The orthodontic–paediatric interface. Part 1

Molar–incisor hypomineralization (MIH)

Molar–incisor hypomineralization (MIH) is a common condition and is estimated to affect up to 14.3% of the children worldwide, while in the UK around one in eight are affected, equating to around 1 million children.^4,5 MIH can be defined as: ‘hypomineralization of systemic origin, presenting as demarcated, qualitative defects of enamel of one to four first permanent molars frequently associated with affected incisors.’⁶

There is a continuum of severity in relation to MIH, with some teeth mildly affected, while others experience post-eruptive breakdown (PEB) of the molars and white and/or brown hypomineralized lesions on the incisor teeth (Figure 1).

The timely management of MIH can be useful to reduce the potential consequences of loss of the first permanent molars. Additionally, clinical guidelines exist for the management of poor-prognosis first permanent molars in relation to the malocclusion.⁷

When considering the management of affected first permanent molars, the extent and severity of the defects is important to take into account alongside other wider patient factors: a simple way to consider these factors is with the acronym ‘M-O-R-S-E C-O-D-E’ (Table 1). Teeth with affected load-bearing surfaces, or with areas of post-eruptive breakdown affecting multiple surfaces with or without cuspal involvement, would be considered to represent increased severity.⁸ Additionally, if the patient is experiencing symptoms with the tooth or rapid caries progression, treatment may be required earlier than the ideal time. Patient cooperation is important to consider because general anaesthetic may require a more comprehensive and invasive plan, to avoid the risk of repeat general anaesthetics. Future orthodontic needs require careful thought prior to extraction of poor prognosis molars. The severity of crowding or an increased overjet may require retention of the first permanent molar in some cases until the second permanent molar erupts, although in severe cases, extraction at an ideal time followed by a future premolar extraction may be required. In the former case, an appliance to aid in space maintenance, such as a removable appliance or transpalatal arch, could be fitted prior to extraction. At an early age, decisions with regards to the need for growth modification treatment, for example twin block or protraction facemask treatment, can be challenging. However, if the teeth are asymptomatic, these cases may require first permanent molars for retention of removable or fixed appliances and therefore extraction of these may be delayed to facilitate this.

The malocclusion also needs to be taken into account because compensating extractions, whereby the same tooth in the opposing arch (usually a maxillary first permanent molar) is extracted to increase the chance of spontaneous space closure, although this is no longer considered routine practice.⁷ In some cases, for example Class II malocclusions, there may be a sufficient occlusal stop to prevent overeruption of the tooth, which could otherwise prevent spontaneous space closure in the lower arch, therefore it should be assessed on a case-by-case basis.

Consideration to maintaining the first permanent molar may be needed if the patient presents with hypodontia or severely ectopic teeth within the same quadrant because this could result in reduced occlusal stability and increased need for restorative intervention owing to spacing. If this is the case, it would be imperative to seek a specialist paediatric or orthodontic opinion.

When aiming for spontaneous space closure following extraction of the first permanent molar, a number of factors have been shown to be positive prognostic factors in terms of timing of extraction. Recent evidence has shown the presence of the third molars and the angulation of the second molar are potentially more important in predicting spontaneous space closure.⁹ Saber and colleagues also described prognostic factors for spontaneous space closure and the importance of the position of the second premolar in the bifurcation of the second deciduous molar in addition to those described above.¹⁰ Unfortunately, delayed or early extraction can result in unfavourable tipping, rotation and incomplete space closure.⁷ The considerations to be made prior to extracting first permanent molar teeth are described in the recently updated guidelines by the Royal College of Surgeons of England.⁷Figure 2 provides an example of how the aforementioned factors can be considered to form a treatment plan for patients in this position.

Impacted first permanent molars

First permanent molars can become impacted against the second deciduous molars. Previous literature quotes a prevalence of 2–6%, with increased presentation in the maxillary arch compared to the mandibular arch.¹¹ This can be a result of: unusually large deciduous molars; ill-fitting preformed metal crowns used to restore carious primary second primary molars; mesial eruption direction; lack of arch length; uncoordinated growth; and delayed first permanent molar development. Genetically, it can present with a familial tendency or in patients with cleft lip and/or palate.¹¹

Impacted first permanent molars or patients with a history of FPM impaction are often noted coincidentally on radiographic assessment. They can be classified as reversible or irreversible depending on the spontaneous correction of the impaction. During a period of monitoring, spontaneous correction may have occurred in approximately 60% of cases.¹¹ In irreversible forms, further intervention may be required. The use of brass wire or separators has been described in the literature.¹¹ Additionally, uprighting of the first permanent molar can be carried out using an upper removable appliance (URA) with a palatal finger spring engaging a button bonded occlusally on the molar tooth (Figure 3), or a Humphrey's appliance. In cases where the prognosis of the second deciduous molar is poor owing to external resorption caused by the ectopic first permanent molar, extraction may be indicated, and subsequent space maintenance can be considered to prevent mid-arch crowding as a result of space loss. Space maintainers, such as transpalatal arches, band and loop and URAs have been used for this purpose.

Extraction of primary teeth

Patients may require early extraction of primary teeth as a result of caries, periapical/interradicular pathology, trauma, infra-occlusion or interceptive management. Those who present with pain or acute infection often require more immediate management, while those with currently asymptomatic chronic conditions, may provide time for a comprehensive treatment plan, particularly if the patient is due to have a general anaesthetic to facilitate the treatment. Sometimes deciduous canine teeth are extracted to allow eruption of lateral incisor teeth where there is likely crowding to allow space for alignment of an unerupted central incisor or correction of a crossbite.

Sequelae

Early loss of deciduous teeth can result in space loss, which can present as crowding of the permanent dentition with associated impactions, centreline shifts and tipping of the adjacent teeth.¹² The centreline is likely to be affected the more anteriorly a tooth is lost; however high-quality experimental evidence is lacking to support this clinical finding. A reduction in arch length may later necessitate the need for extractions of permanent teeth if the patient requires orthodontic treatment.

Space maintenance

A patient with caries is unlikely to be an appropriate candidate for a space maintainer, given the need for good oral hygiene and cooperation. Space maintenance can be considered in cases when an infra-occluded second deciduous molar, especially in a single quadrant, has to be extracted and there is a likelihood of crowding precipitating as a result of early extraction or pre-existing crowding. A removable appliance could be considered for space maintenance, however, it would require strict adherence to wearing it continuously. Alternatively, a band and loop design from an erupted first permanent molar is an effective means of maintaining the space, and is cemented into place, negating the need for patient cooperation with wearing it, although good oral hygiene needs to be maintained. In the upper arch, a transpalatal arch with a nance button could be considered as a space maintainer and in the lower arch, a lingual arch could be used. However, as with a band and loop, sufficient oral hygiene needs to be maintained throughout.

Types of habits

A habit is considered ‘an acquired behaviour pattern regularly followed until it has become almost involuntary.’¹³ Within dentistry, they often present as persistent sucking habits (dummy or digit), but can also present as chewing on objects, such as pens or oral piercings. Digit or pacifier sucking habits have been shown to persist past the age of 7 years in 12.1% of children, with this being more common among females than males.¹⁴

Sequelae

The effects of habits are very specific to the mechanism of the habit. Common effects with sucking habits can include constriction of the maxilla, contributing to a posterior crossbite, which is often unilateral, and can sometimes be associated with a displacement. Proclined upper incisors and retroclined lower incisors may also be a presenting feature resulting in an increased overjet. An anterior or lateral open bite is often seen, potentially being asymmetrical depending on the side the patient is more likely to place their digit or dummy (Figure 4). The presence of an anterior open bite has also been shown to be related to defective speech, for example a lisp.¹⁵ It is also useful to assess the patient's digits if there is a reported history of sucking. The used digits could present with a deformity, or have inflammation surrounding the nail bed.¹⁶ Other habits, such as chewing habits, may cause non-carious tooth tissue loss (NCTTL) and result in gingival recession defects and/or tooth mobility.

Management

Ideally, non-nutritive sucking habits should be stopped prior to the development of the permanent dentition to prevent unintended effects on the occlusion. A Cochrane review, carried out in 2015, suggested that both orthodontic appliances, as well as psychological interventions, such as positive and negative reinforcement, are effective at encouraging the cessation of a sucking habit, although the evidence was low quality.¹⁷ Assessing the mechanism of the habit and understanding the history can be helpful in guiding management. In addition, the need for patient and family compliance is key. Behavioural modification techniques, such as positive reinforcement, could be used. For example, praise and reward methods. Other commonly suggested methods include the use of a deterrent such as an unpleasant tasting varnish, a plaster on the used digit or a sock/glove over the hand. If the patient uses an object such as a pacifier, this should be removed.

Orthodontic appliances can also be used. These are usually placed following less invasive attempts where there has been persistence of the habit. They may include a palatal crib such as a Hayrake appliance or palatal arch similar to that described by Haryett.¹⁸ Use of a removable appliance such as a twin block appliance can also prevent the patient getting satisfaction through the habit and can aid in cessation while also treating a developing malocclusion. Figure 5 provides an example of the treatment received by a patient who initially presented with a significant digit-sucking habit.

If interception of the habit is not successful, the traits that present in the malocclusion may require future treatment with maxillary expansion devices, growth modification, orthodontic camoflauge treatment with extractions and fixed appliances or a joint orthodontic–surgical approach.

Orthodontic management of trauma

Orthodontics can be used to manage both acute trauma as well as the sequelae following trauma. Sandler and colleagues have produced guidelines for the orthodontic management of trauma.²⁰ Orthodontic brackets and archwires (minimum 0.016” stainless steel) can be used to splint traumatized teeth to adjacent non-affected teeth for the time recommended in the International Association of Dental Traumatology (IADT) guidelines, dependent on the type of injury. Although in an acute situation, a titanium trauma splint secured with composite may be used instead of brackets – brackets have the benefit of allowing monitoring of individual teeth at reviews, for example assessment of mobility and tenderness to percussion (Figure 6). Orthodontics is sometimes advocated to be used in intrusion injuries to enable repositioning (Figure 7). In immature teeth, this is considered after 4 weeks of monitoring for spontaneous repositioning. In mature teeth, a tooth intruded 3–7 mm or less than 3 mm (that has failed to re-erupt in 8 weeks) is considered for orthodontic repositioning. This may be guided by the need for root canal treatment (depending on the clinical and radiographic findings at subsequent follow-up appointments) and surgical repositioning may be preferred to allow this to be initiated at an earlier stage, reducing the risk of external inflammatory root resorption.²⁴ Extrusion mechanics can also be employed in cases of crown-root fractures to extrude root fragments sufficiently to provide access for a definitive restoration, although this does compromise the crown-root ratio.

The sequalae of trauma can result in the need for prosthetic replacement of teeth or space closure (Figure 8). Orthodontic appliances can be used to redistribute and optimise spaces for restorations, such as resin-bonded bridges or implants. Fixed appliances can control root movement, encouraging divergence in the region where implants are required. In younger patients, the restorations may not be placed immediately. In particular, implants are not placed until growth has stopped and therefore, these spaces need good retention regimens to prevent space loss and tipping of roots into the proposed implant space. To reduce this risk, it is often the case that orthodontic treatment may be commenced when the patient is slightly older.

Interceptive treatment with orthodontics has been shown to reduce the risk of incisal trauma. Use of a functional twinblock appliance for example, can help a patient gain a lip seal and reduce the overjet, which are key factors increasing an individual's risk of dental trauma.²⁵ This is discussed further in Part 2 of this series.