What are the factors that determine the site on the root where the change in direction of the orientation of the apical portion of the root begins and the acuteness of its angle?

The type of trauma that results in a “classic” dilaceration will have attenuated or killed off all the dentine-producing cells of Hertwig’s sheath on the sharp rim of the forming root on the labial side. This limits or denies dentine output at that point, while the palatal side of the root continues to churn out dentine undisturbed. Thus, the age at which the trauma will have occurred is a critical factor. The earlier the trauma, the greater the degree of dilaceration, simply because there is more dentinogenetic potential to be realized post-trauma in a younger patient. No doubt the force of the trauma is also a factor insofar as it will cause a greater or lesser area of damaged dentine on the labial side, but this can only be conjectured.

At age 8 years, an unaffected central incisor has a wide open apex, which is not scheduled to close until about the age of 10 years. From the clinical perspective, it seems likely that apexification of a trauma-affected incisor may be later than that and, at the age of 9-10 years, resolution of the impaction and the achievement of alignment are likely to be completed before the apex has closed. It follows, therefore, that the root will continue to elongate along the same curved path towards the labial periosteum of the alveolar ridge, for many months thereafter. In practice, the orthodontist will be able to palpate this developing apex in the labial sulcus, because it will generally create a hard protrusion disturbing the smooth continuity of its oral mucosa covering.

Does the continued labial root torque actually cause the root apex to perforate the labial oral mucosa?

Probably not, if it is within certain limits, but it does make the hard protrusion highly vulnerable to traumatic injury even from careless toothbrushing, since it has only the thinnest mucosal covering. From this minimal ulceration, the apex, its tiny nutritive blood vessels and fragile nerve filaments may become exposed. The mucosa is unlikely to re-heal over the protrusion and the tooth will lose its vitality.

For this reason in many of the cases, an apicoectomy of the root needs to be performed, usually together with a root canal filling, in order to be sure that the remainder of the root is surrounded on all sides by alveolar bone.

In that case, is it a good idea to fully torque the incisor in the phase 1 treatment plan, before debanding the case?

The answer to that is the same answer that one gives to any phase 1 case. Since the orthodontic treatment cannot be completed until all the permanent teeth are fully erupted, the aims of early treatment should be limited to what would otherwise be functionally or health compromised, or what is unacceptable from the point of view of the appearance or what will worsen in the absence of suitable treatment. For these reasons most observed discrepancies in tooth position, rotation or axial orientation are not attempted until a phase 2 plan is initiated in the permanent dentition. Appraised on these criteria, the dilacerate incisor usually justifies a phase 1 treatment. The impaction should be resolved and the tooth drawn down and aligned in the arch. An extremely large degree of labial root torque will need to be undertaken, but this should stop when the root end becomes mildly prominent in the labial sulcus.⁶ Final root torque should only be performed towards the end of the phase 2, when an assessment of the need for apicoectomy will be made.

Is apicoectomy always necessary in the treatment of dilacerate central incisors?

No, there are a good number of patients in whom the curvature of the root end is not severe and the crown of the tooth may reach its ideal 3D alignment in 3 places of space, without its apex bulging the labial alveolar ridge.

Can labial root torque of an incisor with an open apex result in a realignment of the growth direction of the developing apical portion of the root?

The answer to this question is the same answer that needs to be offered when asking if it is contraindicated to bodily retract maxillary incisors in a class 2 division I case, or to apply lingual root torque of the incisors in a class 2 division II case, in the early mixed dentition. There are no literature reports and certainly no sound evidence of altered root morphology occurring in these circumstances, despite the fact that root torqueing or root uprighting mechanics are performed very frequently in everyday orthodontic practice on pre-apexified teeth. It seems clear that the apical portion of the tooth follows a pre-determined pattern regardless of the vectors of the forces placed on it. The common argument that a slow “orthodontic dilaceration” of the uncompleted apical third of the root may occur when torque is applied during the final stages of apexification, would seem to have no basis⁷. On the contrary, the fact that this unsubstantiated narrative may be false lends support to the hypothesis explaining how dilacerations occurs, which has been reiterated here and which is specifically based on a trauma-related etiology.

What is the reason for the frequently seen post-treatment relapse?

When orthodontic treatment of most malocclusions is completed, the patient is placed on a retention regime to prevent a deterioration of the fine alignment and occlusion that will have been achieved.

At the end of a phase 1 treatment in which a dilacerate incisor impaction has been resolved, the orthodontist is faced with a dilemma. If no retainer is placed, the affected tooth will quickly move back out of alignment, with the incisal edge tipping labially. This relapse is relatively mild (Fig. 3), although its being at the front of the mouth will make it more alarming to the patient. The reason for the deterioration, aside from the usual post-orthodontic factors, is that the forward-facing and uncompleted root end is developing further and pushing against the labial periosteum of the alveolar ridge. Since the periosteum is resistant, the continued root growth pushes the formed root lingually and the crown labially. If, therefore, retention is instituted, the apexification process may cause the root end to bulge into the labial sulcus and require early apicoectomy. For this reason, retention should only be maintained for as long as there is little or no labial bulge of the developing root end and this will require regular follow-up examination.

Should a retaining device be used at the end of the phase 1 treatment to hold the alignment until phase 2 treatment is initiated?

As with every other decision, there are pro’s and con’s. On the one hand, the parents and child will be most distressed to see a beautiful post-treatment alignment rapidly deteriorate, if no retainer is employed. On the other hand, to rigidly retain in the younger patient is to find the bulge on the labial aspect of the sulcus mucosa covering the alveolar ridge becoming more and more prominent and vulnerable to minor traumas.

Fig. 3a, b. Intraoral frontal and occlusal views of patient B, an 8.6 year old female showing the missing left maxillary central incisor and space closure particularly from the tipped adjacent lateral incisor.

Fig. 3c, d. The cephalogram and panoramic views show a similar picture of the dilacerate incisor to that of patient A.

Fig. 3e. A 3D screen shot after all bone and soft tissue has been eliminated.

Fig. 3f. A series of adjacent cone beam CT cross-sectional cuts of the tooth.

Fig. 3g. A series of cone beam CT axial (horizontal) cuts. Note the change in the orientation of the tooth as the cuts progress downward (from left to right). The 2 cuts on the extreme right show the apical part of the root lying horizontally, with open apex and a distinct and usually palpable bulge on the palatal side (arrows).

Fig. 3h. The end of phase 1, on the day of debonding. Note the long clinical crown of the aligned left central incisor – an apically repositioned attached gingival flap procedure had been advised when the incisor had been brought down and before it had erupted, but was refused by the parents. As a conscious decision, no retainer was placed to hold the alignment.

Fig. 3i, j. Seen 17 months later, in preparation for the phase 2 procedure, the extent of the incisor relapse may be seen.

Fig. 3k, l. Anterior portion of the cephalogram and the panoramic view immediately prior to the commencement of phase 2.

Fig. 3m. Following 6 weeks of orthodontic treatment, re-alignment has been achieved and there is marked improvement of the gingival condition.