Diagnosis

The condition can be diagnosed with ultrasound at 18 to 22 weeks of gestation and with genetic testing, but this is rarely done before birth.⁴ With our current knowledge, the condition should be detected before eight months with the eruption of the primary maxillary incisor.⁹

We must specify the following factors to describe the characteristic tooth present in this syndrome accurately:

Hence the acronym SMMCI syndrome.^{9,10,16-18,20}

Differential diagnosis

No other conditions with this characteristic incisor tooth are known. One of the three forms of nasal obstruction and short stature will occur in most cases. SMMCI should be considered a predictor of holoprosencephaly, especially if microcephaly and hypotelorism are also present.⁹

Although generally mildly affected, patients with SMMCI belong to the holoprosencephaly spectrum and are at risk of having children with more severe forms of this disorder. Therefore, molecular diagnosis and genetic counseling are essential for SMMCI patients and their families.¹²

Etiology and epidemiology

Although its etiology is unknown, it has been associated with deletions of chromosomes 7 (7q.36.1) and 8 and mutations in the Sonic Hedgehog (SHH) gene. It has a prevalence of 1/50,000 live births, which makes it a rare but important anomaly. There is no gender predilection, although more cases are reported in women.^{1,2,4,8,9,12,16,21-25}

SMMCI has five phenotypic characteristics in both dentitions:

1. No labial philtrum and an arch-shaped upper lip⁵

2. A single symmetrical upper central incisor^{1,2,5,10,16,20}

3. Absence of the upper labial frenulum and the papilla between the upper central incisors⁵

4. Fusion of the anterior part of the palatal suture⁵

5. Presence of a bony ridge in the middle of the palate⁵

Treatment

The American Academy of Pediatric Dentistry (AAPD) acknowledges the importance of proper developmental and occlusal management during the early years of life. Therefore, we can enhance the well-being of infants, children, and adolescents.^21,23 Early diagnosis and multidisciplinary management are necessary to achieve such objectives.¹ This approach should include these specialties: pediatric dentistry, maxillary orthopedics, orthodontics, periodontics, and in some cases, maxillofacial surgery. Treatment options reported in the literature include functional orthopedics to manage class II malocclusion,⁷ rapid palatal expansion,^7,14,26 distalization of the posterior zone to open the anterior space with orthodontics and then placing an implant to replace the missing incisor.^{3,5,7,14,21,26} Dental autotransplantation is another reported treatment option, including, e.g., premolars, blending in the transplanted tooth, and replacing the missing incisor.²⁷ A more radical option is removing the single central incisor, closing the space with orthodontics, rehabilitating the lateral incisors with ceramic crowns, and blending in the canines.⁵

Therefore, this study aims to report the initial treatment of a child with SMMCI who had not been previously diagnosed.

The SMMCI case presented has familial causes.

Clinical case description

Male patient, 10 years old, weighs 23 kg, height is 123 cm, from Jamundí, Valle del Cauca, Colombia. He attended the office with his aunt, the adult in charge, who stated the following reason for consultation: “My nephew has only one front tooth”. During the interview, she explains that the child is the second of three term pregnancies. Family history: paternal aunt has diabetes, hypertension, and unspecified cancer. The child’s history is not reported. The aunt said the child’s deciduous dentition included only one upper central incisor. She also noted that his other two siblings have the same problem. The extraoral examination showed that the midline does not coincide with the tip of the nose nor the center of the chin; there is no labial philtrum, and the bipupillary plane is not parallel to the commissural line. There is lip incompetence, ears of increased size, projection, and implantation. (Figure 1) The intraoral examination showed a solitary central incisor on the maxillary midline, absence of labial frenulum and incisive papilla, an oval palate, and class II malocclusion with proinclination of the central incisor. (Figure 2 a, b, and c).

Complementary studies are performed to make the right diagnosis and start the treatment: study models, panoramic and lateral skull radiographs, and extra and intraoral photos.

The panoramic radiograph (Figure 3) showed a solitary maxillary incisor with a single root and root canal. No formation or impaction of the other central incisor is observed.

In the Lavergne and Petrovick cephalometry, performed taking the lateral cephalograms as a reference (Figure 4), the patient has shown neutral mandibular rotation, maxilla larger than the mandible, a distal anteroposterior relation with a normal vertical relation (R2DN).

Pont’s analysis (transverse space) was performed to determine the need for space in the upper and lower arches. This showed that the patient had a space deficit in the anterior and posterior zones of the two arches. Moyer’s analysis (eruption space for canines and premolars) shows a space deficit only in the lower arch.

The cephalometric study showed the following:

Solitary median maxillary central incisor syndrome is diagnosed based on the studies performed.

There was a functional and esthetic compromise. Therefore, a twophase treatment plan was carried out. The first phase lasted approximately one year and used maxillary orthopedic appliances. Two treatment options were suggested for phase two to replace the missing incisor.

The child’s guardian chose the orthodontics treatment, and the second phase is still pending due to the costs to cover.

Phase 1 started on 8 June 2021, and the patient was scheduled for monthly checkups for six months. In December 2021, a photographic control was performed, showing a decrease in the overjet and overbite, an improved profile, and a corrected deep bite (Figures 5 and 6). The patient attended checkups until the first year of treatment.

The patient is being treated at the Pediatric Medicine Department.