How do I get a U-shaped smile? What treatment should I go for? (photos)

From your photos it appears that you were either left with or developed relapse of mild teeth crowding.  Continuing treatment with Invisalign is a great option to broaden the smile and give it more of a continuation of arch form from your central incisors through your canines. This will very likely give you the results you are looking for. However, it is important to note that alignment does NOT change teeth shape, color, anatomy, or gum height over a tooth.  Many cases call for aesthetic restorations ie bonding, veneers, gum lifts, whitening etc. following alignment to meet the patients aesthetic needs.look for an aesthetic dentist who is also an elite Invisalign provider who is in your area. You can find one by checking out the doctor locator on Invisalign's website.  To speak with me personally about your case give our office a buzz to set up a consultation.  In any case I want to wish you good luck and I hope you get the smile you are looking for!

Google Halle Berry and look at pictures in which she smiles. Nice, broad smile. As an adult, your upper arch can only be expanded so much using orthodontic appliances only. There is a surgery that can be done to idealize the upper arch. You need to speak with an orthodontist. Of course, if this type of surgery interests you, then a consult with an oral surgeon will be needed too. 

From the photos you submitted, it does not look like your case is finished. You can certainly improve that with invisalign or braces for a short period of time