Gemination or fusion?

Sir, I read with much interest the very unusual case of a patient who presented with double teeth (BDJ 2007; 202: 508). Although the differentiation between gemination and fusion is very accurately explained, I would like to comment that the authors make the assumption that the case of double teeth was of gemination rather than fusion. As correctly stated, the distinction is made upon the grounds of developmental aetiology with fusion resulting from the union of two separate tooth buds whilst gemination resulting from partial development of two teeth from a single tooth bud.1,2 Thus, although the case described is most highly likely due to gemination, this case may be a result of fusion.

I would like to share with your readers another similar case of a healthy 18-year-old who presented with double teeth, complaining of frequent episodes of infection, swelling and irritation associated with an erupted maxillary third molar. Although clinical examination clearly revealed double teeth, radiographic examination failed to accurately demonstrate the anomalous tooth morphology (Fig. 1). The extracted tooth had five separate roots (Figs 2a-c).

Figure 1

Dental panoramic radiograph

Figure 2

Anterior view; posterior view; apical view

The prevalence of double teeth in the primary dentition is 0.5-1.6%; in the permanent dentition it is in the region of 0.1-0.2%. Both sexes are affected with equal frequency. It most commonly involves the anterior dentition and the clinical manifestation of this anomaly varies considerably from a minor notch in the incisal edge of an abnormally wide incisor to the appearance of almost two separate crowns. There may be continuity of hard tissue either between the crowns or roots of the two elements or between both crowns and roots.3

Double teeth are not always discernible on radiographs. In this case, the dental panoramic radiograph demonstrates an unusual occlusal surface and cusp morphology but fails to demonstrate the large crown and multi-root structure. This is due to the fact that the tooth was joined in the palatal plane rather than in the buccal. In view of this, my impression is that the double teeth are due to fusion between a maxillary third molar with a paramolar rather than due to gemination, although it is impossible to define this with certainty.

The clinical relevance of upper posterior double teeth is in the possibility of unintentionally removing undiagnosed double teeth and/or causing fracture of the maxillary tuberosity upon exodontias.4,5 When such a complication is recognised by the general dental practitioner, the maxillary tuberosity should not be removed and the patient should be referred to a specialist unit.


  1. 1

    Soames J V, Southam J C . Oral pathology. 3rd ed. pp 6–7. Oxford: Oxford University Press, 1997.

  2. 2

    Grover P S, Lorton L . Gemination and twinning in the permanent dentition. Oral Surg Oral Med Oral Pathol 1985; 59: 313–318.

  3. 3

    Welbury R R . Paediatric dentistry. 2nd ed. pp 277–278. Oxford: Oxford University Press, 2001.

  4. 4

    Shah N, Bridgman J B . An extraction complicated by lateral and medial pterygoid tethering of a fractured maxillary tuberosity. Br Dent J 2005; 198: 543–544.

  5. 5

    Norman J E, Cannon P D . Fracture of the maxillary tuberosity. Oral Surg Oral Med Oral Pathol 1967; 24: 459–467.

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Grammatopoulos, E. Gemination or fusion?. Br Dent J 203, 119–120 (2007).

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