Amalgam -- Resurrection and Redemption Part 2:
The Medical Mythology of Anti-Amalgam

Michael J. Wahl, D.D.S.

Myth #10: There are no health concerns about the components of
composite resins, glass ionomers, and other nonamalgam materials.

Fact #10: Although they appear safe and effective, there are health concerns
warranting further study about the components of composite resins,
glass ionomers, and other nonamalgam materials.

Since many anti-amalgamists consider mercury released from dental amalgams to be unsafe, they recommend the use of "nontoxic" nonamalgam alternatives, most commonly composite resins. One group of anti-amalgamists stated, "It would seem that now is the time for dentistry to use composite (polymeric and ceramic) alternatives and discard the metal alchemy bestowed on its profession from a less enlightened era." [1] But Mackert stated:

A frequent claim by the anti-amalgamists is that "no research has shown that dental amalgam is safe," yet the same charge can be leveled against composites and other dental materials. No material can ever be judged "safe" with any kind of finality, because new biological evaluation techniques are always being developed, and previously unanticipated adverse effects are continually being discovered for all materials [2].

Just as amalgam fillings release mercury, so composite resin restorations have been shown to leach between 14 and 22 separate potentially hazardous compounds, including DL-camphorquinone; 4-dimethylaminobenzoic acid ethy ester, drometrizole; 1,7,7-trimethylbicyclo[2,2,1]heptane; 2,2-dimethoxy[1,2] diphenyletanone; ethyleneglycol dimethacrylate; and triethyleneglycol dimethacrylate [3].

In a study of 35 identifiable dental resin composite monomers/additives of commercial composite resin composites (Table 1), investigators found nine severely or moderately cytotoxic components [4]. Other studies have also shown composite resin components to be cytotoxic (causing damage or destruction of cells). [5-15] Several studies have shown that dentin bonding agents and their components are mutagenic (cause mutations in new generations). [16-19] Wataha et al stated, "the components of resin composites are hazardous in that they all cause significant toxicity in direct contact with fibroblasts." [20]

Table 1. Components of Resin Composites

Abbreviation	Compound
BEA BEMA BHT Bis-EMA Bis-GMA	Benzyl alcohol Benzyl methacrylate 2,6-Di-t-butyl-4-methyl phenol Ethoxylated bisphenol-A-di-methacrylate Bowen monomer, isopropyliden-bis (2-hydroxy-3-(4-phenoxy)-propylmethacrylate
Bis-MA BL BME BPE CA CQ DBPA DCHA DCHP DDMA DEAE DEGDMA DHEPT DICH DIPA DMABEE DMAPE DMBZ DMDDA DMPT DMTDA EGDMA HEMA HMBP TEG TEGDMA THA TPP TPSb UDMA	Bisphenol-A-dimethacrylate Benzil Benzoic-acid-methylester Benzoic-acid-phenylester Camphoric acid anhydride Camphoroquinone Dibenzoyl-peroxide Dicyclo-hexylamine Dicyclo-hexyl-phthalate 1,10-Decane-diol-dimethacrylate Diethyl-amino-ethanol Diethyleneglycol-di-methacrylate Dihydroxy-ethyl-p-toluidine 1,6-Diisocyanato-hexane 2,6-Diisopropyl-aniline 4-Dimethylaminobenzoic acid ethyl ester 2-(4-Dimethyl-aminophenyl)ethanol Dimethoxybenzoine Dimethyl-dodecane-amine Dimethyl-p-toluidine N,N-Dimethyltetradecylamine Ethyleneglycol-di-methacrylate 2-Hydroxy-ethyl-methacrylate 2-Hydroxy-4methoxy-benzophenone Triethylenglycol Triethylenglycol-di-methacrylate Trihexylamine Triphenylphosphine Triphenylstibane Urethane-di-methacrylate
Reprinted with permission of Wiley-Liss, Inc., a subsidiary of John Wiley & Sons, Inc. Adapted from Geurtsen W et al [4]

Resin composite components have been shown to cause immunosupression or immunostimulation [21] and to inhibit DNA [22] and RNA synthesis [23]. Resin composite restorative material was shown to be more cytotoxic than amalgam in a comparative in vitro study [24]. Various resin components of dentin bonding agents have been shown to suppress the mitochondrial acitivty of macrophages [25]. Various composite restorative materials implanted into animals have been shown to cause inflammatory responses, including an increase in lymphocytic infiltration as well as fibroblasts and epithelioid cells [26].

There have been several reports of allergy to composite resins and their ingredients [27-31]. It has been suggested that composite resins may be a cause of hand eczema and skin symptoms in dentists [32]. Vinyl, latex, and modified latex gloves are permeable to several resin composite materials [33]. Some resin monomers have been shown to encourage the growth of cariogenic microorganisms [34].

Resin composites [35], sealants [36], and glass ionomers [37] have been shown to release formaldehyde, a possible carcinogen [38]. One dentist, commenting on the fact that some anti-amalgamists describe composite resins as "mercury-free fillings," has called amalgam restorations "formaldehyde-free restorations." [39] Chemically cured composite resins contain the initiator benzoyl peroxide [40], which has been shown to be carcinogenic in many studies [41-43]. There is even concern that there may be environmental harm from the waste in dental offices using composite resin filling materials [44].

Glass ionomer cements have been shown to inhibit macromolecular synthesis [23]. In a review of the side-effects of dental ceramics, Mackert reported that ceramic dental restorations may cause silica granulomas and often contain radioactive fluorescing agents, both of which may cause systemic effects [45]. Even gold can be allergenic [46]. One study showed that the gold itself in gold foil restorations, and not the condensation of the gold foil, caused hemorrhage, destruction of odontoblasts, and inflammation of the pulp [47].

Most reviews have concluded that composite restorative materials are safe [48-51], but there is far more knowledge about dental amalgam than there is about composite resin and glass ionomer filling materials [52]. After extensively reviewing the toxicity of non-amalgam filling materials, Schmalz concluded, "it is not possible to rank dental filling materials in respect to their biocompatibility, and it is evident that biocompatibility must be considered to the same extent for both amalgams and commonly used or recommended alternative fillings materials." [53]

Conclusions

Amalgam restorations release small quantities of mercury, but apparently not enough to cause systemic health problems. Mercury from dental amalgam fillings cannot be linked to kidney damage, Alzheimer's disease, multiple sclerosis, other central nervous system diseases, "amalgam disease," mental disorders, damage to the immune system, increases in antibiotic resistance, or harmful reproductive effects. Dentists occupationally exposed to mercury from the placement and/or removal of amalgam fillings have not been shown to have harmful reproductive or other systemic health effects, provided proper mercury hygiene is used. Just as with amalgam, although they appear safe, there have been health concerns raised about alternative filling materials, including about composite resin. Dentists, physicians, dental assistants, and patients can be confident that based on the available scientific evidence, amalgam remains a safe and effective filling material.

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Dr. Wahl practices dentistry in Wilmington, Delaware. This article was originally published in Quintessence International 32:696-710, 2001, and is reproduced here with the kind permission permission of Quintessence Publishing Co. The author thanks Drs. J. Rodway Mackert, Ivar A. Mjör, and Fred Eichmiller for reading the manuscript and offering several helpful suggestions.