The space (or gap) between two maxillary central incisors is known as mid-line diastema. Any gap between teeth is known as diastema.

The most common cause is missing teeth.
Physiological median diastema/ugly duckling stage
Familial or Heriditary
Imperfect fusion of midline of premaxilla.
microdontia. macrognathia peg laterals.
Extracted tooth.
Retained deciduous.
mesiodens
abnormal labial frenum (High frenal attachment)
midline pathology (like cyst).
Thumb sucking
Tongue thrusting.

No. They will infact get larger as the time goes by. It is better to get the treatment as early as possible. Proper diagnosis and timely treatment is essential.

Temporary – Composite Fillings
Permanent – Veneers, Crowns, Braces or Aligners
Physiological median diastema/ugly duckling stage: No treatment required.
Imperfect fusion of midline of premaxilla: Excision of included Interdental tissue between the incisors: An orthodontic appliance for closure of median diastema is given during healing process.
Microdontia & macrognathia: Orthodontic treatment can be done, or composite build-up can be done.
Missing teeth or extracted teeth: Dental bridge or implant can be done.
Abnormal labial frenum (High frenal attachment): Frenectomy should be done to excise a thick fleshy frenum and orthodontic treatment can be done or composite buildup or veneers or dental crowns can be done.
Thumb sucking & tongue thrusting: Habit breaking appliances can be given.
Retained deciduous & mesiodens: These are to be extracted and can go with orthodontic treatment can be done or composite buildup or veneers or dental crowns can be done.
Midline pathology (like cyst or tumor): It has to be treated by excision.

Frenectomy is removal of abnormal frenum. This can be done surgically or with the use of advanced soft tissue dental laser.

If midline diastema is treated with orthodontics, then retention is considered most important. This condition is easy to treat but difficult to retain. It can be achieved by Lingual bonded retainers, banded retainers or Hawley’s retainer.

Those who are not confident of their smile or based on dentists advice if you are a candidate for treatment, then you should definitely undergo the treatment. Some people tend to leave the mid-line diastema as they dont have any issue with their smile. If it is genetic then it is not necessary, but if the diastema has occurred due any other reason, then it will have a negative effect and there will be issues with teeth sooner rather than later.

In Ugly duckling stage there is no treatment – wait & watch.
Early diagnosis of the problem is a preventive measure in which it can be corrected in growing stage with orthodontic treatment or habit breaking appliances and also any pathology can be treated early.
Frequent dental visits.
Opt for Professional Scaling.