What are class 3 elastics for braces for?

Lower teet back and: Class iii elastics are used from the lower teeth to the upper teeth so the forces move the lower teeth back. Care must be taken to not move the jaw back also as this might cause a non-physiological force on the joint structures. Usually this elastic is used to move the lower front teeth back, but it can also be used to place a forward force on the upper teeth.

For an underbite: Class 3 elastics typically go from the upper back teeth to the lower front teeth in order to move upper teeth forward and/or lower teeth toward the back.

Underbite correction: Cl-3 elastics are most commonly used to correct an underbite, (anterior cross-bite due to a relatively protrusive lower dentition/jaw). Although, there can occasionally be other uses for them such as counteracting unwanted effects from other forces. Ask your orthodontist about them if he/she has prescribed them for you. I'm sure they would be happy to discuss it with you!

UNDERBITE: Usually used wit underbite and strong chin.

Reciprocal force: Elastics pull at both ends. Class III elastics used to draw lower teen back and upper teeth forward. Depending on the Orthodontic biomechanics, there may be more movement in one arch than the other. Ask your Orthodontic Specialist to explain to you what he/she is trying to achieve. Wear elastics EXACTLY as directed.