Filling a Need

Cavity treatment used to be simple. A dentist drilled away the decayed part of the tooth and packed the resulting hole with silver-colored mercury amalgam. It wasn’t pretty, but it did the job--at least until the amalgam started to crack or come out.

But as dental science has become more technologically sophisticated, so too have the options for replacing the enamel, dentin and pulp ravaged by bacteria and plaque. Decayed areas of teeth can now be restored with mixtures of plastics, glass, ceramic and quartz, each with varying degrees of aesthetic appeal and durability.

The variety has been driven, in large part, by cosmetic concerns. Given the choice between a molar full of grayish metal or a synthetic compound tinted to resemble tooth enamel, patients generally opt for the latter.

“Very few people today want anything placed in their mouth that doesn’t match,” said Rella Christiansen of Clinical Research Associates, a Provo, Utah-based nonprofit organization that evaluates dental materials and techniques.

But, with adults today keeping their teeth longer than in generations past, dentists have also been searching for cavity fillers that can last for decades.

Meanwhile, vocal consumer advocates have been fighting to rid dentists’ offices of mercury amalgam, which has been used since the 1850s. Mercury has already been taken out of childhood vaccines because of potential damage to developing brains, and health authorities often warn about the danger of eating mercury-contaminated fish.

Charles Brown, a Washington, D.C., lawyer who as founder of Consumers for Dental Choice has led the anti-mercury charge, is now working to garner support for a bill sponsored by U.S. Rep. Diane Watson (D-Calif.) that would abolish mercury amalgam nationwide. Said Brown: “There is no science in support of mercury fillings.”

The majority of U.S. dentists, following American Dental Assn. guidance, counter that no one has proved that mercury amalgam fillings diminish health, although a small number of people develop allergic reactions to the substance. Although they acknowledge that mercury can be released from fillings when you chew and can be detected in breath vapor and in the bloodstream, they point to reassurances from the ADA and a handful of federal agencies that mercury released by fillings falls well within safe levels.

Some dentists are playing it safe just the same. Figures from the American Dental Assn. show mercury amalgam fillings losing ground to higher-tech materials. In 1990, amalgam accounted for 99.5 million new fillings, including 23 million fillings placed in the mouths of U.S. youngsters ages 2 to 17. By 1999, amalgams accounted for just under 71 million new fillings, including 21.5 million fillings for children.

At the same time, more dentists have stopped using mercury, according to surveys of dental preferences. Last December, Clinical Research Associates found that 27% of randomly sampled subscribers to its newsletter weren’t using mercury amalgam, up from 3% in 1985 and 9% in 1995.

Dental insurance, however, hasn’t caught up with all the developments. Many plans, including Medi-Cal, will pay only for the standard amalgam (except where a front tooth is involved). Consumers who want something else must make up the difference, often 30% or more above the cost of mercury.

“We’re moving toward better access because everybody is paying attention” to how the newer materials are working, said Dr. Van P. Thompson, who heads the dental materials department at New York University College of Dentistry.

Since last year, Californians sitting in the dentist’s chair who need fillings, crowns, bridges or other restorations have been handed a fact sheet that acknowledges controversy about the safety of mercury amalgams and details the pros and cons of alternatives.

Carol Cromer of Marina del Rey, who in February was told that her 6-year-old daughter, Caitlin, needed a handful of fillings, said she carefully reviewed all the listed options with her child’s dentist. Although she considered using amalgam, she eventually decided on composites. “I did have less doubts about it,” she said.

Some experts say dental consumers may be trading one set of health concerns for others as more is known about the long-term effects of newer filling materials, not to mention the cements sometimes needed to make them stick. For example, composite fillings can leach a substance called bisphenol-A, a material found in plastic food can linings that appears to mimic the female hormone estrogen, although the California fact sheet says concerns about it aren’t supported by research studies.

“Like everything in life, there’s a pro and a con,” said Dr. Mark Goldenberg, a Beverly Hills dentist who helped draft the California dental fact sheet.

Here are your options when getting a tooth filled:

Mercury amalgam. This mixture of liquid mercury, powdered silver, tin and copper has long been dentistry’s workhorse for its ease of use, durability and low cost. Over time, it can expand and contract with changes in temperature, leading to cracks in the filling and tooth that may require repair or replacement. While some people experience initial sensitivity to heat and cold, that generally goes away. In the last decade, many dentists have been using special adhesives to improve the way the filling fits and seals the area.

Composite resins. These combinations of resin (liquid plastic) fortified with powdered glass, quartz, silica or ceramic, mimic the look of tooth enamel. The powdered material provides strength and helps reduce the shrinkage that occurs when it hardens. Historically, composites have required more skillful handling than amalgam and can take 10 to 15 minutes longer than amalgams to put in place, said New York University’s Thompson. He said that composites seem to be wearing as well as amalgam, although not all dentists agree. Composites, which must be bonded to the tooth, are either self-hardening or require exposure to 10 to 20 seconds of light to start the hardening process. They require less drilling than amalgams, preserve more of the tooth and can be done in a single appointment. Even with only slight shrinkage, fluid can leak in, however, fostering bacterial decay and creating some sensitivity to heat and cold that might require replacement.

Glass ionomers. Used mostly for cavities below the gum line, these chemical compounds are made by mixing ground-up glass with polyacrylic acid. The glass and acid react chemically to form a gel, which eventually hardens. The reaction also produces fluoride that’s slowly released over time and can fight cavities by inhibiting bacteria. Tricky to handle, glass ionomers require quick, deft placement. Because the material naturally sticks to the tooth and doesn’t irritate tooth pulp, there’s little tooth sensitivity. Because glass ionomers are brittle, can fracture and are susceptible to surface wear, they’re not recommended for biting surfaces.

Resin-modified glass ionomers. These ionomers, to which resin has been added, are tougher, more translucent, more natural-looking and easier for dentists to use than glass ionomers. As with glass ionomers, these slowly release fluoride. But the addition of resin reduces the natural adhesive qualities, so some dentists use cement with them. After sculpting the material, the dentist exposes it to a special light and it quickly hardens. Because the material isn’t as wear-resistant as amalgam and composites, it isn’t good for permanent teeth. Many pediatric dentists use it to fill kids’ baby teeth, however. More resistant to dissolving than glass ionomers, these ionomers are a top choice in areas of the mouth where it’s hard to control the amount of moisture, like at the tooth roots. They create little tooth sensitivity.

Gold. Gold fillings, which must be cast in a laboratory, are durable and expensive, requiring at least two visits to the dentist’s office. Today’s gold fillings are cemented in place with an adhesive. Because gold is a good conductor of heat and cold, gold fillings can irritate sensitive teeth.

Porcelain. Also known as inlays or onlays, these fillings are made in the laboratory by firing glass particles that then melt together. They offer very natural color that can match the tooth, but they tend to break more easily than composite resins and glass ionomers. They are expensive, taking at least two appointments, and are cemented into the tooth. They don’t create sensitivity.

The durability of all these materials depends on the dentist’s handling, knowledge and talent, as well as the patient’s eating habits and care. Habitual chewing on especially hard foods, or eating very acidic foods like lemons, may degrade the fillings.

CAD-CAM: This type of filling, with a shorthand name that refers to the technique that produces it--computer-assisted design/computer-assisted machining--is used by perhaps 10% of U.S. dentists, according to Christiansen of Clinical Research Associates. It removes much of the potential for human error in fitting a filling. Once the dentist removes decay and prepares the tooth, a computer measures the area to be filled, then designs and custom-sculpts the filling from a cylinder of a special ceramic mixture. These fillings can be done in one or two dental visits and offer durability somewhere between amalgam and porcelain.

Even as computers, such as those used with CAD-CAMS, move dentistry into an era of more precision, researchers are trying to create composites that shrink less than current ones, as well as better ways to harden composites and resin-modified glass ionomers.

Ultimately, though, the answer could be to use materials more like those nature gave us. USC researchers have found the genes responsible for the production of dental enamel, and other scientists there and overseas are trying to develop materials that mimic the body’s own tooth tissues, while also working to regenerate enamel.

These approaches, which combine stem cell biology, discoveries about the human genome and biotechnology, would eliminate the toxicity and potential side effects of current compounds, said Dr. Hal Slavkin, dean of the USC School of Dentistry.

At the same time, other researchers are trying to develop a vaccine that would prevent tooth decay altogether.

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The Drill on Fillings

The pros and cons of various dental filling materials:

Amalgam

Pro: Durable, inexpensive, decay-resistant.

Con: Poor aesthetics, more tooth must be drilled away, some controversy over health effects.

Composite Resin

Pro: Durable, resistant to fracture, excellent aesthetics.

Con: May shrink slightly, permitting decay.

Glass Ionomer

Pro: Good aesthetics, bonds well to tooth, releases fluoride.

Con: Brittle, poor resistance to stress of biting.

Resin-Modified Glass Ionomer

Pro: Relatively easy to handle, releases fluoride, little tooth sensitivity.

Con: Poor resistance to wear on biting surfaces.

Gold

Pro: Durable, leak-resistant, rare allergic reactions.

Con: Expensive, poor aesthetics, conducts heat and cold.

Porcelain

Pro: Excellent aesthetics, moderate durability, no allergic reaction.

Con: Expensive, fractures easily.