From Volume 16, Issue 2, April 2023 | Pages 85-90
Infra-occluded primary molars can be challenging in terms of their surgical management and potential sequelae. The prognosis of these teeth needs to considered allowing treatment planning for a stable long-term outcome for the patient. This article outlines the key principles to consider following a diagnosis of an infra-occluded primary molar, and it provides a management tool to aid decision making.
Infra-occlusion is when a tooth has failed to maintain its occlusal level relative to adjacent teeth and is therefore found below the occlusal plane.1 In 1981, Kurol described infra-occlusion as when the occlusal surface of a tooth is 1 mm below the occlusal surface of a fully erupted adjacent tooth.2 The timely management of infra-occluded primary teeth avoids the need for more complex surgical management as well as allows planning for the resultant space. This article highlights the key principles behind management of such cases.
The prevalence of infra-occluded primary molars ranges between 1% and 39%, with mandibular molars being much more affected than maxillary molars.2,3 The incidence is greater the older the patient, with infra-occlusion recorded from the age of 3 years suggesting a cumulative process.3 Bjerklin, however, demonstrated that there was little increase in infra-occlusion after the age of 20 years, suggesting primary molars after this age had a good long-term prognosis.4 There also appears to be equal frequency in males and females, as well as the site of occurrence.
Ankylosis is often suggested as the cause of the deciduous molar failing to maintain its occlusal position. Ankylosis occurs when the cementum of the tooth fuses with the adjacent alveolar bone, with resultant loss of the periodontal ligament space.2 Biederman described a possible genetic aetiology whereby there is a developmental gap in the periodontal membrane.5 This is supported by work carried out on siblings, which showed that the prevalence among siblings was 46% compared with 1.3% in the control group.6 Other theories propose excessive pressure from mastication or possibly trauma, as well as disturbances in local metabolism whereby the normal resorptive process is reversed so that the periodontal ligament is obliterated prior to root resorption.5 Other authors have discussed ankylosis in primary teeth being a transient process whereby the tooth would ‘re-erupt’ once the ankylosed portion of tooth had been resorbed.7
Prior studies have demonstrated associations between missing permanent successors and infra-occlusion, with 17% of cases of infra-occluded deciduous molars associated with missing permanent premolars.8,9 Hvaring et al found that infra-occlusion was the most important factor when considering the prognosis of retained primary teeth without successors.10 Exfoliation is often delayed by approximately 6 months in cases with a permanent successor, although this can be unpredictable and is sometimes significantly longer.11 Infra-occlusion has also been attributed to insufficient eruption force, occlusal trauma, infection and abnormal tongue pressure.1,12,13
When a tooth infra-occludes, the adjacent teeth tip into the area with potential loss of space for the permanent successor (Figure 1a,b), which could also lead to centreline shifts (Figure 1c,d). Tipping with displacement of apices away from the infra-occluded tooth is thought to be related to changes in the direction of transeptal fibres.14 Becker noted the effect on the dental midline, showing a deviation to the affected side.15 The effect of transeptal fibres can also affect the vertical growth of adjacent teeth, resulting in lateral open bites or over-eruption of opposing teeth (Figure 2).16 Over-eruption and tipping have been shown to spontaneously correct in some cases once the permanent premolar erupts.1
The more severe an infra-occlusion, the more difficult extraction becomes, which is why the timing is important in management. If the tooth has infra-occluded and there has been little resorption of the roots (Figure 3), the teeth may require surgical removal involving sectioning.16 This is further complicated by the potential for ankylosis. Surgical removal can risk damage to adjacent teeth and structures, such as the mental nerve, or result in retained root fragments.17,18 Additionally, surgical removal often involves bone removal, which can affect future management options, such as orthodontic tooth movement (OTM) and implant placement.16 This is also compounded by the observation that infra-occluded teeth have reduced bony development, affecting both the ridge width and height. The reduced alveolar bone development can hinder OTM and can complicate restorative intervention.13
Infra-occluded teeth can result in food packing, reduced access for oral hygiene measures and, therefore, increased risk of caries and periodontal disease for the affected teeth as well as the adjacent teeth.18
Infra-occluded teeth may also cause impaction or ectopic eruption of permanent successors (Figure 4), which can worsen an individual's malocclusion and can increase the complexity of surgical and orthodontic treatment required.5,19
There are a number of classification systems proposed in the literature to describe infra-occluded teeth. The most commonly recognized is that by Brearley:
Another commonly cited classification system is that of Kjaer et al who used panoramic radiographic findings to assess the degree of infra-occlusion. The classification ranged from ‘Group I’ to ‘Group IV’, comparing the level of infra-occlusion to the full crown height of the tooth, with the most severe described as ‘deeply subgingival’.21
Clinically, these teeth can present with a high percussion sound and may also be immobile, which could indicate ankylosis, although these indicators may be subjective.22
Angular bony defects can be identified on radiographs (Figure 3) around infra-occluded teeth, although this may spontaneously correct with normal premolar eruption.23 Conventional radiographs provide limited information, and as ankylosis may only affect a small area of the root, CBCT may be indicated, particularly when combined with the need for assessment prior to surgical removal.13
Several factors need to be considered and these are outlined in Figure 6.
In a patient with hypodontia in the permanent dentition, the deciduous tooth may not exfoliate normally and may be retained. Consideration needs to be given to whether treatment would involve retaining the deciduous tooth, with restorative input to maintain its function and position, or loss of the tooth and space closure. If the decision is taken to restore the tooth into occlusion for the short or long term, this could be carried with direct or indirect composite, ceramic or metal onlays, or preformed metal crowns.13
Where there is a permanent successor, it has been reported that 96.7% of infra-occluded primary molars spontaneously exfoliate, although with a delay of approximately 6 months.24 If the infra-occluded molar has not naturally exfoliated within 6 months of the average expected time, then extraction of the submerged primary tooth should be undertaken. In these cases, the surgical risk to the unerupted permanent successor needs to be taken into account.
If, at the time of diagnosis, the patient has not yet passed the pubertal growth spurt, there is an increased chance that the infra-occlusion will worsen. For those who have already experienced the pubertal growth spurt, the rate of infra-occlusion is reduced.10
Hvaring et al found a significant relationship between root resorption and infra-occlusion, although root resorption was not considered to be critical to prognosis.10 A tooth with caries or an associated abscess should be extracted; however, if the space needs to be maintained, thought should be given to restoring the carious tooth.25
In cases of mild infra-occlusion, without any obvious bony defects or ankylosis, retaining the infra-occluded tooth for as long as possible may be indicated to maintain bone and space for a prosthetic replacement where there is no permanent successor. Therefore, consideration of the long-term plan for a patient is vital before any treatment is initiated. When infra-occluded teeth have been extracted, space maintenance can be used in cases with a space requirement.16,18
For severely infra-occluded teeth, particularly in pre-pubertal patients, extraction is indicated.25 Similarly, moderately infra-occluded teeth in a pre-pubertal child are likely to undergo further infra-occlusion, and extraction would be recommended. Conversely, a tooth that has mild infra-occlusion, diagnosed in a non-growing patient, is likely to have better prognosis. Figure 7 shows retained lower deciduous second molars with good prognosis. Additionally, a mildly infra-occluded tooth in a pre-pubertal patient could benefit from regular monitoring, in the knowledge that any further infra-occlusion would require extraction of the affected tooth before the pubertal growth spurt, to reduce the risk of a vertical bony defect developing.13
Future orthodontic treatment may not be suitable for some patients and, therefore, extraction at the optimal time may be indicated. In addition, if looking to restore an infra-occluded tooth into function to maintain space, prevent over-eruption and prevent tipping, a patient needs to be able to cooperate to enable restorative intervention.
Space maintenance may need to be considered when an infra-occluded tooth has been extracted, but a space requirement has been identified. In some cases, it may be beneficial to use a space maintenance device, such as a band and loop (Figure 8).
The aims of restoring the occlusal platform are to maintain contact points, prevent tipping of adjacent teeth over the occlusal surface of the infra-occluding molar, and to maintain occlusal contact with the opposing tooth.
The occlusal height can be increased, and approximal contacts modified, with the use of direct/indirect composite addition, onlay or crown.18 There is, however, limited evidence in the literature for the prognosis and success of different treatment modalities or materials for this clinical scenario. Considerations to take into account include operator experience, moisture control, surface area available to bond, height of the restoration versus the amount of tooth visible, pulp horn size, pathology, previous restorations and patient cooperation.
Tipping of adjacent teeth can compromise the prognosis for restoration more than the severity of the infra-occlusion. The undercuts created by the marginal ridges of adjacent teeth over the occlusal surface of the infra-occluded molar can interfere with interproximal placement of restoration margins and lead to voids or ledges. This reduces cleansability, leading to food packing, caries or loss of the restoration. Interproximal reduction of adjacent teeth can facilitate restoration, but there are risks for sensitivity and pulpal inflammation. As the degree of infra-occlusion becomes more severe, there is less tooth available for bonding, and the greater height of restorative material may also reduce prognosis.
If infra-occlusion is rapid, or tipping of adjacent teeth makes maintaining oral hygiene and restoring the tooth impossible, then extraction may be required, although the option of a dental implant may be limited if infra-occlusion or surgical extraction have led to reduced horizontal or vertical availability of alveolar bone.
Resin-bonded or conventional bridgework may be feasible, but might require preparation of the adjacent tooth if tipping has occurred, to remove undercuts and optimise connector length. Orthodontic treatment can help to optimise the space for restoration.
The flowchart in Figure 9 provides some guidance.
Considering all the relevant factors allows for optimal treatment planning and can aid in preventing future complications that can impact on restorative treatment options. The management of infra-occluded teeth is often multidisciplinary in nature, involving the general dental practitioner, restorative and oral surgery colleagues.
Within the care pathway, orthodontic assessment is vital to fully assess the space requirement that plays a key role in the overall management.
Early identification and accurate diagnosis of patients with infra-occluded primary molars is imperative for the timely and optimal management of these cases, particularly for those who can present with further complicating factors.
