Once the dental laboratory has finished fabricating the porcelain veneer they will deliver it to the dentist's office. The dentist will then place the veneer using the following protocol.
In those cases where the tooth preparation for a porcelain veneer has been very minimal a dental anesthetic may not be needed when the veneer is placed. This is most likely the exception rather than the rule. Many of the steps that take place during the seating process involve touching, washing, and drying a patient's teeth. Each of these activities could be expected to produce some degree of sensitivity.
The dentist's goal will be to create the strongest and most lasting bond between the porcelain veneer and the tooth as is possible. Toward being able to achieve this goal the dentist must remove any debris that may have accumulated on the tooth's surface since that time when it was initially prepared.
In those cases where temporary dental veneers have been placed the dentist will first need to remove the temporaries. They will then scrape, polish, and buff each tooth's surface until all accumulated debris (dental plaque, food, surface staining, cement) has been removed.
The dentist will need to evaluate the porcelain veneer and insure that its shape and form are appropriate. They will examine the way the veneer seats on its tooth. They will also assess the veneer's contours, overall shape, as well as the way it touches neighboring teeth or other veneers.
The dentist will probably offer you a mirror at some point during this fitting process so you can start to provide some input about the veneer's overall shape. If they do so they are doing this for a reason. They want to become aware of your concerns and questions early on, long before they are ready to actually cement the veneer.
Since porcelain veneers are small, fragile objects they can be very difficult to hold and manipulate. Because of this some shape changes are easier to perform after the porcelain veneer has been cemented (and is fixed firmly in place on its tooth). It's important to make all of your concerns known to your dentist. Some of them may however need to wait until later on in the appointment.
While the dentist has been examining the fit of the porcelain veneer they have also had an opportunity to begin to get an idea about the type of color change the veneer can provide. But because porcelain veneers have a degree of translucency the precise color change that can be accomplished by the veneering process will be dependent upon the specific shade of cement that has been used to bond the veneer into place.
As a test of the cement's effect on the veneered tooth's overall color the dentist will evaluate how a number of different test pastes (that are precisely correlated to the shades of cement that the dentist has to use) will affect the appearance of the porcelain veneer. During this testing they will place the trial paste inside the veneer and then seat the veneer on the tooth. They will then compare the color of the tooth to its neighboring teeth. If the color match does not seem adequate they will repeat the evaluation using a different shade of paste.
During this process the dentist will no doubt hand you a mirror so you can provide input. This is one of those times when you need to "speak now or forever hold your peace". Once a porcelain veneer has been bonded into place there's no changing it.
(With just one possible exception.)