There is an age limit where correcting a narrow upper jaw becomes very difficult. What is normally quite comfortable, safe and works very well with an expander teeth for narrow jaw in children and young teenagers becomes a much more difficult procedure in adults with narrow jaws.
Widening the upper jaw with an orthodontic expander starts becoming much more difficult from the ages of 11-12 years upwards. The narrower the upper jaw or the more crowded the upper front teeth are, the more important it is to see an orthodontist for an early orthodontic assessment. Often, there are improvements in mouth-breathing habits, through better nose breathing, and less snoring.
This means that often waiting till all the adult teeth have fully erupted may be too late to obtain the desired benefits of an orthodontic expander. This can also mean that teeth are more likely to shift after braces when starting an orthodontic expander in the mid teens.