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Developmental defects of the teeth

Developmental defects of the teeth
Author:
J Tim Wright, DDS, MS
Section Editor:
Ann Griffen, DDS, MS
Deputy Editor:
Diane Blake, MD
Literature review current through: Sep 2023.
This topic last updated: Aug 23, 2023.

INTRODUCTION — The close relationship among oral, systemic, and psychological health requires that oral health be evaluated thoroughly as part of health maintenance supervision. An understanding of the normal sequence and patterns of tooth eruption is the foundation for identifying and treating children with abnormal dental development and optimizing their oral health. Distinguishing normal from pathologic dental development requires careful evaluation of the patient, including medical, dental, and family history; clinical examination; radiographic evaluation; and possibly special laboratory tests.

Problems in dental development and syndromic and nonsyndromic conditions associated with abnormal dental development are reviewed here. The typical anatomy and development of human dentition are discussed separately. (See "Anatomy and development of the teeth".)

TOOTH ERUPTION PROBLEMS — Abnormalities of tooth eruption include natal and neonatal teeth, premature eruption, and failed tooth eruption.

Natal and neonatal teeth — Teeth that are present in the oral cavity at the time of birth are natal teeth; those that erupt during the neonatal period are neonatal teeth. The majority of natal teeth are the primary mandibular incisors and are not extra or supernumerary teeth (image 1). Natal teeth may be associated with a variety of syndromes including chondroectodermal dysplasia (Ellis-van Creveld syndrome), pachyonychia congenita, Sotos syndrome, and Hallermann-Streiff syndrome [1].

Treatment of natal teeth may involve observation, smoothing of the incisal edge (to prevent potential discomfort during breastfeeding and ulceration of the ventral tongue or the floor of the mouth [Riga-Fede disease]), or extraction [2]. Extraction of natal teeth should be considered only if they cause feeding difficulties for the infant or mother. Excessive natal tooth mobility has been considered to be a risk for aspiration. However, aspiration rarely, if ever, occurs.

Abnormal eruption — Delayed and accelerated eruption of teeth are discussed separately. (See "Anatomy and development of the teeth", section on 'Tooth eruption'.)

Failed teeth eruption — Complete failure of eruption of the primary teeth is rare with the exception of congenitally missing teeth. (See 'Congenitally missing teeth' below.)

Eruption failure of a single permanent tooth in an otherwise healthy child is more common and has several causes, described below.

Inadequate space — The most common cause of permanent tooth eruption failure is lack of space for eruption. Space deficiency in the dental arch frequently causes eruption failure (impaction) of the third molars, the maxillary canines, and the mandibular second premolars [3]. Inadequate eruption space also can lead to eruption out of the normal position or ectopic eruption.

Inadequate space for eruption can be treated with selective extraction of permanent teeth or orthodontic therapy, depending upon the severity and location of the space deficiency.

Widely spaced front teeth — Widely spaced maxillary central incisors (diastema) can result from a discrepancy in the size of the jaws and the teeth, or the labial frenum being attached to the alveolar ridge between the crowns of the central incisors.

Another cause of widely spaced front teeth is the presence of a mesiodens, a supernumerary tooth that is located between the maxillary central incisors (image 2). The frequency of mesiodens is increased in males with Nance-Horan syndrome [4]. Mesiodens in the primary dentition usually require extraction because they impede the eruption of the permanent incisors [5]. (See 'Supernumerary teeth' below.)

Trauma — Trauma to the anterior primary teeth can affect the development of the underlying permanent teeth and result in eruption failure of the permanent incisors. The development and eruption of permanent teeth should be monitored closely in children who have a history of trauma to the anterior primary teeth. (See "Evaluation and management of dental injuries in children".)

Ankylosis — Ankylosis, or fusion of the developing teeth to the underlying bone, can arrest the normal process of tooth eruption [6]. In a child who is still growing, the ankylosed tooth will be overgrown by the surrounding teeth that continue to erupt. Ankylosis should be suspected if a tooth fails to contact the teeth of the opposing arch when the teeth are brought into occlusion (image 3). Ankylosis most often involves the first primary molars and is relatively common in the primary dentition (2 to 3 percent of children) [6-8]. Ankylosed primary teeth typically exfoliate normally without treatment if they have a permanent successor [9]; however, treatment for ankylosis may be necessary depending upon the age of onset and severity of the problem.

Cleidocranial dysplasia — Cleidocranial dysplasia is an autosomal dominant condition characterized by hypoplasia or aplasia of the clavicles, defective bone formation, short stature, supernumerary teeth, defective cementum formation, and abnormal permanent tooth eruption [10,11]. The failure of tooth eruption is thought to be caused by impedance of the migration of the permanent teeth toward the oral cavity by defects in the osteoclastic and resorptive activity of the alveolar bone. Cleidocranial dysplasia is caused by mutations in the runt-related transcription factor 2 gene (RUNX2), a member of the RUNX family of transcription factors, located on chromosome 6p21. The RUNX2 gene encodes core-binding factor alpha 1 (CFBA1) and is responsible for the initial differentiation of osteoblasts to form skeletal structures [12,13]. (See "Skeletal dysplasias: Specific disorders", section on 'Cleidocranial dysplasia'.)

Treatment of the oral manifestations of cleidocranial dysplasia involves extracting the supernumerary teeth and assisting the eruption of the permanent teeth through surgery or orthodontia [14].

Primary failure of eruption — Primary failure of eruption is a failure of tooth eruption that is not caused by mechanical obstruction and has a nonsyndromic hereditary basis. Mutations in the parathyroid hormone receptor (PTHR1) gene are associated with primary failure of tooth eruption in some families and can affect one or multiple permanent teeth [15,16]. Primary failure of eruption most frequently affects the first and second molars.

Other — Other causes of failed tooth eruption include developmental defects of the teeth, abnormalities of bone or jaws, the presence of cysts or tumors, and syndromes. Asymmetry in the eruption pattern is a hallmark of these conditions and should prompt further evaluation and radiographic assessment.

Teeth with developmental defects such as regional odontodysplasia form only rudimentary tooth appendages that can fail to erupt (image 4) [17].

Cysts (eg dentigerous cyst, odontogenic keratocyst), tumors (eg, hemangiomas, odontomas), or gingival overgrowth that form near developing tooth buds can prevent tooth eruption. (See "Soft tissue lesions of the oral cavity in children".)

A variety of genetic conditions are associated with an increased prevalence of unerupted teeth (eg, cleidocranial dysplasia, hereditary enamel defects, amelogenesis imperfecta, trichodentoosseous syndrome) [18,19]. (See 'Cleidocranial dysplasia' above and 'Hereditary enamel defects' below.)

Failure of one or multiple teeth to erupt can occur in other syndromes such as the enamel-renal syndrome, which is associated with mutations in the FAM20A gene. Enamel-renal syndrome is characterized by failure of some teeth to erupt, very thin hypoplastic enamel, and microcalcifications in the kidneys [20].

Supernumerary teeth — Although the reported prevalence of supernumerary teeth varies (typically ranging between 1.2 and 3 percent), they may occur in ≥6 percent of the normal population [21,22]. Supernumerary teeth are more common in the permanent than in the primary dentition [23]. They are more common in males than females.

Supernumerary teeth usually are considered to be idiopathic, although there is some evidence that molecular factors are involved in regulating their development [24]. They have been associated with a variety of conditions, such as oral-facial clefting and several genetic disorders. The presence of supernumerary teeth can provide an early diagnostic clue [21,25]. Supernumerary teeth are associated with the following disorders that are documented or presumed to be related to abnormalities of a single gene:

Cleidocranial dysplasia (see 'Cleidocranial dysplasia' above and "Skeletal dysplasias: Specific disorders", section on 'Cleidocranial dysplasia')

Familial adenomatous polyposis (see "Clinical manifestations and diagnosis of familial adenomatous polyposis", section on 'Extracolonic manifestations')

Trichorhinophalangeal syndrome, type I

Rubinstein-Taybi syndrome (see "Microdeletion syndromes (chromosomes 12 to 22)", section on '16p13.3 deletion syndrome (Rubinstein-Taybi syndrome)')

Nance-Horan syndrome

Opitz GBBB syndrome

Oculofaciocardiodental syndrome

Autosomal dominant Robinow syndrome

Double teeth — Double (or twinned) teeth occur when two teeth are joined together. Double teeth occur in up to 3 percent of children [26]. They most commonly occur in the primary lower central incisors.

Teeth that appear to be double can occur because of gemination (a tooth bud attempts to form a second bud resulting in conjoined teeth) or fusion of two teeth [27]. When double teeth are caused by fusion, the number of teeth is reduced [23]. Two adjacent teeth can be joined by enamel, dentin, or cementum [27]. Joining through cementum (ie, concrescence) usually is related to trauma or abnormal position of one of the involved teeth.

Children with twinned teeth should be referred to a dental home so that they can be monitored for complications including delayed shedding and anomalies of the permanent dentition (eg, hypodontia, aplasia, impaction, supernumerary teeth, permanent twinned teeth) [27,28].

AGENESIS — Tooth agenesis may be acquired or congenital.

Acquired tooth agenesis — Acquired tooth agenesis can result from localized or generalized environmental insults (eg, trauma to a primary tooth, head and neck irradiation, chemotherapy).

Congenitally missing teeth — Congenitally missing teeth may result from genetic disorders that affect the teeth in isolation or as part of a syndrome.

The prevalence of congenitally missing teeth varies by race and tooth type. Congenitally missing teeth are more common in the White population than in the Black population (5 versus 1 percent) [29] and in the permanent dentition than in the primary dentition. The maxillary lateral incisor and second premolar are the permanent teeth most frequently missing, and the mandibular central incisor is the primary tooth most frequently missing.

Many children with missing teeth have a family member with a similar history. Several specific genetic mutations for missing teeth have been identified [30,31]. For example, a missense mutation in the MSX1 gene that codes for a transcription factor can cause the autosomal dominant trait of missing lateral incisors and third molars [30]. WNT10A mutations are associated with the most prevalent clinical phenotypes of nonsyndromic missing teeth [32].

Congenitally missing teeth are a manifestation of numerous genetic syndromes. Some syndromes are associated with only a few missing teeth (eg, Down syndrome); other syndromes, such as the ectodermal dysplasias, are associated with multiple missing teeth (hypodontia) or complete absence of teeth (anodontia) [33].

Young children suspected of having missing teeth or abnormal eruption patterns should be referred for complete dental evaluations. The diagnosis of congenitally missing teeth is confirmed by the absence of a full dental complement on dental radiographs. Genetic testing can be offered to determine the molecular basis of the child's condition and to help establish recurrence risk, risk of potential associated health problems (eg, axis inhibitor 2 [AXIN2] mutations are associated with missing teeth and risk of colorectal cancer), and variability of expression [34].

The treatment for missing teeth varies and can require multiple therapeutic phases. Management of hypodontia or anodontia involves the use of prostheses or dental implants to replace the missing teeth and to enhance oral function and facial esthetics. Children who are missing multiple anterior teeth should ideally receive their prostheses before beginning school [35]. The optimal age for treatment is evaluated individually and determined by the extent of treatment needed and the child's ability to cooperate during the procedures and to maintain the appliances after placement. Dental implant procedures typically are delayed until the child reaches late adolescence or early adulthood [36].

EXFOLIATION PROBLEMS — Premature exfoliation of primary teeth can be caused by local factors or systemic health problems. The eruption of permanent teeth can cause the exfoliation of adjacent primary teeth. For example, two primary incisors can exfoliate when the large permanent incisor begins to erupt; the exfoliation of multiple primary teeth in place of one permanent tooth often indicates a tooth-arch size discrepancy and usually heralds crowding in the permanent dentition.

In addition, premature exfoliation of primary teeth can be associated with systemic conditions, such as hypophosphatasia, Langerhans histiocytosis, and cyclic neutropenia (table 1). The lack of root resorption in the exfoliated primary tooth (picture 1) is a consistent clinical feature and an important clue to the diagnosis of systemic conditions that are associated with premature shedding of the primary teeth.

Children with premature exfoliation of the primary teeth must be evaluated to rule out serious systemic conditions (table 1) and should be referred to a pediatric dentist for prompt initiation of appropriate dental therapy. Making the diagnosis of hypophosphatasia is critical because enzyme replacement therapy is available. (See "Periodontal disease in children: Associated systemic conditions", section on 'Hypophosphatasia'.)

ENAMEL DEFECTS — More than 100 known genetic causes of enamel defects in humans have been identified. There are also more than 100 known environmental conditions associated with enamel defects. Enamel formation is highly regulated at the molecular level. Environmental insults to enamel production that can affect matrix secretion or processing include exposure to trauma, infection, lead, mercury, and fluorine. Defects in dental enamel are reported to occur in 25 to 80 percent of the general population [37-41].

Fluorosis — Fluoride is used widely for the prevention of dental caries; however, excess fluoride consumption (greater than 0.05 mg/kg per day) during ages associated with tooth development can cause hypomineralization of dental enamel or fluorosis [42]. Higher levels of fluoride in the water are associated with the development of fluorosis [43], as is swallowing excessive amounts of fluoride toothpaste. When severe, enamel hypomineralization due to fluorosis makes the teeth more susceptible to wear and breakage [44].

The dental effect of mild fluorosis is limited to surface appearance. Mild fluorosis is indicated by a white flecked or lacy appearance to the enamel (picture 2); moderate fluorosis has an opaque white appearance (picture 3); severe fluorosis is indicated by a brown discoloration. The mechanism by which excessive fluoride consumption causes fluorosis appears to be a direct effect on the rate of mineral formation by ameloblasts, resulting in disruption of the enamel matrix [45]. Mild to moderate fluorosis severity often diminishes during adolescence and young adulthood, likely due to wearing away of the outer effected enamel surface [46]. Fluorosis can be prevented with adherence to appropriate fluoride exposure for children under six years old, which includes following guidelines for toothpaste use [47], knowing whether the local water supply requires fluoride supplementation [48], and limiting excessive fluoride consumption (eg, swallowing mouth rinses).

Molar incisor hypomineralization — The prevalence of molar incisor hypomineralization varies geographically; it is reported to affect approximately 13 percent of children in the United States [49-51]. It is characterized by abnormal enamel mineralization of the first permanent molars (picture 4) but can also affect the permanent incisors; primary molars are affected in some cases [52]. The enamel defects increase the risk of dental caries and breakdown [53]. The severity is highly variable, ranging from enamel that is mildly discolored in localized areas (typically yellow-brown) to enamel that fractures from the tooth during eruption. It can cause extreme sensitivity to thermal and chemical stimuli. The etiology is not clear, but children who experience more childhood illnesses have an increased prevalence, and there may be a genetic component [54].

Hereditary enamel defects — Heritable conditions that cause enamel defects can be part of a syndrome or isolated to the enamel [39]. Enamel defects associated with syndromic conditions vary substantially depending on the molecular defect and the gene's role in tooth formation. There are many syndromes having an enamel phenotype that exists with other nondental phenotypic features.

Trichodentoosseous syndrome — The trichodentoosseous syndrome is an autosomal dominant disorder caused by a mutation in the Distal-less 3, homeobox gene (DLX3) and characterized by enamel hypoplasia that is smooth or pitted and elongation of the pulp chamber [55,56]. The DLX3 gene functions as a transcription factor regulating the expression of other genes and is important in hair, tooth, and bone formation; children with this condition have kinky, curly hair at birth and develop dense or thickened bone [56].

Junctional epidermolysis bullosa — Junctional epidermolysis bullosa is an autosomal recessive disorder characterized by variable expression of skin fragility and blistering and varying severity of generalized enamel hypoplasia [57]. The molecular defects that cause junctional epidermolysis bullosa involve genes that produce proteins essential to maintaining the integrity between the dermis and epidermis and are important in normal functioning of the ameloblasts [58]. (See "Epidermolysis bullosa: Epidemiology, pathogenesis, classification, and clinical features", section on 'Junctional epidermolysis bullosa'.)

Amelogenesis imperfecta — The amelogenesis imperfectas (AI) represent a group of heritable disorders with effects limited to the dental enamel; they include four clinically and genetically distinct types (table 2) and 14 subtypes [59,60]. Mutations in numerous genes (>16) have now been associated with different AI types [61-72]:

Amelogenin (AMELX) – extracellular matrix

Enamelin (ENAM) – extracellular matrix

Kallikrein 4 (KLK4) – proteinase

Matrix metalloproteinase 20 (MMP20) – proteinase

Family with sequence similarity 83, member H (FAM83H) intracellular protein

WD repeat domain 72 (WDR72) – intracellular protein

Family with sequence similarity 20, member A (FAM20A)

Chromosome 4 open reading frame 26 (C4ORF26) – extracellular protein

Solute carrier family 24, member 4 (SLC24A4) – intracellular protein

Ameloblastin (AMBN) – extracellular matrix

Acid phosphatase (ACP4) – ester hydrolyzing enzyme – intracellular protein [70]

Receptor expressed in lymphoid tissue (RELT) [71]

G protein-coupled receptor 68 (GPR68) [73]

Holocytochrome c synthase (HCCS) [74]

Mutations in different genes and allelic mutations of the same gene give rise to diverse enamel phenotypes ranging from hypoplastic, normal-colored enamel to brown, hypomineralized enamel that abrades from the teeth when they erupt into the oral cavity [75]. The affected teeth can be extremely sensitive to thermal and chemical stimuli.

Treatment of enamel defects — The treatment of enamel defects depends upon the diagnosis and specific phenotype. For example, hypoplastic enamel that is well mineralized frequently can be treated with bonding procedures to protect and improve the appearance of the teeth [76]. On the other hand, teeth with severely hypomineralized enamel usually are treated with restorations that cover the entire crown (eg, stainless steel or resin crowns in young patients and gold or porcelain-type crowns in adults). Infants who have conditions known to be associated with enamel defects should be seen for dental evaluation and early intervention assessment before their first birthday.

DENTIN DEFECTS — Although environmental factors can affect the development of dentin (eg, staining with tetracycline), genetic factors are more commonly the cause. Dentin malformations that affect the form and function of the teeth occur in syndromic and nonsyndromic hereditary conditions.

The dentinogenesis imperfectas and dentin dysplasias (table 3) are classified using clinical, radiographic, and histopathologic features [59,77].

Dentinogenesis imperfecta — Dentinogenesis imperfecta (DI) is classified according to its association with or without other conditions:

Type I – Associated with osteogenesis imperfecta and type I collagen defects; diminished pulp chambers are characteristic. (See "Osteogenesis imperfecta: An overview".)

Type II – Not associated with osteogenesis imperfecta; diminished pulp chambers are characteristic.

Type III – Often associated with the Brandywine triracial isolate (a genetically isolated triracial population from southern Maryland); large pulp chambers in young teeth are characteristic. This form is allelic to DI type II and is really a phenotypic variant of DI type II and not a separate entity.

In all types of DI, the teeth have a variable, opalescent blue-gray to yellow-brown discoloration caused by the abnormally colored dentin shining through the translucent enamel (picture 5). The pulp chambers tend to fill in with age and the dental crowns and roots tend to be small in size and altered in shape.

DI type II is an autosomal dominant condition and caused by mutations in the dentin sialophosphoprotein (DSPP) gene [78-80]. It is interesting that the dental phenotypes of DI type I and type II are so similar. This is not surprising because DI type I is associated with type I collagen defects and DI type II is associated with DSPP mutations, and type I collagen and DSPP interact during the development and mineralization of dentin [81].

Because children who have DI and defective dentin that is often unable to support the enamel, the enamel frequently fractures from the teeth, leaving them susceptible to rapid wear and attrition. The teeth affected by DI can be worn down to the gingiva and develop dental abscesses if left untreated.

The treatment for DI depends upon the severity of discoloration and propensity for enamel loss. In children who do not have fracturing of the enamel, discoloration of the teeth can be treated with bonding; when severe fracturing of the enamel occurs, full coverage of the crowns typically is necessary.

Dentin dysplasia — There are two types of dentin dysplasia (table 3). Dentin dysplasia type I is inherited as an autosomal dominant condition with a frequency of 1:100,000 persons. Mutations in the SMOC2, SSUH2, and VPS4B genes have been associated with dentin dysplasia type I [82]. The classic cascading waterfall dentin histopathology is thought to result from the cyclical process of premature odontoblast death, new odontoblast recruitment, dentin deposition, and odontoblast death. The crowns of affected teeth appear normal, but radiographs show short, blunted roots and pulpal obliteration [83], resulting in teeth that are mobile, lost prematurely, and susceptible to abscess formation. No known treatment exists, but dental longevity can be increased by keeping occlusal forces to a minimum and avoiding orthodontic treatment for malalignment [83].

Dentin dysplasia type II also is inherited as an autosomal dominant trait. Mutations in the DSPP gene are associated with dentin dysplasia type II. Because they are caused by allelic mutations in the DSPP gene, the phenotype of dentin dysplasia type II and DI type II is identical in the primary teeth. They have yellow-brown to blue-gray discoloration and pulpal obliteration. The permanent dentition of children with dentin dysplasia type II is normally colored or only minimally discolored but has abnormal pulpal morphology and may be associated with pulp stones [84].

The mechanism leading to different phenotypes in the permanent dentitions of these two conditions is not fully understood. However, one study that involved clinical and genetic evaluation of 23 members of a four-generation kindred, including 10 members with dentin defects, suggested dentin dysplasia type II and DI type II represent the mild and severe forms, respectively, of the same disease [85].

Treatment of dentin dysplasia type II in the primary dentition is the same as that for DI.

Systemic conditions — Systemic conditions can be associated with abnormal dentin formation because of molecular defects that interfere with dentin developmental pathways. For example, because dentin is 60 percent mineral, systemic conditions that are associated with defects of mineralization (eg, hypophosphatasia and vitamin D-resistant rickets) affect dentin development. Other systemic conditions with dentin involvement include Ehlers-Danlos syndrome, the mucopolysaccharidoses, and tumoral calcinosis.

SUMMARY

Evaluation of dental development – Distinguishing normal from pathologic dental development requires careful evaluation of the patient, including medical, dental, and family history; clinical examination; radiographic evaluation; and possibly special laboratory tests. (See 'Introduction' above.)

Tooth eruption problems – Problems in tooth eruption include natal and neonatal teeth, premature eruption, and failed tooth eruption (impaction). (See 'Tooth eruption problems' above.)

The most common cause of permanent tooth eruption failure is lack of space for eruption. Space deficiency frequently causes impaction of the third molars, the maxillary canines, and the mandibular second premolars. Inadequate space for eruption is treated with selective extraction of permanent teeth or orthodontic therapy. (See 'Inadequate space' above.)

Young children with failed eruption or abnormal eruption patterns should be referred for complete dental evaluation.

Congenitally missing teeth are confirmed with dental radiographs. Genetic testing may help establish recurrence risk and risk of associated health problems. Management of missing teeth involves the use of prostheses or dental implants to replace the missing teeth and to enhance oral function and facial aesthetics. (See 'Congenitally missing teeth' above.)

Exfoliation problems – Premature exfoliation of primary teeth can be caused by local factors or systemic health problems. The lack of root resorption in the exfoliated primary tooth (picture 1) is an important clue that an underlying systemic health problem may exist. Children with premature exfoliation of the primary teeth must be evaluated to rule out serious systemic conditions (table 1) and should be referred to a pediatric dentist for prompt initiation of appropriate dental therapy. (See 'Exfoliation problems' above.)

Enamel defects – Enamel defects include fluorosis (picture 3), molar incisor hypomineralization (picture 4), and heritable conditions. Heritable enamel defects occur in numerous syndromes (eg, trichodentoosseous syndrome, junctional epidermolysis bullosa) or isolated to the enamel (eg, amelogenesis imperfecta). The treatment of enamel defects depends upon the diagnosis. (See 'Enamel defects' above.)

Dentin defects – Dentin defects of clinical relevance are primarily genetic; they occur in syndromic and nonsyndromic hereditary conditions, such as dentinogenesis imperfecta (picture 5) and dentin dysplasia. (See 'Dentin defects' above.)

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Topic 6276 Version 29.0

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