What is a dental crown? First, the clinical crown of a tooth is the part of the tooth that sticks out of your gums and jaw, it is the part you can see with your eyes if you open your mouth and look in the mirror. But what a dentist usually means by "crown" is a procedure to restore the crown of your tooth to optimal shape and function. The procedure of doing a dental crown is a cap that covers the entire tooth, and it is often necessary when a root canal has been done or a tooth was cracked or chipped, among other reasons.
But you might not know the difference between a great crown, a good crown or a poor crown. What are the attributes of a well-made crown that works amazingly well in your mouth and lasts you a long, long time? Most dentists don't take time to explain the difference. I want to share an acronym with you that I learned in dental school: CIMOE. Each letter of this acronym refers to an aspect of the crown design that is crucial to its outcome.
C.I.M.O.E - Contacts, Internal, Margin, Occlusion, Esthetics. Before I permanently cement any dental crown, I examine each of these in detail. If they are not up to standard, I would rather have the crown remade than to cement a less than ideal crown. Let me explain what each of these mean.
Contacts - These are the "interproximal contacts", or in other words, where the floss goes in your mouth: between your teeth. For the contact to be ideal, you should be able floss it. If you can't get the floss between or it shreds, then it is likely too tight. But if there is no interproximal contact, then you are left with a space between your teeth where food can get caught. This is both annoying, and if not kept thoroughly clean, it can contribute to decay or gum disease. An ideal contact minimizes the space between your teeth but allows you to keep it clean with floss. We check for the floss to "snap" between the crown and the tooth on either side of it.
Internal - When a crown is made, a tiny bit of space is created for the cement on the inside of the crown, otherwise the fit is too tight. If the internal shape is off, then the crown won't seat the entire way onto the tooth and the margin of the crown won't be sealed.
Margin - The margin of the crown is where the edge of the crown transitions to the tooth. This is typically right at or just under the gum line. If the margin is closed then the crown is sealed around the tooth. With an ideal marginal fit you can run an instrument down the crown and not feel the transition between tooth and crown.
Occlusion - This is the word dentists use for "bite" and refers to the way your teeth fit together when you bite down. If the crown is too big (too tall), it would be the first tooth that hits and prevents your other teeth from touching the way that they are supposed to. It is often necessary to make minor adjustments to the occlusion (the biting surface of the crown) to accommodate the bite. After adjustments are made the crown should always be polished.
Esthetics - Your smile is crucial to your appearance, and so it is important that the way the crown looks meets your expectations. Some crown types are more oriented towards optimal esthetics and therefore look exactly like natural tooth structure. However, there are sometimes extenuating circumstances which require a less optimal material for esthetics. For example, I often will do a crown called "e-max" on a front tooth because of its amazing esthetics. However, for a patient who chronically grinds their teeth a zirconia crown would be a better choice due to strength. Zirconia crowns have slightly less optimal esthetics, but much higher strength.
In the future I will go into more detail about the pros and cons of different crown materials. If you have any questions about what makes a crown great and whether you need a crown, please contact us!
Written by: Harold Henderson, DDS June 13, 2019