Margin and More to Learn
When the model was re-arranged in the evening, the margin was found off quite a bit (Fig.3 buccal view, Fig.4 lingual). The red line was drawn by lab, whereas the blue one was re-defined.
Anyway, can we learn to check margin when a crown does not seat completely? Above the blue line there is a bevel, while between the blue and red lines the walls are parallel.
Jenny may think that crown prep clearance is not enough. What should be done to prevent this, in addition to reduction ring?
We should repeatedly tell the patient to return as soon as possible when a temporary crown is off or broken. It cannot be too overemphasized.
Twenty days later, the patient returns with chief complaint "Top left rubber band is broken". In fact there is no open bite. The crown appears to be completely seated.
Careful examination reveals that there is a fractured piece of porcelain mesiolingual to the crown (Fig.5 *). When the crown is removed, the chip is obvious (Fig.6). In brief, long margin leads to incomplete seating.
Xin Wei, DDS, PhD, MS 1st edition 02/27/2015, last revision 04/04/2015