top of page

Missing, Fused, or Twins?

Author: Shirley Chen

Each of our teeth have unique characteristics that make them distinct from one another. Aside from these normal variances, there can be anomalies with genetic, environmental, or unknown factors that also cause differences between normal and atypical teeth.2 Here, we will discuss tooth agenesis, fusion, and gemination.

Tooth agenesis

Tooth agenesis occurs when one or more teeth do not develop. Anodontia is the term used to describe when no teeth develop, either in one or both of the two sets of dentition - primary dentition (baby teeth), and permanent dentition (adult teeth). Oligodontia refers to when more than six teeth are missing, not including third molars (wisdom teeth). The third form of tooth agenesis is hypodontia, which is when one to six teeth are missing, excluding third molars. Third molars are not included in these definitions because up to 20% of the population do not have them, which means it is relatively common amongst individuals and therefore not an anomaly.1 The permanent dentition more commonly has missing teeth compared to the primary dentition.1 In the permanent dentition, the third molars are the most common teeth that are missing, followed by the mandibular second premolars, maxillary lateral incisors, and maxillary second premolars.1, 2


When two neighbouring teeth join together, it is termed fusion. The fused teeth make one tooth, resulting in an abnormally large tooth and one less tooth in the dental arch. Fusion occurs more frequently in the anterior teeth, such as between a central incisor and its neighbouring lateral incisor. The fused teeth may have a cleft in between them, showing that the two crowns are separate. There are no detrimental effects of having fused teeth, but restorative procedures can be done to improve aesthetics.2


Gemination occurs when one tooth begins to divide during development, but does not do so completely. This process results in a larger tooth, but unlike fusion, there is still a normal number of teeth. As with fusion, no treatment is required, but restorative procedures can improve aesthetics.2

These are just three of many dental anomalies that exist in the human dentition. It is important to identify morphologic variations for functional and aesthetic purposes.2


[1] Klein, O.D., Oberoi, S., Huysseune, A., Hovorakova, M., Peterka, M., & Peterkova, R. (2013). Developmental disorders of the dentition: an update. American journal of medical genetics. Part C, Seminars in medical genetics, 163C(4), 318–332.

[2] Weiskircher, M.A., Gonzalez, S.M., & Palazzolo, M.J. (2016). Diagnosing Developmental Tooth Anomalies. Decisions in Dentistry.

bottom of page