When a tooth requires a crown, the tooth is ground down and shaped, an accurate impression is taken of the prepared tooth and a temporary crown is placed over the tooth for the period of time required for the laboratory to make the prescribed permanent crown.
The final permanent crown is designed to provide excellent fit and relationship to the remaining tooth structure, the gums, the neighboring teeth and the bite. For esthetic situations, the final crown should also provide the correct shade.
The objectives of the final cementation process are to permanently secure the crown onto the tooth and seal the dentine.
The insertion process for the finished crown includes:
- The trial fit of the crown in the mouth, including any necessary adjustments;
- The crown cementing procedure, and
- The final assessment and adjustment.
Prior to your appointment your dentist will assess the crown on the working model. If satisfactory on the model, the crown will be disinfected before trying it in your mouth.
Your tooth should not have any symptoms of pain or sensitivity at this stage and insertion should be delayed if you have any significant discomfort coming from the inside of the tooth. The cause should be found and treated to resolve any symptoms. A new temporary crown may be necessary. If symptoms are present that are subsiding, it is advisable to leave the temporary crown on the tooth a while longer until the symptoms totally subside. If persistent symptoms are present and attempts at resolution are unsuccessful, then root canal treatment may be required.
You may or may not need “freezing” for the insertion process. This depends on the specific condition of the tooth. Teeth that have not had root canal therapy are more likely to require local anaesthetic but this is not always necessary.
The temporary crown is carefully removed and all temporary cement fragments thoroughly cleaned from the tooth.
During the try-in of the crown in the mouth there is a risk of crown dislodgement as it is quite small and difficult to handle. You are advised not to try to talk or make sudden movements. You should remain alert and if the crown slips from the tooth you should immediately bring your head forward and put the crown into your hand. Safety during the try-in is extremely important to avoid you swallowing or inhaling the crown.
With you seated in a semi-upright position, the crown is placed on your tooth and the fit of the crown is assessed thoroughly. The crown margin should fit well and be “flush” with the tooth surface. The crown contours should be continuous with the contours of the tooth. Adjustments may be necessary to ensure the crown is totally seated and fitting well.
Assessment of the relationship of the crown to the neighboring teeth is performed using dental floss. There should be a definite “snap” as the floss traverses the contact to prevent food sticking between your teeth.
The final assessment involves checking the “bite”. With the crown accurately seated, you will be asked to close your back teeth together and the position of the crown is examined. The presence of any space between other upper and lower teeth means the crown is “high’ and will require the use of coloured paper to mark the areas of the crown requiring adjustment.
Once the central bite is satisfactory, side movements will be assessed. You will be asked to “bite” and then to move your teeth slowly from one side to the other, keeping the teeth in contact. Once the occlusion is considered perfect, any areas that have been adjusted will require polishing. When the crown has been completely assessed and no further adjustments are necessary, the crown is ready for insertion.
For tooth-coloured crowns, the shade will be assessed in a natural light and without the dental light shining on the mouth. The overall effect of the crown should be as natural and pleasing as possible. You will be offered a hand mirror or taken to a wall mirror to see the result prior to insertion.
Whereas it is not always possible to ensure a crown is totally invisible at an extremely close distance, the crown should be largely imperceptible and blend in with the remaining teeth at a talking distance. It is important to remember that the crown is not yet fixed to your tooth and may dislodge. Great care is required at this point to avoid swallowing or inhaling a dislodged crown.
If the shade is not acceptable, the crown will need to be sent back to the laboratory with a new prescription for shade correction.
During final insertion, a layer of the chosen cement is placed inside the casting and the crown is seated very firmly on the tooth. The dentist will maintain the pressure for one or two minutes. The objective is to provide the best seating of the finished crown with the minimum possible cement line between crown and tooth. The cement fills the microscopic gap, seals the margin and secures the crown.
Many dentists find that steady pressure can be better maintained by having the patient bite down on a cotton roll or special wooden stick. However, it is essential that the crown not be displaced by eccentric patient movements.
As soon as the cement has set, the excess cement is removed from the margins with hand instruments and floss
The dentist will ensure a final check of the occlusion prior to your leaving the dental chair, as it is possible that during cementation the crown will become slightly elevated. A crown that is “high” to the bite can cause pain. If adjustments are necessary, the biting surface of the crown will be re-polished.
Patients should be aware that:
- every effort has been made to provide a well-fitting crown that will last many years but there is, of necessity, a microscopic “join” between crown and tooth which must be kept clean and
- the most common reason for crown failure over the long-term is new decay at the crown margins and, therefore, it is extremely important for the patient to keep the crown margins free of plaque and food debris through good oral hygiene, that is, brushing and flossing, over the long-term.
A well-fitting and well-placed crown can be an excellent long-term restoration for many years if the area is kept clean by the patient. At future dental recall visits all crown margins will be checked carefully by the dentist for signs of plaque build-up or new decay.