How does a dentist make a dental crown for a patient?
The crowning process usually takes two visits. - It typically takes two separate appointments for a dentist to place a dental crown. These visits are usually scheduled about two weeks apart.
- The first appointment involves shaping the tooth, taking its impression and placing a temporary crown.
- During the time period between the two appointments, a dental laboratory technician will fabricate the crown.
- When the patient returns for their second visit, the dentist will cement the finished crown in place.
As a variation on this basic process, some dentists utilize milling machines in their practice. These CAD/CAM units can fabricate an all-ceramic dental crown in a matter of 15 to 30 minutes. And if one is used, the entire crowning procedure can be completed in just a single visit.
A) The initial dental crown appointment.
1) Numbing the tooth.
Before the process of making your dental crown is begun, your dentist will need to anesthetize (numb up) both your tooth and the gum tissue that surrounds it. In the case that your tooth has had root canal treatment, it won't need numbing. However, your dentist may still feel that anesthetizing its gum tissue is necessary.
2) Shaping the tooth.
A specific amount of the tooth must be trimmed away.
All crowns must possess a certain minimal thickness. This insures that they have adequate strength and, in the case of porcelain crowns, a life-like translucency. For most types of crowns, this minimal thickness lies on the order of about two millimeters (that's just a little more than a sixteenth of an inch).
This means that your tooth must be trimmed by at least this amount. That way, when your crown is cemented in place, your tooth won't be oversized.
Additionally, when your dentist performs the trimming process, they must also remove any decay that is present, as well as any portion of the tooth (or filling material, if present) that is loose or especially unsound.
The trimmed tooth must have a specific shape.
Besides reducing the overall size of your tooth, your dentist must also trim it so it has a specific shape. The tooth must be slightly tapered in form, so the crown (a hard object that can't flex) can easily slip over it.
The tooth's shape helps to insure the crown's retention and stability.
A crown isn't just held in place by dental cement. The shape of the tooth on which it sits plays a significant role in providing for its stability and retention.
The larger the nub of tooth that extends up into the interior of a crown (and the more parallel the sides of this nub are), the better it will stay in place. There can be times when so much of a tooth has broken off or decayed away that a dentist will feel that they must first "build up" the tooth with filling material (make the tooth taller) before they shape it for its crown.
3) Taking an impression of the prepared tooth.
Once your dentist has completed shaping your tooth, they will need to make a copy of it by way of taking a dental impression. There are two different processes by which this step can be performed:
a) Conventional dental impressions - Most dentists will take an impression of your tooth using a paste or putty-like compound that's often referred to as simply "impression material."
The idea is that the completed impression is sent to a dental laboratory where it's used to create a plaster cast that, in turn, is used when they fabricate your crown. Since the cast is a precise representation of your tooth and its neighboring teeth, if the crown is made to fit precisely on it, it should fit accurately on your tooth too. (Normally, a little bit of adjustment is still necessary.)
Depending on the specific arrangements your dentist has made with the dental laboratory, the amount of turn-around time needed to fabricate a crown usually runs on the order of two weeks or so, possibly less.
b) Optical dental impressions - Your dentist may have a CAD/CAM milling machine in their office. These units are attached to a camera that can take an optical impression (picture impression) of your tooth.
Using this image, the machine (with input from your dentist) can design the shape of your crown. It can then fabricate it by grinding down a cube of dental ceramic ("porcelain"). The whole process may take on the order of 30 minutes or so. The obvious advantage of this technique is that a tooth can be shaped and its crown cemented into place, all in one visit.
If your dentist does not utilize a milling machine it can be for good reason. These units can only be used to fabricate all-ceramic ("porcelain") crowns. Your dentist may feel that the physical properties and/or the aesthetics of this type of crown are not the most ideal for your situation.
4) Placing a temporary crown.
In those cases where your dental crown will be fabricated at a dental laboratory, you will have to wait the two weeks or so while your crown is being made.
During this time period, your tooth will need to be covered over with a temporary dental crown. This temporary, which is usually made from plastic or else a thin shell of metal, will be cemented using "temporary" cement, so it can be removed easily and predictably at your next appointment.
(Related information: Precautions you should take while wearing a temporary crown.)
5) Choosing the shade of the porcelain.
If your new crown will have a porcelain surface, your dentist will need to judge what shade of porcelain most closely matches your tooth's neighboring teeth.
To do so, a dentist will use a series of small, tooth-shaped pieces of dental porcelain (each having a different color) that, collectively, are referred to as a "shade guide." Your dentist will select various samples from the guide and hold them, one at a time, in the space that your new crown will occupy, until they find the one that most closely matches the color of your tooth's neighboring teeth.
B) The second dental crown appointment.
1) Cementing the crown.
Once the fabrication of your crown has been completed, your dentist can proceed with the process of cementing it in place.
In those cases where a two-appointment approach is being used (as opposed to a single-visit approach that utilizes a CAD/CAM milling unit), your dentist will first anesthetize (numb) your tooth. (This step may not be needed. It is often quite painless for a patient to have a crown fitted and cemented.) They will then remove your temporary crown and clean off any remnants of temporary cement that remain on your tooth.
Evaluating the fit and appearance of the crown.
Before your dentist can cement your new dental crown in place, they will first need to make sure it fits well and looks right.
As a part of this evaluation, your dentist will place the crown on your tooth, inspect the way it has seated (possibly by way of using dental floss, feeling it with a dental tool, or asking you to bite down gently), remove the crown and adjust it, repeatedly, until they are satisfied with the way it fits and touches against neighboring and opposing teeth.
Additionally, and especially in those cases where the dental crown will hold a prominent position in your smile, your dentist will probably hand you a mirror and ask you to evaluate the crown's overall shape and color. Don't be shy with your comments and questions. After a crown has been cemented, some changes (like color and even some types of shape changes) cannot be made.
Once both you and your dentist agree that all seems right with your new crown, it's ready to be cemented. To do so, they'll first place dental cement inside your crown and then seat it over your tooth. After a few moments, so to allow the cement to set a little, your dentist will use a dental tool and scrape away any excess that has extruded from underneath the edges of your crown. The placement of the crown is now complete.
2) Congratulations, the crowning process has been completed.
Taking precautions with your new dental crown.
At this point, the placement of your crown has been completed. You should ask your dentist if there are any precautions that they feel you should take. For example, with some types of cement, it's best to take it easy with the crown for the first day (consume nothing exceptionally hard or sticky), so to give the cement an adequate time frame over which to cure.
Especially in the case where you are numb, be careful until the numbness wears off. You could easily bite your lip or cheek by accident. Also, once your numbness has worn off, and for the next day or so, make sure that the "bite" of your crown feels right with all types of closing movements. If it's not, let your dentist know so they can correct the problem (a simple matter of buffing down the tooth). Not doing so can lead to (possibly serious) complications.