Dental crowns are recommended when your tooth has a very large filling that exceeds the natural tooth structure, your tooth had root canal therapy, a combination of root canal therapy and a large filling, or cosmetic reasons.
1. Beginning the Dental Crown Procedure: Numbing the Tooth
2. Preliminary Impressions and Shade
The dental laboratory that fabricates your dental crown requires accurate models of both your maxillary and mandibular arches, in order to create a perfect crown for your tooth. If you have chosen a full ceramic or porcelain fused to metal crown (PFM), your dentist will also require the exact shade of your tooth before he begins the preparation of the tooth.
The dental assistant will take alginate impressions of both your upper and lower dental arches. These impressions will be poured in stone to create a stone model of your teeth. The models will be sent to the dental laboratory for use when making your crown.
A small impression of the teeth in the same quadrant of the tooth that requires the crown and the opposing arch is also taken before the tooth is prepared. This impression is used to fabricate a temporary crown for you to wear until your permanent crown arrives back from the dental laboratory.
After the impressions have been finished, the dentist will then use a shade guide to record the exact color of your tooth. If your crown involves one of your front teeth, your dentist may ask you to visit the dental laboratory for the lab technician to take a custom shade of the surrounding teeth. If you have opted for a gold crown, there is no need to determine the shade of the tooth.
3. Preparing the Tooth
A dental crown mimics the entire into of the tooth, with a hollow space inside like a cap. In order for the finished crown to fit correctly, the remaining core underneath the crown needs to be reduced to accommodate the crown on top. A crown is designed to securely fit the tooth, keeping bacteria out from underneath the vulnerable tooth structure.
Once the tooth and tissues have become numb, the dentist may decide to place a rubber dam over the teeth involved. The rubber dam is used to trap old filling material, tooth structure, and water from falling into your mouth.
Preparing the tooth for a dental crown involves removing very precise amounts of the tooth and filling material from the tooth that requires the crown. During this step, the discovery of tooth decay underneath an old filling may occur. If that is the case, all of the decay is removed and a composite core is placed on the tooth. If your tooth has undergone a recent root canal, a composite core may be placed as well during this step.
Once the core is complete, your dentist will continue to shape the tooth, creating a fine margin around the entire core of the tooth, like a shelf, and continue reducing the biting surface of the core until sufficient tooth and filling have been removed.
This step is crucial and generally takes the most time to complete.
4. Taking the Final Impression
Accurate impressions of your prepared tooth are an essential part of the dental crown procedure. Even the tiniest flaw in the impression can result in an ill-fitting crown.
Once the tooth has been prepared, your dentist may decide to use a gingival retraction cord to gently push your gum tissue away from the margins of the prepared tooth. A gingival retraction cord is a thin piece of cord, similar to a piece of yarn, that is gently inserted around the tooth, into the gingival sulcus. Some dentists have adopted other techniques for isolating the tissue, such as gingival curettage.
When the tooth is ready for the impression, your dentist will then take an impression of your teeth. Your dentist will begin the impression by applying a polyvinyl siloxane impression material around the prepared tooth. The dental assistant will begin filling the impression tray with a corresponding impression material. Your dentist will insert the impression tray over your prepared tooth, and ask you to bite down. It is very important for you to remain biting into the impression until the material is fully set. This impression takes between three and five minutes to fully set, so patience is certainly a virtue during this step of the dental crown procedure. Once the impression material has set, your dentist will remove the tray from your mouth and inspect the impression for any air bubbles or another void in the impression. It may be necessary to repeat the impression several times in order to obtain a very accurate impression.
5. Fabricating a Temporary Crown
Placing a temporary crown over the prepared tooth may seem like a cosmetic necessity, but in actuality, the temporary crown is very important for a number of reasons. Some states and provinces allow dental assistants to make a temporary crown for your prepared tooth and in some cases, the dentist will fabricate the temporary crown.
Preparation for the Crown
Using the small impression taken prior to preparing the tooth for the crown, the dentist or assistant will fill the impression tray with an acrylic resin material, in a shade appropriate for your case, and place it over the prepared tooth. Once the material has set, generally after one to two minutes, the impression is removed from your mouth. The temporary crown is shaped to fit your tooth and to remove any rough edges. Once it is ready, a temporary cement is used to secure the temporary crown onto your prepared tooth. The dentist will check to make sure your teeth bite together correctly and will ensure there are no rough or sharp edges around the temporary crown.
Temporary crowns are very important. Because your dentist has removed a substantial amount of tooth structure from the prepared tooth, the temporary crown acts as a barrier, keeping the prepared tooth in its place. Without a temporary crown, the prepared tooth can begin to shift. Any movement from the prepared tooth will prevent the permanent crown from fitting properly. In some cases, the prepared tooth can move so much that the permanent crown simply won’t fit over the prepared tooth. If this happens, the final impression will be taken again and the crown will be sent back to the laboratory to be remade.
Temporary crowns also keep a vital tooth protected. If you had a root canal, there will be no feeling in the tooth. Vital teeth are a different case. Most of the enamel is removed from the tooth during the preparation stage, leaving exposed dentin. Without a temporary crown, your tooth would be extremely hypersensitive to temperature and pressure. A temporary cement that contains eugenol is generally used because of its calming effects on the nerve.
It is vital for you to follow the post-operative instructions given to you for wearing a temporary crown. If the temporary crown does come off your tooth, call your dentist immediately and book an appointment to have it re-cemented.
6. Cementing the Permanent Crown
It generally takes the dental laboratory roughly seven to ten business days to make your permanent crown. Your dentist will ensure you have your cementation appointment scheduled before you leave the office after your tooth preparation appointment.
When you return to the dental office to have your permanent crown cemented, the dentist will begin the appointment by numbing the prepared tooth and surrounding tissues with local anesthetic. Even though the tooth is already prepared, the dentist needs to thoroughly clean the tooth before cementing the permanent crown. If you had a root canal performed on the prepared tooth, you will likely not require any local anesthetic.
Once the prepared tooth is completely numb, your dentist will remove the temporary crown from the tooth. All of the temporary cement is removed from the tooth, and the tooth is completely dried. Your dentist will then try the permanent crown on the tooth. Using a piece of dental floss, your dentist will also check the contacts in between the crown and adjacent teeth to ensure there is an ideal contact between the teeth. Contacts that are too tight or no contact at all pose a problem for you in the long run. A contact that is too tight will cause problems for you when you floss your teeth. No contact in between the teeth will allow food to become lodged in between the teeth causing the potential for tooth decay.
If the contact is too tight, your dentist will reduce a small amount from the adjacent tooth, not the crown. In cases where there is no contact, it may be necessary for the crown to be sent back to the laboratory to be remade.
When your dentist is satisfied with the fit of the crown, the final cementation process begins. This process involves keeping your tooth completely isolated from any saliva or water in your mouth. Cotton rolls may be placed on both sides of the tooth to keep the area dry. When the tooth is isolated any dried, a desensitizing agent may be applied to the tooth. The desensitizing agent will help with any postoperative tooth sensitivity.
Your dentist will then place a bonding material onto the prepared tooth. Some bonding agents require a curing light to set the material. Once the bonding agent has been set, the dental assistant will fill your permanent crown with cement and carefully pass the crown over to your dentist. Your dentist will place the crown on your tooth and remove some of the excess cement that squeezes out from underneath the crown. Depending on the cement chosen, a curing light may be used again to set the cement completely. Floss will be used to remove the excess cement from in between the teeth, and a dental scaler is used to remove excess cement from around the tooth and below the gumline.
7. Checking the Bite
Even though the dental laboratory made your dental crown to exact specification, set out by your dentist, there will be small adjustments that need to be made to ensure your new crown functions as it should.
Your dentist will wait approximately ten minutes for the permanent cement to set. When ready, your dentist will then check how your teeth bite together. Any high spots on the crown will be reduced on the opposing tooth. It is very important to have the bite correct because a high bite can lead to tooth sensitivity and tooth pain.
8. Post-Operative Instructions
Your new crown was made to withstand the normal forces from biting, chewing, and grinding. However, it is very important to understand that crowns are not indestructible.
Once the bite is accurate and your tooth has been cleaned from any excess cement, your dentist will give you very specific post-operative instructions for your new crown. It is important for you to follow these instructions to the letter. Most specifically, what you eat with your new crown is the biggest change you will make due to your new crown. For example, candy and nuts are very destructive to crowns and should be avoided at all costs.
If after a few days you notice anything unusual with your new dental crown, call your dentist immediately to have the crown examined. It is also imperative for you to continue following a strict oral hygiene regimen that includes brushing, flossing, and professional cleanings for your crowns.