Congenital and developmental anomalies of the teeth
Dental lamina
Teeth develop from the dental lamina, a strand of epithelium originating from the oral mucosa, which migrates backwards from the incisor region of both mandible and maxilla beginning in the sixth week of intrauterine life. As it migrates backwards tooth buds are formed which eventually develop into the teeth and roots, each with its characteristic shape, according to the position in the jaw. Abnormalities in its migration may lead to abnormalities that are laid out below. The concept of the dental lamina, however, has changed in recent years, as it would seem that the epithelium responsible for developing the teeth is not the dental lamina as such but modifications of the oral mucosa. This invaginates beneath the alveolus progressively posteriorly from the incisor region under the influence of genes and activators, which are specific for each part of the mouth, in a time-window of 2—3 days.
The total number of the secondary dentition is 32. The third molar or wisdom tooth may fail to develop in any of the four quadrants. Lack of space may cause them to impact into the second molars or backwards into the ramus. These may lead to pericoronal infection later in life and the third molars may require removal. The upper lateral incisors may fail to develop or develop as small, peg shaped teeth. This is normally associated with an impaction of the canines and is thought to be associated with faults in the dental lamina or gene deficiencies during development.
Failure to develop a large number of primary and secondary teeth is known as hypodontia. It may be associated with other forms of ectodermal dysplasia where there is a lack of sebaceous and sweat glands. Considerable problems are encountered in providing a functional dentition, particularly during the growth period.
Supernumerary teeth and odontomes
Supernumerary teeth tend to occur in the same areas where teeth may be absent — the lateral incisor, second premolar and the third molar areas. Generally they are smaller than the normal teeth in the same area and seldom develop little more than a crown and a vestigial root. They may be multiple. In the incisor region they may be responsible for the failure of eruption of adjacent permanent teeth, particularly the central and lateral incisors and canine. They generally lie palatal to their normal counterparts. They have to be removed to allow eruption of the permanent teeth to occur. Rarely, in the third molar region, dentigerous cysts may develop around the crown. These are characterised by a radiographic appearance of a cyst enveloping the crown of the tooth that is displaced.
Odontomes are aggregations of tooth-like material and may take the form of multiple small teeth (denticles, a compound complex odontome) or irregular masses of dentine, cementum and enamel (complex composite odontome). They lie within the alveolus, frequently inhibiting the eruption of the adjacent teeth and are encapsulated. The most common site is the premolar region of the mandible. Odontomes are, in effect, hamartomas. Once formed they do not increase in size. Occasionally they become infected.
Developmental disturbances in the structure of theteeth
The enamel of primary and secondary dentition may be affected by a number of genetic or congenital conditions. There may be effects due to local problems such as trauma during birth or infection. The most notable change affecting all teeth is the result of amelogenesis imperfecta which is genetic and may be dominant or recessive. It is an ectodermal disturbance and the anomalies can range from pits in the teeth to failure of enamel development. It may be associated with osteogenesis imperfecta. By contrast, dentinogenesis imperfecta affects the mesodermal portion of the odontogenic apparatus. The appearance of the teeth is variable with the poorly supported enamel taking on a opalescent tinge. The enamel is readily damaged. Both amelogenesis and dentinogenesis imperfecta result in rapid early tooth loss.
Odontogenic cysts and tumours
Abnormalities in the dental lamina may form benign cysts and odontogenic rumours (keratocyst, odontogenic myxoma). A malignant form, ameloblastoma, is variable between cystic and solid, and is locally invasive. The most common site for these to occur is in the third molar region and ramus of the mandible.
Congenital and developmental abnormalities of the gums
Congenital epulis of the newborn
This uncommon tumour is seen in the anterior mandible and can reach a relatively large size. It is pedunculated and mobile, and can cause extreme concern to parents. It is simple to remove and has no long-term consequences.
Predeciduous teeth
At birth, or shortly afterwards, hard tooth-like structures may be detected in the lower alveolus and can cause the mother considerable discomfort during breastfeeding. These do not represent primary dentition or ‘a third set of teeth’ as. the structures, although calcified, do not take the form of normal teeth. Simple removal is advised where breastfeeding is undertaken.
Dental lamina
Teeth develop from the dental lamina, a strand of epithelium originating from the oral mucosa, which migrates backwards from the incisor region of both mandible and maxilla beginning in the sixth week of intrauterine life. As it migrates backwards tooth buds are formed which eventually develop into the teeth and roots, each with its characteristic shape, according to the position in the jaw. Abnormalities in its migration may lead to abnormalities that are laid out below. The concept of the dental lamina, however, has changed in recent years, as it would seem that the epithelium responsible for developing the teeth is not the dental lamina as such but modifications of the oral mucosa. This invaginates beneath the alveolus progressively posteriorly from the incisor region under the influence of genes and activators, which are specific for each part of the mouth, in a time-window of 2—3 days.
The total number of the secondary dentition is 32. The third molar or wisdom tooth may fail to develop in any of the four quadrants. Lack of space may cause them to impact into the second molars or backwards into the ramus. These may lead to pericoronal infection later in life and the third molars may require removal. The upper lateral incisors may fail to develop or develop as small, peg shaped teeth. This is normally associated with an impaction of the canines and is thought to be associated with faults in the dental lamina or gene deficiencies during development.
Failure to develop a large number of primary and secondary teeth is known as hypodontia. It may be associated with other forms of ectodermal dysplasia where there is a lack of sebaceous and sweat glands. Considerable problems are encountered in providing a functional dentition, particularly during the growth period.
Supernumerary teeth and odontomes
Supernumerary teeth tend to occur in the same areas where teeth may be absent — the lateral incisor, second premolar and the third molar areas. Generally they are smaller than the normal teeth in the same area and seldom develop little more than a crown and a vestigial root. They may be multiple. In the incisor region they may be responsible for the failure of eruption of adjacent permanent teeth, particularly the central and lateral incisors and canine. They generally lie palatal to their normal counterparts. They have to be removed to allow eruption of the permanent teeth to occur. Rarely, in the third molar region, dentigerous cysts may develop around the crown. These are characterised by a radiographic appearance of a cyst enveloping the crown of the tooth that is displaced.
Odontomes are aggregations of tooth-like material and may take the form of multiple small teeth (denticles, a compound complex odontome) or irregular masses of dentine, cementum and enamel (complex composite odontome). They lie within the alveolus, frequently inhibiting the eruption of the adjacent teeth and are encapsulated. The most common site is the premolar region of the mandible. Odontomes are, in effect, hamartomas. Once formed they do not increase in size. Occasionally they become infected.
Developmental disturbances in the structure of theteeth
The enamel of primary and secondary dentition may be affected by a number of genetic or congenital conditions. There may be effects due to local problems such as trauma during birth or infection. The most notable change affecting all teeth is the result of amelogenesis imperfecta which is genetic and may be dominant or recessive. It is an ectodermal disturbance and the anomalies can range from pits in the teeth to failure of enamel development. It may be associated with osteogenesis imperfecta. By contrast, dentinogenesis imperfecta affects the mesodermal portion of the odontogenic apparatus. The appearance of the teeth is variable with the poorly supported enamel taking on a opalescent tinge. The enamel is readily damaged. Both amelogenesis and dentinogenesis imperfecta result in rapid early tooth loss.
Odontogenic cysts and tumours
Abnormalities in the dental lamina may form benign cysts and odontogenic rumours (keratocyst, odontogenic myxoma). A malignant form, ameloblastoma, is variable between cystic and solid, and is locally invasive. The most common site for these to occur is in the third molar region and ramus of the mandible.
Congenital and developmental abnormalities of the gums
Congenital epulis of the newborn
This uncommon tumour is seen in the anterior mandible and can reach a relatively large size. It is pedunculated and mobile, and can cause extreme concern to parents. It is simple to remove and has no long-term consequences.
Predeciduous teeth
At birth, or shortly afterwards, hard tooth-like structures may be detected in the lower alveolus and can cause the mother considerable discomfort during breastfeeding. These do not represent primary dentition or ‘a third set of teeth’ as. the structures, although calcified, do not take the form of normal teeth. Simple removal is advised where breastfeeding is undertaken.
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