If you feel that your temporary veneers look too long, too bulky, or too prominent, I would definitely bring that up with your dentist before the final porcelain veneers are made. The temporary veneer stage is actually one of the best opportunities to fine-tune the shape and proportions of your smile. A very useful approach is to have your dentist recontour the temporary veneers first. They can shorten them slightly, reduce some of the facial bulk, refine the edges, and continue adjusting the shape until you feel comfortable with the length and overall appearance. Once you are happy with the temporary veneers, your dentist can take a digital scan or impression of those exact shapes and send that information to the dental laboratory. The lab can then use the approved temporaries as a guide when fabricating the final porcelain veneers. This is often one of the most predictable ways to communicate exactly what you like. Regarding your specific question, approximately 0.5 mm of length can often be adjusted, but I would prefer to make that decision during the temporary stage rather than relying on grinding down the final porcelain afterward. Final veneers can sometimes be polished and slightly shortened, but larger changes are better designed into the porcelain from the beginning. When the final veneers are ready, I would also ask whether your cosmetic dentist performs a veneer try-in before permanent cementation. During the try-in, the temporary veneers are removed and the final porcelain veneers are placed on the teeth without permanently bonding them. This gives you and your dentist an opportunity to evaluate the length, width, thickness, proportions, and overall appearance. If they still look too long or bulky during the try-in, it may be possible to make minor adjustments or, when necessary, send them back to the laboratory for modification before they are permanently bonded. The important point is that you should not feel pressured to permanently cement veneers when you are already unhappy with their shape. Use the temporary veneers as a prototype, refine them until you like the proportions, and then have the final porcelain designed to closely reproduce that result.