Crowns and veneers are prosthodontic treatments for restoring the structural integrity and/or appearance of teeth. Both involve the replacement of natural tooth material with artificial substitutes, but there are fundamental differences. This discussion describes each of these treatments in terms of hardware, applications, procedures, and outcome expectations.
A dental crown is a sturdy tooth-shaped cap that is cemented to the trimmed stub of the treated tooth. It replaces the entire natural outer surface of the tooth. It is a fixed prosthetic, removable only by a dentist
Crowns are manufactured from a variety of materials, each with its own set of pros and cons. Gold, for example, is very durable, bonds well to the tooth, and doesn’t fracture. However, a conspicuous gold crown doesn’t necessarily make for an appealing smile. Porcelain crowns are strong on aesthetic appeal, but are not as sturdy and can wear down opposing teeth. A detailed comparison of the respective properties of dental crown materials can be reviewed here
Crowns are a treatment option for a variety of conditions involving decay or deformation of the natural material of the tooth. A tooth that can’t support a new or replacement filling due to extensive decay is a candidate. So are fractured teeth, or weakened teeth at risk of fracturing. Crowns are placed on teeth after root canal therapy, on dental implants, and on teeth serving as anchors (abutments) for a bridge
. Cosmetic applications include covering discolored or misshapen teeth. Crowns are sometimes suggested for children at high risk for tooth decay, usually due to non-compliance with basic hygiene.
The crowning procedure requires at least two appointments, occasionally a third.
On the first visit, the tooth and surrounding tissues are numbed with a local anesthetic. The dentist then uses his drill to trim away the outer surface of the tooth, reducing it by at least 2mm. This minimum is established by the thickness of the crown, which has to have the same shape and size as the original tooth.
The dentist then makes an impression of the reduced tooth and of the opposing teeth, either with paste, putty, or a digital scanner. A temporary crown made of acrylic is then placed on the reduced tooth with a temporary cement. The impression is sent to a dental lab and guides the custom fabrication of the patient's crown.
Between appointments, the patient takes some precautions to avoid issues with the temporary crown. It's best to avoid sticky treats like caramel and hard foods. Chewing on the other side of the mouth is prudent. When flossing between the temporary crown and the next-door teeth, the floss should be slid out rather than lifted out to avoid dislodging the temporary.
During the second appointment, the dentist removes the temporary crown, normally a completely painless procedure. It's then time to check out the color matching and fit of the permanent crown returned by the lab. The dentist perfects the fit by emplacing the crown, checking fit and bite, removing it to trim and adjust, repeating until it's perfect. The reduced tooth and surrounding gums are then numbed, and the crown permanently cemented in place.
A crown's life expectancy depends on several factors, mainly materials, and the patient's behavior. Some crowns last a lifetime. Due to prevailing insurance policies, five years is the minimum expectation. Crowns are a one-way street. Once a crown, always a crown: if a crown falls out or is damaged, it has to be replaced. Patients can extend a crown's lifetime by consistent, effective oral hygiene practices that minimize decay and keep the gums healthy. Regular dental checkups provide early detection and correction of any issues posing a risk to a crown.
Dental veneers are very thin pieces of porcelain (or composite) which are cemented to the front surfaces of teeth. They are placed on healthy teeth, with intact structure. Porcelain veneers are best suited to tooth surfaces that are not routinely subjected to strong, dynamic forces.
Veneers are usually, though not exclusively, a cosmetic solution. Discoloration, staining, dullness resulting from worn enamel – all are transformed by veneers into the brilliant white that enhances anybody's smile. A veneer can subtly change the shape of a tooth in the interest of uniformity or symmetry. There are even some applications to minor orthodontic issues
that extend veneers’ shaping and sizing capabilities.
Placing dental veneers is usually accomplished over two appointments, a week or so apart.
The first step is to trim the front surface of the tooth. Only about 1 mm of enamel is trimmed, as veneers are thinner than crowns. The dentist's design is to trim just enough enamel so that the tooth is restored to its original thickness when the veneer is cemented on. Trimming may have to be modified if there's decay or a filling on the front surface.
Trimming may proceed with or without anesthetic. That decision is for patient and dentist to resolve case by case.
At this point, the dentist uses a shade guide to establish the color and translucency specifications for the veneer.
Next, a putty or paste impression is taken of the target tooth and the neighborhood around it. This is what serves as the template for custom-fabrication of the patient's veneer. When sent out to a dental lab, the second appointment is made for a week or so later to allow time for delivery of the finished product. The dentist may opt to install a temporary veneer, much as a temporary crown is placed. The factors affecting that decision are the amount of trimming that was required, and any aesthetic issues the trimming has created.
Cementing the permanent veneer during the second appointment is a little more involved than the counterpart procedure for crowns. As with crowns, the dentist evaluates the veneer's color and fit, but there's a third factor at play because of the veneer's translucency. The color of the cement matters. It affects the final appearance of the cemented veneer.
This permits fine adjustments through a process of “trial pasting”. The dentist mixes a trial paste of cement which has the shade of final cement, but without the “sticking” ingredient. This allows the dentist to apply the trial paste, place the veneer on the tooth, and evaluate the appearance along with the patient’s input. If the appearance is not pleasing, the shade of the trial paste can be adjusted and the process repeated until it is.
At this point, the dentist prepares the surface of the tooth with an etching gel, applies the bonding agent which provides the "stick", applies the final cement blend to the inside surface of the veneer and places it in position on the tooth. The process is completed by exposing the veneer to a curing light which sets the cement. A little cleanup and the patient is good to go.
A reasonable lifetime expectation for veneers is in the range of 10-15 years. When that useful life is over, the tooth’s front surface still has to be protected, most likely by a replacement. The lifetime of veneers can be optimized by consistent dental hygiene practices, regular checkups, and by not subjecting the teeth and veneers to hard objects and strong pressures. An extra precaution is called for with front teeth: mouth guards when playing sports are a good idea.
Crowns and veneers are effective, well-established treatments for restoring and replacing what nature provided but which time or trouble has taken away. The procedures are very well-tolerated and provide years of utility for a small investment of time.