Since having seven crowns (manufac-tured by Lava), my health has taken a serious turn for the worse. My dentist assured me that there was no metal of any sort in these crowns and, indeed, they are marketed as 'metal-free'. However, when speaking to the lab that manufactured my crowns, I learned that they contain zirconia, an oxide form of zirconium, which is a metal. I am now intent on removing all seven crowns and intend to replace them with plastic crowns with the assurance that these will definitely not contain any undeclared metals.
Q) Do you know of any materials in plastic crowns which could cause health problems, or do you have any alternative suggestions?-B.G., viae-mail
A) Dental crowns (some-times called 'caps') are tooth-shaped coverings placed over seriously damaged teeth, which may be too far 'gone' to accept any more fillings. The most inexpensive crowns are made from relatively cheap metals such as nickel; however, as you are already aware, these can be toxic to some people-althoughan adverse reaction usually only occurs in people who are already sensitized to the metal (Dent Mater, 2006; 22: 1163-8; epub 2006 Jan 6).
To avoid this problem, more 'noble' metals such as gold are often used but, of course, this option is more costly. However, all metals are unsightly in the mouth, hence, the increasing use of ceramic porcelains, which can be matched to your natural tooth colour and are visually indis-tinguishable from the real thing.
The Lava crowns your dentist has given you are among the latest up-market ceramic-based dental prod-ucts. Originally developed in Ger-many, they are manufactured by3M, the giant US chemical company, which says this: "Lava crowns are metal-free and composed entirely of a new type of porcelain layering. For strength, they have a zirconium synthetic diamond substrate under the porcelain that is hidden underthe crown. Zirconium is a high-tech ceramic material that is characterized by its outstanding stability and bio-compatibility, as well as strength levels significantly higher than other all-ceramic materials."
Although zirconium itself is a metal, the form used in dental crowns is an oxide of zirconium, which does not behave like a metal at all. Most dentists believe that zirconium-based ceramics are completely non-toxic. Even 'holistic' dentists, who are super-aware of adverse reactions to dental materials, consider zirconium oxide to be a very safe bet, and probably the best choice for tooth repair.
But there is one expert who dis-agrees. He is Walter Clifford, of Clifford Consulting & Research in Colorado Springs, CO. His laboratory offers a test to assess the biocom-patibility of dental materials with an individual patient's immune system. His materials-reactivity test claims to be able to detect antibodies to a range of dental materials in the patient's blood, the finding of which indicates an adverse immunological reaction.
Clifford has tested over 40,000 patients, and found that around one in seven experiences a significant immune-system reaction to zirconi-um salts.
However, Clifford seems to be the only dental researcher to have red-flagged a problem with these compounds.
Nevertheless, the fact remains that most dental materials have not been fully tested for whole-body adverse reactions in humans, as virtually all of the studies concen-trated solely on local irritation responses (Adv Dent Res, 1992; 6: 65-77). So, Clifford may well be right about zirconium.
In fact, laboratory studies using isolated human cells suggest that powdered zirconium oxide can "inhibit cell viability" and, in solid form, may also slowly "leach ions" when exposed to relatively strong acids (about the pH of vinegar) (Clin Mater, 1993; 12: 197-201). When injected into guinea pigs, zirconium com-pounds caused granulomas, possibly as a result of damage to white blood cells and cellular connective tissue (J Pathol, 1978; 124: 51-61).
An alternative possible culprit in your case could be the cement used to fix your Lava crowns to your existing teeth. To make up for the relatively little toxicological testing of dental materials in people, Norwegian researchers at the University of Bergen recently completed a 10-year study of dental patients' adverse reactions. Not surprisingly, at the top of the list came amalgam fillings, but "resin-based materials and cements" also figured in 4 per cent of cases.
However, one limitation of this survey was that, once again, they confined themselves to within-the-mouth rather than whole-body reactions (Community Dent Oral Epidemiol, 2003; 31: 200-6).
In fact, dental cements are known to leach chemicals into the mouth which, according to Dr W. Geurtsen of Hanover University, "could poten-tially cause adverse systemic [whole body] effects" (Crit Rev Oral Biol Med, 2000; 11: 333-55).
You're thinking of swapping your Lava crowns for 'plastic' ones-by which we presume you mean acrylic-but be warned: these, too, can cause adverse reactions. Indeed, according to a recent review by Spanish allergy specialists (who failed to include ceramics in their review), the least allergenic crown materials are platinum and the tried-and-tested gold (Med Oral, 2003; 8: 334-47). However, be aware that some gold crowns may contain nickel, unless the dentist specifies 'high-noble' gold.
Since everyone reacts differently to dental materials, it may be wiseto have your individual sensitivities checked out. An holistic dentist will be able to find out what's best for you by arranging for an appropriate lab test-for example, by Clifford Consulting in the US (www.ccrlab. com) or The Biolab Medical Unit in London, UK ( www.biolab.co.uk ).