location and eruption of a lower lateral incisor
Fig. 1.16 Anodontia in a patient with hypohidrotic ectodermal dysplasia
Fig. 1.17 Hypodontia in a patient with hypohidrotic ectodermal dysplasia
Supernumerary Teeth
Definition
• Refers to a condition characterized by the presence of supernumerary teeth in the dental arch. These teeth may be either of normal morphology (supplemental) or, more frequently, are anomalous, with irregular size and shape (accessory).
Etiology
• The defect results from continuing abnormal activity of the dental lamina, which leads to the formation of supernumerary tooth buds. The etiology of the defect is multifactorial, although there is a strong genetic background under the control of several different loci.
• Frequent finding in patients with Gardner’s syndrome, cleidocranial dysplasia, Hallermann-Streiff syndrome, and orofaciodigital syndrome type I.
Occurrence in children
• Primary dentition 0.3–0.6%, permanent dentition 1.0–3.5%.
• More frequently observed in the maxilla, by a ratio of 9:1.
• Supernumeraries in the primary dentition may be followed by supernumeraries in the permanent dentition in 30–50% of cases.
• Males more frequently affected than females (2:1).
• Ethnic variation.
Localization
• Near the middle line in the incisal region of the maxilla (mesiodens).
• Beyond the third molar (distomolars) or in the molar area (paramolars).
Clinical features
• Supplemental or conical, tuberculate, and odontoma-like shape (Figs. 1.18, 1.19).
• 75% of these teeth remain impacted in the bone, and are diagnosed only radiographically.
Complications
• In the case of impacted supernumerary teeth, there is an increased possibility of inhibited or delayed eruption of adjacent teeth. If the supernumeraries erupt in the dental arch, they usually cause functional and aesthetic problems.
Treatment
• Removal of the supernumerary teeth and orthodontic treatment of the affected area.
Defects of Eruption and Exfoliation
These defects result from the action of various etiological factors during the eruption stage of the dental development.
Eruption Defects
Early eruption
Definition
• This refers to accelerated eruption of either the primary or permanent teeth. In addition, the term "natal teeth" refers to primary teeth that have already erupted at birth (Fig. 1.20), whereas neonatal teeth are teeth erupting within one month after birth. These two defects usually represent regular primary teeth with imperfect roots, although sometimes they are supernumerary.
Etiology
• Multifactorial, implicating local, systemic, and strong genetic factors. Early eruption of primary and permanent teeth can be found in the following syndromes: pycnodysostosis, hemihypertrophy, holoprosencephaly, Sotos, Klippel–Trenaunay–Weber, Sturge–Weber.
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