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A non-invasive treatment option in solitary median maxillary central incisor syndrome Maalini Patel Louise Ormondroyd Dental Update 2024 49:10, 707-709.
Authors
MaaliniPatel
BDS(Hons), MPaedDent RCSEng, FDS RCSEng
Specialty Registrar in Paediatric Dentistry, Guy's and St Thomas' NHS Foundation Trust, Bristol, UK
Solitary median maxillary central incisor (SMMCI) syndrome (OMIM #147250) is a disorder characterized by developmental defects of midline structures with variable expressivity. It presents dentally as a single symmetrical central incisor in the midline position. This is a case report of a child with the isolated dental feature of a single maxillary central incisor, with no medical features of SMMCI syndrome. Under the management of a multidisciplinary dental team, a non-invasive approach was undertaken to improve aesthetics. This case report describes the dental options for managing SMMCI including a non-invasive option that has not previously been reported in detail.
CPD/Clinical Relevance: Dentists should be aware of SMMCI and its potential medical sequelae.
Article
The rare finding of a solitary median maxillary central incisor (SMMCI) can either be observed as an isolated dental feature or part of a wider finding of SMMCI syndrome (OMIM #147250).1,2 It presents clinically as a single central incisor in the midline position, in both the primary and permanent dentitions. Of note, both the crown and the root of the single incisor are symmetrical.3 The single incisor is the characteristic feature of SMMCI syndrome.4 In addition to this dental anomaly, SMMCI syndrome is also associated with craniofacial morphology abnormalities including a retrognathic maxilla and increased incisor inclination.5,6
SMMCI syndrome is a disorder involving developmental defects of midline structures with variable expressivity.4 It involves the midline structures of the head, the nasal airways and brain, in addition to other midline structures of the body.4 It can be diagnosed prenatally via ultrasound.2
Short stature (with or without growth hormone deficiency).3,4
The exact cause is unknown, but it has been shown that some individuals exhibit a missense mutation in the sonic hedgehog (SHH) gene4 on chromosome 7q36. SHH is a signalling molecule that has a vital role in embryonic development, in particular the brain.7 It has been suggested that that the dental anomaly is due to a delay in, or failure of, induction of cell division in the midline at approximately day 38 in utero.1 The estimated incidence is 1:50,000 live births.1
SMMCI syndrome is a predictor of, and has been described as, the mildest manifestation of holoprosencephaly (HPE).2 HPE is the most common structural anomaly of the developing forebrain resulting from incomplete midline cleavage of the forebrain.2 Its results in neurological impairment and dysmorphism of the brain and face, and in the most severe cases cyclopia.3,4 It is one of the most common causes of embryonic lethality.8
SMMCI syndrome is associated with the following syndromes:
An 8-year-old male presented at the paediatric dental clinic following referral from their general dental practitioner (GDP) with one maxillary permanent incisor (and a history of one primary incisor). He was otherwise medically and dentally fit. No dental intervention was warranted at the time because he had no concerns. A referral to the genetics and paediatric medical teams was made to assess for any other midline developmental anomalies given the clinical findings. Medical investigations carried out are detailed in Table 1. There were no medical diagnoses made, and it was found that he had an isolated dental feature of SMMCI only. The patient was referred on to the hypodontia team for a full assessment and he was kept under review.
Bloods (cortisol, thyroid-stimulating hormone, free thyroxine, insulin like growth factor
Assess pituitary function
Normal range
At age 10, an orthopantomogram was taken to assess the developing dentition, which confirmed the presence of a single central incisor (Figure 1). At a subsequent review at age 12, no concerns were raised.
Figure 1. Orthopantogram taken at age 10.
The child was seen again for review by the hypodontia team at age 14 when he reported concerns regarding the appearance of his teeth (Figure 2). He was keen for treatment because remarks were being made at school about his smile ‘looking different’.
Figure 2. Pre-operative photographs showing a single central incisor.
After review by the multidisciplinary hypodontia team (including a paediatric dentist, orthodontist, restorative dentist and oral surgeon) options were discussed including:
No treatment and accept aesthetics as anterior incisors currently symmetrical.
Composite camouflage to create four incisors and to accept a centreline shift.
Composite to be placed on UL2 (to disguise as a central incisors), UR2 (to widen) and UL3 (to disguise as a lateral incisor).
Composite camouflage to widen and lengthen the lateral incisors (UR2, UL2) and to slightly shorten the central incisor. This would give the appearance of three central incisors.
Fixed appliance orthodontic treatment to move the solitary central incisor to one side, creating a space for a matching prosthetic central incisor, likely to have been a resin-retained bridge. This option would require extraction of one or two units in the maxilla.
Extract the solitary central incisor and realign the lateral incisors with fixed appliances, which could then be disguised with composite resin veneers to resemble central incisors. The canines would need to be disguised as lateral incisors at a later date.
The family, after discussion of the above options, wanted to avoid lengthy orthodontic treatment and the need for a prosthetic tooth. Study models were taken and wax-ups were fabricated for options 2 and 3. The family chose option 2 as they preferred the aesthetics of four incisors. It was made clear that this option would involve a centreline shift, compromised aesthetics and ongoing maintenance of composite restorations.
At one visit, composite build-ups of the central incisor, lateral incisors and canine were undertaken using a putty stent (Figure 3).
Figure 3. Post-operative photographs showing aesthetic result after composite camouflage.
The patient was reviewed and he reported that he was pleased with the aesthetics and felt his smile looked ‘less different’. He was then discharged back to the GDP for all care, including upkeep of the composite restorations.
Discussion
In cases of SMMCI, there is one symmetrical central incisor present in the midline of the maxilla. The exact mechanism is unknown, but it has been suggested that there is failure in cell division in the midline around day 38 in utero.1
Where a single central incisor is encountered, a full medical history should be taken with detailed questioning regarding growth (short stature), breathing difficulties and learning difficulties. It is imperative that an early onward referral to secondary care is made because a multidisciplinary dental team is best placed to manage such cases. The team will ensure a referral to medical colleagues and a geneticist is made in view of the wide range of medical anomalies associated in this condition.1 In particular, it is important to be aware of the association of a single incisor tooth with short stature, nasal obstruction and learning difficulties.4 An early referral is necessary to ensure dental and medical investigations are carried out, and the child receives all necessary medical input.
In this case, there were no medical features of SMMCI syndrome, but it is prudent for these to be investigated and ruled out. Individuals presenting with SMMCI may be carriers for HPE, which has serious medical manifestations.7 Some families have been found to have members with severe HPE, with others presenting solely with SMMCI.9,10 It is important, therefore, that a presentation of SMMCI is considered a risk factor for HPE.7
This case demonstrates an acceptable result for a non-invasive option to improve aesthetics for a child with SMMCI. It is important such cases are managed by a multidisciplinary team to ensure input from all specialities; in this case paediatric dentistry, orthodontics, restorative dentistry and oral surgery. This ensures a holistic approach is taken and all aspects of the condition are considered, including the potential craniofacial abnormalities. There are a variety of options available, but some may not suit every child. Although a non-invasive option of composite camouflage was chosen, it is important to allow families to make an informed decision and wax-ups of options will enable them to visualize the final result. In this case, the child chose the aesthetics of four incisors, while accepting a centreline shift. Obviously there are shortcomings for such an option, including suboptimal gingival and restoration contour, and need for excellent oral hygiene in the area, as well as regular polishing and life-long upkeep of the composites. These issues should be discussed as part of the informed consent process.
Conclusion
GDPs should be aware of SMMCI and be able to recognize its features when it presents. Careful questioning about the child's medical history should be undertaken, with emphasis on stature, breathing difficulties, learning difficulties and cardiac conditions. An onward referral to secondary care is required for all cases of a single central incisor, which will lead to the involvement of medical and genetics teams. GDPs should familiarize themselves with the congenital abnormalities that may be associated with the condition. A multidisciplinary dental clinic is likely to be the most appropriate setting for children with SMMCI to ensure all potential cross-specialty treatment options are explored.
