Developmental Disturbances of the Teeth, Anomalies of Structure

Etiology

Dens evaginatus, also known as a talon cusp, results from a developmental tubercle, often seen on the lingual aspect of the tooth structure; however, it can occur on the occlusal surface. A coronal anomaly, these accessory cusps typically project from the cingulum or cementoenamel junction of anterior teeth.[1] The etiology of this condition is attributed to genetic and/or environmental factors, such as trauma to the developing tooth bud or local factors influencing the morphodifferentiation during tooth development.[2]

Dens invaginatus, also known as dens in dente, is a dental malformation that results from an inward folding of the developing tooth germ. Dental anomalies have a multifactorial etiology, with genetic and environmental factors being the most common.[3] The etiology of this condition is not well understood; however, it is likely related to an additional invagination of the inner enamel epithelium into the interior aspect of the developing tooth bud before mineralization.[4] Several other suggested etiologies range from the rapid proliferation of part of the inner enamel epithelium into the dental papilla to trauma and an absence of signaling molecules for morphogenesis.[5]

Amelogenesis imperfecta is a developmental condition with a genetic etiology. It affects both the clinical and structural appearance of some or all of the dentition. Mutations in the amelogenin gene (AMELX) and enamelin gene (ENAM) are also responsible for this condition.[6]

Dentinogenesis imperfecta is a developmental condition that also has a genetic etiology. It is caused by mutations with an autosomal dominant pattern of inheritance that alters the structure of dentin.[7] Mutations are commonly found within the genes that encode for type 1 collagen (COL1A1 and COL1A2).[8]

Epidemiology

Dens evaginatus/talon cusps are relatively common, with a prevalence ranging between 1 and 6%, and are mostly seen in the permanent dentition. 

Dens invaginatus has no gender predilection and a prevalence between 0.3 to 10%, depending on the population studied.[9] This condition is mainly identified on the maxillary lateral incisors, followed by the maxillary central incisors. It is very rarely discovered in any other teeth.[10]

The incidence of amelogenesis imperfecta depends widely on the gene mutation of the population studied. Different studies have found that the incidence of amelogenesis imperfecta ranges from 1 in 700 to 1 in 14,000.[11][6]

Dentinogenesis imperfecta has an incidence ranging from 1 in 6,000 to 1 in 8,000 cases throughout the United States, with no gender predilection.[12]

Pathophysiology

The morphological changes seen in dens evaginatus are thought to occur early in odontogenesis, during the morphodifferentiation stage of tooth development.[13] It is suggested that proliferation and subsequent evagination of the inner enamel epithelium and the odontogenic mesenchyme into the enamel organ result in the “talon cusp” development.[14]

Dens invaginatus results from an alteration of the developing tooth structure during the proliferation and morphodifferentiation stage of tooth development.[4]

Amelogenesis imperfecta is a genetic alteration in the formation of enamel. This condition results from mutations of multiple genes, many of which code for enamel proteins, either structural or enzymatic, various transcription factors, cellular proteins, and calcium carriers.[15] This condition can range from affecting a single tooth to the entire dentition, depending on the combination of genetic mutations.

Dentinogenesis imperfecta is a genetic alteration in the formation of dentin. The formation of dentin (dentinogenesis) arises from an organic pre-dentin matrix calcified by the signal from the odontoblasts. As dentinogenesis progresses, these odontoblasts are responsible for multiple intricate processes that lead to the proper formation of dentin, which affects other dental structures. Mutation in the genes that encode protein constituents of dentin results in hereditary dentin defects.[8]

Histopathology

Dens evaginatus histologically appear as normal dental tissue, with reduced levels of enamel and dentin. Pulpal tissue may or may not be present, depending on the extent of the evagination from the affected tooth bud.[16]

Dens invaginatus histologically appears as normal dental tissue, with an inward folding of enamel and dentin.

Amelogenesis imperfecta histologically presents with normal dentin surrounded by lessened or obliterated enamel.

Dentinogenesis imperfecta histologically presents as a lessened or degenerated dentin surrounded by otherwise normal enamel.

History and Physical

Dens evaginatus, or a “talon cusp,” presents as an outcropped growth of normal tooth structure, commonly affecting the lingual aspect of an anterior maxillary tooth. Talon cusps have been classified into three categories with distinct clinical presentations.[17] Type 1 talon cusps are a morphologically well-differentiated additional cusp that extends half the distance from the cementoenamel junction to the incisal edge. Type 2 talon cusps, known as a “semi-talon,” measure at least one millimeter and extend half the distance from the cementoenamel junction to the incisal edge. Type 2 talon cusps often blend with the surface of the crown. Type 3 talon cusps, or “trace talons,” are enlarged or prominent cingula that can be conical, bifid, or tubercle. 

Dens invaginatus has various clinical presentations, which depend on the severity of the in-folding or the phase of morphodifferentiation where the invagination occurs. Several classifications exist to describe the extent of the in-folded tissue. The most utilized system is the Oehlers classification due to its ease of application.[18] In Type 1, the invagination ends as a blind sac and is limited to the coronal aspect of the tooth. Type 2 invagination extends beyond the CEJ and is retained within the main root canal of the tooth. Type 3 occurs when the invagination of dental tissue extends throughout the interior aspect of the root canal, sometimes even reaching the apical third of the tooth, potentially resulting in multiple apical foramina.[19]

The various clinical presentations of amelogenesis imperfecta depend on the gene that is mutated.[15] Hypoplastic amelogenesis imperfecta, or type I, presents with localized or generalized thinning of the enamel, resulting in the crown of the teeth appearing yellow or light brown in color. The surfaces of these teeth are often pitted or mottled in appearance. There is no pain associated with this subtype; however, thermal sensitivity has been reported.[20] Hypomature amelogenesis imperfecta, or type II, has a defect in matrix protein degradation. Enamel in this condition appears whitish to brown in color with no noted translucency, which commonly presents with enamel breakdown. Radiographic examination reveals a decreased enamel opacity, especially along the dentino-enamel junction. Type II is the mildest form, with the main concern being esthetics.[21] 

Hypominerazlied amelogenesis imperfecta, or type III, is the most severe form of amelogenesis imperfecta due to the reduced enamel mineral content. Teeth with this condition are very sensitive to temperature and tactile pressure, presenting clinically with dark yellow or brown enamel color. On radiographic examination, enamel and dentin may appear to have the same radiodensity.[22]

The clinical presentation of dentinogenesis imperfecta (DI) depends on the extent of the disruption during dentinogenesis. DI is classified into three types based on clinical and radiographic features.[23] DI Type 1 is syndromic and presents with osteogenesis imperfecta, a disorder that results in fragile bones. With this combination of syndromes, it is pertinent for healthcare providers to work together to ask appropriate medical history questions, such as fragile joints, short stature, hearing loss, joint hyperextensibility, and scleral hue (blue). DI Type II is present with or without other etiologically related clinical findings. While the clinical and radiographic findings are indistinguishable from DI Type I, this condition is less severe with fewer related clinical presentations.[24] DI Type III presents with very large pulp chambers and abnormalities in tooth color, size, as well as possible enamel pitting.[25]

Evaluation

Dens evaginatus/talon cusps are likely incidental findings during routine dental examinations. In cases where the outgrowth is less severe, patients may not even be aware of their presence. If patients have issues with the extra tooth structure, a multidisciplinary approach should be utilized for treatment.

Dens invaginatus is likely an incidental finding during a routine dental examination. In less severe cases, patients may be unaware of the presence of an in-folding in the surface of their tooth, while in more severe cases, patients may complain of pain or discomfort in the area, as these teeth can be more prone to trauma or sensitivity. Radiographic evaluation, ideally with a CBCT, should be utilized to determine the extent of the invagination, as the severity of the condition will dictate treatment.

Amelogenesis imperfecta is commonly identified on clinical examination. With this being an inherited condition, family history, clinical observation, and recording of any developmental disturbances will aid in diagnosis.[6]

Dentinogenesis imperfecta is identified on clinical examination. Teeth appear amber, brown/blue, or opalescent brown in color, depending on the extent of the dysplastic dentin.[26] Radiographically, crowns appear bulbous with small to obliterated pulp chambers, and roots are often narrow with small pulp canals.[27]

Treatment / Management

Dens evaginatus/talon cusps are managed with a multidisciplinary approach in mind. Treatment options from a recent consensus study by Smail-Faugeron et al. in 2016 stated the following modalities of treatment: complete reduction of the talon cusp in one appointment, periodic or gradual cuspal reduction, abstention, or the possibility of extraction.[1] Treatment strategies are dictated by the severity of the talon cusp, the patient's chief complaint, whether functionally or esthetically, or to mitigate potential dental complications before they occur.(B3)

Dens invaginatus should be evaluated radiographically with either a series of periapical radiographs from different angles or a CBCT to evaluate the internal structures. Depending on the complexity of the tooth's internal structure or the extent of the invagination, treatment and management strategies of these teeth can range from monitoring to surgical intervention. Treatment has phased into an endodontic approach compared to the previous oral surgery-driven approach with extractions due to the development of better diagnostic aids, such as the CBCT.[5]

Amelogenesis imperfecta ranges from mild to severe, which will dictate the extent of the treatment required. As far as management is concerned, treatment should be considered in symptomatic cases or cases where the patient expresses esthetic concerns. Treatment can range from composite fillings and veneers to full-coverage ceramic restorations depending on the severity of the condition.

Dentinogenesis imperfecta ranges from mild to severe, which will dictate the extent of the treatment required. Due to the esthetic changes in tooth coloration, patients may desire more esthetic restorations for anterior teeth, such as composite resin restorations or porcelain veneers. Associated enamel pits may require minimal intervention with esthetic, non-preparation facial composite restorations.

Differential Diagnosis

Dens Evaginatus/Talon Cusp

• Gemination
• Fusion
• Enamel hyperplasia

Dens Invaginatus

• Fusion
• Enamel hypoplasia
• Gemination 

Amelogenesis Imperfecta

• Dental fluorosis
• Chronological enamel hypoplasia
• Molar-Incisal Hypomineralization (MIH)

Dentinogenesis Imperfecta

• Dentin dysplasia
• Osteogenesis imperfecta
• Amelogenesis imperfecta

Prognosis

Dens evaginatus/talon cusps have a good prognosis with appropriate management. When less severe, patients may be unaware of their presence, while more severe cases may warrant more invasive intervention. As long as proper restorative or endodontic protocol is followed, teeth that present with dens evaginatus have a good prognosis. 

Dens invaginatus have a good prognosis with appropriate management. Due to the altered tooth structure, teeth with this condition should be regularly monitored for early signs of caries to prevent more invasive dental treatment measures.

Amelogenesis imperfecta, as well as dentinogenesis imperfecta, has a good prognosis with appropriate management. In cases where patients are asymptomatic or do not express an esthetic concern, most patients will have a good quality of life with no or little treatment. More involved cases may require more invasive or multi-disciplinary treatment, which can potentially change the prognosis.

Complications

Dens evaginatus/talon cusps may have additional pulpal tissue present, depending on the severity and when the developmental disturbance occurred during odontogenesis. With this complication, the restorative prognosis may be guarded without appropriate endodontic intervention. Additionally, these cusps are prone to traumatic fractures due to their unfavorable location in the plane of occlusion. If the traumatic fracture occurs, endodontic therapy may be warranted due to pulpal exposure. 

Dens invaginatus has a higher predilection for caries formation due to their “funnel shape” that allows food debris or bacteria to progress faster and deeper into the tooth.[28] These teeth should be monitored for early signs of caries. Patients should be counseled on proper oral hygiene measures to reduce their risk of developing carious lesions on these teeth and their entire dentition.

Amelogenesis imperfecta, with the different clinical presentations, often requires an interdisciplinary treatment approach. The generalized form of the condition is commonly associated with an underlying systemic syndrome, such as regional odontodysplasia, in which genetic counseling or genetic workup is indicated to manage any underlying syndrome appropriately.[29]

Dentinogenesis imperfecta, especially DI type II, presents with greater pulpal tissue, which may complicate restorative interventions due to the higher frequency of pulpal exposure during restorative treatment or as a result of parafunctional habits.