The milk dentition usually has 20 teeth, the dentition of the 2nd dentition – the permanent teeth – includes 28 without wisdom teeth, with wisdom teeth it can be up to 32 teeth. However, there are numerous deviations from the norm concerning the number of teeth, i.e. deviations in the number of teeth are possible.
Symptoms – complaints
If there are too few teeth, a distinction is made between hypodontia – the absence of individual teeth – and oligodontia, in which fewer than (normally) 32 teeth are formed, and anodontia (ICD-10: K00.0) – congenital edentulism. Anodontia is an extremely rare malformation.Hypodontia rarely occurs in the primary dentition. However, if it does, the upper lateral incisors and the lower central or lateral incisors are usually affected. Often, the attachment of the corresponding permanent teeth is then also missing. However, the frequency of hypodontia in the primary dentition is less than one percent. Mostly, this malformation affects the permanent dentition. The second premolars (small molars) of the lower or upper jaw are most frequently affected, as are the upper lateral incisors. Supernumerary teeth (hyperodontia; ICD-10: K00.1) occur most frequently in the permanent dentition of the upper jaw, preferentially in the incisor region. Here, too, the permanent teeth are more frequently affected than the deciduous teeth. Supernumerary teeth can correspond to the natural tooth shape and are then called eumorphic. If their shape is atypical, they are called dysmorphic teeth. These include the mesiodentes, distomolars, and paramolars. Mesiodentes are usually cone-shaped and are found between the roots of the maxillary central incisors. They can significantly interfere with natural tooth eruption. Disto- or paramolars are molars that emerge either between the molars or behind the wisdom teeth.Wisdom teeth are absent in about 10-35% of the population.
Pathogenesis (development of disease) – Etiology (causes)
An over- or under-number of teeth is one of the genetically (hereditary) caused malformations. An under-number of teeth often occurs in association with other conditions, such as cleft lip and palate or trisomy 21 (Down syndrome). Conditions that may be associated with hypodontia:
- Anhidrosis hypotrichotica (synonyms: ectodermal polydysplasia; anhidrotic ectodermal dysplasia; Christ Siemens Touraine syndrome) – genetic disorder with autosomal recessive inheritance; lack of sweat secretion due to absence of eccrine sweat glands.
- Bloch-Sulzberger syndrome (synonyms: Bloch-Siemens syndrome; Incontinentia pigmenti; Melanoblastosis cutis; Naevus pigmentosus systematicus) – genetic disease with X-linked dominant inheritance; affects skin, hair and nails in addition to the teeth; occurs only in women (in boys because of the lack of intact second X chromosome usually already prenatally fatal).
- Ectodermal dysplasia – malformations of teeth, hair, skin and sweat glands, anodontia possible.
- Gregg syndrome – rubella embryopathy (rubella infection during pregnancy).
- Hallermann-Streiff syndrome (HSS for short, other names: Bird disease, Hallermann-Streiff-Francois syndrome, oculomandibulodyscephaly with hypotrichosis, oculomandibulofacial syndrome) – rare, sporadic malformation syndrome in humans.
- Cleft lip and palate (LKGS clefts; Latin cheilognathopalatoschisis) – group of congenital malformations that are among the most common congenital malformations in humans, which have in common that during embryonic development parts of the mouth do not develop normally. The cleft lip is often colloquially referred to as “harelip” or cleft palate as “wolf cleft”.
- Marfan syndrome – genetic disease that can be inherited both autosomal dominant or occur sporadically (as a new mutation); systemic connective tissue disease, which is notable primarily by tall stature, spider limbs and hyperextensibility of the joints; 75% of these patients have an aneurysm (pathological (pathological) bulge of the arterial wall).
- Papillon-Leage-Psaume syndrome (orofaciodigital syndrome) – genetic disease with X-linked dominant inheritance; among other things, hyper- or hypodontia possible, occurs only in women.
- Trisomy 21 (Down syndrome) – special genetic mutation in humans in which the entire 21st chromosome or parts of it are present in triplicate (trisomy). In addition to physical characteristics considered typical for this syndrome, the cognitive abilities of the affected person are usually impaired; furthermore, there is an increased risk of leukemia (blood cancer).
Diseases that may be associated with hyperodontia:
- Cleft lip and palate – in 35 percent, double arrangement of the lateral incisors.
- Dysostosis cleidocranialis – congenital skeletal malformation.
Consequential diseases
No secondary diseases occur.
Diagnostics
If an undercount of teeth is suspected, for example if deciduous teeth persist for an exceptionally long time, an X-ray – panoramic radiograph – is taken. Here, the dentist can see exactly whether all permanent teeth are in place. Tooth overcount is usually detected accidentally during routine X-ray examinations at the dentist’s office.
Therapy
Therapy of supernumerary teeth consists in their extraction, i.e., extraction of the teeth, as they may interfere with natural tooth eruption. In the case of eumorphic (supernumerary) teeth, for example, when an upper incisor is duplicated, the tooth that is orthodontically easier to fit into the dentition is always left in the jaw. In case of non-attachment of teeth, there are different therapeutic approaches. On the one hand, the milk tooth, which is not followed by a permanent tooth, can be left in place. It is removed only after the completion of growth and the resulting gap is closed by an implant. However, this is only possible if the deciduous tooth is largely caries-free and worthy of preservation. If the deciduous tooth has to be removed before growth is complete, a space maintainer can sometimes be used to keep the gap open until growth is complete and an implant restoration is possible. The second option is the removal of the deciduous tooth and subsequent orthodontic gap closure. It must be noted here that a compensatory extraction in the opposing jaw may be necessary to adjust the teeth into a correct occlusion (bite together). Extraction therapy begins around the age of ten, and it is important to bear in mind that extraction also has consequences for the soft tissue profile and esthetics. Any remaining growth and the type of growth must also be taken into account. Whenever a genetic disease underlies the tooth anomaly, the therapy usually turns out to be much more complex and has to be tailored to the individual patient.
