Discussion:
SMMCI syndrome is a complex disorder characterized by neurodevelopment
defects of the midline structures6.
If the history of dental trauma was not reported, the absence of a
permanent central incisor may be considered a rare form of hypodontia.
However, the association of anatomical abnormalities in the middle line
is used to alert the clinician to the possible existence of SMMCI
syndrome which may require specialist care.
SMMCI was initially reported by Scott who described a girl with the
presence of a single maxillary central incisor placed in the median
position, in view of an isolated observation.
Later, another cases of SMMCI reported in addition to the single central
incisor, short stature, congenital heart disease, microcephaly and
scoliosis7.
Although, in the present case, differently from what previously reported
in literature, SMMCI may be associated with other systemic disorders
such as autosomal dominant holoprosencephaly, growth retardation and
midline developmental defects4,7,8.
The etiology is uncertain but some studies such as those conducted by
Nanni et al. 2001 have shown, following DNA sequencing, mutations of the
Sonic Hedgehog (SHH) gene both in SMMCI syndrome and in
holoprosencephaly frameworks 9.
The diagnosis of SMMCI can be made prenatally at the 18th-22nd week
owing to the mid-trimester routine ultrasound4.
Increasingly, presumptive diagnoses are being made at birth with
confidence when the multiple defects are present 4,6 .
Once the primary SMMCI tooth has erupted, diagnosis can later be
confirmed by a pediatric dentist clinically and radiologically at 7–8
months of age6.
Kjaer et al. in 2001 examined the clinical features and craniofacial
morphology of 10 patients with SMMCI aged between 8 and 17
years.10
Also Bertolacini et al. study in 2009 consisting of 11 patients with
SMMCI, who underwent radiological investigation.11
The results of the two studies showed that the craniofacial morphology
of the patients with SMMCI compared to the normal craniofacial
parameters showed hypoplasia of the anterior cranial base, a hypoplastic
and post-rotated maxilla, and a retrognathic and post-moved jaw.
In addition, these groups of patients had features such as: nasal
obstruction, septal deviation, absence of frenulum of the upper lip and
incomplete mid-palatal suture10,11.
In the present clinical case the patient showed the same signs of
manifest SMMCI which confirmed our diagnoses.
In this complex disorder, management and treatment are complex and
delicate. First of all, the evaluation of the psychological impact that
this syndrome has on the patient and how the clinician can improve it,
is important. Secondly, an interdisciplinary evaluation is fundamental
for a correct management of the case. The treatment can be either by
extraction of the SMMCI with space closure or by space opening
associated to a prosthodontic replacement for the a maxillary central
incisor with either an implant borne crown or a resin bonded bridge.
Thus, an early orthodontic evaluation for a proper planning of the
treatment timing is encouraged 7.
Conclusion :
Early diagnoses of SMMCI grant more appropriate clinical follow-ups and
an appropriate treatment which could have a great advantage on the young
patient quality of life.
Pediatric dentists should recognize this disorder at an early age since
it is characterized by specific orofacial manifestations and should not
consider it as a simple dental anomaly in order to establish a proper
treatment for these patients.
References:
- CARE Case Report Guidelines. CARE Case Report
Guidelines. https://www.care-statement.org
- Mustafa MM, Zakirulla M, AlShahrani I, Togoo RA, Alkahtani ZM, Ain TS.
Clinical Evaluation of Solitary Median Maxillary Central Incisor
Syndrome. Case Reports in Dentistry . 2019;2019:1-5.
doi:10.1155/2019/2637825
- Lertsirivorakul J, Hall RK. Solitary median maxillary central incisor
syndrome occurring together with oromandibular-limb hypogenesis
syndrome type 1: a case report of this previously unreported
combination of syndromes. International Journal of Paediatric
Dentistry . 2008;18(4):306-311.
doi:10.1111/j.1365-263X.2007.00907.x
- Garcia Rodriguez R, Garcia Cruz L, Novoa Medina Y, et al. The solitary
median maxillary central incisor (SMMCI) syndrome: Associations,
prenatal diagnosis, and outcomes. Prenatal Diagnosis .
2019;39(6):415-419.
doi:10.1002/pd.5451
- El-Jaick KB, Fonseca RF, Moreira MA, et al. Single median maxillary
central incisor: New data and mutation review: Single Median Maxillary
Central Incisor. Birth Defects Research Part A: Clinical and
Molecular Teratology . 2007;79(8):573-580.
doi:10.1002/bdra.20380
- Hall RK. Solitary median maxillary central incisor (SMMCI) syndrome.Orphanet J Rare Dis . 2006;1(1):12.
doi:10.1186/1750-1172-1-12
- Nota A, Ehsani S, Pittari L, Gastaldi G, Tecco S. Rare case of
skeletal third class in a subject suffering from Solitary Median
Maxillary Central Incisor syndrome (SMMCI) associated to
panhypopituitarism. Head Face Med . 2021;17(1):49.
doi:10.1186/s13005-021-00300-3
- Schneider UEM, Moser L. Orthodontic space closure in a young female
patient with solitary median maxillary central incisor syndrome.American Journal of Orthodontics and Dentofacial Orthopedics .
2021;160(1):132-146.
doi:10.1016/j.ajodo.2020.05.018
- Nanni L, Ming JE, Du Y, et al. SHH mutation is associated with
solitary median maxillary central incisor: A study of 13 patients and
review of the literature. Am J Med Genet . 2001;102(1):1-10.
doi:10.1002/1096-8628(20010722)102:1<1::AID-AJMG1336>3.0.CO;2-U
- Kjaer I. Face, palate, and craniofacial morphology in patients with a
solitary median maxillary central incisor. The European Journal
of Orthodontics . 2001;23(1):63-73.
doi:10.1093/ejo/23.1.63
- Bertolacini CDP, Richieri-Costa A, Ribeiro-Bicudo LA. Sonic hedgehog
(SHH) mutation in patients within the spectrum of holoprosencephaly.Brain and Development . 2010;32(3):217-222.
doi:10.1016/j.braindev.2009.02.014