Developmental Disturbances of the Teeth, Anomalies of Number

Etiology

Anodontia is the complete agenesis of the dentition. Hypodontia is defined as the agenesis of fewer than six teeth failing to develop, and oligodontia is defined as six or more teeth failing to develop. Hyperdontia is defined as supernumerary teeth or teeth that appear in addition to the regular number of teeth. 

Although anodontia, hypodontia, and oligodontia have the same etiology, the phenotypic appearance of each depends on the severity of the underlying etiology. The suggested etiology for the failure of teeth to develop has been linked to 15 causative genes in non-syndromic cases.[1] The term syndromic hypodontia is used when the dental agenesis is associated with a syndrome, as seen in ectodermal dysplasia.[2][3] Orofacial clefting has been associated with either the displacement or failure of the development of one or more teeth.[4]

The etiology of hyperdontia is not fully understood, and the condition has been attributed to multifactorial etiologies. When multiple unerupted supernumerary teeth are noted, syndromes such as cleidocranial dysplasia, a rare congenital skeletal dysplasia with an autosomal dominant inheritance pattern, should be considered.[5] Other syndromes associated with multiple supernumerary teeth are cleft lip/palate, trichorhinophalangeal syndrome, and Gardner syndrome.[6]

Epidemiology

Hypodontia and oligodontia are typically grouped as one universal term, “hypodontia,” which is further defined based on its severity. Hypodontia is the most prevalent dentofacial malformation in humans.[7] There is a noted association between hypodontia in the deciduous or primary dentition and the corresponding permanent dentition. If a patient is missing a primary tooth, they will likely be missing its corresponding permanent successor tooth.[8] 

Regarding deciduous dentition, the prevalence of hypodontia is less than 1% in White race populations compared to a much higher frequency in Japanese populations.[9] Depending on the population in question, the permanent dentition shows a higher frequency of hypodontia with an incidence of 1.6 to 36.5%.[7] There is no gender predilection for hypodontia occurring in the deciduous dentition; however, there is a slight female predilection seen in the permanent dentition.[10][11]

Hyperdontia (supernumerary teeth) remains a relatively common dentofacial anomaly. A study by Brooks et al. discovered supernumerary teeth present in 0.8% of primary dentitions and 2.1% of permanent dentitions.[12] There is a slight male predilection for hyperdontia, with a higher incidence noted in Hispanic populations.[13] Supernumerary teeth are most common in the anterior maxillary midline region, with the descriptive name “mesiodens.”[14] Multiple supernumerary teeth are rare in patients without syndromes or associated diseases.[6]

Pathophysiology

Dental agenesis may arise from intrinsic and/or extrinsic factors. In non-syndromic cases, 7 discreet genes (AXIN2, EDA, LRP6, MSX1, PAX9, WNT10A, and WNT10B) have been identified in association with dental agenesis. These genes displaying several mutations were detected in 91.9% of all molecular analyses in patients. The majority of cases showed a mutation in the PAX9 and WNT10A genes.[1] Of note, the WNT/ß-catenin signaling pathway is responsible for many phases of embryonic development. The WNT/ß-catenin signaling pathway would be of great significance during stages of tooth development.[15] Mutations in the WNT10B cause insufficient WNT signaling, limiting odontoblastic differentiation and angiogenesis of dental pulp cells resulting in insufficient tooth structure and/or dental agenesis.[16] The severity and prevalence of the mutations determine the number of teeth missing.

There are numerous theories to the development of hyperdontia or supernumerary teeth, as it is not fully understood.[17] One theory proposes that the developing tooth bud may split into two separate but unequal parts during histodifferentiation resulting in an excess tooth.[18] One of the more readily accepted theories suggests hyperactivity of the dental lamina, which are the cells that ultimately give rise to teeth.[19] With the hyperactivity, excess enamel is produced, resulting in the formation of an additional tooth or teeth.

Histopathology

In areas where a tooth or teeth are missing, normal to a slightly reduced level of bone is seen microscopically.

Hyperdontia presents histologically as a normal tooth with defined layers of enamel, dentin, and pulpal tissues. Most supernumerary teeth, specifically the mesiodens, are smaller in size than a normal tooth; however, they will still demonstrate the defined layers in a reduced size or ratio.[20]

History and Physical

Anodontia presents as the complete failure of the dentition to develop.

Hypodontia is the absence of one to six teeth but is often used to describe the absence of any number of teeth.

Oligodontia is specific to the absence of six or more teeth. 

Hyperdontia is the presence of one or more additional teeth.

Evaluation

Hypodontia of any severity may be detected early in life. They may be discovered when deciduous dentition begins to erupt and a tooth is missing. However, many are discovered later in life as the permanent dentition develops and the tooth fails to erupt. Beyond the clinical examination, a panoramic radiograph is a key diagnostic tool in determining a missing tooth or teeth.[21]

It is rare for patients to present with multiple supernumerary teeth without an underlying syndrome or developmental condition. With a single supernumerary tooth being such a relatively common dental anomaly, a further workup for the patient is not warranted. These teeth are typically found either in the anterior maxilla, mandibular premolar, or third molar regions.[22]

Treatment / Management

Depending on the severity of the hypodontia, treatment may be relatively straightforward to extensive. Early diagnosis can provide optimal management for the patient by initiating treatment planning and treatment at an early age. Detecting a developmental disturbance early can reduce complications later in life and decrease the complexity of treatment.[23] (B2)

Treatment of missing teeth should be performed by licensed dental professionals. The least invasive treatment option for missing teeth is a removable prosthesis. This treatment modality rarely involves the augmentation or removal of tooth structure. There are several restorative options for a single missing tooth, ranging from no treatment to fixed prosthodontics to implants requiring surgery. With multiple missing teeth, treatment modalities can become more complicated and invasive.

Hyperdontia can generally be managed by extraction if the supernumerary tooth presents a periodontal, restorative, or masticatory concern. If there is adequate room in the arch for the tooth, no treatment is an appropriate option. Supernumerary teeth can sometimes be impacted and fully encased in soft tissue or bone, potentially predisposing them to develop pathology. These teeth should be continuously monitored via radiographic imaging to evaluate for any changes. If crowding is a concern due to an additional tooth or teeth, it is important to emphasize good oral hygiene and regular maintenance appointments.

Differential Diagnosis

Any hypodontia should be considered for the following:

• Ectodermal dysplasia if additional symptoms and/or structural involvement are noted
• Early exfoliation of teeth
• Otodental dysplasia

Hyperdontia

• Genetic syndromes, such as cleidocranial dysplasia, Gardener syndrome, or trichorhinophalangeal syndrome
• Variation of normal anatomy

Prognosis

Anodontia, hypodontia, and oligodontia generally have a good prognosis for treatment outcomes, especially with early detection and diagnosis. Depending on the extent and number of teeth missing, different prosthodontic and restorative options exist. With severe hypodontia being associated with syndromes, management of the syndrome itself generally precedes and occasionally precludes management of the dentition.

Hyperdontia and supernumerary teeth typically have a good prognosis, as they are treated or extracted if they pose a threat to erupting teeth, esthetics, or masticatory function.

Complications

Depending on the extent of anodontia, hypodontia, or oligodontia, different potential complications can arise. In patients missing most or all of their dentition, speech and mastication are generally affected, significantly impacting their quality of life. Patients missing two to four teeth may not be as severely impacted as more restorative or prosthodontic treatment options are available.

Supernumerary teeth, if mal-positioned, can prevent the normal eruption of developing teeth which would require removal – a potentially invasive procedure. The multiple supernumerary teeth are generally indicative of an underlying syndromic or developmental condition which should be evaluated by the appropriate healthcare provider.