• 30–50% of the primary cases are followed by defects in the permanent successors.
Localization
• Upper and lower incisors.
Clinical features
• Variable, from a minor notch in the incisal edge of a wide crown to almost two separate crowns. Similarly, the pulp chamber and the root canal may be common to both elements, or separate for each one.
Complications
• Potential crowding of the dental arch. Difficulty in the differential diagnosis between gemination and fusion of a normal and supernumerary tooth.
Treatment
• Aesthetic restoration with composites, or surgical removal of the supernumerary in cases of twinning. Orthodontic treatment of the potential crowding.
Fig. 1.4 Conical teeth in a patient with hypohidrotic ectodermal dysplasia
Fig. 1.5 Gemination of an upper lateral incisor
Fusion
Definition
• Refers to the union of two discrete tooth buds, resulting in the formation of a tooth with an anomalous shape.
Etiology
• The defect is a result of interdental lamina persistence during dental organ development, caused by local factors.
• Genetic factors have also been implicated, such as autosomal dominant inheritance with reduced penetrance.
Occurrence in children
• Including gemination, it is rare in both primary (0.5–1.6%) and permanent (0.1–0.2%) teeth.
• Ethnic variations result in a higher incidence in some populations.
• 30–50% of the primary cases are followed by defects in the permanent successors.
Localization
• Anterior teeth.
Clinical features
• If fusion occurs early during the tooth development, the defect affects the total length of the tooth, resulting in a single tooth of almost normal size.
• If fusion occurs later, the defect only affects the root (Fig. 1.6), resulting in shared dentine and cementum, and one large tooth or a tooth with bifid crown.
Complications
• Fusion most often leads to a reduced number of teeth in the dental arch, although occasionally a normal and a supernumerary tooth may be fused. In the latter case, there is difficulty in the differential diagnosis between this defect and gemination. Fusion in the primary dentition may be followed by aplasia of the permanent successor.
Treatment
• Aesthetic restoration with composites, or surgical separation and removal of the fused supernumerary tooth. Orthodontic treatment of the potential crowding.
Concrescence
Definition
• Refers to a type of fusion in which the formed teeth are joined only along the line of cementum.
Etiology
• This defect can happen before or after the teeth erupt, and is most probably a result of local trauma, dental crowding, and dislocation of tooth germs during root formation.
Occurrence in children
• Rare.
Localization
• Upper second and third molars.
Clinical features
• Diagnosis of the alteration can be definite only with radiographs.
Complications
• The defect does not have any clinical significance except in cases in which extractions are needed and appropriate surgical manipulations should be followed.
Treatment
• No treatment is required, since the affected teeth are asymptomatic.
Dilaceration
Definition
• Refers to an extensive bend in the root on the cervical area of the affected teeth.
Etiology
• The defect results from disruption of the Hertwig epithelial root sheath due to eccentric dislocation of the already formed crown in relation to the developing adjacent soft tissues (Figs. 1.7, 7.8).
• Dilaceration has been associated with trauma of the predecessor primary teeth during the developmental period of the permanent tooth, or with therapeutic irradiation of the area.
Occurrence in children
• Rare.
• 3% of the successors in cases of traumatized primary teeth.
Localization
• Anterior teeth.
Clinical features
• Malformed crown, frequently hypoplastic, and severe deviation of the long axis of the crown or root segment of the tooth.
Complications
• Clinical problems caused by the defect include difficulties in case of extraction, and the frequent impaction of these teeth.
Treatment
• In case of normal eruption, aesthetic or prosthetic restoration. In case of impaction, combined surgical and orthodontic treatment in order to align the tooth in the dental arch, followed by aesthetic restoration.
Fig. 1.6 Fusion of lower primary lateral incisors and canines
Fig. 1.7 Dilaceration, mesial-distal, of an upper central incisor due to trauma in the predecessor primary tooth
Fig. 1.8 Dilaceration, buccal-palatal, of an upper central incisor due to trauma in the predecessor primary tooth
Dens Invaginatus (Dens in Dente)