Gemination (twinning) is the incomplete division of the tooth bud resulting in the formation of two partially or completely independent crowns. The pulp chambers and root may be combined or separate. Geminated teeth give the appearance of an extra tooth and result in potential crowding. The area of defect may vary from a minor notch in the incisal edge of the crown to two separate crowns. The area of the defect may be a focal point for caries formation and should be treated with sealants and composites.
Fusion is the union of two discrete tooth buds to form a tooth with an anomalous shape. It is seen in the anterior region. Fusion of two teeth leads to a reduced number of teeth. Local factors during tooth bud development result in interdental lamina persistence. Genetic factors have also been implicated.
If fusion occurs early in development the defect affects the total length of the tooth resulting in a single normal size tooth. If fusion occurs later in development the defect only affects the root resulting in shared dentin and cementum and one large tooth with a bifid crown. Fusion only along the line of cementum is referred to as concrescence.
The term “supernumerary teeth” refers to the presence of extra teeth in the dental arch. It is due to abnormal activity of the dental lamina leading to the formation of extra tooth buds. There is a greater frequency of occurrence in the maxillary arch (9:1) and in males (2:1). Seventy-five percent remain in bone and are only diagnosed radiographically. They are found in the midline (mesiodens), beyond the 3rd molar (distomolar) or in the molar area (paramolar). Treatment is extraction and orthodontics.
Dens Evaginatus (Talon Cusp)
Dens evaginatus is an elevated conical defect seen on the lingual or occlusal surface of the affected tooth. It is a genetic defect and rarely seen in primary teeth. Evaginations consist of enamel, dentin and pulp. There is an increased risk of pulp exposure due to trauma by the mandibular incisors occluding into the evagination. There is an increased risk of caries in the area between the lingual surface of the crown and the evagination.
Treatment consists of gradual reduction of the evagination to induce formation of secondary dentin. The technique involves carefully removing enamel without local anesthesia until the patient complains of sensation. Fluoride varnish is applied and the patient returns in 3 months for further reduction. Preventive application of sealant or flowable composite in non-hygienic areas is recommended.
Dens Invaginatus (Dens in Dente)
Dens invaginatus is a defect characterized by a prominent lingual cusp and centrally located fossa. The defect results from early invagination of enamel epithelium into the dental papilla of the underlying tooth germ. Its occurrence is more common in permanent teeth. There is increased risk of caries forming in the lingual pit of the tooth that can result in pulp infection and necrosis. Treatment involves preventive filling of the pit and endodontic treatment if indicated.
Microdontia refers to a clinical condition where a tooth appears smaller in size in comparison to other teeth in a normal size jaw. It is rare in primary teeth. It is more common in permanent teeth and in females. The most common locations are the maxillary lateral incisors and third molars. The shape of the tooth may be conical (peg) or normal.
General microdontia may be associated with congenital hypopituitarism, and radiation or chemotherapy exposure. Localized microdontia is frequently associated with hypodontia (missing teeth) and it is not unusual to see a microdontic maxillary lateral incisor and a missing contralateral tooth. These defects may be controlled by different mutations of the same gene. The tooth is treated aesthetically with composites, crowns, and orthodontics for closure of spaces.