I’m not a strong believer of Two-Step or Two-Phase treatment unless it is required for correction of posterior/anterior (back/front) crossbite, limited space preventing adult teeth from erupting and social/self-esteem improvement for a child.
A question a lot of parents ask, do all baby teeth need to be gone before the orthodontic treatment begins for a teenager? It’s a great question and it is something that an orthodontist uses as a gauge to determine the best time to start braces/Invisalign. If a patient is 13 years old and still has baby teeth remaining, it could signal that their overall dental development is either delayed or there is an issue with the permanent teeth eruption or baby teeth exfoliating. Symmetry and patterns of tooth loss are a critical part of diagnosis. If the dental development is delayed within a reasonable time frame (12-13 yrs. old), it is sometimes better to delay the start of orthodontic treatment till the teen looses all baby teeth. However, just like dental development is critical in determining when is the best time to start braces/Invisalign, a child growth spurt is also equally critical. Typically Boys and girls have their exponential growth anywhere from 11 to 14 years of age. Although the above range is the norm, we do see extreme numbers as well for teens going through puberty as early as 10 and as late as 16 years of age.
There are times we recommend extraction of all primary/baby teeth if the child is about to reach puberty and has not lost their baby teeth. The growth during puberty is important to correct bite concerns such as small lower jaw, etc. The treatment is also the more efficient during a growth spurt than outside of this time frame.
Apart from growth spurt, I will sometimes recommend to start treatment prior to exfoliation of all primary teeth when there is no room for the permanent tooth to erupt. Making room for the underlying tooth will help the baby tooth become loose on its own. If not, we may have the baby tooth removed by the family dentist. Another time I’ll start treatment before all of the baby teeth are gone is if the patient’s smile is socially handicapping. Finally, if we’re planning on keeping a baby tooth because the underlying permanent tooth is missing, the presence of the baby tooth will have no bearing on the starting time.
Why do we wait for all the baby teeth to be gone before starting orthodontic treatment: To keep the length of treatment as short as possible.