You are quite right about the fact that most of the time orthodontists will only start full braces treatment when a child has all their adult teeth present.
However, every child is different and there exists certain conditions where early management may help to prevent worsening of the bite condition or may prevent future problems from developing. We refer to such treatment as interceptive orthodontic treatment.
Interceptive orthodontic treatment is usually for a shorter duration to treat the urgent problem before the complex braces treatment will be carried at a later stage when adult teeth have all erupted. If you are in doubt, you can bring your child to an orthodontist for a consultation.
You can also refer to the article I contributed here for more information: The Orthodontist's Complete Picture Guide To Braces For Children (2018).
Dr Elaine Tan
Consultant, Department of Orthodontics
National Dental Centre Singapore