A mesiodens is a supernumerary (extra) tooth that develops between the two maxillary central incisors, making it the most common supernumerary tooth in the human dentition. It affects between 0.15% and 1.9% of the population, occurs approximately twice as often in males as in females, and is the leading dental cause of delayed eruption of the upper front teeth in children. Understanding how a mesiodens is numbered, classified, diagnosed, and treated gives patients and parents the clinical foundation to make informed decisions about a condition that, left unmanaged, causes permanent damage to adjacent teeth.
How Mesiodens Is Numbered in Different Dental Systems
Three numbering systems are used internationally, and the designation for a mesiodens differs in each. Dentists use whichever system is standard in their country, so understanding all three avoids confusion when reviewing records or seeking second opinions.
FDI Two-Digit System (ISO 3950)
The FDI World Dental Federation two-digit system is the internationally adopted standard used across Europe, Asia, Australia, and most of the world outside the United States. In this system, the first digit identifies the quadrant and dentition (permanent or primary), and the second digit identifies the tooth within that quadrant.
Supernumerary teeth in the FDI system are designated with a zero as the first digit. A mesiodens is designated tooth 01 in the permanent dentition. When two mesiodens are present simultaneously (a rare but documented presentation), they may be designated 01 and 02. For a mesiodens in the primary dentition, the designation is tooth 51 (using the 50 series reserved for primary supernumerary teeth in the upper anterior region).
Universal Numbering System (UNS)
The Universal Numbering System is the standard used in the United States. Permanent teeth are numbered 1 through 32 from the upper right third molar around to the lower right third molar. Primary teeth use letters A through T.
Supernumerary teeth in the UNS do not have a formal standardized designation in the same way as the FDI system. Common clinical practice designates a mesiodens as tooth 51 or labels it with the number of the adjacent tooth plus the letter “S” for supernumerary (for example, “8S” or “9S” indicating a supernumerary adjacent to teeth 8 and 9, the upper central incisors). Some practitioners use “M” for mesiodens specifically in clinical records. The absence of a single universal UNS designation for mesiodens is a known limitation of that system for supernumerary documentation.
Palmer Notation System
The Palmer notation system uses a grid-based quadrant symbol and number. Supernumerary teeth are typically designated with a plus sign (+) or the letter “S” added to the nearest tooth’s notation. A mesiodens appearing between the upper central incisors is recorded as +| or |+ depending on its position relative to the midline. Palmer notation is still used in the United Kingdom and by some oral surgery specialists internationally.
What Is a Mesiodens: Developmental Origin
A mesiodens arises from a third tooth bud that develops from the dental lamina between the tooth germs of the two maxillary central incisors. The precise cause is not fully understood, but current evidence supports a combination of factors.
Genetic factors play the strongest documented role. Mesiodens shows familial aggregation, with first-degree relatives of affected individuals carrying a significantly higher prevalence than the general population. The inheritance pattern is most consistent with an autosomal dominant trait with variable penetrance, meaning not everyone who inherits the genetic variant will develop a mesiodens, but the tendency clearly runs in families.
Dichotomy theory proposes that the tooth bud of a central incisor splits during development, producing one normal tooth and one extra smaller tooth. This theory is supported by the supplemental morphological type (discussed below), where the mesiodens closely resembles the adjacent central incisor in form.
Hyperactivity of the dental lamina theory proposes that a localized overdetermination of dental lamina cells produces an additional tooth germ without splitting from an existing one.
Prevalence by population: Studies report prevalence ranging from 0.15% to 1.9%, with Asian populations generally showing higher rates than European populations. The male-to-female ratio is consistently reported at approximately 2:1 across population studies, making mesiodens significantly more common in males.
Four Morphological Types of Mesiodens
The shape of a mesiodens directly determines how it behaves clinically, whether it will erupt spontaneously, and what complications it is most likely to cause. Classifying mesiodens by morphology is the foundation of treatment planning.
Conical Type
The conical mesiodens is the most common morphological form, accounting for approximately 60 to 70% of cases. It has a small, peg-shaped or conical crown, often with a complete or near-complete root, and resembles a miniature version of a lateral incisor more than a central incisor.
Conical mesiodens frequently erupt spontaneously into the oral cavity, either palatally displaced or protruding between the central incisors. Because they often erupt, they are commonly detected earlier through visual inspection. When they erupt, they cause crowding, aesthetic problems, and displacement of adjacent teeth, but they are generally the simplest morphological type to remove surgically due to their small size and often favorable position.
Tuberculate Type
The tuberculate mesiodens has a barrel-shaped or multi-cusped crown with multiple tubercles (rounded projections), an incompletely formed root, and almost always remains impacted. This type is far more likely to cause delayed or blocked eruption of the permanent central incisors than the conical type because it tends to sit directly in the path of the erupting central incisors rather than palatal to them.
Tuberculate mesiodens are almost always found palatally positioned and frequently occur bilaterally (both sides of the midline) in the same patient. The incomplete root development means they may continue to develop slowly after initial detection, making monitoring timing important.
Supplemental Type
The supplemental mesiodens closely resembles a normal-sized central incisor in crown form and may be nearly indistinguishable from the adjacent teeth by visual inspection alone. It results from duplication rather than aberrant development and represents a genuine extra incisor rather than a morphologically abnormal tooth.
This type causes significant crowding of the anterior maxillary segment and may displace one central incisor palatally while occupying its arch position. It is less common than conical or tuberculate forms and requires careful clinical and radiographic evaluation to identify which tooth is the supernumerary and which are the two normal central incisors.
Odontome (Composite Odontoma)
A small subset of mesiodens-region supernumerary teeth develop as odontomas rather than tooth-like structures. A compound odontoma consists of multiple small rudimentary tooth-like structures (denticles) clustered together. A complex odontoma is a disorganized mass of enamel, dentine, and cementum without recognizable tooth morphology.
Odontomas in the mesiodens region are typically detected on radiograph as a calcified mass in the midpalatal region, often with a radiolucent rim. They obstruct central incisor eruption effectively and require surgical removal, but they carry no malignant potential.
Eruption Status and Orientation
Beyond morphology, the eruption status and spatial orientation of a mesiodens determine the surgical approach and the risk to adjacent teeth.
Erupted Mesiodens
An erupted mesiodens has penetrated the gum and is visible in the oral cavity. It may erupt palatally (behind the central incisors), labially (in front of them), or between them. Erupted mesiodens are typically conical in morphology and are the easiest to remove because their position is fully visible and surgical access is straightforward.
Impacted Mesiodens
An impacted mesiodens remains within the bone and has not penetrated the gum. Impacted mesiodens are far more likely to cause complications than erupted ones because their position relative to the central incisor roots and the nasal floor determines both the risk of root resorption and the complexity of surgical removal.
Three orientations of impacted mesiodens are recognized:
Normally oriented (vertical): The crown is positioned apically with the crown pointing toward the oral cavity, mirroring the orientation of a normally erupting tooth. These carry the best prognosis for spontaneous post-removal eruption of blocked central incisors.
Inverted: The crown points toward the nasal floor and the root points toward the oral cavity. Inverted mesiodens have no possibility of spontaneous eruption and are associated with the highest risk of nasal floor penetration if left in place long-term. Surgical removal of an inverted mesiodens requires working deeper into the palatal bone and carries higher risk of proximity to the central incisor roots.
Transverse (horizontal): The tooth lies on its side with the crown pointing toward one central incisor root and the root toward the other. Transverse mesiodens present the greatest surgical challenge and the highest risk of root resorption because the crown is in direct contact with adjacent root surfaces for extended periods.
Complications of Untreated Mesiodens
Leaving a mesiodens in place without monitoring or treatment produces a predictable set of complications, the severity of which increases with time.
Delayed or Blocked Eruption of Central Incisors
The most clinically significant complication of mesiodens, particularly the tuberculate and inverted types, is blocking the eruption pathway of one or both maxillary central incisors. A child whose lateral incisors have erupted but whose central incisors remain absent at age 8 or older requires immediate radiographic investigation for a mesiodens.
When central incisor eruption is blocked, the follicular sac surrounding the impacted incisor may become dilated, complicating surgical exposure and orthodontic traction even after the mesiodens is removed.
Midline Diastema
An impacted mesiodens positioned between the roots of the central incisors generates lateral pressure that forces the central incisors apart, producing a midline diastema. Critically, this diastema does not always close spontaneously after the mesiodens is removed. Research shows that in children under 7 years of age at the time of removal, spontaneous diastema closure occurs in approximately 62 to 75% of cases as the central incisors complete root development and move naturally together. In older patients, orthodontic treatment to close the diastema is typically required after removal.
Root Resorption of Adjacent Teeth
Direct contact between a mesiodens crown or developing follicle and the roots of the permanent central incisors causes pressure resorption of the incisor roots. This is an irreversible process — once root structure is lost, it does not regenerate. Resorption appears on periapical radiographs as a shortening or notching of the central incisor root outline in the area of mesiodens contact.
The clinical implication is that prolonged observation of an impacted mesiodens that is in contact with central incisor roots trades short-term surgical simplicity for the risk of permanent root damage that compromises the long-term prognosis of those teeth.
Dentigerous Cyst Formation
An impacted mesiodens retained in bone over an extended period carries a risk of developing a dentigerous cyst (also called a follicular cyst) — a fluid-filled cyst that develops from the epithelium of the dental follicle surrounding the impacted tooth’s crown. Dentigerous cysts expand slowly into the surrounding bone, displacing teeth, destroying alveolar bone, and in large cases approaching the floor of the nasal cavity or the floor of the orbit.
Treatment of a mesiodens that has developed an associated dentigerous cyst requires both removal of the mesiodens and complete enucleation of the cyst lining. Failure to remove the entire cyst lining results in recurrence.
Midline Rotation and Displacement of Incisors
Beyond diastema, an asymmetrically positioned mesiodens can rotate and tilt the adjacent central incisors, producing an asymmetric midline and crowding that requires full orthodontic correction. When the mesiodens is positioned to one side of the midline, it displaces one central incisor more than the other, creating a canted midline relationship.
Associated Syndromes: When Multiple Supernumerary Teeth Signal a Larger Condition
A single mesiodens in an otherwise healthy patient is an isolated developmental anomaly with no systemic implications. However, a patient presenting with multiple supernumerary teeth, including bilateral mesiodens or mesiodens accompanied by supernumerary teeth elsewhere in the arch, requires evaluation for two systemic conditions.
Cleidocranial Dysplasia
Cleidocranial dysplasia (CCD) is an autosomal dominant skeletal dysplasia caused by mutations in the RUNX2 gene. Its hallmark dental findings include numerous supernumerary teeth (often 30 or more throughout the mouth), delayed eruption of permanent teeth due to the supernumeraries and absent cellular cementum, and persistence of primary teeth well beyond normal exfoliation age.
Non-dental features include absent or hypoplastic clavicles (which allow patients to bring their shoulders together in front of their chest, a near-pathognomonic finding), delayed closure of cranial sutures and fontanelles, frontal bossing, and short stature.
Dental management of CCD is extremely complex and typically requires extraction of all supernumerary teeth, surgical exposure of impacted permanent teeth, and extensive orthodontic treatment over many years.
Gardner Syndrome
Gardner syndrome is an autosomal dominant condition caused by mutations in the APC tumor suppressor gene. Its systemic features include colorectal polyposis (with high risk of malignant transformation if untreated), osteomas of the skull and jaw, epidermoid cysts, and supernumerary teeth. The dental and jaw findings frequently precede the colorectal diagnosis.
A patient with multiple supernumerary teeth, jaw osteomas, or skin cysts should be referred for gastroenterological evaluation because the colonic polyps in Gardner syndrome carry a near 100% lifetime risk of colorectal carcinoma without prophylactic colectomy.
Radiographic Diagnosis: Choosing the Right Imaging
Accurate mesiodens management is impossible without imaging. Clinical examination detects erupted mesiodens but cannot locate impacted ones or assess their orientation, proximity to adjacent roots, or relationship to the nasal floor.
Periapical Radiograph
A periapical radiograph of the maxillary central incisor region provides a detailed view of the root structures of the central incisors and can detect a mesiodens in the same plane. It is the first-line investigation when a mesiodens is suspected in a child presenting with delayed central incisor eruption or visible midline diastema.
Limitations include the two-dimensional nature of the image, which cannot confirm whether the mesiodens is palatally or labially positioned relative to the central incisors. Two periapical films taken at different horizontal angulations (using the parallax or SLOB technique — Same Lingual, Opposite Buccal) address this limitation to a degree. If the mesiodens appears to move in the same direction as the tube shift, it is palatally positioned. If it moves in the opposite direction, it is labially positioned.
Dental Panoramic Tomograph (OPG)
A panoramic radiograph provides an overview of the entire dentition and is useful for identifying multiple supernumerary teeth, assessing general eruption status, and screening for associated pathology in other arch segments. It does not provide sufficient detail of the mesiodens and adjacent root relationships to guide surgical planning on its own.
Cone Beam Computed Tomography (CBCT)
CBCT provides three-dimensional imaging and is the most informative investigation for complex mesiodens cases. It is indicated when the mesiodens is inverted or transverse, when root resorption of the central incisors is suspected, when multiple mesiodens or an associated cyst is present, and when two-dimensional radiographs give conflicting information about position.
CBCT delivers a radiation dose higher than periapical films (though lower than medical CT) and is not indicated as a routine first investigation in straightforward cases. The clinical decision to use CBCT should be justified by a finding that changes the surgical management compared to what two-dimensional imaging provides.
Surgical Removal: Approach, Technique, and Timing
Optimal Age for Removal
The timing of mesiodens removal significantly affects outcomes. Current evidence supports removal before age 7 in most cases, ideally when the central incisor roots are approximately one half to two thirds formed. At this stage, the eruption force of the developing central incisors is at its maximum, and spontaneous eruption after obstacle removal is most likely.
Removal before age 5 carries higher anesthetic risk and risks damage to the forming permanent incisor crypts. Removal after age 10 reduces the probability of spontaneous central incisor eruption significantly, making planned orthodontic traction more often necessary.
For an erupted conical mesiodens with no evidence of incisor eruption obstruction, removal can be timed to align with the child’s dental cooperation and the treating team’s judgment.
Surgical Access: Palatal vs Labial Approach
The position of the mesiodens within the alveolar bone determines whether a palatal or labial surgical approach is used.
Palatal approach: The majority of impacted mesiodens are palatally positioned, making the palatal approach the most commonly used. A palatal mucoperiosteal flap is elevated to expose the bone overlying the mesiodens. Bone removal with a surgical bur or chisel exposes the mesiodens crown, which is then delivered using elevators and forceps. The proximity of the central incisor roots requires careful flap design and bone removal to avoid root damage. A periosteal incision should not extend too anteriorly in young children to preserve the anterior palatal blood supply.
Labial approach: A labially positioned mesiodens is accessed through an incision in the attached gingiva or alveolar mucosa on the facial surface of the alveolus. This approach provides direct access to labially impacted mesiodens but carries a small risk of scarring the visible anterior gingival tissue if the flap is not designed and closed carefully.
Nasal floor proximity: Inverted mesiodens in older patients may be in close proximity to or penetrating the floor of the nasal cavity. Preoperative CBCT to confirm the exact relationship is essential in these cases to prepare for possible nasal floor management during surgery.
Post-Surgical Care
After mesiodens removal, the socket is irrigated and the mucoperiosteal flap is repositioned and sutured. Resorbable sutures are preferred in children to avoid a return appointment for removal. Post-operative instructions include soft diet for several days, avoidance of rinsing for 24 hours, and chlorhexidine gluconate 0.12% mouthwash twice daily from day two onward.
A follow-up radiograph at six to nine months post-removal monitors the eruption progress of the previously blocked central incisors.
Post-Removal Orthodontic Management
Mesiodens removal solves the obstruction but does not always complete the treatment. The follow-up period requires structured assessment to determine whether orthodontic intervention is needed.
Spontaneous eruption monitoring: After mesiodens removal in a child under 7, a period of 12 to 18 months is allowed for spontaneous eruption of the previously blocked central incisors. If the central incisor is visible on radiograph to be moving toward the occlusal plane and its crown is within 2 to 3mm of the gum surface, continued monitoring is appropriate.
Surgical exposure and orthodontic traction: If a central incisor fails to erupt spontaneously within 12 to 18 months of mesiodens removal, or if the tooth is ankylosed, palatally displaced, or has a dilacerated (bent) root, the tooth requires surgical exposure and orthodontic traction. The orthodontist bonds a bracket or gold chain to the crown of the surgically exposed incisor, and gentle traction force applied through an orthodontic appliance guides the tooth into the arch.
Diastema closure: A midline diastema persisting after mesiodens removal in a patient over 7 typically requires orthodontic space closure. Fixed appliances (braces) or clear aligner therapy can close the diastema once the central incisors have erupted fully. Retention after closure is essential because a central incisor diastema has a well-documented tendency to reopen without long-term retention.
Mesiodens Diagnosis and Treatment: Summary Table
| Feature | Conical type | Tuberculate type | Supplemental type | Odontoma |
|---|---|---|---|---|
| Crown shape | Peg or cone | Barrel, multi-cusped | Normal incisor form | Irregular calcified mass |
| Likelihood of eruption | Moderate to high | Very low | Moderate | None |
| Primary complication | Crowding, aesthetic issue | Central incisor eruption blockage | Arch crowding, incisor displacement | Eruption blockage |
| Surgical complexity | Low | Moderate to high | Moderate | Moderate to high |
| Spontaneous post-removal incisor eruption | Good if removed early | Good if removed before age 7 | Good if removed early | Good if removed early |
Clinical References
Rajab, L.D., Hamdan, M.A.M. (2002). Supernumerary teeth: review of the literature and a survey of 152 cases. International Journal of Paediatric Dentistry, 12(4), 244-254.
Ferrés-Padró, E., Prats-Armengol, J., Ferrés-Amat, E. (2009). A descriptive study of 113 unerupted supernumerary teeth in 79 pediatric patients in Barcelona. Medicina Oral Patología Oral y Cirugía Bucal, 14(7), E331-336.
Garvey, M.T., Barry, H.J., Blake, M. (1999). Supernumerary teeth — an overview of classification, diagnosis and management. Journal of the Canadian Dental Association, 65(11), 612-616.
Koch, H., Schwartz, O., Klausen, B. (1986). Indications for surgical removal of supernumerary teeth in the premaxilla. International Journal of Oral and Maxillofacial Surgery, 15(3), 273-281.
FDI World Dental Federation. ISO 3950:2016. Dentistry — Designation system for teeth and areas of the oral cavity. International Organization for Standardization.
This article provides clinical information for educational purposes. A licensed dental professional must evaluate your child’s specific condition for accurate diagnosis and treatment planning.
