Facemask/Reverse Headgear This is often used for patients with dental underbite in the mixed dentition stage. Generally between 7-10 years old is when a Facemask is used most often. Sometimes parents ask me if a Facemask can be used on their 15 y.o child with underbite, and my answer is generally no. Scientific literatures show that Facemask CANNOT stop the lower jaw growth. What this appliance does is use the extra oral structures as much stronger anchor to pull the upper teeth forward within t