Recently I received photos of a beautiful anterior esthetic case where discoloration was occurring. Since seating this case of all porcelain crowns on the upper anterior teeth, one lateral on the upper right began to get darker and darker, ultimately almost a light brown in the photos I was sent. Photos taken at a week post operatively showed that the crown matched perfectly at the time of cementation.
The patient reports that the crown seemed to get darker and darker until it reached it’s current color. The dentist who placed the restorations was already in the process of replacing the one crown, and had photos of the prep from the day of the seat and the day he cut the crown off to replace it. The prep itself had turned a dark brown color in an unusual pattern on the labial. I’m familiar with discoloration of the resin cement when it is contaminated during the seating, but this was the actual tooth. So I went in search of an answer and learned something about the interaction of iron based hemostatic agents and preps. Iron has a very high affinity for hard tissue and is attracted to the cut surface of the tooth. This attraction in combination with the etching of the dentin surface because of the acidic nature of the gingival retraction fluid can result in iron particles being absorbed into the porous dentin. This absorbed iron can react with bacteria that produce hydrogen sulfide, and the final resulting insoluble iron compound is trapped in the dentin structure. It takes a certain set of circumstances for this to happen, but once I started looking found lots of reports from dentists of this same phenomenon. There are lots of astringents, hemostatic agents, and impregnated retraction cords available on the market. One way to prevent this problem is avoid things that contain iron, or don’t result in an acidic fluid environment.