Dental Education Lecture: When Do We Need Crowns? 

Fig.1

Fig.2

Fig.3

Fig.4

Today we are going to show you two instances that we need crowns and how a good or bad crown can affect your daily life.

We need crowns when our teeth are in pretty bad shape.  The tooth in the middle of Fig.1 is crumbing.  Filling is falling out.  Root canal therapy (arrow) is not properly done.  This molar tooth is supposed to have three root canals.  Somewhat only one of them is filled.  The appropriate treatment is to remove the old filling, redo root canal (black arrow in Fig.2), place new filling (we usually call build-up) and a crown (C).  The crown in Fig.2 is fairly well fabricated, seated and cemented.  It has a normal contact with neighboring teeth. Food may not be easily getting into the space between the teeth.  You may also notice that transition from the crown to the tooth (red arrows, so-called margin of crown) is so smooth that you may not feel the existence of the transition when you floss there.

The second reason that we need a crown is fix wear and tear of our tooth.  For complicated reasons, some of our teeth are worn down as shown by arrow in Fig.3.  The biting surface of the tooth is shorter, as flat as a frying pan or like an irregular ditch.  By contrast, the biting surfaces of two neighboring teeth have relatively normal shape, like hills and valleys.  When you have the worn biting surfaces like that one shown in Fig.3, you cannot eat sour food or chew hard food.  Your tooth is very sensitive.  Sometimes we have to make a crown (C in Fig.4).  However this crown has a drawback.  There is abrupt transition from the crown to the tooth (arrows).  Floss may be caught and torn there. You feel a big step when you floss. It is difficult to get rid of food impacted there, no matter what you use, floss or toothpick.  New cavity and/or gum diseases may develop there.  In next lecture, we will show you what will happen if we do not place a crown after root canal therapy.

Xin Wei, DDS, PhD, MS 1st edition 02/12/2009, last revision 12/10/2010