Once you and your dentist have identified a dental problem or problems, it's time to visualize the solution. In my office, I do this with what's called a diagnostic wax-up. An impression is taken of the mouth, which is given to a technician who then perfects the tooth shape and position with a white wax. Spaces get closed up, gum levels are raised (or lowered, or evened out), edges smoothed, and so on.
Sometimes diagnostic wax-ups can be hard for you, the patient, to fully comprehend, so computer imaging and composite mock-ups can be used to show what the technician and the dentist think your ideal smile could look like. This is when you can weigh in with your opinion, and then adjustments can be made to the replica before anything is even done to your actual smile.
This exploratory part of the process is extremely important, as the less a patient knows up front about his options, the greater the chances he will be talked into more dentistry than is actually necessary. Too often, a dentist will recommend a full face of veneers when all the patient really needs is a combination of techniques, such as whitening and bonding, and much fewer veneers.