What ancient civilization used braces on their teeth?

I believe the answer is: catgut tied to crude metal wires

The catgut is made by the intestines of mammals such as horse or sheep.  Ancient Egypt was among the first one to use this method in order to preserve the teeth.

For wealthier citizens, they might use a more expensive metal for the braces. The Etruscans for example use gold as a form of brace in order to prevent tooth collapse.

6.3%

explanation:

the acceptance rate for yale university is 6.3%. this means that only 6 percent of people who apply actually get accepted!