Delayed biological tooth eruption and eruptive potential: a case series

Incidence

Unerupted teeth are a common finding within any new orthodontic patient clinic, with third permanent molars being the most frequently impacted tooth in 24.4% of the population worldwide.¹

The maxillary canine is reported to be impacted in approximately 2% of the population.² It has a long path of eruption³ and is often the last tooth in the upper arch to erupt, making it susceptible to impaction following loss in arch length. In such cases, maxillary canines are often forced out of the line of the arch into buccally ectopic positions.⁴ In contrast, two theories have been suggested to account for palatally ectopic canines: The ‘guidance theory’, proposes that anomalous or absent lateral incisors are a causative factor, as they are instrumental in guiding the path of eruption of the canine.⁵ The ‘genetic theory’ suggests that palatally displaced canines are as a result of polygenetic inheritance.⁶

Mandibular second premolar impaction is seen in 0.2–0.3%⁷ of the population and accounts for 24% of all impacted teeth.⁸ These teeth are also susceptible to impaction, as they are the last teeth in the mandibular arch to erupt.

When is tooth eruption delayed?

Whether or not eruption is delayed can be determined on a chronological or biological basis. A permanent tooth is expected to erupt within 6 months of exfoliation of its primary predecessor. If this time exceeds 12 months, there is cause for concern. A delay of greater than 6 months following eruption of the contralateral permanent tooth has also been considered as a parameter for delayed eruption.⁹

A biological method for determining eruption timing, is the assessment of root development. This was first described by Grøn,¹⁰ where tooth emergence coincided with completion in development of three quarters of the root length. Becker¹¹ has used this as the basis as to determine whether a tooth can be considered impacted and whether further management or monitoring is required. Completion of two-thirds of root development has also been used as a milestone for eruption¹² and a favourable prognostic factor of eruptive potential. Suri et al suggested that where greater than two-thirds of the root has developed and there is no obvious developmental defect affecting the unerupted tooth, then active intervention is recommended.¹³ There is however great biological variability and teeth that have completed their root development have also been shown to erupt spontaneously.

Likelihood of eruption

Once it is established that a tooth is present but unerupted without obstruction, it is important to consider the likelihood for spontaneous improvement in the position, or eruption of the tooth. The likelihood depends on a myriad of factors, including the stage of root development, age of the patient, root morphology, the degree of displacement and angulation of the tooth to the occlusal plane.

Case 1

A 24-year-old female with no significant medical history, was referred to the orthodontic department complaining of pain in both upper quadrants. The patient presented with a Class III incisor relationship with increased vertical proportions, complicated by an anterior openbite, bilateral buccal crossbites, absent maxillary canine teeth (UR3, UL3), a resin-bonded bridge (RBB) replacing UR3, and unerupted, ectopic maxillary second premolars (UR5, UL5).

An OPG confirmed the presence of all permanent teeth, excluding UR3, UL3, LL5, LR5, which had been previously extracted. The lower right second molar (LR7) was heavily restored and the lower left second molar (LL7) had caries extending into dentine.

There was radiographic evidence of generalized shortened roots. All third permanent molars and the maxillary second premolars were found to be present, but unerupted. The UR5 was disto-angularly impacted against the mesio-buccal root of the UR6, and the UL5 was orientated upright with the crown positioned at the root apices of the UL6. Both unerupted premolars showed complete root formation and there was evidence of root resorption of both UR6 and UL6 (Figure 1).

A CBCT was justified to aid treatment planning and revealed extensive root resorption of the UR6, leaving the apical portion of the mesio-buccal root detached, while all three roots of the UL6 were significantly resorbed (Figures 2 and 3).

The patient was reviewed on an orthodontic-restorative-oral surgery multidisciplinary (MDT) clinic to explore the treatment options available.

The age of the patient and stage of root development of UR5 and UL5 limited the prognosis for their spontaneous eruption, and the presence of already shortened roots contraindicated fixed appliance therapy. Both UR6 and UL6 were deemed to be of poor long-term prognosis and were therefore extracted.

An upper Hawley retainer for night-time wear was provided as a space maintainer, and the UR5 and UL5 were monitored for improvement in position. The patient was consented for the possibility of no further movement of these teeth and the possible need for their surgical removal and prosthetic replacement.

Six months following removal of UR6 and UL6, the impacted premolars were clinically palpable, and their positions were confirmed to be favourable on radiographic examination. The position of both teeth continued to improve in the following months. The UR5 had erupted into a favourable position by 9 months, and by 12 months, the UL5 had breached the mucosa without the need for orthodontic intervention, albeit in a rotated position (Figure 4).

Case 2

An 11-year-old female presented for assessment with an infra-occluded upper left second deciduous molar (ULE). Clinical examination revealed this tooth to be severely infra-occluded, according to the Brearley classification¹⁷ (Table 1). The ULE was positioned below the contact points of the adjacent teeth, which had tipped into the space occlusal to the retained deciduous molar. Radiographic examination showed an unerupted, disto-angular UL5 with a root dilaceration, the apex of which was positioned mesial to the UL4 (Figure 5). This tooth appeared to have a hopeless prognosis for spontaneous eruption or alignment and, following discussion with the patient and her parents, it was decided that removal of both the infra-occluded ULE and unerupted permanent successor, would most likely be required. A referral to the oral surgery department was made. At the time of listing for removal of ULE and UL5 under general anaesthetic, a CBCT was requested to allow for better visualization of these teeth. The CBCT confirmed the unerupted UL5 was angled palatally and dilacerated, with an open apex in close association with the floor of the maxillary antrum (Figure 6).

While waiting for surgery, the patient's mother contacted the oral surgery department as she thought that the UL5 was erupting. On examination, the ULE was mobile, the UL4 had fully erupted, and the UL5 was partially erupted. An intra-oral peri-apical radiograph confirmed that, surprisingly, the UL5 had migrated from its position in contact with the antrum into the oral cavity (Figure 7). Surgery was, therefore, considered unnecessary and the patient was advised to encourage exfoliation of the ULE herself.

The patient was reviewed in the orthodontic department for a comprehensive assessment. She presented with a Class II division 2 incisor relationship on a Class II skeletal base with decreased vertical proportions, complicated by Class II buccal segments, mild upper and lower crowding, and an increased overbite (Figure 8). The OPG confirmed the presence of all permanent teeth. The UL5 appeared to have an abnormal root morphology, but given the distance that it had travelled, this was not considered to be of concern (Figure 9).

Case 3

A 10-year-old male was referred to the orthodontic department following failure of eruption of the upper left central incisor (UL1). He presented in the mixed dentition with a Class II division 2 incisor relationship on a mild Class III skeletal base with increased vertical proportions, complicated by ectopic UL1, UL2 and UL3, severe upper labial segment crowding and moderate lower arch crowding (Figure 10). Radiographically, UL1 was horizontally positioned with its crown in the line of the arch and root palatal. The unerupted UL3 crown was transposed with the UL2, which was also horizontal. A CBCT showed significant root dilaceration on the UL1 and UL2 and the absence of pathological root resorption on the upper incisors despite contact with the cervical thirds of these teeth and the UL3 (Figure 11).

Owing to complexity of the case, the patient was referred for an MDT opinion to explore the management options available. The horizontal position of UL1 and the root dilaceration, rendered it unfavourable for alignment. The patient was referred to the oral surgery department for surgical removal of the UL1, together with both maxillary deciduous canines, to facilitate further eruption of the UL2 and allow the UL3 to erupt into the UL1 space. The patient and his parents were consented that, due to the unfavourable position of the UL2 and its dilacerated root, the UL2 may not be alignable and may require removal with future prosthetic replacement.

The patient was reviewed at 3 and 9 months following surgical removal of the unerupted UL1. The UL2 erupted into the line of the arch and UL3 had mesialized and was buccally palpable in the UL1 position (Figure 12). Orthodontic treatment was commenced to encourage eruption of the UL3 into the UL1 position. This involved an upper removable appliance for initial overbite reduction and distalization of the UL2 to create space for the unerupted UL3. This allowed for further spontaneous improvement in the position of the UL3, even in the presence of root dilaceration (Figure 13).

Final eruption and alignment of the UL3 required closed surgical exposure and orthodontic traction. The patient was consented for the possibility that the UL3 may not respond to traction and may need to be removed and replaced prosthetically. However, 3 months after closed exposure and orthodontic traction, the UL3 began to erupt into the UL1 site (Figure 14). Input from the restorative department was planned to camouflage UL3 as UL1.

Discussion

The cases in this series demonstrate situations where eruption was unexpected as a result of an ectopic tooth position, abnormal root morphology or the tooth development being advanced. Removal of an occlusal obstruction and a monitoring period of 6–9 months is a viable option to determine whether there is any considerable improvement in the position of an unerupted tooth. Teeth that may have initially been considered to have a poor prognosis for spontaneous eruption or for orthodontic traction and alignment, may still erupt.

Case 1 showed a patient with impacted UR5 and UL5. The patient's age, the completion of root development of the unerupted teeth, and their ectopic position made the prognosis for spontaneous eruption poor. If there had been no improvement in the position of the unerupted premolars following removal of the obstructing teeth, the need for further management would have to be assessed. As a consequence of the already shortened roots, the option of fixed appliances was not feasible. Alternative management options included: observation for cystic change or surgical removal with or without prosthetic replacement of the missing units

In Case 2, the unfavourable position and abnormal root morphology of unerupted UL5 gave a low chance for spontaneous eruption. The root apex was positioned mesial to the UL4 and the UL5 was high in the maxilla, making it unfavourable for the consideration of surgical exposure and alignment. If improvement in position had not occurred, surgical removal of UL5 with orthodontic space closure was planned.

The dilacerated, unerupted central incisor in Case 3 posed an orthodontic and restorative challenge. The UL3 showed abnormal root morphology and position and, given the complexity of the case, the prognosis for alignment was guarded. Prosthetic replacement of UL1 was inevitable, if UL3 did not respond favourably to exposure and traction.

The value of an observation period for an unerupted tooth following removal of an obstruction cannot be underestimated. Prolonged waiting times for surgical intervention may be frustrating; however, they can allow for improvement in the position of a tooth that had originally been deemed ‘hopeless’. This allows for re-evaluation of the proposed treatment plan and may possibly negate the need for a general anaesthetic, a surgical procedure or prosthetic replacement and the long-term financial and biological burden which accompanies it. The presenting complexity of these cases makes a multidisciplinary approach important. Input from restorative and surgical specialities allows for the most appropriate care for these patients.

Careful patient selection is, however, key. Complex and lengthy treatment plans require patients with good motivation and an understanding of the guarded prognosis for eruption, and an open and honest discussion about the potential risks of prolonged orthodontic treatment is essential for informed consent.