The following procedure applies to traditional bonded porcelain veneers. For a discussion of the newest type of veneer which can be done without preparing, or “drilling down” the tooth, and hence without shots, click here.
In indirect bonding, the artwork is done by a lab technician on a lab bench, and bonded onto the tooth by the dentist. The dentist usually prepares the teeth with the handpiece so that the space where the lab manufactured porcelain veneers (or filling in the case of back teeth) will be cemented will allow the insertion of the finished piece without interferences. That means that the dentist must cut the preparations so that there is a clear “path of withdrawal” with no interfering undercuts. When the dentist is finished preparing the teeth, he or she takes an impression which is poured with plaster to create an exact replica of the prepared tooth which is sent to the lab for fabrication of the appliance
These steps are a form of artwork all by themselves and can be quite demanding. Between the additional laboratory fees for the prefabricated restoration and the time it takes to prepare the teeth, this form of dentistry is quite a bit more expensive than the direct restorations described above (on the order of 5 or more times as expensive).
The image above shows the dentist making .6 mm depth cuts in the enamel of the tooth. He or she uses a special bur that automatically produces the cuts to the proper depth.
A medium grit diamond bur is used next to reduce the remainder of the surface to the the same depth. (See the six images below.) After preparation, an impression is taken and sent to the lab for fabrication of the porceain veneers.
The patient did not like the space between her two front teeth and felt that her teeth were too short and didn’t show when she spoke. In addition, the edges of her teeth were chipped and irregular. The image to the left shows the teeth after they were prepared to receive the veneers. Note the shoulder prepared around the edges (margins) of each tooth. This is done to allow the technician who will fabricate the veneers to place a sufficient bulk of porcelain for strength and color. (The porcelain is somewhat translucent, and if it is too thin, and the tooth structure over which the veneer will be placed is too discolored, which is often the case, the underlying discoloration may not be completely masked by the veneer.)
The preparation image (on the left) shows a tiny piece of string placed just under the gums around each tooth. This is called retraction cord. It is kept in place temporarily to retract the gums away from the margins of the preparations so the impression will be completely clear and the technician will know exactly where to end the porcelain. The string was removed after taking the impression, and the patient went home with the teeth in exactly the condition you see them above. (No temporary veneers were placed.) This is possible because the amount of tooth structure removed is small enough that a layer of enamel is left over the sensitive parts of the tooth, the preps are not very noticeable by anyone other than the patient herself, and we usually expect the finished porcelain to be returned within six working days, so the patient will not remain in this condition for very long.
The teeth were lengthened about one millimeter, but the real magic was accomplished by making the veneers extra thick. This trick tends to push the lip out slightly, making it a bit fuller. It also does not allow the lip to drape as low over the teeth as it did without the extra bulk thus giving the appearance of even longer teeth when the patient’s lip is at rest. The effect is not only startling, but sometimes disconcerting at first because the patient may feel that the teeth “stick out too far”. Within a few days, the patient gets used to the new feel of their teeth. The image to the right shows the veneers as delivered from the lab.
For a thorough understanding of glass and porcelain, Students and dental professionals should consult my five page course “Dental Ceramics for the beginner“
So what’s the difference between direct and indirect restorations besides cost?
In point of fact, both direct and indirect bonded restorations may look identical when they are first done. The difference is that the indirect variety are generally made out of porcelain. Porcelain is harder and more durable than directly placed composites and in general will not wear over time. It remains shiny indefinitely. The surface of direct composite veneers will wear over time and lose their shine.
Direct composite veneers frequently finish down to a knife edge margin in places around the periphery, at least in some areas, and these very thin areas may “curl” and separate after about three to five years leaving tiny areas of brown stain here and there. These defects can usually be repaired, but since indirect porcelain veneers never have knife edge finishes, and have super hard surfaces, no stain or reduction of the shine ever takes place. In addition, indirect porcelain fillings in back teeth have the advantage of not wearing down over time.
Indirect porcelain veneers are more brittle than direct composite restorations, and are somewhat more likely to fracture after taking a sharp blow from a hard object such as a coffee mug, or chewing down on something unexpectedly hard in food. However the newer porcelains are on the order of 12 times stronger than the older standard porcelains that were used only a few years ago, and breakage is now fairly rare. If you can afford indirect dentistry, then porcelain is the way to go. This is the Cadillac in dentistry while the direct composites are the station wagons.
While most general dentists will do composite fillings in any teeth, not all of them will do direct composite veneers preferring indirect porcelain veneers instead. The reason for this is that not all dentists are able to produce the artwork involved in bonding direct veneers quickly enough to turn a profit. If you think about it, it makes sense. There are thousands of dentists all around the country, and every one has different strengths and weaknesses. In the production of services, time is money, and some dentists would need to spend too much time trying to get the contours and color just right. If they offered this service, they would have to charge such high fees that the price of porcelain would become increasingly competitive. To understand how this works,
The newest form of esthetic dentistry involves bonding ultra-thin porcelain veneers, generally without anesthetic, to unprepared or lightly prepared teeth. This has been made possible because of a new innovation in dental materials. Lumineers® BY CERINATE is a cosmetic solution for permanently stained, chipped, discolored and misaligned teeth. It may even be used to revitalize old crowns and bridgework. Lumineers® are a porcelain veneer that can be made as thin as a contact lens and are placed over existing teeth, most of the time without requiring the removal of sensitive tooth structure (unlike traditional veneers discussed above).