Orthodontic
Management of
Hypodontia

Tooth agenesis (hypodontia) is the most common craniofacial malformation; it can occur as an isolated condition (non-syndromic) or in association with other developmental anomalies (syndromic). Lack of one or more teeth is a congenital defect that occurs during the initiation and proliferation stages of tooth formation. The large number of genes involved in the odontogenic process means that there are numerous opportunities for mutations to disrupt this process. Recent advances in genetic techniques have begun to identify the complex process of reciprocal interactions in tooth development and the genetic mechanisms that underlie the odontogenic process.

Congenital absence of teeth has great potential to disrupt normal occlusal development; it can result in abnormal spacing, tipping of adjacent teeth, abnormal tooth relationships, and disturbed intercuspation and interdigitation. Inclined teeth can result in occlusal trauma to the affected teeth, areas of stagnation susceptible to caries, periodontal problems, bone loss, and mandibular shift. Missing anterior teeth can disturb physiologic functions such as speech and mastication and can seriously impair the patient’s esthetics. These issues can profoundly affect the patient’s self-esteem and confidence, resulting in psychologic problems.

Muller et al¹ reported an increased prevalence of hypodontia during the 20th century. Therefore, future identification and analysis of its genetic basis is essential for early detection and intervention to obtain acceptable alignment and occlusal relationships. Timely management of hypodontia can be of great benefit to the oral health and occlusion of children who present with such anomalies. Early intervention reduces the complexity of the problems and, in some situations, may eliminate the need for a second phase of treatment.

Terminology

Hypodontia

Hypodontia is a general term used for the congenital absence of teeth. This anomaly can appear as absence of a single tooth, agenesis of several teeth, or even complete tooth agenesis in patients with ectodermal dysplasia syndrome.

Oligodontia

Oligodontia or partial hypodontia is a term that has been used to describe the absence of multiple teeth. Some investigators use this term to refer to the absence of three or more tooth buds, while others have defined this term as the congenital absence of at least four teeth. Oligodontia can be present concomitant with syndromic conditions or can arise in individuals without a syndromic condition or any general abnormalities.

Anodontia

Anodontia (total hypodontia), or absence of all teeth, is a very rare anomaly that has occurred in some patients with ectodermal dysplasia.

Prevalence

Many studies have been published on the subject of hypodontia, and they have reported a wide range of prevalence rates (Table 7-1). Excluding third molars, the incidence of other missing teeth has been reported to be between 1.6% and 9.6%. Almost all reports show a higher prevalence in girls than in boys. The teeth most frequently absent are the maxillary lateral incisors and mandibular second premolars.

Many of these studies were conducted with regard to specific populations, with some variations in the findings (see Table 7-1). For example, Brekhus et al² conducted a hypodontia survey in American children and found the prevalence to be 1.6%, whereas Hunstadbraten²¹ conducted a survey of Norwegian children and found the prevalence to be 10.1%.

In an unpublished study performed at the Eastman Institute for Oral Health, 800 panoramic radiographs of children aged 6 to 17 years were randomly selected from both active and inactive chart pools with no regard to sex or ethnicity (Bahreman AA, Jensen MO, Lothyan JD, unpublished data, 2007). Patients who were congenitally missing third molars and children who were syndromic or had clefts were excluded from the study. The aim of this investigation was to determine the prevalence of anomalies of tooth number (hypodontia and hyperdontia) of three racial/ethnic groups (whites, blacks, and Hispanics) in the greater Rochester, New York, area.

Prevalence data were calculated from the findings. Fisher exact test was performed to assess the statistical significance of the findings. Among the 800 panoramic radiographs evaluated, 51 children showed hypodontia (6.38%). The incidence was 6.57% in girls and 6.15% in boys (Table 7-2). The racial/ethnic distribution was as follows: 22 of 383 (5.74%) among black subjects, 23 of 292 (7.88%) among white subjects, and 5 of 103 (4.85%) among Hispanic subjects (Table 7-3). The ethnic distribution, when controlled by sex, showed that white females had the highest prevalence of hypodontia, 14 of 155 subjects (9.03%), while Hispanic males had the lowest rate, 2 of 47 (4.26%) (Table 7-4).

The most common congenitally missing tooth was the mandibular permanent second premolar, followed by the maxillary second premolar, followed by the maxillary lateral incisor (Table 7-5).

There were 77 congenitally missing teeth distributed among the 51 panoramic radiographs exhibiting hypodontia. Of those, 36 radiographs revealed only one congenitally missing tooth, and 1 panoramic radiograph showed 7 congenitally missing teeth. The distribution of the number of congenitally missing teeth shown on each panoramic radiograph demonstrating hypodontia is shown in Table 7-6.

A study by Bahreman and Shokoofan²² examined the panoramic radiographs of 610 Iranian children between the ages of 9 and 14 years. The investigators found that, excluding third molars, the prevalence of hypodontia was 4.0% in boys and 6.5% in girls. The most frequently missing tooth was the mandibular second premolar.

According to Muller et al,¹ the prevalence of hypodontia in whites increased during the 20th century.

Grahnén and Granath²³ concluded that hypodontia is less frequent in the primary dentition but that there is a high correlation between primary tooth absence and permanent tooth absence.

Etiology

Different etiologic factors have been proposed for this anomaly:

• Genetic factors

• Environmental factors:

– Allergy

– Facial trauma

-Maternal medications during pregnancy

– Endocrine disturbances

-Maternal health during pregnancy

-Maternal rubella (German measles) during pregnancy

– Evolutionary dental changes

– Localized inflammation and infection during the initial stage of tooth formation

– Systemic conditions (rickets, syphilis)

– Dysplastic syndromes (ectodermal dysplasia) and abnormalities of the ectodermal structures (discussed later in this chapter)

– Chemotherapy and irradiation

Genetic factors

Odontogenesis is a fascinating process consisting of a complex series of epithelial-mesenchymal interactions involving growth factors and other morphogenetic factors. A large number of genes are involved in this process, and the opportunity for mutations to disrupt the process of odontogenesis is very high.

Nonsyndromic agenesis of permanent teeth is the most common developmental dental anomaly. Excluding the third molars, the prevalence of other missing teeth has been reported with a wide range of between 1.6% and 9.6%; the prevalence for third molars is more than 20%. The prevalence of hypodontia in the primary dentition is less than 1%. Hypodontia usually occurs in the incisor region and is associated with missing succedaneous teeth.¹⁴ Mandibular second premolars and maxillary lateral incisors are the most frequently missing teeth in the permanent dentition.

Genetically nonsyndromic tooth agenesis is a heterogenous condition, and it is believed that different phenotypic forms are caused by different mutated genes.²⁴ In a study of families, Burzynski and Escobar²⁴ established that lateral incisor and premolar hypodontia is inherited via an autosomal-dominant gene that demonstrates incomplete penetrance. This form of hypodontia, affecting one or a few teeth (maxillary lateral incisors and mandibular second premolars) is the most common.

Arte et al,²⁵

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