A solitary median maxillary incisor can occur as a rare single dental anomaly or a symptom of the early-intrauterine developmental brain disorder of holoprosencephaly. The few published case reports about orthodontic treatment for this disorder have only described space opening for prosthodontic replacement of a central incisor. In contrast, the present patient was treated with extraction of the solitary median maxillary central incisor and orthodontic space closure with subsequent minimally invasive restorations in order to avoid looming esthetic or periodontal sequelae associated with any type of fixed bridgework or implant-borne crowns in the sensitive maxillary anterior area—which is especially indicated in young girls with a hyperdivergent growth pattern.
Solitary median maxillary central incisor syndrome is a rare genetic mutation.
A girl with Class II Division 1 malocclusion and a missing maxillary central incisor was treated.
The solitary incisor was extracted, and the space closed.
Minimally invasive restorative treatment was finished while the patient was young.
The solitary median maxillary central incisor (SMMCI) syndrome is a rare early-intrauterine (from 35th to 38th day intrauterine) developmental disorder of unknown etiology, with a prevalence of 1 in 50,000 live births, first described by Scott as an isolated defect in 1958. Associations with defects, for example, deletions on chromosomes 7 and 18, and mutations on the sonic hedgehog gene have been reported.
In its least expression, the SMMCI appears only as an isolated trait of the complex holoprosencephaly spectrum. In the worst case, patients present incomplete cleavage of the embryonal forebrain leading to mental retardation, growth impairment, malformations of the sella turcica, choanal atresia, and midnasal pyriform aperture stenosis, and abnormal formation of the midface soft tissues and the maxillary alveolar bone.
The perfectly symmetrical central incisor that erupts exactly in the maxillary midline is attributed to the fusion of the mesial halves of 2 maxillary central incisors. ,
The 5 typical features that are phenotypical for SMMCI children are an indistinct philtrum with an arc-shaped upper lip, a single symmetrical maxillary central incisor, the absence of both the upper labial frenulum and the papilla between the maxillary central incisors, fusion of the anterior part of the palatal suture, and a bulging bony midpalatal ridge. , In a study by Kjaer and Balsev-Olesen, the condition has been described for both the deciduous and the permanent dentition.
Although a substantial number of articles illustrating the clinical findings in subjects affected by SMMCI syndrome is available in the literature, only 3 case reports of comprehensive orthodontic treatment have been published up to date. In all 3 patients, the treatment goal was to maintain and to distalize the SMMCI and to open space for a second maxillary central incisor. Bolan et al reported tentative rapid maxillary expansion in a 6-year-old boy, but the cone-beam computed tomography evidenced that correction of the posterior crossbite had merely occurred by dentoalveolar tipping without any opening of the midpalatal suture. Similarly, Lygidakis et al described a 2-phase treatment of a male SMMCI patient during which, after 2 failing attempts of early maxillary expansion when aged 4 and 7 years, an anterior space was finally created by maxillary molar distalization with fixed appliances for insertion of a double-winged Maryland bridge when aged 16 years. In 2014, Pseiner published a case report of a female patient with an SMMCI with space opening and subsequent autotransplantation of a mandibular second premolar. After 4 years of active treatment, the transplanted premolar was restored with a ceramic crown.
To our knowledge, no SMMCI patient has ever been treated orthodontically with the extraction of the fused cyclops tooth followed by orthodontic space closure, although this approach offers several advantages compared with maintenance of the SMMCI and substitution of a maxillary central incisor. Therefore, we consider this approach worthwhile presenting in the following case report.
Diagnosis and etiology
A 9-year-old girl was referred to our office with the request for a second opinion by a befriended orthodontist. The preliminary diagnosis was Class II Division 1 malocclusion with a congenitally missing maxillary central incisor.
The parents and the patient were disturbed and worried about the altered smile esthetics and reported episodes of bullying at school because of the unusual appearance of the solitary maxillary median cyclops tooth.
The lateral view exhibited a balanced profile. Facial frontal inspection revealed a slightly asymmetrical slender face with a mild chin deviation to the patient’s right side. An atypical arch-shaped outline of the upper cupid’s bow with an indistinct philtrum, albeit good lip competence, was evident. The patient presented a mild gummy smile with an altered smile arc and smile line display because of the overerupted single central incisor. Intraorally, the patient presented an early mixed dentition with only 1 single, totally symmetrical, large central incisor with equal crown height and length (9 × 9 mm), positioned exactly in the maxillary midline. Closer inspection revealed the absence of the upper labial frenum but the presence of the incisive papilla and a thick median palatal raphe because of an underlying prominent bony ridge.
Both maxillary lateral incisors, especially the left, were reduced in width (7 mm and 5.5 mm), which contributed further to the existing anterior spacing. On model analysis, an anterior Bolton ratio between the maxillary and mandibular incisors of 112% was calculated. Bilaterally, the deciduous canines and the first molars were in full Class II occlusion, and a 4 mm overjet could be assessed between the SMMCI and the mandibular incisors. The overbite was mildly increased (5 mm) because of a steepened lower curve of Spee. The lower midline was mildly deviated to the right side by 1 mm ( Figs 1 and 2 ).
The panoramic radiograph evidenced an SMMCI exactly in the maxillary midline and an age-typical development of all other permanent teeth. The cephalometric analysis revealed a Class I hyperdivergent skeletal pattern (A-N-Pg, 2.0°; SN/Go-Gn, 36.7°) and a normal inclination of the maxillary and mandibular incisors (U1/SN, 105°; L1/Go-Gn, 89.4°) ( Fig 3 ).
The parents reported that they had already noted the condition around 2 years of age when a solitary median deciduous maxillary incisor had erupted. Subsequent pediatric and neurologic consultations had not revealed any other health issues and the girl performed normally at school.
As no history of dental trauma with avulsion of a central incisor was reported, and all 5 typical extraoral and intraoral traits of the SMMCI phenotype were present, the final diagnosis of SMMCI syndrome was made.
Treatment objectives and alternatives
The main treatment goal was to create pleasing and symmetrical smile esthetics without the need for a future invasive restorative treatment and to establish incisor guidance while maintaining a solid posterior intercuspation with full Class II relationships. As the patient did not exhibit major skeletal discrepancies and the posterior teeth were already in full Class II occlusion before treatment, extraction of the SMMCI with space closure deemed the most appropriate approach, requiring the least biomechanics and tooth movement. This space closure treatment option would lead to a symmetrical array of the anterior dentition in the very sensitive esthetic zone and provide a healthy periodontal outcome with natural-looking transition areas in the long term. These treatment objectives were explained to the parents, who emphasized their preference for the least invasive postorthodontic restorative treatment.
The parents were thoroughly informed about all possible alternative treatment strategies.
The first strategy was orthodontic space opening by distalization with either headgear or palatal temporary anchorage devices (TADs).
Maxillary molar distalization with headgear would require excellent patient compliance during phase I, a comprehensive retention protocol to maintain the molars in Class I relationship during the eruption of the permanent dentition, followed by a second phase of fixed appliance treatment for anterior space opening. Maxillary molar distalization with noncompliance palatal TADs would need to be either delayed until after the eruption of the permanent dentition or performed in 2 phases. Although the presence of the maxillary third molar buds could not be assessed at the time of the first consultation with the patient’s parents, any distalization approach would have necessitated early surgical removal of subsequently developing third molars and additional burden for the patient.
Moreover, this treatment approach would require enameloplasty of the SMMCI to normalize its shape in conjunction with subsequent prosthodontic substitution of one central incisor. Because of the fusion etiology, the panoramic x-ray evidenced a relatively large root of the SMMCI, so that slenderizing of the crown might have caused an unnatural crown-root transition area with potentially looming periodontal sequelae ( Fig 3 ). It was explained to the parents that the least invasive restorative option after orthodontic space opening would be a bonded single-winged cantilever resin-bonded bridge without any tooth preparation. Admittedly, this prosthodontic approach would have been the least invasive restorative approach after space opening and would achieve a good esthetic result. ,
However, without the bony support of an incisor root in the area of the pontic, vestibular alveolar bone atrophy would very likely occur in the long term, making connective tissue grafting necessary for restoring acceptable dental esthetics.
The idea of a central incisor implant-borne crown was discarded because of the invasiveness, the poor long-term predictability, and the problem of infraoclusion over time because of the patient’s young age. ,
The second strategy was unilateral space closure supported by temporary palatal skeletal anchorage with the future restoration of the mesialized lateral incisor, canine, and first premolar, and the small opposite lateral incisor. ,
In this instance, orthodontic treatment would have been delayed until after the eruption of the entire permanent dentition and carried out as a 1-phase treatment with the advantage that the overall treatment time would have been much shorter.
Both the required biomechanics for unilateral space closure and several interdisciplinary treatment results of former patients affected by maxillary incisor agenesis were shown and explained to the patient and her parents. Because of the necessity of palatal TADs and the difficulty to achieve a truly symmetrical display of the maxillary anterior dentition despite intense restorative therapy, this treatment alternative was rejected by the patient and her parents.
As the patient was bullied at school because of the uncommon esthetic aspect of her large single central incisor in the facial midline during smiling, she and her parents requested immediate onset of treatment, concentrating only on the maxillary anterior area with the aim to improve smile esthetics with a short first interceptive approach. After the eruption of the permanent dentition, a second orthodontic phase with fixed appliances followed by minimally invasive restorative treatment mainly performed with additive composite techniques would then provide the patient with an esthetically pleasing and functionally acceptable result during her teenage years. Only after the end of the growth period, definitive restorative therapy with ceramic veneers/crowns would optimize the achieved teenage result even further. Given the existing full Class II canine and molar occlusion, extraction of the SMMCI and orthodontic mesialization of the maxillary canines and lateral incisors seemed the most efficient and appropriate option, although the 6 anterior teeth would require restorative treatment to correct the significant Bolton discrepancy and to achieve satisfactory esthetics.
Orthodontic treatment started when the patient was aged 10 years 2 months and was performed in 2 phases:
After extraction of the SMMCI, two 0.022-in lateral incisor brackets (MBT Prescription Victory Series; 3M Unitek, St Paul, Minn) for a sectional arch (0.016-in nickel-titanium followed by a 0.019 × 0.025-in stainless steel archwire) were bonded on the maxillary lateral incisors with overangulation (negative tip) to avoid mesial crown tipping during space closure. During the first 2 months, a denture tooth with a central incisor bracket was inserted to cover the large extraction space for improved esthetics ( Fig 4 ). Two different kinds of elastomeric chains (Power chain generation II with wide space and closed space; Ormco Corporation, Glendora, Calif) were applied according to the amount of residual space in order not to exert too much force on the lateral incisors. It was not intended to completely close the SMMCI space but to merely narrow the large extraction site, as future restorations of the maxillary anterior teeth were regarded as inevitable. After 4 appointments at 8-weeks intervals, space closure was finished simply changing the power chain every 2 months. On the day of bracket removal, provisional in-office composite restorations of the small mesialized lateral incisors were performed to further reduce the remaining diastema ( Figs 5 and 6 ).
Because of the long journey to our office, arising family and professional issues, and the necessity for a second phase of orthodontic treatment, the joint decision was made not to apply any type of retainer and to take the risk of partial space opening of the SMMCI extraction site. The patient was not seen until the complete eruption of the permanent dentition ( Figs 7-9 ). As expected, the SMMCI space had partially reopened, but the posterior occlusion had remained unchanged. Phase II deemed to be straightforward, aiming merely at orthodontic leveling of the lower curve of Spee and at strategic positioning of the 6 maxillary anterior teeth, including the first premolars, to avoid invasive tooth preparation by the restorative dentist and to improve the final interdisciplinary treatment outcome. The interdisciplinary treatment plan was established with the prosthodontist who was present during the consultation with the patient and her parents before the onset of phase II.