Variation in form of teeth: Dilaceration, Taurodontism, Double teeth, Concrescence
Disturbances in tooth form may involve the crown, the root, or both. The most frequent variations of the crowns of teeth affect maxillary permanent lateral incisors, which may be peg-shaped or show an accentuated cingulum – either variation sometimes being associated with an invagination. Premolars or molars with an increased or decreased number of cusps are also frequently seen. Variations in the number, course, form, and size of roots are particularly common.
The term dilaceration is used to describe a deformity in which the crown of the tooth is displaced from its normal alignment with the root, so that the tooth is severely bent along its long axis (Figs). Dilaceration is usually the result of acute mechanical trauma and most frequently
involves the maxillary incisors.
A taurodont tooth (bull-like tooth) is one in which the pulp chamber has a greater apico-occlusal height than in normal teeth, with no constriction at the level of the amelocemental junction. The result is that the chamber extends apically, well beyond the neck of the tooth (Fig). The anomaly affects multirooted teeth and is thought to be caused by the failure of Hertwig’s sheath to invaginate at the proper horizontal level. It is rare in the primary dentition. Taurodont teeth may occur as incidental findings or be associated with other rare craniofacial or dental anomalies. There is also an association with abnormalities in the number of the sex chromosomes such as in Klinefelter and poly-X syndromes.
Double teeth is a descriptive term used to describe a developmental anomaly where two teeth appear joined together. The degree of union is variable and may involve the crown, the roots, or both. It is very unusual for teeth to be united by enamel only, joining of the dentine and also the
pulp chamber being much more frequent (Figs).
However, the aetiology remains unclear although a genetic basis has been suggested. For this reason the general term ‘double teeth’, which describes the appearance with no implication regarding aetiology, is preferred. The developmental anomaly of double teeth must be distinguished from concrescence which is an acquired condition where teeth are joined by cementum only.
Double teeth are more common in the primary than in the permanent dentition, the prevalence in different series ranging from 0.5-2.5 per cent for the primary and 0.1-0.2 per cent for the permanent dentitions. The incisors (and also the canines in the primary dentition) are most frequently affected and the condition may be bilaterally symmetrical (Fig.). In the primary dentition the majority of cases involve the anterior mandibular teeth.
Concrescence is an acquired disorder in which the roots of one or more teeth are united by cementum alone after formation of the crowns (Fig.). This is most frequently seen in the permanent dentition where the roots of teeth develop close together (for example, between maxillary second and third molars) or following hypercementosis associated with chronic inflammation.