Why don’t dental restorations last a lifetime?
When I was in dental school, one of my professors said, “If you want to make monuments that will last until the end of time, be sure you don’t work in the human mouth.”  Another called the mouth “a hostile environment.”   Both were correct.
The bacteria that cause decay are extremely small;  about one micron in diameter. (one thousandth of an inch is about 30 microns).  Silver-mercury fillings corrode over time;  when a space opens up around an old filling that’s as wide as one of the hairs on your head, 150 bacteria can walk abreast into that space.   Result:  decay around the old filling.
That’s one of the reasons that dental restorative materials—fillings, onlays, and crowns—don’t last a lifetime.
Insurance company statistics show that the average crown done in the U.S. lasts about 5 years.  That’s why many insurance company plans will at least partially cover a new crown if it’s needed five years after the original crown was placed.

Is the situation improving?  In some ways, yes.   Here’s how:

A dentist can do things to increase the longevity of dental restorations. The precision of fit is extremely important.  The bonding agent that holds restorations in place is like a thinned-out version of the plastic resin we use for fillings and tooth-colored onlays.  It can’t possibly be as strong as the material it bonds in place.  The more accurately the restoration fits, the less bonding agent is needed to seal the restoration to the tooth.  Since the bonding agent is the “weak link” in the chain, restorations with very precise fit tend to have greater longevity.

A dentist also needs to use advanced materials and techniques to enhance the longevity of restorations.  For example, until about 12 years ago, every available cementing agent for crowns had one very undesirable property;  it could dissolve in saliva over time.  The newer cements are much more saliva-resistant and  actually chemically bond to the tooth. I’m lucky that I’ve developed relationships with the two top experts on bonding  techniques and materials.  That helps keep me up on the best treatment options for you.

Choice of materials is intimately related to their longevity. Some materials intrinsically tend to last longer than others. Laboratory-fabricated plastics are hardened under heat, pressure, and intense light, often in a vacuum or specially controlled atmosphere. These materials are harder and more wear-resistant than the usual plastics used for smaller fillings, and tend to last longer for large restorations like onlays. Recently developed ceramics are even stronger than advanced plastics. Gold tends to last even longer; in fact, gold tends to last longer than any material ever developed for dental use. I’m one of the few dentists in delaware county who frequently places gold restorations. Who wants gold? People who are phobic, who tend to break restorations, or who want the restoration that will last “as close to forever as possible.” it’s not uncommon for gold to last 10, 20, 30, 40 years or longer.

What can you do to help increase the longevity of restorations?   Remember the line about the mouth being a “hostile environment?”  I’ve seen mediocre dentistry placed by mediocre dentists last years longer than it deserved just because the patient was a fanatic about brushing and flossing.  There is no substitute for this effort.
If great home care can make mediocre dentistry last longer, imagine what it can do for really well-crafted dentistry.
The other thing you can do is to keep to whatever checkup schedule we recommend as best for you (three months, four months, or six months).  That way, if you do develop a problem around any restoration, we have the best chance of catching the problem early and doing more conservative treatment to fix things.

This brings up another closely-related issue.  Do you know someone who will only do “point-and-shoot” dental treatment?  By that I mean that the person goes to a dentist only when he or she perceives a problem, points to the problem, gets it fixed, and disappears until the next perceived problem.  People who do this are doing themselves a big disservice.  The most cost-effective service I provide is a treatment PLAN based on a  comprehensive examination, thorough cleaning, and necessary x-rays.  There is no substitute for a thorough overview of your entire mouth.  I  suggest that, if you know a point-and-shoot dental consumer, you nicely slap that person upside the head (just kidding about the slap part) and try to educate that person on the benefits of comprehensive treatment.

Insurance company statistics aside, what is a reasonable life-expectancy for complex dental restorations?  In my experience, the crowns I place last 10-20 years on average, tooth colored onlays 10-15 years, veneers 10-15 years, and gold onlays 10-50 years.

FDA changes its position on silver-mercury fillings
The Food and Drug Administration recently modified its long-held position on the safety of silver-mercury (amalgam) fillings.  While the FDA does not recommend wholesale removal of  existing amalgams, they recommend that no new amalgams be placed in children or pregnant women.
The FDA’s recommendations come as no surprise to me.  I  stopped using amalgam 10 or 12 years ago.   I also have installed a special filter for separating the mercury and amalgam debris created when I remove old amalgams (this keeps this debris out of the wastewater). Also, this removal is usually done with the rubber dam in place to protect your throat from that debris.
What do I think the future will hold?  I think amalgam separators will be required in dental offices in the near future, and I think that political pressure from anti-amalgam groups will force a complete ban on amalgam placement within the next 10 years.