It is very rare that braces can be done on only the upper teeth because the most important reason for braces is to correct the bite and alignment of the teeth and it is much more difficult to do this when you only have control of half the teeth. Even though the bottom teeth may look straight to you, your Orthodontist would be able to show you the corrections that are necessary. Good luck.
The most important thing to do is to see the Orthodontist that treated you because they have your initial records and can determine how much your teeth have relapsed. They may be able to make you new retainers or you may need braces or Invisalign to correct your relapse. You must wear the retainers as instructed by your Orthodontist or the teeth will continue to worsen. Good luck.
Both types of retainers work well as long as you wear them correctly. I would return to your Orthodontist to determine how much relapse of your teeth has occurred and together you can decide on the proper retainer for the problem that you had. Be honest and let them know how much you are willing to wear the retainer. Good luck.
I agree with Dr. Stachel. I would not have any veneers done until you have a full treatment plan established. Have a consultation with an Orthodontist who may then refer you to an Oral Surgeon to determine if a combination of orthodontic treatment and Orthognathic ( jaw straightening ) surgery would yield the best correction for you. Veneers would be done after you have achieved the final tooth and jaw positions and your general dentist will work in conjunction with the Orthodontist and Oral Surgeon. Good luck.
I would have a consultation with an Orthodontist to find out the different options available for correction. Many Orthodontists such as myself offer free consultations. If that one tooth is your only problem, it may be able to be corrected with a retainer or clear aligners. This way you will have all the information to make an informed decision. Good luck.