Can wearing my vivera retainers longer than 3 months cause my teeth to shift back. i changed it at 4 months. do i need to restart invisalign?

No: If the retainers are properly fit and not worn out wearing them will not allow very much shift. Switching to the new retainer should provide a tighter fit and correct what slight change may have occurred. You must wear them as directed... usually every night.

Reexamination: Please don't self-diagnose. Go back to the Dentist or (preferably) Orthodontist who treated you yor an evaluation of your current problem and a discussion of the best method of resolving your problem. Remember 1) retainers hold teeth where they are, they are not treatment appliances, and 2) you need at least a year of full/time retention after tooth movement, followed by prolonged part-time rets

No: Retainers, by their nature are designed specifically to KEEP your teeth from shifting, not cause them to shift. You should be wearing your retainers for life-- at least while sleeping.