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Trauma modifies the development of an unerupted incisor

Published: May 2017

Bulletin #66 May 2017

Trauma modifies the development of an unerupted incisor

Trauma that affects the anterior region of the mouth in the very young child can easily result in damage to the deciduous dentition, but it may sometimes additionally cause damage to developing permanent teeth by the transference of the force through the long axis of the deciduous teeth to these unerupted adult teeth, in the higher areas of the ridge. For the most part, the damage caused may result in disturbance of amelogenesis which, in its simplest form will cause white or brown patches of hypoplasia of the enamel. There may be more serious implications when the trauma is particularly severe and these may take the form of crown malformation, cystic change of the follicle, damaged root development and even sequestration of the tooth germ. It is true to say that the results of trauma to the altered development of the involved teeth take many forms and few of these subsequent anomalies are the same as any others.

In several of the preceding bulletins that have appeared on this website, I have described what I have termed the “classic” dilacerated central incisor, in which I have shown how a very specific and unusual direction of force will cause a partial or attenuated production of root dentine on the labial side of the root of a developing and unerupted tooth. At the same time, Hertwig’s root sheath in the remainder of the root continues to generate a normal dentine output, resulting in curvature of the root labially and superiorly, often causing the incisal edge of the crown to end up in the anterior nasal spine. The reader is invited to re-read bulletins #10, #11, #28 and #46, which describe the phenomenon and the salient points of its natural development. They also show how the consequences of the trauma affect each of the cases in the identical way and that each “classic” dilacerate central incisor is thus characteristically similar to the next.

There is an alternative developmental scenario in which the central incisor will behave quite differently during its disturbed development, from a similar traumatic incident in the very young child. If the early developing central incisor is oriented vertically and lingual to the traumatized deciduous central incisor, it is conceivable that the blow to the deciduous predecessor will be transmitted upwards and clash with the labial surface of the permanent tooth. The impact may then be conducted upwards and lingually, thereby to damage the dentine-forming cells of Hertwig’s sheath on the lingual side of the crown. This may attenuate or arrest further dentinogenesis at this site, while the remainder of Hertwig’s sheath is still maintaining its normal dentine output. Thus, the further development of the tooth produces a lingually directed crown.

The “classic” dilacerate central incisor is not very frequently seen and I would not be surprised if the majority of my readers have not seen more than 1 or 2 cases in 10 years of specialist orthodontic practice. By comparison, the lingually-directed dilacerate incisor is a rare finding and, in almost 50 years of orthodontics, which has been characterized by a special interest in impacted teeth, I doubt if I have seen more than a handful of such cases.


Fig. 1a. A panoramic radiographic view of a young child exhibiting “classic” dilaceration of the right maxillary permanent incisor.


Fig. 1b. The anterior portion of lateral head film of the same patient showing the labial displacement of the dilacerate incisor crown. The inferior surface of the tooth is its lingual aspect.

The first is a case that was sent to me by my CBCT technician, who had never before seen this type of anomaly. Unlike the “classic” labially deflected dilacerate tooth, where the inferior and forward-facing surface seen on the film is the anatomical palatal aspect of the incisor (Fig. 1a, b), the inferior surface in a palatally deflected dilacerate incisor is formed by the anatomical labial aspect.


Fig. 2a. A panoramic radiographic view showing an unerupted right maxillary central incisor. An attachment has been bonded to the labial aspect of the crown, which faces downward, while the lingual aspect of the crown faces upward.

The lingually deflected dilacerate tooth seen on the panoramic view has the smooth curvature of the labial aspect of the tooth on the underside (Fig. 2a). I would guess that most of us orthodontists would have difficulty believing that the crown is not labial and the root palatal! The CBCT 3D video clip (Fig. 2b) clearly demonstrates the form of the dilaceration and its orientation.

Fig. 2b. Click here A CBCT video clip shows the abnormal form of the tooth and its location in the 3 planes of spaces. The crown is directed lingually, while its root is labially displaced away from the alveolar ridge.

The second case was sent to me by a firm of lawyers to present a written expert opinion on a claim brought by a patient against the community dental clinic, where he had been treated. The patient charged the clinic, its 2 orthodontists and its oral surgeon in a Court of Law, for alleged negligent orthodontic and surgical treatment. The circumstances of the case are not relevant to the present discussion. However, there was some disagreement between the parties on determination of the identity of the anterior teeth.


Fig. 3a. A panoramic of a young male with a neglected dentition, including deep caries in the maxillary first molars and severe periodontal bone loss in the mandibular molar area. You are invited to identify the individual teeth in the maxillary anterior area, before reading further.


Fig. 3b. The same patient as in Fig. 3a. A periapical view of the incisor/canine calamitous relationship.

For this reason and as a simple exercise, I would ask you to please study the panoramic and periapical views (Fig. 3a, b respectively) and see if you can correctly identify and name the anterior teeth in the maxilla from right first premolar to left first premolar. Accurately identifying the individual teeth is critical for the planning of treatment, so you should do this before you read on. The answers are provided at the end of the bulletin.


The anterior portion of the lateral head film of the patient juxtaposed with a tracing of the same view showing the normally erupted right incisor (in blue) and the inter-relationship between the unerupted canine (in red) and the dilacerate central incisor (in green).

The third radiograph, which accompanied the request for my professional opinion, was a lateral head film (Fig. 3c). In general, this is not a film which is prescribed to provide supplementary and corroborative information regarding accurate positional diagnosis. Thus, the film is usually considered irrelevant in the present context and is rarely referred to for anything other than the cephalometric analysis, for which it was developed. Nevertheless, when the film is present, as it usually is for orthodontic treatment planning, it should not be ignored within this context, but should be scoured for additional valuable information. In the present case, it was highly informative in terms of determining the orientation and form of the incisor and the probable cause of the impaction of the left canine (Fig. 3a-c).

In an earlier clinical research paper, we found that when maxillary central incisors are impacted, whether this be due to trauma, to dilaceration or to supernumerary teeth, there is a statistically significant increase in the occurrence of eruption disturbance of the canine of the same side.1 In the present case, this is illustrated by the canine migrating mesially and becoming ensnared in the cul-de-sac formed by the pre- and post-trauma portions of the dilacerate root of the incisor. Please note also that the deciduous canine of the same side has a virtually unresorbed root.

I would imagine that the best compromise that one may expect to achieve in the treatment of this case would be to aim to align the right anterior teeth in their correct order, but not so the anterior teeth of the left side. It is reasonable to assume that the dilacerate impacted central incisor and impacted canine cannot both be brought into the dental arch by orthodontic means without serious periodontal complications. Accordingly, the central incisor should be extracted and the canine brought down into its place eventually to be reshaped/crowned to simulate the missing central incisor. The lateral incisor and the deciduous canine would then require minimal movement to bring them into good positions and, given the long, unresorbed root of the deciduous canine, the result should enjoy a fairly good prognosis long term.


1. Chaushu S, Zilberman Y, Becker A. Maxillary incisor impaction and its relation to canine displacement. American Journal of Orthodontics and Dentofacial Orthopedics, 2003; 124:144-150

Answers to figure 4, from right to left: first premolar, canine, lateral incisor, central incisor, inverted dilacerate central incisor with canine above it, lateral incisor, deciduous canine, first premolar.

Incidentally, the oral and maxillofacial surgeon who had provided a written expert opinion commissioned by one of the defendant’s lawyers, had mistakenly identified the teeth from right to left, thus: first premolar, canine, lateral incisor, central incisor, supernumerary tooth (!), with central incisor above it (!), lateral incisor, permanent canine (!), first premolar.