The time zones known as Greenwich Mean Time and the International Date Line are sometimes alternatively used to demark the western from eastern hemispheres, but the would not be true hemispheres as those time zones are not straight longitudes.
The final part of braces are interarch rubber bands, which are used to adjust bite and jaw position. These are connected to the brackets with hooks, often connecting the top tooth bracket with the bottom tooth bracket to help adjust the position of the teeth in the mouth and the position of the jaw.
Besides the larger rubber bands just described to help move the bite, smaller elastics are also used for braces. These tiny rubber bands are used to hold the wire into the brackets (as shown below) and are what most people talk about when they choose colors for their braces.