Crowns are used when teeth are too broken down or decayed to be restored with fillings. As a rough rule of thumb, if more than about 40% of the tooth is gone, a crown is a better choice, although a filling can sometimes be placed as a short term solution. Placing a crown will sometimes require a foundation or “buildup” filling first, then about 1.0 mm of tooth structure is removed from all surfaces of the tooth. An impression of the prepared tooth is taken, and the assistant will make a temporary crown out of plastic to wear while the laboratory makes the final crown out of gold, porcelain, or a combination of gold and porcelain. Usually the lab will have the crown ready in about two weeks, at which time the temporary crown is removed, the tooth is cleaned up, and the permanent crown is adjusted and cemented permanently into place. (Often this final appointment does not involve any local anesthetic.)
In the past several years, we have been doing same-day crowns, taking an optical impression, designing the crown with CAD-CAM software, and milling it from a block of ceramic on a CNC machine in the waiting room. We can’t do all crowns this way–gold crowns, for example, must still be made the traditional way, and front teeth frequently we still take impressions and place temporaries. When we can do an optical impression, it saves you having to get an impression, then come back another day, and there are no worries about losing the temporary. Since it takes awhile to design and mill the crown, we typically schedule half the appointment before lunch, and seat the crown right after. The system we use is called CEREC, and it’s been around for about 25 years, made by a German company, Sirona. Until recently, Sirona was the only company making this equipment. Remember how great the phone service was back when there was only one phone company? Yeah, right. Sirona’s software is every bit as bad as Ma Bell was, and at least once a day I want to shoot the software engineers with one of their own ceramic blocks. There’s now a competitor, but Sirona’s software is as abysmal as ever in my opinion.
Bridges are used when teeth are missing and implants are not appropriate. A bridge involves preparing the teeth on both sides of the gap for crowns, and taking an impression as above. When the lab makes the crowns, a false tooth or “pontic” is welded between the two crowns. The entire assembly is then permanently cemented into place, and the end result feels just like your own tooth.
How long do crowns and bridges last? This varies, but typical lifespans are 15 years or so for a single crown, and 12-15 years for a bridge. Of course, some bridges last longer than that, and there are a few 40 year old bridges, but 12-15 years is a reasonable estimate.
Below are links to illustrated descriptions of crowns and bridges. They may take awhile to download.
WARNING: THESE ARE GRAPHIC, CLOSE-UP PHOTOS OF ACTUAL TEETH, AND VIEWER DISCRETION IS ADVISED.