Dental Education Lecture: What does crown do?
Earlier we discuss when we need a crown and why we need a crown. Basically, a crown gives our tooth a protection against cracking particularly after root canal (R in Fig.1). Mrs. Chai has a filling (F) after root canal. The tooth has not cracked, but she finally agrees to get a crown (C in Fig.2), because food is easily trapped between the tooth with the filling and next tooth (Fig.1). The contact area of a normal tooth is rounded (yellow arrowheads in Fig.2), but the contact area of the filling is abnormally flat (red arrowheads in Fig.1). When our cavity is too big, it is extremely difficult for a dentist to make a nice normal contact area with a filling. It is much easier for a technician to make a nice rounded contact area for the crown in lab (red arrowhead in Fig.2). After we cement the crown, Mrs. Chai no longer has the problem of food impaction. In brief, a crown provides us with normal anatomy which a filling sometimes cannot.
By the way, before making a nice crown, we need to remove tartar (white arrowheads in Fig.1) by deep cleaning to get rid of gum infection. Because the margin of a crown is closely related to the gums. Bleeding gums because of infection makes it difficult to prepare a crown. One year after deep cleaning and crown, we cannot find tartar anymore (Fig.2). Mrs. Chai is very pleased with the results.
Xin Wei, DDS, PhD, MS 1st edition 12/10/2010, last revision 12/10/2010