How good are elastics in fixing overbites/overjets?

Can be effective: You should seek an orthodontic referral. There have been may advances in teeth straightening. Some may use rubber bands. Others may use expanding device prior. Your orthodontist will direct you in the best treatment for you.

Determine cause: Elastics are an integral part of orthodontics. The cause of your overjet needs to be determined... Is it skeletal or a tooth discrepancy issue? A local orthodontist will be able to determine that, and advise you of the proper course of treatment.

Very: Orthodontists utilize "controlled force" to guide teeth and jaws into the best relationships with each other. Directed by a competent orthodontic specialist and worn as directed by a cooperative orthodontic patient the results can be spectacular. Know that elastics are just one of the many treatment modalities available to your orthodontist.