Developmental Disturbances of the Teeth, Anomalies of Shape and Size

Etiology

Microdontia is a rare dental anomaly in which teeth appear smaller than is normally expected. Patients who present with true generalized microdontia, a rare condition where all teeth are affected, often have other systemic syndromes, such as pituitary dwarfism, oro-faciodigital syndrome, or oculo-mandibulo-facial syndrome.[1][2][3] Microdontia can also present in younger patients who have undergone chemoradiotherapy in the past, altering the formation of the developing dentition.[4] It is extremely rare for patients with no underlying genetic or developmental syndromes to present with true generalized microdontia.

Macrodontia, also known as megalodontia, has an unknown etiology; however, genetic and environmental factors have been attributed to the development of this condition.[5][6] Contrary to larger-than-normal teeth being present throughout the dentition, known as generalized macrodontia, isolated macrodontia is not typically associated with syndromes or underlying systemic pathology.[7] Generalized macrodontia has been attributed to several conditions, notably insulin-resistant diabetes, otodental syndrome, and hypophyseal gigantism.[8]

Taurodontism has commonly been attributed to the failure of sufficient invagination of the epithelial root sheath during tooth development, which results in misplaced dentin deposition, creating a larger than normal pulp chamber.[9][10] Taurodontism has been associated with several underlying syndromes, such as amelogenesis imperfecta, Klinefelter syndrome, and Down syndrome.

Fusion involves joining two developing tooth buds that result in a larger-sized tooth with two distinct tooth germs. This fusion may be due to tooth germs being in too close approximation, or the developing supernumerary tooth bud is in too close a proximity to a normally developing tooth bud.

Epidemiology

Microdontia has a predilection for females with an overall incidence of 1.5 to 2%.[11] The most commonly affected tooth is the maxillary lateral incisor, known by the descriptive term “peg lateral.[12]

Macrodontia has no sex predilection and has a reported prevalence in permanent teeth of 0.03 to 1.9%.[13] This condition typically presents in patients aged 8 to 13, which is the age range for the eruption of the permanent dentition.

Taurodontism has a male predilection and is associated with X-linked syndromes.[14] The incidence of taurodont teeth is reportedly less than 1%, with a predilection for Eskimos and Native American populations.[15]

In a population of 1200 patients, fusion was present with a frequency of 0.21%.[16] There is no gender predilection.[17]

Pathophysiology

Microdontia results from the disruption of normal dental developmental processes, where steps are halted prior to completion. These changes may be environmental and/or genetic in nature.

Macrodontia results from over-expression of dental developmental structures, resulting in hyperactivity of the tissues produced during tooth development. This change results in larger than normal teeth, which are often attributed to systemic, syndromic, or environmental factors.

Taurodontism results from one of the three suggested pathologic processes: an unusual developmental pattern that results in the subsequent delay in the calcification of the pulp chamber, a deficiency of odontoblasts with a resultant alteration in Hertwig’s epithelial root sheath, or the result of disrupted developmental homeostasis.[18]

Fusion occurs when two developing tooth buds are in close enough proximity to one another to begin to develop simultaneously as one single unit. This joining can be simply because the teeth are so close together or due to the presence of supernumerary teeth. It has also been suggested that signaling mediated through the Jagged2 gene plays a role in tooth development and the subsequent fusing of teeth.[19]

Histopathology

Microdontia histologically presents as a normal tooth; however, the enamel and dentin layers are not as robust as a normal-sized tooth. 

Macrodontia histologically presents as normal teeth histologically; however, the layers of enamel and dentin are thicker and more pronounced than normal-sized teeth.

Taurodontism presents as a normal tooth. However, due to the hyperplastic and abnormally large pulp chamber, there is excess pulpal tissue. Though the tissue is greater in volume, it is histologically normal.

Teeth that exhibit fusion appear histologically as normal teeth; however, depending on where and at what point in development the teeth began to fuse, certain elements – pulpal chambers, roots, and/or crowns – may appear fused or duplicated.[20]

History and Physical

Microdontia often will produce teeth that are “conical” or “peg-shaped” in appearance, with most cases related to an underlying developmental or syndromic condition.[11] Microdontia of an entire dentition without an underlying syndrome is rare. Therefore patients presenting with true generalized microdontia require further evaluation.

Macrodontia will present as generally larger teeth than expected, with generalized cases related to an underlying syndrome or systemic condition. Macrodontia of premolars, termed “molarization,” is an extremely rare condition where the premolar is large enough to appear as if it is a molar. There are only 36 documented cases in the literature.[21] Patients presenting with generalized macrodontia should be evaluated for an underlying syndromic or systemic condition.

Taurodontism is typically diagnosed radiographically at routine dental visits.[22] Patients are normally unaware of this condition. 

Fusion is the resultant “combined tooth” appearance where two normally separate tooth germs unite as one developing tooth. Depending on the stage of development when the fusion occurred, the fusion may be complete or incomplete. It is considered complete if the entire tooth continues to develop or incomplete if there is a fissure or cleft in the tooth surface.

Evaluation

Microdontia is where teeth appear smaller than expected. Classification is dependent on severity. Localized microdontia describes a singular tooth that is smaller than normal, relative generalized microdontia, describes teeth that appear smaller due to the larger relative size of the maxilla or mandible, and true generalized microdontia describes the involvement of the entire dentition.[23]

Macrodontia is commonly detected on routine dental radiographs between the ages of 8 and 13 when most of the permanent dentition begins to erupt. Isolated teeth that appear larger than normal are typically left untreated; however, generalized macrodontia should be noted, as this condition is likely attributed to a genetic or developmental condition.[24] 

Taurodontism presents radiographically as teeth with larger than normal pulp chambers and shortened roots, two findings that cannot be observed clinically.[22]

Fusion is generally identified during a routine dental examination or when the fused teeth are in the esthetic zone, as seen when a large single tooth occupies the normal space of two teeth. Patients may not be aware of their abnormality unless the condition poses an esthetic or functional challenge.

Treatment / Management

Microdontia is typically treated for cosmetic purposes or to aid in function. Patients with abnormally small teeth will typically present with diastemas (gaps) between adjacent teeth. These gaps may be best addressed by orthodontic interventions.[4] Patients should be evaluated for potential underlying syndromic conditions, especially if generalized.

Macrodontia is a dental anomaly that likely requires an interdisciplinary approach to treatment. The determination should be made whether or not the macrodont can and be maintained in the dental arch due to their abnormally robust size or altered dental anatomy.[21] A combination of oral surgery (exodontia) with subsequent orthodontic therapy is the most common treatment modality.[25](B3)

Taurodont teeth present a challenge to almost every dental specialty. Due to the large pulp chamber and subsequent large pulp horns, the risk of pulp exposure due to decay is increased. Taurodont teeth have a wide variety of shapes and sizes of the pulp chambers, resulting in the potential for apically positioned canal orifices and accessory root canal systems, complicating endodontic therapy.[26] (B3)

From a prosthodontic perspective, post-placement is extremely difficult and, in most cases, contraindicated due to the unpredictability of the pulp chamber and the inability to achieve an intimate fit of the post with the surrounding tooth structure.[18] Extractions of taurodonts are complicated by the positioning of the furcation to the apical third of the root, which makes intimate adaptation of forceps or elevators difficult.[26] Periodontally, taurodontism actually increases the prognosis of affected teeth. Because the root furcation is located more apically, which reduces the frequency of periodontally-driven furcation involvement.[27](B3)

Teeth that exhibit fusion are prone to restorative, periodontal, endodontic, and surgical complications. Patients should be counseled on maintaining optimal oral hygiene and care for these teeth to prevent further complications.

Differential Diagnosis

Microdontia

• Pituitary dwarfism
• Hypopituitarism
• Defects in growth hormone

Macrodontia

• Gemination
• Fusion
• Facial hemihypertrophy

Taurodontism

• Amelogenesis imperfecta
• Dentinogenesis imperfecta
• X-chromosomal Aneuploidy

Fusion

• Macrodontia
• Gemination
• Talon cusp

Prognosis

Microdontia generally has a good prognosis. The fact that it is developmental in origin does not necessarily affect the function of the dentition. Restorative and orthodontic interventions usually address any difficulties or concerns that the patient may have.[28]

Macrodontia has a good prognosis, as the function of the dentition typically remains intact. Restorative and orthodontic interventions usually address any difficulties or concerns that the patient may encounter.[29]

Taurodontism typically presents with a favorable prognosis as long as adequate oral hygiene measures are maintained. As mentioned earlier, many dental interventions are complicated by an enlarged and potentially unpredictable pulp chamber and/or pulpal system.[30]

Fusion generally has a good prognosis, as long as the patient maintains optimal oral hygiene. These teeth are more prone to require restorative, periodontal, and endodontic therapy if not properly maintained.[31]

Complications

Microdontia may present an esthetic or functional challenge for patients, depending on the severity and extent of the condition. Underlying syndromes usually cause more difficulties for the patient than the microdontia itself.[32]

In the anterior maxilla, macrodontia often presents with an esthetic challenge for patients. Macrodonts towards the posterior of the dental arch may lead to further crowding and difficulty with the eruption of teeth. Radiographs should be utilized to monitor for abnormal eruption patterns.[29]

As previously discussed, taurodontism presents several restorative, prosthodontic, endodontic, and surgical complications. Beyond the complications associated with dental interventions, patients are typically unaware of this condition.[30]

Fusion can pose an aesthetic concern due to the altered shape and size of the tooth. With their abnormal presentation, these teeth can have a high risk for decay and periodontal disease and can potentially complicate endodontic therapy.[31]