CERAMIC TEETH PRODUCTION
The steps of the dental crown procedure. -
How a dentist makes a crown for a patient- 1) Tooth preparation, 2) Taking the impression, 3) The temporary crown and 4) Cementing the permanent crown.
The crowning process usually takes two visits.
It typically takes two separate appointments for a dentist to place a dental crown.
- The first appointment involves: 1) Preparing (shaping) the tooth, 2) Taking its impression and 3) Placing a temporary crown. The time needed to perform these steps can range from 30 minutes to an hour.
- During the time period between the two appointments, a dental laboratory will fabricate the crown. Two weeks or so are usually allotted for this process.
- When the patient returns for their second visit, the dentist will cement the finished crown into place. This step can usually be completed in about 20 minutes or so.
(CAD/CAM units that can fabricate a crown. As a variation of this basic process, some dentists have a dental milling machine in their practice. These are CAD/CAM units that can fabricate a crown quickly.)
A) The initial dental crown appointment.
1) Numbing the tooth.
Before the process of making your 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) Preparing (shaping) the tooth.
a) A specific amount of tooth structure must be trimmed away.
All crowns need to have a certain minimal thickness.
- This insures that they have adequate strength.
- And in the case of porcelain crowns, enough ceramic thickness to create a life-like translucency.
For most crowns, this minimal thickness lies on the order of around two millimeters (that's just a little more than a sixteenth of an inch). So, each and every tooth that is prepared for a dental crown will end up being reduced (ground down) by at least this much, pretty much on all sides.
Also, as the trimming process is performed your dentist must also remove any decay that's present along with any tooth structure (or filling material if present) that's loose or unsound. Due to this, some portions of your tooth may be trimmed substantially.
b) The prepared 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 given a slightly tapered form, so the crown (a hard object that can't flex) can be slipped over it.
c) 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 opposite sides of the 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 the dentist 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 -
How the impression is taken.
Most dentists will take an impression of your tooth using a paste or putty-like compound that's often just referred to as "impression material."
- 1) The prepared tooth is washed and dried.
2) Small diameter yarn ("retraction" cord) is tucked around the tooth, in the space between it and its surrounding gum tissue.
(The idea is that the cord pushes the gum tissue back away from the tooth. Then later, after it's been removed, the gums will stay back long enough for the impression material to seep around the tooth, thus allowing it to capture a copy of the entire tooth preparation.)
- 3) A small amount of runny impression material is squirted around the tooth.
- 4) A tray that's been filled with a thick impression putty is then squished over the tooth and its neighboring teeth and allowed to sit for some minutes.
- 5) As the different impression materials set, they fuse together into a single unit.
- 6) When removed from the mouth, the impression (see picture) contains a copy of both the prepared tooth and the teeth on that jaw.
An impression of the opposing teeth (the teeth that the crown will chew against) will need to be taken too. As well as some sort of "bite" impression to record the way the patient bites their teeth together.
How the impression is used.
- 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 on it, it should fit accurately on your tooth too. (In most cases, 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 is usually on the order of two weeks, possibly less (especially is arrangements have been made in advance).
b) Optical dental impressions.
Some dentists have a crown milling (CAD/CAM) unit in their office.
- These units have an attached camera (intraoral scanner) that can be used to take an impression of your tooth optically (a picture impression).
- Using this image, the machine's software (with input from your dentist) can reference it's library of digital tooth forms and design the shape of your crown.
- It can then fabricate it by grinding down a cube of dental ceramic ("porcelain"). The whole process is completed in about 30 minutes or so.
If your dentist doesn't utilize a milling machine it can be for good reason. These units can only be used to fabricate all-ceramic crowns. Your dentist may feel that this type of restoration is not best suited for your situation.(or they dont have one!)
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 it is being made. During this time period, you'll wear a "temporary" crown.
- Temporaries both protect your tooth and keep it from shifting position.
- They are usually made out of plastic, or possibly metal. They may be preformed shells that are then customized to fit your tooth, or made from scratch by your dentist.
- A temporary crown is cemented using "temporary" cement, so it can be removed easily and predictably at your next appointment.
5) Choosing the shade for your crown.
Determining the shade of a patient's teeth.
If your new crown will have a porcelain surface, your dentist will need to judge what shade of ceramic most closely matches your tooth's neighboring teeth.
- Your dentist will have a series of small, tooth-shaped pieces of dental porcelain, each one having a different color. Collectively these samples are referred to as a "shade guide."
- Samples will be selected and held in the space that your new crown will occupy, until one is determined to be the best color match.
B) The crown placement appointment.
Once the fabrication of your dental crown has been completed, your dentist can proceed with the process of cementing it into place.
1) Removing the temporary crown.
In those cases where a two-appointment process is being used (as opposed to the single-visit CAD/CAM milling method), your dentist will:
- Anesthetize (numb up) your tooth. (This step isn't always needed. It's often quite painless for a patient to have a crown fitted and cemented.)
- They'll then remove your temporary crown and clean off any remnants of temporary cement that remain on your tooth.
2) Evaluating the fit and appearance of the crown.
Before your dentist can cement your new dental crown into place, they will first need to make sure it fits well and looks right. As a part of this evaluation:
Checking the fit. - Your dentist will seat the crown on your tooth and inspect the way that it fits (possibly by way of using dental floss, feeling it with a dental tool, or asking you to bite down gently).
They'll then remove and adjust the crown, and possibly repeat this process several times, until they're satisfied with the way it fits and touches against neighboring and opposing teeth.
Checking the appearance. - Additionally, and especially in those cases where the dental crown will hold a prominent position in your smile, your dentist will likely 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 modifications) cannot be made.
3) Cementing the crown.
Once you and your dentist both 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 (at a point where the cement has just started to set), your dentist will use a dental tool and scrape away any excess that has extruded from underneath the edges of the crown.
The placement of the crown is now complete.
4) Taking precautions with your new dental crown.
At this point, your dentist may give you some instructions. For example, with some types of cement it's best to take it easy with the crown for the first day (eat nothing exceptionally hard or sticky), so to give the cement an adequate time period over which to cure.
Especially in the case where you have been numbed up, be careful until normal sensation has returned. You could easily bite your lip or cheek by accident, possibly severely.
Once your numbness has worn off, and for the next day or so, gently test the "bite" of your crown so to make sure that it feels right with all types of closing movements. If it doesn't, let your dentist know so they can correct the problem (a simple matter of buffing down the surface of the crown).