Midline discrepancy is a common and persistent problem that all orthodontists encounter. Asymmetry of bone tissue, soft tissue and dental cavities may occur alone or simultaneously in patients with midline discrepancy. Correct diagnosis of the causes of this complication and the role of the mouth components in midline discrepancy are essential in proper diagnosis and planning for orthodontic treatment. A successful orthodontic treatment depends on correct diagnosis of this malformation.
Midline discrepancy can arise from jaw/skeletal problems, jaw deviation or dental problems such as unilateral deciduous or permanent tooth eruption, teeth crowding, and missing one or more teeth. If midline discrepancy is due to jaw deviation and if the patient refers to a dentist before puberty, this malformation can be easily treated with removable orthodontic appliances. However, if the patient refers to the dentist after puberty and midline discrepancy is due to jaw/skeletal problems, midline discrepancy should be treated through jaw surgery and orthodontics. Therefore, priority is given to early treatment with orthodontics without surgical intervention. Patients with tooth problems need fixed treatment, which can be done at any age given their gum conditions.
As mentioned, midline discrepancy is a common problem associated with difficult diagnosis and treatment. Midline discrepancy may be of dental or bone origin, or a combination of both. Occasionally, a change in the functional direction of the mandible can lead to midline discrepancy.
Therefore, it is crucial to determine whether the cause of the discrepancy is of a dental or bone origin, or a combination of both. According to orthodontic textbooks, the maxillary midline is exactly in the mouth middle in about 70% of people, but the maxilla and mandible only match in one fourth of the population. Midline discrepancy is found in all types of cases.
Midline discrepancy is located at the esthetic point of the face and is very obvious, necessitating correction and treatment. Causes and diagnosis of this malformation are discussed below.
Etiology of midline discrepancy
Midline discrepancy usually has two common causes regardless of its type:
In general, the causes of midline discrepancy are divided into two categories:
– Genetic factors
– Non-genetic factors
- Genetics: Deficiencies in the genetic of symmetry-generating mechanism as well as environmental factors lead to definitive deviation of midline to the right or left.
Examples: Multiple neurofibromatosis, dominant gene-related familial incidence, hemisfacial microsomia (facial asymmetry), and cleft lip and palate.
- Local and non-genetic factors:
– Jaw trauma
– Early loss of deciduous teeth
– Ankylosis of primary molar teeth (Ankylosis: fusion of the tooth root surface with its surrounding alveolar bone)
– Improper tooth eruption
– Congenital missed teeth or extra teeth
– Tooth decay
– Tooth size
Midline position measurement
The position of the maxillary midline relative to the facial midline is considered an important diagnostic component in orthodontic treatment. In most patients undergoing orthodontic treatment, the maxillary and mandibular midline is not aligned with the midline of the facial soft tissue. This may arise from bony asymmetries in which the maxilla or mandible have an abnormal position relative to the face bony structure, or from dental asymmetries due to upward or downward displacement or deviation of teeth, upper or lower teeth arches, teeth rotation or difference in teeth size.