This tends to be a much shorter appointment.
Anaesthetic is required if the tooth is alive as it can be very sensitive once the temporary crown has been removed. This is probably not needed if the tooth has had root canal therapy
but some dentists like to put some in anyway for peace of mind.
The temporary crown will then be removed- sometimes it can be levered off and other times it may have to be cut off. The tooth underneath is then cleaned to remove all traces of temporary cement and the permanent crown tried in.
The dentist will assess:
- The margins- is the crown sitting down fully on to the tooth preparation?
Here we run a probe from the tooth onto the crown- the probe should not slip underneath but pass smoothly from one surface to the other. If the margins are above the level of the gum, then you may be able to feel where the tooth and crown meet.
- Are the contacts points good?
You should be able to hear a definite click as floss is passed through. If this is not present then there is a chance that you might get food stuck in this area.
Often I will sit the patient up in the chair, particularly if it is a front tooth and have them check they are happy before we stick the crown in.
To check this, they will put the trusted blue bite paper in between the teeth and get you to tap your teeth together and slide your teeth across each other. Any high spots will be adjusted and the porcelain re-polished. In an ideal world (which unfortunately we don't live in) the porcelain isn’t adjusted at all- this maintains the maximum glaze and means minimal wear will occur to the opposing teeth.
On rare occasions, it may be necessary if the bite is very tight to adjust the tooth or teeth that bite onto the crown. It is better to adjust a filling than natural tooth but sometimes we don't have a choice. This is done as a last resort when further adjustment of the crown may compromise the crown’s strength or reveal the metal underneath if the tooth is a porcelain fused to metal crown. If the opposing tooth is on a denture
or is also a crown, it can easily be adjusted.
Cementing and bonding-in:
Once the dentist and you are happy, the crown can be cemented or bonded in. This depends on the circumstances and the type of crown
used. Different procedures are followed for each, materials can be chemically cured (i.e. set on their own) or light cured (set with the blue dental light) and are either a glass ionomer cement, a composite resin or some combination of the two.
Cementing a crown is like using a super strength glue to connect the tooth and the crown. Bonding is stronger and involves the same technology as composite fillings
–both the inside of the crown and the tooth are etched with an acid to create micro pores which the material then flows into and sets to firmly attach the two together.
We use bonding and cementing in different circumstances. One is not necessarily better than the other- more they are appropriate at different times. If the crown preparation is short and tapered, there is not a lot of natural shape to hold the crown in, so to get some extra retention we may consider bonding. On the other hand, bonded crowns are considerably more difficult to remove which can cause damage to the tooth underneath in the process if it needs to be taken off. Because of this, for a naturally retentive tooth preparation, cementing will be more than adequate. As with everything, different dentists have different preferences!
During the process of sticking the crown in, it is essential that the tooth remains completely dry so the dentist will pad you out again with cotton wool, dry tips and a saliva sucker, or isolate the tooth with rubber dam.
They will dry the tooth with air, then follow the instructions of the particular cement they have chosen, ultimately mixing the material, putting it into the crown and seating it down on the tooth. When correctly in place they will remove the excess cement and floss in between the teeth to ensure material doesn’t set here. Sometimes with light cured materials they will shine the blue light for just a couple of seconds to allow the excess to be peeled away more easily before setting it fully.
Once the material has sufficiently set, the margins will be polished with burs, the contacts flossed to ensure they are clear and the bite checked again and adjusted if necessary. And hey presto! The procedure is complete.